OCR Gateway (9-1) Combined Science Teacher Pack sample pages

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Chapter 1: Cell level systems

Chapter 1: Cell level systems

Cell level systems: Introduction

• Practical: Investigate the effect of light intensity on the rate of photosynthesis using an aquatic organism such as pondweed

When and how to use these pages

Lesson title

Overarching objectives

This chapter builds on the idea that the cell is the building block of life. Plant, animal and bacteria cells are studied using microscopy and important cell level processes of photosynthesis and respiration are explored. This chapter links to all chapters in which the structure and functions of different systems are considered. There are links to Chapter 5, Genes, inheritance and selection, and several spreads in Chapter 2 Scaling up, particularly to 2.4 Cell division and 2.7 Cell development.

1

The light microscope

How to observe animal and plant cells using the light microscope and its limitations.

2

Looking at cells

Overview of the chapter

Describe the structure of eukaryotic cells and functions of subcellular components.

3

Practical: Using a light microscope to observe and record animal and plant cells

How to look at everyday materials and cells using a light microscope. Understand the difference between low and high power; draw and describe images at high and low magnification.

4

Primitive cells

Describe the differences between prokaryotic and eukaryotic cells, and how they might have evolved over time.

5

Looking at cells in more detail

Compare the light microscope with the electron microscope, explaining how the development of the electron microscope has increased our understanding of cells.

6

Making estimates, ratio and proportion, standard and decimal form.

This chapter offers a number of opportunities for the students to use mathematics to carry out magnification calculations, plan and carry out investigations into the use of anaerobic respiration in baking, plan and carry out investigations into factors affecting photosynthesis.

Maths skills: Size and number

7

The structure of DNA

Describe the structure of DNA in terms of DNA bases, double helix structure and having complementary strands

Obstacles to learning

8

Explaining enzymes

Describe what enzymes are and how they work.

Students may need extra guidance with the following terms and concepts:

9

Practical: Investigate the effect of pH on the rate of reaction of amylase enzyme

How to manage safety, use apparatus, and make accurate measurements. Understand how representative samples are taken; draw and interpret graphs from secondary data.

10

Cells at work

Explain the process of aerobic respiration.

11

Living without oxygen

Describe the process of anaerobic respiration and compare it to aerobic respiration.

12

Enzymes at work

Investigating the digestive enzymes.

13

Looking at photosynthesis

Explain how plants use the products of photosynthesis.

14

Explaining photosynthesis

Describe the process of photosynthesis.

15

Practical: Investigate the effect of light intensity on the rate of photosynthesis using an aquatic organism such as pond weed.

How to use scientific ideas to develop a hypothesis. Use the correct sampling technique; present the results in a graph.

16

Increasing photosynthesis

Identify factors that affect the rate of photosynthesis and explain the interaction of factors in limiting the rate of photosynthesis.

17

Maths skills: Extracting and interpreting information

To extract and interpret information from tables, charts and graphs.

In this chapter, students will learn about the structure of plant, animal, prokaryotic and eukaryotic organisms, and the functions of major structures. They will compare the level of detail revealed by light and electron microscopes, calculating magnifications. They will then learn about the role of enzymes in digestion and investigate the effect of pH on enzyme activity. Students will consider the differences between aerobic and anaerobic respiration, and learn about the uses of anaerobic respiration in baking and brewing. Students will learn about the process of photosynthesis, including the many uses of glucose in the plant. They will also test a leaf for the presence of starch and investigate how to change the rate of photosynthesis.

• Cells and related topics use abstract concepts and are hard to visualise. The use of cell models may help

some students to make connections between different types of cells. Students often believe that cells are inactive, two-dimensional structures and the use of videos and electron micrographs will enable them to see this is not the case.

• Students may believe that bacterial cells are the same as animal cells. • Most students will understand that enzymes speed up reactions but few will understand why. Opportunities to interpret enzyme-controlled reactions will help with this understanding.

• Respiration is often confused with breathing (ventilation), and needs to be linked to the mitochondria within cells so its role within each cell can be emphasised.

• Students need to appreciate that the process of photosynthesis only produces sugars. All the other

substances that a plant needs are made from this sugar and plants often need additional minerals to supply other elements.

