AQA GCSE Physics Teacher Guide

201 Pages·2017·4.62 MB·English

AQA
GCSE
9–1
Physics
Teacher Support
Guide
Ian Horsewell
References to the textbooks in this teacher resource guide
References to the student textbooks are given in the following style:
■ The first figure or page number always refers to the GCSE Physics book.
■ The numbers in brackets refer to the Combined Science Trilogy books.
■ Where there are two numbers in brackets, the first is for Combined Science Trilogy 1 or 2; the second
number refers to the all-in-one Combined Science Trilogy book.
Use Figure 14.6 (21.4) from page 181 (31; 387) to show …
The figure number The figure number The page The page number The page
in the GCSE in the Combined number in the in the Combined number in the
Physics book Science Trilogy GCSE Physics Science Trilogy 2 Combined
books book book Science Trilogy
all-in-one book
The Publisher would like to thank the following for permission to reproduce copyright material.
Every effort has been made to trace all copyright holders, but if any have been inadvertently
overlooked, the Publisher will be pleased to make the necessary arrangements at the earliest
opportunity.
Although every effort has been made to ensure that website addresses are correct at time of
going to press, Hodder Education cannot be held responsible for the content of any website
mentioned in this book. It is sometimes possible to find a relocated web page by typing in the
address of the home page for a website in the URL window of your browser.
Hachette UK’s policy is to use papers that are natural, renewable and recyclable products and
made from wood grown in sustainable forests. The logging and manufacturing processes are
expected to conform to the environmental regulations of the country of origin.
Orders: please contact Bookpoint Ltd, 130 Milton Park, Abingdon, Oxon OX14 4SB.
Telephone: [phone]. Fax: [phone]. Lines are open 9.00a.m.–5.00p.m.,
Monday to Saturday, with a 24-hour message answering service. Visit our website at www.
hoddereducation.co.uk
© Ian Horsewell 2018
First published in 2018 by
Hodder Education,
An Hachette UK Company
Carmelite House
50 Victoria Embankment
London EC4Y 0DZ
Impression number 10 9 8 7 6 5 4 3 2 1
Year 2022 2021 2020 2019 2018
All rights reserved. Apart from any use permitted under UK copyright law, no part of this
publication may be reproduced or transmitted in any form or by any means, electronic or
mechanical, including photocopying and recording, or held within any information storage
and retrieval system, without permission in writing from the publisher or under licence from
the Copyright Licensing Agency Limited. Further details of such licences (for reprographic
reproduction) may be obtained from the Copyright Licensing Agency Limited, Saffron House, 6–10
Kirby Street, London EC1N 8TS.
Typeset in 11.5/13 Officina Sans by Aptara, Inc.
A catalogue record for this title is available from the British Library
ISBN 978 1471 851186
Contents
Physics States of matter 57
Heat and temperature 57
1 Energy 1
Specific heat capacity 58
Energy stores and systems 2 Measuring latent heat 58
Counting energy, energy conservation 3 Cooling graphs 59
Transferring energy (circuits) 3 Brownian motion 60
Calculating energy 4 Pressure and volume (Physics only) 60
Changes in energy 5 Work and energy (Higher tier and Physics only) 61
Work 5 Answers 61
Power 6
4 Atomic structure 68
Energy changes in systems 7
Required practical 1(14): Calculating specific Subatomic particles 69
heat capacity 7 From the periodic table 69
Calculating specific heat capacity (debrief) 8 Science in action – electrons 70
Reducing energy dissipation 9 Changing models of the atom 71
Keeping warm at home 9 Nuclear decay and equations 71
Required practical 2: Investigating thermal Ionisation and detectors 72
insulation (Physics only) 10 Alpha, beta and gamma 73
Investigating thermal insulation (debrief) (Physics only) 11 Sources of background radiation (Physics only) 73
Efficiency 11 Half-life in theory 74
Increasing efficiency 12 Simulating half-life 75
Fossil fuels, (thermal) power stations 13 Half-life in reality, C-14 dating 75
More power stations 13 Hazards (Physics only) 76
Answers 14 Diagnosis and therapy (Physics only) 77
Irradiation versus contamination 77
2 Electricity 29
Energy from nuclear fission (Physics only) 78
Circuit symbols 30 Chain reactions, reactor design (Physics only) 79
Current and charge 30 Nuclear fusion in stars (Physics only) 79
Controlling the current 1 – cells 31 Answers 80
Controlling the current 2 – components 32
5A Forces 90
Ammeters, voltmeters and resistance 33
Required practical 3(15): Resistance – wires 33 Scalars and vectors 90
