Electricity and Magnetism - Maton, Hopkins, McLaughlin, Johnson, Warner, LaHart & Wright by Blog da Engenharia de Produção

Annotated Teacher's Edition

Electricity AND

Magnetism

THIS BOOK ?;tate

THE PROPER!

Digitized by the Internet Archive in

2009

http://www.archive.org/details/electricitymagneOOmato

IT'S

HERE!

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FINALLY, THE PERFECT r* M.^

FIT.

NOW YOU CAN CHOOSE THE PERFECT FIT FOR ALL

YOUR CURRICULUM NEEDS.

The new Prentice Hall

program so you can

Science program consists

choose the perfect

of 19 hardco\'er books,

your particular

each of which covers a

curriculum needs.

fit

to teach those topics to

represented in the

to teach,

and

you

them in-dqjth. Virtually any approach

possible with Prentice

Hall Science.

teach

—general, integrated, coordinated, thematic, — to science

particular area of science.

All of the sciences are

want

The flexibility of this program will allow you

etc.

Above

all,

the

designed to

program

make your

teaching experience easier

and more fim.

/Prentice //all

iiiiiiiiiliii

ELECTRICITY

AND

MAGNEnSM Ch.

Ch.

Charges and Currents Magnetism Electric

Ch. 3 Electromagnetism Ch.

Electronics

and

HEUDirr:

ECOLOGY:

THE CODE OF UFE

EAMH'S LiVINC KESOUKCES

Among

Ch.

Work

Ch.

Cycles in Nature

Ch.

Viruses and Monerans

Ch.

Exploring Earth's

Ch.

Protists

Biomes

Ch.

Fungi

Wildlife Conservation

Ch.

Plants Without Seeds

Ch.

Plants

CKLUTiat is Genetics? Ch.

PAKADE or L0C: MONOANS. PKonsT S, niNai, and nAins

Ch.

Human Genetics

Ch.

Applied Genetics

Computers

Interactions

Ch.

Classification of

Living Things

How Chromosomes

With Seeds

Exploring E.arths

Weather

EXPLORING THE UNIV Ch.

Ch. Ch.

2. 3.

and Galaxit The Solar System Earth and Its Moon Stars

EVOltmON: CHANGE OVER TIME Ch. i Earth's History in Fossils Ch. 2 Chcinges in Living Things Over Time Ch.

The Path .Modern

Humans

EXPLORING EARTH'S

THE NAIVRE OF SCHNCf

WEATHER

Ch.l.

What is Science?

Ch.

Measurement and

Ch.

Tools and the Sciences

Ch.l.VNTiat

Weather?

WTiat

Climate?

Climate in the United States

Ch. Ch.

the Sciences

ECOLOGY: EAKTH'S NATUmU. RESOURCES Ch. 1. Energy Resources Ch. 2. Earth's Nonliving Resources

MOTION, FORCES,

PARADE OF

AND ENERGY

Ch.

What

Ch.

Motion? The Nature of Forces

Ch.

Forces in Fluids

Ch.l.

Ch.

Pollution

Ch.

Conserving Earth's Resources

Ch.

LIFE:

ANIMALS

Sponges, Cnidarians, Worms, and Mollusks

Ch.

Work, Power, and Simple Machines

Ch.

Arthropods and Echinoderms Fish and Amphibians Reptiles and Birds

Energy: Forms

Ch.

Mammals

CELLS:

BUILDING BLOCKS OF UFE Ch.l. The Nature of Life

Ch.

Cell Structure

Ch.

Cell Processes

Ch.

Cell

and

Function

Energy

and changes

Human Bioloo w. Health

DYNAMIC EARTH 1 Movement

Ch. Ch. Ch.

of the

Earth's Crust

Ch.

Earthquakes and Volcanoes

Ch.

Erosion and Deposition

General Properties of Matter

Ch.

Mixtures, Elements, and

Compounds Ch.

CHEMISTRY OF MATTER Ch. 1. Atoms and Bonding Ch.

Ch.

Physical and Chemical

Changes

Plate Tectonics

Rocks and Minerals Weathering and Soil Formation

Ch.

MATTER: BUILDING BLOCK OF THE UNIVERSE

Chemical Reactions Families of Chemical

Systems

Chemical Technology Radioactive Elements

explori.sc

Ch.

Earth's Interior

Digestive System

Ch.

Circulatory System

Ch.

Respiratory and Excretory Systems

Ch.

Nervous and Endocrine Systems Reproduction and

Ch.

Development Immune System

Ch.

Alcohol, Tobacco,

Classification of Elements:

and Drugs

Pl.anetE.\rth

EXPLORING PLANET EARTN 1 Earth's Atmosphere Ch. 2. Earth's Oceans Ch. 3. Earth's Fresh Water Ch. 4. Earth's Landmasses

Ch.

Atoms: Building Blocks

The Periodic Table

Ch.

HEALTH 1. The Human Body Ch. 2. Skeletal and Muscular Ch.

Compounds

of Matter

Ch.

HUMAN BIOLOGY AND

SOUND AND LIGHT

HEAT ENERGY Ch.l. What

Ch.

Heat?

Uses of Heat

Ch.

Characteristics of

Sound and

Its

Waves

Uses

Light and the Electro-

magnetic Spectrum Ch.

Light and

Its

Uses

A COMPLETELY INTEGRATED LEARNING

SYSTEM...

The Prentice Hall Science program is an integrated learning system with a variety of print materials and multimedia components. All are designed to meet the needs of diverse learning styles and your technology needs. THE STUDiNT

BOOK

Different sciences,

and

model of excellent writing and

other disciplines, are in-

djTiamic visuals designed to be exciting

text

and

(the connections

Each book

â&#x20AC;&#x201D;

niotivating to the

student and the teacher, with relevant examples

tegrated throughout the

and reinforced

in the

"Connections" features is

integrated throughout,

and more opportunities for

many different activi-

which apply everyday life. ties

Problem-solving activities emphasize the

TEACHER'S

RESOURCE PACKAGE In addition to the stu-

dent book, the complete

"Discovery Activities" throughout the book fos-

integrate the sciences,

and /or

ANNOTATED

ing and cooperative-

ing is easy to implement through the use of Discovery Strategies, ActivSuggestions, and

Teacher Demonstrations. hitegration of

all

Designed to provide

teaching strategies.

tlACHER'S RESOURCE PACKAGE

activity for each chapter,

including problem-solv-

Activity-based learn-

TEACHER'S EDITION

ter active learning.

BOOK

Includes a discovery

plus other activities

components

"teacher-friendly"

ACTIVITY

refer.

curriculum areas.

ity

contains:

to integrate the

wrapped

around the student pages to which they

sciences vdth other

teaching package

thinking process, so

problems may be more open-ended.

Help is readily availif you choose to

gestions are

able

teach thematically, to

between

computers and viruses one example).

support regardless of instructional approach:

part of the

For instant accessibility, all

of the teaching sug-

learning activities.

THE REVIEW

AND

REINFORCEMENT GUIDE Addresses students' different learning styles in a clear

and compre-

hensive format:

Highly visual for visual learners.

FOR THE PERFECT Can be used

in con-

junction with the pro-

gram's audiotapes for auditory and language

More than

a study

it's a guide to comprehension, with activities, key concepts,

guide,

and vocabulary.

TO YOUR TEACHING NEEDS.

answers and teaching suggestions on lab preparation and safety.

TEST

learners.

FIT

BOOK

Contains traditional and up-to-the-minute strategies for student assess-

ment. Choose from performance-based

tests

in addition to traditional

ENGLISH

AND SPANISH

AUDIOTAPES

chapter tests and com-

puter

test

bank

questions.

Correlate with the

Review and Reinforcement Guide to aid

STUDENT

auditory learners.

MANUAL

LABORATORY MANUAL ANNOTATED

Each of the 19 books also comes with its own Student Lab Manual.

TEACHER'S EDITION Offers at least one additional

LABORATORY

hands-on oppor-

tunity per chapter with

ALSO INCLUDED IN THE INTEGRATED LEARNING SYSTEM: Teacher's Desk

Transparencies

Reference

Computer Test Bank

English Guide for

(IBM, Apple, or VHS Videos

Language Learners Spanish Guide for Language Learners Product Testing Activities

MAC)

Videodiscs Interactive Videodiscs

(Level

III)

Courseware

All components are integrated in the

teaching strategies in the Ar.notated Teacher's Edition, where

ey directly

relate to the science content.

THE PRENTICE HALL SCIENCE INTEGRATED LEARNING SYSTEM The following components are integrated

ELECTRICITY

Laboratory Manual

Spanish Audiotape English Audiotape Activity

in the teaching strategies for

AND MAGNETISM. Videos: Electric

English Guide for Language Learners

Book

Currents and

Circuits Electricity

Spanish Guide for Language Learners

Review and Reinforcement Guide Test

Book

and Magnetism

Interactive Videodiscs:

Invention: Mastering

â&#x20AC;&#x201D; including

Sound

Transparencies:

Performance-Based Tests

Series

and

Parallel Circuits

Laboratory Manual, Annotated Teacher's Edition

INTEGRATING OTHER SCIENCES Many of the other 18 Prentice Hall Science books can be integrated into ELECTRICITY AND MAGNETISM. The books you will find suggested most often in the Annotated Teacher's Edition are: MATTER: BUILDING BLOCK OF THE UNIVERSE; MOTION, FORCES, AND ENERGY; CHEMISTRY OF MATTER; EXPLORING EARTH'S WEATHER; HEAT ENERGY; HUMAN BIOLOGY AND HEALTH; PARADE OF LIFE: ANIMALS; ECOLOGY: EARTH'S NATURAL RESOURCES; EXPLORING THE UNIVERSE; THE NATURE OF SCIENCE; EXPLORING PLANET EARTH; SOUND AND LIGHT; and DYNAMIC EARTH.

INTEGRATING THEMES Many themes can be

integrated into

ELECTRICITY

AND MAGNETISM.

commonly suggested in the Annotated Teacher's Edition: ENERGY, STRUCTURE, SYSTEMS AND INTERACTIONS, and STABILTTY

Following are the ones most

SCALE AND

For more detailed information on teaching thematically and integrating the sciences, see the Teacher's

Desk Reference and teaching

strategies

the Annotated Teacher's Edition.

For more information, call 1-800-848-9500 or write:

^^ PRENTICE HALL Simon 113

& Schuster Education Group 9W

Sylvan A\'enue Route

Englewood Simon

Cliffs, Nev\' Jersey

07632

& Schuster A Paramount Communications Company

throughout

Annotated Teacher's Edition

Prentice Hall Science Electricity and Magnetism Anthea Maton Former

NSTA

National Coordinator

Project Scope, Sequence,

Coordination

Washington,

Jean Hopkins

Charles William McLaughlin

Science Instructor and Department Chairperson John H. Wood Middle School

Science Instructor and Department Chairperson Central High School

San

Antonio, Texas

St.

Joseph, Missouri

Maryanna Quon Warner

Susan Johnson

Science Instructor Del Dios Middle School Escondido, California

Professor of Biology Ball State University

Muncie, Indiana Jill

Wright

Professor of Science Education

David LaHart

Director of International Field

Senior Instructor Florida Solar Energy Center

University of Pittsburgh

Cape Canaveral,

Pittsburgh, Pennsylvania

Programs

Florida

Prentice Hall

Division of

Englewood

ÂŠ

Simon & Schuster

Cliffs,

1993 by Prentice-Hall,

All rights

reserved.

New

Inc.,

Jersey

Englewood Cliffs, New Jersey 07632. book may be reproduced in any form

part of this

or by any

means

Printed

the United States of America.

without permission

writing

from the publisher.

ISBN 0-13-986183-1

345678910

96 95 94 93

Contents of Annotated Teacher's Edition

To the Teacher

Teacher's Guide

To the Teacher Welcome

to the Prentice Hall Scimce

program.

Prentice

Hall Science has been designed as a complete program

Ecology: Earth's Living Resources

Himian

disciplines of science into your daily lessons, as well as to

Biolog)' and Health Exploring Planet Earth Dynamic Earth Exploring Earth's Weather Ecology: Earth's Natural Resources Exploring the Universe Matter: Building Block of the Universe Chemistry of Matter

enhance the thematic teaching of science.

Electricity

for use with

middle school or junior high school science

The program covers all relevant areas of and has been developed with the flexibility

students.

science

meet xirtually all your curriculum needs. In addition, the program has been designed to better enable you the classroom teacher to integrate various

â&#x20AC;&#x201D;

The Prentice Hall Science program consists of nineteen books, each of which covers a particular topic area. The nineteen books in the Prentice Hall Science program are

and Magnetism Heat Energy Sound and Light Motion, Forces, and Energy Each of the student editions

listed

above also comes

with a complete set of teaching materials and student

The Nature of Science

ancillary materials. Furthermore, videos, interactive

Parade of Life: Monerans, Protists, Fungi, and Plants Parade of Life: Animals Cells: Building Blocks of Life Heredity: The Code of Life

videos and science courseware are available for the

Evolution:

Change Over Time

About the

you purchase a textbook in the Prentice Hall program, you also receive a copy of the Teacher's

Desk Rfference.

The

Teacher's Desk Reference includes all

the standard information you need to

know about

Prentice Hall Science.

The

program. This combination of

multimedia products makes up your complete Hall Science Learning System.

Prentice

Teacher's Desk Reference

When Science

Prentice Hall Science

student texts and ancillaries, teacher materials, and

an overview of the program, including a full description of each ancillary available in the program. It gives a brief summary of each of the student textbooks available in the Prentice Hall Science Learning System. The Teacher's Desk Reference also demonstrates how the seven science themes incorporated into Prentice Hall Science are woven throughout the entire program. Teacher's Desk Reference presents

In addition, the Teacher's Desk Reference presents a

Edition and the features of the Annotated Teacher's Edition, as well as an overview section that simnmarizes issues in science

education and offers a message about

teaching special students. Selected instructional essays in the Teacher's Desk Reference include English as a

Second Language (ESL), Multicultmal Teaching, Cooperative-Learning Strategies, and Integrated Science Teaching, in addition to other rele\ant topics. Further, a discussion of the Multimedia

components

that are part of Prentice Hall Science, as w ell as

can be integrated with the textbooks,

how

included

they in the

Teacher's Desk Reference.

The

Teacher's Desk Reference

iso

contains in blackline

master form a booklet on Tr hing Graphing student use. which may be reproduced

Skills,

detailed discussion of the features of the Student

)

Prentice-Hall, Inc.

T-3

Integrating the Sciences The Prentice Hall Science Learning System has been designed to allow you to teach science from an integrated point of view. Great care has been taken to integrate other science disciplines, where appropriate, into the chapter content and visuals. In addition, the integration of other disciplines such as social studies and literature has been incorporated into each

within blue bullets beside selected passages and visuals.

textbook.

This enables you to further integrate a particular science topic by using the complete Prentice Hall Science

On the reduced student pages throughout yotir Annotated Teacher's Edition you will find numbers

Learning System.

An Annotation Key in

the

wraparound maigins

indicates the particular branch of scieiice or other

been integrated into the student where appropriate, the name of the textbook and the chapter number in which the

discipline that has

text,

hi addition,

particular topic

discussed in greater detail

provided.

Thematic Overview When

teaching any science topic, you

may want

focus your lessons around the underlying themes that pertain to

all

areas of science. These vmderlying themes

are the framework from which

constructed and taught.

all

science can be

The seven underlying themes

A detailed discussion how

of each of these themes and

they are incorporated into the Prentice Hall Science

program are included

your

Teacher's Desk Reference. In

addition, the Teacher's Desk Reference mcXwAe^ thematic

matrices for the Prentice Hall Science program.

incorporated into Prentice Hall Science are

A thematic

matrix for each chapter in this textbook Each thematic matrix is designed with the list of themes along the left-hand column and in the right-hand colimin a big idea, or overarching concept statement, as to how that particular theme is taught in

Energy

follows.

Evolution Patterns of Change Scale

and Structure

Systems and hiteractions

the chapter.

Unity and Diversity Stability

The primary themes and

Interactions,

and

del II lied by an asterisk.

T-4

and Structure, Systems themes throughout Prentice Hall Science diVe

in this textbook are Energy, Scale

Stability. Priiiiarv

Teacher s Guide

CHAPTER Electric

ENERGY

Charges and Currents

CHAPTER Magnetism *ENERGY

Teacher s Guide

CHAPTER

Electromagnetism

ENERGY

CHAPTER 4 Electronics

and Computers

*ENERGY

•

CHANGE

*SCALE

large machinery to the

•

AND

•

vacuum tubes and and microcomputers.

future of

computers

is in

the very large and very small.

The

release, behavior,

and control

of electrons constitutes the foundation of

Diodes and transistors usually play different roles in an electronic device. Diodes serve as a one-way path for current. Transistors amplify current. But both have been essential to the development of modern electronics.

DIVERSITY

T-8

of integrated circuits

electronics.

AND

STABILIPr

development

Microprocessors can hold the entire processing capability on one small chip. Groups of computers are being linked together to form supercomputers.

INTERACTIONS

UNITY

form of energy from

Sound and picture broadcasts are converted into electric signals and then placed on electromagnetic waves (radio waves) that are sent out through the air. Receivers convert the signals back into their original forms.

The

STRUCTURE

SYSTEMS AND

in \.he

to another.

Electronics has undergone a rapid evolution from an era of

EVOLUTION

PATTERNS OF

Electromagnetic waves can be used to carry information

one place

•

Radio waves used

radio

communication

all

travel at the

same speed.

Teacher's Guide

Comprehensive

List

of Laboratory Materials Quantities per

Item

Aluminum

foil

Group

Chapter

small sheet

Abacus Box, cardboard, to

fit

compass

Coins nickel

dime penny Compass Copper sheet Dry

1,3 1

1,2 (or penny)

3 3

cell

Lemon

Magnet bar

horseshoe

Nails, 10

Paper

long

clips

Sandpaper

Scissors

Wire

bell,

150

ÂŠ Prentice-Hall,

Inc.

T-9

Prentice Hall Science

Electricity

and Magnetism

Student Text and Annotated Teacher's Edition Laboratory Manual Teacher's Resource Package Teacher's Desk Reference

Computer Test Bank Teaching Transparencies Science Reader

Product Testing Activities Computer Courseware Video and Interactive Video

The

illustration

circuit

Credits begin

cover, rendered by Keith Kasnot, shows an integrated computers and many other electronic devices.

on the

board used

on page

129.

FIRST EDITION

ÂŠ

Englewood Cliffs, New Jersey 07632. All book may be reproduced in any form or by any means without permission in writing from the publisher. Printed in 1993 by Prentice-Hall,

rights reserved.

Inc.,

part of this

the United States of America.

ISBN 0-13-981044-7 3 4 5 6 7 8 9 10

96 95 94 93

Prentice Hall A Division of Simon

Englewood

Cliffs,

& Schuster

New Jersey 07632

STAFF CREDITS Editorial:

Harry Bakalian, Pamela Robert

Christine A.

Design:

E. Hirschfeld,

Maureen

Grassi,

Letendre, Elisa Mui Eiger, Lorraine Smith-Phelan,

AnnMarie

Caputo Carmela

Roselli,

Pereira, Susan Walrath,

Leslie Osher, Art Soares

Photo Research:

Cioffi, Joan McCulley, Elizabeth Torjussen, Christina Burghard, Marlys Lehmann Libby Forsyth, Emily Rose, Martha Conway

Publishing Technology:

Andrew Grey Bommarito, Gwendollynn Waldron, Deborah Jones, Monduane Harris, Michael Colucci, Gregory Myers,

Marketing: Pre-Press Production: Manufacturing:

Andy Socha, Victoria Willows

Production:

Suse

Cleasta Wilburn

Laura Sanderson, Denise Herckenrath Rhett Conklin, Gertrude Szyferblatt

Consultants Kathy French William Royalty

National Science Consultant National Science Consultant

CONTENTS Electricity and CHAPTER^!

CHAPTERV^

CHAPTER ^J

CHAPTER yl

Electric

Magnetism

Charges and Currents

10 12

Charge

1-1

Electric

1-2

Static Electricity

1-3

The Flow

1-4

Electric Circuits

1-5

Electric

of Electricity

Power

Magnetism 2-1

The Nature

Magnets

2-2

The Earth As a Magnet

2-3

Magnetism

Action

Eleciromagneiism Electricity

From Magnetism

and Computers

3-1

Magnetism From

3-2

Electricity

Electronics 4-1

Electronic Devices

4-2

Transmitting

4-3

Transmitting Pictures

Sound

4-4 Computers

88 95 99 102

SCIF\XE GAZETTE The Search Electricity:

for

Superconductors

Cure-Ali or End-Ail?

The Computer That Lives!

112

114 117

Reference Section For Further Reading Appendix A: The Metric System Appendix B: Laboratory Safety: Rules and Symbols Appendix C: Science Safety Rules Glossary Index

Features Laboratory Investigations Electricity

From a Lemon

Magnetic Fields Electromagnetism Plotting

The

First Calculator:

The Abacus

Find Out by Doing Electric Forces Balloon Electricity

Spark, Crackle,

Move

Observing Static Magnetic Forces

Electricity

Mapping Lines of Magnetic Force Paper Clip Construction Magnetic Domains Cork-and-Needle Compass Making an Electromagnet Changing Direction

Compass Interference An Electrifying Experience Electronics

Your

Home

Find Out by Calculating Ohm's Law How Much Electricity Do You Use? Computing Speed

Find Out by Thinking Power and Heat Helpful Prefixes

Find Out by Writing Where All Began The History of Electromagnetism It

Telephone and Radio History

120 121

122 123 125 126

Concept Mapping Throughout your study of science, you will learn a variety

and concepts. Each new topic you its own collection of words and ideas which, at times, vou may think seem endless. But each of the ideas within a particular topic is related in some way to the others. No concept in science is isolated. Thus it will help vou to understand the topic if you see the whole picture; that is, the interconnectedness of all the indi\idual terms and ideas. This is a much more effective and satisfying way of learning than memorizing separate facts. of terms,

facts, figures,

encounter

will

pro\ide

â&#x20AC;&#x201D;

should be a rather familiar process for you. think about it in this way, you analyze manv of the elements in your daily life by looking for relationships or connections. For example, when you look at a Actually, this

â&#x20AC;˘Although vou

mav not

you may di\ide them into groups: roses, and daisies. You may then associate colors with these flowers: red, pink, and white.

collection of flowers,

carnations,

The general

topic

flowers.

And

t\pes of flowers.

The

subtopic

the colors are specific

A topic makes more easily understood if you understand how it is broken down into individual ideas and how these ideas are related terms that describe flowers.

more sense and

one another and It is

to the entire topic.

often helpful to organize information

you can see how it all fits technique for describing related ideas is called a concept map. In a concept map, an idea is represented by a word or phrase enclosed in a box. There are several ideas in any concept map. A connection between two ideas is made with a line. A word or nvo that describes the connection is written on or near the line. The general topic is located at the top \isuallv so that

together.

One

then broken down into by branching lines. The most specific topics are located at the bottom of of the map. That topic

subtopics, or

specific ideas,

the map.

To construct

a concept

map,

first identii)'

ideas or kev terms in the chapter or section.

include too

much

the important

not

try to

information. Use your judgment as to what

of your map. an example to help illustrate this process. Suppose you decide that the key terms in a section you are reading are really important. Write the general topic at the top

Let's use

School, Living Things, Language Arts, Subtraction, Grammar, Mathematics, Experiments, Papers, Science, Addition, Novels. The general topic is School. Write and enclose this word in a box at the top of your map.

â&#x20AC;&#x201D;

Now choose the subtopics Language Arts, Science, Mathematics. Figure out how they are related to the topic. Add these words to your map. Continue this procedure until you have included all the important ideas and terms. Then use lines to make the appropriate connections between ideas and terms. Don't forget to write a word or two on or near the connecting line to describe the nature of the connection. Do not be concerned if you have to redraw your map (perhaps several times!) before you show all the important connections clearly. If, for example, you write papers for Science as well as for Language Arts, you may want to place these two subjects next to each other so that the lines

do not

provides courses

overlap.

One more thing you should know about concept mapping: Concepts can be correctly

mapped

Language

includes

teaches about

learn

many

different ways. In fact,

Grammar

it is

unlikely that any two

people will draw identical concept maps for a

Science

Mathematics

Arts

Living things

perform

write I

Papers

Addition

Subtraction

Experiments

complex topic. Thus there is no one correct concept map for any topic! Even though your concept map may not match those of your classmates, it will be correct as long as it shows the most important concepts and the clear relationships among them. Your concept map will also be correct if it has meaning to you and if it helps you understand the material you are reading. A concept map should be so clear that if some of the terms are erased, the missing terms could easily be filled in by following

the logic of the concept map.

Electricity

FLECTRICITY

and

Mapetism

^A"" MAGNETISM^

TEXT OVERVIEW In this textbook students are introto electricity. Electric charge is ex-

duced

plained on the basis of atomic structure,

and

static

electricity

discussed. Stu-

dents also learn about voltage, current, and resistance as well as electrochemical cells.

They gain a practical understandpower as utility and learn

ing of electric

about the safe use of

electricity.

Next, students study magnetism and magfnetic poles, fields, lines of force, and

domains. They learn about Earth's magnetic properties and compasses. They also relate magnetism to Van Allen radi-

—

and the aurora as well as to the study of astronomy and applications in ation belts

nuclear fusion. if made of flesh and blood, these computer-controlled dinosaurs appear to be munching on assorted fruits.

Students study electromagnetism and electromagnetic

induction,

and

they

identify practical applications of these

concepts. Finally, students read about electronic tubes, cuits.

devices,

including

—

and

vacuum

and integrated The operations of radios and transistors,

Huge dinosaurs roar wildly as they tower ovei your head. Some cause the ground to tremble m< by walking past you. Have you been transported back in time? No. You are at Epcot Center in W; Disney World where animated creatures are desij and controlled bv computers. Although this computer application is specific designed to amuse and entertain you, other computer applications have more scientific and infor tional uses. Researchers can enter available data into computers in order to build complete, movii models of subjects that can only be imagined observed. For example, computers have enabled scientists to design a wide range of new products simulate various aspects of prehistoric life, and hypothesize about the features of distant planets and galaxies. The beauty of such applications is t designers whether they are interested in the pa present, or future can build, experiment with, and improve upon models with the speed, accura safety of a

—

computer and

its

display devices.

cir-

tele-

visions are described next. Students also

learn about the development

and oper-

ation of computers. The design of many new products IS aided by computers- In this way designers can observe a new product, such as this

TEXT OBJECTIVES 1.

Describe the forces between electric

charges and the atomic basis of electric

shoe, and test various features of the product before it is manufactured.

charges. 2.

Identify the effects of static electricity.

Define voltage, current, and ance and apply these concepts to 3.

resist-

circuit

situations.

What do you see in the top photograph on page P8? (A dinosaur.) • Is this dinosaur alive? (No. It is a computer-operated mechanism.) •

INTRODUCING ELECTRICITY

AND MAGNETISM USING TH£ TEXTBOOK

•

Begin your introduction of the textbook by having students examine the textbook-opening s'lotographs and captions. Before student read the textbook introduction, questions.

ask

the

;

the

following

Why

shown at the botthe page? (The shoes were de-

are the shoes

tom of

signed and tested bv computers.) •

What

taking place in the photo-

graph on page P9? (A computer model of a car •

being tested for aerodynamics.)

What do

common?

all

the photographs have in

(The photographs

illustrate

computer applications in product design, testing, and operation.) • Based on your examination of the photographs, what role do you think computers play in modern life? (Answers

will varv',

but students

may

computers are involved in every facet of life from entertainment to the products and services we use.) • How do you think computers are related to electricity and magnetism? (Answers will var\ Point out that computers that

P T E R S

Charges and Currents 2 Magnetism

3 Electromagnetism

1 Electric

Describe the safe use of electricity.

Discuss

poles, fields,

4 Electronics and

magnetic

Explain electromagnetism and elec-

Computers

magnetism and and domains.

tromagnetic induction' and identify practical applications of these concepts.

Much of

the technology that makes computer

Cite details about the use of electronic

more familiar than you might you will discover that the ihenomona of electricity and magnetism reach far leyond household appliances and industrial devices, pplications possible

devices and computers.

hink. In this textbook

'hey reach into the heart of present

CHaP^'TR DESCRIPTION'^

and future

Charges and Currents

Electric

echnology.

Chapter

the characteristics of electrical

forces are explored. Electric charges are would be quite cosily

for

discussed in terms of atomic structure.

automobile

Properties of static electricity are dis-

lanufacturers to constantly build test lodels of new cars. Instead,

cussed, and concepts of currents are in-

omputers enable designers 1 create models on a creen. This computer model being tested for erodynamic efficiency. W'

troduced. Electric circuits and safety devices

;

such as fuses and circuit breakers

are described. Finally, wattage

and

electric

energy

defined,

related to time

and

power.

2 Magnetism Chapter 2 introduces concepts of magnetism, defining magnetic poles, fields, and domains. The

Flying Through Air With the Greatest of Ease a balloon and

Inflate

Bring the balloon within centimeters of a plate and pepper. Observe for 3 to 5 minutes.

Take

the balloon

Repeat step a

lie

magnetic properties of Earth are disand the chapter explains that

the end.

away from the

plate.

Rub the

filled

cussed,

with a mixture of salt

Earth's

How is the behavior of the salt and pepper different before and after you

rub the balloon with wool? 4.

Arrange small piles of each of the following materials; paper clips, rubber bands, pieces of paper, assorted metal and plastic buttons. Make sure thai each of the piles is separated from the others.

Hold a magnet above the first pile without touching it. Observe what happens. Repeal this procedure over each of the remaining piles.

magnetic

history

stripes

traced

nuclear fusion.

3 Electromagnetism In Chapter 3 the relationship between electricity

What happens to each of the materials when you place the magnet above ii? What can you conclude about how different materials are affected by a magnet?

and

magnetism, known as electromagnetism, is explored. The experiments of Oersted illustrate that the direction of a magnetic generated by an electric current depends on the electric current's direction. The electric motor and galvanometers are described, as are generators and field

transformers.

and their applications are possible because of the technologies resulting from electricity

and magnetism.)

DISCOVERY ACTIVITY

cover that magnets will pick up some items and not others. Ask students to hypothesize about ways in which static electricity and magnets are alike. Explain that

this

textbook,

they

similarities in

With the Greatest of Ease Begin your introduction to the textbook by having students perform the Dis-

electricity

and magnetism.

covery Activity. In the activity students

will

Through

Air

discover the effects of static electric-

salt

and pepper. They

will

learn

the forces of

about the

Flying

ity

magnetic

molten rocks. Finally, the chapter examines magnetism in action in Earth's magnetosphere and the role of magnetism in scientific pursuits such as astronomy and through

balloon with a piece of wool.

some

stu-

dents have a basic knowledge about electricity and magnetism, ask them if there

any relationship between and magnetism.

4 Electronics and Computers Chapter 4 introduces students to the

electronics. is

given,

ics

The

world of

definition of electronics

and the application of electron-

everyday appliances

The chapter

disc ii.sses

tronics in radios

explored.

the use of elec-

and televisions. It then about computers and

details inform. ition

their development.

electricity

will also dis-

Chttpter

Electric Charges and Currents SECTION

CHAPTER PLANNING GUIDE*^ OTHER ACTIVITIES

6 87

3 22

Chapter

Electric Charges and Currents

CHAPTER OVERVIEW Electricity plays a very important role in our lives. From the moment we w/ake up in the morning to the time vje go to bed, w/e power our lives by electricity. Atoms are a combination of protons, neutrons, and electrons. The protons and electrons have

The electric current in a wire is a constant flow of The flow of electrons through a wire is called current. measured in amperes. Electrons flow in a wire due to

electric charge.

electrons.

Current is an electromotive force called voltage. Opposition to the flow of electrons is called resistance. Resistance is measured in ohms. Current electricity can be direct current (DC) or alternating cur-

opposite electrical charges. Electrons have much less mass than protons have and are outside the protons, making it easier for electrons to move. Electricity can be defined as the energy associated with electrons that move from one place to another. Static electricity results from the buildup of electrical charges on objects. When an object loses or gains electrons, it has a static

rent (AC). Direct current means that the is in one direction. Alternating current is that reverses

its

learn about three

The purpose of this section is to introduce students to protons, neutrons, and electrons, and the electric charges of these particles. Forces of attraction between unlike charges and forces of repulsion between like charges are then

and induction. Conductors and insulators are described and contrasted. Light-

discussed.

this section are

be focused on section are energy and stability.

The themes this

methods of electrically charging objects: friction, conduction,

that can

*Energy: Energy

required to make

electric charges leave their

atoms and

tricity

then explained as a

phenomenon

'Stability:

Charge

nor destroyed.

It is

neither created

merely transferred.

involving electric

that can be focused

systems and interactions

and

'Systems

The

interactions:

will

conduct

poorlv. or not at

elec-

all.

Patterns of change: An object can acquire charge by friction, conduction, or induction.

PERFORMANCE OBJECTIVES 1-1 Name the three principal subatomic 1 particles

and

state their charges.

PERFORMANCE OBJECTIVES 1.

Describe the nature of forces that act between unlike charges and like

charges.

Define electric

field.

The purpose of this section is to introduce students to the concept of electric current.

The concept of is

voltage, or pointroduced as a mea-

sure of the energ)- available to

move elec-

and and current are related through Ohm's law, 1 = V/R. The themes that can be focused on in this section are unity and diversity and systems and interactions. trons.

Then, resistance

discussed,

resistance, voltage,

properties of the atoms of a substance

determine whether

of electrons

1-3 THE FLOW OF ELECTRICITY THEMATIC FOCUS

tential difference,

and patterns of change.

tricitv well,

nio\e.

static elec-

discharge.

The themes

of electrons

direction regularly.

1-1 ELECTRIC CHARGE THEMATIC FOCUS

ning

movement movement

1-2

Define and explain static electricity. Compare friction, conduction, and

induction.

Explain the difference between inand conductors. Explain what causes lightning. Describe the structure and use of the

Unity

and

diversity: Current

the

rate at which charge flows through a

conductor. Current may be direct, moving in only one direction, or alternating,

changing direction repeatedly.

'Systems and interactions: The opmovement of charge in a material is known as the resistance. The

position to the

sulators

voltage divided bv the resistance determines the amount of current in a mate-

rial.

SCIENCE TERMS 1-1

atom

electroscope.

PERFORMANCE OBJECTIVES

SCIENCE TERMS 1-2 friction p.

Define electric current and state the unit in which it is measured. 2. Describe the structure and uses of

insulator p.

dry cells and wet cells. 3. Define voltage, state the unit in which it is expressed, and name the de-

P12

proton p. P12 neutron p. P12 electron p. PI charge p. PI force p. PI electric field p.

PI conduction p. PI conductor p. P17

P14

PIT

induction p. PI

vice used to

P18 electric discharge p. P19 electroscope p. P21

static electricity p.

1-2 STATIC ELEt RICITY THEMATIC FOCUS The purpose of this seciinn is to introduce students to static electricity, which involves a buildup of charge. They also 10c

1-3

measure

it.

Define resistance and state the unit in which it is measured. 5. State and apply Ohm's law. 6. Contrast direct current and alternating current.

CHAPTER PREVIEW ICIENCE

TERMS

attery p.

P23

1-5 ELECTRIC

1-3

otential difference p.

P24

lermocouple p. P24 hotocell p. P24 ircuit p. P25 urrent p. P25 oltage p. P26 esistance p. P28 uperconductor p. P29 )hm's law p. P29 irect current p. P30 Iternating current p. P30

•

The purpose of this section is to show students how the watt, the unit of electric

volt

power,

defined. Electric energy

then

power and time by the equaE = P X t, and the kilowatt-hour is

related to tion

introduced. Finally, important rules for electrical safety are presented.

The themes

on in and structiue and

that can be focused

this section are scale stability.

*Scale and

how that

structure:

large a current

is,

its

matter

in the particles within the

make up

The purpose of this

to intro-

—

uce students to the electric circuit omplete path for an electric current. Se-

is al-

atoms

the conducting material.

Understanding the concepts of electricity will foster its proper and safe use.

1-5

Define electric power and state and apply the formula that relates it to volt-

re described.

age and current.

The themes

that can be focused

section are unity

and

on in and

diversity

and

diversity:

circuit pro-

ides a closed path for current.

A circuit

State the units of

Calculate

electric

given

energy,

time.

4. State six

important safety rules

relat-

hat

interrupt

hrough a

the

flow

Making a Battery You can make a simple

battery by cut-

20 5-centimeler squares of zinc sheeting, of copper sheeting, and of blotting paper. Pile them on top of one anting

order:

this

copper, blotting

square of copper should be on the bottom and a square of zinc on the top. Tie the pile together with a paper, zinc.

thread.

Attach one wire to the top plate and

one

to the bottom.

Immerse

the entire

of sodium bicarbonate. the blotting paper is soaked, re-

pile in a solution

move the pile. Touch the free ends of voltmeter to

test

the wires to a

the voltage. Ask stu-

•

What

happening

produce a cur-

rent? (Electrons are flowing from the zinc end around to the copper end, and zinc

inside

the copper

below.)

What is the purpose of sodium-bicarbonate solution? (It serves as an electrolyte, whose ions, or charged particles, conduct electricity.)

SCIENCE TERMS 1-5 p.

The

•

ing to electricity.

power

cell electricity.

than the flashlight bulb.)

from each

power and

nay be series or parallel.

•Systems and interactions: Fuses nd circuit breakers are safety devices

10-

dents the following.

power and

energy. 3.

ystems and interactions. Unity

flashlight

table-lamp bulb was brighter and hotter

When

PERFORMANCE OBJECTIVES

and parallel circuits are disussed and compared. Finally, safety deices such as the fuse and circuit breaker

les circuits

his

uses a batter)', or diy

'Stability:

section

house current, whereas the

other

source

ELECTRIC CIRCUITS

HEMATIC FOCUS

How are the two electrical systems dif-

ferent? (The table lamp uses regular

ways

1-4

POWER

THEMATIC FOCUS

P35

current

circuit so that wires will not

•verheat.

Discovery

>ERFORMANCE OBJECTIVES 1-4 .

Define electric circuit. State the parts of a circuit and their

unctions.

Learning

•

TEACHER DEMONSTRATIONS MODELING Comparing Light Sources

Compare series and parallel circuits.

Place a table lamp and a flashlight on

Explain the use and operation of uses and circuit breakers.

the demonstration table. Tell the class to

SCIENCE TERMS 1-4 leries circuit p. P32 >arallel circuit p. P32 use p. P34 :ircuit breaker p. P34

watch and think about what happens during the demonstration. Plug in the lamp and turn it on and off

Hold up the flashlight and on and off several times. Discuss

several times.

turn

(he demonstration using questions similar to the following. •

How

are the two electrical systems

similar? (Both systems use electricity,

have bulbs, have a switch, and light/unlight the bulbs.)

10d

CHAPTER

Electric Charges

and

Currents INTEGRATING SCIENCE This physical science chapter provides

you with numerous opportunities

to in-

tegrate other areas of science, as well as

other disciplines, into your curriculum. Blue numbered annotations on the student page and integration notes on the teacher wraparound pages alert you to areas of possible integration. In this chapter you can integrate phys-

and atoms (p. 12), physical and force (p. 13), physical science and ions (p. 1 5), physical science and friction (p. 16), physical science and metals (pp. 17, 28), earth science and meteorscience

ical

science

ology ical

(p. 19), social

science

studies (p. 20), phys-

and work

(p. 22),

ence and electrolytes science

and heat

physical

(pp. 24, 28),

arts (p. 25), life science

sci-

23), physical

(p.

language

and muscles

(p.

and zoology (p. 27), physical science and hydroelectric power 27),

life

science

(p. 29), mathematics (p. 30), physical science and power (p. 36), and life science

and genetics

(p. 39).

SCIENCE, TECHNOLOGY AND

SOCIETY/COOPERATIVE LEARNING that

is a modern convenience most of us would rather not have to

live

without! But, the cost of generating

Electricity

is increasing both economiand environmentally. Most electricity is generated when power plants burn fossil fuels to produce steam. The steam then turns huge turbines to produce electricity that can be delivered to our homes. Fossil fuels are nonrenewable resources that are being consumed at an alarming rate. Another concern with fossil fuels is the environmental problems associated with burning them in power plants— thes produce emissions that are causing acid [> cipitation to fall in some

electricity cally

•;

parts of the cousury.

Advocates of nuclear energy have long used the argument that nuclear-fueled power plants could pr.>,'ice an econoinical alternative to fossa 'el generated electricity.

Opponents

/ lear

power

INTRODUCING CHAPTER

USING THE TEXTBOOK 1

Have students observe the photograph on page PIO.

DISCOVERY LEARNING

•

Activity

Book

Begin your introduction to this chapter by using the Chapter 1 Discovery Activity

from the

activity,

Activity Book.

students

scope and use

will

Using

make an

this

Where did the electricity for this old come from? (Most students

laboratory will

have noticed the lightning bolt

Discuss with students the importance

electro-

to detect static electric-

hit-

ting the top of the tower.)

evei7day

of the role of electricity

They should be able

come up

ity.

great

life.

with a

many applications and can be led to many of the impor-

the conclusion that

have always raised the threat of safety to both the public and the environment in opposing the licensing of these plants.

Charges

Electric

In a recent California election, a 15-

power plant was closed by the community. The campaign

year-old nuclear

ind

Currents

juide for Reading

Relate electric charge to atomic structure.

Describe the forces that exist between charged particles.

Static Electricity

or to destroy

Describe the effects of static electricity.

Electricity

Describe the nature of current electricity.

-4 Electric Circuits Identify the parts of

series

and a

parallel circuit.

-5 Electric Power Explain

power

how is

it.

For hundreds of years, many people were frightened by electricity and believed it to have mysterious powers. Today a great deal is known about electricity. And although it is not mysterious, electricity plays a powerful role in your world. Electricity is involved in all interactions of everyday matter from the motion of a car to the movement of a muscle to the growth of a tree. Electricity makes life easier and more comfortable. In this chapter you will discover what electricity is, how it is produced and used, and

—

electric circuit.

Compare a

dark nights thunder Creepy characters castles and Ughtning crashing in the background with trap doors and secret laboratories. Do these descriptions sound familiar to you? Perhaps you have seen them in monster movies such as Frankenstein and The Bride of Frankenstein. These exciting movies often express people's hidden hopes and fears about a world in which scientific knowledge can be used for either good or evil. Usually, electricity is used at some point in the movie to mysteriously create life .

-1 Electric Charge

-3 The Flow of

on economics, not on the emotional issues of personal against the plant centered

you read the following ections, you will be able to

\fter

-2

down

why

electric

so important.

may have about

Frankenstein at work

Cooperative learning: Using preas-

following assignments: •

Have groups prepare

electricity.

the electricity that is used in community. If possible, invite a representative from the power company to class for the purpose of answering the intheir

sign

the

utility

one group

not

many phone

company), randomly asconduct the inteniew

by phone. •

Have students

react to the following

statement: Nuclear-fueled power plants

should continue to be built and allowed to operate. Reactions can take the form of posters, public service announce-

in tiis laboratory.

make up their days rely

or indirectly on electricity

—

or radio,

billboards,

such as Star Wars, Return ofthejedi, Back

;he

duction. Discuss the use of light and/or

cause of their properties, depict powerful forces in a startling and dramatic

of an electric alarm clock

preserving and cooking food to trans-

Dortation to extending the activities of

daytime by means of electric lights. Have students read the chapter intro-

horror or science-fiction movies. Students may mention movies

letters to the ed-

bumper

stickers,

T-

or any format that you approve, in

some way explain the

reason(s) for the group's reaction.

and so on. movie makers use lightning, light, and electricity as a means to show the power and strength of evil and good? (Responses might include that light, lightning, and electricity can, be-

ev-

from waking up on time because

of interview

Who) about

but they must

electricity

list

W's" (What, When, Why, Where, and

shirts,

questions that would answer the "five

itor,

ant activities that

the fu-

the United

signed lab groups or randomly selected teams, have groups complete one of the

ments for

jf the ringing

States?

calls to

Journal Activity Did you switch on a light, shut off an alarm clock, listen to the radio, or turn on a hair dryer today? In your journal, describe the importance of electricity in your daily life. Include any questions you

irylhing

power

ture of nuclear

available (and to prevent too

You and Your World

directly

What

sociated with the plant.

terview questions. If this option

calculated and

purchased.

)r.

and environmental safety. The plant produced only 40 percent of the electricity that had been expected, and the electricity that was produced cost twice as much as electricity purchased from conventional power plants. Residents in the area felt that the economic reality of nuclear power did not justify the potential risk as-

to the

•

Future,

Why do

way.)

See

Cooperative

Learning

the

Teacher's Desk Reference.

JOURNAL ACTIVITY You may want tivity as

You may

Journal Ac-

wish to suggest that students

also includt

with gas

to use the

the basis of a class discussion.

devices that are powered

(I light

energy.

Which source of

energy seems to be used most frequently, electric, gas, or solar? Students should be instructed to keep their Journal .\ctivity in then portfol-.o.

—

— Guide for Reading

1-1 Electric Charge

Focus on these questions as you read. What IS the source of

MULTICULTURAL OPPORTUNITY 1-1

electric

charge^

do electric charges behave?

Depending upon the backgi-ound of fering experiences with electricity.

or tape? Believe

dif-

Some

electricity.

shocks whereas other students might understand how the wiring in their own homes operates. Begin this section by discussing electricity with your students and eliciting some of these miscon-

cause

All matter

trons, point out that the

many

word

and

in the

matter.

Electricity

made of atoms. An atom

all

the

the prop-

of that element. An element contains only one kind of atom. For example, the element lead is made of only lead atoms. The element gold is made of only gold atoms. Atoms themselves are made of even smaller particles. Three of the most important particles are protons, neutrons, and electrons. Protons and ( neutrons are found in the nucleus, or center, of an atom. Electrons are found in an area outside the nucleus often described as an electron cloud. Both protons and electrons have a basic property called charge. Unlike many other physical properties of matter, charge is not something you can see, weigh, or define. However, you can observe the effects of charge more specifically, how charge affects the behavior of particles. The magnitude, or size, of the charge on the proton is the same as the magnitude of the charge on the electron. The kind of charge, however, is not the same for both particles. Protons have a positive charge, which is indicated by a plus symbol (-I-). Electrons have a negative charge, which is indicated by a minus symbol — ). Neutrons are neutral, which means that they have no electric charge. The terms positive and negative, which have no real physical

the elec-

charge has

different

then write three sentences to demonstrate their understanding of the three

—

meanings of charge. Have students form two sentences stating the rule of electric charges by unscrambling the following words. The sentences should include proper capitaliza-

and punctuation.

— charges — unlike — each charges — — each — repel — other other

or not, the answer has to do with

erties

meanings other than its scientific usage. Have students find two other meanings in their dictionaries and

tion

smallest particle of an element that has

ESL STRATEGY 1-1 discussing that charge

on your clothing Or have you

the origin of electricity

make up

Atoms and

ceptions.

When

And

particles that

students fear that D-cell batteries will

basic property of both protons

a balloon to a wall?

ever pulled your favorite shirt out of the clothes dryer only to find socks sticking to it? How can objects be made to stick to one another without glue

How

your students, they may have widely

Have you ever rubbed make it stick to you or

attract

(

Electron

Figure 1-1 The diagram of the carbon atom shows the arrangement of subatomic particles known as protons, neutrons, and electrons. Carbon is found in all living organisms, including this hungry hippo.

Proton

TEACHING STRATEGY 1-1

FOCUS/MOTIVATION Ask students to imagine a world in which there were no electrical devices and to think of how their ancestors were

•

out the benefit of electricity.

Use the discussion of subatomic particles to integrate concepts of atoms into your lesson.

CONTENT DEVELOPMENT After students have been given a lea<s

them

wonder about

this ;-henomenon. Introor reintrodui the concept of the atom to them. Dismss the most im-

duce

Integration

•

• •

feel-

ing for the nK^nv applications and aspects

of electricity, the basis of

—

portant subatomic partu is and the concept of charge.

• • •

able to carry out evei7day functions with-

•

Electrons are particles that have a neg-

ative charge.

Where

shown

diagram? (Near the outer

in the

edge of the •

Where

circle.)

are the protons and neutrons?

GUIDED PRACTICE

(Grouped together

Development

cleus, of the atom.)

Skills Skill:

Interpreting illustrations

Have students examine Figure 1-1, which shows the subatomic particles in a carbon atom.

•

What

are the electrons

in the center,

or nu-

the difference between a pro-

ton and a neutron? (A proton has a positive charge. A neutron is neutral it has

—

no charge

at all.)

ignificance,

IN D OUT BY

were originally decided upon by

Jenjaniin Franklin

when he

first

discovered charge,

ZZZZZZ2ZZZZZZL.

..pc:>iisi<^|

rhey have been used ever since.

Electric

Iharge and Force

ANNOTATION KEY

Forces

Answers

Take a hard rubber (not plastic) comb and rub \N\ih a woolen cloth. 1.

The difference between the two charges has to do k-ith how they behave and the forces they exert. A orce is a pull or push on an object. You are already amiliar with various types of forces. Your foot xerts a force (a push) on a ball when you kick it. An )cean wave exerts a force (a push) on you when it nocks you over. The Earth exerts a force (a pull) on he moon to keep it in its orbit. Charged particles charged particles come near one another, hey give rise to two different forces. A force that )ulls

objects together

a force of attraction.

Integration

thread. 3. Allow the

one another, just

comb

O Physical Science:

to touch

the cork, and then take the

Repeat steps

O Physical 1

Atoms. See Matter:

Building Block of the Universe, Chapter

comb

Bring the

to 3

Forces,

Science: Force. See Motion,

and Energy, Chapter

using a glass rod rubbed with

silk.

orce of attraction exists between oppositely harged particles. So negatively charged electrons re attracted to positively charged protons. This orce of attraction holds the electrons in the elecron cloud surrounding the nucleus. A force that pushes objects apart is a force of epulsioii. A force of repulsion exists between tarticles of the same charge. Negatively charged •lectrons repel

generalizations)

toward the cork again.

When

charges attract each other.

Like charges repel each other. (Making

2. Bring the comb near a small piece of cork that is hanging from a support by a

comb away.

xert similar pushes and pulls.

O Unlike

Then bring the rubber

comb rubbed

with wool near

the cork.

Record and explain your observations,

ELECTRIC FORCES

as positively

Discovery Learning

harged protons do. Electric charges behave ccording to this simple rule: Like charges repel

Skills:

ach other; unlike charges attract each other.

observations, making comparisons

Applying concepts, making

Materials: hard rubber comb, woolen cloth, cork, thread,

igure 1-2 When charged particles come near each other, a orce IS produced. The force can be either a force of attraction ir a force of repulsion. What is the rule of electric charges?

This activity

glass rod,

silk

help to introduce the

concept that electric forces build up when electrons are forced to inove from one object to another. Students should

will

be able to relate their observations to the concepts that like charges repel each other and opposite charges attract each other.

No charge

Unlike charges attract

Like charges repel

tion

CONTENT DEVELOPMENT You can

help to

make

clearly

clear the con-

cept of attractive and repulsive forces by means not only of charged objects (for

example,

like-

and unlike-charged

light-

weight objects suspended near one another from strings), but also of magnets.

not

cifics

become

too involved in the spe-

of the nature or magnitudes of

forces; simply deal qualitatively with at-

tractions

and repulsions.

dents' attention to Figure

Direct

stu-

1-2, which

bilities

shows the three different for charge interaction.

possi-

and repulsion. They may come up

with any of a wide variety of ways to measure how great a push or pull is exerted

when • • • •

Integration

• • • •

the objects are at different dis-

tances apart.

Use the discussion of the forces exerted by charged particles to integrate

concepts of force into your lesson.

REINFORCEMENT/RETEACHING Book

Activity

Students

ENRICHMENT

standing

Ask students to design an experiment way in which distance between charged objects affects forces of attrac-

Chaptci

to test the

who have

difficulty

under-

concepts of attraction and repulsion ^llould be provided with the ilu

activity called Electric

Charge

and Force.

ANNOTATION KEY Ansvvers Accept

dents static

all

logical answers.

Most

stu-

probably have experienced electricity. (Applying concepts) will

Integration

O Physical Science: of Matter, Chapter

Ions. See Chemistry

Figure 1-3 Lines of force show the nature of the electric field

surrounding a charged particle

When two charged

particles

come

near each other, the electric fields of both particles are altered as shown.

FIND OUT BY

DOING BALLOON ELECTRICITY Skills:

The

will find

days.

Remind them

static electricity leaks

cules in the

damp

the strongest near the

particle increases, the strength of the electric field .^s shown in Figure 1-3, the electric field can be visualized by drawing lines extending outward from a charged particle.

out that balloons do

or humid

because onto water mole-

that this

As the distance from the charged

particle.

decreases,

3 or 4 medium-sized balloons

Students

electric field

charged

observations, making inferences

not stay on the wall on

The attraction and repulsion of charged particles occurs because charged particles have electric fields around them. \x\ electric field is an area over which an electric charge exerts a force. When a charged particle moves into the electric field of another charged particle, it is either pushed or pulled depending on the relationship between the two particles.

Applying concepts, making

Materials:

Electric Field

1-1 Section Review

air.

Describe the charged particles in an atom. is a force? Give some examples. is the rule of electric charges? 3. 4. is an electric field? 1.