• Many students, even at A level, think that plants respire at night and then switch to photosynthesis during the day. The continual nature of respiration needs to be emphasised.

Practicals in this chapter In this unit students will do the following practical work:

• Practical: Prepare plant and animal slides and observe them using a light microscope • Modelling DNA structure

• Investigate the amount of energy in food • Test a leaf for the presence of starch • Investigate the effect of amylase on starch • Practical: Investigate the effect of pH on the rate of reaction of amylase enzyme OCR GCSE Biology Combined: Teacher Pack

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OCR GCSE Biology Combined: Teacher Pack

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Chapter 1: Cell level systems

Chapter 1: Cell level systems

Lesson 2: Looking at cells

• Provide students with the card sort from the appropriate worksheet. They should group the cards into sizes of the same dimension. For example, 1 m could be grouped with 1000 mm and 100 cm. This card sort is differentiated for different learners. [O2]

Lesson overview

• Show students worksheet task 2. Ask students to imagine the diameter of a human hair scaled up to 70 mm.

OCR specification reference

Ask higher and standard demand students to work out the relative lengths of the other cells in the table. Ask all students to draw these lengths on their graph and compare the diameter of a hair as given on the worksheet. Ask students to draw conclusions about the sizes of cells. [O2]

OCR B1.1b

Learning objectives • Describe the structure of eukaryotic cells. • Explain how the main sub-cellular structures are related to their functions.

Explain • Ask students to read page 16 of the Student Book to remind themselves of the different parts of animal and plant cells. Students should answer all the questions from the Student Book. [O2, O3]

Consolidate and apply • Ask students to draw and summarise the differences between animal and plant cells in the table given on

Learning outcomes • Name the parts in a eukaryotic cell. [O1] • Relate the size of a cell to other objects. [O2]

the worksheet. [O2, O3]

• Students could work in small groups and make a three-minute presentation about cells to the class. They

• Explain the function and reasons for sub-cellular structures. [O3]

should include ideas about size, as well as explaining what a cell is and explaining the differences between animal and plant cells. [O1, O2, O3]

Skills development • WS 1.4a Use scientific vocabulary, terminology and definitions. • WS 1.4b Recognise the importance of scientific quantities and understand how they are determined. • WS 1.4e Interconvert units.

Extend Ask students who are able to progress further to:

• research the history of the development of cells and identify on the timeline when eukaryotic cells first

Maths focus • 1b Recognise and use expressions in standard form. • 2h Make order of magnitude calculations.

evolved. [O1, O2, O3]

• compare the structure of the ‘cyanobacteria’ with that of a typical plant cell. [O1, O2, O3]

Resources needed Worksheet 1.2.1 (low demand); Worksheet 1.2.2 (standard demand); Worksheet 1.2.3 (high demand) Digital resources PowerPoint Key vocabulary chloroplast, chlorophyll, chromosome, eukaryotic, order of magnitude

Teaching and learning

Plenary suggestions • Use the PowerPoint slide showing plant and animal cells with many mistakes on it. Ask students to correct the mistakes. • Provide students with a list of structures from the PowerPoint. Ask them to put them in order of magnitude.

Answers to Worksheet 1.2 1.

1m 1 cm 1 mm 1 μm 1 nm

Engage • Ask students to write down 10 things they already know about cells. Show students slide 1 on the

PowerPoint and discuss students’ responses as to what the images have in common. Elicit what a cell is and what features they have. [O1]

• Use slide 2 to introduce the term ‘eukaryotic’ to describe a cell with a true nucleus. Ask students to compare the images and identify what they have in common. [O1]

• Ask students to imagine how big a cell might be. Discuss what they would compare the size to. [O2]

Challenge and develop • Show students the simulation which will help them to identify the order of magnitude of cells in relation to other objects. This can be found using the search terms ‘cell size’ and ‘scale’ at http://learn.genetics.utah.edu. In addition, students could look at page 17 of the Student Book. [O2]

• Discuss the different units of size. Ensure students understand the relationships between mm, μm, nm and m. Ensure they are familiar with standard form. Use page 17 from the Student Book to help or use PowerPoint slide 3 to demonstrate how to compare orders of magnitude.

