Electric Circuits by bala Sadasivan

CLASS VI

SCIENCE

ELECTRIC CIRCUITS

CLASS

VI SCIENCE ELECTRIC CIRCUITS

SYLLABUS

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Introduction to Electricity

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Electric Electriccell cell

 Electric bulb/Torch Electric bulb/Torch bulb bulb

Electric Electric switch Electric circuit and circuit Electricand switch Y L L A

 used Symbols used in Electric circuits Symbols in Electric circuits

Electric Conductors and insulators ElectricConductors and insulators 

Extension Extension

B U S

Scope Document Intended learning outcomes: At the end of this unit, students would be able to: 

Understand that electricity is a form of energy which can perform different tasks

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Give examples of different domestic tasks performed by using electricity

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Recognize that simple electric cell is a source of electric energy.

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List uses of an electric cell.

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Identify different parts of an electric bulb.

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Understand the meaning of the term an electric circuit.

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Construct simple electric circuits consisting of a cell, electric bulb, electric switch

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Recognise different components of an electric circuit

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Give examples and uses of electric conductors and insulators.

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Take precautions while handling electrical appliances.

Introduction: We all use electricity to run gadgets and devices such as fans, air-coolers, airconditioners, refrigerators bulbs, tube lights, computers, washing machines etc. to make our lives more convenient and comfortable. We enjoy watching television, listen to music and use many other sources of entertainment using electricity. It would be difficult to imagine how life would be affected in the absence of electricity. It is certainly one of the most convenient and useful forms of energy which has completely changed our lifestyles. You might have wondered at times about the nature of electricity, how and where it is produced, how it reaches our homes, how it is distributed to different appliances in the house etc. You might have also used simple electric cells used in a torch, a TV remote control, toys, a time clock and observed that these cells are of different sizes, shapes and designs. Questions might have arisen in your minds as to how the electricity used in running electrical devices at home or offices is different from the one obtained from a cell or a battery used in cars. The scope of this unit does not include the answer to all such questions. However, it does try to explore and explain some basic concepts related to a simple cell, an electric bulb, an electric switch, insulators and conductors and principles of electrical circuits.

Nature of Electricity The term electricity comes from a greek word electkron or amber. In order to understand the nature of electricity, one needs to know that all matter is made up of atoms. This smallest constituent of matter, called an atom, has negatively charged electrons in it. Under normal conditions, the positive and negative charges present in the atom balance each other. However, under certain situations, this balance gets disturbed and the electrons start moving in the material. This movement of electrons (electric charge) is called an electric current. 4

Activity 1 Objective: To enable the students to understand that electricity is a form of energy. Switch on an electric bulb. What do you observe? The bulb starts glowing due to flow of electricity from the source to the filament, a thin metallic wire inside the bulb. What is a source of light energy? What do you observe when we switch off the bulb?

Switch on an electric fan. What do you observe? It starts rotating. Have you ever wondered what makes the fan rotate? What is the source of energy for making the blades of the fan rotate?

Similarly when we switch on an electric heater, oven or an electric iron, these become hot. What is this form of energy which is heating them up

We can observe that electricity can heat up the filament of a heater or electric iron, make a fan rotate and make the element of a bulb glow and give out light. All these tasks require an energy which is provided by the source of current. Electricity is, thus, a form of energy. This energy gets transformed into different other forms of energy in different gadgets. Electric Cell Have you ever carefully looked at cells used in a TV remote, an alarm clock, a camera, portable radios or a simple torch? You might have observed that the cells used in different devices are of different shapes and sizes. Electric cells are devices which produce electricity from the chemicals stored inside them. Once the chemicals get used up, the cell stops working. The most common cells, we use in electric torches, and so many other devices, are called dry cells. Most of these cells are marked + and â&#x20AC;&#x201C; on it representing positive and negative terminals. There is a protruding metal cap in the front end of the cell which is its positive terminal. The flat metal base (disc shaped) on the other end of back side is the negative terminal.

The electric cells, we use in our wrist watches, looks like a button and are called button cells.

Activity 2 Objective : To learn the correct placement of cells in a torch. Procedure : Take two or more cells and a torch. Insert the cells one after the other into the torch and switch on the torch. Observe whether the bulb glows or not. If it glows, to note the arrangement of cells and record their observation. If the bulb does not glow, ask the students to again note the arrangement of cells in the torch.