1-1 (continued)

INDEPENDENT PRACTICE Section Review 1-1 1. Protons are positively charged and are found in the nucleus of the atom. Electrons are negatively charged and 2.

â&#x20AC;&#x201D;

Thinking Drawing Diagrams charged particle is placed 1 centimeter from positively charged particle X. Describe the forces experienced by each particle.

Critical 5.

travel in orbits

What What What

positivelv

Compare would

these forces with the forces that

exist if a negatively

charged particle were

placed 10 centimeters from particle X. Draw the electric field surrounding each particle.

around the nucleus.

A force is a push or pull on an object.

Examples may include magnetic, gravitational, and nuclear forces as well as electric forces.

Like charges repel each other; unlike charges attract each other. 4. The region surrounding a charged particle in which an electric force on other charged particles is noticeable. 3.

The

Student diagrams should resemble those shown in Figure 1-3. Encourage student creativity in showing the difference between the strengths of the two

Review and Reinforcement Guide Have students complete Section 1-1 the Review and Reinforcement Guide.

periences a force of repulsion, whereas the negatively charged particle experi-

Students might use a greater number of arrows or heavier lines for the stronger field.

ences a force of attraction. The force of repulsion is stronger because the posi-

REINFORCEMENT/RETEACHING

FOCUS/MOTIVATION

Review students' responses to the Section Review questions. Reteach any material that is still unclear, based on stu-

fur or cloth, preferably wool. Stick the

tively ticle

positively charged particle ex-

charged particle

closer to par-

X than the negatively charged par-

ticle is.

fields.

dents' responses.

CLOSURE

TEACHING STRATEGY 1-2

Rub

several balloons with a piece of

balloons to a classroom wall.

— Guide for Reading

1-2 Static Electricity

Focus on these questions as you read

From your

experience, you know that when you it on a chair, pick up a pen, or put on your jacket, ou are neither attracted nor repelled by these ibjects. Although the protons and electrons in the toms of these objects have electric charges, the

How do

neutral objects

MULTICULTURAL OPPORTUNITY 1-2

acquire charge?

What

IS static electricity?

The Eskimo

themselves are neutral. Why? An atom has an equal number of protons and lectrons. So the total positive charge is equal to the otal negative charge. The charges cancel out. So ven though an atom contains charged particles, it is has no overall charge. How then do objects such as balloons and clothig develop an electric charge if these objects are lade of neutral atoms? The answer lies in the fact hat electrons, unlike protons, are free to move. In ertain materials, some of the electrons are only iosely held in their atoms. Thus these electrons can

cultures are exposed to a

fascinating exam|}le of electricity

ibjects

the

aurora borealis, or northern lights. Have your students investigate the factors necessary for the northern lights to appear.

lectrically neutral. It

ESL STRATEGY 1-2 Write the following sentences on the chalkboard and ask for volunteers to complete them, reading them aloud.

be separated from their atoms. If an atom 3ses an electron, it becomes positively charged ecause it is left with more positive charges (protons) lian negative charges (electrons). If an atom gains n electron, it becomes negatively charged. Why? An tom that gains or loses electrons is called an ion. asily

igure 1-4

magic

that

makes

to ttie comb'' No, just static xperienced static electricity'^

thiese

pieces of paper Have you ever

Neutral objects get electrical charges

they

tion

an electron.

occurs

when

electrons

one object to another. —tion occurs when a neutral 3. object comes close to a charged object. tion occurs when two objects 4. are rubbed together. (Answers: 1. gain, lose; 2. Conduc; 3. flow through

Balloon Electricity 1.

Blow up three

or tour

medium-sized balloons. 2. Rub each balloon vigorously on a piece of cloth. Wool

rise

w/orks especially well.

electricity.

out by Find A 77777777777777777: YZZZZZZZZZZZl. ->c:>iisi<^ // E

Indue;

"Stick" each balloon on

the wall. Record the day, time,

play a game of "Jeopardy" using electricity as the category. Students take turns giving the terms for each of the following definitions. An-

and weather conditions. 4. Every few hours, check the position of the balloons. 5. Repeat your experiment on a day when the weather

conditions are different

—

swers

for

ai"e

• Static

example, on a dry day versus on a humid or rainy day.

How

4. Fric.)

Have students

charges

given in parentheses.

electricity

move

off

lost

electric

an object. (Electric

dis-

charge.)

long did the balloons

stay attached to the wall? Why did they eventually fall

•

A dramatic example of static

electricity

occurring when charges move off an ob-

off the wall?

ject. (Lightning.)

Does weather have any

•

effect'' Explain.

Electrons

move from one

object to an-

other, cause buildup of electric charges,

and then remain

at rest. (Static electric-

ity.)

• Principle

by which lightning rods work.

(Grounding.) •

Instrument

used

detect

electric

charge. (Electroscope.)

What causes

the balloons to stick?

other because they have the same charge,

They have gained electrons from the ioih, and now they repel electrons in the

and like charges repel.) Push several well-charged balloons

leaving that area of the wall nearest

close together to demonstrate what oc-

vail,

hem

positively charged.

The opposite

curs.

Bring out that the reasoning, hyand experimenta-

harges attract one another.)

pothesis formation,

Why

tion that are involved illustrate scientific

is this

kind of electricity called (The electric charges

tatic electricity?

lave built

up but do not

flow.

•

neans "unchanging.")

What do you

predict will

happen

harged balloons are brought close toWhy? (They will repel one an-

[ether?

method.

Static

•

• •

Integration

•

Use the discussion of the charges gained and lost by electrons to integrate concepts of ions into your lesson.

TIND

OUT BY

Spark, Crackle,

MOVE

SPARK, CRACKLE,

times

Discovery Learning Skills:

Comb

Move

your hair several

the

same

direction.

Then bring the comb near

Applying concepts, making

your

but do not touch it. Repeat step 1 but now

hair,

observations, making inferences

atom can become a negatively or posicharged ion, so can an entire object acquire a charge. A neutral object acquires an electric charge when it either gains or loses electrons. Remember, onlv electrons move. .AJso remember that charge is neither being created nor destroyed. Charge is only being transferred from one object to another. This is known as the Law of Conservation of Charge. Just as an

tively

Methods of Charging

comb near a weak stream of water from a faucet. 3. in a darkened room, walk across a wool carpet and then touch a doorknob with a metal pen or rod. E Provide an explanation bring the

Materials: comb, running water from

wool carpet, metal pen, doorknob faucet,

This activity

help students obsen e

will

the effects and buildup of static electricity. These activities work best on diy, cool

for

When you

rub a balloon against a piece of cloth,

the cloth loses

some

electrons and the balloon gains

these electrons. The balloon is no longer a neutral object. It is a negatively charged object because it

has

electrons than protons. As the negatively

charged balloon approaches a

each observation.

trons in the wall.

The

wall,

repels the elec-

electrons in the area of the

move away, leaving that area of the wall positively charged. See Figure 1-6. Using the rule of charges, can you explain why the balloon

wall nearest the balloon

days.

Have students

relate

their

obsena-

tions to the discussion in the textbook. In

now

each case rubbing has caused an object to lose some of its electrons and become

sticks to the wall?

Rubbing two objects together is one method by which an object can become charged. This method

positively charged.

known

method. In the previous exam-i balloon acquired a charge by the friction

as the friction

pie. the

method. That

is,

was rubbed against cloth.

Figure 1-5/4 Van de Graaff generator produces static electricity by friction. Electrons ride up a rubber belt to the top of the generator, where they are picked off and transferred to the metal sphere. The charge that has built up on the generator at the Ontario Science Center is large enough to make this girl's hair stand on end.

1-2 (continued)

CONTENT DEVELOPMENT Direct students' attention again to Fig-

ure 1-3, which depicts lines of force between pairs of charges. Tie this field concept to the discussion of static electricity, pointing out the static nature of the field in this case. Later,

you can contrast

Metal comb (soufce of electric

charge)

this

with the changing electric field characteristic

of flowing

electricity.

This

will

also help to prepare students for the con-

cept of magnetic fields (treated in the fol-

lowing

chapter),

changing

which

result

from

electric fields.

FOCUS/MOTIVATION Ask students

experiment on a num-

ber of dift'erciu materials (such as various plastics and faorics) in order to determine which substances tend to be

charged easily when rubbed. Students should work with diftt rent combinations of substances. They car: ,;lso attempt to determine whether positi e or negative

in each by observing whether attraction or repulsion results when a negatively charged balloon, for example, is brought near the charged ob-

charge develops

has

become

negatively charged.

has lost electrons and

become

The rod

positiveh

charged.)

ject.

CONTFM T ncv/Pi

â&#x20AC;˘

nOMPMT

Explain that charging objects through

rubbing

Which object has become negatively charged? Positively charged? (The silk

â&#x20AC;˘

called the friction

method of

creating electric charge. For example, a glass rod

rubbed with

silk,

electrons

are transferred from the rod to the

silk.

Which object would be attracted to the

balloon described in the textbook? Why? (The balloon is negatively charged, it would attract the rod. The balloon and the silk would repel each other.)

HISTORICAL NOTE THALES One

Negatively

charged Metal rod

people to produce written observations concerning static electricity and magnetism was the Greek philosopher and mathematician Thales of the

(640-546

first

Bc). Tliales

experimented with

amber and found that it would attract objects such as feathers, bits of dried grass,

and straw. He noticed that although the amber would attract light objects, it would not attract metal.

BACKGROUND INFORMATION WATER AS A CONDUCTOR Chemically pure water

actually a

rather poor conductor of electricity.

Any

nondistilled water, however,

ordinar)',

contains in every milliliter large numbers

of ions, or charged particles, that do conduct electricity. Thus ordinary water, which is actually a solution of salts, is a relatively efficient conductor. Even distilled

water can quickly become a good

conductor

any part of the body or

clothing comes in contact with

become

dissolved in

and ions

it.

INTEGRATION MATHEMATICS The magnitude of the tric field

force in an elec-

proportional to the product

of the charges of the two objects, divided

by the square of the distance separating the centers of the objects. This inversesquare relationship accounts for the fact that the

magnitude of electric forces de-

creases rapidly as distance increases.

rod,^

>"^^

because charges cannot escape into the air.) When the charged object loses its static electricity, it becomes neutral once again. The balloon eventually falls off the wall because it loses its charge and there is no longer a force of attraction between it and the

"Annotation key

Answers

wall.

The loss of static electricity as electric charges move off an object is called electric discharge. Sometimes Sometimes

O By

charge of

is the same as the charge on the charged rod. By induction, the charge on the metal rod is opposite the charge on the charged rod. (Interpreting diagrams)

static electricity

lightning.

During

storm, particles contained in clouds are

conduction, the charge on the

metal rod

slow and quiet. it is very rapid and accompanied by a shock, a spark of light, or a crackle of noise. One of the most dramatic examples of the diselectric discharge

moved about

by the wind. Charges may become separated, and there are buildups of positive and negative charges

Integration

O Earth Science:

Meteorology. See Ex-

ploring Earth 's Weather, Chapter

Figure 1-10 Lightning is a spectacular discharge of static electricity between two areas of different charge. Lightning can occur between a portion of a cloud and the ground, between different clouds, or

between

different parts of the

same

cloud.

Benjamin Franklin's famous experiments provided evidence that lightning is a form of static electricity.

INTEGRATION SCIENCE

LIFE

+ +

+ Some

biochemists and biologists have suggested that the energ)' from lightning

atmosphere of the Earth complex organic (carboncontaining) molecules from the simple, inorganic atnmonia, iTiethane, and water vapor atmosphere present at the lime. These molecules made possible the eventual development of life, these scientists in the primitive

+ + + + + _

_ -

produced

+ + + + +

conjecture.

CONTENT DEVELOPMENT Have students look at in •

the photog[raphs

Figure 1-10.

What causes

lightning?

(.4

jumping of

electrons to or from clouds that contain particles that have

square of corkboard and thai can be

lansfened

another corkboard.

"un•harged" board (that is, one that does lot contain excess "electron" pins) can 3e brought near a "negatively charged" llustrate

induction,

another,

and some of the pins in the unrharged one can be tnoved to the end farhest from the charged board. 3ne,

FOCUS/MOTIVATION

charged.

Ask students to describe what they have observed during lightning storms that have occurred in the past. •

Where did

the lightning originate,

and in what direction did it move? (Although most students believe that all the lightning bolts they have observed moved from the sky downward toward the Earth, in

many of the

bolts probably

moved

the other direction, appearances to

the conliai"v.)

discharge •

become

Some of the is

electrically

energ) during the

released as

light.)

What causes thunder? (Some of the en-

erg) during the

ciisi

barge

released as

sudden expansion of and theiefore generates sound

heat, VN'hich causes a

the

air,

waves.)

• • • •

Integration

• • • •

Use the discussion of lightning tegrate

to in-

concepts of meteorolog)' into

your lesson.

— of the cloud. If a negativelv charged edge of a cloud passes near the surface of in different parts

BACKGROUND

the Earth, objects on the Earth

INFORMATION SAFETY Xewh manufactured

electrically

from the cloud, and positive charges are left closest to the cloud. Soon electrons jump from the cloud to electrical appli-

the Earth.

ances include three-wire power cords that ha\e a safety ground. The ground wire is connected to the case of the apcircuit

The

result of this transfer of electrons

giant spark called lightning.

pliance. .\n accidental short circuit will

blow a fuse or throw a

become

charged bv induction. Negative charges move aw^y

breaker

a situation far preferable to the user's recei\ing a dangerous electric shock. Extension cords used with this type of electrical plug must also be of the three-

prong t\pe Older electrical appliances have a twowire power cord and should be used with extra caution. In all cases, be sure power cords are in good condition, not cracked

Figure 1-11

firaved.

„r„"

.'.

_c'"r^"^c' '?::?

'I'.l.

- =

y./-'-

''-'-rig

/- f--;-= 5:_;. -: ~: r_ : -c a-:e a-:^~:s of "" - ~ '~'~ ^

£;--_-j

/C--

BACKGROUND

such

"=--

;

-^;

Lightning can also occur as electrons jiunp from cloud to cloud. As electrons jump through the air. thev produce intense light and heat. The light is the bolt of lightning vou see. The heat causes the air to expand suddenlv. The rapid expansion of the air is the thunder vou hear. One of the first people to understand lightning as a form of eleciricirv was Benjamin Franklin. In the mid-1 700s. Franklin performed experiments that provided evidence that lightning is a form of static electricity, that electriciri' moves quicklv through certain materials, and that a pointed surface attracts electricitv more than a flat surface. Franklin suggested that pointed metal rods be placed above the roofs of buildings as protection from lightning. These rods were the first lightning rods. Lightning rods work according to a principle called grounding. The term grounding comes from the fact that the Earth (the ground) is extremelv large and is a good conductor of electric charge.

INFORMATION ELECTROSCOPES The leaves of a charged electroscope become discharged and come together from Charged particles enter the electroscope at enormous speeds and produce electrical neutralitv in the leaves bv depositing or caixving awav electrons. partlv because of cosmic radiation

space.

1-2 (continued)

CONTENT DEVELOPMENT Discuss the role of lightning rods in

providing

You

from

protection

nia\ wish to

research on

lightning.

have students do

some of

library

die \arious designs

for such devices. Students can also

or in nearbv

public buildings. 0;her safetv aspects related to the subject

ample, precautions

caught storm

—

lightning .

take

for ex-

one

outdoors dunr.c a lightning also be discu -'=^d.

—can

•'

Integration

• • • •

Use the discussion of Benjamin Frankexperiments to integrate concepts of social studies into your lesson. lin's

the top end of the wire to make a loop and the bottom end of the wire to make a hook. Drape an aluminum strip about 1

centimeter bv

hook

re-

search on whether such devices are used in the school, in iheir homes,

• • • •

FOCUS/MOTIVATION An electroscojje can be from a

leaves

constructed

clean, clear bottle. Fit the bottle

with a one-hole rubber stopper. Push the

end

of a heavT. noninsulated copper wire

through the stopper (a coat hanger that has been sanded mav also be used). Bend

centimeters over the

bottom of the wire. The two of the aluminum strip vrill move

at the

apart \\hen a charged object

near or on the loop

Charge a comb bv rubbing limes on a piece of wool. to the loop

placed

the top of the wire. it

three

Touch the comb

and have students notice how aluminum strip

far apait the leaves of the

The Earth can

FlND OUTBY

or give up electric

easily accept

charges. Objects in electric contact with the Earth are said to be grounded.

discharge of static electricity usually takes the easiest path from one object to another. So lightning rods are attached to the tops of buildings, and a wire connects the lightning

»<::>iiM<^ Observing Static

Electricity

O The top of the umbrella might attract

table.

some

the lightning. (Applying concepts) Cut

tiny

paper

dolls or

other objects out of

O A golf course has few,

tis-

other

sue paper and place them on the table between the books, 3.

est

Place a 20- to 25-centi-

the glass vigorously.

The Electroscope

tall

objects.

any, trees or

You might be

the

tall-

object in the area and thus attract the

lightning.

meter-square piece of glass on the books so that the glass covers the paper dolls. 4. Using a piece of silk, rub

Answers

Place two books about 10 centimeters apart on a 1.

rod to the ground. When lightning strikes the rod, which is taller than the building, it travels through the rod and the wire harmlessly into the Earth. Why is it dangerous to carry an umbrella during a lightning storm? Unfortunately, other tall objects, such as trees, can also act as groimders. That is why it is not a good idea to stand near or under a tree during a lightning storm. Why do you think it is dangerous to be on a golf course during a lightning storm?

ANNOTATION KEY

(Making inferences)

O Because both leaves develop the same charge,

and

charges

each

repel

other. (Applying concepts)

Observe

what happens.

Integration

Using the rule of electric charges and your knowledge

charge can be detected by an instrument called an electroscope. A typical electroscope consists of a metal rod with a knob at the top and a pair of thin metal leaves at the bottom. The rod is inserted into a one-hole rubber stopper that fits into a flask. The flask contains the lower part of the rod and the metal leaves. See Figure 1-12. In an uncharged electroscope, the leaves hang straight down. When a negatively charged object electric

of static electricity,

O Social Studies

explain

what you observed. r

OBSERVING STATIC ELECTRICITY Discovery Learning Skills:

Applying concepts, making

observations, making comparisons, relating

cause and effect

Materials: 2 books, tissue paper, scissors, square piece of glass, piece

of silk Figure 1-12 An electroscope

used Charged

Charged Electroscope Using Glass Rod

the leaves in the

electroscope move apart when either a negatively charged rubber rod or a positively charged glass rod makes contact?

six

times with

the wool.

What do you predict will happen if the comb touches the loop at the top of the wire? (The leaves of the aluminum strip will

move

farther apart than in the pre-

vious demonstration.) •

What can you conclude from

the dis-

tance the leaves of the strip move?

(There

more charge on

the

comb

than

Make

up on

various objects

of unlike charges charges repelling.

effects like

sure students relate their observa-

CONTENT DEVELOPMENT Explain the use of the electroscope,

•

and observe the attracting and

tions to the textbook discussion. P

move. Next, rub the comb

electricity to build

to detect electric charges.

Why do Electroscope Using Rubber Rod

In this activity students cause static is

directing students' attention to Figure

REINFORCEMENT/RETEACHING Activity

Book

Students

who have

difficulty

under-

an electroscope is available, demonstrate its ability to be charged by conduction and induction, using

stand' ig the concepts of conduction

charged rubber and

scope.

1-12.

Ask students to attempt to explain what happens on the basis of their knowledge of electric

glass rods.

and

induction should be provided with the

Chapter

activity called

A Giant

Electro-

charge.

there was before.)

— touches the metal knob, electric charges travel down the rod and into the leaves. The leaves spread apart, indicating the presence of an electric charge. Since the charge on both leaves is the same, the leaves repel each other and spread apart. If a positively charged object touches the knob of

1-3 The Flow of Electricity

the electroscope, free electrons in the leaves and metal rod are attracted bv the positive object. The

MULTICULTURAL OPPORTUNITY 1-3

of electrons causes the leaves to become posicharged, .^gain, thev repel each other and spread apart. loss

tivelv

Have vour students investigate the life and work of the .\frican-.\inerican inventor, Garrett Morgan (1875-1963). Morgan's manv contributions include

the invention of the first automatic traffic hght in 1923. This invention was the forerunner of the modem red-vellow-

green

traffic signals that

2. 3.

energ\'

Critical 5.

chemical energy' into electrical energ\(.\nswers:

photocells: 2. thermocou-

ples: 3. batteries.)

Have students

word the group and the

circle

does not belong in

static electricitv?

electric discharge? Give an example. bodv of a kangaroo contains millions of

Thinking

Making

Inferences

What would happen if a lightning rod were made of an insulating material rather than of

1-3 The Flow of

Focus on these questions as you read. ^ How can a flow of charges be produced? ^ What is the relationship

The

run for long. Useful electricitv involves the continuing motion of electric charges. Electric charges can be made to continue flowing.

electnc current, voltage, and resistance?

give

vou use when vou plug an is certainly not were, the appliance would not

electricity that

static electricity. If

among

that

Electricity

electrical appliance into a wall outlet

reasons for their choice. •

conducting material?

Guide for Reading converting

electricity

What What

charged particles, why aren't different kangaroos electricaUv attracted to or repelled by one another?

batteries, photocells.

Ask students to give the singular form of each term. (Thermocouple, batten', photocell.) Then have them use the terms and the following three descriptions to write complete sentences. 1. change light into electrical energy2. produce electrical energ\ from heat produce

are three wavs an object can acquire an

4. If the

Write these three terms on the chalk-

What

electric charge?

see today.

ESL STRATEGY 1-3 board: thermocouples,

-2 Section Review

amfjeres, bolts, ohms, volts

Producing a Flow of Electrons

The others are units of measurement related to electricitv.) (.\nswer: Bolts.

continuing flow of electric charges is a device that changes other forms of energ}.' into electrical energi.-. Energ^ is defined as the abilit\ to do work. Vou use ener^N when

produced bv

A 1-2 (continued)

INDEPENDENT PRACTICE Section Review 1-2 1. Friction, conduction, and induction. 2.

The buildup of

object.

The

tric

electric charges

move

off an object.

One ex-

ample is lightning. 4. Each atom in the kangaroo has an equal number of protons and electrons. So the charges cancel out one another, and the kangaroo is electrically neutral. 5. The lightning would not be able to iher

down the rod. pathway

it ^^

— probabh

ould find anilirough the

building that the lightning rod

Thus, a lightning rod made

trying

REINFORCEMENT/RETEACHING Re\ iew students' responses to the Section Review questions. Reteach anv material that is still unclear,

based on stu-

dents' responses.

CLOSURE ^ Review and Reinforcement Guide Have students complete Section 1-2 in the

TEACHING STRATEGY 1-3

useless.

loss of static electricity as elec-

charges

ravel

to protect.

from an insulator woidd be

Review and Reinforcement Guide.

FOCUS/MOTIVATION Have students arrange marbles in a Have them add another marble to one end of the row, pushing so that the new marble takes the place of the one ahead of it. Thev should see that the marbles all along the row move and that the marble at the far end has been pushed to a new place. row.

you throw a

ball, lift a suitcase, or pedal a bicycle. Energ)' is involved when a deer runs, a bomb or when electricity flows explodes, snow falls through a wire. Although there are different types of energy, each type can be converted into any one of

—

the others.

ANNOTATION KEY

Answers

device that converts other forms of is known as a source of

O A battery. (Applying definitions)

energ)' into electrical energy electricity. Batteries

and

electric generators are the

But thermocouples and photocells are other important sources. Electric generators will be discussed in Chapter 3.

main sources of

electricity.

BATTERIES A battery is a device that produces electricity by converting chemical energy into electrical energy. A battery is made of several smaller units called electric cells, or electrochemical cells. Each cell consists of two different materials called electrodes as well as an electrolyte. The electrolyte is a mixture of chemicals that produces a chemical reaction. The chemical reaction releases electric charges. Electric cells can be either dry cells or wet cells, depending on the type of electrolyte used. In a wet cell, such as a car battery, the electrolyte is a liquid. In a dry cell, such as the battery in a flashlight, the electrolyte is a pastelike mixture. Figure 1-14 will help you to understand how a simple electrochemical cell works. In this cell, one of the electrodes is made of carbon and the other is made of zinc. The part of the electrode that sticks

acid.

called the terminal.

The

electrolyte

sulfuric

acid attacks the zinc and dissolves

Integration

O Physical Forces,

O Physical

Science:

See

Electrolytes.

Chemistry of Matter, Chapter 3.

Figure 1-13 Imagine plugging a car into the nearest outlet rather than going to the gas station! Researchers have been attempting to design efficient cars that use a rechargeable battery as a source of power.

HISTORICAL NOTE GALVANI AND VOLTA Some

of the best-known early experi-

ments with

electricity

were conducted by

the Italian biologist Luigi Galvani

737-

1798). While dissecting a frog, Galvani

observed muscular reactions in the frog's leg when the leg was placed in contact with two dissimilar metals. Frog nerves turned out to be extremely sensitive de-

Figure 1-14 Electrochemical cells, which include dry cells and wet cells, convert chemical energy into electric energy.

it.

Science: Work. See Motion, and Energy, Chapter 4.

What

series of dry cells called'^

What

Wet

Dry Cell

tectors of electrical charges.

an example of a wet celP

Inspired by published reports of Galvani's

Cell

Alessandro

experiments,

745-1827) was eventually able

Volta

dem-

phenomenon of current The device Volta used became

onstrate the Wax

seal

electricity. I

Air

known

space

as Volta's "pile,"

liest electric

Cardboard

and was the

ear-

battery.

cover Zinc can

the class or even demonstrate the work-

Chemical paste

Paper

ings of an automobile battery

lining

Carbon

Zinc electrode

Carbon rod

and of an

engine thermocouple.

electrode

Electrolyte

CONTENT DEVELOPMENT Direct students' attention to Figure

1-14, which shows a diy and a wet cell. Go over the features of these sources of current, and,

each

CONTENT DEVELOPMENT Explain that electrons

in a

similar to that of marbles in a long tube.

When

the tube

full

You may wish

way

of marbles, one

needs to push only one marble into one end of the tube, and a marble will immediately emerge from the far end of the tube.

to ask a .student

who

has

knowledge of automobiles to research and to present to the class information on automobile batteries, which are made

up of a series of wet cells. The student may also explain the role of the batter\' and of the automobile electrical system

•

• •

Integration

•

Use the definition of energy to integrate concepts of work into your lesson.

Alternatively,

Explain that

when

takes place in a

cell,

you may wish

to tiy to ana-

to arrange

have an indusirial/automotive-arts teacher or a local auto mechanic address

the chemical action

electrical force

called electromotive force, or electrical

potential (voltage), causes a current of electricity to llow.

Have students observe

the positive and negative terminals in the figure. Point out that the electron llow is

from the negative

as a whole.

•

possible, denionstrate

Ask students

lyze the processes occurring in each.

FOCUS/MOTIVATION

move

in class.

• • • •

to the positive.

Integration

• • • •

Use the discussion of dry and wet

cells

to integrate electrolytes into your lesson.

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Electric

When

Current

connected to the terminals of a source, a complete path called a circuit is formed. Charge can flow through a circuit. .\ flow of charge is called an electric current. .More precisely, electric current is the rate at which charge passes a given a wire

Faster the electric

Find out by RE/KDINC^ SiriiriiiiiirrTi

measure current.

You may wonder how charge can flow through a conductors are made of elements *hose atoms have some looselv held electrons. When *ire. Recall that

connected to the terminals of a source, the be pulled away from their atoms and to flow through I

Northeast without 6

The higher

the electric current in a wire, the charges are passing through. The svinbol for current is the letter I. .And the unit in which current is expressed is the ampere (A). The ampere, or amp for short, is the amount of current that flows past a point per second. Scientists use instruments such as ammeters and galvanometers point.

yarn Cdy ^to aartmore than 30 mUc

vtire

potential difference causes the loose electrons to :he material.

You may

wonder how lights and other elec:rical appliances can go on as soon as you turn the i^^itch even though the power plant mav be quite a distance away. The answer is that vou do not have to *ait for the electrons at the power plant to reach our switch.

also

.Ml the electrons in the circuit flow as

>oon as the switch is turned. To help understand this :oncept, imagine that each student in Figure 1-17

the erectricai aevices tnat make your ife easy, comfortatiie. and entertanng. In Uttie House on the Prarieand its

related books. Laura

In-

galls Wilder teils defightfii

stones about growing up

days tiefore etectridty. These stones are especialy wonderfii because they xe not tainted by fictional drama. The author simpty dettie

sc'ces

A^A

ECOLOGY NOTE THERMAL POLLUTION Generating plants that produce eleccreate waste heat as one b%pro(iuci of the process. Released into the en%ironment in the form of hot water, this heat can cause environmental problems for organisms Li\"ing in nearbv bodies of water. Excess heat in ecos)^tems can kill organisms that require narrow temperature ranges or can affect the ability" of

Switch

tricirv"

(^AREERg

organisms to reproduce. An increase in temperature can have a negative effect on an entire aquatic communitv. Two approaches to the problem of thermal pKjUution are finding ways to recvcle and make use of waste heal and using closed-oicle cooling.

In closed-

cvcle cooling, cooling f>onds.

cooUng

Electrical

Engineer

The people who design and develop electrical and

Figure 1-17

:re diagrarn

:a 5: electrical engineers.

"-.;

'-r-

.:..

is closed, the rs -iaz-^es the r :- 3 s.::ch to

.Tjnediately^

ca-

or cooling towers are used to safely dispose of heat energ\' through water nals,

evaporation.

has a red ball. When the switch is turned on. each student passes the ball to the person on the right. So almost as soon as the s^^itch is turned on. a red ball reaches the switch. \\"hen the s\%itch is turned off, each person still holds a ball even though it may not be the original ball. This is basicallv how electrons shift through a conductor. The electrons shift positions, but no electrons leave

—

1111

1-3 (continued)

9tn.

ington,

Street. .NW.

Wash-

20036.

FOCUS/MOTIVATION number of times flo\%

•

the circuit.

mentaUv coimt the

Tell students to

Voltage

thev have tiuned on the

You have

of electricitv that dav.

electricity?

already learned that a current flows

is a potential difference between the ends of a wire. The size of the potential difference determines the current that \vill flow through the

whenever there

on the flow of

WTiat did you do to turn

(Responses might include

turned on a s\\itch. plugged somediing or pushed douTi a lever.)

wire.

in.

The greater the

potential difference, the faster

The term voltage is often used to describe potential difference. The SMnbol for voltage is the letter \'. X'oltage is measured in units the charges will flow.

CONTENT DEVELOPMENT Carefullv contrast current and voltage,

vou see the marking 12 V, vou means twelve volts. .\n instrument voltmeter is used to measure voltage.

called volts (V). If

both as to the nature of these quantities and as to the units used to measure them. Be sure to f>oint out that current, which dep>ends on the number of electrons, is not simph' the flow of electrons but also the rate of their flow per unit time. • What is measured in amperes? Cur-

know

that

called a

(

rent. •

\Miat

•

What

measured

in volts? (Voltage.)

the difference between cur-

rent and voltage? iCunent

flow of electrons. \ oltage

a measure of

energ\' available to • \\'hat is

and

move

the rate of

number of

electrons, high-voltage con-

ditions being involved onl\

manv

volts? i.\nip> are used to

amps

measure

current. \ olts are u,^ed to measure volt-

Students sometimes receive the fauln is

related to the

electric energ\"

of electrons in differ-

The

oltage acts as

a sort of electromotive force that causes

depends on the energs" of each electron and not at all on the number of electrons,

electrons to flow from the area of high

which, as students

potential energ%

will discover, is related

to current.

fKJtential energ\'

•

CONTENT DEVELOPMENT \'oltage

REINFORCEMENT/RETEACHING

tial

ent parts of a svstem.

electrons move, .\ctuallv. \oltage

age.)

a great

electrons.)

the difiference between

impression that voltage

when

which there

in\ol\ed in smv situation in is

a difference in the poten-

•

toward the area of low

Integration

L'se the discussion

•

of the potential

•

dif-

ference in the human heart to integrate concepts of muscles into vour lesson.

Voltage is not limited to the electrical wires that run your appliances. Voltage, or potential difference, is crucial to your survival. A potential difference exists across the surface of your heart. Clhanges in the potential difference can be obser\ed on a monitor and recorded as an electrocardiogram (EKG). An EKG is a powerful tool used to locate

LOW CURRENT AND LOW VOLTAGE

ANNOTATION KEY Each electron carries litlle energy, there are lew electrons Little total energy is delivered per second

defects in the heart. Potential differences arc also responsible for the movements of your muscles.

be made to begin beating again by applying

pacemaker

O Voltage

represented by the size of

the load carried by each person; current,

by the

number of

people. (Interpreting

diagrams) Each electron there are total

—

electric current. If the natural

Answers

LOW VOLTAGE

HIGH CURRENT AND

In the heart a small region called the pacemaker sends out tiny electrical signals as many as sixty times ever)- minute. This is what causes the heart to beat. Perhaps you may already know that if the heart stops beating, doctors sometimes apply an electric curpotential difference to the patient's chest. rent Because the heart is controlled by electricity, it can

—

and

carries

many

energy

energy, but

little

electrons Moderate

Integration

delivered per second

LOW CURRENT AND

O Life Science: Muscles. See Human

HIGH VOLTAGE

and Health, Chapter

ology

O Life Science:

this

fails to

Each electron

work, surgeons can implant an electronic pacemaker. Humans are not the only organisms that use electricity produced in their bodies. Have you ever heard of electric eels? They truly are electric! An electric eel can produce jolts of electricity up to 650 volts to defend itself or to stun prey. Another tvpe of fish, an electric ray, has a specialized organ in its head that can discharge about 200 volts of electricity to stun and capture prey. Although these voltages may not sound like a lot to you, remember that only 120 volts powers just about everything in your home!

carries

much

but there are few electrons.

energy

total

Life:

energy,

Bi-

Zoology. See Parade of

Animals, Chapter

Moderate

delivered per second

HIGH CURRENT AND HIGH VOLTAGE

BACKGROUND Each electron carries much energy, and there are many electrons High energy

total

INFORMATION

delivered per second.

PEIZOELECTRICITY

Figure 1-18 This diagram shows the relationship

and

current.

Peizoelectricity

between voltage

How

rial to

current

represented^ Voltage'^

the ability of mate-

generate electricity

when pressure

applied or released. In other words, a

peizoelectric material will generate an

charge when squeezed! Certain asymmetric crystals, such as quartz and

electrical

tourmaline, effect. First

tric effect finds

tors,

may appear move could

applications in ultrasonic

ultrasonic

flameless pilot lights.

interesting-looking fish

touchable, such a

peizoelectric

the late 1880s

submarine detecmicrophones, depth finders, and

cleaners, this

Pierre Jacques Curie, the peizoelec-

b)-

Figure 1-19 Although

the

exhibit

discovered

an electric ray. which, like an electric eel. IS capable of producing

prove

strong

jolts

fatal

This is

electricity.

INTEGRATION P

MYTHOLOGY

Early

humans often explained mystephenomena by creating

rious electrical

myths. For example, the Vikings believed

REINFORCEMENT/RETEACHING A gravitational analogy may help

CONTENT DEVELOPMENT

dents understand the concept of voltage.

Two

points at different distances from a

body exerting diff^erent

a gravitational force have

potential energy".

The

closer

point has greater potential energy- than the farther point has

and

will

toward the attracting body.

move

faster

that Thor, the

Have students study Figure

stu-

1-18.

Point out that the diagrams illustrate

four different combinations of current

and

voltage.

The

figure shows

total electrical energ)'

the

how

the

related to both

amount of current and

the

amount of

voltage.

•

• • •

Integration

Use the discussion of

•

electric eels

god of thunder, created

lightning by hurling a magic

down ley,

to Earth. In the

the

morous

Dutch

hammer

Hudson River Val-

set i lei s

often told a hu-

which thunder was caused by the gods of the nearby hills knocking down pins in a bowling game. This latter i.ilo was the basis for the stoiy of Rip Van Winkle by Washington Irving. folk tale in

•

and

rays to integrate concepts of zoology into

your

lesson.

— Resistance

HISTORICAL NOTE

The amount of current that flows through a wire does not depend only on the voltage. It also depends on how the wire resists the flow of electric charge. Opposition to the flow of electric charge is known as resistance. The symbol for resistance is the letter R. Imagine a stream of water flowing down a mountain. Rocks in the stream resist the flow of the water. Or think about running through a crowd of people. The people slow you down by resisting your movement. Electric charges are slowed down by interactions with atoms in a wire. So the resistance of a wire depends on the material of which it is made. If the atoms making up the material are arranged in such a way that it is difficult for electric charge to flow, the resistance of the material will be high. As you might expect, resistance will be less for a wider wire, but more for a longer wire. Higher resistance means greater opposition to the flow of charge. The higher the resistance of a wire, the less current for a

GEORGE OHM The German relationships

first

Ohm

to define the

among voltage,

current, re-

Ohm

and power.

sistance,

George

physicist

(1787-1854) was the

not

only

showed the relationship among these quantities, but he also specified them in

Many people

mathematical terms. lieve that

Ohm's law

be-

the most impor-

tant single electric formula a student will

ever learn.

Ohm is

also

honored

in that his

used as a unit of measure for

ance.

One ohm

allow one

ampere

name Figure 1-20 Light bulbs light because of the phenomenon of resistance. The metal filament in

resist-

the resistance that will to flow with

motive force of one

volt.

the center of the bulb offers

an electro-

An ohm

enough resistance

to the electric current flowing through it so that heat and light are given off.

also

defined as the resistance, at 0°C, of a col-

umn

of mercury 106.3 centimeters

given voltage.

The

length, of mass 14.4521 grams, and of

BACKGROUND

indeed, necessary.

an instrument used

An ohmmeter

consists of two

at first, this

energy.

The

filament

when

atures,

FOCUS/MOTIVATION

use

scientific

Ohm's law

(at least

on their own, with your supervision, and before they are formally qualitatively)

the textbook.

• If

caption to Figure 1-20. Discuss

the

resist-

some of

re-

used, what should happen to

should be brighter.) • Why should the bulb be brighter with a filament with greater resistance? the light bulb?

(It

(More of the electrical energ)- would be converted into light energ\'.)

What should happen

current through a

Have students observe and read ance, current, and voltage with

a different filament with

sistance

•

CONTENT DEVELC ^lENT

the following questions.

a very thin piece of metal it.

The same

resistance a material has

depends

its

atoms move around more randomly and thus way of flowing electric charges. At very

get in the

Allow students do some hands-on work with low-voltage dry cells, ammeters, voltmeters, light bulbs, and wires. Students can be asked to hypothesize on the effects of varying voltages and resistances, and they can then demonstrate experimentally what actually occurs. En-

introduced to

temperature. The resistance of a metal increases with temperature. At higher temper-

1-3 (continued)

to "discover"

often quite useful

How much

method

responsible for toasting your pita bread you place it in the toaster.

principle

Q somewhat on

resistance

that resists the flow of electricity within

and a small iron needle whose deflection shows a measure of the resistance.

students

less

through the wires that lead from the wall. Rather, some of the electric energy passing through the filament of the bulb is converted into light and heat

placed at right angles to each other

courage

Different

(H).

Copper wire has Copper is a good

You know that light bulbs give off light and heat. Have you ever wondered where the light and heat come from? They are not pouring into the bulb

for measuring resistance in an electrical

coils

ohm

the

conductor; iron is a poor conductor. Nonconductors offer such great resistance that almost no current can flow. All electric devices offer some resistance to the flow of current. And although it may not seem

INFORMATION OHMMETER An ohmmeter

resistance than iron wire does.

uniform cross-sectional area.

circuit.

unit of resistance

O wires have different resistances.

amount of filament with more

down

flow of electrons, and electron flow

same

the the

as current.)

What would you need to move the same amount of current through a

•

higher-resistance filament? (More force

or voltage.)

to the

resistance? (The current should be

less.)

Why should the current be less through a filament with more resist-

•

ance? (The resistance slows

•

• • •

Integration

• • • •

Use the discussion of the resistance of wires to integrate concepts of metals into

your lesson.

,nfimlK»r^ TU

ANNOTATION KEY

Integration

O Physical Science: Figure 1-21 This is no magic trick At low temperatures, certain materials that have almost no

O Physical Science:

resistance are said to be superconducting. Superconducting materials, such as the one at the bottom of the photograph, repel magnets. For this reason the

magnet

Metals. See Matter:

Building Block of the Universe, (Chapter

Chapter

ergy,

O Physical

Heat. See Heal En-

Science:

Hydroelectric

Power. See Ecology: Earth's Natural Resources, Chapter 1.

floats in midair.

low temperatures, however, the resistance of certain

metals

becomes

state are said to

essentially zero. Materials in this

be superconductors. In supercon-

no energy is wasted. However a jreat deal of energy must be used to keep the Tiaterial cold enough to be superconducting. Scientists are currently working to develop new ductors, almost

COMMON ERRORS While completing computation prob-

materials that are superconducting at higher temperitures. \i\\

When

lems using Ohm's law, students may re-

accomplished, superconductors in industry. Superbe used in large generating plants

this

arrange the formula in incorrect ways. For example, in solving for V, given I and

become extremely important

ronductors will ind in motors where negligible resistance for very large currents.

There are

will

R, they

allow

may

tiplying the

also plans for

superconducting transmission cables that will reduce jnergy loss tremendously. Electric generating plants ire usually located near major population centers ather than near the fuel source because too much energy is lost in carrying a current. Superconducting ransmission lines will make it practical for generatng plants to be situated next to fuel sources rather han near population centers. Superconductors are ilso being tested in high-speed transportation

divide I by R instead of multwo quantities.

Review the algebra involved in such rearrangements and also analyze the units that result from rearrangements. Demonstrate to students that such dimensional analysis can help to reveal errors in manipulating equations and carrying out

(

calculations.

systems.

Ohm's Law An ifies

important expression called

the relationship

"esistance.

vire

(I) is

among

Ohm's Law

iden-

current, voltage, and

Ohm's law states that the current in a equal to the voltage (V) divided by the

Use the discussion of superconductors

-esistance (R).

to integrate concepts of hydroelectric

power

into your lesson.

CONTENT DEVELOPMENT Remind

students that the

ohm

the

Then, after reviewing the concepts of voltage and current, introduce Ohm's law: unit of resistance.

CONTENT DEVELOPMENT

GUIDED PRACTICE Skills

Development

Have students look

Making comparisons, making diagrams Skills:

Have students plan and execute drawings that illustrate, in their

own

creative

ways, the concepts of voltage, current,

at the

photograph

Figure 1-21 and speculate on what

causing the magnet to

Then have

float

temperature can

affect the resistance of a material.

• • • •

and low voltage and current

Use the discussion of the relationship between resistance and temperature to integrate concepts of heat into your les-

situations.

•

= R

a volunteer read the caption.

Explain that changes

and

resistance. Before students begin, have them review Figure 1-18, which illustrated the difference between high

midair.

Integration

•

• • •

Carry oin sample calculations involving this equation in rearranged forms; use it, in separate problems, to solve for I, V,

and

Re sine to pay attention to the and bring out the general

units in\' il\ed

point

liiat

and R vary

inversely, given a

constant v.

son.

TIND

OUT BY

y/////////////////\

ANNOTATION KEY Ohm's Law

Answers

O 5 ohms. (Making calculations) O No; nothing happens. (Applying concepts)

O The O The

bulb lights up. (Appl>ing con-

cepts)

light

bulb

will light

up. (Relating

cause and effect)

Integration

O Mathematics FIND OUT BY CALCULATING

OHM'S LAW Skills:

Applying concepts, making

calculations, calculator

Students should use Ohm's law to arrive at the following calculations:

0.16 amps;

Row

16 ohms;

Row

110 volts; Row 4: 0.24 amps; Row 5: 22 ohms. Integration: Use the Find Out by Cal2:

culating feature to integrate mathematics

into vour science lesson.

1-3 (continued)

REINFORCEMENT/RETEACHING Encourage slower students

to carry

out many simple practice calculations involving Ohm's law. They can make up charts that

show the various correct

re-

arrangements of the equation and that display an assortment of values obtained by substituting different numbers and solving for the

unknown.

INDEPENDENT PRACTICE Section Review 1-3 1. A chemical reaction causes the release of electrons. These electrons flow

from a negative terminal terminal.

Then

pumped back

the

to a positive

electrons

are

to the negative terminal

begin the cycle again. thermocouple generates electricit)' from heat energy by .making use of temperature differences. A photocell to 2.

Complete the following chart.

lamps)

1-4

Guide for Reading

Electric Circuits

Perhaps you wonder why electricity docs not How from the outlets in your home at all times? You can find the answer to this question if you try the following experiment. Connect one wire from a terminal

a dry cell to a small flashlight bulb.

thing happen?

Now

1-4 Electric Circuits

Focus on these questions as you read. What IS an electnc circuif^ What is the difference between series and parallel

MULTICULTURAL OPPORTUNITY 1-4

circuits'^

Have your students investigate the life and work of the African-American inventor Lewis Howai d Latimer (1848-1 928).

Does any-

connect another wire from the

bulb to the other terminal on the dry cell. What happens? With just one wire connected, the bulb will not light. But with two wires providing a path for the flow of electrons, the bulb lights up. In order to flow, electrons need a closed path through which to travel. An electric circuit provides a complete, closed path for an electric current.

Latimer,

African-American

only

the

member of

the Edison Pioneers, was in-

strumental

the development of the

electric light bulb.

mer was

As a draftsman,

blueprints necessary

Edison to receive

Parts of a Circuit

son's

electric circuit consists of a source of energy;

and a

energy can be a battery, a thermocouple, a photocell, or an electric generator at a that the source of

a machine, or a motor. In

some

all

cases the load offers

resistance to the flow of electrons.

energy is converted into heat, mechanical energy. electric

As a

light,

result,

Figure 1-22

electricity

claims

court

—

task

can

ESL STRATEGY 1-4

flow through an open circuit (left). When the switch is flipped, the circuit IS closed and electrons

Ask students

word

to change the underlined each of the following sentences

so that the statements are true.

flowing

• Electricity

circuit.

Closed Circuit

Circuit

He was also defend Edi-

published a book entitled Incandescent

indicates that a current through the circuit?

Open

upon

Electric Lighting.

have a complete path through which to flow (right). What

Thomas Alva

which he did ably because of his vast knowledge of electricity. In 1890, he

switch. Recall

power plant. The load is the device that uses the electric energy. The load can be a light bulb, an appliance,

patent

for

his patents.

frequently called

a load, or resistance; wires;

Lati-

responsible for developing the

• Electricity

circuit.

cannot flow through a closed

(Answer: can.)

can flow through an open

(Answer: cannot.)

CONTENT DEVELOPMENT Reintroduce students to the

circuit

parts with which they are already familiar.

Then

discuss the nature of a circuit

and the fact that circuits must be closed. Ask them to observe the circuits shown in Figure 1-22, which helps to make

this

fact clear.

GUIDED PRACTICE

CLOSURE

Open and

Review and Reinforcement Guide Have students complete Section 1-3 the Review and Reinforcement Guide.

close the .switch several times

and encourage students to do so as well. What is happening? (Electrons are flowing from tme terminal of'the dry cell, through a closed circuit, hack lo the

•

What happens when the switch is opened? Why? (Current tan no longer flow because there

students a simple electric circuit

containing a small light bulb, a voliage diy

ceil,

wires,

and

Applying concepts, making

observations, making comparisons

Have students Chapter

Electricity

coiiipii'ic

Laboiatory

From

Lemon.

the in-lext

Investigation:

In the inves-

tigation students will explore the flow of

by a simple wet

cell.

•

FOCUS/MOTIVATION Show

Development

Skills:

electi icity created

other terminal.)

TEACHING STRATEGY 1-4

Skills

lovv-

switch.

plete, closed

along.)

no longer

com-

path for electrons to travel

ENRICHMENT Activity

Book

Students can build another simple wet cell in the triciiv

chapter

From an

activity called Elec-

Olive.

â&#x20AC;&#x201D; The switch in an electric circuit opens and closes Vou will remember that electrons cannot

BACKGROUND

the circuit.

flow through a broken path. Electrons must have a closed path through which to travel. When the switch of an electric device is off, the circuit is open

INFORMATION CONDUCTANCE The conductance of circuit

the reciprocal of

Conductance

its

and electrons cannot flow. WTien the switch is on, the circuit is closed and electrons are able to flow.

cunent

a direct

resistance.

Remember

usualh' represented by

a closed

the letter G.

G = Conductance

used to help calculate Figure 1-23

ss'.ere

-s^ch as the

â&#x20AC;&#x201D; :s -vage power lines.

spelled backw ards!

^::ncity

important rule:

ST. St.

ELMO'S FIRE

Elmo's Fire

a glow or a flame

sometimes seen on the masts of ships during stormv weather. .\lso called corona discharge. St. Elmo's Fire is caused bv the ionization of the air surrounding the tip of the mast. ization

The color of the

Figure 1-24 A series circuit c:. jes only one path for the ;.'. c' electrons.

parallel circuit

proiiOes several paths. the circuits in your

How

home

are

wired''

Why''

ion-

cannot flow

can flow only through

and

Parallel Circuits

There are two tvpes of electric circuits. The tv-pe depends on how the parts of the circuit (source, load, wires, and switch) are arranged. If all the parts of an electric circuit are connected one after another, the circuit is a series circuit. In a series circuit there is onlv one path for the electrons to take. Figure 1-24 illustrates a series circuit. The disadvantage of a series circuit

HISTORICAL NOTE

Electricity

circuit. Electricity

circuit.

Series

the total resistance of a parallel circuit. One unit for conductance is the mho

ohm

this

through an open

that if there

a break in

anv part of the circuit, the entire circuit is opened and no current can flow. Inexpensive holiday tree lights are often connected in series. WTiat will happen if one light goes out in a circuit such as this? In a parallel circuit, the different parts of an electric circuit are on separate branches. There are several paths for the electrons to take in a parallel circuit. Figure 1-24 shows a parallel circuit. If there is a break in one branch of a parallel circuit, electrons can still move through the other branches. The

(

a function of the energ\" of the Series Circuit

ions. Different materials require diff^er-

Parallel Circuit

ent energy levels to ionize, and thus result in different colors.

1-4 (continued)

CONTENT DEVELOPMENT WTien you introduce lel circuits,

series

and

paral-

direct students" attention to

Figure 1-24, which brings out the difference between the two types of circuits. If possible, construct actual series allel circuits in .\sk.

and par-

make

their

own

dia-

grams of series and of parallel circuits. Thev can use colored pencils to trace the various paths of electrons.

GUIDED PRACTICE

transparencv in the Transpar-

and Parallel Cirhelp students understand the

ency Binder called Series

the classroom.

students to

Multimedia L'se the

ad-

cuits to

concepts in

this section.

Laboratory Manual Skills

Development

Skills:

Applying concepts, making

observations, making comparisons,

INDEPENDENT PRACTICE

with the Chapter

the chart.

Circuitrw

Activity

Students

and

making inferences

Book

vanced students can also do library research on the \oltage, current, and resistance relationships for the two types of circuits and can include iheir findings in

.\i this

who need practice with

parallel circuits 1

series

should be provided

acti\ itv called Electric

mav want

to have stu1

Labora-

tory Investigation in the Laboratory

Man-

ual called Building Electric Circuits. In

the in\estigation students will explore

both

point vou

dents complete the Chapter

series

and

parallel circuits.

Why do tree lights connected in parallel have an advantage over tree lights connected in series? Why do you think the electric circuits in your home are parallel circuits? current continues to flow.

ANNOTATION KEY

Household

Circuits Have you ever wondered what was behind the outlet in the wall of your home? After all. It is rather

Answers

to the outlet

Two

third wire that

and have a between them. The

connected to ground. (Recall that

grounded provides the

its

your

home

to operate,

a wire

outlets

switch

shortest direct path

the

must have one of

in the

home

circuit?

diagram

flipped

circuit

in parallel so

flow. (Relating cause

and

effect)

O So that a problem on one circuit all

house to go

>=l

will

the electricity in the entire

off.

(Making inferences)

closed, current

problem

one prong of the plug, through the appliance, and back into the wall through the other prong of the plug. Many appliances have a third piong on the plug. This prong is attached to the third wire in the cable, which is connected directly to ground and carries no current. This wire is a safety feature to protect

wired

circuits are

one

not cause

flows into

on the string will go out no longer a complete,

opened, the others remain closed and electricity can still that

if all the appliances in are attached to this

and the other terminal connected to the low potential wire. The two prongs of a plug of an appliance are connected to the terminals inside the appliance. the switch of the appliance

closed path. (Applying concepts)

What happens when the

What

off?

terminals connected to the high potential wire

When

because there

switches control only certain

for current to travel into the Earth.) For any appli-

ance

All the lights

Figure 1-25 The outlets in a home are connected in such a way that several may rely on the same switch. A home must have several circuits so that different

the wires run parallel to each other potential difference of 120 volts

that the cir-

closed. Thus the elec-

current cannot flow. (Ap|)lyiiig con-

tric

a cable consisting of

three wires enclosed in a protective casing.

means

to wires

no longer

cepts)

operate.