• High demand, standard demand and low demand students to carry out the appropriate card sort: low demand, Worksheet 1.2.1; standard demand, Worksheet 1.2.2; higher demand, Worksheet 1.2.3.

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Card sort activity

2.

1 metre 1 centimetre 1 millimetre 1 micrometre 1 nanometre

–2

10 m –3 10 m –6 10 m –9 10 m

100 cm

3

10 mm 10 mm –3

10

–7

cm

10 mm –6 10 mm

1 000 000 μm 4 10 μm 1000 μm 10

–3

μm

1 000 000 nm 3 1000 (10 ) nm

Comparing the scale of objects

Object Original size (μm) New size (mm) Human hair diameter 70 70 Bacterium 1 1 Red blood cell 7 7 Leaf cell 70 70 HIV 0.1 0.1 All lengths are drawn to the new size and graphs are labelled. 3.

Comparing plant and animal cells

Animal cell nucleus cell membrane cytoplasm

Plant cell nucleus cell membrane cytoplasm vacuole chloroplasts cell wall

Function of structure in the cell controls reactions in the cell; contains DNA; controls reproduction of the cell controls which substances enter and leave the cell where all the chemical reactions in the cell take place contains cell sap to provide internal strength to the cell absorb light energy for photosynthesis made from cellulose; provides strength and protection for the cell

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Chapter 4: Predicting and identifying reactions and products

Lesson 2: Exploring Group 1

Chapter 4: Predicting and identifying reactions and products

Consolidate and apply Low and standard demand

Lesson overview

• Students use the trends down the group to make predictions using Worksheets 4.2.1 and 4.2.2. [O2]

OCR Specification reference

• Students complete Worksheet 4.2.3. [O3]

OCR C4.1

High demand

Learning objectives

• Students use the trends in melting point down the group to make predictions using Worksheet 4.2.2. [O2]

• Explore the properties of Group 1 metals. • Compare their reactivity.

• Point out francium at the bottom of Group 1. Explain that it is very rare and that all its isotopes are

radioactive, so it is nearly impossible to study. Ask students to predict how it reacts with water and to justify their predictions using evidence from reactions they have seen. [O2]

• Relate their reactivity to their electronic structures.

• Show Presentation 4.2 ‘Ions’ and discuss the similarity between the electronic structures of lithium and

Learning outcomes

sodium. [O3]

• Explain why Group 1 metals are known as the alkali metals. [O1] • Use the trends down the group to make predictions. [O2]

• Ask pairs or small groups to explain how the electronic structures of these elements make them have similar

• Relate the properties of alkali metals to their electron configurations. [O3]

Skills development

chemical properties. [O3]

Extend Ask students able to progress further to research the reactions of beryllium, magnesium and calcium with water, compare them with Group 1 elements and describe any similarities and differences they notice.

• WS 2.4 Identify the main hazards associated with Group 1 metals. • WS 2.6 Make and record observations.

Plenary suggestion

• WS 4.1 Use scientific vocabulary, terminology and definitions.

Maths focus Interpolate and extrapolate graphs Resources needed Equipment as listed in the Technician’s notes;; Worksheets 4.2.1, 4.2.2 and 4.2.3;; Technician’s notes 4.2 Digital resources Presentation 4.2 ‘Ions’ Key vocabulary alkali, density, indicator, ion, reactivity, stable electronic structure

Teaching and learning

Ask students to draw a large triangle with a smaller inverted triangle that just fits inside it (so they have four triangles). In the outer three ask them to write something they’ve seen;; something they’ve done;; and something they’ve discussed. Then add: something they’ve learned in the central triangle.