One can observe that when the positive terminal of one electric cell is connected to the negative terminal of the next cell, the bulb in the torch glows. If the positive of one cell touches the positive of next cell or negative of two cells touch each other, the bulb

does not

glow. Thus, the correct way of putting the cells in a torch, TV remote or other devices is to put the cells in such a way that positive of one cell touches the negative of next cell and so on. What is inside a dry cell? If we break open the cell, we will observe that it contains a powder (chemicals) inside it. The chemical energy stored inside the cell gets transformed into electric energy when it is in use. The energy flows in the form of electric current through the bulb in the torch and changes into light energy. The kind of electric cells used in torches, electric toys etc. stop producing electricity once their Chemicals get used up. They have to be then replaced by new ones. These 7

cells are called primary cells. Cars, inverters, mobile phones use batteries which are rechargeable. i.e. They can be used again and again for quite a long time through regular periodic recharging. They are known as secondary cells. A group of properly connected cells is called a battery. Can you guess why more than one cell is used sometimes to run a device?

Activity 3 Aim: To design a simple cell using fruits/vegetables. Material Required: One large potato, a Zinc nail, a piece of thick copper wire, a torch bulb or LED and a pair of Alligator clips/Leads.

Procedure: Insert the copper wire and the zinc nail into the potato. Keep them close but not touching each other. Use Clip leads to connect the zinc nail and the copper wire to connect to the torch bulb. The activity is based on the use of a potato, but many citrus fruits and vegetables can be used to design cells. Students may be asked to explore the use of different fruits/vegetables for which the set up works!

Illustration

Electric Bulb An electric bulb has an outer case of glass that is fixed on a metallic base. A coiled wire is called the filament of the bulb. The filament is connected to thicker wires. One of these wires is connected to the metal case at the base of the bulb and the other is connected to the metal tip at the center of the base. The two terminals of the bulb, the base of the bulb and the metal tip of the base, are connected to the positive and negative terminals of the cell. An inert gas (which does not react with its surroundings) like helium and also some nitrogen is filled inside the bulb. So that the filament may be prevented from burning outâ&#x20AC;&#x2DC; in the oxygen, that is present in the air. Environmentalists are advocating switching over to the use of CFLs or Compact Florescent Lamps instead of bulbs. They give the same light as an electric bulb but consume much less power and have much longer life. Now a days, LEDâ&#x20AC;&#x2DC;s [Light Emitting Diodes], are also used as light sources. They are inexpensive, have long life and consume very little power but with very faint light.

Torch Bulb A commonly used torch bulb has an outer case of glass which is fixed on a metallic base. The metallic case usually has grooves in the lower part. A small spiral thin wire, called filament inside the glass case is supported by two slightly thick wires, One of these two wires is connected to the bottom tip of metal case and other to the metal casing separated by using one insulation between the two. These two points act as the two terminals.

Electric Circuit Lighting up a torch bulb with a dry cell Electric current can flow only when a complete and closed path of conductors is provided. Such a complete path, through which an electric current can flow, is called an electric circuit. A simplest circuit consists of mainly four elements. These are; 

A source of electricity – cell/battery

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A path for flow of electric current – connecting wires

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A switch that can start or stop the flow of current.

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A device through which the electric current flows .e.g a bulb Activity-4

Objective: To study the correct way to connect a torch bulb and a cell Procedure: Take two thin wires and connect one end of each wire to two terminals of the bulb holder having a torch bulb held in it. Touch the other end of one of the wires with one terminal of the cell. Does the bulb glow? Remove this contact and touch the other wire with other terminal of the cell. Does the bulb glow in this case? Now touch the two ends of the two wires coming from the bulbs holder simultaneously with the two terminals of the cell. Does the bulb glow in this case? Why does it so happen? It can be observed that the bulb glows only when the cell, the torch bulb and the wires form an complete path. The current does not flow and the bulb does not light up if there is some gap anywhere in this path. This complete path is called electrical circuit.

Activity 5 Aim: To study complete (closed) and incomplete (open) circuit. Material Required: i) A battery ii) A lamp iii) Wires/leads Procedure: Make connections as shown in the diagram and note the observations in each case.

(No battery)

Procedure: Make connections as shown in the diagram and note the observations in each case.We observe that the electrical current flows in the path and the bulb glows only when 12

there is no break in the path. The complete path is called a closed circuit and the incomplete path is called open circuit.

Activity 6 Objective: To make simple electrical circuits. Material Required: Bulb in a holder, Copper wires, a cell, cello tape and cardboard.

Procedure: Take an electric cell. Place the cell on the card board and fix it with the cello tape. Connect two copper wires from the two terminals of the cell with the help of the cello tape. Connect the other two ends of the wires to the bulb in the holder. Observation: One will observe that the bulb glows. Such a simple complete path in which the current flows is called an electric circuit.

Electrical Switch A switch is an electrical component which allows or does not allow the flow of electric current through an electric circuit. It can break and make the electrical circuit.