Required practical 3(15): Resistance – combinations 34 Contact and non-contact forces 91
Components that resist 35 Weight 92
Required practical 4(16): Resistors that vary 35 Combining forces along a line 92
Required practical 4(16): I–V graphs 36 Free-body diagrams (Higher tier) 93
I–V graphs (debrief) 37 Resultant forces at right angles, diagrams 93
Series and parallel circuit rules 37 Work done 94
Solving circuit problems 38 Elastic and inelastic deformation 95
Oscilloscopes – direct and alternating p.d. 38 Required practical 6(18): Force and extension 95
Electrical safety at home 39 Force and extension (debrief) 96
Electrical power equations 40 Proportionality limit, energy stored 96
Choosing fuses (calculating current) 41 Investigating moments (Physics only) 97
The National Grid 41 Calculating moments – levers, loads (Physics only) 97
Making static (Physics only) 42 Moments and gears in action (Physics only) 98
Forces on charged objects (Physics only) 43 Pressure in a fluid (Physics only) 99
Electric fields (Physics only) 43 Hydraulic machines (Physics only) 99
Answers 44 Pressure at depth (Higher tier) (Physics only) 100
Floating and sinking (Higher tier) (Physics only) 101
3 Particles 55
Atmospheric pressure (Higher tier) (Physics only) 101
Required practical 5(17): Calculating density 56 Answers 102
Calculating density (debrief) 56
s 5B Observing and recording motion 111 Properties of EM waves 150
t
n
Required practical 10(21): Investigating emission
e Average versus instantaneous speeds 112
nt Vectors and scalars 112 and absorption 151
o
C The story of a (distance−time) graph 113 Investigating emission and absorption (debrief) 152
More properties 152
Acceleration 114
Using EM waves 153
Velocity–time graphs 115
Drawing diagrams for refractive lenses (Physics only) 154
Using data loggers/cameras/tickers 115
Comparing convex and concave lenses (Physics only) 154
Parachutes 116
Making a spectrum (Physics only) 155
No force, no acceleration 117
Mixing colours of light (Physics only) 156
Required practical 7(19): Testing the relationship
Defining a black body (Physics only) 157
between force and acceleration 117
F Temperature of the Earth (Physics only) 157
Using a = (debrief) 118
m Answers 158
Force pairs 119
7 Magnetism and electromagnetism 169
Investigating friction 120
The Highway Code 120 Poles and fields 170
Investigating reaction times 121 Making electromagnets 170
Defining momentum (Higher tier) 122 (Induced) magnetic fields 171
Momentum and force (Higher tier and Physics only) 122 Force on a wire 172
Closed systems (Higher tier) 123 The motor effect 173
Answers 124 Motors and loudspeakers 173
Inducing potential (Physics only) 174
6 Waves 141
Alternators (Physics only) 175
Waves 142 Dynamo (Physics only) 175
Wave properties and equation 143 Microphones (Physics only) 176
Required practical 8(20): Measuring and Investigating transformers (Physics only) 176
calculating wave properties 144 Explaining transformers (Physics only) 177
Measuring and calculating wave Transformers in the National Grid (Physics only) 178
properties (debrief) 144 Answers 179
Reflection, absorption, transmission and refraction
8 Space physics (Physics only) 187
(Physics only) 145
Required practical 9: Investigating reflection Our sun and the planets 188
and refraction of light (Physics only) 146 Gravity and galaxies 188
Investigating reflection and refraction of Birth of a star 189
light (debrief) (Physics only) 147 Death of a star 190
Diagrams and calculations (Physics only) 147 Orbiting 191
Sound (Physics only) 148 Red-shift 191
Ultrasound and seismic waves 149 The big bang theory 192
The ‘colours’ of the EM spectrum 150 Sun at the centre 193
Answers 194
iv
1 Energy
1 Energy
• Practical video: Investigating factors that affect
thermal insulation
Overview • Practical video: Investigating factors that may affect
the thermal insulation by varying the thickness of a
Specification points
material
4.1.1 Energy changes in a system, and the ways
• Homework tasks (a) and (b)
energy is stored before and after such changes,
• Quick quizzes 1–4
4.1.2 Conservation and dissipation of energy and
• Half-term test 4.1: Energy and power
4.1.3 National and global energy resources
• Half-term test 4.1.2: Conservation and dissipation of
Textbook chapter references energy
AQA GCSE (9-1) Physics: Chapter 1 pages 1–35 • Answers for homework tasks
• Answers to all questions
AQA GCSE (9-1) Combined Science Trilogy 1:
Chapter 15 pages 258–90
Useful prior learning
AQA GCSE (9-1) Combined Science Trilogy:
l Energy allows things to happen but does not
Chapter 15 pages 258–90
cause them to happen.
