Ideas about energy
10 minutes
What do scientists think?
The material covered in this part of session 5 is the same as that outlined in the
energy section of the Misconceptions in science CPD unit. Some participants will
have attended that unit and so will have seen this material. Key Stage 3
consultants and/or tutors will know, from Misconceptions in science attendance
registers, who these participants are. You will need alternative activities for them.
One approach is to ask these participants to evaluate a range of energy-related
starters and plenaries that you provide, or to generate some that they can use in
their own schools.
Show slide 5.5, which contains a statement from Richard Feynman about the
abstract nature of energy.
Slide 5.5
Slide 5.5
Energy – a most abstract idea
‘There is a certain quantity, which we call energy, that does not change in the
manifold changes which nature undergoes. That is a most abstract idea, because it
is a mathematical principle; it says that there is a numerical quantity, which does not
change when something happens. It is not a description of a mechanism, or
anything concrete; it is just a strange fact that we can calculate some number and
when we finish watching nature go through her tricks and calculate that number
again, it is the same.’
Richard Feynman
The text is also reproduced on handout 5.5.
Handout 5.5
Allow participants time to read the slide or handout.
Say that:
•
Richard Feynman (a Nobel laureate) was renowned for his ability to
communicate scientific ideas.
•
Energy is particularly difficult for pupils to understand because it is, as Richard
Feynman said, ‘not a description of a mechanism, or anything concrete’.
•
Feynman goes on to illustrate how a block model for energy transfer could be
used to help understand the use of energy conservation as an accounting
system.
Show slide 5.6 and ask participants to read the story on handout 5.7.
Slide 5.6
Handout 5.7
Richard Feynman’s model: Dennis the Menace
Slide 5.6
Read handout 5.7.
Richard Feynman
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| Strengthening teaching and learning of energy in Key Stage 3 science | Session 5
| Notes for tutors
© Crown copyright 2003
Handout 5.7
Dennis the Menace
Imagine Dennis who has blocks that are absolutely indestructible and cannot
be divided into pieces. Each is the same as the other. Let us suppose he has 28.
His mother puts him with his 28 blocks into a room at the beginning of the day.
At the end of each day, being curious she counts them and discovers a
phenomenal law. No matter what he does with the blocks, there are always
28 remaining.
This continues for some time until one day she only counts 27, but with a little
searching she finds one under a rug. She realises she must be careful to look
everywhere.
One day later she can only find 26. She looks everywhere in the room, but cannot
find them. Then she realises the window is open and the two blocks are found
outside in the garden.
Another day, careful counts show there are 33 blocks. This causes considerable
dismay until it is realised that Bruce came to visit bringing his blocks with him and
left a few.
She removes the five extra blocks and gives them back to Bruce and all returns to
normal.
We can think of energy like this except there are no blocks.
We can use this idea to track energy transfers during changes. We need to be
careful to look everywhere to ensure that we can account for all the energy
(Adapted from Richard Feynman)
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Say that:
•
Feynman’s idea of using blocks to represent little packets of energy and of the
need to look carefully to locate all the energy has been used by many teachers
as a basis of an energy transfer teaching model. The blocks set a limit on
what can be transferred.
•
You saw in session 3 how transferring blocks can help pupils visualise energy
transfers.
•
Blocks or counters can also be used to introduce a quantitative aspect to
energy transfer.
Show slide 5.8 about energy transfer in an electric torch.
Slide 5.8
Energy transfers in an electric torch
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Slide 5.8
© Crown copyright 2003
Say that:
•
The numbers of blocks transferred to each place begin to suggest the relative
amounts of energy transferred by each process.
•
For example, relatively little of the energy transferred from a conventional
filament bulb (on the right-hand side of slide 5.8) is transferred by light
(represented by one block) – most is transferred by heating (represented by
four blocks).
•
In contrast, almost all of the energy on the left-hand side of slide 5.8 is
transferred from the cell to the bulb, when the electric current flows in the circuit
(represented by five blocks). Relatively little is transferred from the cell to the
surroundings by heating (represented by one block). In fact, the amount of
energy represented by one block is much too high here. Participants might like
to discuss how to show a smaller amount by considering fractions of a block or
smaller blocks.