Answers to Worksheet 4.2.1

1. They will react more violently with water than potassium;; because the reactivity of Group 1 metals increases going down the group;; 2. 2Li + 2H2O → 2LiOH + H2;; 2K + 2H2O → 2KOH + H2;; 2Rb + 2H2O → 2RbOH + H2;; 3. Caesium hydroxide;; hydrogen;; 4. The hydroxides dissolve in water to make alkaline solutions

Answers to Worksheet 4.2.2

• Show the bottles of Group 1 metals (Technician’s notes 4.2) and elicit students’ ideas about why they are stored under oil and why the pieces being used are so small. [O1]

Challenge and develop • Demonstrate the reactions of lithium, sodium and potassium with water following the method detailed in

Technician’s notes 4.2. Emphasise the similarities between them, the way they become softer and less dense going down the group and the way their reactivity increases going down the group. [O1]

• Follow up the demonstration with a video clip so students can see close-­ups of the metals and their reactions with water. [Google search string:] Alkali metals in water [O1]

Explain Low demand

• Students read ‘Properties of Group 1 elements’ and ‘Reaction trends of alkali metals’ on pages 160–161 in the Student Book and answer questions 1–5. [O1]

Using graphs to make predictions: potassium, melting point 55–65 °C;; francium, melting point 26–30 °C Melting point (°C)

Engage

Standard and high demand

Answers to Worksheet 4.2.3

• Students record the similarities and differences between the reactions of lithium, sodium and potassium with

1. They both have one electron in their outer shell;; 2. 2,8,8,1;; 3. One of the positive charges in the nucleus is no longer + + cancelled out;; 4. Na ;; K

water. [O1]

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OCR GCSE Chemistry: Combined: Teacher Pack

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Chapter 4: Predicting and identifying reactions and products

Chapter 4: Predicting and identifying reactions and products

Check your progress

Worked example

you should be able to:

Sam and Alex are researching some properties of Group 1 metals.

■ describe the unreactivity of the noble gases

■ predict the reactions with water of Group 1 elements lower than potassium

➞ ➞

■ recall the colours of the

halogens and the order of reactivity of chlorine, bromine and iodine

■ explain that a stable outer shell of electrons makes noble gases unreactive

■ use experimental results of

displacement reactions to confirm the reactivity series

Group 0 of increasing boiling point

■ predict and explain the relative reactivity down the groups

➞ ➞

■ describe the order of

➞ ➞

■ describe the reactions, if

any, of metals with water or dilute acids to place these metals in order of reactivity

■ explain the trend down

reactivity and explain the displacement of halogens

■ predict the properties of

‘unknown’ elements from their position in the group

related to the tendency of the metal to form its positive ion

■ use the reactivity series

to predict displacement reactions

1

0 of increasing boiling point in terms of atomic mass

➞ ➞

1

This is incorrect. The first column needs to be shaded.

hydrogen

1.0 3

Li

outcomes of halogens other than chlorine, bromine and iodine.

beryllium

6.9 11

9.0 12

reactivity in terms of electron structure

magnesium

23.0 19

24.3 20

potassium

calcium

scandium

titanium

39.1 37

40.1 38

45.0 39

47.9 40

rubidium

strontium

yttrium

zirconium

85.5 55

87.6 56

88.9

91.2 72

caesium

barium

lanthanides

132.9 87

137.3 88

Rb

metals based on experimental results

Cs

■ write ionic equations for

Fr

displacement reactions

Mg

sodium

K

■ explain the trend of increasing

4

Be

lithium

Na

■ deduce an order of reactivity of

Shade the section of the periodic table where the Group 1 metals are found. H

■ explain the trend down the group of increasing reactivity by electron structure ■ predict displacement reaction

■ explain how the reactivity is

■ explain the trend down Group

francium

Ca Sr

Ba Ra

radium

21

Sc Y

57-71

22

Ti

Zr

Hf

hafnium

178.5 104 89-103 actinides

Rf

rutherfordium

The two metals they are researching are sodium and potassium. 2

Write down two properties that these metals have.

They are shiny when cut They have a very high density

Sam and Alex find out that sodium and potassium react with water. They find that sodium reacts with water to make sodium hydroxide and that hydrogen is given off. 3

Write a word equation for the reaction

The first property is correct. However, sodium and potassium float on water so have a density less than water. The student may be confusing Group 1 metals with transition metals, which have high density.

The reactants are correct but hydrogen needs to be written as a product on the right hand side.

sodium + water → sodium hydroxide

Sam says that potassium reacts more vigorously than sodium but Alex says that they are in the same group so they react the same. 4

a Explain why Sam is correct about the trend.

This answer could be expressed more clearly by substituting the word ‘better’ with ‘more vigorously’.

The lower down the group the better they react b Explain why Sam is correct using ideas about the structure of atoms.