Recommended number of lessons: 18 l Energy is a quantitative idea, and we can
count or calculate the energy associated with
Chapter overview particular systems or stores.
AQA required practical(s) Physics – RP1 l The principle of conservation of energy
CS Trilogy – RP14
states that energy can be neither created nor
Physics – RP2
destroyed; effectively this means that the
Contains higher-tier material Yes
numbers always add up.
Contains physics-only material Yes
l Heat can be considered as an energy store,
whereas temperature gives information about
Useful Teaching and Learning resources the average energy of particles in a sample. A
small amount of heat may cause a large increase
• Learning outcomes
in temperature or vice versa.
• Prior knowledge catch-up student sheet
l Our primary source of energy is the Sun. Energy
• Prior knowledge catch-up teacher sheet
reaches us from the Sun via electromagnetic
• Topic overview
(EM) radiation.
• Lesson starters 1–3
l Plants use this EM radiation in a process called
• Key terms photosynthesis to make glucose, a compound which
• Animation: Energy, power and efficiency provides animals (including us) energy to live.
• Personal tutor: Energy and efficiency l We generate electricity using fossil fuels and
• Personal tutor: Generating electricity other resources.
• Personal tutor: The usefulness of electrical l Energy can be transferred from a hot object to
appliances colder objects by several processes. Metals are
• Personal tutor: Work done good thermal conductors, which allow energy to
• Practical: Determining the specific heat capacity of a be transferred quickly. Fluids (liquids and gases)
material transfer energy by convection.
• Teacher and technician notes: Determining the l Energy is measured in joules, J.
specific heat capacity of a material
Common misconceptions
• Practical: Investigating factors that affect thermal
insulation – material l It is not a misconception as such, but many
students will be more familiar with the ‘types
• Teacher and technician notes: Investigating factors
and transformations’ model than the ‘stores and
that affect thermal insulation – material
pathways’ model described here and in recent
• Practical: Investigating factors that affect thermal
insulation – thickness textbooks. The mathematics has not changed,
only the description we use in place of numbers.
• Teacher and technician notes: Investigating factors
that affect thermal insulation – thickness l Heat and temperature are often confused by
• Practical video: Collecting the correct data students.
• Practical video: Determining specific heat capacity l Energy and power are frequently mixed up
using the data or used incorrectly; students will need to be
1
y reminded to use precise physics language rather that there are measurable changes in the system
g
r than ‘everyday’ English. as the fuel is consumed. Having students list
e
n l The principle of conservation of energy seems changing variables is a good link to the different
E
1 to suggest that energy cannot be wasted (and possible stores, but postpone discussing the
students think of ‘energy conservation’ as saving mechanism if possible.
energy by turning off lights). Describing energy
Once chemical stores are associated with fuels,
as ‘lost’ makes this worse, and it is better to
students should be introduced to thermal, kinetic
suggest that we have ‘lost track of’ the energy,
and gravitational stores. These are associated
which has been shared widely or dissipated.