Connected

Damage

cuits are

amazing that by inserting a plug into the wall outlet, you can make your television, refrigerator, vacuum cleaner, hair dryer, or any other electrical appliance

cause them

any one appliance could to stop working. (Inter-

all

Light bulb

preting diagrams)

A short circuit is an accidental connection that allows current to take a shorter path around a circuit. A shorter path has less resistance and therefore results in a higher current. If the high-potential wire accidentally touches the metal frame of the appliance, the entire appliance will become part of the circuit and anyone touching the appliance will suffer a shock. The safety wire provides a shorter circuit for the current. Rather than flowing through the appliance, the current will flow directly to ground thereby protecting anyone who might touch the appliance. Appliances that have a plastic casing do not need this safety feature. Can you explain why?

is a poor conductor of electric(Making inferences)

against short circuits.

FACTS AND FIGURES ALTERNATING CURRENT The

which alternating current in cycles per second. One cycle per second is called one hertz. The domestic power supply in the United varies

rate at

expressed

States alternates at the rate of 60 hertz.

The same

—

(from electric

rate

not used worldwide.

company)

CONTENT DEVELOPMENT Divide the class into teams of three to six students.

mon

Show

students

electrical appliances,

some com-

such

as a light

bulb, blow diyer, heating pad, fan,

and/

or steam iron. Point out that most elec-

ENRICHMENT

rent from a dry cell or battery

Advanced students can be encouraged to do library research on other devices,

rect current

electrons flows in only one direction.

such as capacitors, used in electronic

current in houses and schools

cuits.

They can

cir-

also find out about the

symbols for the various circuitry

ele-

called di-

(DC) because the current of is

The

called al-

ternating current (AC) because the current alternates

and reverses directions

trical

appliances aie rated according to

power Mention that these figures normally can be found on a side plate on appliances and on the top of a the line voltage needed and the

consumed

in watts.

light bulb.

many

times a second.

grams.

rent

REINFORCEMENT/RETEACHING

change direction at regular intervals. Point out that most of the current stu-

watts or ,unps.

dents

appliaiucs until each team has had a

ments that are used

Remind students

schematic dia-

that there are

two

The

cur-

basic types of electrical current.

u.se is

current in

alternating cur-

which electrons

alternating current.

Distribute an appliance to each team.

Have

the teams find, read, and record

the naitif of the appliance, voltage, and

chaiu

c to

Have

the teams exchange

record the data from each ap-

pliance.

â&#x20AC;&#x201D; Figure 1-26 Fuses protect circuits from overloading. Tlie fuse on ttie ieft is new. The fuse on the right, however, has been blown and cannot be blown again. How did the blown fuse

ANNOTATION KEY

protect the circuit

Circuit Safety Features

Answers

was part of?

Your home has

of metal in the fuse melted,

strip

ning through

breaking the electric circuit. This pre\ented too much heat from building up

on wires in the and effect)

circuit. (Relating

it.

cause

too

once on the same

become old and

amount of electricity runmany appliances are running

a great

circuit

the wires have

frayed, heat can build

in the

wiring. If the wires in the walls get too hot, there

the danger of

fire.

Two

devices protect against this

potential danger.

FUSES

protect against too

ing at once, your

home may have

much current flowfuses in a fuse

is a thin strip of metal through which current flows. If the current becomes too high, the strip of metal melts and breaks the flow of electricity. So a fuse is an emergency switch.

box. Inside each fuse

PROBLEM SOLVING FAULTY WIRING

CIRCUIT BREAKERS that

In this activity students will have a

this

chance to do some creative detective work. Before assigning the Problem Solving feature, it may be useful to review the topic of series

and

As a

parallel circuits.

cabin has

result, the

disadvantage of fuses

of fuses. Like fuses, circuit breakers protect a circuit from becoming overloaded. Modern circuit breakers have a switch that flips open when the current flow becomes too high. These circuit breakers can easily be reset and used again once the problem has been found and corrected. Circuit breakers are easier to use than fuses.

Students should realize that Ms. Fix-It must have wired the cabin using series circuits.

One

once they burn out, they must be replaced. For reason, circuit breakers are often used instead

some

inconvenient peculiarities. In order to solve these inconveniences, the wiring will

have to be redone using one or more

-4 Section Review

parallel circuits. This will allow visitors to

use each electrical appliance on

its

own.

After students have completed their

diagrams and the class has discussed their solutions, point out that correcting problems in electrical wiring can be much

more complicated than wiring.

installing

nections and parallel connections? Explain your answer. 4. What would happen if your home were not wired in parallel?

new

Both processes can be dangerous

for the amateur.

The

Connection You and Your World Does your home have fuses or circuit breakers? Explain the purpose of each device.

family described in

the Problem Solving feature might be well advised to call

on the

What is an electric circuit? Compare a series circuit and a parallel circuit. Can a circuit be a combination of series con-

services of a

qualified electrician.

REINFORCEMENT/RETEACHING Multimedia <

1-4 (continued)

CONTENT DEVELOPMENT Point out that a fuse

Students

a safety device

an electric circuit. Explain that fuses present overloading of a circuit. In a house and f)ther buildings, each

this

may review

nesses, street lights, automobile headlights.)

the concepts in

section by using the video called

Electric Currents

and

arate fused circuits allow the rest of the circuits to

one

circuit

remain undi.sturbed, even goes out.

After students have seen the video, have them list several examples of each of the

following

(possible

responses are

Electric energy

converted into

light.

homes and

busi-

(Light bulbs used in

energy

converted into mo-

(Kitchen blender or mixer, electric

3. Electric

(Heat

saw.)

energy

converted into heat.

in a light bulb, electric heaters,

heat in electric wires.)

energy is converted into sound. (Stereo system or record player, sound created by electric motors, door4. Electric

given in parentheses). 1.

tion.

drill, electric

Circuits.

installed in

circuit has a fuse or circuit breaker. Sep-

2. Electric

bell.)

—

1-5 -I— rr-j

Have your students read iluii electric meter each day, al the same time of day, for one week. Next they siiouid plot the electrical usage per day over the oneweek period. Are there some days when they use more electricity? If so, what ex-

Faulty Wiring You and your

family arrive at the site

summer

vacation

— an

old but

edge

quaint cabin situated at the

of a

she must have made a mistake or two. The kitchen light must remain on in order to keep the refrigerator going.

beautiful lake.

As you pile out of the car, you are greeted by the superintendent

order to turn on the television, the fan must be on. And the garbage disposal

responsible for taking care of all the cabins in the area. The neighbors call

will

her Ms.

must the cabin be wired? How should the cabin be rewired? Draw a diagram showing the mistakes and the

tvls.

tells

Fix-It

you

that everything

working order. However, she was working on the wiring.

the cabin

when

work only when the oven

on.

planations can they generate for this

Drawing Diagrams

is in

in-

creased use?

How

Fix-It.

Power

MULTICULTURAL OPPORTUNITY 1-5

Iving of your

Electric

•

ESL STRATEGY 1-5

corrections.

Have students create a six-frame

illus-

tration of the safety rules of electricity.

>\V</

They should number each frame match the rules listed in this section.

\ \.

REINFORCEMENT/RETEACHING

Review students" responses to the SecReview questions. Reteach any material that is still unclear, based on stution

1-5 Electric

the word power in a number of mean strength, or force, or lergy. To a scientist, power is the rate at which ork is done or energy is used. Electric power is a leasure of the rate at which electricity does work

You probably use

ifferent senses

—

dents' responses.

Guide for Reading

Power

Focus on these questions as you read. ^ What IS electric power''

^ How

IS electric

CLOSURE ^ Review and Reinforcement Guide

power

Have students complete Section 1-4

related to energy?

in the

Review and Reinforcement Guide.

provides energy.

TEACHING STRATEGY 1-5

FOCUS/MOTIVATION Ask students,

advance, to bring in

(with their parents' permission) an elec-

hJDEPENDENT PRACTICE Section .

Review 1-4

A complete,

closed path for the flow

»f

electrons.

In a series circuit, there

only one

)ath for electron flow. In a parallel ciruit, >.

there are several paths.

Yes. Separate sections of a circuit

:ould be in parallel but be connected to

tric utility bill.

allel.

information stated on the

4. If

one

light or appliance

went

off, all

would not work. Answers will vary. In a fuse, a strip of

the others is

another in series. Also, separate lections could be connected in series.

In class, explain that the

but be connected to one another in par-

metal melts when the current is too high. In a circuit breaker, a switch turns off if too much current flows through a circuit.

bill

and the

price of service relates to the cjuantity of electric energ)' used,

which

turn de-

pends on voltage, nu rent, and time. As you go on to teach students the specifics regarding elect lic power and energy, explain in more detail how knowledge about these quantities and iheir calculations can be used to understand the information on their utility bills.

POWER USED BY COMMON APPLIANCES

HISTORICAL NOTE JAMES WATT The unit the watt,

for measuring electric power,

named

after the British en-

gineer James Watt (1736-1819). Watt was a successful inventor of many things,

but his most famous work was in the development of the steam engine. In the mid-1 700s, he took an interest in the Newcomen steam engine, and he set about making it more efficient. Working together with Matthew Boulton, Watt created an experimental engine embodying the essential characteristics of the modern steam engine.

1-5 (continued)

CONTENT DEVELOPMENT Explain that the unit of power in watts

when

current

the force

in volts

stated

and the

amperes. Have students ex-

amine Figure 1-27. Discuss the power ratings of the appliances and encourage students to compare the appliances listed.

Which appliance listed uses the least number of watts? (The clock.) Show the class how to use the equa-

•

tions

below to find watts,

volts,

and amon

peres. Write the following equations

the chalkboard.

Power = Force x Current = Volts X Amperes Volts = Watts H- Amperes Amperes = Watts -^ Volts Watts

• • • •

•

Integration

Use the discussion of watts concepts of power into your

•

• •

to integrate

lesson.

GUIDED PRACTICE Skills Skill:

Development

Making calculations

Have students

the

solve

following

problems. Remind students to use the proper imits of measure. •

What is the current u.sed by an electric

marked 120 volts and 1000 watts? (1000/120 = 8.33 amps.

iron

Figure 1-28

Electricity tor

home

your

purchased on the

basis of the amount of energy used and the length of time for which It IS used. Power companies install an electric meter in

your

home

and the electric

record

total

usage

this

time they are used.

energy

ANNOTATION KEY

in kilowatt-hours.

The formula

Answers

for

OThe

200

E = P X Electric energy

measured

range

oven.

(Interpreting

charts)

Energy = Power x Time

watts.

(Making calculations)

ÂŠ $0.04; $0.24. (Making talculai ionsl

in kilowatt-hours

Integration

(kWh).

O Physical Science: = Power x Time Kilowatt-hours = Kilowatts x Hours Energy

Forces,

One kilowatt-hour is equal to 1000 watts of power used for one hour of time. You can imagine how much power this is by picturing ten 100-watt bulbs in a row, all burning for one hour. One kilowatthour would also be equal to a 500-watt appliance running for two hours. To pay for electricity, the energy used is multiplied by the cost per kilowatt-hour. Suppose the cost of electricity is $0.08 per kilowatt-hour. How much would it cost to burn a 100-watt bulb for five hours? To use a 1000-watt air conditioner for three hours?

FIND OUT BY

THINKING

POWER AND HEAT Discovery Learning

Skills:

data,

Electric

one of the most useful energy resources. But electricity can be dangerous if it is not used carefully. Here are some important rules

remember when using

Students should be able to include the

^THINKIN<9

power ratings of various appliances on a chart and infer that those with the highest power rating often produce the most

Power and Heat

electricity.

Examine the appliances In your home for their power rating. Make a chart of this

Never handle appliances when your hands are wet or you are standing in water. Water is a fairly good conductor of electricity. If you are wet, you 1.

Applying concepts, recording

making comparisons, making

inferences

Find out by

Safety

Electricity

Power. See Motion. and Energy, Chapter 4.

heat.

Information.

could unwillingly become part of an electric circuit. 2. Never run wires under carpets. Breaks or frays in the wires may go unnoticed. These breaks cause short circuits. A short circuit represents a shorter and easier path for electron flow and thus can cause shocks or a fire.

What

the relationship

between an appliance's power of

heat

and the amount produces?

rating it

ECOLOGY NOTE ENERGY CONSERVATION Increasingly, manufacturers are pro-

viding energy-usage information to help

consumers choose more energy-efficient appliances.

Refrigerators,

freezers,

water heaters, and air conditioners make use of new technologies to cut down on actually

represent

multiplication

units.

inefficient

INDEPENDENT PRACTICE Activity

Book

CONTENT DEVELOPMENT

Students can investigate the ways in which people protect themselves against

You can easily demonstrate the validity of the E = P X t equation by noting that

sudden power

power is simply energy divided by time. Thus the right side of the equation, P X

Sources.

reduces to

activity

failures in the

called

Chapter

Emergency

Power

energy use.

Improvements in efficiency in electric power generation are also being implemented. For example, cogeneration is a process that uses a jet engine and a conventional boiler one after the other. Anpromising technolog)' is called magnetohydrodynamics. This process involves seeding combustion gases with poother

tassium.

Ener sx

which clearly equals energy.

â&#x20AC;&#x201D;

rigure i-^a nsniemoer lo exercise care and good judgment when using electricity. Avoid unsafe conditions such as the

FIND OUT BY CALCULATING

HOW MUCH

ones shown

ELECTRICITY

here.

YOU USE? Skills: Applying concepts, making comparisons, making calculations,

calculator

Never overload a circuit bv connecting too appliances to it. Each electric circuit is designed to carr)' a certain amount of current safely. 3.

Students will be able to get a practical understanding of the cost of electricity through tliis simple acti\ity. They uill also have to relate the concepts and equations presented in the textbook to make their calculations. You may want to call

manv

short circuits. 5.

power company yourself

the local

cost of elecper kilowatt-hour in voiir area.

and inform students of the tricitv

Find out by ^<;g^M,CMi->vTiisiia

How Much

BACKGROUND INFORMATION Government

For a period of several

Also record

and and en-

agencies, both local

tfie

amount

time eacfi appliance

stick

vour fingers

electric socket

1-5 Section Review

run.

down the power each appliance you The power rating in watts should be marked on the appliance. You can also use in2. Write

rating for

homes and industries. The National Electric Code is a national set of standards for home and industrial instalsafetv in

cific

Never

or stick a utensil in an appliance that is plugged in. The electricitv could be conducted directlv into vour hand or through the utensil into your hand. Exposure to electricitv with both hands can produce a circuit that goes through one arm. across the heart, and out the other arm. 6. Never come close to wires on power poles or to wires that have fallen from power poles or buUdinss. Such wires often cam vers hi^h currents.

days, keep a record of every electrical appliance you use.

force regulations to help ensure electric

lations.

Electricity

You Use^

SAFETY STANDARDS national, provide information

overloaded circuit can cause a short circuit. worn or frayed wires to avoid

4. .\lwavs repair

formation

Local communities also have spe-

amount

that

electric

power? What

the formula for is

how much elec-

costs per kilowatt-hour your area. Calculate the cost of the electricity you use

elec-

power measured?

What

electric energy?

What

the formula for is

elec-

energ\ measured? What happens if you touch an exposed electric wire? Whv is this situation worse if vou are wet or standing in water? tric

you use each day.

4. Find out

calculating electric energy? In what unit

electricity in kilowatt-hours

through a housing, building, or wiring inspector. In some communities, all wiring must be done bv a licensed electrician, even in pri\ate homes.

tric

Figure 1-27.

3. Calculate thie

regulations, which are administered

WTiat

calculating electric power? In what unit

list.

tricity

Thinking Making Calculations running unused, which appliance would waste more electricitv. an iron left on for half an hour or a television left on for one hour?

Critical 4.

each day.

If left

1-5 (continued)

ENRICHMENT Activity

Book

Students

who have mastered

the con-

cepts in this section will be challenged bv

GUIDED PRACTICE

the Chapter

Skills

activitv

called

Electric

Math. Skill:

CONTENT DEVELOPMENT

Applying concepts

.Ask students to analvze their

remind students

of the role of fuses and circuit breakers and encourage students to learn the location of these devices in their homes.

dents should record what the problems are and how the% might result in a dangerous situation. Students should then

sufficient lime to deal with prin-

ciples involving electric safety.

Review

the rules given and ask students to

up with

others. Finallv,

come

ENRICHMENT homes

tenns of the electric safetv rules discussed. They should check to see that none of the relevant rules is violated. If there are any potential difficulties, stu-

Take

inform their parents and should see to that the problems are corrected.

Development

Benjamin Franklin believed

that sub-

stances contained what he called "elec-

He thought that friction between objects, such as that between rubber and fur or between clouds, removed some of the "fluid"" from one object, causing it to be deficient in the "fluid. and transferred it to the other. tric fluid."

s^8agÂŠirii(QS^^ Electrifying Personalities Your

hair color,

other personal

traits

O responsible for maintaining the genetic

are not the haphaz-

code and reproducing each time a new cell is made. Your body is con-

color, height,

determined and controlled by a message found in every one of your body cells. The message is referred to as the

stantly producing

of genes.

The genetic information contained in a gene is in a molecule of DNA (deoxy-

Of the four bases available for pairing with C, only one will be electrically attracted to C. The charges on the other three bases are not arranged in a way that makes it possible for them to get close enough to those on C. Electric forces not only hold the two chains together, they also operate to select the bases in proper order during reproduction of the genetic code. Thus the genetic information is passed on ac-

actually consists of

two long DNA molecules wrapped around each other in the shape of a The two strands are held

helix.

a precise shape by electric forces the attraction of positive charges to negative charges.

curately to the next generation. So,

â&#x20AC;&#x201D;

addition to holding the

DNA

together,

electric

essen-

CONNECTIONS ELECTRIFYING PERSONALITIES

Suppose, for example, that after DNA unwinds, a molecule of C is exposed.

There are only four types of bases in a DNA molecule: adenine (A), cytosine (C), guanine (G), and thymine (T). The order in which the bases are arranged determines everything about your body.

together

paired with C.

A DNA molecule consists of a long chain of many small molecules known as nucleotide bases. ribonucleic acid).

double

bases exposed. Of the four bases, only certain ones will pair together. A is always paired with T, and G is always

chromosomes, which

A chromosome

cells.

that the same genetic message be given to each cell. When DNA is reproduced in the cell, the two strands un wind, leaving the charged parts of the

genetic code. The genetic information passed on from generation to generaall living things is contained in

made

new

Genetics. See Heredity:

The Code of Life, Chapter

tial

tion in

are

O Life Science:

ard results of chance. Instead, they are

structures called

Integration

and

eye

ANNOTATION KEY

though

may

Electricity

surprise you,

for 99.9 percent of the

al-

fact:

partly responsible for your

your overall size.

forces are

DNA. The

tions determine the differences

features, from your twinkling eyes to

two strands

By the late 1970s, molecular biologists had learned how to determine the bases on a given segment of DNA; that is, they had learned how to "read" DNA. The base sequence is the same in all humans

individual

human

varia-

between

beings.

Using restriction enzymes, gene engineers have been able to cut out genes from human DNA and splice them into bacteria for mass production of human proteins. These proteins are then used to cure or prevent disease. Examples include insulin for diabetes and interferon for some forms of cancer. Students may already be familiar with the genetic information contained in DNA from other science courses or articles in the popular press. If you are teaching thematically, you may want to use the Connections feature to reinforce the themes of systems and interactions or patterns of change. Integration: Use the Connections feature to integrate genetics into your science lesson.

causing

"fluid."

have an excess of the

theorized that these differ-

ences created the conditions for

electri-

and repulsion. His theoalthough crude, helped to pave the

cal attraction ries,

way for progress

in the

understanding of

electricity.

INDEPENDENT PRACTICE Section Review 1-5 1.

The

rate at

which

electricity

does

work or provides energy; P = V x

2. The total power used by appliances operating for a certain length of time; E

= P

kilowatt-hour.

3. "You may receive an electric shock. The electricity will go through one arm,

REINFORCEMENT/RETEACHING Review students' responses to the SecReview questions. Reteach any material that is still unclear, based on stution

dents' responses.

across the heart, and out through your

body. Water is a fairly good conductor of electricity. 4. Accept all reasonable answers. The amount of electricity will depend on the power used by the two appliances.

CLOSURE Review and Reinforcement Guide Have students complete Section 1-5 in the Review

and Reinforcement Guide.

watt.

Laooraiory mvesiigaiion Laboratory Investiption ELECTRICITY FROM A LEMON

Electricity

BEFORE THE LAB

Problem

Gather

all

materials at least one day

prior to the investigation.

You should

have enough supplies to meet your class

Can

electricity

For motivation purposes, you may

wish to allow students to bring in their own coins and lemons.

PRE-LAB DISCUSSION Quickly review the basic concepts of such as current and the elec-

electricity,

propose and what will occur during the investigation and why it will occur. Ask them also to consider what experimental findings will support tric circuit.

Ask students

to discuss hypotheses regarding

or refute the hypotheses. Also, before they can7 out the investigation, warn

them not

oversand the coins, as they

may expose base metal by doing

so.

vAFETY TIPS I

Remind

students to be careful using

them that juice from lemons that are used in the experiment should not be consumed, as metal salts have become dissolved in the juice. scissors. Also, tell

be produced from a lemon, a

penny, and a dime?

Materials

needs, assuming six students per group. 2.

From a Lemon

bell

wire

(per group)

Study Guide

GOING FURTHER: ENRICHMENT Parti

Make

Summarizing Key Concepts

voltmeter

1-1 All

Charge

Electric matter

made

tain positively

Opposition to the flow of charge

atoms. Atoms con-

charged protons, negatively

resistance (R). Resistance units called

Opposite ctiarges exert a force of attraction on each) othier. Similar charges exert a

(S2).

states that the current

reverse

conduction, or induction.

The buildup

of electric

The Flow of

1-4

their direction regularly.

charge

called

Electricity

electric circuit provides

a complete

closed path for an electric current. Electricity can flow only through a closed circuit.

There

charges can be made to flow by a source such as a battery, thermocouple, Electric

The flow

of electrons through

measured

(I).

units called

A measure

connected

in series.

This device

will

pro-

only

one path

for the current in

series circuit. There are several paths

0.5 volts.

Part 2

Ask students to consider what may be happening on the chemical level during the investigation. Ask them also to con-

parallel circuit.

photocell, or electric generator.

called electric current

You may also wish them with an ammeter to be

them with information on current magnitude and direction. The lemon setup should produce a current of about

Electric Circuits

static electricity. 1 -3

to provide

one

alternating current (AC), electrons

vide

can acquire charge by

neutral object

ad-

repeal

differences involved. direct current (DC), electrons flow

Static Electricity

friction,

tlieni lo

the investigation, using it in place of the compass, and connnecting it in parallel. In this way they will be able to obtain quantitative information on the potential

called

measured

in a wire equal to voltage divided by resistance.

direction.

force of repulsion.

1-2

ohms

Ohm's law

ctiarged electrons, and neutral neutrons.

available

vanced students and allow

a wire

Electric current

amperes

(A).

of the potential difference

across a source is voltage (V), which sured in units called volts (V).

1-5

Electric

Power

sider

power measures the rate at which electncity does work or provides energy. The unit of electric power is the watt (W).

how

the quantitative data that are

obtained might change

Electric

the data were

collected over an extended period of time.

mea-

Reviewing Key Terms Define each term

1-1

a complete sentence.

Charge

induction

superconductor

atom

static electricity

Ohm's law

proton

electric

discharge electroscope

direct current

Electric

neutron electron

charge force electric field

1-2

Static Electricity friction

conduction conductor insulator

-3 The Flow of

alternating current

1-4

Electricity

battery

Electric Circuits series circuit

potential difference

parallel circuit

thermocouple

fuse

photocell

circuit

1-5

current

Electric

resistance

lyte.

The lemon juice

in this investigation

No.

serves as the electrolyte.

Yes.

3. Yes.

The needle on

netic

and

will

netic field set

ANALYSIS AND CONCLUSIONS 1.

No. Yes.

Power

power

voltage

OBSERVATIONS

breaker

circuit

allow the coins to touch the acidic

lemon juice; lo remove any grease or unwanted chemicals coaling the coins. 3. Two different metals and an electro-

the compass

mag-

be attracted to the mag-

up when

the electric cur-

produced. Thus, the needle deflection shows whether or not an electric current has been produced. rent

There would not be two different metand no current would be produced.

als,

i^napter

Kevtew

Chapter Review Content Review ALTERNATIVE ASSESSMENT

Choice

lultiple

program includes a variety of testing components and methodologies. Aside from the Chapter Review questions, you may opt to use the Chapter Test or the Computer Test Bank Test in your Test Book for assessment of important facts and con-

The

cepts.

Prentice Hall Science

Choose

the letter of the

An atomic

answer

charge

tive electric

neutron.

electron.

positron.

proton.

would an elecoccur?

particles

proton-proton

The

methods

of giving an electric an object are conduction, induction, and

three

charge

called a(n)

tric force of attraction

In addition, Performance-Based

a nega-

Between which

completes each statement.

that best

particle that carries

fnction.

direct current.

resistance.

alternating current.

6. Electricity resulting from a buildup of

electric

charges

electron-electron

alternating current.

Tests are included in your Test Book.

neutron-neutron

magnetism.

These Perfomiance-Based Tests are de-

electron-proton

electromagnetism.

static electricity.

signed rather

test

than

science

factual

process

content

the following?

recall.

Since they are not content dependent,

Performance-Based Tests can be distributed after students complete a chapter or after they complete the entire textbook.

senes

open

Electric

circuit

power

d b b

4. 5.

write "true. "

change

make

the statement true.

the underlined

electric charge.

series current.

alternating current.

Complete the following concept map

If it is

word or words

Section 1-1. Refer to pages struct

The number of electrons atom equals the number

a concept

map

for

P6-P7 to

con-

chapter

for the entire

a neutral

of protons

neutral object develops a negative

it loses electrons. instrument that detects charge

electroscope

Rubber

surrounded by an

a(n)

do not allow electrons

flow freely are called insulators 5.

relatively

poor conductor of

electricity.

gains 6.

photocell generates electricity as a

temperature differences. 7. Once a circuit breaker burns out,

re-

contains charged

contains uncharged

exerts

particles called

sult of

must

be replaced.

6. F,

thermocouple

7. F,

fuse

An electnc circuit provides a complete open path for an electric current. Electnc power is the rate at which work

closed is

called

direct current.

charge when

T T T

8. F,

Concept Mapping Is true,

false,

2. F,

current

circuit

volts.

4. Materials that

closed

electron-hours.

the statement

True or False 1.

measured c.

/;"

forth,

reversing their direction regularly, the

True or False

move back and

parallel circuit

b. watts.

Multiple Choice 1. c

electrons

ohms.

When

circuit

CONTENT REVIEW

cannot flow through which of

Electricity

skills,

of attraction

of repulsion

charges f fare same

done.

Concept Mapping

Row 1: Row 2: Row 3: Row 4:

a property of particles in

Electric field

Protons, Neutrons, Force Charges are different

CONCEPT MASTERY 1.

Atoms

are

made of

smaller particles,

and an

electrolyte.

including protons, neutrons, and elec-

Chemical reactions

trons. Protons have a positive charge,

lease electric charges that create

and electrons have

site

a negative charge.

2. The first is a repelling force; ond is an attracting force.

An electrochemical cell consists of two

different electrodes

Conduction

the sec-

(direct contact); friction

in the electrolyte re-

oppo-

charges on the electrodes. Thus,

charge flows between the terminals to which the electrodes are connected. A batten^

made of

(rubbing to separate charges); induction

cal cells.

(approach of a charged object near a

5. Insulator:

neutral object).

tric

several electrochemi-

does not conduct an elec-

current or does not allow electrons

CRITICAL THINKING

AND PROBLEM SOLVING

Concept Mastery Discuss each of the following 1.

brief paragraph.

How

Describe the structure of an atom.

are atoms related to electric chiarge?

How does

the force exerted by a proton on a proton compare with the force exerted by a proton on an electron at the same distance? 3. Describe the three ways in which an object can become charged. 4. Describe how a simple electrochemical cell operates? How are electrochemical 2.

Jse the 1.

skills

2a. both, b. series,

How

series.

ance

of a wire

What

Explain

short circuit?

why a tiny 1 .5-V cell can operate a calculator for a year, while a much larger 1 .5-V cell burns out in a few hours in

What

How much

the

power

of the light

d. series, e.

prong would defeat the grounding plug. not grounded.

the

The bird is Check student

letters for scientific ac-

curacy. Letters should explain that the

a toy robot.

umbrellas may act as lightning rods.

KEEPING A PORTFOLIO

Making inferences

Electric current

can

line

and not be

You might want to assign some of the Concept Masteiy and Critical Thinking and Problem Solving questions as homework and have students include their responses to unassigned questions

in their

portfolio. Students should be encour-

aged to include both the question and the answer in their portfolio.

injured?

the cost of operating the

c. parallel,

safety function of the

be said to take the path of least resistance. With this in mind, explain why a bird can perch with both feet on a power

bulb?

energy does the light bulb order to operate for 8 hours?

need in c. What

9. Discuss three safety rules to follow while

operates at 60 volts and 2 amps. a.

chapter to answer each of the following.

this

bulb

light

Removing

can be increased.

a circuit?

using electricity.

you have developed in

0.96 kilowatt-hours,

Compare an

Thinking and Problem Solving

Making calculations A

6.7 cents.

insulator and a conductor. might each be used? 6. Describe two ways in which the resist5.

cells related to batteries?

Critical

120 watts,

la. In

bulb for 8 hours at a rate of $0.07 per kilowatt-hour?

ISSUES

issues can be used as springboards for discussion or given as

characteristic of (a) a series circuit, (b) a

both a series and a

writing assignments.

parallel circuit:

V/R The total resistance

a. b.

sum

the

The

sum d. is

the circuit

tric

of the individual resistances,

total current in the circuit

break

the

each resistance, each part of the circuit

of the current

The current the same,

any part of the

circuit

causes the current to stop, Applying concepts Explain why the third prong from a grounded plug should not be removed to make the plug fit a two-prong

Do you think a

third basic type of eleccharge is possible? If so, how might a particle having such a charge be recog1

SCIENCE

The following

of the following statements as being a

parallel circuit, (c)

each

2. Identifying relationships Identify

outlet.

Using the writing process Imagine that from your window you can see the farm that belongs to your neighbors, whom you have never met. You rarely notice the neighbors, except when it rains. During rainstorms, they protect themselves with huge umbrellas as they walk out to check the crops. Write them a friendly but direct letter explaining why it is dangerous for them to use umbrellas during thunderstorms.

nized? (Students

may

point out that

al-

though there is no experimetnal evidence in favor of its existence, such a charge

at least theoretically possible.

They may suggest that a particle having such a charge would be attracted to both positive and negative charges because it would be unlike either, and unlike charges attract.)

The

ing the temperature.

cost per kilowatt-hour of electriccharged by utility companies often decreases as the number of kilowatt-hours used increases. Does this seem fair? What might be an undesirable effect of this practice on energy conservation as related to individual households and com-

used for safety purposes to prevent the

7. A circuit is a complete path through which charge can flow. A short circuit is an accidental connection that allows current to take a less resistant path around

such discounting for increased use is fair and is analogous to other economic practices in which goods or services are in-

flow of electrons.

a circuit.

volved. Others

ity

to flow;

conductor: allows electrons to

[low easily.

\ conductor jlectric

used when you want an

current to flow, such as in an

electric wire. Insulators are

The

the

most often

depends on material used, thickness, length, and resistance of a wire

temperature.

Resistance

can

in-

:reased by using a less conductive material,

decreasing the thickness of a wire,

increasing the length of a wire, or chang-

The robot

uses

the

energy

quickly than the calculator does. 9.

Answers

will vai"y

but should reflect

panies? (Some students

may

feel

that

may stress the negative ef-

of not sufficiently discouraging overuse of energy resources by housefect

holds and companies.)

the basic safety rules discussed in the chapter.

Chupter

Magnetism

SECTION

SSJC^

CHAPTER PLANNING GUID JID^ OTHER ACTIVITIES

Gvjpter

Magnetism

CHAPTER OVERVIEW tion.

are grouped together

forces are usually strongest. Like poles repel each other, and unlike poles attract each other. The region in which such magnetic forces act is called the magnetic field, which is represented by

magnetic

The region

which the magnetic fields of individual atoms is called the magnetic domain. Earth has magnetic properties. Its magnetic field is strongest at its magnetic poles, which are not located at the geographic poles. A permanent record of Earths magnetic history is found in the magnetic stripes of molten rocks. Compasses point to the magnetic poles of Earth because their needles are magnetized. Like Earth, the planets Jupiter and Saturn as well as the sun have strong magnetic fields. Earth is surrounded by a strong magnetic field known as the magnetosphere. The Van Allen radiation belts in the magnetosphere trap charged particles, preventing them from reaching Earths surface. When charged particles come near Earths surface, they collide with particles in the atmosphere, causing the au-

The ancient Greeks discovered magnetite, a naturally occurThe magnetism it exhibits is a force of attraction or repulsion due to the electron arrangement in the mineral. Magnets have a north pole and a south pole, where the magnetic ring mineral.

lines of force.

magnets such as lodestone are found in nature. The most commonly used magnets are made by stroking a magnetic substance with the poles of a permanent magnet. A permanent magnet is one that is difficult to magnetize but retains its magnetism for a long time. A temporary magnet is one that is easy to magnetize but loses its magnetism quickly. A substance becomes magnetized when all its domains align in the same direcNatural

rora.

One pole, howan attractive force, whereas

2-1 THE NATURE OF

strongest at the poles.

2-2 THE EARTH AS A MAGNET

MAGNETS

ever, exerts

THEMATIC FOCUS

the other pole exerts a repulsive force.

THEMATIC FOCUS The puq>ose of this

All magnets, regardless of their size or

section

to intro-

duce students to the concept of magne-

shape, have a pair of poles. 'Stability:

tism. Students first identify characteristics

of magnets including the regions of

strongest magnetic force, the north and

circle

south poles. Like poles repel each other, and unlike poles attract each other. The area over \vhich a magnetic force is e.x-

pole.

erted

the magnetic

field.

The atomic

structure of materials are responsible for

the properties of magnetism, and the re-

which the magnetic fields of indi%idual atoms are grouf>ed together is called the magnetic domain. Materials become magnetic when their domains align with one another. Once sttidents are familiar with the properties of magnets, thev define magnetism. The themes that can be focused on in gion

this section

unitv

and

are systems and interactions,

diversit)% stabilin,',

and

scale

structure.

â&#x20AC;˘Systems and interactions: Even magnet has a north and a south pole.

The

force of a magnet

magiietic lines of a

move

each other, the magnetic field of each one will be affected bv the other. Unity and diversity: The magnetic forces exerted bv any magnet are

44c

complete

the magnetic field of a magnet.

manv

times throughBecause of its magnetized needle, a compass can be used to identifv the north pole. The needle points to the magnetic pole, which does not coincide with the geographic pole. The sun has a strong magnetic field, as do the planets Jupiter and Saturn. Sunspots are ven strong fields of magnetism. They alwavs appear in pairs, with one sunspot acting as the north pole and one acting as

versed themselves

*Scale and structure: Even magnet. regardless of its size or strength, has two

ends, called the north and south poles,

where the magnetic

effects are usuallv

strongest. In magnets, the poles alwavs

come

in pairs that

cannot be separated.

PERFORMANCE OBJECTIVES

2-1

Define magnetism.

Describe the property of magnetic

poles.

Explain the appearance and use of magnetic lines of force in relationship to magnetic fields. 4. Identifv" the magnetic domain.

out Earth's histon

Compare and contrast permanent and temporary magnets.

the south pole.

The themes this

section

that can be focused

evolution,

are

scale

on in and

and patterns of change.

structure,

Evolution: Changes in Earth's mag-

netic field over time are recorded in the

patterns of magnetic rocks. These rocks

Like magnetic poles repel each other.

and unlike magnetic poles attract each other. If two magnets are placed near

in a

from the north pole to the south The magneuc lines of force trace

The purpose of this section is to introduce students to the magnetic properties of the Earth. The Earth is like a large bar magnet with magnetic north and south poles. The magnetic histon of Earth can be traced through the magnetic stripes in molten rocks. The patterns of the stripes show that Earth's magnetic poles have re-

SCIENCE TERMS 2-1 magnetism p. P46 pole p. P46 magnetic field p. P48 magnetic domain p. P50

provide e\idence that Earth has reits poles many times throughout

versed its

histon'.

*Scale

and

structure: Objects

magnetic

fields

and the sun produce evident throughout the

large as the Earth

CHAPTER PREVIE v3i solar system. Yet the source of

tism

in the

atom

magne-

— the building block

of matter.

Patterns of change: The patterns of magnetic stripes in molten rocks are fixed at the time that the rocks solidify. The patterns in rocks of different ages

'Energy: Energy is required to overthe magnetic forces of attraction and repulsion. Energy is released in the form of light when charged particles move near the Earth's surface close to the poles and collide with atmospheric

come

particles.

'Systems

are different, indicating that the Earth's

magnetic poles have reversed themselves over time. The number of sunspots varies in is

The

1-year cycles.

cycle

believed to be related to variations in

the sun's magnetic

Every

field.

1 1

years,

the sun's north and south poles reverse

themselves.

and

interactions:

charged particle moving in the same direction as a magnetic field has no force exerted on it. A charged particle moving at an angle to a magnetic field has a force acting on it that causes it to spiral around the magnetic-field lines. The charged particle spirals from pole to

pole within the magnetic

field.

PERFORMANCE OBJECTIVES 2-2 1. Describe the magnetic poles and magnetic field of Earth. 2. Explain the behavior of compasses. 3. Distinguish between geographic and magnetic poles. 4. Identify sources of magnetism in the

Patterns of change: The motions of a charged particle will be altered by the magnetic forces exerted in a magnetic field. Charged particles near Earth's surface collide with atmospheric particles and cause the aurora.

and diversity: The aurora boand aurora australis are identical phenomena. They are produced, how-

solar system.

Unity

gated (rather than a spherical) shape. Do not tell students the name of the mineral.

Use a string

hang the sample from

support. Ask students to observe the magnetite's orientation. Carefully rotate the support 90 degrees. doing so, ask: •

What

will

turned?

happen

Why? (The

But

before

the support

keep its orientation. It is naturally magnetic, and its north pole points toward the Earth's magnetic north pole.) Use a compass to reveal the sample's magnetic orientation. Also use the sample to pick up paper clips t)r small nails. If more than one magnetite mineral is available, allow students to examine the mineral and use it to pick up various mineral

will

items.

Why does the magnetite pick up the paper clips? (It is magnetized, and the paper clips become slightly magnetized.)

•

Will the magnetite pick up paper? 'Why? (No. Paper does not have magnetic properties and cannot be magnetized by

•

realis

ever, by interactions of particles at op-

2-3 MAGNETISM THEMATIC FOCUS

ACTION

The purpose of this section is to introduce students to the impact of magnetism on charged particles. The Earth is surrounded by the region in which the magnetic field of Earth is found known as the niagnetosphere.

charged

particles,

The region

traps

preventing them from

reaching Earth's surface. The Van Allen radiation belts are parts of the in

Earth's surface.

Charged

poles.

PERFORMANCE OBJECTIVES

2-3

Describe the magnetosphere.

Explain the

3. Identify

phenomenon of aurora. how magnetism relates to as-

tronomy and the development of nuclear fusion.

SCIENCE TERMS 2-3 magnetosphere p. P57

P57

aurora

particles spiral-

ing in magnetic fields release radiation.

Radio waves, a type of radiation, are studied by astronomers to learn about objects

space.

fields, scientists

By using magnetic

may be

able to solve en-

ergy needs through nuclear fusion.

The themes

on in this section are energy, systems and interactions, patterns of change, and unity and diversity. that can be focused

Magnetic Force and Distance Explore the dependency of magnetic force on distance. Ask students to write a

how an object's may affect the attractive force of the magnet. Then perform the demonstration. Make use of a pole of a strong magnet in this demonstration. Hang a small iron object on a hypothesis explaining

distance from a magnet

to measure measure the force of gravity, in newtons, acting on the object when it is far from the magnet. Subtract this value from subsequent readings. Record the values obtained on a data chart on the chalkboard. Hold the object (suspended from the spring balance) at various short distances above the magnetic pole and record the resulting force on the object. Demonstrate that the

spring force,

magne-

which most charged particles are trapped. The aurora is a phenomenon that results when charged particles collide with atmospheric particles near tosphere

Aurora borealis occurs near the North Pole and aurora australis occurs near the South Pole. posite

the magnetite.)

Discovery, ^

Learning

•

TEACHER DEMONSTRATIONS MODELING

balance

and

designed

first

force decreases rapidly

Have students check

w'ith

distance.

their hypotheses.

Observing Magnetic Properties

Did the demonstration support

Obtain a sample of the naturally magnetic magnetite (lodestone). The sample should be large enough to be easily visible to the class and should have an elon-

potheses? (Answers

will

their hy-

van.)

44d

CHAPTER 2

Magnetism INTEGRATING SCIENCE This physical science chapter provides

you with numerous opportunities

to in-

tegrate other areas of science, as well as

other disciplines, into your curriculum. Blue numbered annotations on the stu-

dent page and integration notes on the teacher wraparound pages alert you to areas of possible integration. In this chapter you can integrate earth science

science

and cosmology (p. 47), and scientific method (p.

physical 48), lan-

guage arts (pp. 49, 51), physical science and heat (p. 51), earth science and geology (pp. 52, 53), earth science and as-

tronomy and light

(pp. 54, 56), physical science (p. 57).

telescopes

fusion

earth science and radio

physical science and and earth science and con-

(p. 58),

tinental drift (p. 59).

SCIENCE, TECHNOLOGY, AND

SOCIETY/COOPERATIVE LEARNING Using technology developed by Amerscientists, Japanese and German companies are waiting for advancements in superconducting magnets to put the first magnetic levitation trains into production. These trains float above the tracks at speeds approaching 480 kilometers per hour. Magnetic levitation trains (maglev) can work on magnetic repulsion or magnetic attraction. One type of maglev uses superconducting magnets to propel the train forward and keep the train 6 to 8 centimeters above the guideways. The superconducting magnets in the train and the guideways repel each other to mainican

tain the separation

and prevent

friction

Another type of maglev uses the principle of mag-

from slowing the

train's speed.

netic attraction to propel the train

the tracks in the

down

high rates of speed. Magnets

guideways and on the train are of

opposite

polarity,

and the

force pulls the train forward

attraction

down

the

"tracks."

The gridlock overtaking United States highways and airports and our rapidly deteriorating infrastructure makes the

United States a prime location for magMaglev trains also have very

lev trains.

low energy requirements and have only minimal iinpact on the environment.

Magnetism

Once maglev

technology has been per-

fected and placed in |)ic)duction, the real

be to get Americans out of and onto this efficient, high-speed form of transportation. challenge

will

their individual cars

Cooperative learning: Using preasgroups or randomly selected teams, have groups complete one of the

sigiicd lab

following assignments:

More than 2000 years ago, the Greeks living in Turkey known as Magnesia discovered an unusual rock. The rock attracted materials that

Guide for Reading you read the following sections, you will be able to

After

2-1 The Nature of Magnets Describe magnetism and the behavior of magnetic poles.

Relate magnetic fields

and magnetic

field lines

of force,

Explain

magnetism

terms of magnetic domains.

Describe the Earth's magnetic properties

how

compass

Identify other

sources of

magnetism

the solar

vertising

happens

a charged particle

magnetic

maglev

that will increase the

transit system.

ride on the new Encourage groups

to first consider reasons that people choose not to use public transportation

and then their ads.

eliininate these objections with

You may want

sign a specific type of

randomly asmedia to each

group or have them prepare ads that would be appropriate for different types

it then, but they were observing a property of matter called magnetism. In this chapter you will discover what magnetism is, the properties that make a substance magnetic, and the significance of magnetism in your life.

of media. Maglev technology holds a great deal of promise, but American scientists are con-

•

cerned that government support of maglev research and money to fund maglev construction projects may be lacking. What role should the U.S. government take in these areas? Have groups discuss

field

this

Journal Activity

magnet

that exhibits

question and suggest possible posi-

tions for the federal government.

You and Your World You probably use several magnets in the course of a day. In your lournal, describe some of the magnets you encounter and how they are used. Also suggest other uses for magnets. Magnetite, or lodestone. is a natural properties as attracting iron tilings.

campaign

number of people who

Action

Explain what

selected by the

Department of

the city of Los Angeles to design an ad-

contained iron. Because the rock was found in Magnesia, the Greeks named it magnetite. As the Greeks experimented with their new discovery, they observed another interesting thing about this peculiar rock. If they allowed it to swing freely from a string, the same part of the rock would always face in the same direction. That direction was toward a certain northern star, called the leading star, or lodestar. Because of this property, magnetite also

system.

2-3 Magnetism

Your group has been

Public Transportation

became known as lodestone. The Greeks did not know

2-2 The Earth As a Magnet

Explain works.

•

a part of

See

Cooperative

Learning

the

Teacher's Desk Referetice.

JOURNAL ACTIVITY

such

You may want tivity as

to use the Journal Ac-

the basis of a class discussion. As

students discuss their daily experiences

with magnets, ask them to identify the

function of the magnet. Encourage stuall parts of their envi-

dents to explore dents scribe

who have

seen such a rock to de-

it.)

Have students read the chapter

intro-

duction on page P45. Explain that

known who first found magwhen it was found. A rock with

not really netite or its

properties was mentioned in Greek

the rock could be used as a navigational

for uses of magnets. Students should be instructed to keep their Jour-

instrument.)

nal Activity in their portfolio.

ical

•

answers. Lead students to realize that

What

the

name of a

direction-find-

ing instrument that uses magnetism? (A compass.) Explain that the compass

the oldest

But it is possible that the Chinese knew about magnetite as early as

magnetism but that the actual origin of the compass is unknown.

2600

The

texts in

•

800

bc.

BC.

What would be

useful about a rock

that always points north? (Accept

all

ronment

practical use of

existence of the lodestone

compass

made

the

possible.

log-

)

2-1 The Nature of Magnets

Guide for Reading Focus on these questions as you read. What are the charactenstics of a

2-1 The Nature of

Mupets

magnetic

MULTICULTURAL OPPORTUNITY 2-1

How

Have you ever been fascinated by the seemingly mvsterious force you feel when vou try to push two magnets together or pull them apart? This strange phenomenon is known as magnetism. You mav not realize it, but magnets plav an extremely important role in vour world. Do vou use a magnet to hold notes on vour refrigerator or locker door? Do you plav video- and audiotapes? Perhaps vou have used the magnet on an electric can opener. Did you knowthat a magnet keeps the door of vour freezer sealed tight? See. vou do take advantage of the properties of magnets.

field?

magnetism related

to the atomic structure of a material?

Have your students investigate the life and work of Kotaro Honda (18701954).

Honda

discovered that the addi-

tion of cobalt to tungsten steel

formed an

powerful magnetic properties. This led to the discover) of alnico, a magallov with

netic allov that sive resistant,

stronger,

more immune

Find out by

corro-

Magnetic Poles

temper-

ature and vibration change, and cheaper

Magnetic Forces

Take two bar magnets the same size and hold one

each hand.

than steel magnets.

ESL STRATEGY 2-1

When discussing magnetism, point out the

textbook's description of

"strange phenomenon."

know

dents forms:

the

Make

singular

phenomenon,

sure stu-

2. Experiment with the magnets by bringing different combinations of poles together. What do you feel in your hands?

and plural

phenomena.

Give

other examples of phenomena, such as lightning and auroras. Can students

Explain your observations

terms of magnetic

.\11 magnets exhibit certain characteristics. Any magnet, no matter what its shape, has two ends where its magnetic effects are strongest. These regions are referred to as the poles of the magnet. One pole is labeled the north pole and the other the south pole. Magnets come in different shapes and sizes. The simplest kind of magnet is a straight bar of iron. Another common magnet is in the shape of a horseshoe. In either case, the poles are at each end. Figure 2-1 shows a variety of common magnets.

forces. <

think of other examples?

The

Intruder:

Have students

circle the

term that does not belong in the group and then write definitions for the imcircled words.

magnetic lines of force, magnetic tape, magnetic poles, magnetic fields

•

Figure 2-1 Modern magnets in a variety of sizes and shapes, including bar magnets, horseshoe magnets, and disc magnets.

come

TEACHING STRATEGY 2-1

FOCUS/MOTIVATION

Bring the X-pole of a bar magnet near the X-pole of a freelv suspended magnet. • WTiat do you observe? (The suspended

magnet moves awa\ from the other mag-

net.)

this rule describes the

Repeat bringing the S-pole of the bar magnet near the S-pole of the suspended magnet. Now place the S-pole of the bar magnet near the N-pole of the suspended magnet. • What do you observe? (The suspended magnet moves toward the other magnet. Ask students to si ate their observations as a rule. The statement should be "Like magnetic poles repel, and unlike magnetic poles attract." Point out that

netic poles.

Make available

behavior of mag-

CONTENT DEVELOPMENT As the various properties of magnets

to students a

number of

small horseshoe magnets with labeled

north and south poles, strings, and metal

paper clips. .AJlow students to use the materials to investigate the magnetic properties of attraction and repulsion and alignment of the magnets in north-south directions when allowed to swing freely. Ask students to consider what may account for the properties of magnets.

are introduced and explored,

properties

list

the

on the chalkboard. Ask

stu-

dents the following: •

the attraction and repulsion prop-

magnets remind you of propyou studied earlier? (Objects with and unlike electric charges have simproperties of attraction and repul-

erties of

erties like ilar

sion.) • Is it

possible that magnets are simply

ANNOTATION KEY

Answers

O Left;

Repulsion

Attraction

—

poles;

right:

unlike poles. (Inteipreting

photographs)

Same; Like charges repel each other, and unlike charges attract each other, (Making comparisons)

O Magnetic Figure 2-2 T<fio bar magnets suspended by strings are tree to move. What force is occurring between the magnets in each photograph'^ Why?

pairs

—

This

poles

a north pole

always

appear

and a south

pole.

not true of electric charges.

Integration

When two magnets thev exert a force

O Earth

are brought near each other,

on each

other. Magnetic forces,

Science; Cosmology. See Ex-

ploring the Universe, Chapter

and repultwo north poles are brought close together, thev will repel each other. Two south poles do the same thing. However, if the north pole of one magnet is brought near the south pole of another magnet, the poles will attract each other. The rule for magnetic poles is: Like poles repel each other and unlike poles attract each other. How does

like electric forces, involve attractions

sions. If the

this rule

compare with

the rule that describes the

behavior of electric charges? Magnetic poles always appear in pairs a north pole and a south pole. For many years, physicists have tried to isolate a single magnetic pole. You might think that the most logical approach to separating poles would be to cut a magnet in half. Logical, yes; correct, no. If a

magnet

—

Figure 2-3 No matter how many times a magnet is cut in half, each piece retains its magnetic properties. How are magnetic poles different from electric charges?

MAGNETIC FORCES Discovery Learning Skills: Manipulative,

observing,

comparing, hypothesizing Materials:

cut in half,

2 bar magnets

vsill enable students to acmagnetic forces caused by bar magnets. Students will be able to feel the force of attraction when unlike poles are brought together, as well as the force of repulsion when like poles are brought

This activity

two smaller magnets each with a north pole and a south pole are produced. This procedure can be repeated again and again, but a complete magnet is always produced. Theories predict that it should be possible to find a single magnetic pole (monopole), but experimental evidence does not agree. A number of scientists are actively pursuing such a discovery because magnetic monopoles are believed to have played an important role in the early history of the

tually feel the

together.

universe.

charged objects, with a poscharge at one end and a negative charge at the other? How might you inelectrically

attraction

itive

net electric charges.)

vestigate this possibility?

(Some

stu-

and

that

magnets do not have

tion

on the discovery of magnetism and Have them re-

the properties of magnets.

port their findings to the

• • • •

Integration

class.

• • • •

Use the discussion on the possible ex-

dents inay incorrectly conclude that inagnetism and electric charge are identical

istence of a magnetic

rather than simply related, as they turn

grate concepts of cosmology- into your

monopole

to inte-

REINFORCEMENT/RETEACHING Activity

Book

lesson.

Students who need further practice with the concept of magnets and their

magnets to see whether they attract electrically charged objects, such as rubber

ENRICHMENT

activity called

balloons or glass rods. Actually carry out such tests to show that there is no such

Advanced students may wish to do library research to obtain more informa-

out to be. Students

may

suggest testing

properties should complete the chapter

Magnets.

'IN

FIND OUT BY

Place the horseshoe

magnet on a

flat

surface.

Place the cardboard on top of Be sure the cardboard

piece of cardboard, pencil

it.

In this acti\ity students observe the

covers the entire magnet. 2. Sprinkle iron filings over

of force produced by a horseshoe magnet through the use of iron filings. lines

the cardboard.

Make a draw-

ing of the pattern

Check students' drawings for accuracy. Students should note fiom the pattern that the poles of the horseshoe magnet

Explain lar

pattern

why

you see. this particu-

formed.

What does the

pattern

you about the location of the poles of a horseshoe tell

are at each end.

magnefr"

to be

It is

answered

that can be

continually developing

often the case that a scientific new collection of questions

— perhaps by

inquisitive

minds

yours.