The bigger the atom the quicker the reaction

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This answer needs more detail. The further away the outer electron is from the nucleus the more easily it is ‘lost’, as the pull by the positive nucleus on the negative electron is less.

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Chapter 2: Forces

Chapter 2: Forces

Lesson 2.19: Potential energy

Challenge and develop

Lesson overview

energy and elastic potential energy. • After the practical is done, discuss how the practical could have been improved, first in pairs, then groups of four, then groups of eight. Finally, someone from each group shares ideas for improvement with the class. [O1, O2, O3]

• The students should then carry out Practical 2.19, where they will investigate transfers between gravitational

OCR Specification reference P2.3f

Explain

Learning objectives • Consider what happens when a spring is stretched. • Describe what is meant by gravitational potential energy. • Calculate the energy stored by an object raised above ground level.

• Challenge students’ thinking and understanding of elastic potential energy and gravitational potential energy from the practical activities using the evaluation section of Practical sheet 2.19. [O1, O2, O3]

Learning outcomes • [O1] Describe different types of energy store, including elastic potential energy and gravitational potential energy. • [O2] Calculate, using the elastic potential energy equation. • [O3] Calculate, using the gravitational potential energy equation.

Skills development • Evaluate methods and suggest possible improvements and further investigations. • Carry out and represent mathematical and statistical analysis. • Use SI units (for example, grams, metres, joules) and IUPAC chemical nomenclature unless inappropriate. Maths focus • Change the subject of an equation. • Substitute numerical values into algebraic equations using appropriate units for physical quantities. • Solve simple algebraic equations. Resources needed clamp stands, clamps, bosses, springs of known spring constant, 100 g mass holders, 100 g masses, metre rules, clear sticky tape, card, scissors; Worksheets 2.19.1, 2.19.2 and 2.19.3, Practical sheet 2.19, Technician’s notes 2.19 Digital resources elastic potential energy video (https://youtu.be/5yGj9JooT_Q), gravitational potential energy video (https://youtu.be/BVohVKn0qwU) Key vocabulary energy store, energy transfer, elastic potential energy, gravitational potential energy, gravitational field strength

Teaching and learning Engage • Watch the elastic potential energy video showing archers shooting arrows. Challenge students’ thinking and

understanding of the energy involved. You could ask: What energy does the arrow have when moving? Where does this energy come from? What type of energy does the bow have when the bowstring is pulled back? How can the energy be increased? Why would different bows contain different amounts of energy? • Lead a discussion on the energy being stored in the bow until released by the archer – all stored energies are 2 called potential energies. Then introduce the equation for elastic potential energy: Ee = ½ ke . Formula triangles are trickier when there are more than three quantities, but show that it is possible with Ee at the top. 2 Emphasise that to determine e, students should use the triangle to find e , then take the square root. Note: students will always be given this equation in examinations on the physics equation sheet. [O1, O2] • Watch the gravitational potential energy video showing pole-vaulters. Challenge students’ thinking and understanding of the energy involved. You could ask: What energy does the pole-vaulter have at the top of motion? Where does this energy come from? What type of energy does the pole have when it is bent? How would this be different for a heavier athlete? How would this be different on different planets? • Re-emphasise the idea of stored energies as potential energies. Then introduce the equation for gravitational potential energy: Ep = mgh. Formula triangles are trickier with more than three quantities, but show that it is possible with Ep at the top. Note: students are expected to remember this equation in examinations. [O1, O3]

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Consolidate and apply The students should now be given the potential energy worksheet suitable to their ability:

• Low demand – Worksheet 2.19.1 [O1, O2, O3] • Standard demand – Worksheet 2.19.2 [O1, O2, O3] • High demand – Worksheet 2.19.3 [O1, O2, O3] Extend Ask students able to progress further to do the following: • Each student or student pair suggests how to produce a catapult that would fire an object to the greatest height. Discuss how you could test this. [O1, O2, O3]

Plenary suggestions What’s in the picture? Have a picture of an object such as a catapult concealed by rectangles, each of which can be removed in turn. Ask for suggestions as to which tile should be removed and what the partially revealed graphic shows. Encourage speculation and inference; ask for suggestions as to which tile should go next and continue until a full image has been produced. Hot seat: Ask each student to think up a question, using material from the lesson. Select someone to put in the hot seat. Ask students to ask their question and say at the end whether the aswer is correct or incorrect.