with changes in temperature, motion and height,
l Students will frequently assume that nuclear
respectively. Students are likely to be more
power stations are highly dangerous, while
confident if the equations are left until later.
ignoring the more serious (but gradual) concerns
associated with fossil fuels, in both health and Examples of other stores should be presented,
environmental contexts. perhaps as diagrams or photographs. Take care
when choosing examples from previous versions
Preparation
of the ‘energy circus’ (often taught during KS3
The T&L Topic overview gives a brief introduction
and usually including kettles, hairdryers, etc.).
of the equations introduced during the topic, and
Elastic stores involve a stretched or compressed
is a useful reference for abbreviations and SI units.
object; magnetic and electrostatic stores are
In most cases the mathematical approach will
relevant when poles or charged objects move
follow thorough consideration of the ideas with
towards or away from each other; all atoms can
students, rather than serve as a starting point. It
be considered as nuclear stores, with an equation
is probably best saved for student use as a review.
that most students will suggest with little
The T&L Prior knowledge catch-up teacher sheet prompting.
has a good discussion of heat transfers, which
Plenary
students are likely to be familiar with from KS3
Students can complete a table that links stores
work. Depending on setting, the students will have
with the changing variables and, where relevant,
had different experiences of energy language, and
an equation. Be clear about which of these
may not be familiar with the stores and pathways
will need to be recalled in the exam, as some
approach in the current KS3 specification.
are not covered quantitatively until after GCSE.
Alternatively, the Test yourself questions 1–3 on
Energy stores and systems: Lesson 1
page 4 of the textbook are a useful recap.
Learning outcomes Support
Students who lack confidence in maths may
find the kinetic store equation intimidating.
1 Discuss energy store/fuel analogy.
All students may hesitate if they have not
2 List eight stores.
encountered the stores and pathways model before.
Reinforce which measurements can be made to
show a change in a particular variable, such as
Suggested lesson plan
height or extension. The examples can be treated
Starter
as a ‘trailer’ for lessons to come over the whole
Show students several examples of chemical fuels,
course.
both foods and those that are more recognisably
‘fuels’. Challenge them to identify what they
Extension
have in common. Combustion and (biological)
Able students may be familiar with some equations
respiration may feature in their answers, which is
already, and should be encouraged to consider the
an excellent starting point.
details of necessary measurements. If they suggest
Main that the ‘stores’ are temporary, challenge them to
Aim to move on quickly from the idea of ‘potential’ suggest where the energy has gone; for example,
energy. Some fuels provide more energy than as a moving bowling ball slows, the energy in its
others, but all are stores of energy; they need the kinetic store is ‘lost’ to the thermal store of the
right circumstances for this to result in action. ground (which warms up via friction) and the
Showing students a steam engine, or a turbine kinetic store of the air (the molecules of the gas
spinning above a Bunsen flame, will soon suggest are moved because of collisions).
2
1 Energy
Homework Where else does the energy ‘go’? Is the energy truly
Students could list examples of some stores lost, or just hard to measure?
from home or daily life. Nuclear, magnetic and
Support
electrostatic stores should probably be avoided at
Calculator errors are likely to be the reason for
this point.
mistakes, rather than a failure to understand the
principle. Explain that this is why prefixes are
Counting energy, energy conservation:
used and establish a routine for calculations; for
Lesson 2 example, ‘convert all numbers in a question to SI
units and/or standard form before reaching for
calculator’.
Learning outcomes
Some students will revert to energy transformations
when explaining; encourage them to think of
1 Define the joule.
transfers between stores instead. Reminding them
2 Practise/recall prefixes (kilo, etc.).
of the link to a measurable quantity may help:
3 Recall the principle of conservation of energy.
for example, an object that is carried upstairs
(observable) has more energy in the associated
Suggested lesson plan gravitational store (abstract).