Magnetic

Fields

Although magnetic forces are strongest at the poles of a magnet, they are not limited to the poles alone. Magnetic forces are felt around the rest of the magnet as well. The region in which the magnetic forces can act is called a magnetic field. It may help you to think of a magnetic field as an area mapped out by magnetic lines of force. Magnetic lines of force define the magnetic field of an object. Like electric field lines, magnetic field lines can be drawn to show the path of the field. But unlike electric fields, which start and end at charges, magnetic fields neither start nor end. They go around in complete loops from the north pole to the south pole of a magnet. A magnetic field, represented by lines of force extending from one pole of a magnet to the other, is an area over

which the magnetic force

2-1 (continued)

GUIDED PRACTICE

Figure 2-4 You can see the magnetic lines of force mapped out by ttie iron filings placed on a glass sfieet above a magnet. The diagram illustrates these lines of

Laboratory Manual

Development

force.

Making observations, drawing

Skills:

the answers

of paper.

Materials: horseshoe magnet, iron

Skills

knowledge

discovery creates a whole this activity

all

been discovered

and changing.

you need iron filings, a horseshoe magnet, a thin piece of cardboard, a pencil, and a sheet

observing,

science has

discovered. But the quest for monopoles illustrates

Force

diagramming, relating

tfiink that

that everything has

Mapping Lines of Magnetic For

Discovery Learning

filings, thin

You may and

that scientific

DOING MAPPING LINES OF MAGNETIC FORCE Skills: Manipulative,

D OUT BY |E>QHSI<^

Where are the

strongest?

conclusions

exerted.

Magnetic lines of force can be easily demonstrated by sprinkling iron filings on a piece of cardboard placed on top of a magnet. See Figure 2-4. Where are the lines of force always the most numerous and closest together?

lines

Have students complete the Laboratory Investigation called Properties of

Magnets and Magnetic

Fields.

They

use simple bar magnets and iron

will

filings to

explore properties of magnets and to observe a magnetic

field.

CONTENT DEVELOPMENT The

strengths of the magnetic fields of

different

magnets can

The magnetic

differ consider-

can thus be thought of as a quantity that can have different magnitudes. It is also a directional

ably.

field

quantity. Because both

direction are involved,

magnitude and it

vector quantity. Magnetic

therefore a

field,

or more

magnetic induction of a field, is symbolized by the letter B with an arrow written above it to indicate its vector nature: ^. The units in which B is

tegrate concepts of the scientific

method

precisely, the

measured are the tesla

=10^

• • • •

lesla

and the gauss

gauss).

Integration

Use the discussion of the questions raised by the study of magnetism to in-

GUIDED PRACTICE

should make sketches of what they ob-

Skills

Development

serve.

Skills:

Making observations, identifying an

INDEPENDENT PRACTICE

relationships, performing

Activity Bool<

experiment

• • • •

serve magnetic lines of force for one

magnet alone, and for N-S, N-N, and SS interactions between magnets. They

into your lesson.

Provide students with two bar magnets, sheets of paper,

Have students use

and iron

filings.

these materials to ob-

Students can gain a better understanding of magnetic fields by completing the

chapter activity Magnetic Fields,

which

they observe magnetic fields for a single

i3mBsmmt,-i3f\!x^nmrm,

Answers

O Near the poles of the inapiet. (Inter[ireting illustrations)

O Near the poles of the magnet

(Inter-

pieiing illustrations)

O Like poles attract; unlike poles repel. (Interpreting illustrations)

Integration

Physical Science: Scientific Method. See The Nature of Science, Chapter 1

O Language Arts Figure 2-5 Whal do the lines of force around these magnets tell you about the interaction of like and unlike magnetic poles?

Figure 2-5 shows the lines of force that exist between hke and unhke poles of two bar magnets. The pattern of iron fiHngs shows that like poles repel each other and unlike poles attract each other.

Magnetic Materials

OOIISI^ >}>>f> >ii>ifir Paper

Explain your results. 2.

How many

can you attach

highly magnetic materials are called

to a bar

ferromagnetic materials. The name comes from the Latin name for iron, ferrum. Ferromagnetic materials are strongly attracted to magnets and can be made into magnets as well. For example, if you bring a strong magnet near an iron nail, the magnet will attract the nail. If you then stroke the nail several times in the same direction with the magnet, the nail itself becomes a magnet. The nail will remain magnetized even after the original magnet is removed.

paper

clips

a single row

magnet?

What would happen

you placed a plastic-coated paper clip in the second po-

clips,

plastic-coated paper clips

Students

will

Sl(ills

Development

Skills:

Making observations, applying

concepts point have students complete

Laboratory Investigation called Plotting Magnetic Fields. They will draw representations of the magnetic

that

the greatest

clips will stick to the

poles where the magnetic force est.

The

exact

number of paper

depending on the

size

strong-

clips will

and strength

of the magnet. Students will find that many paper clips will stick even if they do not actually touch the surface of the magis also demonstrated in the sinrow of paper clips. In each case, the magnet induces magnetism in the paper clips each clip becomes a magnet itself.

gle

—

fields of a bar magnet and a horseshoe magnet.

Give each student a small magnet and a few sinall samples of metal and nonmetal objects such as a paper clip, brass or aluminum key, aluminum foil, brass screw, copper penny or wire, iron nail,

in-text

find

number of paper

•

What have you observed about mag-

nets? (The attiact metals and do not tract nonmetals.

GUIDED PRACTICE

this

Observing, inferring, relating

net. This

sition''

FOCUS/MOTIVATION

Skills:

vary,

Explain your results.

like poles.

the

Discovery Learning

Materials: bar magnet, metal paper

Clip Construction

1. How many paper clips can you make stick to the surface of a bar magnet?

others are not?

bar magnet, two bar magnets with opposing poles, and two bar magnets with

DOING PAPER CLIP CONSTRUCTION

INDOUTBY

you bring a magnet near a piece of wood, aluminum, or plastic, what happens? You are right if you say nothing. There is no action between the magnet and any of these materials. In addition, none of these materials can be magnetized. Yet materials such as iron, steel, nickel, and cobalt react readily to a magnet. And all these materials can be magnetized. Why are some materials magnetic while If

glass,

The most

FIND OUT BY

at-

Only the objects of iron

and steel are attracted to the magnet. Aluminum, copper, and brass do not seem to stick to the magnet.)

• • • •

Integration

•

• •

of Styrofoam, wooden

Use the discussion of the derivation of the word fciromagnetic to integrate lan-

toothpick, and/or other available mate-

g[uage arts concepts into your science les-

thumb rials.

lack, piece

Have students

test

the magnetic

properties of these materials.

TriND FIND OUT BY

////^i

DOING MAGNETIC DOMAINS

OUT BY

) J > >

Some materials, such as soft iron, are easy to magnetize. But they also lose their magnetism quickly. Magnets made of these materials are called temporary magnets. Other magnets are made of

i i J / J i 1 J i

Magnetic Domains

into small strips to

Skills: Comparing, modeling, hypothesizing

materials that are

magnetize, but made of thes materials are called permanent magnets. Cobalt, nickel, and iron are materials from which strong permanent magnets can be made. Many permanent magnets are made of a mixture of aluminum, nickel

represent

magnetic domains. Label each strip with a north pole and a south pole. 2. On a sheet of poster-

Materials: index cards, posterboard

In this simple acti\itv students are asked to make models of magnetized and

unmagnetized substances. Check

difficult to

they tend to stay magnetized. Magnets

Cut several index cards

cobalt,

and iron called

alnico.

board, arrange the strips to

represent an unmagnetized substance.

stu-

On another sheet

dents' models, as well as their written ex-

a material depend on its atomic structure. Scientists believe that the atom itself has magnetic properties. These magnetic properties are due to the motion of the atom's electrons. Groups of atoms join in such a way that their magnetic fields are all arranged in the same direction, or aligned. This means that all the north

posterboard, arrange the

planations, for accuracy.

strips to represent

a magnet-

ized substance.

Provide a written explanation for

Explanation of Magnetism

The magnetic properties of

your model

poles face in one direction and face in the other direction.

all the south poles region in which the

fields of individual atoms are grouped together is called a magnetic domain. You can think of a magnetic domain as a miniature magnet with a north pole and a south pole. All materials are made up of many domains. In unmagnetized material, the domains are arranged randoml (all pointing in different directions). Because the domains exert magnetic forces in different directions, they cancel out. There is no overall magnetic force in the material. In a magnet, however, most o the domains are aligned. See Figure 2-6.

magnetic

2-1 (continued)

INDEPENDENT PRACTICE Activity Bool<

Students can learn more about mag-

netism by completing the chapter activity

Magnetic Transparency. They

will

dis-

cover which materials allow magnetic

to become aligned. When a ferromagnetic material placed in a strong magnetic field, the poles of the magnet exert a force on the poles of the individual domains. This causes the domains to shift. Either

FOCUS/MOTIVATION Figure 2-6 The sections represent ttie various domains of a material. The arrows point toward the north pole of each domain. What IS the arrangement of the domains in an unmagnetized material^ In a magnetized

Stroke an iron nail repeatedly with a strong magnet. Use the nail to attract a

paper clip and support the nail and attached clip so that they are easily visible. • What has happened to the nail? (It has

material'^'

become magnetized.) Why has this happened? (Answers will vary. The magnetic domains in the nail have lined up in the same direction.) will

Unmagnetized

•

After a short time, the clip

magnet can be made from an unmagnetized

material such as an iron nail by causing the domains

through and to what extent the magnetic fields remain unchanged. fields to pass

Material

Magnetized Material

drop

off.

•

Why

netic

has this happened? (The magdomains have returned to a random

arrangement.)

grouped together and

ability

CONTENT DEVELOPMENT Direct students' attention to Figure

Use

this

of magnets to be cut in two to pro-

duce two smaller magnets, each with north and a south pole.

•

ing care first to explain the concept of such domains as regions in which the magnetic fields of large numbers of

Use the discussion of magnetized and unmagnetized objects to integrate concepts of heat into your lesson.

in a sense.

• • •

Integration

•

ENRICHMENT Activity Bool< will be intrigued by the chap Magnetic Shielding. They us( a magnet, a paper clip, and string to tes

Students

ter activity

different

2-6. Discuss the diagram in terms of random and aligned magnetic domains, tak-

atoms are overlapped and,

unified.

concept to explain the property of certain materials to be magnetized and the

•

materials'

ability

provide

shielding against the effect of a magnetii field.

â&#x20AC;&#x201D; most of the domains rotate (turn) to be in the direction of the field, or the domains already aligned

become larger while those in other become smaller. In both situations, an overall magnetic force is produced. Thus the material becomes a magnet. This also explains why a magnet can pick up an unmagnetized object, such as a paper clip. The magwith the field

ANNOTATION KEY

directions

Answers

O Randomly; they directions.

alignment of the domains in the paper clip so that the clip becomes a temporary magnet. Its north pole faces the south pole of the permanent magnet. Thus it is attracted to the magnet. When the magnet is removed, the domains net's field causes a slight

aligned in

O Stroke the

nail wiih a

(Applying facts)

Even a permanent magnet can become unmagnetFor example, if vou drop a magnet or strike it too hard, you will jar the domains into randomness. This will cause the magnet to lose some or all of its magnetism. Heating a magnet will also destroy its magnetism. This is because the additional energy (in the form of heat) causes the particles of the material to move faster and more randomly. In fact, every material has a certain temperature above which it cannot be made into a magnet at all. Now that you have learned more about the nature of magnets, you can better describe the phenomenon of magnetism. Magnetism is the force of attraction or repulsion of a magnetic material due particularly its to the arrangement of its atoms

Integration

O Physical Science:

ized.

â&#x20AC;&#x201D;

Figure 2-7 This iron nail attracts metal paper clips. How can an iron nail be turned into a magnet''

ergy,

Where

All

WRITING IT ALL BEGAN

WHERE of

mag-

was

actually understood. Various references to this "magical" property can be found in ancient Chinese and Greek mythology. Using reference materials from your library, find out about the

a magnetic field related to mag[netic

poles and lines of force? the rule that describes the behavior of magnetic poles. What is magnetism? What is a magnetic domain? How are magnetic domains related to magnetism?

2. State

3. 4.

Critical 5.

Thinking

discovery and history

magnet

lodestones. Write a report describing how lodestone was discovered, what people first thought of it, and how it has come to be understood and used.

Applying Concepts the origin of mag-

From what vou know about netism, explain why cutting

in half

produces two magnets.

INDEPENDENT PRACTICE

magnetic field, represented by lines of force extending from one pole of a magnet to the other, is an area over which the magnetic force is exerted. 2. Like poles repel each other, and unlike poles attract each other. 3. The force of attraction or repulsion of a magnetic material due to the arrangement of its atoms particularly 1.

â&#x20AC;&#x201D;

its

electrons.

region in which

the magnetic atoms are grouped together; in magnetized material, the magnetic domains are aligned in the same direction, whereas in unmagnetized material, the magnetic domains 4.

fields of individual

Section Review 2-1

Heat, See Heal En-

Language Arts

Began

netism has been known for many centunes, well before it

2-1 Section Review

Chapter

strong magnet.

FIND OUT BY

The phenomenon

electrons.

How

point in different

concepts)

return to their random arrangement and the paper clip is no longer magnetized.

all

Most of the domains are the same direction. (Applying

Students should be sure to include ideas about magnetism, especially the story of the shepherd Magnes. Also have them investigate the contri-

Roman

butions of Petrus Peregrinus de Maricourt and William Gilbert.

You may

wish

to have students present their reports to

the class and compare their findingfs. To emphasize how long people have known about magnetism, have students work together to make a time line showing major events in the study of magnetism. Integration: Use the Find Out by Writing feature to integrate language arts skills into your science lesson.

REINFORCEMENT/RETEACHING Monitor students' responses to the Section Review questions. If students ap-

pear to have difficulty understanding any of the concepts, review this material with them.

are arranged randomly. 5.

When a magnet is cut in half, its mag-

netic

domains are

still

aligned in the

same direction in each half. Therefore, each half becomes a magnet with a north pole and a south pole.

CLOSURE Review and Reinforcement Guide At this point have students complete Section 2-1 in the Rn>iew arid Reinforcement Guide.

2-1 The Earth As a

Magnet V.ULTICULTURAL

Mix- Up

OPPORTUNITY 2-2 Have vour students investigate some who live near the North is

the

life like

how you reached yoor concluDevise an experiment for your lab assistant to fjerfofm to p)rove your cofv dusion so that the sampie can be cor-

a research labo-

ing the c'"a'acte"S''CS o* "^ac^ets

for these cul-

tures that li\e in cold regions

the Lab Explain

ratory conducting experiments regard-

of the peoples Pole. \N"hat

You are wofkjig

havese.ea 5a~r

~a:"5:

sion.

You ma-

a-: se.ea sa-c es :' -aierials that are ":: ~ = z-i .-'ortunatefy. you aisc "a.e a :::e~ One of your

where they

rectty labeled.

terials

experience months of no sunlight?

ESL STRATEGY 2-2 Dictate the questions

belo\%'.

dents work in small groups.

Have

One

stu-

student

reads the question, another student re-

sponds, and a third confirms or correcis

Drawing Conclusions

the answer. 1.

What

-a

the scientific term used to ex-

between a magnetic

plain the difference

-e

:a a

5a~c

;

a -nagnetiG dO'-

asampleamac

pole and a geographic poler 2.

In addition to Earth,

how do scientists

explain magnetism's existence ter.

on Jupi^cc^s ;.Cv>

c :rese questions as

raso-

Vou have read earlier that as the ancient Greeks experimented %»ith magnetite, thev discovered that the same part of the rock alwavs pointed in the same direction. \\"hv does one pole of a bar magnet suspended from a string alwavs point north and the

What are the magnetic properties of the Earth?

TEACHING STRATEGY 2-2

How does a

cxxnpass

work''

FOCUS/MOTIVATION Draw

2-2 The Earth As a Magnet

Guide for Reading

Saturn, and the sun?

other pole alwavs

students" attention to a world

would be obsen able Lf the Earth were a magnet, as Gilben correctlv proposed. Then actuallv hold a strong bar magnet

more or

less parallel to

f)oint

south? .After

all.

the poles of

a magnet were originallv labeled simpiv to describe the directions thev faced •v.-vh resjject to the Earth.

globe and ask them what proj>enies

the north-south

of the globe and ask students to imagine the magnet embedded in the axis

globe.

The first person to suggest an answer to this question was an English phvsician named William Gilben. In 1600. Gilbert proposed the idea that the Earth itself is a magnet. He predicted that the Earth would be found to have magnetic poles. Gilbert's theon turned out to be correct. Magnetic [Doles of the Earth were eventuallv discovered.

How would free-swinging magnets and compasses behave when placed at different points of the globe? Thev would align themseh es in a north-south

•

[relative to the globe] orientation.

mav then

Some

realize that the true

with magnetism and wTOte his findings in

magnetic north pole of the Earth must be in the geographic south, in order for the north poles of magnets to point northward. Do not as vet remark on the correctness of this conclusion, which will be taken up shortl\.)

a lengthv treatise. Not onlv chd he pro-

students

Explain that William Gilbert was phvsician to

gland.

spent

•

Integration

vour lesson.

objects that are charged bv friction. Gil-

GUIDED PRACTICE

bert also conducted earlv experiments

Skills

Because of this, he is considered to be the founder of the modem sciences of electricitv and magnetism.

•

posal to integrate geology concepts into

Development

electricitv.

Skill:

Interpreting a

diagram

Direct students" attention to Figure

of En-

2-8. First explain that the geographic

7 years experimenting

North and South poles are not the same as the magnetic north and south poles. In

OLzabeth

•

Use the discussion of Gilben 's pro-

pose that the Earth was a huge magnet, he also introduced the term electric to describe the force that exists between two

CONTENT DEVELOPMENT

•

and James

—

Figure 2-8 You can see in this illustration that the magnetic poles

Geographic north pole

are not located exactly at the

ANNOTATION KEY

geographic poles Does a

Magnetic pole

compass directly

needle, then, point

north?

Answers

O No.

points to the magnetic south

pole, which does not exacilv align with

the geographic North Pole, (liiierprei-

w *

ing illustrations)

Integration

O Earth

Science: Geology. See Explor-

ing the Universe, Chapter 3.

Magnetic pole-

O Earth

Geographlc south pole-

Science: Geology. See Explor-

ing Planet Earth, Chapter

scientists know that the Earth behaves as if has a huge bar magnet buried deep within it. The

Today,

Earth exerts magnetic forces and is surrounded by magnetic field that is strongest near the north and the south magnetic poles. The actual origin of the Earth's magnetic field is not completely understood. It is believed to be related to the motion of the Earth's inner core, which is mostly iron and a

PROBLEM SOLVING

Figure 2-9 When volcanic lava hardens into rock, the direction of the Earth s magnetic field at that time IS permanently recorded.

MIX-UP

THE LAB

Students should be able to determine

nickel.

that the photog;raph

Scientists have been able to learn a great deal about the Earth's magnetic field and how it changes over time by studying patterns in magnetic rocks formed long ago. Some minerals have magnetic properties and are affected by the Earth's magnetism. In molten (hot liquid) rocks, the magnetic mineral particles line up in the direction of the Earth's magnetic poles. When the molten rocks harden, a permanent record of the Earth's magnetism remains in the rocks. Scientists have discovered that the history of the Earth's magnetism is recorded in magnetic stripes in the rocks. Although the stripes cannot be seen, they can be detected by special instruments. The pattern of the stripes reveals that the magnetic poles of the Earth have reversed themselves completely many times throughout Earth's every half-million years or so. history

shows a pattern of

random magnetic domains and therefore, the unlabeled object

that

not a

magnet. If it were a magnet, the magnetic domains would be aligned in the same direction.

The

simplest test that the labo-

ratory assistant could perform to con-

firm this conclusion would be to place

metal items near the object and see they are attracted to if

it,

as they

would be

the object were a magnet.

—

addition, the magnetic south pole

lo-

cated near the geographic North Pole,

and the magnetic north pole is located near the geographic South Pole. Use the world globe and the magnet again to demonstrate these facts. Explain that the north pole of a compass points toward the geographic North Pole, but because a magnet is attracted to an opposite pole, not a like pole, the north pole of the compass must be pointing to the magnetic south pole. .'Vlign the magnet in the

proper direction and use a compass or a second magnet to reinforce this concept.

•

CONTENT DEVELOPMENT

properties of molten rock to integrate geology concepts into your lesson.

There

•

• •

Integration

•

• •

Use the discussion of the magnetic

strong geolog[ical evidence

that the Earth's north

and south mag-

number of Some scientists who

netic poles have "switched" a

times in the past.

have examined

this

evidence, which

in-

volves the orientation of magnetic minerals at different strata, think that an-

other switch of magnetic poles may occur

REINFORCEMENT/RETEACHING Students might wish to sketch or obmaps of the Earth and label the

tain flat

magnetic poles. They can also draw in compasses at different geographic locations on the map and show the directions in whi( h the

needles point.

in the not-too-distant future.

Compasses

INTEGRATION EARTH SCIENCE

If you have ever used a compass, vou know that a compass needle alwavs points north. The needle of a compass is magnetized. It has a north pole and a south [K)le. The Earth's magnetic field exens a force on the needle just as it exens a force on a bar magnet hanging from a string. The north pole of a compass needle points to the North Pole of the Earth. But to exactlv which north pole? .\s vou have learned, like poles repel and unlike poles attract. So the magnetic pole of the Earth to which the north pole of a compass points must actually be a magnetic south pole. In other words, the north pole of a compass needle points toward the geographic North Pole, which is actuaUy the magnetic south pole. The same is true of the geographic South Pole, which is actually the magnetic north pole. The Earth's magnetic jxjles do not coincide

Recent space probes, such as Voyager 1 and Vor\ager 2, have revealed interesting details about the magnetic propenies of other planets. Jupiter, for example, has an extremely strong magnetic field. The magneiosphere of this planet is one of

the largest field "structures" in the solar system, and the temperatures reached bv

excited atomic particles in parts of this Figure 2-10

measured.

field are the highest yet

est survivrig

HISTORICAL NOTE "MAGICAL" COMPASS

~pass.

direcdy wixh its geographic poles. Scientists have discovered that the magnetic south pole is located in northeastern Canada, about 1500 kilometers from the geographic North Pole. The magnetic north pole is located near the .-Vntarctic Circle. The angular difference between a magnetic pole and a geographic pole is kno%%Ti as magnetic variation, or declination. The extent of magnetic variation is not the same for all places on the Eanh. Near the equator, magnetic variation is slight. .\s vou get closer to the poles, the error increases. This must be taken into account when using a compass.

Compasses have had a great inspiraon a nimiber of scientists in

tional effect

the past, .\lben Einstein, for example, in describing his earlv childhood, wrote that his favorite toy

given to

him by

was a compass needle father.

Einstein

lost the

sense of

his

claimed that he never

Figure 2-11

he first felt when he plaved with that "magical" needle. scientific

wonder

that

Other Sources of Magnetism in

2-2 (continue d)

the Solar System

Magnetic fields have been detected repeatedlv throughout the galax\. In addition to Earth, several other planets produce magnetic fields. The magnetic field of Jupiter is ten times greater than that of Earth. Saturn also has a ven strong magnetic field. Like Earth, the source of the field is believed to be

CONTENT DEVELOPMENT Because the Earth's magnetic south is located in northeastern Canada, the divergence of compasses from true north in the United States is greater in the nonhwestem part of the countrt". Compasses in the state of Washington, for example. jDoint in a more or less northeastward, rather than northward, direction. In parts of Alaska, compasses pole

related to the planet's core.

The sun is another source of a magnetic field. The solar magneuc field extends far above the sun's surface. Streamers of the sun's corona (or outermost

actually point eastivardi

•

Integration

•

Lse the photograph of the

•

earlv

•

com-

pass to integrate social studies concepts into your science lesson.

INDEPENDENT PRACTICE Activity

Book

Students can learn about the connec-

between the sun and the Earth's magnetosphere h\ completing the chaption

ter acUNitv \'an .\llen Radiation Belts

They

will

research the location and im-

portance of these

belts.

CONTENT DEVELOPMENT

rounding areas. xhe\

Explain that Jupiter has a gigantic magnetic field, called the magneto-

patches.

sphere, that stretches millions of kilo-

meters from the planet. Jupiter's magnetosphere is probably caused bv a liquid metallic laver

around the planet's

Saturn's huge magnetic field

core.

second

that

sunsf)ots

are

dark

\side. Periods of hea\-i sunspot can interfere with communication systems on Earth, and astronomers are cominced that sunspot actintv has an

lometers

acti\ity

effect

on Earth's weather and

•

• •

climate.

si/e to Jupiter's.

Explain

appear

Some are manv thousands of ki-

actually

storms that occur on the sun's surface. Because sunspots are cooler than sur-

•

Integration

•

• •

Lse the discussion of magnetic fields on other planets to integrate concepts of astronomy into vour lesson.

in Action

MULTICULTURAL OPPORTUNITY 2-3

Focus on this question as you read How do magnetic fields alter ttie motion of charged

You learned

model of a

them

paper small

to cut out of hea\T stock

that

when

charged is

moving. If a charged particle moves in the same direction as a magnetic field, no force is exerted on it. If a charged particle moves at an angle to a

rows onto the block of St)Tofoam. The arrows can represent the spinning orientation of the electrons in the metal bar. A magnet can be represented by having

magnetic field, the magnetic force acting on cause it to move in a spiral around the magnetic field lines. See Figure 2-14.

will

same direcnonmagnetic object is represented by arrows, with some arrows pointing in one direction and others in the opposite direction. You might ask students if thev can use this model to explain why a falling magnet will change its the arrows pointed in the

tion.

especially the direction in which the particle

ar-

rows. Using straight pins, place the ar-

all

Chapter

Action

exerted on it (it is either pulled or pushed away). But what happens when a charged particle enters a magnetic field? The magnetic force exerted on the particle, if anv, depends on a number of factors,

block of Styrofoam can rep-

resent the magnetic steel bar. Ask

particle enters an electric field, an electric force

particles?

Have your students build magnet.

2-3 Magnetism

Guide for Reading

2-3 Mapetism

SOLAR WIND The Earth and the other planets are immersed in a wind of charged particles sent out by the sun. These particles sweep through the solar system at speeds of around 400 kilometers per second. If this tremendous amount of radiation (emitted charged particles) reached the Earth, life as we know it

could not survive.

Figure 2-13 Because of its interaction with the solar wind, the Earth's magnetic field differs from that of a bar magnet The solar wind causes the magnetosphere to stretch out into a tail shape on the side of the Earth that is experiencing nighttime.

orientation.

ESL STRATEGY 2-3 Have students complete the following paragraph on magnetism in action. They should fill in the missing information by choosing from the following list: magnetosphere aurora solar wind with charged particles

Van

Allen radiation belts

Earth's magnetic field

The

blocked by the

WTien which is called the charged particles do penetrate it, they are found in two large regions known as As the particles approach the the Earth's surface, they cause the air to

glow; this

phenomena

called

TEACHING STRATEGY 2-3

CONTENT DEVELOPMENT Refer students to Figure 2-13, which shows the Earth's magnetosphere. Explain the interaction between the magnetosphere and the "solar wind," or charged particles streaming outward from the sun. Explain that the asymmetrical shape of the magnetosphere, which streams outward away from the sun, is due to this interaction with the charged particles.

• • • •

Integration

• • • •

Use the discussion about the solar wind to integrate earth science concepts of astronomy into your lesson.

P56. Then refer them to Figure 2-14. Have them identify the movement of the

charged particles

Skills

Development

Skills: Interpreting

diagrams, drawing

conclusions

Have students reread the boldface first paragraph on page

sentences in the

Allen radi-

From what

direction did charged partrapped in the Van Allen radiation behs move in Earth's magnetosphere? Explain your answer. (From an angle, because the trapped particles move in a spiral around the magnetic

•

GUIDED PRACTICE

in the \'an

ation belts. (Spiral movement.)

ticles

field lines.) • If

a charged particle

moves parallel

Figure 2-14 Charged particles from the sun become trapped in spiral paths around the Earth s magnetic field lines. What are the two regions in which the particles are confined called?

Charged

particle

ANNOTATION KEY

Fortunately, however, these charged particles are deflected by the Earth's magnetic field. The mag-

Answers

netic field acts like an obstacle in the path of the

The region

O Van

which the magnetic field of the Earth is found is called the magnetosphere. Without the solar wind, the magnetosphere would look like the lines of force surrounding a bar magnet. However, on the side of the Earth facing away from the sun the magnetosphere is blown into a long tail by the solar wind. The solar wind constantly reshapes the magnetosphere as the Earth rotates on solar wind.

field

belts.

O Radiation from the sun

(Relating

collides with

atmosphere to produce a called an aurora. (Relating

particles in the Earth's magnetic

field

sheet of light

concepts)

Integration

its axis.

Sometimes charged penetrate the

field.

from the sun do

particles

The

O Earth

particles are forced to

named

When

known for

a large

O Physical Science: Light. See Sound and

and forth between magnetic poles. Generally, these charged particles are found in two traveling back

large regions

Science: Astronomy. See Ex-

ploring the Universe, Chapter

continually spiral around the magnetic field lines,

belts,

Allen radiation

facts) Magnetic

Light,

Van Allen radiation their discoverer, James Van Allen. number of these particles get close

Chapter

as the

atoms in the atmosphere, causing the air to glow. Such a glowing region is called an aurora. Auroras are continually seen near the Earth's magnetic poles, since these are the places where the particles are closest to the Earth. The aurora seen in the northern hemisphere is known as the aurora borealis, or northern lights. In the southern hemisphere, the aurora is known as the aurora australis, or southern lights. Many scientists believe that short-term changes in the Earth's weather are influenced by solar particles and their interaction with the Earth's magnetic field. In addition, during the reversal of the Earth's magnetic field, the field is somewhat weakened. This

Path of trapped particle

to the Earth's surface, they interact with

allows

more high-energy

Some

ECOLOGY NOTE LIGHT POLLUTION

The aurora

species of plants

a magnificent

Unfortunately,

many

people are prevented from seeing this display because of light pollution. Suggest that students research to find out

what light pollution is and how it might be controlled so that people can enjoy such phenomena as the aurora. Have students consider

particles to reach the

how

light pollution

may

affect scientific study at obsei"vatories.

hypothesize that these periods during which the magnetic field reversed might have caused the extinction of certain Earth's surface.

borealis

display of light.

scientists

and animals.

Figure 2-15 A band of colors called an aurora dances across the sky near the Earth 's magnetic poles. This one is in northern Alaska. Why do auroras form?

The

the magnetosphere, will a force be ex-

electrons.

moving in the same direction of the magneto-

varying levels, starting at roughly 1000

erted on

it?

(No. Because

it is

belts encircle the Earth at

kilometers above the Earth's surface and

extending to roughly 20,000 kilometers When a large number of the charged particles penetrate the Van

sphere.)

• • • •

Integration

• • • •

Use the information about the aurora to integrate concepts of light into your lesson.

or more.

CONTENT DEVELOPMENT The Earth

from from the sun by the Earth's magneto-

largely protected

Allen radiation belts and escape into the

high-intensity radiation

upper atmosphere above Earth's

broad

regions, they collide with molecules in

belts

sphere called the Van Allen radiation belts.

These

James Van

belts,

Allen,

named

for scientist

whose work

led to their

discovery, trap high-energy protons

the atmosphere.

The

pcilar

collision causes the

atmospheric particles to give off known as an aurora.

light,

and

— ASTRONOMY Radiation from particles spiraling around in magnetic fields also plavs an important role in learning about the universe. Particles trapped by magnetic fields emit energ\ in the form of radio waves. Radioastronomers studv the universe bv recording and analvzing radio waves rather than light waves. In this way. scientists have been able to learn a great deal about manv regions of the galaxv. For example. energ% received from the Crab Nebula indicates that it is a remnant of a supernova (exploding starl.

FIND OUT BY

READING A LONELY VOYAGE Reading comprehension

Skill:

Point

out

students

tliat

history

books usually credit Admiral Robert Pearl's expedition in 1909 as being the first expedition to reach the North Pole. however, about arose, Contro\ers\' whether Pear\' e\er actually made it to the pole. William Hunt's book examines the controN eisy. After students read the

Figure 2-16 This

map

NUCLEAR ENERGY Utilizing the behavior of charged particles in magnetic fields may be a solution to the energv' problem. .\ tremendous amount of energ\ can be released when two small atomic nuclei are joined, or fused, together into one larger nucleus. .-Accomplishing this, however, has been impossible until now because it is extremelv difficult

of the

constellation Sagittarius

was made

from information collected by a radio telescope.

book, encourage them to express opinions.

Who do

of the

first

thev believe was the leader

expedition to reach the North

overcome the repulsive electric forces present nuclei approach each other. .\t high temperatures, atoms break up into a gaseous mass

IN D OUT BY

when two

Pole?

of charged particles known as plasma. In this state, nuclear reactions are easier to achieve. But the required temperatures are so high that the charged particles cannot be contained bv anv existing vessels. Bv using magnetic fields, however, scientists hope to create a kind of magnetic bottle to contain the particles at the required temperatures. Massive research projects are currentlv undenvav to achieve this goal.

A Lonely Voyage The dangerous quest to reach the North Pole was at one time only a

vision

the

minds of adventurous explorers. But during the 1800s several different explorers set out on difficult and sometimes fatal missions to the

North Pole.

Two

2-3 Section Review

different ex-

plorers reached the pole, but

the matter of sial.

2-3 (continued)

CONTENT DEVELOPMENT

arrived

The answers

lie

magnetic declination. Read To Stand at the Pole: The Dr. Cook-Admiral Peary North Pole Controversy by William Hunt to discover the details

How does the magnetosphere protect the Earth from the sun's damaging radiation? What

are \'an .-Vllen radiation belts? they related to auroras?

How

might magnetic fields enable from atomic nuclei?

How

are

scientists to

utilize energ)'

Connection Earth Science 5. Whv would a planet close possess a strong magnetic

of the story

from nuclear

Describe what happens to a charged particle in a magnetic field.

whether the explorers made appropriate corrections for

Point out that todav's nuclear power plants use heat energ)'

who

remains controver-

first still

i7Vi-X.

fis-

to the

sun have to order to

field in

sustain life?

Nuapart of an

sion to produce electrical power. clear fission

the splitting

atomic nucleus, which releases energv-. Nuclear fusion, the combining of two atomic nuclei, produces even more energ\- than fission. Scientists are tning to

develop controlled fusion reactions to

meet future energ)' needs. Because hvdrogen from water would be used as the

• • • •

Integration

•

• • •

Use the information about radio

tele-

scopes to integrate earth science con-

is renewable and in large supplv. The development of a magnetic bottle to

contain the h\drt)gen particles so that fu-

fusion.

of cold fusion excited scientists

around the world. L'se the information about the use of nuclear energ)' to integrate concepts of fusion into your lesson.

produced at the required temperatures would help to meet energy needs with a renewable fuel

ENRICHMENT

source.

Martin Fleischmann claimed to have

sion reactions could be

cold

quicklv rejected.

sibilitv

cepts of astronomv into vour lesson.

fuel in a nuclear fusion reactor, the fuel

source

The claim was Have students investigate what cold fusion is and whv the poscovered

INDEPENDENT PRACTICE Section Review 2-3 No force is exerted on a charged par1 .

ticle

In 1990. chemists Stanlev Pons and dis-

moving

in the

same direction

as a

magnetic field. A magnetic force will cause charged particles moving at an

(

ANNOTATION KEY

Magnetic Clues to Giant-Sized Mystery Have you ever looked at a world map and noticed that the Earth's landmasses

Integration

Alfred Wegener proposed that the giant landmass that once existed split apart and its various parts "drifted" to their

up through the rift valley and hardens into rock, new ocean floor is formed This process is called oceanfloor spreading. This evidence showed that the ocean floor could indeed move. Further evidence came from information about the Earth's magnetic field. When the molten rocks from the midocean ridges harden, a permanent record of the Earth's magnetism remains in

present positions. His theory, however,

the rocks. Scientists found that the pat-

met with great opposition because

tern of

look

pieces of a giant

jigsav*;

puz-

many scientists, all was once connected.

zle? According to

the Earth's land

How In

then, did the continents

form?

the early 1900s, a scientist

named

movement of sections of the solid ocean floor. Conclusive evidence to

magnetic stripes on one side of matches the pattern on the other side. The obvious conclusion was that as magma hardens into rocks at

support

the

order for

true,

would involve

the

theory of continental

his

could

come

of the

ocean

drift

only from a detailed study floor.

the 1950s

mountains, called midocean ridges. These mountains have a deep crack, called a

rift

valley, running

center.

at the

through

their

great deal of volcanic activity

midocean

The Nature of Science, Chapter

ridges.

O Physical Science: Fusion. See Chemistry

of Matter, Chapter 5.

O Earth Science: Continental Dynamic Earth, Chapter

the ridge

Drift.

See

CONNECTIONS MAGNETIC CLUES TO GIANT-SIZED MYSTERY

midocean ridge, half the rocks move one direction and the other half move were not for in the other direction. If knowledge about magnetism and the in

You might make copies of a world map

and 1960s, new map-

ping techniques enabled scientists to discover a large system of underwater

occurs

O Earth Science: Radio Telescopes. See

lava wells

and encourage students

Earth's magnetic field, such a conclusion could not have been reached. Yet thanks to magnetic stripes, which provide clear evidence of ocean-floor

fit

the

Conwant to demonstrate the concept of the magnetic stripes supporting the concept of oceanfloor spreading by drawing horizontal lines on a sheet of paper and then tearing the paper vertically. Students should see that the lines on both sides of the paper are similar, just as the magnetic stripes on both sides of the midocean ridges are as an introductory activity for the

nections feature.

spreading, the body of scientific knowl-

edge has grown once

to tn' to

continents together in a large landmass

again.

When

You may

also

similar.

you are teaching thematically, you to use the Connections feature to reinforce the themes of evolution and If

may want

patterns of change. Integration: Use

the

Connections

feature to integrate earth science con-

cepts of continental drift into your

les-

son.

angle to a magnetic field to

move

in a

atmosphere. The collision causes the

around the magnetic-field lines. 2. It traps charged particles and forces them to spiral around the magneticfield lines, thus preventing them from

aurora.

reaching the Earth's surface. 3. The Van Allen radiation belts are two large regions where most charged particles are found in the magnetosphere. When a large number of

temperatures. 5. Without a strong magnetic

spiral

The magnetic

REINFORCEMENT/RETEACHING Monitor students' responses to the

fields

may be used

create a magnetic bottle that could con-

Section Review questions. If students appear to have difficulty with any of the

tain particles for fusion at the required

concepts, review the appropriate material.

field,

the

charged particles of the sun would reach the planet and destroy the life on

CLOSURE

charged particles in the belt get close to

Review and Reinforcement Guide now complete Section 2-3 of the Review and Reinforcement

Earth, they collide with particles in the

Guide.

it.

Students may

Lahoratory Investigation Laboratory Plotting Magnetic Fields

Investiption

Problem

PLOTTING MAGNETIC FIELDS

How

Gather

all

materials at least one day

prior to the investigation.

Materials

class

needs, assuming three to six students per

PRE-LAB DISCUSSION

horseshoe magnet

sheet of white paper

compass

lab-

the purpose of the laboratory

investigation? (To plot and

magnetic

fields

Why do you

Remove

Using a clean sheet of paper, repeat steps 1 through 5 using a horseshoe magnet.

the magnet from the paper. Observe the pattern of the magnetic field you have plotted with your arrows.

Remove

mark the ends

compare the

Observations

Place a bar magnet in the center of a sheet of paper. Trace around the magnet with a pencil.

magnet and your drawing to show

magnet back on the sheet

think two different types

paper

in its

outlined position.

of magnets are used in the investigation? (For comparison purposes.)

Do you think the compass needle will point in different directions as you •

a spot about 2 cm beyond the north pole of the magnet. Place a compass on this mark.

Draw a mark

Note the direction dle points.

move the compass around the magnets? (Answers will vary; some students may

that the

compass

of the north pole of the

greater at the poles.)

compass

field at

there that the magnetic

strongest near the poles of a

What can you conclude about the path of magnetic field lines between the poles of any magnet?

On Your Own

needle.

the point marked.

field

magnet?

This arrow indicates the direction of the

magnetic

What evidence field is

compass

needle by drawing a small arrow. The arrow should extend from the mark you made in step 2 and point in the direction

From which pole does the magnetic emerge on the bar magnet? On the horseshoe magnet?

Analysis and Conclusions

nee-

the paper, mark the posi-

tion of the north pole of the

move because

the strength of the magnetic force

Describe the pattern of arrows you have to represent the magnetic field of the bar magnet. How does it differ from that of the horseshoe magnet?

drawn

the

the north and the south poles. Put the

of magnets.)

suggest that the needle will

Repeat steps 2 and 3 at 20 to 30 points around the magnet. You should have 20 to 30 tiny arrows on the paper when you have finished.

(per group)

bar magnet

oratory procedure. is

Procedure

Have students read the complete

•

surrounding a bar

pencil

group.

What

lines of force

You should

have enough supplies to meet your

•

can the

magnet be drawn?

BEFORE THE LAB

See

The pattern of magnetic a bar magnet will change if another bar magnet is placed near it. Design and complete an investigation similar to this one in which you demonstrate this idea for both like poles and unlike field lines for

the accompanying diagram.

poles.

TEACHING STRATEGY You may want

DISCOVERY STRATEGIES to the chapter ideas by asking

come

tions similar to the following:

familiar with the process.

2. Tell

students to keep the magnet they

are not plotting away from the work area so that

its

magntfic force does not inter-

fere with the ploitmg of the other

mag-

net. 3.

Discuss

•

Have groups compare

their patterns

plotted similar patterns.

all

groups

The

the investigation relates

open ques-

How are the forces of magnetism in all

magnets

alike? (The magnetic forces are

strongest at the poles and weaker around the rest of the magnet.) •

of arrows to note whether

how

demonstrate the laboratory procedure to help groups be1.

How far away would a paper clip have

be from a magnet not to be attracted it? (Just outside the magnetic field.

distance would vary, depending

the strength of the magnetic force.) •

Could you plot the magnetic

field

the magnets without a compass? Explain. (Answers will vary.

Lead students

understand that they could use iron filings, for example, to plot the field of magnetism of the magnets.) to

OBSERVATIONS 1.

The pattern around

arcs

around each

the bar magnet

pole, with

more arrows

Study Guide

GOING FURTHER: ENRICHMENT Parti

Have students design an experiment demonstrating the range of the magnetic of magnets of different attraction strengths. Have them measure the range

Summarizing Key Concepts 2-1

The Nature of Magnets

Sunspots on the surface of the sun are

â&#x20AC;&#x201D;

a north pole A Every magnet has two poles and a south pole. Like magnetic poles repel each other; unlike poles attract each other.

The region act

which magnetic forces can

called a magnetic

are traced by magnetic

field.

repulsion exerted

magnetic

by a magnet through

* The Earth

particles

the protection of the Earth

strengths, a metric

Magnet

a data

The region Earth

exerted

Part 2

which the magnetic field of is known as the magneto-

Have students imagine that they are loin a field on a cloudy day and that they do not know which direction they are facing. Ask them to tell how they

cated

particles from the sun be-

Earth's magnetic field. They two regions known as the Van belts. If charged particles

reach Earth's surface, usually they create auroras.

determine

could

they are facing

at the poles,

direction

that

they had with

them

the

if all

was a bar mag^net and a

string.

and the south poles.

A compass needle does to the Earth's

not point exactly

geographic poles.

points to

Chapter Review

The difference in the the Earth's magnetic and geo-

the magnetic poles. location of

graphic poles

called magnetic declination.

ALTERNATIVE ASSESSMENT The

Define each term

Prentice Hall Science

program

in-

cludes a variety of testing components and methodologies. Aside from the

Reviewing Key Terms 2-1

and

energy.

Allen radiation

surrounded by a magnetic

ruler,

table.

applications of nuclear reactions to produce

strongest around the magnetic

field that is

north

charged

each pole. Suggest that they use these materials in their experiment: a paper clip, three bar magnets of different

from solar wind; radio astronomy; and future

are located

Action

responsible for several

field is

Some charged come trapped by

its

field.

2-2 The Earth As

sphere.

the force of attraction or

deflection of

a magnetic

phenomena:

domains are regions in which the magnetic fields of all the atoms line up in the same direction. The magnetic domains of a magnet are aligned. The magnetic domains of unmagnetized material are arranged randomly.

field.

from the center of the magnet and

2-3 Magnetism The

Ivlagnetic fields

lines of force.

IVIagnetic

Magnetism

related to the sun's magnetic

Chapter Review questions, you may opt to use the Chapter Test or the Computer Test Bank Test in your Test Book for assessment of important facts and concepts. In addition, Performance-Based Tests are included in your Test Book. These Performance-Based Tests are de-

a complete sentence.

2-3 Magnetism

The Nature of Magnets

magnetism

magnetosphere

pole

aurora

Action

magnetic field magnetic domain

signed to test science-process skills, rather than factual content recall. Since they are not content dependent, Perfor-

mance-Based Tests can be distributed after students complete a chapter or after they complete the entire textbook.

CONTENT REVIEW closer together near the poles.

The

pat-

somewhat oval. The pattern of the arrows around the horseshoe magnet also radiates toward the poles, with more tern

ANALYSIS AND CONCLUSIONS 1.

More arrows

are located there,

Multiple Choice

and

they are closer together. 2.

The path

radiates toward the poles.

1. c

arrows closer together near the poles. The pattern is arclike between the two

3. Investigations

and the

poles.

repulsion of like poles are clearly delin-

In both cases, the direction of the magnetic field is from the north to the

eated

d d

should be designed so

that the attraction of unlike poles

the plot.

4. a

south pole.

Chapter Review

True or False 1.

2. F, 3.

4. F, 5. 6.

Multiple Choice

can

Choose

T T

7. F,

Content Review

repel

magnetic pole

Concept Mapping

Row Row Row

pole.

region

Pole

Dalton.

Oersted.

Faraday.

Gilbert.

CONCEPT MASTERY

attract

each other.

When

magnet

false,

change

the statement true.

the underlined

and a south

pole, are

The magnetic

lines

north

to the other

over which magnetic force

the time that they solidified.

changes

The

align-

stripes provides evidence of

in Earth's magpnetic field

over

time. 6.

Materials are magnetic

they have

aligned domains. Unmagnetized materials

have domains arranged randomly.

substance

magnetized by causing the

domains to become aligned. A substance loses magnetism when the domains rearrange in random order. 7. Like a bar magnet because it exerts magnetic forces and the magnetic field is strongest at the poles

Jupiter

a source oi

magnetism with

a magnetic field ten times greater than

of a

aurora.

nickel

magnetic

field

magnetosphere.

particles from the sun that get close to the Earth's surface produce

supernovas. volcanoes. plasma.

auroras.

Complete the following concept map for 1. Refer to pages P6-P7 to cona concept map for the entire chapter.

Section 2-

point

will

a magnet attract each

which magnetic forces .

cannot be magnetized. a magnetized substance, magnetic

domains point in the same direction. Ivlagnetic domains exist because of the magnetic fields produced by the motion

known

Magnetism 1

A compass

The Earth's magnetic

needle points to the Earth's geographic pole

caused by alignment of 1

field

protects

against the harmful radiation

winds.

cobalt

Charged

magnet suspended

ment of the

stratosphere.

struct

called a magnetic field

of electrons

A magnetic domain is a region in which magnetic fields of atoms align in the same direction. 5. The magnetic stripes in molten rocks aligned with the Earth's magnetic poles

atmosphere.

4. Steel

exerted.

The region act

of the Earth's

other. 3.

of force extend

from one pole of a magnet in the area

word or words

horizontally from a string

cut in half, two

produced because magnetic poles always appear in pairs. 3.

The north pole

2. Like poles of is

smaller magnets, each with a north pole

write "true. "If

make

Like poles repel each other; unlike poles

not a

Concept Mapping is true,

Magnetic poles are the ends of a mag-

net where magnetic effects are strongest.

called the

ridges.

True or False the statement

The region is

The results of the sun's magnetic field can be seen as a. sunspots. c. magnetic stripes. solar winds.

of the following

glass

Which

magnetic material? a. lodestone

magnetosphere. The idea of the Earth as a magnet was first proposed by

field of attraction.

a magnet in which the magof atoms are aligned is a c. compass.

domain.

completes each statement.

that best

d. in

ferrum.

Magnetic lines of force Magnetic domains; South

answer

which magnetic forces act is called a c, magnetic field. a. line of force.

netic fields

act in a

the letter of the

The region

solar

Concept Mastery Discuss each of the following 1.

What

a brief paragraph.

are magnetic poles?

How do

magnetic poles behave when placed

What happens when a magnet half?

Why?

How

a magnetic

magnetic

How

cut

7. field

represented by

evidence of changes in the field be found in

10.

rocks?

Use the 1.

you have developed in

this

how an

the significance of the fact that

aurora

produced.

4. Identifying

patterns Describe the dif ference between a permanent magnet and a temporary magnet.

when two like poles are placed together? Use a diagram in your

that arise

Applying concepts Why might an inexpenenced explorer using a compass get near the geographic poles? Making comparisons One proton is traveling at a speed of 100 m/sec parallel to a magnetic field. Another proton is traveling at a speed of 1 m/sec perpendicular to the same magnetic field. Which one experiences the greater magnetic force? Explain.

Relating cause and effect Stroking a magnet causes

material with a strong the material to

explanation.

become magnetic.

Ex-

what happens during this process. Making inferences Why might a material be placed between two other materials so that magnetic lines of force are not allowed to pass through? Using the writing process Write a plain

lost

Explain

What

chapter to answer each of the following.

Making comparisons How do the lines of force that arise when north and south poles of a magnet are placed close together compare with the lines of force

sources of magnetism

the solar system.

Thinking and Problem Solving

skills

acf How?

charged particles can become trapped by magnetic fields?

Earth's magnetic

Critical

materials magnetic while

How can a material be magnetized? How can a magnet lose its magnetism? Like what type of magnet does the Earth

are magnetic domains related to

How can

some

8. Describe several

field lines of force''

the atomic structure of a matenal? 5.

are

others are not?

next to each other'' 2.

Why

poem

or short story describing the im-

portance of magnets

your daily

life.

Include at least five detailed examples.

Chapter

Electromagnetism

SECTION

CHAPTER PLANNING GUIDE^ OTHER ACTIVITIES

"•r^WS^MBS

43i

Electromagnetism

Chapter

CHAPTER OVERVIEW Electromagnetism is a term used to describe the relationship electricity and magnetism. The experiments of Hans Christian Oersted illustrated that an electric current gives rise to a magnetic field whose direction depends on the direction of the applied current. These experiments led to the development of

between

temporary magnets called electromagnets; the electric motor, a device that converts electrical energy into mechanical energy; and the galvanometer, an instrument used to detect small cur-

Faraday and Henry experimented with electromagnetic inducor the production of a current by the motion of a conductor across magnetic lines of a force in a magnetic field. These experiments led to the development of the generator a device in which principles of electromagnetic induction are applied to convert mechanical energy into electrical energy such as alternating and transformers devices that increase or decrease current the voltage of an alternating current.

tion,

—

rents.

3-1 MAGNETISM ELECTRICITY THEMATIC FOCUS

The purpose of this section is to introduce students to the concept of obtaining magnetism from electricity. More than 1 50 vears ago, an experiment by the Danish physicist Hans Christian Oersted led to an important scientific discover)' about the relationship between electricity and magnetism, known now as electromagnetism. Oersted found that an electric current flowing through a wire giyes rise to a magnetic field whose direction depends on the direction of the applied current. This discover)' led to the

into mechanical energy'

and contains an

electromagnetic armature that

magnet

When

a shaft within a

that

cvcle current.

electric motors.

The armature of an

spinning armature causes the shaft to spin, enabling the motor to do work. The

shaft can

vice that uses mechanical energy.

The

Sewing

machines, refrigerators, vacuum cleaners,

power

and most few of the

saws, subw'ay trains,

industrial machiner\' are a

many

free to

permanent

become mag-

devices that

would be

practically

The themes this section

and

that can

be focused on

diversity,

*Energy: The principles of electro-

magnetism can be applied to convert one form of energy' into another form of

electromagnetism

P66

solenoid p. P67 electromagnet p. P67 electric

motor

galvanometer

p. p.

P69 P70

ways

exist

Unity

magnetic

field will

al-

around a current.

and

diversity: Electric motors

ergy into mechanical energ\

Patterns of change:

the wire changes direction, causing the

Once

again, the opposite poles of the armature

and the fixed magnet attract, so the armature continues to rotate. This process occurs over and over again, keeping the continuous rotation. The

ternating current supplied to an electric

motor switches the poles of the armature 120 times each second, or switches com-

—

electrical en-

electric cur-

rent flowing through a wire will create a field whose direction depends on the direction of the current.

magnetic

PERFORMANCE OBJECTIVES

This section

will

introduce students to

the concept that electricity can be pro-

1831 by

the English scientist Michael Faraday

American

scientist Joseph Henr\'.

cause Faraday published his results

and Befirst

and investigated the concept in more detail, his work is better known. Faraday's experiments showed that although a steady magnetic field produced no electric current, a changing magnetic field did produce an electric current. Such a current is called an induced current, and the process by which a current is produced bv a changing magnetic field

3-1

Describe Oersted's experiment on currents and magnetic fields and state the principle he discovered. 2. Define electromagnetism. 1.

al-

FROM

THEMATIC FOCUS

the

the armature Just before reaches the poles, the current through

attract).

3-2 ELECTRICITY

investigated independently in 'Stability:

of energy into another

SCIENCE TERMS 3-1

duced from magnetism. This concept was

energy'.

use electromagnets to convert one form

64c

Describe the structure and use of galvanometers.