Answers to questions Worksheet question 1 (2.19.1 – a, b, d, e and f; 2.19.2 – a, c, d, f and g; 2.19.3 – a, c, d, g and h) a) stored energy b) any sensible answers, including: bows, wind-up toys, car suspensions c) increase extension, higher spring constant 2 d) Ee = ½ ke e)

f) g) h)

e)

f) g)

Worksheet question 3 (2.19.1 – a and b; 2.19.2 – a, b and c; 2.19.3 – a, b, c and d) a) 62.5 J b) 62.5 J c) 318.9 m d) air resistance

147 J 20 N/m 0.20 m

Practical sheet evaluation 1. The greater the mass, the greater the loss in gravitational potential energy. 2. The greater the extension, the greater the gain in elastic potential energy. 3. Probably B, with the explanation that there is a difference due to air resistance; if students’ results show A, then allow, with the explanation that as the mass falls, Ep converts to Ee. 4. Any sensible answers, including accounting for mass of spring and determining whether k changes over range of extension used.

Worksheet question 2 (2.19.1 – a, b, d, e and g; 2.19.2 – a, c, d and g; 2.19.3 – a, c, d, g and h) a) any sensible answers, above ground (technically anything not at infinity; values would be negative but this isn’t A-level) b) increase height, greater mass c) different value of g (gravitational field strength) d) Ep = mgh

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Student Book answers 7

Chapter 1: Matter Lesson 1.1 Key Concept: Developing ideas for the structure of the atom 1

No it only includes the electrons. The rest of the atom was a positively charged sphere.

2

Yes – although it is unclear how they are balanced.

3

The results were very surprising and other scientists needed to peer review the work to check that they had not made any mistakes. The work is useful for other scientists to develop in order to produce further scientific theories.

4

The experimental results could not be explained by the current model of the atom.

5

Rutherford’s model explained why most of the alpha particles went through the gold foil and only a few bounced back. It also went on to explain what was happening in radioactive decay.

6

8

Student Book answers

The mass of the air stays the same but the volume of the air decreases slightly. Since density = mass / volume, this means the density of the air will increase slightly. 3

Density of cork = mass / volume = 3 / 12 = 0.25 3 g / cm

6

Density of oak = mass / volume = 17 / (2.0 × 3.0 3 × 4.0) = 0.71 g / cm

3

1 g / cm means that each cm of the substance will have a mass of 1 g. There are 100 × 100 × 3 3 3 100 = 1000 000 cm in 1 m , so 1 m of the substance will have a mass of 1000 000 g. 1000 3 000 g = 1000 kg, so 1 m of the substance has a mass of 1000 kg – giving a density of 1000 kg 3 /m .

Lesson 1.3 Key Concept: Particle model and changes of state

More people do experiments to test whether the results agree with the predictions of the scientific theory. If the theory correctly predicts the results of many experiments over a long period of time it becomes gradually accepted. However just one experiment’s results can force a theory to be changed as shown by Geiger and Marsden’s experiment.

5

1

In a solid, the atoms and molecules vibrate around a fixed point. In a liquid the atoms and molecules can move past each other.

2

The particles vibrate with a larger amplitude. Therefore, their average separation increases.

3

The internal energy increases. This is because the potential energy increases from the particles getting further apart and the kinetic energy increases from the particles vibrating with a greater speed.

4

Density of tin = mass / volume = 365 / (2.5 × 2.5 3 × 8.0) = 7.3 g / cm 7

8

solid

1b

gas

1c

liquid

2

The particles in a solid are usually closer together than they are in a liquid or a gas. Therefore, the same mass of material will occupy a smaller volume which makes the density higher.

3

You would need to measure the mass of the necklace and the volume of the necklace.

10

Density = mass / volume

11

There are many errors in the experiment such as not reading the measuring cylinder very accurately. Perhaps your eyes weren’t lined up with the bottom of the meniscus or you weren’t holding the measuring cylinder completely vertically. Also the volume of the necklace is quite small and the measuring cylinder would not be sensitive enough to measure small changes in the volume accurately.