Starter
Extension
How big a chemical store is an apple/chocolate
Able students can be encouraged to compare the
bar/can of fizzy drink, etc? Display nutrition labels
quantity in joules for common situations; many will
for a range of products and establish the different
be surprised by just how much energy a chemical
unit systems, calories (kcal) and joules (J). Why
store involves compared with the energy stores
do we use more than one unit system? (As a hint,
of objects that are being lifted up or are moving
ask why we don’t often measure human height in
fast. All equations give values in joules, and this
millimetres.)
demonstrates the principle of conservation of
Main energy.
Define the joule (J) as the amount of energy
Homework
needed to lift a weight of 1 newton (N) by 1 metre
T&L Quick quiz: Energy 1 would be a good review
(m). Give some example values for common foods.
of the first two lessons. Alternatively, the Test
This will quickly show why prefixes such as ‘kilo’ and
yourself questions from page 4 of the textbook
‘mega’ are necessary (1 kJ = 1000 J, 1 MJ = 1000 kJ
could be used if not already attempted in class.
= 1 000 000 J). Students may recognise higher
prefixes (‘giga’ and ‘tera’) from computer memory.
Transferring energy (circuits): Lesson 3
Provide practice questions and check answers.
Lift the apple in the air and repeat that its
Learning outcomes
gravitational store has now gained a joule of energy
(assuming a 100 g apple lifted 1 m). Ask students
under what conditions other energy stores would 1 Recap eight stores, snapshot idea.
be relevant; for example, a moving apple has more 2 Consider examples of transfers.
energy in its kinetic store. In each case, the value of 3 Discuss common pathways/processes.
energy, measured in joules, can be calculated and/
or measured – which equations can they remember?
Suggested lesson plan
The energy must come from somewhere. Students Starter
should recall the principle of conservation of Provide a blank table as used in Lesson 1 and
energy and be able to explain simple situations challenge students to fill in as many energy stores
in terms of total energy in stores being the same as possible. Remind them of the ‘before and after’
before and after an event. Any apparent losses approach used in the previous lesson.
are usually due to neglecting a store, often the
Main
thermal store of the environment.
Up to this point, energy stores have been
Plenary discussed, but not how energy has been transferred
Link these ideas by comparing the chemical store between them. Return to the simple examples from
of the food eaten by a human in a day with the the ‘energy circus’ and ask students to suggest
thermal store of the person and their surroundings. possible mechanisms.
3
y Model an explanation, emphasising the Suggested lesson plan
g
r descriptions of particles and forces. It helps if Starter
e
n verbs are used to make clear that the processes Have student ‘volunteers’ lift up empty and full
E
1 are ongoing, and can happen quickly or slowly. boxes; ask which gravitational store will have
Students should be able to recognise common more energy. Then have the same box lifted up
themes, becoming more fluent as they encounter by different heights and ask the same question.
more examples. Figures 1.2 to 1.5 (15.2 to 15.4) in Finally, ask students to imagine identical boxes
the textbook may be useful prompts. lifted by the same height – but one on Earth and
the other on the Moon.
If a current flows then energy is being transferred
by electrical working. Examples of heating by Main
particles (conduction and convection) should Even students who think they struggle with maths
be contrasted with heating by electromagnetic can give good intuitive answers to the starter
(EM) radiation. Often they will happen at the questions. Explain to the students that they have
same time! If objects or particles collide and a just told you the equation. In scientific language,
force is exerted, this is described as mechanical the three factors are mass, height and strength
working; this includes mechanical waves such as of gravity (or gravitational field strength). Each
earthquakes and sound. It may also be useful to energy store has an associated equation, but they
describe chemical reactions as a ‘reacting process’, only need to know a few of them. Record these,
which can be exothermic or endothermic. with definitions of variables and units.
Plenary Give a worked example for each equation to
Students could be challenged to give two examples supplement those on page 6 (263) of the textbook.
of each common pathway, one in the classroom Students should attempt Test yourself questions
and one from outside. 5–9 on page 7 (263) of the textbook, and could
write their own questions for familiar situations.
Support
Reinforce good layout and working, possibly by
Some of the ideas are abstract and students should
adding commentary to example answers that show
be encouraged to return to familiar descriptions of
explanations of reasoning and marks gained.
particles and forces, rather than forcing processes
into specific categories. A careful choice of Plenary
examples will help them to see straightforward Read out old exam questions and have students
comparisons. write down which equation they would use; bonus
points if they can rearrange them correctly!