Activity 7 Aim: To make a simple electrical switch. Materials Required: Two drawing board pins, a small wooden block or a cardboard, a safety pin, a small (pencil) cell, three pieces of wire and a small torch bulb paper clips. Procedure: Insert the two drawing pins at a distance of 5-6cms from each other that will act as two terminals of the switch. Connect wires from the two pins. Connect two paper clips from the two board pins. The connection between the two drawing pins is made or broken with the help of the paper clips which will make the circuit either get closed or open. The switch is ready.

Make a small circuit with the help of a cell, a bulb, wires and the switch as shown in diagram. First join the two paper clips and note down the observation. Open the two paper clips and separate them so that they are not in contact with each other. Tell them to Note down the observation. Observe that in the first case the bulb will glow as the switch makes a closed circuit whereas in the second case the switch is open, it is an incomplete circuit and the bulb does not glow. Symbols used in Electric circuits The components of an electrical circuit such as a cell, a bulb, a switch, a battery etc. are usually shown by using symbols some of these symbols are shown below:

Electric Conductors and Insulators We observe in our daily life that some materials allow electricity to flow through then whereas others do not. Can you name few such materials of each kind? Electric current flows through a metallic key and safety pin but not through wooden scale and pencil. The materials that do not allow electricity to pass through them easily are called insulators. In insulators, all the electrons are tightly bound in the atom and therefore these electrons cannot move freely. As a result flow of electric current is not possible. Plastic, wood, glass and rubber are few examples of common insulators. That is why plastic is used to cover materials that carry electricity. Thus, they help to save the users from possible electrical shocks. In other materials like silver, copper, aluminum, iron etc. some electrons are loosely bound to the atom and can move easily in the material and thus flow of electric current is possible. Such materials are called conductors.

Worksheet 1 Aim: To classify materials as Conductors and as Insulators. Material Required: An eraser, a pencil, a paper pin, a coin, a scale, an electrical circuit. Procedure: Make a simple circuit using a cell, bulb, connecting wires and drawing pins (used as a switch). Remove the paper pins from the prepared switch and keep the objects on the switch in such a way that the material is in contact with the two drawing pins. Note down the observation. Observation: Material

Observation

Conductor/Insulator

Additional examples: 

An electrical cord has a plastic coating which is the insulator. The conducting copper wires are inside this coating.

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The glass of a light bulb is an insulator (bulb).

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The wires inside the glass bulb and the filament are the conductors of electricity.

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The surface (wooden, glass or plastic) where you switch on, and where the light bulb is inserted, are all insulators. 17

Extension: The cells/batteries batteries give us electricity called direct current (DC) and the supply we get in our household is called alternating current (AC). This current is available at high voltage of about 220V. Hence it is absolutely essential to follow certain precautions while using electrical appliances and devices at home, school or work place. 

Do not touch electrical connections with wet hands. Since water is a good conductor of electricity and if it were to flow through one‘s body, it could lead to shock or serious injuries.

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Always use rubber gloves or thick sole shoes/ wooden stool, while working with electrical devices.

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Keep away from the caption “DANGER”, as it is the warning sign to avoid any electricity related accident

Series Circuit An electric circuit, connected so that current passes through each circuit element, in turn, without branching is known as a series circuit. The arrangement of cells in a torch that we learned is an example of cells connected in series. Activity 8 Aim: Making series circuits. Material Required: Wires with alligator clips, batteries, light bulbs, light bulb holders and switches. Procedure: Divide the whole class in groups of four. Give each group a set of wires, a light bulb (with light bulb holder) and a switch. How to use the clips to attach the wires to the battery, bulb holder, and switch. Guide them to assemble a series circuit using two or more lamps

Concept of parallel circuits can also be introduced at this stage. A very common example is the circuit used in household electrical wiring. In this type of circuit, the total current in the circuit gets divided through different components of the circuits. Essential Key Words:

Essential Information 

Electric cell is a source of electric energy. It has two terminals positive and negative.

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In a cell, a chemical reaction between the chemicals in the cell and the metal of the container produces electrical energy.

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An electric bulb has a filament that is connected to its terminals.

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A group of connected cells in series forms a battery.

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The path, along which a current flows, is called a (complete) circuit. A circuit can be complete (closed) or incomplete (open).

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In a closed circuit the electric current passes from one terminal of the electric cell to its other terminal via the connecting wires and the devices present in the circuit.

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A switch is a simple device that can ' break' or 'complete' an electrical circuit.

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A material that allows electricity to pass through it, is called a conductor. The one, that does not allow electricity to pass through it, is known as an insulator.