4b

m = ρV = 7700 × 2 = 15 400 kg.

4c

Aluminium is less dense than steel. Therefore, aeroplanes made from aluminium are likely to be much lighter.

5

5

1 2

Subtract the mass of the empty measuring cylinder to get the mass of the liquid.

3

Density = mass / volume

Acetone: 19.6 / 25 = 0.784 g / cm

3

Volume = 5 × 4 × 3 = 60 m .

Freezing

2

You could place a block of ice in a sealed container and then place the container on a balance. Record the mass and then wait for all of the ice to melt. Record the mass again and see whether the mass has changed.

4

223

3

e.g. Dry ice changing from a solid to a gas (sublimating). The material involved is carbon dioxide. (Dry ice is solid CO2)

4

A freezing temperature is not necessarily a cold temperature. Some materials (e.g. tungsten) freeze at thousands of degrees Celsius. We are really only referring to the temperature at which water freezes.

3

3

Sea water: 51.3 / 50 = 1.026 g / cm

Cork is less dense than water so it floats. Iron is denser than water, so it sinks.

OCR GCSE Physics: Combined: Teacher Pack

The balance would also be recording the mass of the measuring cylinder.

Coconut oil: 18.5 / 20 = 0.925 g / cm

m = ρV = 1.3 × 60 = 78 kg. 6

The material is cooling down.

1

Lesson 1.3 Practical: To investigate the densities of regular and irregular solid objects and liquids

3

ρ = m ÷ V = 5400 ÷ 2 = 2700 kg/m

The fastest moving particles are the ones which evaporate. When they leave the liquid, the average speed of the remaining particles is lower (since the fastest ones have left). The temperature is related to the average speed and so the temperature decreases.

7

When you are burned by steam, the steam transfers energy to your skin when it is condensing. This is extra to the energy transferred to your skin when the hot water cools down.

8

Sweat is no colder than your skin. The cooling effect occurs because the sweat evaporates. Not all of the water molecules in the sweat move at the same speed and it is the ones that move the fastest that evaporate. Therefore, the average speed of the molecules decreases as the sweat evaporates and this results in a lower temperature.

Lesson 1.6 Internal energy 1

They have kinetic energy because they are moving.

2

Ek = ½ mv and the particles have the same kinetic energy at the same temperature. This means that the heavy particles are moving slower than the light particles at the same temperature.

3

The particles store potential energy because they are separated from each other.

4

The Pacific Ocean has more internal energy than the tea. Each particle in the tea does store more kinetic energy (the tea is hotter) and more potential energy (the particles are further apart). However, there are many more particles in the Pacific Ocean so the total of the kinetic and potential energies stored by the particles in the Pacific Ocean is a much bigger value.

5

The internal energy increases.

6

The water cools down, freezes and cools down again. All of this results in a decrease in internal energy.

7a

The internal energy of steam at 100 C is much higher than that of water at the same temperature. This is because the particles in steam at 100°C are much further apart than water particles at 100°C.

7b

Steam is able to transfer much more energy than water at the same temperature as its internal energy is so much higher.

Lesson 1.5 Changes of state

The particles in a gas are far apart. Therefore, the volume of a certain mass of gas is much bigger than the same mass of liquid and solid. This makes the density small.

4a

You could half fill a measuring cylinder with water. Record the volume of the water. Then place the necklace into the water and make sure it is fully submerged. Record the new volume of the water. The volume of the necklace is the difference between the two volumes you measured. Then you could find the mass of the necklace by placing it on a balance. Repeat the measurements and find an average to reduce the effects of random errors.

9

Lesson 1.2 Density 1a

The data is only measured to 2 significant figures. Therefore, the answer can only be given to two significant figures. It is incorrect to give any more significant figures as this suggests that the calculation is more accurate than it actually is.

6

3

5 3

Volume of cork = 2.0 × 2.0 × 3.0 = 12 cm

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0

Lesson 1.7 Specific heat capacity

This makes the surface area of the clothes larger and so evaporation can take place more quickly.

OCR GCSE Physics: Combined: Teacher Pack

2

1a

224

Energy is transferred to the liquid which gives the particles greater kinetic energy (as they

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