Extension
Students can be challenged to describe situations Support
in which more than one process acts, for example Encourage students to be clear about the
a filament bulb will heat the environment by the difference between the symbols for the quantities
action of particles and by radiation, only some of and the abbreviations for the units; for example,
which is visible. h is the symbol for height, measured in metres,
which is shortened to m. Rearranging equations
Homework
(described as ‘changing the subject’ in maths
Sketch something that illustrates each store or
lessons) can be an extra layer of confusion. A
describe common processes that transfer energy
checklist approach may help: ‘First I underline the
between them. Alternatively, attempt Chapter
numbers in the question, then I convert the values
Review questions 1 and 2 from page 29 (284) of
to SI units, then I write the symbol next to them,
the textbook.
then I choose the equation…’.
Calculating energy: Lesson 4 Extension
Converting units to SI, for example kilometres into
metres, is a natural next step. Able students may
Learning outcomes
be tempted to skip steps; have them add their own
commentary instead to enforce clarity of thought.
1 Introduce equations.
Homework
2 Use/explain worked examples.
More questions are the obvious work to set; try
3 Recall/choose correct equation to solve
Chapter review question 4 on page 29 (284) of the
exam-style problems.
textbook. Alternatively, provide worked examples
4
1 Energy
for one or two questions with mistakes and have a process. Does this contradict the principle of
students correct them, adding explanations of what conservation of energy? Dissipation is covered in
went wrong. a later lesson, but this reinforces the idea that we
can rarely keep track of all relevant stores.
Changes in energy: Lesson 5
Support
Using not one but two equations to find an answer
Learning outcomes is likely to be one of the most mathematically
challenging ideas in the course. Using a ‘word
equation’ will help students to grasp the
1 Test recall of equations.
relationship before the calculations overwhelm
2 Link equations in worked examples.
them. Figures 1.2 and 1.3 (15.2) help to show the
3 Solve problems independently.
transfer between stores in a simple way before the
equations are needed.
Suggested lesson plan
Extension
Starter
Challenge students to add a third column to Figure
Use Lesson starter 1 to check the students
1.5 (15.4) for the elastic store. Can they explain
understanding of stores and pathways. This
in words what is happening at each stage? Precise
should not replace a test of their recall of the
language (accelerating, compressing, etc.) should
equations. Ideally, a short low-stakes recall test
be expected for a clear explanation.
should continue at regular intervals throughout
the course, with each new equation added to the Homework
possible questions. Students should focus on identified areas; some
will need to consolidate their recall and use of one
Main
equation at a time, while others will be ready for
If not already done, a short recall test of equations
more practice questions that link two equations to
would be a good idea. Hints could be provided,
find a single value.
such as the units or abbreviations, or the
measuring device used for each variable. Although
Work: Lesson 6
not strictly needed, including equations for the
elastic and thermal stores will make the test more
worthwhile. Learning outcomes
Return to the examples from previous lessons and
have students choose the relevant equations for 1 Recap force acting in newtons.
starting and ending stores. Remind students that 2 Use work done equation.
the principle of conservation of energy means that 3 Link this to previous energy stores.
with careful measurements the energy changes
before and after will be equal, allowing calculation
Suggested lesson plan
of unknowns. Pages 7–8 (264) of the textbook has
Starter
some worked examples, but take time to discuss in
Use Lesson starter 2, which gives answers and asks
words before the numbers are introduced.
students to suggest possible questions.
l Falling object: gravitational store to kinetic store
The second example is mgh. Write as E = (mg)h
l Object thrown upwards: kinetic store to
alongside or under work done = force × distance
gravitational store
and challenge students to explain the link. The
l Object fired by spring: elastic store to kinetic
best answers will recognise that weight is the force
store
towards the centre of the Earth caused by gravity
l Object heated by burning fuel: chemical store to
acting on a mass (W = mg), and that lifting an
thermal store(s)
object up by a height h means exerting a force
Students should attempt Test yourself questions over a distance.