MAGNETISM

and patterns of change.

then begin to rotate to the opposite poles

al-

are energy, stability, unitv

of the fixed magnet (because opposites

armature

Distinguish between direct and

ternating current.

impossible to design without electric mo-

poles of the armature

poles of the armature to switch.

Describe the structure and use of

be connected to pulleys, fan

blades, wheels, or almost any other de-

current flows into the armature,

netic poles.

held in a fixed position.

the ends of the armature

motor is and the

electric

usually connected to a shaft,

of practical devices use the

concept of electromagnetism in their design, for example, the electric motor. An electric motor changes electric energ\'

rotate

of electromagnets.

tors.

development of the electromagnet.

A number

Explain the structure and function

and forth) 60 times each second. Consequently, alternating current is referred to as 60-hertz or 60plete cycles (back

FROM

called electromagnetic induction.

Farada\ also conducted other experiments into the nature of electromagnetic induction, but the one common element in all his experiments was a changing

— CHAPTER PREVIEW does not matter whether the magnetic field changes because the magnet moves, the current moves, or the cur-

Unity and diversity: Generators use electromagnets to convert one form of energy into another. A generator converts mechanical energy into electric en-

rent giving rise to the magnetic field

erg).

Patterns of change: A changing magnetic field gives rise to an electric

shell.

magnetic duction,

In electromagnetic in-

field. it

changes.

magnetic

matters only that a changing

field

experienced.

important application of electromagnetic induction is the generator. A generator

a device that converts

me-

chanical energy into electrical energy.

Generators that manufacture electricity in power plants account for about 99 percent of the electricity consumed in the United States.

The

electricity gener-

ated in pow-er plants reaches

its

destina-

through wires, and the use of step-up and step-down tranformtion by traveling

ers has

made

this

method of

delivery

efficient.

Other important applications of

elec-

time in the future. Play the tape for stu-

dents so that they can see or hear the quality of the recorded material. Then allow a strong magnet or electromagnet

come

into contact with the tape

PERFORMANCE OBJECTIVES 3-2 1. Describe Faraday's and Henry's experiments and state the principle of electromagnetism they discovered. 2. Define electromagnetic induction. 3. Describe the structure, operation, and uses of a generator. 4. Explain tlie production of alternat-

back the area of the tape that

came into contact with the magnet, and some of the remaining tape. • What happened? (Students should note that the sound or picture quality of the tape has been reduced significantly

because of

its

exposure to the magnet.)

Point out that magnetism caused the

changes

in the

students

will

this

magnetic tape and that more about things like

learn

and the relationship between mag-

ing current. 5. Describe the structure, operation,

netism and electricitv in

and uses of step-up and step-down

People Have the Power

transformers.

Contact your

devices called geophones and electro-

and ask the public

this section are

energy, scale and struc-

and interactions, imity and and patterns of change.

ture, systems diversity,

P73

electromagnetic induction p. P73 generator p. P74

*Scale and structure: Electric current is produced and used at low voltages, but it is most efficiently transmitted at high voltages. Transformers change the voltage of alternating current for practical use

•Systems and

and

distribution.

that

A magon a wire

interactions:

netic field will exert a force

carrying current.

local electric

company

relations

the representative arrives, have the stu-

transformer p. P78

dents develop a

might

*Energy: Energy in the form of alternating current can travel from one place to another more efficiently with the use of transformers.

this chapter.

department to send a representative to speak to your class. (Most utility companies have such representatives and programs.) Before

SCIENCE TERMS 3-2 induced current

its

depending on the strength of your mag-

tromagnetic induction include seismic

magnetic pumps for circulating blood. The themes that can be focused on in

and

After several seconds (or longer

net), play

current.

like to

list

of questions that they

ask the representative.

Sam-

ple questions might include these:

^SSSaSSy Learning.

TEACHER DEMONSTRATIONS MODELING

affect the

How

•

What

•

sound

or picture quality of the previously recorded

material you choose to use, although the tape

can be rerecorded and reused again

Where does

•

Observing Magnetism Obtain a cassette musical tape or a cassette videotape of which the recorded material is no longer needed. Note: This demonstration will adversely

•

electricity

come from?

electricity created?

done with excess electricity

that

generated but not used?

How do

devices use electricity?

Have the representative make a special effort to electricitv

emphasize the relationship of and magnetism. Point out to

students that this information will help them in their study of generators, trans-

formers, and the relationship between

magnetism and

electric current.

any

64d

CHAPTER 3

Ekctromapetism INTEGRATING SCIENCE This physical science chapter provides

you with numerous opportunities

to in-

tegrate other areas of science, as well as

other disciplines, into your curriculum. Blue numbered annotations on the student page and integiation notes on the teacher wraparound pages alert you to areas of possible integration. In this chapter you can integrate social studies (pp. 66, 72), language arts (p. 74),

and hydroelectric power and hertz (p. 76), earth science and seismology (p. 78), and life science and electron microscopes (p. physical science (p. 75),

physical science

81).

SCIENCE, TECHNOLOGY, AND

SOCIETY/COOPERATIVE LEARNING

We netic

forces trical

are surrounded by electromag-

These fields are invisible produced by anything that is elec-

fields.

— computers,

TVs, blenders, mi-

many we would not want to

crowaves, radios, hair dryers, and

devices that

Some people are concerned dangerous doses of electromagnetic radiation from electrical devices may cause cancer and other types of illnesses. Others say that their fears are unfounded because the electromagnetic radiation generated by electrical devices is weaker than the Earth's magnetic field and the live

without.

that

natural electrical activity of the

human

body.

Evidence from a number of studies suggests that workers in electrical industries

mal

develop cancer at higher than norprolonged exposure to

rates after

electromagnetic clusive, this

fields.

Although incon-

evidence has created some

USING THE TEXTBOOK

INTRODUCING CHAPTER 3

Have students observe

public concern because electromagnetic

—

found everywhere home, the shopping mall, and even outdoors. This concern has also led to protests over power-line construction and personal-infields are

jury lawsuits.

found to cause cancer, America will have to be rewired! Billions of dollars will have to be spent in redesigning electric power facilities, appliances, and office equipment. If

electromagnetic

fields are

Activity

Book

Begin teaching the chapter by using the Chapter 3 Discover)- Activity

from

the Activity Book. Using this activity, stu-

dents

will

works.

explore

how an

the picture

page P64 and read its caption. • Describe the picture. (Students should

DISCOVERY LEARNING

electric

motor

describe

touching

tracks.)

train

that

travels

without

Have students read the chapter

intro-

duction on page P65.

Describe a maglev train. (A train using and magnetism would move at speeds of about 500 km/hr without

•

electricity

touching

its

tracks.)

Cooperative learning: Using preassigned lab groups or randomly selected teams, have groups complete one of the

Electromagmtism

following assignments: •

Design a warning symbol for

pliances that can be used lo

home

ap-

make con-

sumers aware of the possible danger of electromagnetic

fields.

Using their collective imagination and knowledge of electromagnetism, have each group design a useful electromag-

•

Guide for Reading

Traveling by train can be convenient. But by today's standards, a long train ride can also be time-

you read the following sections you will be able to

After

3-1 Magnetism From Electricity Describe how a magnetic field IS created by an electric current,

Discuss ttie force exerted on an electric current by a magnetic field.

Apply tfie principles electromagnetism to devices such as the

electric motor.

3-2

Electricity

Explain

From Magnetism how electricity

can be produced from magnetism. Apply the principle

induction to generators

and transformers.

consuming. The speed of modern trains is limited by the problems associated with the movement of wheels on a track. Engineers all over the world, however, are now involved in the development of trains that "float" above the track. The trains are called maglev trains, which stands for magnetic levitation. Because a maglev train has no wheels, it appears to levitate. While a conventional train has a maximum speed of about 300 kilometers per hour, a maglev train is capable of attaining speeds of nearly 500 kilometers per hour. Although this may seem to be some sort of magic, it is actually the application of basic principles of electricity and magnetism. Maglev trains are supported and propelled by the interaction of magnets located on the train body and on the track. In this chapter, you will learn about the intricate and useful relationship between electricity and magnetism. And you will gain an understanding of how magnets can power a train floating above the ground.

netic device.

Each group should pro\ide

a diagram of their device and an expla-

nation of

its

function and

how

See Cooperative Learning er's Desk Reference.

works.

in the Teach-

JOURNAL ACTIVITY You may want tivity as

to use the Journal Ac-

the basis of a class discussion. As

students think about electricity, ask them to describe the electricity

used

in places like their

brought to and homes, school,

and the business areas of nity.

Remind students

details that tion.

their

commu-

to provide specific

support their written descrip-

Students should be iristructed lo

keep their Journal Activity

in their port-

folio.

Journal Activity

You and Your World Have you ever wondered where the electricity you use in your home comes from'' In your journal, descnbe the wires you see connected across poles to all the buildings in your area. you cannot see them, explain where they must be. Describe some of the factors you think would be involved in providing electricity to an entire city. If

A maglev

• List

tram travels at high speeds without even touching

one advantage of a maglev

(Answers gest that

will varv. it

its

tracks

train.

• List

Students might sug-

train.

much

faster than other

one disadvantage of a maglev (Answers

will vary.

Students might

suggest that there currently

no existing

•

would be used for such trains.) • Where do you think we could build "tracks" for maglev trains? (Accept log-

Why? (Smooth.

responses. Students might suggest above existing interstate highways.) • Do you think a maglev train would make noise? (Most students might suggest that it would not make noise.)

track that

trains.)

Will the maglev train pollute our atmosphere? (No.) • Do you think a maglev train would provide a smooth or a bumpy ride? only with •

What kind of

maglev

has physical contact

air.)

"fuel"

required by a

Point out that a inaglev would displace air quickly

because of

its

veiT fast speed.

—

would make noise perhaps some of a "swoosh" sound. It

sort

ical

train? (Electricity.)

Guide for Reading

3-1 Magnetism From

Focus on this question as you read. What IS the relationship between an electric current and a magnetic field?

Electrictty MULTICULTURAL OPPORTUNITY 3-1

make

What are all

You can prove

a large

ESL STRATEGY 3-1 of a

Figure 3-1 A current flowing through a wire creates a magnetic field. This can be seen by the

solenoid and an electromagnet, labeling

components and mag-

their respective

deflection of the compasses around the wire. Notice that the

To help explain the drawhave students complete the follow-

netic fields. ings,

A coiled wire, known as a solenoid, acts when current

through

field is in

the wire.

What determines

force?

needle parallel to it. Observe what happens to the compass needle when electricity is flowing through the wire and when it is not. What do you observe? This experiment is similar to one performed more than 150 years ago by the Danish physicist Hans Christian Oersted. His experiment led to an

important scientific discovery about the relationship electricity and magnetism, otherwise known as electromagnetisin.

between

a circle around

magnetic

direction of the

ing definitions:

by performing compass near a wire

carrying an electric current. The best place to hold the compass is just above or below the wire, with its

the different ways

illustrations

surprise you to learn also a source of

this to yourself

a simple experiment. Bring a

which motors are used?

Have students make

magnetism?

When

electrical motors.

the students return to class,

think of a source of magnetism, you

envision a bar magnet or a horseshoe magnet. After reading Chapter 2, you may even suggest the

Earth or the sun. But would

chart of all the applications of motors to their lives.

When you may

that a wire carrying current

Have your students do a survey around their homes of all the devices that they can find that use

Electricity

magnetic

the

lines of

flows

it.

A(n)

a solenoid

with a core of iron.

The

Intruder:

Have students

write the

definitions of each of the following terms

and

word

select the

that does not

group, stating why

in the

belong

should be

considered misplaced. armatine, commutator, galvanometer,

•

electric

motor Battery

TEACHING STRATEGY 3-1

FOCUS/MOTIVATION Illustrate Oersted's experiment by connecting copper wires and a switch to

the terminals of a low-voltage dry

cell,

You may

also

creating an

open

circuit.

choose to insert a low-voltage lamp ries) into

the circuit, providing additional

evidence to students that current ing

when

compass close to)

(in se-

the circuit

flow-

closed. Place a

above or below (and a wire of the circuit, orienting directly

the wire so that the compass needle parallel to •

Ask:

What do you

think will happen

expect that nothing

happen, either because they do not expect a magnetic force to be produced or because they expect that if such a force is produced, it will be directed parallel to the wire and thus will tend to keep the compass needle in

when

will

parallel alignment. Actually, closing

the circuit creates a magnetic force, and

thrown closing the circuit and a current begins to flow through

flected

the circuit? (Most students, before read-

to the direction of the wire.)

the switch

it.

ing about Oersted's experiment, might

the needle of the compass will be de-

and therefore no longer

parallel

Close and open the circuit several times.

Ask students

pass while the circuit

to observe the is

com-

being opened and

closed.

What did you observe? (Students should observe the compass needle de-

•

from and to its original position.) can you explain what has happened? (Current flowing through the wire created a magnetic field that was not present when current was not present in the circuit. This magnetic field in turn flecting

•

How

Oersted's Discovery

'IN

D OUT BY ZZZZZZZZZZZZZL

For many years. Oersted had believed that a connection between electricity and magnetism had to exist, but he could not find it experimentally. In 1820, however, he finally obtained his evidence. Oersted observed that when a compass is placed near an electric wire, the compass needle deflects, or moves, as soon as current flows through the wire.

When

the direction of the current

needle moves

in the

reversed, the

opposite direction.

When no

through the wire, the compass needle remains stationary. Since a compass needle is deflected only by a magnetic field. Oersted concluded that an electric current produces a magnetic field. An electric current flowing through a wire gives rise to a magnetic field whose direction depends on the direction of the current. The magnetic field lines produced by a current in a straight wire are in the shape of circles with the wire at their center. See Figure 3-1. electricity flows

^pc:>irsi<

Making an Electromagnet

and length

of thin

O The needle

in-

sulated wire.

Remove

the insulation

through the wire.

lated

mag-

when current

flows

When

there

deflected. (Relating cause

no curis

not

and eHcct)

O The direction of the current. (Relat-

at least

dellec tod by the

rent present, the compass needle

25 turns. Connect each uninsuof the wire to a post end

have

netic field generated

from the ends of the wire. 2. Wind the wire tightly around the nail so that you

ing concepts)

on the dry cell. 4. Collect some lightweight metal objects. Touch the nail to each one. What

Integration

O Social Studies

happens? Explain why the device you constructed behaves as it

Oersted then realized that

Answers

Obtain a low-voltage dry cell, nail,

does.

Electromagnets rent

ANNOTATION KEY

FIND OUT BY

a wire carrying cur-

twisted into loops, or coiled, the magnetic

DOING MAKING AN ELECTROMAGNET

produced by each loop add together. The result is a strong magnetic field in the center and at the two ends, which act like the poles of a magnet. A fields

Discovery Learning

long coil of wire with many loops is called a solenoid. Thus a solenoid acts as a magnet when a current passes through it. The north and the south poles change with the direction of the current.

The magnetic field of a solenoid can be strengthened by increasing the number of coils or the amount of current flowing through the wire. The greatest increase in the strength of the magnetic field, however, is produced by placing a piece of iron in the center of the solenoid. The magnetic or aligns the magfield of the solenoid magnetizes netic domains of the iron. The resulting magnetic field is the magnetic field of the wire plus the magnetic field of the iron. This can be hundreds or thousands of times greater than the strength of the field produced by the wire alone. A solenoid with a magnetic material such as iron inside it is called an electromagnet.

—

Skills:

Making observations, applying

concepts Figure 3-2 A

Materials: low-voltage dry

current

length of thin, insulated wire

coil of wire carrying a solenoid. As a wire is wound into a solenoid, trie magnetic field created by the current becomes strongest at the ends and constant in the center, like that of a bar magnet. is

Students build a simple electromagnet and then determine w-hich

in this activity

objects the electromagnet

pick up.

—

cell, nail,

The dry

cell

will

not

emits an electro-

magnetic force that attracts the metal objects.

ENRICHMENT Students might be interested to learn that

Oersted made

his discoveiT while

lecturing a physics class. Dining the lec-

he noticed a wire lying above a comand he observed that when current flowed through the wire, the compass needle was deflected about 90 degrees. When the direction of the current was reversed, the needle moved 90 degrees in ture,

deflected the compass needle so that

no longer was

this

fact.

Oersted's experiment,

parallel to the wire.)

As you explain use

the

chalk-

board to illustrate that magnetic-field lines of force flow around the curient-

CONTENT DEVELOPMENT Review the concept of electric current by reminding students that current

illustrating

measure of the flow rate of electrons. Have them recall that in a circuit, the flow of electrons is directional, flowing or moving away from a negative terminal

toward a positive terminal. Have a volunteer draw a diagram on the chalkboard

carrying wire, causing objects such as compass needles to align with these

the opposite direction.

When no electric-

flowed through the wire, the coinpass needle remained stationai^. For many

forces.

• • • •

pass,

ity

Integration

• • • •

Use the experimt'iit performed by the Danish physicist Oersted to integrate social studies concepts into your lesson.

Oct sted had believed that electricand magnetism were related, and he finalK found evidence of this relation-

years, ity

ship.

BACKGROUND INFORMATION MAGNETIC LINES OF FORCE The direction of the lines of force of a magnetic field produced by a current can be predicted by means of the "left-hand rule." If the thumb of the left hand points in the direction of the flow of electrons, the fingers curl in the direction of the magnetic field. This rule is more constated

ventionally

rule," in which the

hand points

the

The type of

"right-hand

thumb of

in the direction

Figure 3-3 An electromagnet is produced when a piece of soft

the right

iron

of flow of

the direction of the magnetic the direction of force

field,

placed

in the

center of a

solenoid. Large electromagnets

current, the extended fingers point in

can be used

to pick

up heavy

pieces of metal. What factors determine the strength of an electromagnet?

and

on a line perpen-

iron used in electromagnets acquires

magnetism when the electric current is turned on and off. This makes electromagnets strong, temporary magnets. Can you think of other ways in which this property of an electromagnet

and

loses

its

might be useful?

Magnetic Forces on

dicular to the plane of the palm.

You have

Electric

Currents

just learned that an electric current

exerts a force on a

magnet such

as a

compass. But

forces always occur in pairs. Does a magnetic field

exert a force on an electric current?

To answer

Figure 3-4 A magnetic exert a force current.

on a

field will

wire carrying

On what does

direction of the force

the

depend?

this question,

consider the following placed in the magnetic field between the poles of a horseshoe magnet. When a current is sent through the wire, the wire jumps up as shown in Figure 3-4. When the direction of the

experiment.

wire

3-1 (continued)

GUIDED PRACTICE Skills

Development

Skills:

Applying concepts, making

observations

You may

wish to construct a simple

electromagnet, wrapping a length of soft iron with

into a

can then be asked to read aloud and cuss what they have written.

mechanical energy.

in the circuit. Scatter iron filings

paper clips very near then close the

circuit.

several

or small

to the iron core

and

Open and close the

times.

Ask students to

what they have observed. Also ask them to propose an

write, without conferring,

useful type of energy called

Explain that a simple electric motor consists of a wire coil that

CONTENT DEVELOPMENT

to a low-voltage dry tell. Include a switch

circuit

dis-

many loops of insulated copper

wire and cormecting the ends of the wires

explanation for what has occurred. They

Point out that a tions,

number of

applica-

or practical devices, can be built

because a magnetic a wire that

field exerts a force

cari-ying current.

practical of these applications bly the electric motor. is

The most is

electric

permanent magnetic

rent

applied into the wire

netic field

produced by the

When

coil,

a cur-

the mag-

coil interacts

with the permanent magnetic

field.

The

interaction of these magnetic fields pro-

proba-

duces a force that

motor

tate the coil.

a device that converts electrical energy

placed into

field.

great

enough

Stress to students that this

to ro-

an expla-

is reversed, the wire is pulled down. So the answer is yes. A magnetic field exerts a force on a wire carrying current. Actually, this fact should not surprise you. After all, as you learned in Chapter 2, a magnetic field can exert a force on a charged par-

current

ticle.

electric current

ANNOTATION KEY Changing Direction

simply a collection of

Obtain a dry cell, a compass, and a length of thin insulated wire.

moving charges.

Applications of Electromagnetism

A number of practical devices use solenoids and electromagnets because they can move mechanical parts quickly

electric

motor

3. Connect each uninsulated end of the wire to a post on the dry cell. Put the center of the wire across the compass. Observe the needle. 4. Disconnect the wires and reconnect them to the opposite terminals without moving the wire over the compass. What happens? Repeat

a device

changes electric energy into mechanical energy is used to do work. (Mechanical energy is energy related to motion.) An electric motor contains an electromagnet that is free to rotate on a shaft and a that

that

permanent magnet that is held in a fixed position. The electromagnet that is free to rotate is called the armature. The armature rotates between the poles of the permanent magnet.

When

a current flows

through the

the ends of the electromagnet

coil

through the wire changes direcof the armature to switch. Once again the poles of the armature and the poles of the fixed magnet repel. So the armature continpoles, the current

tion. This causes the poles

ues to rotate. This process occurs over and over,

keeping the armature

in continuous rotation. current that switches direction every time the armature turns halfway is essential to the operation

of an electric motor. The easiest way to supply a changing current is to use AC, or alternating current, to run an electric motor. Recall that alternating current is constantly changing direction.

motor can be made

run on DC, or

direct current, by using a reversing switch

commutator.

A commutator

known

attached to the

procedure.

How IS the magnetic field produced by an electric cur-

magnet

whose poles depend on the direction of the current.) Because the poles of the armature are next to the same poles on the fixed magnet, they are repelled. The armature begins to rotate toward the opposite poles. But just before the armature reaches the

electric

this

of wire,

become magnetic

poles. (Recall that an electromagnet acts as a

the insulation

rection of the needle.

and accurately.

ELECTRIC MOTOR

Remove

from both ends of the wire. 2. Place the compass flat on the table. Observe the di-

rent related to the direction of

the currenf? 1' I

Figure 3-5 A motor can be found within

most

practical devices.

INTEGRATION MATHEMATICS The strength of an electromagnet can be determined using the formula

mmf = mmf is

where

(in gilbens). I is

and

the

1.25

X X

the magnetomotive force the current (in amperes),

number of turns

in the coil.

strength of an\ electromagnet de-

The

pends on the amount of current and the number of amperes. For example, an electromagnet with 50 turns and 2 amperes of current is equal in strength to an electromagnet with 1 turns and 1 am-

Figure 3-6 When alternating current flows thr~^

energy

is cxxtverted

mto mecfianicai energy.

movable electromagnet (or armaturel. .-^s the electromagnet turns, the commutator switches the direction of current so that the magnetic poles of the electromagnet reverse and the electromagnet spins. Electric

peres.

Have mula

interested students use the for-

current

to determine the strength of the

electromagnets used in

supplied to the commutator through conThe brushes do not move: thev

tacts called brushes.

this

chapter.

simplv touch the commutator as it spins. The mechanical energ\ of the spinning armature turns the shaft of the motor, enabling the motor to shaft can be connected to pullevs. fan

do work. The Figure 3-7 As

-5

.â&#x20AC;˘,

current flows

n a

~e:e- r-e Tagne! forces

3-1 (continued)

blades, wheels, or almost anv other device that uses

Sewing machines, power saws, subwav

mechanical energ\

vacuum

refrigerators,

trains, and most industrial machinerv are a few of the manv devices that would be practicallv impossible to design

cleaners,

without electric motors.

CONTENT DEVELOPMENT

GALVANOMETER Another instrument that depends on electromagnetism is a galvanometer. A galvanometer is an instrument used to detect small

Explain that most electric motors work the

same wav:

permanent magnetic

used to rotate a coU. which carries current. Point out. however, that the strength of a motor must change according to its application. Motors that are used in children's tovs. for example, usu-

currents.

field is

on a small permanent magnet and mav have coils that contain fewer allv relv

than 100 turns. Large industrial motors require strong magnetic fields and con-

powerful electromagnets that are powered bv electricir\". Thev also ma\' have coils that contain sequentlv use

ver\'

thousands of turns. Regardless of the size of a motor, the principle of small motors and large motors remains the same except for their different sources of magnetic fields and size of coil windings.

GUIDED PRACTICE Skills

Development

Skills:

Relating concepts, making

comparisons At

this

point have students complete

the in-text Chapter 3 Laboratorv' Inves-

It is

including the

the basic component of manv meters, ammeter and voltmeter vou read about

in Chapter 1 A galvanometer consists of a coil of wire connected to an electric circuit and a needle. The wire is suspended in the magnetic field of a permanent magnet. When current flows through the .

r'n

wire, the magnetic field exerts a force

causing

The

size

move

on the

wire,

the needle of the galvanometer.

of the current

will

force on the wire, and the

determine the amount of

amount

the needle will

â&#x20AC;&#x201D; move. Because the needle direction ter

when

will

the current

move

in the

opposite

FACTS AND FIGURES ELECTROMAGNETIC NORTH AND SOUTH

reversed, a galvanome-

can be used to measure the direction of current

as well as the

amount.

OTHER COMMON USES A simple type of electromagnet consists of a solenoid in which an iron rod

The north and south pole of an electromagnet can be determined by observing the needle of a compass when it is in the vicinity of each end of the t oil. The north pole of an electromagnet will repel the north pole of a compass needle, and the south pole of an electromagnet will attract the north pole of the compass needle, and vice versa.

only partially inserted. Many doorbells operate with this type of device. See Figure 3-8. When the doorbell is pushed, the circuit is closed and current flows through the solenoid. The current causes the solenoid to exert a magnetic force. The magnetic force pulls the iron into the solenoid until

strikes

a bell.

The same

basic principle

an automobile. circuit

When

used

in the starter

the ignition key

turned, a

closed, causing an iron rod to be pulled

into a solenoid located in the car's starter.

movement of

The

the iron rod connects the starter to

other parts of the engine and moves a gear that enables the engine to turn on. Another example of the application of this principle can be found in a washing machine. The valves that control the flow of water into the machine are opened and closed by the action of an iron rod moving into a solenoid.

Some other uses of electromagnets include telephones, telegraphs, and switches in devices such as tape recorders. Electromagnets also are important in heavy machinery that is used to move materials, such as moving scrap metal from one place to another.

Figure 3-8 Whenever you

ring a

you are using a solenoid. the button is pushed, current flows through the wire causing the solenoid to act as a doorbell,

When

3-1 Section Review 1.

How

What

magnetism related

magnet. Once magnetic, the solenoid attracts the bar of iron until the iron stril(es the bell, which

to electricity?

is an electromagnet? What are some uses of electromagnets? How is an electromagnet different from a

then rings.

permanent magnet? 4.

How does an electromagnet change electric energy to mechanical energy in an electric motor? Thinking

Critical 5.

How

continual

Making Comparisons

on a compass needle different from the effect of the Earth's magnetic field on a compass needle? is

attraction

and

repulsion

causes the electromagnet to spin. The mechanical energy of the spin is used to

the effect of an electric current

turn a shaft to do work.

The Earth's magnetic field will always cause a compass needle to point toward the same direction north. An electric current will cause a compass 5.

â&#x20AC;&#x201D;

needle to point in a direction that

de-

pendent on the direction of the current.

depends on the direction of the

current.

turning

magnetic properties entirely by it off; and its poles can be re-

versed.

The properties of a permanent

rection

electromagnet is produced when an electric current is passed through a coil of wire with a magnetic material such as iron inside it; depending on the amount of current and number of coil windings, electromagnets are usually very strong and are used to lift heavy pieces of metal. 3. An electromagnet can be made stronger or weaker; it can be made to 2.

lose

its

magnet are constant except

that

its

REINFORCEMENT/RETEACHING Monitor students' responses to the Section Review questions. If students ap-

pear to have

difficulty with

any of the

strength decreases naturally through

questions, review the appropriate mate-

time and use.

rial in

As alternating current

passed through the electromagnet, its north and south poles continuously reverse. The electromagnet is alternately attracted to and repelled by the exterior permanent magnet in the motor. This 4.

the section.

CLOSURE Review and Reinforcement Guide this point have students complete Section 3-1 in the Review and ReinforceAt

ment Guide.

)

3-2

Guide for Reading

Electricity

From

Focus on thfs question as you read. How does magnetism produce electricity?

Mapetism

can

MULTICULTURAL OPPORTUNITY 3-2 who live in mav not ha\e

Persons \\orld

From Magnetism Electricity

magnetism can be produced from electricitv. be produced from magnetism? Scien-

electricitv

tists

who

learned of Oersted's discover, asked

Faradav and the American scientist Joseph Henr\ independentlv provided the answer. It is interesting to note that historically Henr\' was the first to make the discovers But because Faradav published his

rural areas of the

access to electric

power were it not for h\droeIectric genHave vour students research the work of the Tennessee \'allev Authorirs% which brought power to persons Li\ing in the Appalachian Mountain area.

and investigated the subject work is better known.

results first

erators.

detail, his

In his attempt to produce an electric current a magnetic field. Faradav used an apparatus similar to the one shown in Figure 3-9. The coil of

from

Have students write a short paragraph comparing Oersted's investigation of magnetism and electricitv wth Joseph

wire on the

related discover).

Electromagnetic Induction

ESL STRATEGY 3-2

Henr\s

this

vers question. In 1831. the English scientist Michael

.\lso,

left

connected

to a batters

When

current flows through the wire, a magnetic field is produced. The strength of the magnetic field is increased bv the iron, as in an electromagnet. Faradav hoped that the steadv current would produce a magnetic field strong enough to create a current in the wire on the right. But no matter how strong the current he used. Faradav could not achieve his

have

them explain whv Michael Faradav's work on this subject is better known than Joseph Henrv's. Ask students to give the antomins (words that are opposite in meaning) of

and set-up tratuformer. Have them define all four terms.

generator

TEACHING STRATEGY 3-2

Figure 3-9 Using this setup, Faraaa-j found that whenever the current in the wire on the left changed, a current was induced in the wire on the right. The

FOCUS/MOTIVATION

changing c-e" z-zz^zed a changing ~iZ'i: : z z ,;hich

Before introducing students to the

principles associated \sith electromag-

turn

demonstrate Faraday's and Henr\'s experiments. Twist copper wire to produce a number of loops large enough to allow a bar magnet to move within the helix fomied bv the loops. .\sk: • 'VMiat will happen if a bar magnet is placed in the space within the loops of

gave 'se

z.-e"

netic induction,

copper wire? (.\nswers will var\ .\ctualh nothing will happen unless the magnet or wire is moving. Place the magnet within the loops and set the device down. .Attach the ends of

this

the copper-coil wires to the posts of a gal-

vanometer. Without allowing students to see the gab anomeier reading, ask: •

How much

current will be produced

in this scenario? (No current wUl be produced. .Mlow a volunteer to check the

72 « P

galvanometer reading, or displav

to the

•

Why do you

cept

class.)

What will happen if the magnet or the is moved? i.A current will result,

net

though most students will not expect this, especiallv if vou have made it a point to mention that there is no dr\ cell or

ible

the gal\ anometer results

be produced in the wire.

—

a current will

think this happens? (Acinferences. Students

logical

might infer that the motion of the mag-

wire

other power source in the circuit.) Move the magnet and then mo\e the copper-wire loops. Have students note

all

causing the wire to intersect in\ismagnetic lines of force, causing elec-

trons to flow in the wire.)

CONTENT DEVELOPMENT Introduce the topic of electromagreminding students

netic induction bv that

magnetism and

electricitv are re-

desired results.

The magnetic

a current in the second wire.

field did not produce However, something

rather strange caught Faraday's attention.

The

ANNOTATION KEY

needle of the galvanometer deflected whenever the current was turned on or off. Thus a current was produced in the wire on the right, but only when the current (and thus the magnetic field) was changing. Faraday concluded that although a steady mag-

Compass

Interference

Use a compass

to explore

O The direction of the moving magnet.

room. Take the compass to

(Interpreting illustrations;

room

different parts of the

produced no electric current, a changing magnetic field did. Such a current is called an induced current. The process by which a current is produced by a changing magnetic field is called

see which way the needle

electromagnetic induction. Faraday did manv other experiments into the nature of electromagnetic induction. In one, he tried moving a magnet near a closed loop of wire. What he found out was that when the magnet is held still, there is no current in the wire. But when the magnet is moved, a current is induced in the wire. The direction of the current depends on the direction of movement of the magnet. In another experiment he tried holding the magnet still while moving the wire

point

netic field

circuit. In this case, a

current

The one common element ments

points.

Can you

Integration

places

find

O Social Studies

where the compass does not point north? Why does it in

different directions?

What precautions must a when compass^

ship's navigator take

using a

3 COMPASS INTERFERENCE Discovery Learning

again induced. Faradav's experi-

in all

a changing magnetic field.

does not matter whether the magnetic field changes because the magnet moves, the circuit moves, or the current is

Answers

the magnetic properties of a

Making observations, cause and effect Skills:

Figure 3-10 A current in

a wire that

induced

exposed

changing magnetic field. Here the is moved past a stationary wire. On what does the direction of the current depend'^

magnet

Material:

relating

compass

This activity allows students to relate

magnetic influences to their environment. Students should discover that there are places within the classroom environinent at which the compass does not point true magnetic north, and ihey

should conclude that the proximity of metallic objects influences the compass. Students should infer that a ship's navigator using a magnetic compass should use the compass

on the ship

at places

that

are located as far away as possible from the influence of metallic objects.

lated.

Have students recall

that Oersted's

experiments showed that magnetism can be produced by an electric current that involves a changing electric field. Stress that the electric field

now

Because this connection or relationship between electricity and magnetism, ing

integration

•

• • •

Use the work of Michael Faraday and Joseph Henry to integrate social studies concepts into your science lesson.

changing.

exists

suggest that

• • • •

should not be too surpris-

an electric current could be pro-

duced from a changing tnagnetic field. Faraday's and Henry's experiments showed that such production does occur.

ENRICHMENT

common

in science.

Many

theoretical sci-

symmetries and, as a often hvpothesize their existence

entists expect these result,

before finding experimental evidence

support of them. Such examples help to bring out what are sometimes called aes-

Point out that symmetries, such as an

thetic considerations (beliefs in the sym-

being produced from a changing magnetic field (or conversion of mechanical energy into heat energy, suggesting the possible conversion of

metry, beauty, and underlying simplicity

electric current

and

unit\'

of nature), which

role in the creation of new

pla}' a major and important

hypotheses and theories.

heat energy into mechanical energy), are

FIND OUT BY

WRITING THE HISTORY OF

ELECTROMAGNETISM Completing

this activity will

help stu-

dents obtain background information

about many important

scientists

who

contributed to the discovery of electricity

and

its

many

Check stuand scientific

applications.

dents' reports for historical

moved

accuracy.

the

through a stationary

magnetic

Integration: Use

Writing

Figure 3-11 A current is also induced in a wire when the wire field.

Find Out by language

activity to integrate

arts skills into

your science lesson.

PTIND OUT BY

K^ WRITINOJ The History of Electromagnetism Several scientists were

re-

sponsible for establishing the

between electricand magnetism. Using materiand reference books relationship ity

in the library, write a report about the scientists listed below. Include information about their lives as

3-2 (continued)

als

REINFORCEMENT/RETEACHING Activity

Book

Students

well

who need

practice in under-

standing the relationship between electricity

and magnetism should complete

the chapter activity called Effect of a

Magnet on students

a Television. In this activity

will

observe the effect a magnet

causes on the image produced by a black-

and-white television. (Remind students that this activity

not to be performed

using a color television, as serious dam-

age to the television would

result.)

CONTENT DEVELOPMENT Have students

recall the principles

an electric motor

â&#x20AC;&#x201D; an

electric

motor

converts electrical energy into mechanical energy. Point

out that in terms of en-

ergy conversion, a generator posite of an electric

motor

â&#x20AC;&#x201D;

the op-

a generator

converts mechanical energy into electrical energy.

Explain that a generator coil

of wire placed

field.

field,

As the it

in a

a rotatable

constant magnetic

coil rotates in the

cuts

magnetic

lines

magnetic of force

their contributions to

a better understanding of electromagnetism.

Hans Christian Oersted Andre Ampere Michael Faraday Joseph Henry Nikola Tesia

Loop

ot wire

ANNOTATION KEY

Answers

O AC, or alternating tuMiiit. (Relating Figure 3-12 Inside a basic generator, a loop of wire is rotated through a stationary magnetic field. Because the wire

concepts)

continuously changes its direction of movement through the field, the induced current keeps reversing direction. What type of current is

O Language Arts Science: Hydroelectric PowO

produced?

Integration

Hhy.sical

See Ecology: Earth 's Natural Chapter 1.

er.

Resource.^,

no current is produced. Further rotation moves the loop to a position where magnetic lines of are cut, so

force are cut again. But this time the lines of force are cut from the opposite direction. This means that the induced current

the opposite direction.

HISTORICAL NOTE MICHAEL FARADAY

Because the direction of the electric current changes with each complete rotation of the wire, the current produced is AC, or alternating current. The large generators in power plants have many loops of wire rotating inside large electromagnets. The speed of the generators is controlled very carefully.

The current

also controlled so that

Michael Faraday (1791-1867)

con-

menters and theoreticians of all time. As

well as discovering the principle of elec-

20 times each second. Because two reversals make one complete cycle of alternating reverses direction

sidered to be one of the greatest experi-

tromagnetic induction, he was the prin-

of the classical field theory was later modified by James Clerk Maxwell and Albert Einstein.

cipal architect

that

Among his other accomplishments, Faraday discovered the principle of the electric

of one. Figure 3-13

In the operation of a generator, a source of

modern

mechanical energy water

â&#x20AC;&#x201D; spins a

turbine

â&#x20AC;&#x201D; such as

turbine.

encased

namo, stated the basic laws of electrolysis, and discovered that a magnetic field will

The

moves

large electromagnets in coils of insulated wire.

motor and built a simple model He also produced the first dy-

rotate the plane of polarization of

light.

As Water from

the electromagnets move, the coiled wire cuts through a magnetic field, inducing an electric current in the wire.

dam

concept of how generators produce electricity and to extend understanding of

generators, finding out about their uses

3-11. Ask students to construct a similar

and how

the relationship between motion, elec-

sary to generate electricity.

and magnetism. The video explores how the forces exerted by moving electric charges and magnets are related,

model, using a wire and a horseshoe magnet, and have them demonstiate that as the wire loop is tin-ned through a revo-

REINFORCEMENT/RETEACHING

the)'

provide the motion neces-

tricity,

how magnetic

fields are

concentrated to

produce powerful electromagnets, and how interacting magnetic fields produce rotary motion in electric motors. After viewing the video, have students perform research concerning portable electric

For some students, the production and nature of alternating current may be a difficult concept to understand. For the benefit of such students, analyze carefully the structures and processes involved in alternating-current production, (hawing their attention to Figure

anv given segment of it cuts through the lines of force first from one direction (say, up to down), then from lution,

the opposite direction (down to up). This

produces differing directions of electron flow, and thus the changing or alternation of current direction.

O ECOLOGY NOTE HYDROELECTRIC DAMS

second, measured in hertz.) Alternating current in the United States has a frequency of 60 hertz. In many other countries, the frequency of alternating

Every hydroelectric dam constructed has had an impact on the environment of

is 50 hertz. Generators can also be made to produce direct current. In fact, the system proposed and developed by Thomas Edison distributed direct-current electricity. However, the method of alternating current, developed by Edison's rival Nikola Tesla, eventually took its place. When only direct current is used, it has to be produced at high voltages, which are extremely dangerous to use in the home and office. Alternating current, however, can be adjusted to

current

was built. Have interested students choose an ecosystem and a hydroelectric dam, researching the dam's environmental impact on the lothe area in which

cal

and regional ecosystems. Findings

should be shared with the

current, the electricity generated has a frequency of 60 hertz. (Frequency is the number of cycles per

class.

safe voltage levels.

You may wonder about what type of power source is responsible for turning the loop of wire in a generator. In certain generators it can be as simple as a hand crank. But in large generators turbines provide the mechanical energy to turn the axles. Turbines are wheels that are turned by the force of moving wind, water, or steam. Most of the power used in the United States today is generated at steam

Figure 3-14 The force of moving water can be used to spin turbines in generators located in a power plant sucti as this one at Hoover Dam. What energy conversion takes place in a generator'^

3-2 (continued)

CONTENT DEVELOPMENT Point out that most large power plants

use sophisticated generators to create

Because of the enormous size used in these generators, very large magnetic fields are required. These fields are supplied by powerful electromagnets. electricity.

of the

coils

power plant generator, the

In a

rotat-

ing coils need energy to spin, and this en-

ergy

usually provided by a turbine.

turbine

—

something

fan with

• • • •

•

What

providing mechanical energy

Use the examples of alternating cur-

blades to spin or rotate, in turn causing

rent in other countries to integrate hertz

the mechanical energy.)

the coil to spin within the magnetic

concepts into your lesson.

•

falling water

If falling

water

a hydroelectric

field.

used to spin turbine

blades, the large generators

power

form part of

plant. Direct stu-

GUIDED PRACTICE Skills

Development

How do

you know

providing

that the water rep-

Relating concepts

Ask students to observe Figure 3-14 and examine the generators used in the power plant at Hoover Dam.

moving;

as a result,

has mechanical

energy.) •

Skill:

steam is used to turn the turbine blades, the steam is usually provided by the burning of fossil fuels or by the heat energy released by nuclear fission.

to this system? (The water

resents mechanical energy? (The water

dents' attention to Figure 3-14. If rising

Integration

or steam causes the

blades

What

mechanical energy?

(It is

the

energy of motion.) Have students observe Figure 3-15

and note the generator used on the cycle.

bi-

There the heat from the burning of fossil or from nuclear fission water to produce high-pressure steam that

plants.

fuels (coal, oil, natural gas) boils

turns the turbines. In

many modern

ANNOTATION KEY

generators, the

loop remains stationary, but the magnetic field rotates. The magnetic field is produced by a set of

Answers

electromagnets that rotate.

\| Mechanical energ) into electrical'eiv

vou own a bicycle that has a small generator attached to the back wheel to operate the lights, you

ergy

light stops shining. (Inferring)

O No. (Inferring)

the lights on, a it

(Relating facts)

J The

power for the generator. To turn knob on the generator is moved so touches the wheel. As you pedal the bike, you

are the source of that

provide the mechanical energy to turn the wheel. The wheel then turns the knob. The knob is attached to a shaft inside the generator. The shaft rotates a coil of wire through a magnetic field. What happens to the lights when you stop pedaling? A small electric generator, often called an

Integration

O Physical and

Light,

Science: Hertz. See Sound

Chapter

used to recharge the battery in a is running. Even smaller electric generators are used extensively in the conversion of information into electric signals. When you play a conventional record, for example, the grooves in the alternator,

car while the engine

record cause the needle to wiggle. The needle is connected to a tiny magnet mounted inside a coil. As the magnet wiggles, a current is induced that corresponds to the sounds in the record grooves. This signal drives loudspeakers, which themselves use magnetic forces to convert electric signals to sound. When you play a videotape or an audiotape, you are again taking advantage of induced currents. When information is taped onto a videotape or audiotape, it is in the form of an electric signal. The electric signal is fed to an electromagnet. The strength of the field of the electromagnet depends on the strength of the electric signal. The tape is somewhat magnetic. When it passes by the electromagnet, the magnetic field pulls on the magnetic domains of the tape. According to the electric signal, the domains are arranged in a particular way. When the recorded tape is played, a tiny current is induced due to the changing magnetic field passing the head of the tape player. The magnetic field through the tape head changes with the changing magnetic field of the tape, inducing a current that corresponds to

Figure 3-15 A light powered by a generator on a bicycle uses ttie mechanical energy of the spinning tire to

light

FACTS AND FIGURES MAXWELL'S EQUATIONS

Can the the bicycle is not

rotate the wire.

be on when

in use''

1864, James Clerk Maxwell de-

interrelationship between and magnetism with a set of four famous equations known as "Max-

scribed

the

electricity

well's equations."

Also point out that another type of generator, called an alternator, powers the electrical system of an automobile. Explain to students that the electrical needs of an automobile are great by using the chalkboard to list some systems in an automobile that require electricity to operate. After these systems have been listed, ask students to decide how long all these systems

_J â&#x20AC;˘

What

providing mechanical energy

CONTENT DEVELOPMENT

to this system? (The person pedaling the

moving ical

bicycle

providing the mechan-

energy.)

Remind students of

the piacticai ap-

plication of devices, such as generators, that create electricity using

induced cur-

you could look inside this generator, what would you expect to find? (Be-

rents. Point out that usually the electric-

cause the system is a simple generator, students should expect to find a coil that

home is manufactured somewhere

â&#x20AC;˘ If

rotates within a magnetic field.)

would work

a car did not

have a mechanical source of electricity and was powered instead by small batteries such as those used in portable radios, cameras, remote control units, and so forth. Point out that even a large battery is too small to power the electrical needs

of an automobile. When an automobile is working pioperly, the batter) is simply

the windmill will be connected to a gen-

used to start the car. After the automobile is running and the spinning alternator is producing electricity, the electrical needs of the vehicle are met by the alternot by the batteiy. That nator's output is why car batteries can last for several

erator.

years.

ity

used by students

school and

by the

use of generators in a large power plant. Even if a home is powered by an alternative energy system such as a windmill,

â&#x20AC;&#x201D;

the information

FIND OUT BY

DOING AN ELECTRIFYING EXPERIENCE Discovery Learning

Making observations, making comparisons Skills:

—

Materials: thin insulated wire,

OUT BY TTlND ^^^^77777777777:

galvanometer, strong and weak bar

^^K^2ZZZZZZZZZZZL -1-

magnets This activity helps to reinforce understanding of the process of electromagnetic induction. Although the degree

^K An

lated

minal of a galvanometer.

in-

Move

in-

the end of a bai

magnet halfway into the loops of the wire. Observe the gal vanometer needle. 5. Move the magnet fastei and slower. Observe the nee

are the variables that have the greatest in-

on the galvanometer.

Increase and decrease

number

the

of loops of the

Observe the needle.

wire.

Move

the

magnet

ther into the loops

GUIDED PRACTICE

far.

Skills Skill:

net

Development

Observe the needle. Use a strong bar magand a weak one. Observe

the needle.

What process have you demonstrated?

Making comparisons

Explain

Have students complete the Chapter 3 Laboratory Investigation in the Laboratory Manual called Studying Electromag-

all

your observa-

tions.

What variables

affect the

process the most^ The least?

netic Induction. In this investigation stu-

dents

explore

will

far-

and not as

Laboratory Manual

various

When

the Earth moves, a changing magnetic experienced and an electric current is induced. This electric current is converted into an electric signal that can be detected and measured. Why is a geophone a valuable scientific instrument? ^

move.

magnetic

transformer

a device that

increases or decreases the voltage of alternating cur-

A transformer operates on the principle that a current in one coil induces a current in another coil. A transformer consists of two coils of insulated wire wrapped around the same iron core. One coil is called the primary' coil and the other coil is called the secondary coil. When an alternating current rent.

passes through the primary coil, a magnetic field created.

die.

3-2 (continued)

when the Earth moves. The other part of the geophone is suspended by a spring so that it does not

TRANSFORMERS

Connect each uninsu end of the wire to a ter-

creasing the distance the magnet moves fluences

Coil the wire into at least

those associated with earthquakes. A geophone consists of a magnet and a coil of wire. Either the magnet or the wire is fixed to the Earth and thus moves

field

the insulation

7 loops.

of their observations and discover that increasing the number of coils, increas-

of the magnet, creasing the speed of the magnet, and

Experience

thin insulated wire.

conditions, students should explain each

strength

Remove

from both ends of a length of

and direction of galvanometer deflection the activity, depending on

the

Electrifying

will var)' in

ing

— audio, video, or computer data —

recorded on the tape. Magnetic disks used for information storage in computers work on the same principle. For this reason, placing a tape next to a strong magnet or a device consisting of an electromagnet can destroy the information on the tape. Devices that use electromagnetic induction have a wide variety of applications. In the field of geophysics, a device called a geophone, or seismometer, is C used to detect movements of the Earth especially

The magnetic

field varies as a result

of the

alternating current. Electromagnetic induction

causes a current to flow in the secondary coil. If the number of loops in the primary and the secondary coils is equal, the induced voltage of the secondary coil will be the same as that of the pri-

mary

coil.

However,

there are

more loops

in the

secondary coil than in the primary coil, the voltage of the secondary coil will be greater. Since this type of transformer increases the voltage, it is called a step-up transformer. In a step-down transformer, there are fewer loops in the secondary coil than there are in the primary coil. So the voltage of the secondary coil is less than that of the primary coil. Transformers plav an important role in the transmission of electricity. Power plants are often situated

conditions that create electricity.

CONTENT DEVELOPMENT Direct students' attention to Figure 316,

which

down

illustrates

step-up and step-

transformers. Detail the structure

and operation of each. Have students note the change in the number of loops or windings in each situation

—

a step-up

transformer has fewer windings on the primary coil than on the secondary coil,

and

a step-down transformer has fewer

windings on the secondaiy the primarv

coil.

coil

than on

GUIDED PRACTICE Skill:

• • • •

Making comparisons

You may struct

wish to have students con-

simple

step-up

Integration

• • • •

Use the explanation of the geophone

Development

Skills

integrate

seismology concepts into

your lesson.

and step-down

transformers that are similar to those pictured in Figure 3-16.

CONTENT DEVELOPMENT Because our

electricity

light

lives

and

are quite dependent

its

transmission, high-

some of these concepts

to students.

Point out that long-distance transmission wires pose much resistance to the flow of

Figure 3-16 A transformer increases or decreases the

STEP-UP TRANSFORMER

Low 10

volts

decreases voltage. Which the greater

number

coil

ANNOTATION KEY

has

Answers

of loops in

each type of transformer?

Primary

either

voltage of alternating current. A step-up transformer increases voltage. A step-down transformer

voltage

Accept logical answers. Students might suggest that it may help to predict major earthquakes. (Inferring!

coil

ÂŠ Step-up:

secondary; step-down; pri-

mary. (Relating STEP-OOWN TRANSFORMER

Low

High voltage

volts

facts)

ÂŠ The current and voltage

voltage

levels neces-

10 volts

sary for direct-current transmission are

ir?\n7>si

extremely high and more hazardous than

Soft

Alternating

iVfCsT^W

current

Jj\

â&#x20AC;&#x201D;

iron

.^1

core

ivV

those required for alternating-current transmission. (Applying concepts)

Integration Secondary

coil

O Earth

Science: Seismology. See Dy-

namic Earth, Chapter long distances from metropolitan areas. As electricity is transmitted over long distances, there is a loss of energ)'. At higher voltages and lovs-er currents, electricitv can be transmitted with less energy wasted. But if power is generated at lower voltages and also used at lower voltages, how can high-voltage trans-

BACKGROUND INFORMATION CHANGES IN VOLTAGE

mission be achieved? By stepping up the voltage before transmission (step-up transformer) and stepping it back down before distribution (step-down transformer), power can be conserved.

One ted in

Step-up transformers are used by power companies to transmit high-voltage electricity to homes and offices. They are also used in fluorescent lights and X-ray machines. In television sets, step-up transformers increase ordinary household voltage from 120 volts to 20,000 volts or more.

reason why electricity

rather than

transmit-

form

that

easy, using devices such as transform-

change the voltage for an AC curThere is no convenient way to do

ers, to

rent.

this for a

current. Because the rela-

tively low-voltage,

high-current electric-

produced by generators (whose moving parts would have to turn at impractical high speeds to produce high ity

Figure 3-17

Electric current is most etficiently transmitted at high voltages. However, it is produced and used at low voltages- For this reason, electric companies use transformers such as these to adjust the voltage of electric current. Why is alternating current more practical than direct current?

voltage) would, in transmission through wires, heat the wires

and

lose energy,

step-up transformers are used before the generated electricity is transmitted. This

high voltage, however, turns out to be too dangerous and inconvenient for

electricity,

generating heat and causing

energ)' to be lost.

To reduce

losses, cur-

must be kept as small as possible, and voltages must be increased significantly from the levels at which they were rents

generated. This

accomplished by the

use of step-up transformers at a power plant. The electricity traveling through the lines, however, is not able to be used until it travels through a step-down transformer near the place where it is u.sed.

household use, so a step-down transformer is used to reduce voltage before it enters household wiring or leaves the outdoor power lines.

ENRICHMENT Activity

Book

Students

Chapter 3

will

be challenged by the

activity in the Activity

Rook

called Transformers. In this activity stu-

dents

will

explore the relationship be-

tween the number of turns on a coil to voltage and will use this relationship to determine the primaiy or secondary voltage of various transformers.

â&#x20AC;&#x201D; HISTORICAL NOTE TRANSFORMERS

Low

voltage

Most engineers during the nineteenth century incorrectly believed that only electricity

was useful

Step-down transformer

in practical appli-

As a

cations of electricity.

result, early

generators included inconvenient commutators, which converted (what was in reality

usable)

into

DC. Even

though transformers (which could have been used in the transmission of AC current) were invented as early as 1838 by Joseph Henry, they were not used in

Step-up transformer

transmission until after the usefulness of

AC svstems was demonstrated in Paris in 1883. American patent rights for the tem, which was used in a

London

Figure 3-18 Low-voltage current produced at a power plant stepped-up before being sent over long wires. Near its destination, high-voltage current is stepped-down before it is

sys-

railway

distributed to

New

falo,

other buildings. Current

may be

further transformed in appliances that require specific voltages.

and in Italy in 1884, were purchased bv George Westinghouse, who set up the Westinghouse Electric Company. This, the first United States company to distribute alternating current, began transline

mitting

homes and

Step-down transformers reduce the voltage of from a power plant so it can be used in the home. Step-down transformers are also used in doorbells, model electric trains, small radios, tape players, and calculators. electricity

for lighting purposes in Buf-

York, in 1886.