10–12 on pages 8–9 (265). If more are needed,
Main
direct them to Chapter review questions 5 and 6 on
Students should remember that forces are measured
page 29 (284) of the textbook.
in newtons (N), and that forces have a direction.
Plenary Remind them that dragging or pushing an object
Lead discussion of why real measurements may not does not mean that you are exerting the same
show an exact match of energy before and after force as the object’s weight!
5
y Give students a selection of objects and distances to Suggested lesson plan
g
r raise/drag them through. Ask them to predict which Starter
e
n will, in everyday language, be ‘harder work’. Then Batman and Wonder Woman compete to carry a
E
1 have them calculate the work done in each case heavy load to the top of Gotham Tower. Wonder
using the equation. Unsurprisingly, their intuition Woman carries it in one trip while Batman takes
that larger forces acting over greater distances will longer because he splits it into 10 smaller loads.
require more effort is correct. Point out that simple Who has done more work on the load?
machines such as ramps might allow the necessary
Some students will recognise this is a trick
force to be reduced, but the distance is greater.
question, as the work done is the same. The
Whenever a force is involved in moving energy instinctive answer, that Wonder Woman has ‘done’
between stores, we can say that work is done on more, is about the power she has exerted.
an object.
Main
Plenary Introducing power as how fast work is done will
Challenge students with situations in which a force allow students to grasp it quickly. Avoiding light
is applied that they must link to the store which bulbs will reduce confusion about ‘wasted’ energy,
gains energy, such as: but speakers are likely to be familiar. Playing a
louder sound requires more power so exhausts
l lifting an object (gravitational)
the chemical store of the battery faster. Graphs
l pushing a trolley to cause motion (kinetic)
showing how electric cars deplete their battery
l causing (slip) friction between surfaces (thermal)
over time are a good way to show the link to
l pushing magnets together or pulling them apart
gradients. Depending on your setting, reaction rate
(magnetic)
and/or population graph curves may also be useful.
l stretching a spring (elastic).
Define the watt (W) as the unit of power, equal
Support
to 1 joule transferred per second. In many cases,
The terms ‘force’ and ‘energy’ are often confused in
kilowatts (kW) and megawatts (MW) are needed.
everyday language, and it is important that students
The worked example on page 11 (267) of the
recognise when they must be more precise. It can be
textbook is a good starting point, but try to give
helpful to describe situations using a table with three
examples of changes to other energy stores too.
columns. The first has what is observed (‘I push the
You can give abstract values for the energy or have
trolley’), the second includes an explanation of forces
students calculate them using the equations.
(‘a push is a force’) and the third covers energy (‘it’s
moving so there is energy in the kinetic store’). The Test yourself questions on page 11 (268) of
the textbook should not take students long.
Extension
Comparing two forces is surprisingly difficult, A classic practical here (explained on page 11 (267)
particularly if the students are supplying them; one of the textbook, and including Figure 1.12 (15.11)
person’s gentle push is another’s violent shove. Ask is to have students calculate their personal ‘power’.
students to explain how a newtonmeter works with They need to first find the work done when they
reference to forces and elastic stores. walk/run upstairs, which means measuring or
calculating their weight (obviously sensitive in
Homework
some cases, so having some sample data is helpful)
Link the ideas covered so far in a mind map. Ask
and measuring the height of the stairs. They can
them to choose one colour for key words, another for
then, with all due care for health and safety, race
maths and a third for everyday examples. This forces
to the top. This provides work done and time taken
them to think about the ideas and how they link
for a power calculation.
together, rather than using a hundred pretty colours.
Plenary
Power: Lesson 7
T&L Quick quiz: Energy 2 can be used here and
also offers a good recap of previous lessons.
Learning outcomes Support
Most students will grasp this idea without
difficulty, but be prepared to prompt the use of
1 Discuss ‘energy’ versus ‘power’.
2 Define rate of energy transfer. correct ‘scientific English’ to distinguish between
3 Calculate ‘personal power’. energy and power now and in the future. If in
doubt, ask them which units they would use.
6