3-2 Section Review

3-2 (continued)

CONTENT DEVELOPMENT

What

number

How

of loops in transformer coils and voltages was expressed by Michael Faraday and is

is electromagnetic induction? can an electric current be produced from a magnetic field? What is the purpose of a generator?

What

The

known

relationship between the

as Faraday's law:

Number

is the difference between a step-up and a step-down transformer?

Primary \'oltage

Connection

of Loops

in Primary' Coil

What

You and Your World

are

some common

objects that use either

electromagnetism or electromagnetic induction?

Secondare Voltage

Number

of Loops

Secondary Coil

formula on the chalkboard and have students determine various answers, given three of the four values in Write

this

Some of

many

the

additional applica-

tions of electromagnetism include elec-

tron microscopes, certain types of spectrometers, and electromagnetic pumps.

electromagnetic

health-care industry

be pumped.

pump

a mechanical

used

in the

tween electricity and magnetism, a pump for blood has been built that contains no

should be provided with the Chapter 3 Magnetism. activity called Electricity

Have interested students find out more about electromagnetic pinnps and other health-related applications of electricity and magnetism and

In this activity students will predict the

moving

parts.

share their findings with the

pump is pump because

INDEPENDENT PRACTICE

pump

consists of

moving

damage to blood Because of the relationship be-

impact of changes to a circuit and will graphically represent the strength of various electromagnets.

class.

ENRICHMENT

electromagnetic

parts that might cause cells.

when blood needs

favorable to a mechanical

formula.

ENRICHMENT

Have

Students

concept

who need

practice

of electromagnetic

interested students perform

li-

on the

brary research concerning the uses of step-up and step-down transformers. En-

strength

courage these students to prepare charts

Activity Bool<

IK1'KIE(ST[|ÂŠM O

Smaller Than Small

seeing a

High precision microscopes have enabled researchers lo peer into the world of the

very small object, do you use a magnifying glass to help you? A magnifying glass enlarges the image of the object

scale you may hardly recognize an ant's head, the cells responsible lor pneumonia, or a stylus traveling through the grooves of a record.

When you have

difficulty

you are looking at. If you want to see an even smaller object, you may need a microscope. A microscope is an instrument that makes small objects appear larger. The Dutch biologist Anton van Leeuwenhoek is given credit for developing the

first

ANNOTATION KEY

tiny

Integration

this

the properties of

light,

light

there

The Connections

then can objects requiring In

1920s, scientists realized that a

beam

feature gives stu-

use of electron microscopes. As

you discuss the implications of the

microscopes can

greater magnification be seen?

dents an opportunity lo relate the concepts of electricity and magnetism to the real-life

limit

:hapler 3.

CONNECTIONS

that an object is magnified. Light microscopes are very useful. But due to

the magnification

(

SMALLER THAN SMALL

way

How

Science: Electron Microscopes.

microscope. His invention

used glass lenses to focus light. The light microscope, which has descended from Van Leeuwenhoek's original device, still uses lenses in such a

achieve.

I'ife

See The Nature of Srietire,

cle,

the

why

ask students

arti-

the use of an elec-

tron microscope to view only nonliving specimens is a disadvantage. Also discuss ways that the electron microscope may be able to improve the quality of our lives. If you are teaching thematically, you may want to use the Connections feature

be used in much the same way as light was. But microscopes that use electron beams cannot use glass lenses. Instead, they use of electrons could

lenses consisting of magnetic fields that exert forces on the electrons to bring

to reinforce the

them into focus. The magnetic fields are produced by electromagnets. Electron microscopes have one major drawback. The specimens to be viewed under an electron microscope must be placed in a vacuum. This means that the specimens can no longer be alive. Despite this disadvan-

and and

themes of energy, scale and interactions,

structure, systems stability.

Integration: Use

the

Connections

feature to integrate the use of electron

microscopes into your lesson.

tage, electron microscopes are extremely useful for studying small organisms, parts of organisms, or the basic structure of matter. Electron micro-

scopes have opened up a new

world!

age and has fewer loops in the secondary coil than in the primary coil. 5.

Answers

suggest

Students might motors, telephones,

will vary.

electric

and generators.

current can be produced by mov-

or other illustrations that include cut-

away drawings of the transformers, with labels depicting their major features. All the information gathered and created

a current can

can then be presented to the

class.

ing a wire through a magnetic field, or be produced by passing a

REINFORCEMENT/RETEACHING

magnet

tion

and out of coils of wire,

cut-

ting the magnetic lines of force.

A generator converts mechanical energy into electrical energy. step-up transformer increases 4. A voltage and has more loops in the sec3.

INDEPENDENT PRACTICE Section Review 3-2

Electromagnetic induction is the process by which a current is produced by the motion of a conductor in a mag1.

netic field.

ondary coil than in the primary coil. A step-down transformer decreases volt-

Review students' responses to the SecReview questions. Releach any material that is still unclear, based on students' responses.

CLOSURE Review and Reinforcement Guide now complete Section 3-2 in the Review und Rfiiijoro'innil Students may

Gtiidi'.

Lahoratory Investigation laboratory Investigation

Electromagnetism

ELECTROMAGNETISM

Problem

BEFORE THE LAB 1.

Gather

What factors affect the strength of an magnet? What materials are attracted

materials at least one day

all

prior to the investigation.

You should

electro-

electromagnet?

gather enough to meet your class needs,

assuming 2.

Make

six

voltage, that the nails used are

of low dry

made of

iron or steel, and that the wire used

Among

nickel

cell

6 paper clips 5 iron nails, 10

in-

sulated bell wire. 3.

(per group)

Materials

students per group.

certain that the dry cell

2 meters of

"other

the

objects

dime

bell

long

wire

small piece of aluminum

penny

foil

copper sheet other objects to be tested

tested," include nonmetallic as well as metallic objects.

Connect the wire once again to the dry cell. Determine the number of paper clips the electromagnet can now hold. Record your results.

8. Carefully

PRE-LAB DISCUSSION Have students read the complete

Briefly review the basic principles of

magnetism

and

dure •

What

Oersted's

discovery.

five nails together and neatly wrap the wire around them. Do not allow the coils to overlap. Leave about 50 cm of wire at one end and about 1 00 cm at

Hold the

2. Attach the shorter

end

terminal of the dry

cell.

the purpose of this investiga-

3. Momentarily touch the

tion? (To determine what factors affect

CAUTION: Do

the electromagnet.)

each

all

the objects that

magnet 4.

will test in

test objects.

for

one

Observations

of the

not operate the electro-

Analysis and Conclusions

more than a few seconds

time.

When

the electromagnet

each Record

What do the materials attracted magnet have in common?

When you

on, test

of wire,

your results.

can 6.

msp.

SAFTEY TIPS Before beginning the investigation, caution students not to operate the electromagnet that is, not to have the cir-

increase the number of turns what effect does this have on

How does

removing the

nails affect the

strength of the electromagnet?

hold.

Wrap

to the

the strength of the electromagnet?

electromagnet is on, determine the number of paper clips

predictions.)

materials are attracted to the

electromagnet?

cell.

5. During the time the all

Determine whether the electromagnet attracts the penny, nickel, dime, and other

What 100-cm end

material for magnetic attraction.

this investigation, which of them do you predict will be attracted to the elec-

tromagnet? (Accept

of the wire to

wire to the other terminal of the dry

the strength of an electromagnet and to determine what materials are attracted to

•

from the

the other end.

the laboratory proce-

clear to students. is

nails

mine the number of paper clips the electromagnet can hold. Record your results.

-Ih

lab-

orator)' procedure.

Then make sure

remove three

windings. Connect the wire and deter-

Procedure

the 100-cm end of wire over the

On Your Own

How can you increase decrease the strength of an electromagnet without making any changes to the wire or to the nails? Devise an experi-

first

winding to make a second layer. You should use about 50 cm of wire. There should be approximately 50 cm of wire

remaining.

ment

to test your hypothesis.

—

closed with both wire ends confor nected to the dry-cell terminals more than a few seconds at a time.

cuit

—

TEACHING STRATEGY Make

sure students take enough time

during the investigation to ensure that each electrical connection is mechanically sound.

you think would happen if additional layers of coil windings were made on the nail? (The electromagnet would increase strength • If

investigation,

DISCOVERY STRATEGIES how

the investigation relates

to the chapter

by asking open questions

Discuss

similar to the following: •

Based on what you studied about the

properties of electromagnets, what do

—

inferring, predicting.)

a compass were present during the

how could we change its deflection when the

the direction of

electromagnet is turned on? (Change relating, the direction of the current

—

applying.) •

Does the battery

in this investigation

represent alternating current or direct

Study Guide

periment to observe whal will happen, because of potential safety hazards.

Summarizing Key Concepts Magnetism From

3-1 A

Electricity

A magnetic

that

field is created around a wire conducting electric current.

The relationship between electricity and magnetism is called electromagnetism. * A coiled wire, known as a solenoid, acts as a magnet when current flows through it. A solenoid with a core of iron acts as a strong magnet called an electromagnet.

A magnetic field exerts a force on a wire conducting current. An

electric motor converts electric energy mechanical energy that is used to do

into

GOING FURTHER: ENRICHMENT 3-2

Parti

From Magnetism

Electricity

form additional steps of

induced in a wire exposed to a changing magnetic field. current

One

of the

most important uses

tative nature,

into electric energy.

number of paper

clips

ber of turns of

coil

held versus

num-

wire and battery

Ask students

propose hypotheses

regarding variables untested in

this in-

vestigation, for example, the effect

the

a device consisting of an electromagnet attached to a needle that

can be used

number

Part 2

step-down transformer decreases voltage.

work.

A galvanometer

iht-

strength.

A transformer is a device that increases or decreases the voltage of alternating current. transformer increases voltage.

such as var)ing

to per-

quanti-

of turns of wire and making plots of the

of electro-

magnetic induction is in the operation of a generator, which converts mechanical energy

A step-up

may wish a more

Interested students

During electromagnetic induction, an electric

number of paper

high-voltage dry

cell

have them actually

measure the strength and

direction of small currents.

clips attracted if a

Do not hypotheses

were used.

test their

experimentally, as a higher-voltage dry cell

could present safety hazards. In-

stead,

encourage them

library re-

search to determine the answer.

Reviewing Key Terms Define each term

3-1

a complete sentence.

Magnetism From

Electricity

3-2

Electricity

electromagnetism solenoid

electromagnet electric motor galvanometer

current?

transformer

Why? (The

battery represents

direct current because electrons are con-

tinuously

moving

through the wire

in the

â&#x20AC;&#x201D;

same direction

relating, comparing.)

Answers used

will vary,

The strength of

the electromagnet

strength of the electromag[net

increased. 3.

The

decreased. 4.

OBSERVATIONS terials

From Magnetism

induced current electromagnetic induction generator

The

of the dry

size

cell

could be

in-

creased to increase the amount of cur-

depending on ma-

rent applied to the electromagnet. Ex-

periment

in the investigation.

designs

will

var)'.

Remind when

students, however, to use caution

ANALYSIS AND CONCLUSIONS 1.

The

ture

materials are magnetic in na-

â&#x20AC;&#x201D; probably made of iron or

designing an experiment with unknowns,

such as increasing the current of an ex-

steel.

Chapter Review

ALTERNATIVE ASSESSMENT

Multiple Choice

program includes a variety of testing components and methodologies. Aside from the Chapter Review questions, you may opt to use the Chapter Test or the Computer Test Bank Test in vour Text Book for assessment of important facts and con-

The

cepts.

Content Review

Prentice Hall Science

Choose 1.

science

process

completes each statement.

that best

magnetic

field of

number

of coils

amount

of current

increasing the increasing the

all

skills,

dependent, Performance-Based Tests can be distributed after students complete a chapter or

Faraday.

Henry.

Oersted.

Maxwell.

of iron in the

transformer.

generator.

electric motor.

galvanometer.

True or False

Multiple Choice

device with an electromagnet that continually rotates because of a changis

a(an)

doorbell.

solenoid.

galvanometer. electric motor.

The creation

of an electnc current by a changing magnetic field is known as a.

electromagnetic induction.

generation.

transformation.

stepping-up.

Concept Mapping '

a(an)

CONTENT REVIEW

ing electnc current

that an a magnetic

of these.

alternating current

complete the entire textbook.

who discovered

generator can be considered the opposite of a(an) c. electric motor. a. galvanometer. d. electromagnet. b. transformer. 3. A device that changes the voltage of

scientist

field is

amount

The

electric current creates

center only. d.

the\ are not content

the

the wire only.

rather than factual content recall. Since

after they

answer

wire only. b.

These Performance-Based Tests are detest

ttie

of the

a. increasing the

In addition, Performance-Based

electromagnet can be increased by

Tests are included in your Test Book.

signed

ttie letter

The strength

the statement

is true,

write

'true.

If it is

false,

change the underlined word or words

make

the statement true.

Complete the following concept map for Section 3- 1. Refer to pages P6-P7 to construct a concept map for the entire chapter.

2. c 3.

b d

solenoid with a piece of iron

center

called an electromagnet

the .

A commutator and in

True or False 1.

The relationship between electricity and magnetism is called electromagnetism

brushes are found motor running on direct

electric

current.

generator

used

to detect small cur-

rents.

5. In a generator, mechanical energy converted to electric energy.

galvanometer

Large generators at power plants often get their mechanical energy from

An induced

steam

magnetic

current

produced by a

electric field.

transformer changes the voltage of

an electnc current.

Concept Mapping Row 1 makes possible a Row 2: Electricity, Magnetism

ÂŁ

Row Row

Magnetism; Electromagnet Current

4: Electric

CONCEPT MASTERY

current.

Changing the poles of the magarmature to rotate con-

placed within a magnetic

field.

net, allowing the

rotates,

tinuously.

various directions, producing

posite direction.

in a

Yes.

electric

changes

motor

electric

a device that

energy into mechanical

an AC electric motor switches direction 120 times per second, changing the poles of the magnet, allowing the armature to rotate conenergv'.

The current

A galvanometer that detects small cur-

rents consists of a coil of vrire suspended

AC, or

al-

ternating current.

wire, causing the nee-

dle of the galvanometer to deflect. As the

coveries are essentially "opposite sides of

current changes direction, the direction

the

field

electric circuit.

and connected

When

on the

a current flows

through the wire, the magnetic erts a force

field ex-

tinuously. tric

able coil attached to a

coil

Oersted discovered that a magnetic is produced around a wire that is conducting an electric current. Faraday discovered that electricity can be induced from a magnetic field. The two dis-

magnetic

of the needle deflection also changes. 4. A tvpical generator consists of a rotat-

The commutator in a DC elecmotor switches the direction of thr

As the

cuts magnetic lines of force in

WTien a wire carrying electric current is placed in a magnetic field, the wire moves. When the direction of the current is reversed, the wire moves in the op1.

the form of

changing 8.

Co"eit ceates

power source and

field

same coin": They both show that magnetism and electricity are related in such a wav that one can be produced in the presence of the other.

â&#x20AC;&#x201D; 3.

Electromagnetic induction does not

involve creation of energy, but rather the

conversion of energy. Energy from the

Concept Mastery

changing magnetic held becomes energy

Discuss each of the following

Does a magnetic

field

a bnef paragraph.

exert a force on a

wire carrying electric current? Explain. 2. Describe fnow an electric motor operates. How does its operation differ

Describe the discoveries of Oersted and Faraday. How are these discoveries

a solenoid? An electromagnet? a step-up transformer? A stepdown transformer? Why are transformers important for the transmission of

What What

is IS

the

skills

you have developed in

Making comparisons

The current induced from

coil results

step-down

field.

the second

a changing magnetic

changing magnetic

field

cre-

ated only by a changing, or alternating,

production was direct

mutators to change

into alternating

The development of

current.

dif-

the trans-

former gradually changed production of electricity to alternating current, which was more convenient to generate and

Examand direct current use depending on the student.

transmit than direct current was. ples of alternating

first

will vary,

direction.

Short stories or poems will vary but should reflect dependence on electricity 7.

Applying concepts The process

electromagnetic induction might seem to disobey the law of conservation of energy, which says that energy cannot

be created. Explain why

both: b,

cinrent and used the assistance of com-

induces a current in one direction and then a current in the other 3.

6. Early electricity

ference between an electric motor and an electric generator in terms of energy conversion. 2. Making diagrams Use a diagram to show how the rotation of a wire loop in a

generator

c, d;

electric current.

chapter to answer each of the following.

this

Explain the

Step-up transformer:

transformer:

electricity?

Critical Thinking and Problem Solving

the electric field that results.

related? 6.

depending on the type of current used to run the motor? 3. Explain how a galvanometer works. 4. Describe how a generator operates.

Use

in 4.

our

daily lives.

KEEPING A PORTFOLIO

this is actually

not so.

Applying definitions Indicate whether each of the following characteristics descnbes (a) a step-up transformer, (b) a step-down transformer, (c) both a stepup and a step-down transformer.

Voltage

the secondary coil

greater. b.

Involves electromagnetic induction.

Voltage

Used

doorbells and model trains.

the primary coil

greater. 7.

Consists of two wrapped around opposite sides of an insulated coils

iron core.

More loops

the secondary

Making inferences transformer

will

Explain

Making comparisons Thomas Edison designed a power plant that produced direct current. Alternating current, however, has become standard for common use. Compare and contrast the two types of currents in terms of production and use. Using the writing process Several devices that work on the principle of electromagnetism and electromagnetic induction have been mentioned in this

originally

chapter.

coil.

Choose

three of these devices

and imagine what your

why a

life

would be

without them. Write a short story or a poem that describes your imaginings.

not operate on direct

current.

You might want to assign some of the Concept Mastery and Critical Thinking and Problem Solving questions as homework and have students include their responses to unassigned questions in their portfolio. Students should be encouraged to include both the question and the answer in their portfolio.

ISSUES

SCIENCE

following issue can be used as a springboard for discussion or given as a

The

writing assignment:

of the electricity consumed in is generated in nuclear power plants. In these plants, water is heated to steam, and (he steam is used to

Some

the United States

A solenoid is a coil of wire that acts as

a magnet

when current

electromagnet

applied.

step-up transformer

sisting

it.

a device con-

of two coils and an iron core that to increase the voltage of alter-

combine

nating current. is

A step-down transformer

a device consisting of two coils

iron core that

combine

and an

to decrease the

voltage of alternating current.

The

sistance of lengthy transmission

re-

wires

causes heat to be generated and energy to

lost

turn turbine blades, which in tinn rotate coils within generators, producing electricity.

mag-

a solenoid with a

netic material such as iron inside 7.

formers decrease the amount of energy lost through transmission.

â&#x20AC;&#x201D; step-up and step-down

trans-

After the steam into

the

leased

AND PROBLEM SOLVING

warm water is piped

An electric motor converts electric en-

ergy into mechanical energ)'. An electric generator converts mechanical energy

used,

re-

atmosphere, and the

CRITICAL THINKING

to cooling

ponds for

has cooled. Are these steam and hot-water waste products of a nuclear power plant contributing to global

reuse after

warming?

Why

or why not?

into electric energy. 2.

Diagrams

will vary,

depending on the

student. Diagrams should clearly indicate the various stages in the rotation

perpendicular to the lines of force, then then perpendicular, and so on.

parallel,

Chpter

Electronics and Computers

CHAPTER OVERVIEW can replace many large vacuum tubes with a

The development of electronic devices has led from their inception to their applications in computers. Electronics is the study of the release, behavior, and effects of electrons as it relates to use in helpful devices. Electronics began with the invention of the diode vacuum tube, v^hich serves as a one-way gate for electrons. Diode vacuum tubes are used as rectifiers, and triode vac-

grated

Radio and television are created by producing, transmitting, and amplifying audio and visual signals. Computers have become relatively pervasive in our society today. The main components of a computer are the CPU, main memory, input device, disk dhve, and output device. A computer needs programs, or operating instructions, to function. The binary number system is used by computers.

uum tubes

are used as amplifiers. began with the use of semiconductors to make solid-state diodes and transistors. Produced by doping, or loading, crystals like silicon with impurities, solid-state devices

Modern

electronics

Evolution: Electronics

4-1 ELECTRONIC DEVICES THEMATIC FOCUS The purpose of this section is to introduce students to various electronic devices. Electronics

lease, behavior,

the study of the re-

and

effects of electrons

relates to use in helpful devices.

PERFORMANCE OBJECTIVES 1.

began with the invention of the vacuum tube and its applications as diodes, amplifiers, and rectifiers. Modern electronics began with the invention of solid-state devices, or sandwiches of semiconductors that behave in the same manner as vacuum tubes, but ^vith more power, precision, and efficiencv. Transistors and integrated circuits have miniaturized the world of elec-

will

learn

that

tronics.

The themes unitv

and

that can be focused

are svstems and interactions,

this section

diversitv.

and evolution.

under-

a rapid evolution

constitute the foundation of electronics.

The development of new technolo-

and devices can be traced back to an understanding of electrons and how

gies

Unity

and plav

diversity: Diodes different

roles in

and an

and have

specific

applications in electronic theory. Transistors amplify currents and also have

Even though the\ are both different, both have been essential to the development of modern specific applications.

and

finallv

back into

sound.

The themes

that can be focused

and

stability.

*Energy: Electromagnetic waves can be used to carry information in the form of energ) from one place to another.

Compare

uum

'Stability:

Radio waves used

ccinmiunicaiion transistors to a triode vac-

all

in radio

travel at the

same

speeds.

tube.

PERFORMANCE OBJECTIVES SCIENCE TERMS 4-1

4-2

Describe the operation of a

phone

P88 vacuum tube p. P89 rectifier p. P90 diode p. P90 amplifier p. P90 triode p. P90 electronics p.

tele-

transmitter.

2. Identifv the energy conversions required to complete a telephone call. 3. Trace the energy conversions required to hear a radio broadcast.

SCIENCE TERMS 4-2

P91 semiconductor p. P91 doping p. P92 transistor p. P93 integrated circuit p. P93 chip p. P93

electromagnetic wave p. P95

4-3 TRANSMiniNG PICTURES THEMATIC FOCUS how

4-2 TRANSMiniNG SOUND

pictures are transmitted by the use of a

THEMATIC FOCUS

cathode-rav tube, or CRT. The operation of a CRT is examined, and students dis-

In this section students are introduced to telephone

and radio communication.

The telephone and is

a receiver,

consists of a transmitter

and the operation of both

explained.

The production,

transmission, and re-

cover that electrons are emitted bv a hot filament and directed at a screen that is

coated with one or more fluorescent materials. The position and intensity of the electron

beam

are changed so that as the

ception of radio signals are also ex-

fluorescent material in different areas of

plained. Particular emphasis

a screen are hit bv electrons, the areas

given to

the energ\ conversions that are required

86c s P

into electrical

This section explains to students

for currents

electronics.

electrical signals,

Compare two dififerent types of semi-

conductors.

electronic device. Diodes ser\e as one-

way paths

sound waves

electromagnetic waves, back into

fier.

the\ function.

transistors

signals,

4-1

Define electronics. Describe the function of an ampli-

solid-state device p.

'Systems and interactions: The release, behavior, and control of electrons

to convert

this section are energy'

electronics

Students

has

from an era of vacuum tubes and large machinerv to the development of integrated circuits and microcomputers. gone

single, tiny inte-

circuit.

CHAPTER PREVIEW emit different amounts of picture

light,

and a

formed.

color television picture tube has

three electron

beams aimed

screen

consisting of millions of vacuum tubes,

occupied an entire warehouse and was constantly breaking down. As the demand for computers increased, so did

SCIENCE TERMS 4-4 hardware

PI 04

central processing unit p.

main memory

materials that emit light of different col-

the technology.

input device p. P104

Various color pictures are formed as three materials emit different the amounts of the primary colors.

The computers of today consist of hardware and software. The hardware of a computer includes such things as the

disk drive p. P104 output device p. P105

ors.

The theme this section

can be focused on patterns of change. that

Patterns of change: Picture and sound broadcasts are converted into electric signals and then placed on electromagnetic waves (radio waves) that are sent out through the air. Receivers convert the signals back into their original

forms.

processing

central

unit

(CPU),

"brain" of the computer; main memory, or a place for information storage; an input device such as a typewriter key-

board or optical scanner; a disk drive

Describe the operation of a cathode-

ray tube.

monitors and printers. The role of software to computing

Discovery

and students learn that software is the program or set of instructions that the computer follows. A computer follows instructions by counting

SCIENCE TERMS 4-3

as base two.

many

Computer

electronic

circuits contain

switches,

switches can either be

on or

and off.

these

com-

puter stores information or follows structions based

The purpose of

in-

on the arrangement of

on/off switches.

4-4 COMPUTERS THEMATIC FOCUS

The theme this section

this section

P106

byte p. Pi 06

Explain why a color television picture tube requires three electron guns.

cathode-ray tube p. P99

bit p.

two numbers at a time. The system that uses only two numbers is the binary system of numbers, more commonly known

modem p. PI 06 software p. PI 06 binary system p. P106

read information such as programmed instructions; and output devices such as

also explained,

PERFORMANCE OBJECTIVES 4-3

P104

PI 04

that can be focused scale

and

structure.

to ex-

Learning

â&#x20AC;˘

TEACHER DEMONSTRATIONS MODELING A Glimpse

of the Past

Display two radios: one, a

modern

transistor radio, the other a table-top

model containing vacuum

tubes.

Making

unplugged, carefully remove the cabinet of each and allow stusure each radio

dents to visually inspect the contents. If the parts of a

vacuum tube

are visible,

point these out to students.

After assembling each radio, turn on both devices for the same amount of time and at the same volume. After several minutes, have students note the energy wasted in the forms of heat and light by

development of the computer. Students learn that a computer is an electronic device that performs calculations and processes and stores information. Modern computers have tremendous potential they guide

*Scale and structure: The future of computers is, in a sense, very large and

sometimes thousands of miles apart,

Your Blinker Is On To show that household electricity or current is AC, or alternating current, ob-

and diagnose disease. But computers were not always like the computers of today. Students learn that the first computer was developed in the late 1 800s and used punch cards to help count the census sta-

are being linked together electronically

tain a digital clock that has red light-emit-

plain to students the

â&#x20AC;&#x201D;

spaceships, forecast weather,

tistics

The

of 1890. first

large-scale

1946 by the United States Army. Costing millions of dollars and veloped

entire processing capabilities

very small chip. ers,

And groups

on one

of comput-

ting diodes

form supercomputers.

forming the numerals. With

the clock plugged

PERFORMANCE OBJECTIVES 4-4 1.

Trace the role of electronics in comthe parts of a computer and their

Describe the binary system and relationship to computers.

move

rapidly in

darkened room

works best and should allow the numbers to appear as dashed lines, showing that they are actually flashing on and off at 60 Hz.

function. 3.

in,

front of the students.

puters. 2. List

computer was de-

the older radio.

very small. Microprocessors can hold

its

86d

CHAPTER 4 Electronics

and

Computers INTEGRATING SCIENCE This physical science chapter pro\ides

vou with numerous opportunities

to in-

tegrate other areas of science, as well as

other disciplines, into your curriculum. Blue numbered annotations on the stu-

dent page and integration notes on the teacher wraparound pages alert you to areas of possible integration. In this chapter you can integrate physical

science and electrons

(p. 88),

physi-

and kinetic energ\ (p. 89), life science and EKG (p. 91), language arts (pp. 95, 106, 107), physical science and

cal science

electromagnetic waves studies (pp. 97,

(p.

95),

social

103), physical science

and fluorescence (p. 99), physical science and color (p. 100). mathematics (pp. 103, 1 06), earth science and ozone depletion (p. 103), and life science and the nenous system

(p.

105).

SCIENCE, TECHNOLOGY, AND

SOCIETY 'COOPERATIVE LEARNING Computers, perhaps more than any other devices, illustrate the relationship

among

science, technolog\', and society. By apphing the scientific principles of electronics, computer technology' was

developed. This technology, in turn, has

had an impact on every facet of our lives entertainment, communication,

â&#x20AC;&#x201D;

business, travel, medicine, banking, law

enforcement, and so forth. Using coinputers to age missing

chil-

dren can pro\ide ne\v leads for la^\ enforcement officials and encouragement to parents.

Computer age-progression

produce an accurate image of what a child would look like as he or she gets older. This process of aging children improves the chances of a child being spotted, identified, and returned to his or her parents. Computer robots that can replace workers in a \ariety of industries are specialists

can

INTRODUCING CHAPTER 4

Ha\e students observe and read the

DISCOVERY LEARNING Activity

Book

Begin teaching the chapter bv using

caption to the picture on page P86. \\Tjat do you obser\e in the picture? (Electronic components.) â&#x20AC;˘

the Chapter 4 Disco\er\ Activity from the Activity Book. Using this activity, stu-

dents

will

simulate the actions of a com-

puter and sort data by asking questions that require only a yes or no ans\ver.

USING THE TEXTBOOK

WTiat are

some of the names of the difcomponents shown in

ferent electronic

this picture? (.Accept logical answers. If

some students

are

able

recognize

printed circuit boards and semiconductors or ""chips."" ask them to volunteer

viewed as a way of reducing manufacturing costs so that oiM' goods can compete in an increasingh' competitive world mar-

and

Electronics

Computer-operated "money machines" enable us to conduct our banking business without ever going to a bank or interacting with a person. ketplace.

Computers

Increasingly, ccjmputers are allowing

us to perform functions that required

Guide for Reading After

you read the following you will be able to

sections,

4-1 Electronic Devices

the

The

Describe the structure

and applications

pact will

What

vacuum

tubes,

Relate semiconductors to the operation of

transistors

and integrated

circuits

4-2 Transmitting Sound Explain

how a

and

radio

a telephone work,

4-3 Transmitting Pictures Describe the operation of a cathode-ray tube and Its use in a television set,

UNIVAC

and the components modern computer.

of a

was not wrong, however.

When

happen

Cooperative learning: Using preassigned lab groups or randomly selected teams, have groups complete one of the

following assignments:

Using the information in this chapter and reference books, make an illustrated time line that traces the development of the computer. • Provide groups with the following sce•

all

nario:

the votes were counted, the computer's prediction turned out to be remarkably close to the actual

Discuss the development

are the political implications of an

automated society? What our environment in this "age of computers"?

will

did.

4-4 Computers

for our society?

increasingly

presidential contest that year pitted Republi-

can Dwight D. Eisenhower against Democrat Adlai E. Stevenson. Early in the evening, even before the voting polls had closed, newscaster Walter Cronkite announced to viewers than an "electronic brain" was going to predict the outcome of the election. The "electronic brain" was the huge UNIVAC I computer. What UNIVAC predicted, based on just 3 million votes, was a landslide victory for Eisenhower. An amazed nation sat by their television sets into the early hours of the morning, convinced that the "electronic brain" could not have predicted as

fulme hold

nology

the computer age. Define electronics,

What will What imapplication of computer techindustry have on our economy?

liinnan assistance in the past.

—

was 1952 and not many people were familiar with computers. In fact, there were some who had never heard the word. But on Election Day of that year, millions of Americans came face to face with It

The automobile

industry has de-

cided to completely automate the man-

ufacturing and production of cars and trucks by using computerized robots on

chapter you will learn about some of the devices that have brought the computer age and industry to where it is now. the electronic results. In this

the assembly

line.

Predict the economic,

and environmental consuch a decision were made

political, social,

Journal Activity

You and Your World shows do you watch? widespread use

Do you watch not, why not?

modern

sequences

television often?

Television

society. In your lournal,

contributions television has

made

you would improve the use

of television.

with

its

so,

what kinds

an electronic device

compare

Use

the positive

negative aspects. Explain

today.

Cooperative

Learning

the

Teacher's Desk Reference.

how

JOURNAL ACTIVITY view of some of the electronic components that computer technology possible.

A photographer's

make

You may want

to use the Journal Ac-

tivity as

the basis for a class discussion.

Discuss

how

television technology has

changed over the

years, using

your own

other things they know, as a niotivational

•

elections are held today, and

experiences to stimulate the discussion or using the experiences of a volunteer parent or grandparent. Also discuss with

activity for others.)

the predictions of winners and losers

students the kinds of changes that they

•

In what ways do you use electronic

components such your

life?

as these, or others, in

(Answers

might suggest

will vary.

Students

home computers,

systems, calculators,

and so

stereo

on.)

Point out that electronic components

have greatly inlluenced the lives of students, whether they realize it or not. Have students read the chapter introduction on page P87.

When

are

made

tions,

with respect to those elec-

do people

react the

same way

they did in 1952? (No.) Why not? (Accept reasonable explana-

•

tions.

Lead students

to infer that

com-

puter technologies have become a routine ])arl of our lives.) Ask student to list the computer-con-

would make in their lifestyles if television were not a\ailable to watch and whether it is fair to limit the amount of television someone could watch. Students should

be instructed

keep their Journal

.Activ-

ity in their |K)rtfolio.

trolled devices that they might encounter dining the course of an average day.

—

Guide for Reading

Dmces

4-1 Electronic

4-1 Electronic Devices

Focus on these questions as you read. What is electronics?

Multicultural opportunity 4-1

> How are

electrons related to electronic devices?

Have vour students conduct a survey of electrical appliances in their homes. -After a discussion of the \ariet\ of appliances available, have them think about

how

their lives

would be different

didn't have electricitv. things that thev

now

What

they

kinds of

take for granted

Were you awakened this morning by the buzz of an alarm clock? Did vou relv on a radio or a cassette plaver to get the dav started v»ith music? Did vour breakfast include food that was warmed in a microwave oven? Can vou get through the day vsithout using the telephone or watching television? You probablv cannot answer these questions vvithout realizing that electric devices have a profound effect on vour life. The branch of technologv that has developed electric devices is called electronics. Electronics is a branch of phvsics closelv related to the science of electricitv Electronics is the study of .

the release, behavior, and control of electrons as relates to use in helpful devices, .AJthough electronic technologv' is relatively nev» it can be traced back onlv 1 00 years or so

would ihev not be able to do?

ESL STRATEGY 4-1

—

Have students circle the word that is not part of a vacuum tube: emitter, col-

electronics has rapidlv

Figure 4-1

changed people's

lives.

For

example, telephones, radio, television, and compact disc plavers have revolutionized cominiuiicadon and

lector, filament, protector. .\sk students

to pro\ide definitions for the remaining

-fl

terms and explain how a vacuum tube controls the flow of electrons it creates when current passes through it. Pair ESL students with English-speaking partners to prepare to answer these

questions orally: 1

WTiat are the

t^*'0

main groups of elec-

tron devices? 2.

WTiat advantage does one group have

o\ er the other? 3.

What does a semiconductor do? are the most commonly used

4. \\"hich

semiconductors?

"SiUcon

\'allev"' is

name used

to de-

scribe a sjjecific region in California.

sign a

group project

.•\s-

to research this

name. Have students report their

find-

ings to the class.

as agriculture, medicine,

TEACHING STRATEGY 4-1

FOCUS MOTIVATION

and

cannot escape the influence of

modem

name

world. Chal-

list

25 careers

other students. discuss

to the chalkboard

that are suggested by

When the list is complete,

how electronic technologv has in-

a career that has

fluenced each of the careers.

not been influenced bv improvements in electronic technologv (Thev shotild have

CONTENT DEVELOPMENT

lenge students to

difficultv

naming such a

career.) Point

out that understanding electronics

now

essential for professions as diverse

ergy and information .\C carries get transferred from place to place. In this

Have a volunteer go

electronics in the

and auto me-

chanics.

For those students unsure of hovv .\C (or alternating current) manages to do anvihing, discuss

and review how the en-

transfer the electrons themselves

do not

have to move verv far to pass energv' and information to other electrons. This situation has a loose analogv to the motion of the particles of a mecUum disturbed by a longitudinal wave. (Have students recall

the motion of panicles in these

waves.) .\lso fvoint out that

we do not

purchase batteries to get electrons and that v\-e do not buv electrons from the

entertainment. Computers and robots have increased speed in business and industry. Electronic devices help physicians diagnose diseases and save lives. All forms of travel depend on electronic devices.

ANNOTATION KEY

Perhaps you wonder how electronics differs from the study of electricity. After all, both deal with electrons and electric currents. The study of electricity concentrates on the use of electric currents to power a wide range of devices, such as lamps, heaters, welding arcs, and other electrical appliances. In such devices, the kinetic energ>' of

moving electrons

converted into heat and

energy. Electronics

light

treats electric currents as a

means of carrying

Answers

O Answers

pictures,

air

basically a

vacuum, thus the name. (Relating concepts)

infor-

mation. Currents that carry information are called electric signals. Carefully controlled, electrons can be made to carry messages, magnify weak signals,

draw

depending on the

O A sealed tube without {

will vary,

student. (Applying concepts)

Integration

O Physical Science: Electrons. See Mai-

and even do arithmetic.

ler:

Building Block oflhe Universe, Chapter

Vacuum Tubes The

O Physical Science: Kinetic Energy. See

ability to carefully control electrons

Motion, Forces, and Energy. Chapter

began

with the invention of the vacuum tube. The American inventor Thomas Edison (also known as the inventor of the phonograph) invented the first

vacuum tube but unfortunately did not realize its importance. A simple vacuum tube consists of a filament, or wire,

and

called electrodes.

When

filament,

much

FIND

two metal parts through the does through a light bulb, the at least

filament gives off heat. This heat

warms

out by Findy/////////77\

the elec-

One

of the electrodes gives off electrons when heated. For this reason, it is called an emitter. This electrode is negatively charged. The other electrode, which does not give off electrons, is positively charged. This electrode is called the collector because electrons flow to it from the negatively charged emitter. As a result, a current of electrons flows through the vacuum tube. Thus a vacuum tube is a one-way valve, or gate, for a flow of electrons. Electrons are permitted to move in only one direction through the vacuum tube. Both the electrodes and the filament are contained in a sealed glass tube from which almost all the air has been removed. How does this fact explain the name given to this tube? A vacuum tube may have several other parts between the electrodes. It trodes.

"^^ > f 1 1

Electronics

Your

OUTBY

WRITING ELECTRONICS IN YOUR HOME

a current flows

In this activity students reinforce the

terms they have studied

in this section

discovering electronic devices in their

Home

homes

Over the course of a day, observe and make a list of all the electronic appliances you use In your home. Which of these appliances contain transistors? Cathode-ray tubes? Vacuum tubes? Integrated circuits?

that

Most

cuits.

employ various tubes and lists

cir-

contain television

will

computand the like. Students may not be aware of many other devices in their sets, radios, stereos, calculators,

ers,

homes

that also use basic electronic con-

cepts in their design or construction.

Do some appliances contain multiple types of devires'^

so,

which ones'^ "I-

CONTENT DEVELOPMENT Point out that the invention of the vac-

uum

tube was,

that

sparked

Though local

power company when we use

elec-

tricity.

•

Integration

• • • •

Use the introduction and definition of the term electronics to integrate concepts of electrons into your lesson.

grate concepts of kinetic energy into V'our lesson.

to students that elec-

tronic devices have already been a part of

this chapter may stand alone terms of other chapters, it employs many terms and concepts that are men-

one

tioned in other areas of science, including

chemistry,

light.

electricity,

waves,

and

View each piece of technology as an

application of science that students

Use the example of how electronics differs from the study of electricity to inte-

may seem

the catalyst

technologies.

REINFORCEMENT/RETEACHING Although

•

in essence,

electronic

already

know by

may

calling attention to any

and thus of the lives of everyremind them that the creation

their lives, else,

of electronic technologies (and electricity) is

a relatively recent innovation.

You

might wish to ask students if they have ever seen a picture of a farm windmill or have actualh seen one have,

|)()iTit

in person. If they

out that windmills are a tes-

words and concepts developed previ-

tament lo the

ously.

alwa\s .i\ailable and

fact that electricity is

was not

only a recent

in-

vention and creation of science.

mav also have charged plates or magnets that can bend the stream of electrons. Because vacuum tubes produce a one-^vav current, thev have manv applications in electronics. Two important applications of vacuum tubes are as rectifiers and as amplifiers. Vacuum tubes also

BACKGROUND INFORMATION FORCES

INVISIBLE

There are two primary- t\pes of

Negative

in\isi-

electrode

acted as switches in earlv electronic computers.

ble forces in electronics: electric fields

and magnetic energv field

and

fields.

Electric potential

Rectifiers

stored as voltage in an electric

magnetic

as current in a

Regardless of how the energ\ the potential energ%' cuit in the

field.

stored,

released into a

rectifier

vacuum tube

that converts

The current

alternating current to direct current.

supplied to vour

cir-

home

alternating current. Certain

household appliances, however, cannot operate on alternating current. Thev need direct current. So these appliances have rectifiers built into their circuits. .\s the alternating current passes through the rectifier, it is changed into direct current. The t\pe of vacuum tube used most often as a rectifier is called a diode. .A. diode contains two elec-

fonn of electric current.

trodes.

When

alternating current

sent to a diode,

the emitter will be charged by the current. However, it will emit a current onlv when it has a negative

when the current is flowing in one direction. Thus the current leaving charge. .And this happens only the diode

direct current.

Rectifiers are used in de\ices such as televisions, stereos, and computers. Converters that allow you to plug batter\-operated de\"ices into household electric outlets also contain rectifiers.

Amplifiers Figure 4-2 A diode is the simplest type of vacuum tube. diode, electrons flow in

one

vacuum tubes for in-

spection. Allo\s' students to use a magni-

f)ing glass to \ie\v the electrodes of var-

ious tubes. If the tubes are

no longer

vou might choose to carefully break the surrounding glass of a tube and functional,

then allow students to closelv inspvect

components of a vacuum tube are fragile and can be easily damaged. (\'acuum tubes ma\ be available at a local tele\ ision repair

no or minimal

Skill:

shop

circuit

and idendfv

manv

pairs of the

â&#x20AC;˘

out

the\ are

that

working properlv.

WTiat causes the glow in a

tube.

Have

stu-

tube sults

been

hit

by electrons. The

color, orange,

caused by the

CONTENT DEVELOPMENT vacuum tubes glow

vacuum

tube? (Accept logical responses. Point out that the area enclosed bv a vacuum

the chalkboard, diagram a circuit

after thev have

dominant

hot filament emitting the electrons.)

ENRICHMENT when

Applying concepts

vacuum

output current produces a stronger signal. The strengthening of a weak signal is called amplification. Amplification is perhaps the most important function of an electric derice. .Another tvpe of vacuum tube, a triode, is often used for amplification. .A triode consists of a filament, a plate, and a wire screen, or grid. The

circuit as they can.

Point

Development

that includes a

(Remem-

a current that carries infor-

mation.) In an amplifier, a small input current converted to a large output current. The large

dents indicate the electron flow in the

cost.)

GUIDED PRACTICE Skills

the tubes carefullv, as the

an electronic derice that

its

broken for inspection, make sure the tube does not contain remnants of sharp glass and caution students to handle and distribute contents. If the glass of a tube

ttte

CONTENT DEVELOPMENT

amplifier

increases the strength of an electric signal. ber, an electric signal

negative electrode to the positive electrode Diodes are used as rectifiers in many electronic devices. Why? direction,

4-1 (continued)

Distribute several

from

An In

not a pure \acuum. The glow re-

from some gas atoms deexciting

Students who are familiar with the law concerning the conservation of energy might be confused with the idea expressed in

this section that a small signal

produces a larger dents,

make

signal.

For these

stu-

the distinction that the small

signal fed to an amplifier does not pro-

a addition of the grid allows the tlovv ol electrons between the negatively charged emitter and the positively charged collector to he better controlled.

The invention of

ANNOTATION KEY

the triodc was responsible for the

rapid growth of the radio and television industry. Amplifiers strengthen both sound and picture signals. The signals that carry sound and picture infor-

Answers

® Rectifiers

mation are often very weak as a result of traveling long distances through the air. By the time an antenna picks up the signals, they are loo weak to produce an accurate copy of the original sound. Radio and television amplifiers strengthen the incoming signals. Kully amplified signals can be millions or billions of times stronger than the signal picked

lent, or

convert

alternating

lo direct current, or

cur-

—

two-way flow to a one-way How. (Applying definitions)

3 ^ »

Integration

©Life

up by the antenna.

Without amplifiers, devices such

AC,

Science:

EKG. See Human Biology

and Health, Chapter

as hearing aids,

public-address systems, tape recorders, and radar would not operate. Amplifiers are also essential to the operation of medical instruments used to diagnose certain injuries and diseases. Human heart

waves and brain waves can be studied by doctors because the weak electric signals given off by these organs are amplified.

Solid-State Devices Electron devices can be divided into two main groups according to their physical structure. The vacuum tubes you have just read about make up one group. The other group consists of solid-state devices. Solid-state physics involves the study of the structure of solid materials. From the 1920s until the 1950s,

dominated the world of

vacuum tubes •

electronics. In the 1950s,

however, solid-state devices took over. The reason for this is obvious: Solid-state devices have several advantages over vacuum tubes. They are much smaller and lighter than vacuum tubes and give off much less heal. They also use far less electric power, are more dependable, and last longer. And in most cases, they are less expensive.

In solid-state devices, an electric signal fiows

stethoscope

made by

noises

used to

listen to the

stethoscope

a heart.

usually does not contain any electronic Figure 4-3 A tnode vacuum tube consists of a filament, a plate, and a grid. The addition of a grid allows the electron flow to be amplified, or strengthened. Triodes are used in microphones to amplify sound

components of any kind.

Is the stetho-

scope an amplifier? Why or why not? (Encourage debate and accept all logical responses.)

CONTENT DEVELOPMENT

through certain solid materials instead of through vacuum. The use of solid-state devices was made possible by the discovery of semiconductors. Semiconductors are solid materials that are able a

Point out that an amplifier

an elec-

tronic device that increases the strength

of electric (sound or picture) signals. The text mentions that without amplifiers

and amplification, devices such

as hear-

ing aids, public-address systems, tape recorders, radar systems, and medical in-

duce a large output

signal. Rather,

trols a large curieni,

con-

prompting the large

current lo take the shape of the stnall input signal. If students are having ditticulty

understanding

analog)' might be

this

drawn

concept,

to a sporting

event: At a sporting event, the

crowd

capable of creating large noises. The cheerleaders cannot

make

much

sounds of the crowd with their own weaker signals.

erate without the use of amplifiers.

GUIDED PRACTICE Skills

Development

Most students may be familiar with a stethoscope, which is worn by many doctors. If

crowd

leaders

make create

certain noises.

The

cheer-

and control the loud

they are not, describe a stetho-

scope to them or obtain one,

and allow students

to use

You

might issue this challenge in the form of a class brainstorming activity, allowing students several minutes to think of as

Skill: Inferring

noise

crowd, but they can signal the

as the

struments would not operate. Challenge students to create lists containing the names of other devices thai could not op-

possible,

many •

•

devices as possible.

•

Integration

•

Use the discussion of the use of amplification by the health-care industry to in-

it.

tegrate

KKG

concepts into your lesson.

to conduct electric currents better than insulators do but not as well as true conductors do.

FACT AND FIGURES SEMICONDUCTOR CRYSTALS

Silicon and germanium are the most commonly used semiconductors. These elements have structures that are determined by the fact that their atoms have four outermost electrons. Silicon and germanium acquire their usefulness in electronics when an impurity (atoms of another element) is added to their structure. Adding impurities to semiconductors increases their conductivity. The process of adding impurities is called doping. There are two types of semiconductors. These types are based on the impurity used to dope the semiconductor. If the impurity is a material whose atoms have 5 outermost electrons (such as arsenic),

A semiconductor, by its very nature, conducts electricity. But certain properties of a semiconductor depend on its temperature. At a temperature of absozero, most pure semiconductors would become insulators. lute

the extra electrons will not

and cumbersome.

Tliey also

oft a considerable

amount of

gave heat.

Devices that use semiconductors can be made extremely small. In addition, they are

dependable, energy,

and

last longer,

fit

into the structure of

Thus the doping contributes extra electrons that are somewhat free to move and that can form a current. This type of semiconductor is called an n-type, meaning negative-type. Silicon doped with arsenic is an n-type semiconductor. If a semiconductor is doped with a material whose atoms have three outermost electrons (such as gallium), there will be empty holes in the semiconthe semiconductor.

Figure 4-4 Devices that used vacuum tubes were large, lieavy,

use less

give off less heat.

ductor's crystal structure. These holes can also be

used to form a current. Semiconductors doped with atoms that have fewer electrons, which is equivalent

Figure 4-5 Doping a semiconductor material increases its conductivity. In an n-type. the impurity

adds

to saying extra protons, are called p-type semicon-

ductors. Silicon

extra electrons that

a p-type, doping creates holes that are missing

can

flow. In

What impurity is used to make an nlype semiconductor? A electrons.

p-type''

o-o-a â&#x20AC;˘-

4-1 (continued)

CONTENT DEVELOPMENT Explain that a crystal diode of a very small size can be constructed

from

a tiny

piece of silicon and a thin platinum wire.

The

silicon acts as a cathode,

and the

platinum acts as a collecting plate. Because the electrons travel directly from the silicon to the platinum, the cathode does not have to be heated, nor does the device require a vacuum. Semiconductor diodes are even smaller replacing the platinum wire with another tiny crystal. These principles require that a crystal's

â&#x20AC;&#x201D;

be enhanced or diminished by doping it with impurities; in other words, loading it with extra protons or electrons. affinity for electrons

doped with gallium

a p-type

semiconductor. What do you think p-type means? The arrangement of impurities on one type of semiconductor allows current to flow in only one

(

Thus

of semiconductor acts as a diode. A different arrangement of impurities produces another solid-state device, which you are now going to read about. direction.

this type

ANNOTATION KEY

Answers Transistors

O Positive-type. (Inferi ing) O Arsenic; gallium. (Applying (Applying O Amplifies an electric

sandwich of three layers of semiconductors. A transistor is often used to amplify an electric current or signal. It is the arrangement of the impurities in the semiconductor that enables it to act as an amplifier. A weak signal, corresponding to a weak current, enters the transistor and is amplified so that a strong signal is produced. Transistors come in a variety of shapes and sizes. Perhaps you are familiar with some of them. Transistors are commonly used in radios, televisions, stereos, computers, and calculators. The small size, light weight, and durability of transistors have helped in the development of communication satellites. transistor

facts)

signal.

definitions)

Integration

O Earth Science:

Satellites.

ing the Universe, Chapter

See Explor-

Figure 4-6 Transistors come in a variety of shapes and sizes. What does a transistor do?

Integrated Circuits

When you studied electric circuits in Chapter 1 you learned that a circuit can consist of many parts connected by wires. Complicated circuits organized in this fashion, however, become very large. In the 1960s, scientists found a way to place an entire circuit on a tiny board, thereby eliminating the need for separate components. This new type of circuit is known as an integrated circuit. An integrated circuit combines many diodes and transistors on a thin slice of silicon crystal. This razor-thin piece of silicon is often called a chip. A single integrated circuit, or chip, may often contain thousands of diodes and transistors in a variety of complex combinations.

To it

turn a silicon chip into an integrated circuit, in some places with arsenic and in

amplifier can be.

must be doped

Have

interested stu-

other places with gallium. Certain areas of the chip become diodes, while other areas become transistors.

dents research the electronic technolo-

Connections between these diodes and transistors are then made by painting thin "wires" on the chip. Wires are attached to the integrated circuit so it can be connected to other devices.

such as the Voyager program. Specifically, have them discover the strength of the signal reaching Earth, billions of

gies associated with space exploration

miles away,

from the Voyager

spacecraft.

Giiinpn poAPTirp Skills Skill:

Development

Making observations

The components discussed collector.

The base

acts as a barrier be-

tween the two currents. The current to the collector is controlled by the current to the emitter because there is voltage created between the edges of the base.

• • • •

Integration

•

• • •

Use the role of transistors in the development of communication devices to integrate concepts of satellites into your

signal by allowing the

weak

signal to

control a large current. For example, the large current in a portable radio plied by the battery.

comes from the radio

The weak station.

sup-

signal

realize just

how small

these

com-

ponents are unless they could be compared against other objects of known Display

several

transistors

and

ENRICHMENT

other electronic components, such as coinputer boards, to the class. Allow stu-

Students have studied the connection between transistors and amplification

dents sufficient time to handle and examine the objects, giving them the op-

Point out that the transistor amplifies a

weak

may not

sizes.

lesson.

in this sec-

tion of the text are veiy small. Students

devices.

just

They may not

how weak

realize,

however,

the signal amplified by an

portuiiiiN to realize the actual size of the

different

components explained

in this

section.

ANNOTATION KEY integration

Language Arts Electromagnetic Science: See Sound and Light, Chapter 3.

ij Physical \S'a\es.

FIND OUT BY

WRITING TELEPHONE AND RADIO HISTORY This acti\itv

\%iU

help students better

understand some historical developments of the radio and telephone. Check students"

work for

scientific

and

histori-

cal accuracy.

Integration: L'se the Find Out by Writing feature to integrate language arts skills into your science lesson.

4-1 (continued)

CONTENT DEVELOPMENT Point out that because the effects of a semiconductor involve onlv a few atoms, the size of a diode or a transistor needs to be onlv a few atoms thick. Integrated circuits combine manv diodes and transistors on single crystals. A thin slice of silicon called a wafer is coated with an insulator that leaves the silicon exjx)sed in certain locations. These exposed locations receive a coating of a

conductor of opposite

second semiform-

vrpe. thus

ing a diode. Transistors are formed third laver

nent

added before the comjXH

sealed with another insulating

la\er.

Connections between these diodes and mav be made bv painting thin "wires"" on them or even by scratching the insulating laver to expose a channel of silicon. Wires are then attached so that external circuits mav be connected to the ti^ansistors

integrated circuit chip.

INDEPENDENT PRACTICE Section Review 4-1 1

Electronics studies the release, be-

havior,

and

effects of electrons

used

Figure

4-2 Transmitting Sound

Guide for Reading

Since the first telegraph line was connected and the first telegraph message was sent in 1844, people have become accustomed to instant communication. Each improvement in the speed, clarity, and reliability of a communication device has been based on a discovery in the field of electronics. One particular discovery that is the basis for many devices used to transmit information is an interesting relationship between electricity

netism.

The

and others

discoveries

made by Oersted,

Focus on you read.

Ihis

How do

4-2 Transmitting Sound

question as

sound-transmitting

MULTICULTURAL OPPORTUNITY 4-2

devices work?

Have your students investigate the life and works of Granville T. Woods (18561910). Sometimes known as the "Black specializing

Faraday, vices.

you have read about in Chapter 3 clearly illustrate that electricity and magnetism are related. Another scientist, James Clerk Maxwell, used that

de-

His patents include a device that

ESL STRATEGY 4-2

Telephone and Radio History

The invention of the telephone and the invention of the radio were two important advances in electronic technology. Using books and

other reference materials

Make sure students understand the usage of the term vice versa before beginning the activity. Have students determine which source radio, telephone,

—

Sound

lowing questions.

sound.

Who

invented the de-

When was

Were

Invented?

there any interest-

ing or unusual circumstances

surrounding the invention? 4.

familiar with electromag-

signals,

How was

the invention

— produces

each phenomenon or product:

invention of each. Be sure to include answers to the fol-

vice?

wave

electromagnetic

the library, find out about the

changing electric field will also produce a changing magnetic field. The two will keep producing each other over and over. The result will be a wave consisting of an electric field and a magnetic field. Such a wave is called an electromagnetic wave. Electromagnetic waves are like waves on a rope except that they do not consist of matter. They consist of fields.

a prolific inventor,

electromechanical

ater lights.

changing, like the up and down movements of a wave, a changing electric field will form. But a

are already

was a cross between a telephone and a telegraph (which he termed a "tclegraphony"), an invention that allowed telegraph messages to be sent to moving trains, as well as a diminer system for the-

the discoveries of his predecessors to open a new world of scientific technology. Maxwell showed that all electric and magnetic phenomena could be described by using only four equations involving electric and magnetic fields. Thus he unified in one theory all phenomena of electricity and magnetism. These four equations are as important to electromagnetism as Newton's three laws are to motion. Perhaps the most important outcome of Maxwell's work is the understanding that not only does a changing magnetic field give rise to an electric field, but a changing electric field produces a magnetic field. In other words, if a magnetic field in space is

You

Woods was

Edison,"

and mag-

vibrations change into electric which are then changed back into

Change

changing

magnetic

field

electric field to form,

causes a

and

vice

versa.

Sound vibrations change into electromagnetic waves and are changed back

into sound.

modified through the years? Present the results of your

you may realize. The most familiar electromagnetic wave is light. All the light that you netic waves than

research

is composed of electromagnetic waves. The microwaves that heat food in a microwave oven are also electromagnetic waves. The X-rays that a doctor takes are electromagnetic waves. And as you will

see

report.

a written or oral your re-

Accompany

port with illustrations.

in their lives.

Examples may include teleand the like.

vision, radio, stereo systems,

Then have students describe a typical day in their life in which none of these soundtransmitting devices were available. Stu-

dents

will realize

how

these iitiportant

and convenient devices are often taken for granted and what society might be like

Examples of how these words are used in everyday language and reasons why these words are appropriate for use in electronics will vary, depending on the student. greater."

CLOSURE ^ Review and Reinforcement At

this

Guide

point have students complete

pear to have difficulty with any of the questions, review the appropriate material in

the section.

Remind students of call that

ment Guide.

these

TEACHING STRATEGY 4-2

the energy con-

versions studied earlier.

Section 4- 1 in the Review and Reinforce-

REINFORCEMENT/RETEACHING Monitor students' responses to the Section Review questions. If students ap-

without these electronic devices.

CONTENT DEVELOPMENT

although energy

conversions,

Have them is

re-

conserved

amplifiers

are

re-

quired becau.se of losses, mainly in the form of heat hence the role of the tran-

—

sistor.

FOCUS/MOTIVATION Have students ious ways in

and discuss the varwhich sound is transmitted list

• • • •

Integration

Use the description of

•

• •

dift'erent types

of light to integrate concepts of electromagnetic waves into your lesson.

Q HISTORICAL NOTE GUGLIELMO MARCONI engineer Gugsometimes referred to as "The Father of Radio." Building on an established body of work by the German mathematician and physicist Heinrich Hertz. Marconi built a de\ice to detect, or recei\e, radio \\a\es. Gradually, Marconi built devices that were able to send and receive radio waves. In 1 895, he sent

The

Italian electrical

lielmo Marconi

a signal

soon learn, the prediction and venficanon ol electromagnetic waves opened up a whole new world of communication from the first wireless telegraph to radio and television to artificial space satellites.

—

mile; in 1896, 9 miles; in 1897,

12 miles; in 1898,18 mUes. On December 12, 1901, Marconi succeeded in

sending a radio wave from England to Newfoundland, Canada. The date of this transmission of radio waves across the Atlantic

Ocean

Radio Communication Would vou be surprised to learn that radio broadcasting once plaved the same role that television plavs todav"- People would gather around a radio to listen to a varietv of programs: musical performances, comedv shows, mvster\ hours, and news broadcasts. Today, radio broadcasting is still a great source of entertainment and information. But its role has been greatly expanded. Radios work bv changing sound vibrations into electromagnetic waves called radio waves. The radio waves, which travel through the air at the speed of light, are converted back into sound vibrations when

reference date

the

often given for the invention of radio.

thev reach a radio receiver. Figure 4-8 Electromagneic waves in the form of X-rays enable you to see the forks, pen. and toothbrush in this person 's intestine! Another type of EM wave allows scientists to study the composition of the brain and other

4-2 (continued)

parts of the body. Believe not. this

taken

GUIDED PRACTICE Skills Skill:

photograph of a river was total darkness using

What type of electromagnetic wave can be seen infrared waves.

Development

the bottom photograph?

Sequencing events words or phrases resound on the chalkboard. As stu-

List the following

lated to

dents are completing the radio softly,

transmitter

•

receiving antenna

•

radio wa\ es

INDEPENDENT PRACTICE ^ Multimedia -4

microphone

•

transmitting antenna

•

sound w a\es

You might want \'ideodisc called

Sound

• receiver

sound and

usuallv begins at a radio station.

small groups to discuss

to use the Interactive

Invention;

Mastering

reinforce

the

concepts

its historv'.

The

rideodisc ex-

loudspeaker

plores the various criteria that describe

•

audio signal

manv

students

sequence

the

inventors, describes an introduc-

and

es-

the contributions related

tion to the process of inventing,

pieces of information to describe the

tablishes

process of being able

sound of three inventors.

t(j

hear the sounds

the videodisc,

and debate the Have the

futine evolution of sound.

•

transmitted bv a radio station.

program

activitv. plav a

amplifier

•

Instruct

radio

possible.

•

• receiver

Here, a microphone picks up the sounds that are being broadcast. An electric current running through the microphone is disturbed by the sound vibrations in such a wav that it creates its own ribrations that match the sound. The electric signals that represent the sounds of a broadcast are now sent to a transmitter. The transmitter amplifies the signals and combines them with a radio wave that will be used to carrv the information. How the wave carries the information determines if the information will be broadcast as .-Wl or FM radio. The final wave carrying the signal is then sent to a transmitting antenna. The antenna sends

.After

viewing

have students work

groups decide what thev feel will be the next major sound-related invention.

CONTENT DEVELOPMENT Students' familiaritv with using the

telephone mav not alwavs enhance their interest in studving or understanding this de\ice. Point out that manv people todav

install

their

own

and sometimes even senice

telephones. Mention that

ANNOTATION KEY

Answers

O Visible

light.

(Applying concepts)

To minimize interference and absorption of wave energy

from other buildings and to increase the distance that the wave is

able to travel. (Inferring)

Amplifies them. (Inferring)

Integration Figure 4-9 Radios work by the radio

waves out into the

many radio

Why do

air.

you think

stations locate their antennas at high

elevations, in

open

areas, or

on top of towers?

Radio waves are converted back into sound waves

means of a radio receiver. A radio receiver picks jp and amplifies the radio waves originally sent out from a radio station. When a radio receiver picks up sounds corresponding to a specific frequency, it is described as being tuned in. Have you ever wondered how a telephone call :an be made from a moving vehicle such as a car 3r an airplane? Cellular telephones (movable telephones) use signals that are sent out by an antenna IS radio waves. Other antennas pick up the radio .vaves and convert them back into sound. To understand more about cellular telephones, you must first earn how a telephone operates. 3V

converting sound vibrations into electromagnetic waves. The waves are amplified and sent out into the air. Picked up by a receiving antenna, the radio waves are converted back into sound waves.

What

else

O Social Studies

does the receiver do waves?

with the radio

relephone Communication Have you ever stopped to think about the amazng technology that enables you to talk to someone ;lse, almost anwhere in the world, in seconds? The device that makes this communication possible is the ;elephone. The first telephone was invented in 1876 3y Alexander Graham Bell. Although modern telephones hardly resemble Bell's, the principle on A'hich all telephones work is the same. A telephone sends and receives sound by means of electric signals. A telephone has two main parts.

method of sending a narrow beam of light through a plastic strand no thicker than a human hair. The fiber acts as a pipe or a path for

light.

laser (or

even

a light-emitting diode) sends a pulsed

beam of

light

corresponding

rhythm

with the varsing sound waves into one students

and how

know it

the parts of a telephone

works, they

avoid a future repair

may be

bill

able to

at least

able to speak intelligently to a repair per-

son

the event something

wrong with

the telephone.

•

• • •

Integration

•

ENRICHMENT

end of the

Amplifiers are required to prevent

telephone signals from fading and losing The energy

strength over long distances.

of a transmission

gradually lost because

a wire possesses resistance

and current

To improve

transmission

heats the wire.

telephone signals are often converted into light, which loses less energ\', requires no wires, and travels some-

efficiency,

Use the example of worldwide communication by telephone to integ[rate concepts of social studies into your sci-

ence lesson.

traveling what faster than signals through a wire. Fiber optics provides a

fiber.

The

light

bounces off

the walls of the fiber again and again in

glancing refiections as the fiber were a mirror.

diode

the far

the surface of light-sensitive

end converts the

light

back into an electrical signal. In other situations, telephone transmission mav be extended to include a transformation of the signal into electro-

magnet ii waves if a portable telephone is used oi if the signal is sent long distances via sau llite or microwave relay towers.

TRANSMITTER

The transmitter is located behind Sound waves pro-

the mouthpiece of a telephone.

duced when a person speaks

ANNOTATION KEY

into a telephone cause a

thin metal disk located in the transmitter to vibrate.

These vibrations var% according to the particular

Answers

sounds.

O In the transmitter; to amplify the

the

(Applying concepts)

tric signal.

SouTid

and

Chapter

The pattern of vibrations regulates produced and sent

electiic current

receiver.

Science: Fluorescence. See

Light.

vibrations, in turn, are converted to an

amount of

out over telephone ^dres. You can think of the electric current as "'copNing"" the pattern of the sound waves. The electric current travels over wires to a

Integration

O Physical

The

electric current.

elec-

RECEIVER The receiver, located in the earpiece, converts the changes in the amount of electric current sent out bv a transmitter back into sound. The receiver uses an electromagnet to produce this conversion. WTien the electric current transmitted bv another

Figure 4-10 was '.e':ej

telephone goes through the coil of the electromagelectromagnet becomes magnetized. It puUs on another thin metal disk, causing it to vibrate. The vibrations produce sound waves that the listener net, the

ca s r. teec-:-

hears.

.\lexander Graham Bell used carbon grains in the transmitter to convert sound to electricity. Today's

piease

telephones use a small semiconductor crvstal. Transistors then amplify the electric signal. In modem telephone earpieces, semiconductor devices have replaced electromagnets. .\nd fiber-optic systems, in which the vibrations travel as a pattern of changes in a beam of laser light, are replacing copper cables used for ordinary transmission.

4-2

Pemianent

magna

(continued)

CONTENT DEVELOPMENT Vitxating metal disk

If possible, have students disassemble an old or nonworking telephone. Ask

them

phone, using Figure 4-11

Transmittef

Electromagne

to identify the parts of the teleFigure 4-11

as a reference.

GUIDED PRACTICE Laboratory Manual Skills

Development 98

Skill:

Applying concepts [his piiini

mi ma\ want to have

stu-

dents complete the Chapter 4 Laboratory In\ estigation in the Laboratory

Man-

ual called Constructing a Telephone. In this investigation

students wih build a

simple device that illustrates the operation of a telephone transmitter.

mitter

them

Section Review 4-2 1. In devices that transmit

.\nswers

might sound,

sound vibrations are changed into electromagnetic waves, which are then converted back into sound vibrations. 2. Transmitter and receiver. The trans-

vibrations,

changing

changes the electric current back into sound vibrations. 3.

INDEPENDENT PRACTICE

detects

into electric current: the receiver

may vary

suggest

sUghtly. Students

these

steps:

sound

waves, microphone, audio signal, transmitter, transmitting antenna, radio waves, radio receiving antenna, receiver, amplifier,

and sound.

Accept logical responses. Students might suggest that telephones and ra4.

dios have

become smaller

in size

and

portable.

Accept logical responses. Students might suggest that industry- and business can now be conducted on a global, almost instantaneous scale. 5.

REINFORCEMENT/RETEACHING Review students" responses

to the Sec-

tion Review- questions. Reteach anv

ma-

based on

stu-

terial that is still unclear,

dents' responses.

— 4-2 Section Review 1.

3. 4.

i-'i

Describe the relationship between sound and electric current in devices that transmit sound. Describe the two main parts of a telephone. Describe the broadcast of a radio program. How do you think solid-state devices have

Transmitting

Pictures MULTICULTURAL OPPORTUNITY 4-3

affected telephones and radios?

Vladimir You and Your World you think radio communication has affected the development of business and

Connection 5.

first

practical television camera, or

iconoscope.

Focus on you read

game

was responsible for

ESL STRATEGY 4-3

does a catliode-ray tube operate?

Have students explain

the difference

between the parts of a regular vacuum tube and a simple cathode-ray tube (or CRT), and the type of screen necessary' for cathode rays to produce a picture. Then ask students to state another difference between a cathode-ray tube and the kind of screen used in a color televi-

tube.

Cathode-ray Tubes Figure 4-12 Wlien you play a

Television images are produced on the surface of a type of vacuum tube called a cathode-ray tube, or CRT. Cathode-ray tubes are also responsible for

also

question as

How

would be far less exciting if the images were unclear and did not move very quickly. The same is true of your favorite television show. The images on a video screen and a television screen are produced by a

vacuum

this

important refinements to the electron microscope.

Guide for Reading

4-3 Transmitting Pictures

special type of

cit-

During his work at the Radio Company of America (RCA), he developed the

that a video

Zworykiii was horn in

izen.

industry?

You would probably agree

Kosma

Russia but later became an American

How do

video game, you are taking advantage of a catt^ode-ray tube.

sion.

images produced by video games, computer displays, and radar devices. A cathode-ray tube is an electronic device that uses electrons to produce images on a screen. This special type of vacuum tube gets its name from the fact that inside the glass tube, a beam of electrons (cathode rays) is directed to a screen to produce a picture. The electrons, moving as a beam, sweep across the screen and cause it to glow. The screen glows because it is coated with fluorescent material. Fluorescent material glows briefly when struck by

Have students imagine what their lives would be like without such devices. • What do you think people did before television and radio? (.Accept reason-

electrons.

able responses. Students might suggest

The electrons in a CRT come from the negatively charged filament within the sealed glass vacuum tube.

people spent more time reading

that

than they do today.)

electric current heats the metal filament

You might want

to discuss whether the people read more years ago than they read now is an advantage or a disadvantage to the people of today. fact that

CONTENT DEVELOPMENT CLOSURE

through the

Review and Reinforcement Guide Students may now complete Section 4-2 in the Review and Reinforcement

name name

Guide.

Also ask students to pictures

that

they use or observe pictures transmitted

Point out that a cathode-ray tube, or

CRT,

an electronic device that uses

electrons to produce images

and videocassette recorders, and the

games, televisions, and computer

various

Then

ask students to

name

are

various

ways that pictures are transmitted with the aid of light signals. (Students are likely to mention laserdiscs or video-

FOCUS/MOTIVATION Ask students to naine various ways

television.)

(Students are likely to

ways that transmitted through electric signals. (Students are likely to mention videotape

like.)

TEACHING STRATEGY 4-3

air.

discs.)

and

that

a screen

CRTs are responsible for the im-

ages produced by such things as video dis-

plays or monitors.

• • • • Use

the

Integration discussion

• • • • cathode-ray

tubes to integrate the concept of fluorescence into your lesson.

BACKGROUND INFORMATION SCREEN PHOSPHORS The

Screen coated ivrth

fluorescent

matenal

fluorescent materials, or phos-

phors, that are used to coat a \ideo display are usually light metals in the form

Source Sealed evacuated

pounds. These compounds are manufactured into tiny, fine particles that are then used to coat the inside of a display. .\

monochrome

ally receiyes

Figure 4-13 A cathode-ray tube IS a sealed evacuated tube in which a beam of electrons is focused on a screen coated with

(one-color) display usu-

one extremely

thin,

uniform

fluorescent material.

coating. In a color display, the dots or yertical lines

coatings

blue,

and

The

green).

ftjbe

and causes electrons to "boil off it. The electrons are accelerated toward the screen and focused into a narrow beam. Because the electrons moye so quickly in a concentrated beam, the source is sometimes referred to as an electron gun. The moving electrons produce a magnetic field that can be used to control the direction of the beam. Electromagnets placed outside the CRT cause the beam to change its direction, making it move rapidlv up and down and back and forth across the screen. At each point where the beam of electrons strikes "

electrons

stnke the fluorescent matenal. visible light is given off and an image is formed.

of a screen receiye three

(red,

electrons

of sulfate, sulfide, and phosphate com-

spaces around these color dots or lines

made to appear black to improye the contrast of the screen. are usually

the fluorescent material of the CRT screen, visible light is given off. The brightness of the light is determined bv the number of electrons that strike the screen. The more electrons, the brighter the light. The continuous, rapid movement of the beam horizontally and vertically across the screen many times

per second produces a pattern of light, or a picture screen. In the United States, the electron

on the

in a CRT traces 525 lines as it zigzags up and down, creating a whole picture 30 times each second. In some other countries the beam moves

beam

4-3

twice as fast, creating an even clearer image.

(continued)

CONTENT DEVELOPMENT

Television Transmission

Point out that although the creation, transmission, and reception of a tele\i-

from a simple cathode-rav tube

sion signal are

wavs. First, the screen of a color television set is coated with three different materials placed close

more complicated than

those of a radio, for example, the pro-

duction of the picture

itself is

much

cathode-ray tube in a color television set differs in two important

sim-

pler.

Explain that the behayior of the electron beam is easy to explain according to

together in clusters of dots or in thin stripes at each point on the screen. Each material glows with a difwhen red, blue, or green ferent color of light struck bv a beam of electrons, \arious colors are

—

the principle that opposite charges attract

and

charges repel. Haye stu-

dents obser\e the electrostatic deflection

system pictured in Figure 4-13. In

it,

the

negatiye electrons are accelerated from

•

Integration

• • • •

the negatiye electrode toward the posi-

Use the description of television trans-

tiye plate. Some electrons pass through a narrow opening in the plate and form a beam. The charging plates change the direction of the beam, with the size of the opposite charges on each pair of charg-

mission to integrate concepts of color

ing plates carefully controlled so that as

izontal paths

100

change accordingly.

first set

of numbers called might rep-

resent the specific location on the grid,

into your lesson.

for example, and the second number might represent the brightness of a

GUIDED PRACTICE

bright white.

spot

Skills Skill:

Development

Applying concepts

the size of the charges change, the force

on the negatiye electrons in the beam changes. The electron's yertical and hor-

The

Students can transmit a picture to other students by establishing a grid system, then calling out a series of numbers.

— from zero

for black to three for

Students should agree on a particular format or stvle for the grid and then practice transmitting simple pictures to

one another.

—

Speaker Receiving antenna

Audio

ANNOTATION KEY

strike red, blue,

and

green fluorescent materials (Inferring)

Primary color signals

Video

Integration

signal

Decoder

Electron

"^^1?

Answers O When electrons

amplifier

Audio signal

O Physical and

Electronic

guns

circuits

Science: Color. See Sound

Chapter

Light,

Television signal

Fluorescent material

ECOLOGY NOTE ELECTROMAGNETIC RADIATION

-Electron

beams

The produced by adjusting the strengths of the electron beams. For example, red is produced when electrons

Figure 4-14 The

Purple is produced when electrons strike both red and blue material. When do you think while is produced? Second, a color television CRT contains three one for each color (red, green, and electron guns blue). The information for controlling and directing the beams from the three electron guns is coded

guns

a color

for red, blue,

and

electromagnetic

called

The screen of the coated with three different fluorescent materials, each of which glows with a different

CRT

from a

— one each

green

—

within the color picture signal that

CRT

television contains three electron

strike only the red material.

proliferation of color televisions

and computers increases our chances of being exposed to what is sometimes

signals.

EMR.

EMR

radiation,

given off by screens such as

those found on television sets and com-

Have

puters.

primary color of light when struck by a beam of electrons.

interested students use re-

search materials to discover the amount of radiation that is given off by these de-

environmental impact of that is being done and can be done to limit the amount of radiation people might receive while watching tele-

vices, the

transmitted

radiation,

station.

4-3 Section Review

vision or

and what

working

in front

of a computer

screen.

What

a cathode-ray tube? Describe

how

works.

How

does a color television

simple

CRT

differ

from a

CRT?

Thinking Making Inferences Photographs of a TV picture taken with an ordinary camera often show only part of the

Critical 3.

screen

filled.

the shutter speed

Explain why.

on the camera is photograph will

faster than this, the

show only

a partial picture because the

entire picture will take 1/30 of a second to

INDEPENDENT PRACTICE

the electrons strike the fluorescent ma-

Section Review 4-3

terial

of the

an electronic device that uses electrons to produce images on a

given

off.

screen.

electric

current

heats

metal filament in the

CRT, which then

The

electrons are ac-

emits electrons. celerated

through a magnetic

field,

which focuses the electrons into a beam. Electromagnets placed outside the

CRT cause the beam of electrons to

change direction. At each point where

CRT screen, visible light is

2. In a color CRT, the screen is coated with three different materials that can

glow with red, blue, or green light. A simple CRT has a coating of one material. A color CRT also differs from a simple

CRT in that

has three electron

"guns" rather than just one. 3.

The

electron

beam

in a

CRT

appear on the screen.

REINFORCEMENT/RETEACHING Monitor students' responses to the Section Review questions. If students appear to have difficulty with any of the questions, review the appropriate material in

the section.

CLOSURE Review and Reinforcement Guide this point have students complete Section 4-3 in the Review and ReinforceAt

creates

whole picture 30 times per second.

ment Guide.

101

4-4 Computers

Guide for Reading

4-4 Computers

Focus on these questions as you read. What IS a computer?

MULTICULTURAL OPPORTUNITY 4-4

Computers have quickly become a common sight over the past few decades. You see computers in

How

are the basic components of a computer related to

Have your students research the life and work of Admiral Grace Hopper.

its

stores, doctors'

dentists' offices, schools,

and

home. A computer is an electronic device that performs calculations and processes and stores information. A modern electronic computer can do thousands of calculations per second. At equally incredible speed, it can file away billions of bits of

Admiral Hopper was a pioneer in the development of the computer and remained an ardent educator about computers until her death in 1992.

information in its memor)'. Then it can rapidly search through all that information to pick out particular items. It can change numbers to letters to and back to numbers again. pictures to sounds

—

ESL STRATEGY 4-4

Using these

Assign a group research project on futuristic computer techniques currently

being developed to enhance the process as Virtual Reality. Have other stu-

modern computers

are guid-

make robots move, and obey commands. Computers can play games and make music. They can even design new computers. The pages of this textbook were composed and printed with the help of a computer (although people still do the writing)! searching for ore. Computers talk,

dents investigate twenty-first-centun' career opportimities in the area of elec-

and entertainment. Require and have stu-

brief individual reports

dents share their findings with the

abilities,

ing spaceships, navigating boats, diagnosing diseases and prescribing treatment, forecasting weather, and

known

tronic arts

and

businesses. Perhaps you even have one in your

operation'^

class.

Figure 4-15 Early computers, which used large vacuum tubes were neither fast nor reliable. And like the ENIAC. they certainly were

enormous in size! A modern computer that fits on a desk top once required an entire room.

i#i

.1.1

TEACHING STRATEGY 4-4

4>i

Computer Development The starting point of modern computer development is thought to be 1890. In preparation for the United States census that year, Herman Hollerith

^ ^ #1

i.!

FOCUS/MOTIVATION Computers seem to be evei"\"\\'here. Mthough each integrated-circuit chip is a computer, it is difficuh to obsene because integrated-circuit chips can be very small and are often hidden in toys, watches, appliances, and many other items. Discuss with students the pervasive

use of computers and computer

technologies. Also discuss

how an under-

standing of computer limitations can

man

onlv enhance one's ability to use com-

chine allowed small electric currents to

puters advantageously (even profession-

pass through holes that were

are occasionally misled by computer

into cards, activating counters.

als

program

results if they do not fullv understand what the computer can and cannot do for them).

Hollerith. His electromagnetic

Point out that computers did not

when compared

tive

turning currents on and

standards.)

standards, the machine

But

in its day, the

off. is

Bv today's

in comparison to the way things were done previ-

ously. • If Hollerith's

counting machine could

to contemporary-

Point out that Hollerith's machine

primitive, at

machine repre-

sented a radical technology al-

ways look and perform as they do todav. Cite the example of the invention of Her-

102

punched The cards

be seen in a museum today, what do you think it might look like? (Accept all reasonable descriptions. Lead students to infer that it would probablv look primi-

were, in a sense, mechanical switches,

best.

CONTENT DEVELOPMENT

ma-

now more than 1 00

vears old.

Think of the computers used today. years from now, how do you think people might describe our computers? (.Accept reasonable answers. •

One hundred

ievised an electromagnetic

machine

Find out by

that could

landle information punched into cards. The holes illowed small electric currents to pass through and ictivate counters. Using this system, Hollerith

jied a warehouse.

Shuffle a

maintain.

expensive,

deck

of playing

cards. Have a friend time you as you sort the cards, first

into the four suits,

Integration

O Social Studies O Mathematics O Karth Science: Ozone Depletion. See

and

then from the 2 through the

ace

each

how many

cost millions of dollars to btiild

suit.

Determine

sorts you

Calculate

was constantly breaking down and lad to be rebuilt each time a new type of calculation vas done. ENIAC required great amounts of energy, generated huge amounts of heat, and was very ;xpensive. By today's standards, ENIAC was slow. It :ould do only 100,000 calculations per second. The first general-purpose computer was introiuced in 1951. It was called the Universal Automatic "omputer, or UNIVAC. UNIVAC was certainly an mprovement over ENIAC, but it was still large,

ANNOTATION KEY

Computing Speed

ompleted the 1890 census in one fourth the time had taken to do the 1880 census! Hollerith's junch card became the symbol of the computer age. The first American-built computer was developed n 1946 by the United States Army. The Electronic Mumerical Integrator and Calculator, or ENIAC, onsisted of thousands of vacuum tubes and occuI

made.

how many

Exploring Planet Earth, Chaptci

sorts

you made per second. A bank check-sorting machine can make 1800 sorts per minute.

How much you

this

faster than

machine?

FIND OUT BY CALCULATING COMPUTING SPEED

and slow. Skills:

demand for computers encouraged nore advanced computer technology. Technical ireakthroughs such as transistors and integrated Increased

Making comparisons, making

computations Materials:

deck of playing cards, timing

device

The number of sort.s that students will be able to perform per second will vaiy,

Figure 4-16 The uses of computers are wide and varied. Computer applications include the identification of worldwide ozone concentrations (bottom left), the analysis of the body nechanics of a runner (top), and the study of fractal geometry 'n mathematics (bottom right)

depending on the student. The sorting speeds of students, however, stantially

will

be sub-

slower than the sorting speed of

Have

a bank check-sorting machine.

stu-

dents relate the speed of the machine to the

many

require

applications of computers that

fast

computational calculations. Out by Cal-

Integration: Use the Find

culating feature to integrate mathematics

Many

students

will

probably suggest that

our computers will look primitive when compared to machines of the future, just as Hollerith's 100-year-old machine appears primitive

tti

Skill:

us now.)

ENRICHMENT

GUIDED PRACTICE Skills

Ask students woiking

Development point have students complete

the in-text Chapter 4 Laboratory Inves-

• • • •

Integration

• • • •

Use the discussion about the 1890 United States census to integrate social studies concepts into your science lesson.

tigation called

Abacus. In

The

First (lalculator:

this investigation

identify ten objects in their

Making computations this

concepts into your science lesson.

students

determine how an abacus works counting machine.

will

groups to

homes

that

were manufactmed to some degree with the use of computer technologies. Have gioups identif) the specific way or ways in which computer technologies are incorporated into each object. Then have groups discuss how the objects might be diffeient if computer technologies were not used

in their

manufacture.

Use Figure 4-16 to integrate concepts of ozone depletion into your lesson.

103

INTEGRATION

(^AREERÂ§

ASTRONOMY

Computer Programmer

Computers

provided

Voyager perform re-

the

spacecraft with the ability to

Have students interested in astronomy use reference materials to discover more about the use of computers on exploratory spacecraft and have stusearch.

dents share their findings with the

class.

A computer programmer uses computer languages to

computers what to do. Programmers must be able to

tell

think logically

order to un-

derstand the processes of the computer.

Computer

programmers

are trained in vocational schools or junior colleges.

Many

also have college degrees. For information write to the American Federation of Information Processing Societies,

1899 Preston White

Drive, Reston,

4-4 (continued)

REINFORCEMENT/RETEACHING Activity

Book

who need

Students

practice

on the

concept of computer-information systems should complete the chapter activity

Whose Data Bank Are You In? In this some of the

activity students will discover

various gioups and organizations that

may have information about them in

stored

computers.

CONTENT DEVELOPMENT Point out that every computer break-

through has consisted of either a better way of storing information, such as replacing the holes in the pimch cards of the counting system used in the 1890 census, or a faster way of turning a circuit

on and

off,

such as replacing the me-

chanical switches. Stress that these im-

provements are based on electronic technolog)'

â&#x20AC;&#x201D;

first

vacuum now

semiconductors, and

tubes,

then

integrated

cir-

Students might be interested to learn that some integrated circuits can cuits.

perform a

billion calculations a second.

GUIDED PRACTICE Laboratory Manual Skills Skill:

Development

Relating facts this

point you ma) want to have stu-

dents complete the Chapter 4 Labora-

22091.

disk drive reads information off a disk and it into the computer's memory or into the vPU. Information from a disk drive can be placed nto a computer very quickly. Information produced by a computer can be •nters

emoved and stored on

a disk.

a disk drive

ANNOTATION KEY

Answers

also

O CPU:

output device receives data rom the central processing unit. Output devices ncludc printers, cathode-ray tubes, magnetic tape ,n

output device.

erating instructions; input device: feeds

and voice synthesizers. Even robots are

Irives,

data to

>utput devices.

from

mm The organization

and

receives data

displays the data,

Apply-

Integration

O Life Human

Science;

Nervous System. See

Biology and Health, Chapter 6.

human body

of the

pretty amazing, isn't

CPU; output device:

CPU

ing definitions)

O The Human Computer is

controls all computer operamain memory: stores data and op-

tion;

it?

Think of

all

the various organs constantly vs/orking

independently as well as interacting with

one another to keep you alive, healthy, and functioning normally. What's even more amazing is that the body does all its work without your having to think You don't even have to worry about about nourishing your body because reminds you to do so by making you feel hungry. Now that's pretty awesome! What is even more incredible, perhaps, is that you have the ability to think, reason, reach conclusions, and

CONNECTIONS THE HUMAN COMPUTER

it!

use your imagination. What a wonderful device the human body is! The organ of your body that controls the various body systems and is also the seat of intelligence

the brain. Dif-

have different functions. One part enables you to coordinate your movements quickly and gracefully. Another part controls body processes, such as heartbeat, breathnot to mening, and blood pressure tion swallowing, sneezing, coughing, and blinking. And still another part is referent parts of the brain

—

sponsible for your

perform during the course of a

typical

day.

GUIDED PRACTICE Skills Skill:

the

Have students observe Figure 4-17. Then have them imagine a piece of information that they might want to have entered into the computer, acted upon by the computer, and demonstrated on

of their bodies

—

and reasoning

humans.

and

Currently, however, such attempts to

holds

its

many

vous system into your lesson.

any of your students have taken a

computer programming class, have them volunteer to demonstrate

how

computer program

two numbers.

Connections

secrets.

ENRICHMENT

detailed

the

feature to integrate concepts of the ner-

the computer screen. Have students sequence the events that would occur, using the terms ynain memoiy, CPU, input device, and output device.

artificial intelli-

stability.

Integration: Use

unravel the interconnections of the human brain have proved largely unsuccessful. For now, at least, the human still

their brain.

gence with students or have them debate the advantages and potential hazards. If you are teaching theniatically, you may want to use the Connections feature to reinforce the themes of energy, scale and structure, systems and interactions,

Many attempts have been made to simulate the activities of the brain. There is, in fact, a field of computer research that aims to create artificial intelligence that is, computers capable of thinking

—

to discuss the advantages

and potential hazards of

Development Sequencing events

"CPU"

You may want

brain

ability to think.

will enable students to reconcept of a computer CPU to

This feature late the

Reniiiicl

to write a that

CPU can

perform only one

task at a time,

including checking to see that data are

and retrieving data, reading and so on. When the program to add two numbers is finished, display it on the chalkboard and have students determine and count the number of individual steps required to add the two numbers. present;

data, storing data,

adds

students that a

105

Like a disk drive, a modem is an input and output device. A modem changes electronic signals from a computer into signals that can be carried over telephone lines. It also changes the sounds back into

FIND OUT BY

THINKING HELPFUL PREFIXES This activity ulary

sei-ves to

and

skills

computer signals. A modem allows a computer to communicate with other computers, often thousands of kilometers away. As computers link in this way, they form a network in which information can be shared. A modem allows use of this network by accessing (getting) information from a central data bank. A data bank is a vast collection of information

reinforce vocab-

to give students a better

knowledge of word derivations. Check students' sentences carefully to ensure

stored in a large computer.

that they have used each prefix correctly.

Find Out by Integration: Use Thinking acti\ it\ to integrate language arts skills into \our science lesson. the

The Binary System Computer hardware would be useless if computer software did not exist. Software is the program or set of programs the computer follows. Software must be precise because in most cases a computer cannot think on its own. A computer can only follow instructions. For example, to add two numbers, a

4-4 (continued)

program must tell a computer to get one number from memory, hold it, get the other number from memory, combine the two numbers, and print the answer. After completing the instruction, the computer must be told what to do next. A computer can execute instructions by counting with just two numbers at a time. The numbers are and 1. The system that uses just these two numbers

1N D OUT BY

CONTENT DEVELOPMENT Describe the basic functions of com-

problem solving and computer simulation, along with several

Helpful Prefixes

of their specific applications. Also point out the prolific use of computers in data

electronic devices

puters, including

processing,

Several terms related to

word processing, and com-

meaning

Explain that a computer that uses only

two numbers to execute instructions performs its work using the binary system of numbers. If students appear to have some difficulty determining how a binary number system works, you might wish to ask a mathematics instructor to visit your

each

underlined

the

composed of diodes. As previous sections, diodes are gates that are either open or closed to electric current. If the gate is open, current is off. If the gate is current closed, current is on. To a computer,

Computer

words

off and

circuits are

in the

current on. Each

digit, then, acts as a

tiny electronic switch, flipping

on and off

unbe-

lievable speed.

binary system

Each

diode

single electronic switch

integrated circuit

string of bits

micro processor semi conductor

letters,

— usually 8 —

called a bit.

called a byte.

Numbers,

and other symbols can be represented as a For example, the letter A is 01000001. The letter K is 11010010. The number 9 is 0000 1001. You do not need to be reminded of the importance of computers. You have only to look around you. The uses of computers are many, and their presence is almost universal. Any list of computer byte.

triode

• • • •

called the binary system.

you learned

prefix that

the definition of the word.

ing strategies.

Integration

Find out the

below. Then write a sentence explaining how the prefix will help you to learn

or provide you with helpful teach-

• • • •

you know the meaning

their prefixes.

puter-aided design.

class

may be

easier for you to understand

transistor

Use the introduction of the binary system to integrate mathematics concepts into your science lesson.

INDEPENDENT PRACTICE Activity

Book

who need help on the conhow computers work should be

Students cept of

provided with the chapter activity called Checkers Computer. In this activity

students

will

bits

and

how a computer number system to create

explore

uses the binaiy bytes.

toiy Investigation in the Laboratory ual

Constructing

called

Computer students

Man-

Simple

Circuit. In this investigation

will

explore

how an

off-on

com-

puter system works.

Your Fingers. In

Laboratory Manual Skills Skill:

Development

Applying concepts

At this point you may want to have students complete the Chapter 4 Labora-

106 e P

INDEPENDENT PRACTICE Activity

Book

Students

who need help on the connumber systems should be

cept of binary

provided with the chapter

Counting

activity called

One Thousand Using Only

students

will

computers.

ENRICHMENT Activity

GUIDED PRACTICE

this activity

explore the system of numbering used by

Book

will be challenged by the Chapter 4 activity in the Activity Book called Hexadecimal Numbers. In this ac-

Students

tivity

students

will

explore a 16-digit

sys-

tem of numbers used by computers perform calculations.

? Solving Go With

the Flow Symbols of a Flowchart

A computer ities thiat

follows a series of activ-

take place

or process.

you

a definite order,

think

about

so do at a you add

It,

you.

You get dressed one step

time.

When you

each ingredient It

useful to

follow a recipe, In

order.

have a method

to de-

scribe such processes, especially when writing computer programs. A flowchart Is

one method

of describing a process. a flowchart the activities are written

within blocks

whose shapes

Indicate

what is involved In that step. Designing a Flowchart It Is a good thing you know how to write a flowchart because you are hosting the class luncheon today. But the chef that you have hired can cook only from a flowchart. Write a flowchart showing the chef how to prepare today's menu.

Laboratory Investigation Laboratory Investiption

The

THE FIRST CALCULATOR: THE

ABACUS Gather

The Abacus

Problem How

can an abacus serve as a counting machine?

BEFORE THE LAB 1.

First Calculator:

all

materials at least one day

Materials

prior to the investigation.

an abacus cannot be obtained, one can easily be constructed by stringing beads or other objects on a string in a cardboard box. Do not let the lack of commercial apparatus deter you from

(per group)

2. If

Procedure The columns

this investigation.

beads on the abacus

represent, from right to

left,

units of

ones, tens, hundreds, thousands, and

PRE-LAB DISCUSSION

millions.

Have students read the complete

lab-

oratory procedure. •

What

the purpose of this investiga-

tion? (To find out

how an abacus can be

used to count.) • What is an abacus?

single bead in the upper section of each column, above the partition, equals 5 beads in the lower section of that column.

The

Always the far

start right,

a system of

Count to 3 by sliding 3 beads ones column to the partition.

Continue counting to

8. Slide

your abacus. (The greatest place value may vary, depending on the abacus the ones through the millions place are usu-

—

umn down

to the partition.

of the

abacus in

Count

How

Remember

Remind students

correctly.

Discuss

how

the investigation relates

to the chapter by asking

During the investigation, circulate through the room, offering assistance to

similar to the following:

students

who

are having difficulty learn-

ing to use an abacus. 3.

Point out that although students

may

not perform computations quickly first,

their

speed

will

increase as

practice using the abacus.

108 m P

they

•

open questions

How is an abacus like a computer? (Ac-

puter perform computations

— compar-

this

compare

with the opera-

a computer?

On Your Own

Try designing a number uses more than 2 numerals but fewer than 10. Count to 20 in your system.

system

that

source and a computer does, or that a computer can perform computations much faster than an abacus can con-

—

•

The abacus was once

mon

tations.

Why do

not used

comcompu-

a relatively

tool used for performing

you think an abacus

much anymore? (Lead students

newer technologies, such as and computers, tend to offer convenience and efficiency, which are to infer that

ing-)

How

How does

trasting.)

cept reasonable answers. Students might suggest that both an abacus and a com-

an abacus different from a computer? (Accept reasonable answers. Students might suggest that an abacus does not require an electrical energy

•

the operation

lished laboratory procedure. 2.

abacus based?

tion of

the ones column up to the parti-

DISCOVERY STRATEGIES

to follow the estab-

On what number system of the

You should now have a total of 9. And you should be out of beads in the ones column. Slide all these beads back

TEACHING STRATEGY

would you find 8 -I- 7 on the abacus? Start by counting to 8 on the abacus. Then continue adding 7 more beads Find the following sums: 7 + 8, 3 -I- 4, 125 -I- 58.

Analysis and Conclusions

tion.

108

the ones column

to each of these numbers on the abacus: 16, 287, 5016, 1,816,215.

6. Continue counting to 12. Slide the last

bead

12.

Observations

the fourth

bead equals 5 lower beads. Continue counting from 6 to 8 by sliding the beads in the lower section of the ones column up to the partition. Before doing any further counting, check with your teacher to see that you are using the

to the partition. This represents

you reach

until

the lower section of the tens col-

10. Continue counting

that the top

represented.)

umn up

bead up to the partition. You should be out of beads in this section. Slide all 4 beads back down and slide the single bead from the upper section of this col-

represent a specific place value? (Yes.) • Name the place values represented by

ally

bead

from the lower section of or ones, column.

beads used for counting.) • Does each column or row of beads

(It is

to their original zero position. Slide

calculators

not offered in older technologies ferring, analyzing.)

—

in-

Study Guide

ANALYSIS AND CONCLUSIONS Base 10, or decimal number system. in base 2, or the binaiT number system. 1.

Summarizing Key Concepts 4-1 *

Electronic Devices

Electronics

havior, to

use

and in

the study of the release, be-

control of electrons as

relates

—

an electronic device

rectifier is

amplifier

that con-

current to direct current.

^'erts alternating

two main

parts:

a transmitter and a receiver.

an electronic device that

increases the strength of an electric signal.

Semiconductors are materials that are able to conduct electnc currents better than insulators do but not as well as true conductors do.

4-3 Transmitting

Pictures

cathode-ray tube, or CRT, is an electronic device that uses electrons to produce

images on a screen.

cathode-ray tube in a color television set one each for contains three electron guns red, blue, and green signals.

—

Individual design.s will vary, depend-

ing

on the student. Designs may be tested

using computations with

known answers.

semiconductors

called doping.

integrated circuit

transistors

on a

combines diodes and

thin slice of silicon crystal.

4-2 Transmitting Sound

4-4 Computers can hold the entire processing capability on one small chip.

Computer hardware consists unit, main storage, and output devices.

processing

A computer program

Radios work by changing sound vibrations electromagnetic waves, or radio waves.

into

tions that

tell

the

GOING FURTHER: ENRICHMENT Parti

Have students perform simple subon the abacus. You may wish to demonstrate several sample traction exercises

exercises,

necessary.

Part 2

Integrated circuits called microprocessors

Adding impunties

A computer works

practical devices.

In a tube in which most of the gases have been removed a vacuum tube— electrons flow in one direction.

telephone sends and receives sound by of electric signals. A telephone has

means

of a central

Have students design an abacus that works on the binary system. Have them repeat the investigation using this abacus.

input devices,

a series of instructo perform a

computer how

certain task.

Reviewing Key Terms Define each term

4-1

a complete sentence.

Electronic Devices electronics

vacuum tube rectifier

diode

4-2 Transmitting Sound electromagnetic

wave

4-4 Computers hardware central processing unit

4-3 Transmitting

Pictures

cathode-ray tube

main memory input device

amplifier

disk drive

triode

output device

solid-state device

modem

semiconductor doping

software

transistor

bit

integrated circuit

byte

binary system

chip

OBSERVATIONS The

be as follows: (16) ones column: upper bead down, one lower bead up; tens colum: upper bead up, one lower bead up; (287) ones column: upper bead down, two lower beads up; tens: upper bead down, three lower beads up; hundreds: upper bead up, two lower beads up; (5016) ones: upper bead up, one lower bead up; tens: upper bead up, one lower bead up; hundreds: upper bead up, no lower beads up; thousands: upper bead down, no lower beads up; 1.

settings should

(1,816,215) ones: upper bead down, no lower beads up; tens: upper bead up, one lower bead up; hundreds: upper bead up, two lower beads up; thousands:

upper bead down, one lower bead up; ten thousands: upper bead up, one lower bead up; hundred thousands: upper bead down; three lower beads up; millions: upper bead up, one lower bead up. 2. Students must add the proper number of beads to show the correct answers: 1 5, 7, and 183, respectively.

109

%^nupLt^r ixt^uit^cv Chapter Review Content Review

ALTERNATIVE ASSESSMENT The

Prentice Hall Science

program

Multiple Choice in-

Ctioose the

cludes a variety of testing components and methodologies. Aside from the

Chapter Review questions, you may opt to use the Chapter Test or the Computer Test Bank Test in your Test Book for assessment of important facts and concepts. In addition. Performance-Based Tests are included in your Test Book. These Performance-Based Tests are deprocess

of the answer that best completes each statement

transistors.

rectifiers.

d. triodes.

diode

Which

a semiconduc-

copper

silicon

rather than factual content recall. Since thev are not content dependent, Perfor-

plastic

oxygen

science

test

terials

mance-Based Tests can be distributed complete a chapter or after thev complete the entire textbook.

after students

diode.

integrated

transistor.

modem.

True or False

Multiple Choice

b a

the statement true.

The beam

increased cost

better amplification

greater energy efficiency

The physical parts

The

software.

a computer are

computer

printer

program

disk drive

memory

Complete the following concept map for Section 4- 1. Refer to pages P6-P7 to construct a concept map for the entire chapter.

a cathode-ray

studies release

picture.

CRT

and

has two electron

American-built computer

control of

Vacuum tube

first

was

made

possible by

toui

a computer on one chip. Output devices feed data to a compability of

EN I AC

Amplifier

puter.

ailowed

A data bank

a vast collection of information stored in a large computer. 9. A string of bits, usually eight in number, is called a byte. 8.

7. F,

6. Microprocessors are integrated circuits that can hold the entire processing ca-

4. F, three

color television

UNIVAC

T T T

5. F,

guns.

True or False

telephones and radios?

smaller size

electric current.

of electrons

tube produces a

is a rectifier telephone sends and receives sound

by means of

b d

bytes.

rays.

not an advantage of solid-

that converts alternating cur-

If it is

change the underlined word or words

8. c

write "true. "

false,

A device

electric signals.

programs. d. hardware. b. peripherals. 8. Which is computer software?

circuit.

make

5. c 6.

is true,

rent to direct current

gamma

Concept Mapping

the statement

3. c

cathode rays.

a{an)

collectively referred to as

of three

CONTENT REVIEW 1.

semiconductor maused to amplify an electnc signal

A sandwich

vibra-

Which

state devices

tor material? a.

disk drive

of the following

Radios work by changing sound tions into

Which electronic device was particularly important to the rapid growth of the radio and television industry? c. punch card a. triode

skills,

signed

amplifiers.

letter

Diode vacuum tubes are used as

input

T T

tor

development

of chip called

Concept Mapping

Row Row Row Row

Electronics

has produced the

3: Solid-state devices; 4: that

electrons

strengthens a signal

Semiconductors

Row

5: Rectifier;

CONCEPT MASTERY

able to conduct electric currents better

is a;

Integrated circuit

Electron beams produce images on

than insulators but not as well as metals.

screens coated with fluorescent materi-

Semiconductors are doped to increase

and the predictable beha\ior of electrons allows science and technolog^ to create devices that use electrons and imals,

prove the quality of our lives. 2. A rectifier is a diode vacuum tube that converts alternating current (AC) to direct current (DC). .\n amplifier uses a

ode vacuum tube

to increase the strength

of an inpiu signal. 3. A semiconductor

110

tri-

a material that

their conductivity.

Radio communication uses electromagnetic waves. telephone transmitter converts 5. A sound waves into electric waves, and a

telephone receiver converts the electric waves from the transmitter back into

sound waves. 6. Sounds waves enter a microphone, are converted into electromagnetic waves, and are sent bv a transmitter to a trans-

electromagnet

energized, and

(a)

vi-

brating magnet produces sound.

loncept Mastery 'Iscuss

each of the following

Why

devices? Give

Compare

used

for

What type

each?

Describe a semiconductor. Why are semiconductors doped? 4. What connection between electricity 3.

and magnetism is used In radio communication systems? How does a telephone work?

How Is a radio show broadcast? In what ways are semiconductor diodes better than their vacuum tube ancestors? 8. Describe how a cathode-ray tube creates a picture. 9. What IS a computer? What are some uses of computers? 10.

What system

used

calculators? Explain

program could to be

works.

chapter

tell

6. Stories

answer each of the

Making diagrams Draw a diagram that shows how the four mam hardware com-

Making calculations The

ponents of a computer are

Sequencing events The sentences below describe some of the energy con-

a second. How many pictures are flashed on a screen during 30 minutes? Using the writing process The elec

versions required for a local telephone

tronlcs Industry

proper order. Sound vibrates a metal plate. An electromagnet Is energized. A vibrating magnet produces sound. Vibrating vocal cords produce sound. Mechanical energy is converted Into

call.

b. c.

d. e.

Arrange them

related.

an electric signal. Classifying computer devices IVIany methods for putting data Into a com-

following.

television screen last for

pictures on a

one

life

sponses to unassigned questions in their portfolio. Students should be encour-

aged to include both the question and the answer in their portfolio.

devices will affect your years from now.

ISSUES

waking up and

your

first

Vacuum tubes are essentially now that the production of

lete,

the telegraph are two such inventions.

arriving at school for

What other "modern" inventions are obsolete? Can you predict several items that

class.

on antenna. The radio waves

travel

hrough the air, are received by a receivng antenna, and are amplified and con'erted into sound waves. 7. Semiconductors are smaller, lighter, onger lasting, more dependable, and rooler, and use far less power than vaclum tubes. cathode-ray tube, powered by i. The

The uses of computers may vary, depending on the application. 10. The binary system controls the opinformation.

eration of computers.

giving off visible light. is

an electronic device

hat performs calculations

and processes

Could the inventors have

of television?

the positive effects out-

weigh the negative? Should the development of television have been stopped until only positive effects could be assured?

AND PROBLEM SOLVING 1.

A computer

â&#x20AC;&#x201D;on or

society.

foreseen the positive and negative effects

CRITICAL THINKING

a system of

be replaced by improved versions?

Television has had a profound impact

off.

electrons that strike fluorescent materi-

emits a controlled

It is

two-position electronic switches

beam of

ils,

semi-

become obsolete within a centuiy of their invention: The fountain pen and

your task

electricity,

obso-

conductor devices has been perfected. Many other modern inventions have also

will

nitting

can be used as

writing assignments:

Applying concepts A program Is a list of instructions that tells a computer how to perform a task. Write a program that of

issues

springboards for discussion or given as

synthesizer.

SCIENCE

The following

punched cards, voice

describes the steps Involved

thirty or forty

data out of a computer. Identify each of the following as an Input device, an output device, or both: typewriter keyboard, CRT, printer, optical scanner, magnetic

depending

You might want to assign some of the Concept Mastery and Critical Thinking and Problem Solving questions as homework and have students include their re-

puter are similar to methods for getting

tape, disk drive,

will vary,

KEEPING A PORTFOLIO

thirtieth of

and the development of computers have evolved quite rapidly. You yourself are even witnessing obvious changes In the size and capabilities of electronic devices such as calculators, video games, computers, VCRs, compact disc players, and videodiscs. Write a story or play about how you think electronic

or plays

on the student.

computer programmers, but they

the computer. 54,000 pictures.

the

this

com-

should be able to apply what they have learned to what the program would need

Thinking and Problem Solving you have developed in

actually be run by a

puter. Students should not be expected

'se

skills

for

the logic they employ than whether the

Iritical

cards, op-

Check students' progiams more

computers and

how

punched

scanner; output: (>RT, voice synthe-

sizer, printer.

and

vacuum tube

tical

some examples.

the functions of rectifiers

amplifiers.

typewriter keyboard,

a brief paragraphs

are electrons Important to elec-

tronic

Both; magnetic tape, disk drive; input:

3. in

Check each diagram for accuracy. The correct order is (d) vibrating vocal

tords produce sound, (a) sound vibrates a metal plate, (e) mechanical energy is

converted into an electric

signal, (b)

111

ADVENTURES

SUPERCONDUCTORS Background Information Superconductivity was discovered in 1911 bv H. Kamerlingh Onnes. Onnes was studying the electrical conductivity of mercury- within a few degrees of ab-

— 273°C).

sened that the dropped sharply

Imagine tracks their

an almost immeas-

—

is the temperature at which resistance to conducting an elecohms. tric current drops to nearly Soon after its discovery superconductivity was found to be a property of such ,

metals as lead and

lieved that the

conductivity

first,

tin, in

this

—

SEARCHING FDR

super-

that

property occurs quite frequently.

Some 26

metallic elements are

BETTER CONDUCTOR

of our electricity runs through copper wire. Copper is an example of a conductor, or a material that carries electricity well. However, copper is not a perfect con-

was quite rare and was

showed

Much

limited to only a few substances. After a while, however, experiments

airplane

addi-

scientists be-

phenomenon of

speeds and powerful computers that fit in the palm of your hand. Picture unlocking the secrets of the atom, or skiing on slopes made of air. Purely imagination? Not really. .\11 of these things and more have been brought closer to reality by the work of Dr. Karl Alex Mueller and Dr. Johannes Georg Bednorz. These two dedicated scientists have changed fantasy to fact through their work with superconductors.

He named this point the transition

tion to mercurv.

offers resistance to the flow

15 percent of the electric power passing through a copper wire is wasted as heat. A superconductor has no resistance. Therefore, it can conduct electricity without any loss of power. With superconductors, power plants could produce more usable electricitv at lower costs and with no waste. Electric motors could be made smaller and more powerful. Superconducting wires connecting computer chips could produce smaller, faster computers. Scientists have known about superconductors for more than 75 years. But although the principle of superconductivity was understood, the method of creating one remained a secret ... a secret that seemed to be "locked in a deep freeze." For until the time of Mueller and Bednorz's discovery, materials would not become superconductors unless thev were chilled to at least -250°C!

trains that fly above

Onnes ob-

temperature, which

common

of electricity. As a result of resistance, about

urably small ainount at a temperature of 4.2°K.

:i :U:

ductor because

resistance of mercury to

THE SEARCH FOR SUPERCONDUCTORS

SCIENCE THE SEARCH FOR IN

solute zero (0°K or

known

jSuipstcoiidiiclivity

pioiMWS Kori

MuwMr (Mtt) and Johonnos Bodnofx*

be superconductors, and 10 others become superconductors under pressure or

when prepared

as thin films. In addi-

thousands of compounds and alloys have been found to really be supercontion,

ductors.

CONTENT DEVELOPMENT TEACHING STRATEGY:

Remind students

ADVENTURE

erties

Go on

Display a copy of the periodic table.

ductor

Where on

the periodic table are meelements found? (To the left of the zigzag line that appears on the right side of the table.) • Where are nonmetallic elements tallic

found? (To the

112

right of the zigzag line,

to explain that

move

electrical con-

defined more precisely as a ma-

terial that

permits electrical charges to

Emphasize that at normal temperatures, no metal is a perfect conductor; some resistance still impedes the easily.

flow of electric charge.

•

What happens to the electrical energy

is blocked by resistance as it flows through a wire? (It charges into heat en-

that

erg\-.)

heat and electricitv.

FOCUS/MOTIVATION •

of metals

one of the propthe ability to conduct that

Point out that this is why wires and other current-earning devices often feel the electricity impeded bv resisthot

—

ance is lost as heat. Continue the discussion bv asking students the following questions:

How is a superconductor different from an ordinary conductor of electric-

•

—

Sbitnut, itbnnuLUbT h aubitn

To cool materials to such extremely low temperatures, scientists had to use liquid helium, which is very costly. The supercold superconductors were just too expensive to

Additional Questions

and Topic Suggestions 1.

costs as

little

expensive than milk or soda. But what substances might become superconductors at these relatively high temperatures? That was the problem Dr. Mueller and Dr. Bednorz had to solve.

NEW DIRECTION

experts thought that superconductors simply did not exist at temperatures higher than -250°C. But Dr. Mueller, a highly respected physicist at IBM's research laboratory in Zurich, Switzerland, remained fascinated by high-temperature superconductors. In fact, he had already devised a new approach to finding one! To some, his idea seemed impossible. But Dr. Mueller and his partner Dr. Bednorz were wiUing to follow their unusual approach under the guidance of what Dr. Mueller de-

"my

intuition."

Mueller thought the oxide looked promising. They decided to test it for superconductivity. On January 27. 1986, Dr. Mueller and Dr. Bednorz broke the temperature barriand broke it by a er to superconductivity

(A superconductor has no

conduct heat.

(Scientists

conductivity.) 2.

Find out which elements are superThen make a copy of the pe-

conductors.

may seam to be jdefying gravity. Actually, it is floating above a disic made of a superconductive material. The superconductive disk repels magnetic fields and causes the magnet to

riodic table

JA Thif magnetic disk

the textbook. Using in the

elements

that are superconductors.

Find out about the research on superdone in 1933 by VV. Meissner and R. Ochsenfeld. Also find out

float in midair.

They achieved superconduc-243°C. By April. Mueller and Bedtemperature of the raised norz superconductivity to a new record, -238°C. Around the world, scientists began to duplicate the experiments and make even high-temperature advances in greater superconductors. In February 1987. a team of researchers at the University of Houston led by Dr. C.W. Chu created a new oxide that shows superconductivity at -175°C. This is the first superconductor that can be cooled with liquid nitrogen the first superconductor that might be used for everyday purposes. Mueller and Dr. Bednorz received the Dr. 1987 Nobel Prize for Physics for their pioneering work on superconductors. Their work, however, does not end here. They look forward to the development of a roomtemperature superconductor!

found

colored pencils, shade

conductivity

what aspect of superconductivity ferred to as the Meissner Effect.

large amount. tivity at

re-

Thinking Questions you think superconductivity occurs at such low temperatures? (Ac-

Critical 1.

resist-

Why do

cept

all

logical answers. Relevant to the

question

may be

solute zero,

—

the fact that 0°K, or ab-

the temperature at which

all

molecular motion ceases.)

What would be some advantages of

superconductor that could function at rooin temperature? (Accept all logical answers.)

l^x^}^~:^^.J%^s^,f:<^/^t::!-xmfr^^^^;:<^^ll^^

ity?

superconductivity affects a materiability to

had

For almost three years, the two scientists mixed powders, baked them in ovens to form new compounds, and then chilled them to see if they would lose their resistance to electricity. And for three years, the two scientists kept their work a secret. "We were sure anybody would say, 'These guys are crazy,' Dr. Bednorz later said. But despite endless hours of hard work and dedication, none of the new compounds was the superconductor Mueller and Bednorz sought. Then in December 1985, Dr. Bednorz read about a new copper oxide. He and Dr.

—

how

conduct heat than usual and that at very low temperatures, the ability to conduct heat approaches zero. This is contraiT to what happens in the nonsuperconductive state, in which high electrical conductivity is accompanied by a high heat

Many

scribes as

conduct electricity also conduct Use reference sources to find out

have found that materials in superconductive state generally have less ability to

as a nickel a liter

IN A

heat.

al's

less

LOOKING

L'nder iioiinal tondilions, materials

ihat

be of general use. If a substance could become superconducting at -196°C or higher, then it could be cooled with liquid nitrogen. Liquid nitrogen

ISSUES SCIENCE ELECTRICITY; CURE-ALL IN

OR END-ALL? Background Information Since Xancv Wertheimer published her study on the possible link bet^veen exposure to electromagnetic waves and cancer in 1979. a large number of researchers have also studied the possible link. Most studies show that there is a

Ml time. But long-term exposure to levels of

conelation between exposure to extremeh low frequencv fields of electromagnetic waves and particular cancers

such as leukemia and brain cancer.

Some

may exist between the incidence of miscarriages or the birth of babies with abnormalities and exposure to the electromagnetic waves by pregnant women. None of the studies shows a cause-and-effect link. It seems likely that electromagnetic waves do have a biological effect, but researchers have not identified what the effect is. There is no concorrelation

clusive evidence available that the effect

^'^/^K'i- the string. The shork they received by touch g the key proved that the hghtning's charge was conducted through the string and into the metal key. But could Franklin have imagined the impact of his discovery? The modern world of electric appliances, computers, stereos, washing machines, air conditioners, healers, and more has been built upon his insight. In fact, much of society has come to rely on electricity for most of its needs. Electricity seems like the perfect symbol of the answer to every modern technology

—

hannful to health. Some researchers suggest that the waves ma} reduce the

need.

trict to

close the school because lines.

forced a

utilitv

it is

may have harmful

rent is

number

biological effects.

not the danger of the electric current

>elf that

It it-

has people worried. Rather, it is produced by cer-

the electromagnetic fields

tain le\els of electric current in sources such as i

one

household wiring, and elecappliances. Such emissions are referred

power

trie

to as

lines,

electromagnetic radiation. In particu-

there are suggestions that there is a link between exposure to these electromagnetic

lar,

Florida school ha\ e sued the school dis-

power

is it?

In recent vears. an increasing

among

the public. Parents of students at

scientific reports suggest that electric cur-

amount of melatonin, a hormone that mav prevent the growth of some cancers. The possible correlation between cancer and exposure to electromagnetic waves from electrical wires and electrical appliances has caused concern

high intensity are rare. Concern over dangers caused by low levels of electrti

near

fields

Houston school district companx to remove lines

and incidents of cancer.

A connection between

high levels of elec-

tromagnetic radiation and harmful biological effects has been recognized for quite some

that ran close to schools in the district.

magnetic radiation, which began in the lat 1970s, created new fears, \irtually dustrialized populations are commonh exposed to such levels of electromagnetu radiation.

The subject came under close scrutinv when Nancy Wertheimer. an epidemiolosi-t (scientist who studies diseasesl. set out study the homes of children who had ili.

in a Colorado neighborhoinl in order to establish some connection. To hi

from cancer

surprise, she found a statistical connecti"ii

between childhood cancers and exposure

high-current power lines. Wertheimer's work heralded a series of investigations and a bitter controversy. A similar study in the Colorado area supports her general conclusions, as did another stud

conducted in Europe. Several other researih projects went on to show that workers reg ularly exposed to strong electromagnetii

—

electricians, power-station operators, telephone line workers developed and died from leukemia, brain cancer, and brain tu mors at significantly higher rates than work

fields

ers

—

other

fields.

These

studies

also

suggested a link between exposure to elec tromagnetic fields and low-grade illnesse: such as fatigue, headaches, drowsiness, and

nausea. Additional studies showed a link b< tween the use of electric blankets and mi carriages ilost pregnancies 1.

Citizens can take precautions that help to

reduce exposure to electromagnetic wa\es given off bv appliances. The\' can sit

at least 3 feet

from

their televisions;

thev can keep their clock radios and

other appliances their

at least

•

a few feet from

TEACHING STRATEGY:

heads when they are sleeping.

ISSUE

dents

ances, such as electrical blankets, televi-

•

and can open-

or pictures of them.

What do

these have in

gers

from electromagnetic radiation

the appliances give .\fter

common?

(.\11

article

that

off.)

reading the

article, ask

are operated with electricitv.)

114

be aware that the operation of is danger-

ous: few will be aware of the possible dan-

Display a varietv of electrical applisions, hair dryers, toasters,

will

these appliances near water

FOCUS/MOTIVATION

ers,

Are there anv dangers associated with

the use of these appliances? (Most stu-

title

of the Gazette

students what the\ think the

about.

{

SCItNUt:,

ItUnNDLUbT & SUUItIT

Prolonged exposure to electromagnetic fields, a hazard of certain jobs, may be related to a high incidence of brain tumors. The gamma image shows a brain with a tumor.

Additional Questions

and Topic Suggestions 1.

Louis Slesin publishes the Microwave

News, a bimonthly newsletter that reports stories

on electromagnetism.

If possible,

obtain a copy of an issue. Based on the articles,

what do you think

Slesin's po-

sition in the controversy?

between cancer and is proved, what do you think should be done? How might our lifestyles be changed? 3. Research information about electromagnetic waves. What are they? What is the difference between extremely low fiecjuency fields and very low frequency 2.

If a correlation

electromagnetic waves

fields?

Find out what position the Environmental Protection Agency has taken on the controversy by writing for information from the agency or by researching

The electromagnetic fields in the area surrounding these high-voltage power lines are strong

enough

Some

magazine

articles in a library.

to light the fluorescent bulbs.

of these studies

and

their related

have prompted electric companies to reroute their wiring and change the transformers. Often, howof their location

the

ever, cases regarding electromagnetic radi-

fields

hazards have been dismissed or postponed due to lack of clear evidence. De-

tics'

spite the seriousness of the issues, the re-

tists

search found to date does not prove a clear, direct link between electromagnetic radiation and cancer. For this reason such findings have not convinced everyone in the scientific and medical communities, the nation's courts, or those in industry of the possible dangers of electromagnetic fields. Skeptical researchers and judges complain that the studies lack scientific foundations, and that they show only a statistical link. Critics say that they need to see actual proof of a cause-and-effect relationship between

show how electromag-

legal battles

electromagnetic

and illness. To meet the skep-

ation

challenges, scien-

In addition, scientists are also trying to

discover the actual mechanisms by which

that

>7i>tiv^/:ii.<v="ii\v^:c^^.i^^?-:/4^r^v.^^

0, > ""

xviv

.115

=//;

u MSV^

who developed

Have students list the electrical appliances that they and their families use during a typical day. After the list is comstudents

actually

and harm human cells. Researchers have found that exposure to electromagnetic fields actually promotes faster growth of cancer cells that are more resistant to anticancer drugs. Other studies indicate that exposure to electromagnetic fields inhibits human production of melatonin, a cancerinhibiting hormone.

CONTENT DEVELOPMENT

tell

trying

fields

affect

11 -^^

piled,

are

netic

all

electrical

cancer, an alarm was sounded. Children exposed to electromagnetic fields because of the location near power lines were developing cancer at about 2.5 times the rate of other chil-

The study

indicated a correlation

appliances and electrical wires emit an

dren.

field of radiation. In the was no concern about possible risk from exposure to the electromagnetic field emitted by appliances and high wires. Beginning, however, with a

between incidence of childhood cancer and exposure to electromagnetic fields. Since the initial study, conducted by Nancy Wertheimer, other studies have supported the findings and have linked the incidence of certain diseases and

electromagnetic past, there

late

1970s study of children

Colorado

to electromagnetic however, do not show

problem pregnancies fields.

The

studies,

cause-and-effect

relationship.

Some

scientists claim that the incidents are co-

incidental; others suggest that the re-

search data cannot be attributed to coincidence.

The

issue

continues

debated, and researchers are to find out

still

tt)

trying

whether or not elediomag-

netic fields are responsible for harmful effects

on human biology.

115

-v^^,

tT ' vn^'TV 1 tnr rr

Class Debate

Numerous

research studies have not

proven that the

effects of

exposure to

electromagnetic waves are harmful. Research money is limited, and research studies are time consuming.

Have

stu-

dents consider other research needs, for

example, finding cures for diseases such as cancer and multiple sclerosis. Then have students debate whether research

money should be

allocated for continued

research on the effects of exposure to

electromagnetic waves or not.

Low-level electromagnetic fields are created by common electrical devices such as hair dryers, electric blan-

kets,

and computers. Whether or not

these fields are dangerous

yet to be

proven.

magnetic magnetic electromagnetic fields do their damage. They are focusing on the effect of electromagnetic fields on the flow of ions into and out of

of electromagnetic radiation becomes increas-

on and society reelectric components produce electromagnetic radiation. Until answers and resolutions to the problem are found- we shall continue to use and rely on electricity to assist and enhance our lives. .\nd in one sense, we shall continue to be human guinea pigs in an unresolved scien-

ingly serious as time goes

that

membrane

about the possible detrimental effects of exposure to electromagnetic fields is sponsored or conducted by the Electric Power Research Institute, an agency funded by the nation's utility companies. Ask students to consider whether the association with the utility companies may bias the findings of the institute.

CONTENT DEVELOPMENT Although it has not been established that exposure to electromagnetic fields is dangerous to humans, many people reccertain

116

that

some people recpeople reduce their use of

taken. For example,

ommend

precautions

an increased

and membrane. Othunder certain con-

possibly damaging the cell

ENRICHMENT Much of the research being conducted

that

lies

rate, thus leaving the cell too quickly

er research suggests that

ommend

ditions,

the

interaction

the

ions in the

membrane

quency) with ions already present in the cell. Such vibration causes the valuable ions to pass through the

unnatural electro-

may knock

Some experiments have shown that the fields may resonate (vibrate at the same fre-

cells.

ISSUE (continued)

fields

out of place. This disrupts cell functioning, perhaps leading to illness. The controversy over the safety or threat

cell

field with

Earth's

tific

more and more on

experiment.

^1 y^^^iai?s{v^^m^^::::/^j^'}i>i7iK^v7^:;~f\

electric blankets.

They

say that the blan-

used to warm up the bed before you get into it and then turned off. Others say it would be even better if the electric blanket were given up and that people should use quilts or other ket should be

blankets instead. â&#x20AC;˘

How

else can people

minimize expo-

sure to electromagnetic forces? swers will van.)

(.An-

How might the concern about exposure to electromagnetic waves affect the

â&#x20AC;˘

property values of homes near

electri-

and transmitters? (Property \alues may drop because people will be hesitant to buy homes in areas that may cal

lines

present a health

risk.)

INDEPENDENT PRACTICE Activity Booli

After students have read the Science article, you may want to hand out

Gazette

the reading

skills

worksheet based on the

article in the Activity Book.

|f plfp^lf^i^ii

U7UR

n c

FUTURES IN

onda and her family

lived in

The Computer That

a spare settlement on Pluto.

One day.

a strung; radiation

storm swept across the PurMountains of their planet. There had been many such storms on the planet in the year 2101. The module in whioh Ronda and her family lived had heen directly in the path of the storm. Somehow, radioactive dust penple

module. .4s a result. Ronda was blind. Radiation had destroyed the nerves that carried the electrical signals from Ronda's eyes to her brain. Her brain could no longer interpret what her eyes were "seeing

LIVES!

in the

clearly."

Months after the storm. Ronda sat nervously in a plush armchair in the waiting room of Venus General Hospital. Today was the day the bandages would be removed from her eyes. Ronda was terrified that the operation to restore her sight might have been a failure.

She did not want

rely

seeing-eye robot for the rest of her

messages her brain could understand. The computer was designed to work exactly like the eye nerves that had been destroyed. The bandages fell from Ronda's eyes. She could see! The living computer inside her head had restored her sight.

life.

vision center in the brain

LIVES!

p)ossible

TIME MARCHES ON Today

eye to the brain. Light enters the pupil of the eye and passes through the lens.

com-

puters will be a reality in the not-so-distant Living computers. like the one in

future.

Ronda's brain, require no outside power source and never need to be replaced. To understand how living computers may be possible, let's look briefly at how computers have evolved since the 1800s.

image then forms on the retina, which is at the back of the eye. The retina contains light-sensitive cells that produce nerve impulses that travel along the optic nerves to the vision center of the brain. In the vision center, the images are in-

and the person "sees." any part of the three compo-

terpreted,

— — are impaired, the

nents of sight

scientists believe that living

and on the

optic nerves that relay images from the

When

on a

As the doctors removed the bandages. Ronda thought about the computer that had been implanted in her brain. No larger than a grain of rice, the computer was programmed to record all the images Ronda's eyes picked up and then translate them into

Background Information Human sight is not made

the eyes alone; sight also depends on the

etrated the sealed glass that served as win-

dows

SCIENCE

THE COMPUTER THAT

sion center see

is lost.

eye, optic nerves, or

The

in the article

living

vi-

ability to

computer described

taking the place of optic

nerves that have been destroyed by radiation.

Relevant to the concept of a living

computer computer

the present-day use of a

to help a paralyzed girl walk

again. In 1983, Dr. Jerrold Petrofsky de-

vised a system in which a high-speed

com-

puter delivered tiny shocks to the leg muscles of a girl who had been paralyzed for five years.

The computer

controlled

the firing of impulses in just the right

order to make the

girl's

tinv sensing devices

on her

muscles work; legs told the

computer what the muscles were doing. Dr. Petrofsky hopes someday to make the system small enough to be put inside the

human

TEACHING STRATEGY: FUTURE FOCUS/MOTIVATION Begin by asking students the following question:

What makes it possible for you to see? (Answers may vary. Most students will probably say their eyes.)

•

CONTENT DEVELOPMENT Continue the discussion bv explaining to students that sight is not made possible by the eyes alone; the eyes can only pick up images. In order for a person to see,

the images

formed

the back of the eye

(on a part of the eye called the retina) must be relayed to the vision center of the brain via optic nerves.

The images are

•

body.

According

to the article,

what part of

the sight process was disrupted for

Ronda?

(Tlie part in

which images are

re-

layed to the brain.)

Why could images from Ronda's eyes no longer be transmitted to the brain?

•

(Her •

opli( nerves

What made

had

lieen destroved.)

possible for

Ronda

see again? (A tiny computer that could

interpreted in the vision center, and the

function

person "sees."

her biain.)

.is

optic nerves was implanted in

117

Additional Questions

and Topic Suggestions 1. Space colonies may be tion in the future.

you want to

Does

live in a

make

space colony?

or why not? (Accept students

a lifestyle op-

this stoiy

all

answers.

Why

Some

may be wan' of radiation storms may be

that could cause blindness; others

intrigued by the possibility of traveling to other planets and living in a strange world.) 2.

Find out more about ways in which

bacteria break

down

substances.

Two

you might research include the importance of bacteria in soil and the topics that

role of bacteria in foods such as yogurt. 3.

Why

soning

might creative thinking and reaability

be possible with a "living

computer"? (Accept all answers. A logical answer is that because reasoning and creative thinking are functions of hu-

mans, a computer made of living substances might more closely resemble the

human

brain.)

SCItniDt,

ItUHNULUbf &:ÂťULItlf Critical every minute of every day. Some scientists

can

spei'ial

molecules.

These

m.decules.

when mixed er.

i-ould

the

flow

will

make

"taufiht"

lives

Today/ thousands of transistors are packed onto a silicon chip. \

A complex network

tein molecules, such as the

one

drawing,

in this

of pro-

may be

rontrol

needed to make computer.

diation storm that swept across the space

Of course,

colony?

teria

bac-

cannot

vary.

taught in the same people sense that

tensive

of the most popular current ideas concerning how these molecules could be pro-

duced are

is:

all

Let bacteria do

around

us.

for us! Bacteria

They constantly break

many

There are new techniques available that allow scientists to combine two different types of bacteria to produce a third, totally dif-

down

very complicated chemicals into molecules. Bacteria are at work in our bodies,

our food, and

may

our environment

pro-

i /J

molecules. These bacteria could be grown container and fed a particular

in a special

substance to produce certain molecules. If the molecules could be told, or programmed, to do the right things, you would have a computer. And the computer would actually be alive because the bacteria would live. grow,

and produce molecules inside their container. Think about the living computer implanted in Ronila's brain, which allowed her to see again. Remember that bacteria need food to make molecules. Suppose that the computer in Ronda's brain was fed by her own

"/A

bl If

this

like all the

other

cells in

and long-ieim damage;

can

what unrealistic because no mention is made of the damage caused to other members of Ronda's family or of the long-term effects of ladiaiion contami-

In terms of a living computer, imagine that some bacteria have been taught to make special

may

realize that ra-

many other physical impairments and even death. The stoiT is also some-

before.

One

may

cause

can nowunusual ways.

duce chemicals that have never been seen

TO BACTERIA

or why not? (Answers

students

diation contamination usually causes ex-

ver, scientists

ferent, type. In the future, bacteria

LEAVE

Why

Some

learn." How. bacteria

Ron-

da's blindness be the only result of the ra-

can. Bacteria are not Millie

this story

totally realistic in letting

ele.tri

the electrical switches in com- t, puters of the future. I

than today's lomputfr could stort- in an i-n lire roomrni of chips. As you can iniapinc. the molecules in this computer of the future would have to he pretty special. And they would have to be produced in a new way.

you know

be a normal activity? (Ronda, who on Pluto, goes to a hospital on

was being

produce

citv \

aspt-ci oliliis sti>n k-ts

Venus for ireatinenl.) 2. Do you think the authoi of

tog(*th-

Thinking Questions

What

thai in llie fiiluif, intcipianetaiy travel

that

feel

bacteria

nation on the space colony.) 3. What possible hazards can be associated with the area of implanting a computer in the human brain? (.Answers may

An obvious answer is the possibility of the body's rejecting a foreign subvaiT.

stance.)

her body.

were the case. Ronda's computer

live as long as Ronda herself. may be many years before the

would It

Ronda's new computer in

place of nerves

living

computer becomes a reality. Scientists must learn more about such things as how molecules react together and how they can be programmed. But many scientists await the day when they can look at a computer and sav. "It's alive."

*//

.^^\ili^:^^^^^^ l:^^^^Xij:li^:^?.:;^ll^^

GUIDED PRACTICE Skills Skill:

Development Making diagrams

Have students make creative diagrams show how computers have changed in size since the 1800s. Have students into

clude the tiny coinputer described in this article as part of the diagiam. Students

may wish to do additional research If) find out more about the actual appearance and dimensions of the computers that are described in this article.

ENRICHMENT Encourage interested students to study the mechanisms of other physiosuch as digestion, hearing, and locomotion. Challenge students to consider how living computers might

logical functions,

be able to restore these functions should become impaired.

they

INDEPENDENT PRACTICE ^ Activity Book After students have read the Science article, vou may want to hand out

Gazette

the reading

skills

woi ksheet based on the

article in the Activity Book.

or Further

Reading

you have been intrigued by the concepts examined in this textbook, you may also be interested in the ways fellow thinkers novelists, poets, If

—

essayists, as well as scientists

imaginatively explored the

Chapter

Electric

— have

same

ideas.

Chapter

Charges and Currents

Cosner, Sharon. The Light Bulb: Inventions that Changed Our Lives. New York: Walker. Franklin, Benjamin. Autobiography of Benjamin

New York: Airmont. Mary. Frankenstein. London, England:

Franklin.

Shelley,

Silverstein, Shel.

Chapter

Light in the Attic.

New

York:

& Row.

Magnetism

New York:

Barron.

Clark, Electra. Robert Peary: Boy of the North Pole.

New York: Macmillan. Clarke, Arthur C. The Wind from the Sun: Stories of the Space Age. New York: New American Library. Mason, Theodore K. Two Against the Ice: Amundsen and Ellsworth. Spring Valley, NY: Dodd, Mead. Vogt, Gregory. Electricity and Magnetism. New York:

Watts.

Ellis, Ella

Electromagnetism

T. Riptide.

New York:

Macmillan.

Evans, Arthur N. The Automobik. Minneapolis,

MN:

Lerner Publications. Thomas Edison Alexander Farr, Naunerle C. Graham Bell. West Haven, CT: Pendulum Press. Mazer, Harry. When the Phone Rang. New York:

—

Scholastic.

Snow, Dorothea

New York:

120

New American Francis,

Library.

Dorothy.

Computer Crime.

Samuel Morse: Inquisitive Boy.

Macmillan.

A Day Mahwah, NJ:

Trainer, David. Reporter.

Averons, Pierre. The Atom.

Chapter

and Computers

New

York:

Lodestar.

Penguin.

Harper

4: Electronics

Chetwin, Grace. Out of the Dark World. New York: Lothrop, Lee & Shepard Books. Clarke, Arthur C. 2007; A Space Odyssey. New York:

in the Life of a Troll.

TV News

ppendix

THE METRIC SYSTEM 1

100mm

The

metric system of measurement is used by throughout the world. It is based on units often. Each imit is ten times larger or ten times smaller than the next unit. The most commonly used units of the metric system are given below. After you have finished reading about the metric system, try to put it to use. How tall are you in metrics? What is your mass? What is your normal body temperature in degrees Celsius? scientists

Commonly Used The

Length

distance from

1 1

one point

object takes

= 1000 miUiliters (mL,)

A gram

clip.

1000 grams =

Temperature

object

has a mass equal to about

one paper

kilogram (kg)

The measure of hotness or coldness

degrees

0°C = freezing point of water

Celsius (°C)

100°C = boiling point of water

Metric-English Equivalents 2.54 centimeters (cm) = 1 inch (in.) 1 meter (m) = 39.37 inches (in.)

kilometer (km) = 0.62 miles (mi) Hter (L) = 1.06 quarts (qt) 250 milliliters (mL) = 1 cup (c) 1 1

a yard.

kilogram (kg) = 2.2 pounds grams (g) = 1 ounce (oz)

28.3

°C = 5/9x(°F-32)

TRIPLE-BEAM BALANCE

kilometer (km)

The amount of matter in an (g)

Beams

another

A liter is slightly more than a quart. 1 liter

Mass

The amount of space an

liter (L)

gram

meter = 1000 millimeters (mm) meter = 100 centimeters (cm)

1000 meters =

Volume

Riders

Metric Units

A meter is slightly longer than

meter (m)

METRIC RULER

(lb)

210^

ppendix

LABORATORY SAFETY Rules and Symbols

Glassware Safety Whenever you see this symbol, you 1 know that you are working with .

glassware that can easily be broken. Take particular care to handle such glassware safely. And never use broken or chipped glassware. 2.

Immediately rinse with water any chemicals, particularly acids, that get on your skin and clothes. Then notify your

6. will

Never heat glassware that is not thoroughly dry. Never pick up any glassware unless you are sure is not hot. If it is hot. use heat-resistant gloves. Always clean glassware thoroughly

teacher.

1 -%

<S>

Eye and Face Safety Whenever you see this symbol, you 1 know that you are performing an experiment

before putting

away.

Whenever you see this symbol, you know that you are working with fire.

Sharp Instrument Safety Whenever you see this symbol, you will know that you are working with a sharp

—

instrument. 2.

container.

Never reach across a flame. Always use a clamp, tongs, or heat-

Always maintain a clean work area,

resistant gloves to handle hot objects.

particularly

when

Whenever you see this symbol, you know that you should put on heat-

will

II ~

instructed to

Never mix chemicals unless instructed do so. Never touch or taste any chemical unless instructed to do so.

when chemicals

Keep

all lids

not

use. Dispose of

closed

all

chemicals as

instructed by your teacher.

122

are

Never touch an electrical appliance or wet hands.

outlet with

Animal Safety

so.

to 4.

Never use long extension cords to plug in any electhcal device. Do not plug too many appliances into one socket or you may overload the socket and cause a fire.

—

when

Whenever you see this symbol, you will know that you are using electricity in the

will

chemicals that could be hazardous. Never smell any chemical directly from its container. Always use your hand to waft some of the odors from the top of and the container toward your nose only

is cut.

laboratory. 2.

hands.

toward you: always cut away from you. Immediately notify your teacher if your

Electrical Safety

resistant gloves to avoid burning your

Chemical Safety 1. Whenever you see this symbol, you know that you are working with

Always use single-edged razors; double-edged razors are too dangerous. Handle any sharp instrument with extreme care. Never cut any material

skin

using a flame.

Heat Safety

are heating a test tube or always point it away from you and others. Chemicals can splash or boil out of a heated test tube.

will

Never use any source of fire without wearing safety goggles. Never heat anything particularly unless instructed to do so. chemicals Never heat anything in a closed

—

When you bottle,

Fire Safety 1.

which you must take

precautions to protect your eyes and face by wearing safety goggles.

will

Whenever you see this symbol, you know that you are working with live

will

animals. 2.

Do to

not cause an animal.

pain, discomfort, or injury

Follow your teacher's directions when Wash your hands

handling animals.

thoroughly after handling animals or their

cages.

ppendix

SCIENCE SAFETY RULES your teacher about the proper cleanup procedure. Never simply pour chemicals or other substances

One

of the

first

things a scientist learns

into the sink or trash container. is

that

working in the laboraton' can be an exciting experience. But the laboratory can also be quite dangerous if proper safety rules are not followed at all times. To prepare yourself for a safe year in the laboratory, read over the following safety rules. Then read them a second time. Make sure you understand each rule. If you do not, ask your teacher to explain any rules you are unsure of.

Never eat

in the laboratory.

Wash your hands before and

10.

after

each ex-

periment.

First 11.

how 12.

such

Aid

Immediately report all accidents, no matter minor, to your teacher. Learn what

as getting acid in

in case of specific accidents,

your eyes or on your

skin.

(Rinse acids from your body with lots of water)

Become aware of the location of the first-aid But your teacher should administer any required first aid due to injury. Or your teacher may send you to the school nurse or call a physician. 14. Know where and how to report an accident or fire. Find out the location of the fire extinguisher, phone, and fire alarm. Keep a list of important phone numbers such as the fire department and the school nurse near the phone. Immediately report any fires to your teacher 13.

kit.

Dress Code 1. Many materials in the laboratory can cause eye injury. To protect yourself from possible injury, wear safety goggles whenever you are working with

chemicals, burners, or any substance that might get into your eyes.

Never wear contact lenses

in the lab-

oratory. 2. Wear a laboratory apron or coat whenever you are working with chemicals or heated sub-

â&#x20AC;&#x201D; â&#x20AC;&#x201D;

Heating and

Fire

Safety

stances. 3.

Tie back long hair to keep

away from any

chemicals, burners and candles, or other labora-

16.

tory equipment. 4.

Remove or

tie

back any

jewelry that can hang

article

of clothing or

down and touch chemicals

and flames.

General Safety Rules 5.

Read

all

directions for an experiment several

times. Follow the directions exacdy as they are writ-

you are in doubt about any part of the experiment, ask your teacher for assistance. 6. Never perform activities that are not authorized by your teacher Obtain permission before "experimenting" on your own. 7. Never handle any equipment unless you have specific permission. 8. Take extreme care not to spill any material in the laboratory. If a spill occurs, immediately ask ten. If

15. Again,

never use a heat source, such as a can-

dle or burner, without wearing safety goggles.

Never heat a chemical you are not instructed

A chemical that is harmless when cool may be dangerous when heated. 17. Maintain a clean work area and keep all materials away from flames. 18. Never reach across a flame. to heat.

19. Make sure you know how to light a Bunsen burner (Your teacher will demonstrate the proper procedure for lighting a burner) If the fiame leaps out of a burner toward you, immediately turn off the gas. Do not touch the burner It may be hot.

And

never leave a lighted burner unattended! When heating a test tube or bottle, always point it away from you and others. Chemicals can splash or boil out of a heated test tube. 21. Never heat a liquid in a closed container The expanding gases produced may blow the container 20.

apart, injuring

you or others.

123

Before picking up a container that has been first hold the back of vour hand near it. If vou can feel the heat on the back of vour hand, the container mav be too hot to handle. Use a clamp or tongs \shen handling hot containers. 22.

heated,

pear hot. Never pick up glassware uiihout checking to see if it is hot See #22. 33. If

vou are instructed

first

to cut glass tubing, fire-

polish the ends immediatelv to

remove sharp

edges.

Never use broken or chipped glassware. If vour teacher and dispose of the glass\\'are in the proper trash container 35. Never eat or drink from laboratorv gla5s%\'are. Thoroughh- clean glass^v'are before putting it awav. 34.

glass^vare breaks, notify-

Using Chemicals Safely 23. Never mix chemicals for the "fim of it." You might produce a dangerous, possibh' explosive sub-

stance. 24. Never touch, taste, or smell a chemical unless vou are instructed bvvour teacher to do so. Manv chemicals are poisonous. If vou are instructed to note the fumes in an e>q)eriment. gendv wave vour hand over the opening of a container and direct the fumes toward vour nose. Do not inhale the fumes direcdv fi-om the container. 25. Use onlv those chemicals needed in the acmiv.: Keep all lids closed when a chemical is not being used. Notify' vour teacher whenever chemicals are spilled.

26. Dispose of all chemicals as instructed

bvvour

teacher To avoid contaminauon. never return chemicals to their original containers. 27. Be extra careful when working \%iih acids or bases. Pour such chemicals over the sink, not over

vour workbench. 28. When diludng an acid, pour the acid into \sater. Ne\"er pour \\ater into an acid. 29. Immediatelv rinse ^dth water anv acids that get on vour skin or clothing. Then notify %our teacher of anv acid spiU.

Using Sharp Instruments 36. care.

Handle scalpels or razor blades wth extreme Never cut material tow^ard vou: cut awav from

vou.

37. Immediatelv notih" your teacher if vou cut our skin when working in the laborator%.

Animal Safety 38. fort,

No or

experiments that

harm

\rill

mammals,

cause pain, discom-

birds, reptiles, fishes.

and amphibians should be done in the classroom or at home. 39. .\nimals should be handled onlv if necessar%". an animal

feeding, or \rith

excited or frightened, pregnant, its

voung. special handling

re-

quired. 40. Your teacher \dll instruct vou as to how to handle each animal species that mav be brought

into the classroom. 41. Clean vour hands thoroughlv after handling animals or the cage containing animals.

Using Glassware Safely 30. p>er.

Never force

glass tubing into a

rubber stop-

when

inserting glass tubing into rubber stoppers or rubber tubing. Your teacher mU demonstrate the proper wav to insert glass tubing. 31. Never heat glass\N-are that is not thoroughlv drv. Use a wre screen to protect glassware from anv flame. 32. Keep in mind that hot glassivare \'.i\\ not ap-

124

End-of-Experiment Rules

A turning motion and lubricant \\ill be helpful an experiment has been completed, up vour work area and renirn all equipment

42. -\fter

clean

proper place. hands after everv experiment. 44. Turn off all burners before lea\ing the laboratory-. Check that the gas Une leading to the burnto

its

43. ^^'ash vour

off as well.

Glossary alternating current: current in which the elections reverse their direction regiilarh

amplifier: device that increases the strength of an electric signal

atom: smallest part of an element that has all the properties of that element aurora: glowing region of air caused by solar particles that break through the Earth's magnetic field battery: device that produces electricity by converting chemical energy into electrical energ)-; made up of electrochemical cells binary system: number system consisting of only two numbers, and 1, that is used by

computers bit:

motor: device that uses an electromagnet convert electrical energy to mechanical energ\ that is used to do work electromagnet: solenoid with a magnetic material electric

single electronic switch, or piece of information

make up a byte \acuum tube that uses

such as iron inside its coils electromagnetic induction: process by which a current is produced b\ a changing magnetic field

electromagnetic wave: wave made up of a combination of a changing electric field and a changing magnetic

field

electromagnetism: relationship between electricir\' and magnetism electron: subatomic particle with a negative charge found in an area outside the nucleus of an atom electronics: study of the release, behavior, and

byte: string of bits; usuallv 8 bits

control of electrons as

cathode-ray tube: t\pe of

practical devices

on a screen computer that controls the operation of all the other components of the computer electrons to produce an image

central processing unit: part of a

charge: physical propert}' of matter that can give rise to

an electric force of attraction or

repulsion

chip: thin piece of silicon containing an integrated circuit circuit:

electricity

can flow circuit from becoming overloaded conduction: method of charging an object by allowing electrons to flow through one object to another object conductor: material which permits electrons to

freeh'

current: flow of charge

diode:

vacuum tube or semiconductor

that acts as

a rectifier

one direction computer that can

push or pull on an object opposes motion that is exerted when t\vo objects are rubbed together in some way fuse: thin strip of metal used for safety because when the current flowing through it becomes too high, it melts and breaks the flow of force:

friction: force that

galvanometer: de\ice that uses an electromagnet to detect small amounts of current generator: device that uses electromagnets to convert mechanical energv' to electrical energ^ hardware: phvsical parts of a computer induced current: current produced in a wire exposed to a changing magnetic field induction: method of charging an object by rearranging its electric charges into groups of positive charge and negative charge input device: device through which data is fed

computer

insulator: material

bound

that flow constantly in

act as

input de\ice by reading information off a disk and entering it into the computer or as an output device removing information from a

computer and storing it on a disk doping: process of adding impurities to semiconducting materials electric discharge: loss of static electricity as electric charges move off an object electric field: area over which an electric charge exerts a force

electroscope: instrument used to detect charge

into a

direct current: current consisting of electrons disk drive: part of a

relates to use in

electricitv'

complete path through which

circuit breaker: reusable device that protects a

flo\\'

made up

of atoms with tightly

electrons that are not able to flow freely

integrated circuit: circuit consisting of many diodes and transistors all placed on a thin piece of silicon, known as a chip magnetic domain: region of a material in which the magnetic fields of individual atoms are aligned field: area over which the magnetic exerted magnetism: force of attraction or repulsion of a magnetic material due to the arrangement of

magnetic force

its

atoms

125

semiconductor: material that is able to conduct electric currents better than insulators but not as well as true conductors series circuit: circuit in which all parts are connected one after another: if one part fails to operate properly, the current cannot flow software: set of instructions, or program, a

magnetosphere: region in which the magnetic field of the Earth is found main memory: part of a computer that contains data and operating instructions that are processed bv the central processing unit device that changes electronic signals

modem:

a computer into messages that can be carried over telephone lines

from

computer follows solenoid: long coil of wire that acts like a when current flows through it

neutron: subatomic particle with no charge located in the nucleus of an atom Ohm's law: expression that relates current. voltage, and resistance: \' = I x R output de\1ce: part of a computer through which information is removed parallel circuit: circuit in which different parts are on separate branches; if one part does not operate properly, current can still flow through

magnet

solid-state device: device, consisting of semiconductors, that has come out of the study of the structure of solid materials static electricit}': mo\ement of charges from one object to another witirout further movement superconductor: material in which resistance is essentialh zero at certain low temperatures

thermocouple: device that produces electrical energ\- from heat energ\'

the others

dence that uses electrons emitted from a metal during the photoelectric effect to produce current pole: regions of a magnet where the magnetic photocell:

transformer: device that increases or decreases the \oltage of alternating current transistor: device consisting of three lavers of semiconductors used to amplifv an electric

effects are the strongest

potential difference: difference in charge as created bv opposite posts of a batterv power: rate at which work is done or energ\ is

signal

tvpe

triode:

vacuum tube used

for

amplification that consists of a wire grid as well as

used

its

electrodes

tube: glass tube, in which almost all gases are removed, which contains electrodes that produce a one-wav flow of electrons voltage: potential difference; energ\' carried bv

vacuum

proton: subatomic particle located in the nucleus of an atom uith a positive charge rectifier: de\ice that converts alternating current to direct current: accomplished bv a vacuum

charges that

tube or semiconductor called a diode resistance: opposition to the flow of electric

make up

a current

charge

Index -Auroras,

and electric motor, P69 and generators, P75-76 .\ltemators, P77 .\mpere (A) P25 Amplifiers. P90-91 operation of, P90-91 triode. P90-91 .Armature. P69-70 .Artificial intelligence, P105

.Automobile

Central processing unit, computers,

P57

.\ltemating current (AC) P30

Batteries,

starter,

P71

P23-24

dn and wet

P23 P23-24 potential difference. P24 Bell. .Alexander Graham. P97. P98 Bits. P106 operation

cells.

of.

126

of subatomic particles. P12 Chips, P93 Circuit breakers. P34 Circuits circuit safet)- features.

and

B\tes, PI 06

fuses.

P93-94 Cathode-rav tubes, P99-101 of color telerision. PlOO-101 and computers. PI 05

Calculators. structure.

operation

of.

P99-1 00 P97

Cellular telephones,

P34

P33-34 P32 parts of. P31-32 series circuit. P32 Color telerision, PlOO-101 Commiuator. P69-70 Compass, P54 household

.Atoms

and electricit), PI 2-1 magnetism smd atomic P50 parts of, P12 .Attraction, force of, P13 .Audiotape, P77-78

P104 Charge and force. PI

circuits,

parallel circuit.

Computers. P90. P93, P94,

7 23

Magnetic materials

Printers,

destroying magnetism of, P51 ferromagnetic materials, P49 permanent magnets, P50 temporary magnets, P50 types of, P49 Magnetic poles of Earth, P52-53

location of,

reversal of, P53,

Protons, charge

of,

P57

poles of magnet, P46-48 tape, PI 04 tape drives, PI 05 variation,

P54

P92-93

Public-address system, P91

Radar, P91 Radio, P93, P94, P96-97

operation of, P96-97 radio waves, P97 Radio waves, P58, P97 Receiver, telephones, P98

Record

player,

P77

P90 diode, P90

Rectifiers,

Magnetism definition of, P51

magnetic domain, P50 magnetic fields, P48-49 magnetic force, P56-58 magnetic lines offeree, P48-49 magnetic materials, P49-50 magnetic poles, P46-48 nature of, P50-51 Magnetite, P45 Magnetosphere, P57 Main memoiy, computers, P104 Maxwell, James Clerk, P95 Metals, as conductors, PI 7 Microscopes, P81 electron microscopes, P81 Modem, P106 Monopole, P47

P28-29 ohm as unit of, P28 symbol for, P28 and temperature, P28-29

Resistance,

Robots, P94, PI 05

and

electricity,

P37-38

of,

P12

Northern lights, P57 North Pole, P54 N-type, semiconductors, P92

Nuclear

energ)',

and magnetism, P58

Ocean-floor spreading, P59 Oersted, Hans Christian, P66-67

Ohm, P28 Ohm's

law,

equation

P29-30 P30

for,

Parallel circuit,

P32

Photocells, P24 Picture transmission, P99-101 cathode-ray tubes, P99-100

PlOO-101 magnetic fields

television,

Planets,

of,

P54

Poles of magnet, P46-48 magnetic poles of Earth, P52-53 Potential difference, P24, P27

Power definition of, P35 See also Electric power

128

m p

cellular telephones,

P97

fiber-opdc systems, P98 invention of, P97

P98 sound waves, P98 transmitter, P98 receiver,

PlOO-101 cathode-ray tubes, P99-101 color television, PlOO-101

Temperature, and resistance, P28-29 Temporarv magnets, P50 Tesla, Nikola, P76 Thermocouples, P24 of,

P24

uses of, P24

P92-93 P92 P93 Series circuit, P32 Sihcon, P92

Transistors,

definition of, P78 step-down transformers, P78,

step-up transformers, P78-79 uses of, P78-80

P93 construcdon of, P93 uses of, P93

p-type,

silicon,

Transmitter, telephones, P98 Triode, P90-91

Software, PI 06 Solar system, magnetic fields in,

UNIVAC,

P87, PI03

P54-55 Solar wind, P56-57 Solenoid, P67, P71 Solid-state devices,

Vacuum P91-93

advantages of, P91 semiconductors, P91-93 Solid-state physics, P91 transmission, P95-99 P95 and electromagnetic waves, P95 radio, P96-97 telephone, P97-98 Sound waves, telephones, P98 Southern lights, P57 Static elecu-icity, P15-22 conduction, P17 definition of, P18 anddryair, P18-19 electric discharge, P19 formation of, P15-16 friction method of charging, PI 6 induction method, P18 and insulators, PI lightning, P19-21 Step-down transformers, P78, P80 Step-up transformers, P78-79 Stereos, P90, P93 early discoveries,

advantages of, P32-33 Permanent magnets, P50, P51

recorders, P91 Telephones, P97-98

Transformers, P78-80 construction of, P78

Sound

Optical scanners, P104 Output devices computers, PI 05 types of, PI 05

Tape

Seismometer, P78 Semiconductors, P91-93 doping, P92 germanium, P92 nature of, P92-93 n-type, P92

transistors,

Neutrons, charge

Superconductors, P29 Switch, of electric circuit, P32

operation Safety,

P54-55

field of,

sunspots, P55

Television, P79, P90, P93,

operation of, P90 Repulsion, force of, PI

Earth as magnet, P52-55

Sim magnetic

P-type, semiconductors,

AM and FM, P96

P54

magnetic variation, P54

Magnetic Magnetic Magnetic Magnetic

and computers, P105

tubes, P89-90, P91

invendon

of,

operation

of,

P89 P89-90

uses of, P90 Van Allen, James, P57 Van Allen radiation, P57

Videotape, P77-78 Voice synthesizers, P105 Voltage, P26-27 in animals, P27 in human body, P27

measurement

of,

P26

potential difference, P27 Volts (V),P26

Washing machine, P71 Watches, P94 Watts (W),P36 Wegener, Alfred, P59 X-rav machines, P79 X-rays,

Zinc,

P95-96

and

batteries,

P23-24

P80

Picture Archives; bottom Tony Stone Worldwide/Chicago Ltd 20 left G V .

Faint/Image Bank, nghi A d'Arazien/image Bank. 23 Paul Shambroom/Pholo Re-

Cover Background: Ken Karp Photo Research: Omni-Photo Communications. Inc Contributing Artists: Illustrations Warren Budd Assoc Ltd Geny Schrenk, Martinu Sctineegass Charts and graphs Function Thru Form Photographs: 4 top, Phil Degginger; bottom left Dennis Purse/Photo Researchers, Inc bottom nght Michael Philip Manheim: 5 lop Dr Jeremy Burgess/Science Photo Library/Pholo Researchers, Inc bottom NASA, 6 top Lefever/Grushow/ Grant Heilman Photography; center: Index Stock Photography, Inc bottom Rex Joseph, 8 top Kobal Colleclion/Superstock; bottom Jerry Mason/Science Photo Library/Photo Researchers, Inc., 9 Hank Morgan/Science Source/Photo Researchers, Inc 12 Robert Weslem/Tony Stone Worldwide/Chicago Ltd.; 15 Fundamental Photographs; 16 Michael Philip Manheim, 18 Phil Jude/Science Photo Library/Photo Researchers, Inc 19 top North Wind ,

;

25 left J Alex Langley/ Henry Grossman/DPI. 26 Ron

searchers. Inc DPI. right

Scott/Tony Stone Worldwide/Chicago Ltd 27 Bob Evans/Peter Arnold, inc 28 Gary .

Gladstone/Image Bank; 29 Phil Degginger, 32 Brian Parker^om Stack & Associates. 34 Paul Silverman/Fundamental Photographs: 37 Ken Karp. 43 R J Erwin/Photo Researchers. Inc 44 and 45 Fundamental Photographs. 46. 47 left and right. 48, 49 top and bottom, and 51 Richard Megna/Fundamenial Photographs, 52 GE Corporate Research and Development, 53Dr E R Degginger, 54 top Granger Collection, bottom Francois Gohier/Photo Researchers, Inc 55 Science Photo Library/Photo Researchers, Inc 57 Jack Finch/Science Photo Library/Phoio Researchers, Inc 58 Max-Planck-lnstitut Fur Radioastronomie/Science Photo Library/ Photo Researchers, Inc 64 and 65 Kaku Kurita/Gamma-Liaison, Inc.; 68 left: Dick .

Ourrance ll/Woodfin Camp & Associates, right Ken Karp; 69 Don Klumpp/lmage Bank, 76 left; Brian Parker/Tom Stack & Associates, nght

DOE /Science Source/

Photo Researchers, Inc 77 Richard Megna/Fundamental Photographs, 79 Dr E R, Degginger; 81 top and bottom Dr Jeremy Burgess/Science Photo Library/ Photo Researchers, Inc center CNRI/Science Photo Library/Pholo Researchers, Inc 85 U S Department of the Interior, National Park Service. Edison National Historic Sile/Omni-Pholo Communications. Inc 86 and 87 Joel Gordon. 88 lop left: Hank Morgan/Rainbow; top right .

Mitchell Bleier/Peler Arnold. Inc.. bottom

Dennis Purse/Photo Researchers.

left

Inc

center Morton Beebe/lmage Bank, S Ferguson. 98 Culver

bottom. Slephenie

99 Dan McCoy/Rainbow. 102 left IBM. nght Granger Collection. 103 lop Srulik Haramaly/Photolake, bottom left NASA, bottom right Gregory Sams/Science Photo Library/Photo Researchers, Inc 104 Ken Karp/Omni-Photo Communications. Inc 105 Eric Kroll/ Omni-Photo Communications. Inc Ill Phil Degginger. 112 left and right IBM Research, 113 Chns Rogers/Slock Market, 114 Peter Poulides/Tony Stone Woridwide/Chicago Ltd 115 left Mike Borum/ Image Bank, right Barry Lewis/Tony Stone Worldwide/Chicago Ltd nght inset; Scott Camazine/Photo Researchers. Inc 116 top teft Hank Morgan/Photo Researctv Pictures. Inc

bottom right Walter BibikovÂť/lmage Bank. 90 Ken Karp; 91 Robert Matheu/

ers. Inc.. nght

Retna Limited. 92 and 93 Ken Karp. 94

ers. Inc..

Inc

O RearA/Voodfin Camp &

Chuck

left

sociates, center

Arnold. Inc

As-

Alfred Pasieka/Peter

nght Joel Gordon. 96 top lefl Biophoto Associates/Photo Researchers. Inc top right; Petit Formal/Guigoz/Steiner/Science Source/Photo Researchers. ;

toedit:

Ken Lax/Photo Research-

bottom

118

left

Tony Freeman/Pho-

Dan McCoy/Rainbow,

Dick Luria/Sclence Source/Photo Researchers. Inc.. 119 Roger Du Buisson/ Stock Market; 120 Kaku Kunla;Gammaright

Liaison. Inc.

"RENTICE -^ALi

Electricity AND

Magnetism CHAPTER 1 Electric Charges and Currents

CHAPTER

Magnetism CHAPTER 3 Eiectromagnetism CHAPTER

Electronics and Computers

ISBN D-13-TfiLlfi3-l I

PRENTICE HALL

~a^C 35 861 833 -r