•
It is important to remember that the model needs to be ‘good enough’. It would
be possible to have 100 blocks and then to represent the energy transferred
from the cell to the surroundings by heating more accurately using one block.
However, using a large number of blocks would make it less obvious on slide
5.8 that all the blocks have been accounted for.
Conservation of energy as a useful
accounting system during energy
transfers
25 minutes
Many teachers introduce pupils to Sankey diagrams in Year 9. Sankey diagrams
should be seen as one way to demonstrate the energy transfer teaching model.
Show slide 5.9, which shows how a Sankey diagram can be used to illustrate
energy transfer in an electric torch.
Slide 5.9
A Sankey diagram showing energy transfers in an
electric torch
Cell
Bulb
Slide 5.9
Surroundings
Light
Electric
current
Heating
Heating
Surroundings
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Demonstrate the animation of slide 5.9.
Say that:
Slide 5.10
•
Blocks or tokens are used here to reinforce the idea of accounting for all the
energy – none of the blocks/tokens can be missed off the diagram.
•
Pupils can construct their own Sankey diagrams using squared paper and
tokens.
•
This ‘hands on’ approach helps pupils visualise energy transfers. This is an
important step in their understanding of energy.
Show slide 5.10, which illustrates how pupils use tokens on Sankey diagrams.
Using tokens with Sankey diagrams
Task N Helping pupils use the idea of energy
conservation as an accounting system
Slide 5.11
Slide 5.10
10 minutes
Show slide 5.11, which gives instructions for task N.
Task N
Helping pupils use the idea of energy
conservation as an accounting system
Slide 5.11
• Choose one of the energy stories from handout 5.12.
• Use the squared paper (handout 5.13) and tokens supplied to make a Sankey
diagram representing the energy transfers in your chosen story.
Ask participants to work in pairs and to choose an energy story from
handout 5.12. Make sure that each story has been chosen by at least one pair.
Distribute squared paper (handout 5.13) and tokens and ask participants to use
these to represent their chosen story as a Sankey diagram.
Handout 5.12
Handout 5.13
Tell participants that handout 5.14 is supplied so that they can make tokens to use
with pupils back in school.
Handout 5.14
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Handout 5.12
Task N Energy stories
Choose one of the energy stories below.
Use the squared paper and tokens to draw a Sankey diagram to represent the
energy transfers in your chosen story.
Jayesh eats a chocolate bar at break time. The label says there is 1000 kJ of
energy stored in the chocolate. As he runs around he transfers 600 kJ to the
surroundings by heating and 5 kJ by sound (that’s a lot of shouting!). How
much of the energy from the chocolate bar is left to be stored by Jayesh’s body
at the end of break?
3
A ‘low-energy’ light bulb typically transfers about 80% of its energy to the
surroundings by light and the rest by heating.
4
Of every 1000 J of energy transferred to a hairdryer by the electric current, the
hairdryer typically transfers about 800 J to the warm air by heating and moving
it, about 190 J through the case to the person’s hands and about 10 J to the
surroundings by sound.
5
For every 50 J of energy transferred to the surroundings by sound, a portable
CD player transfers another 300 J by heating.
6
The journey to the seaside uses 40 l of petrol. Janice has read that each litre of
petrol stores 40 000 kJ of energy. She is curious to know where this energy has
been transferred to by the time the car stops. She wants to know how much of
the energy is transferred to the moving car. Charlie says if all she wants to know
is where the energy is at the end, she doesn’t need to know anything about the
car at all!
7
Chris finds that a toy bow and arrow can store 20 J of energy when it is fully
pulled back. When it is released, the bow transfers 10 J to the arrow, 6 J to the
surrounding air by heating, 3 J to the elastic of the bow itself by heating and
1 J to the surroundings by sound.
8
A car engine is typically only 25% efficient. For every 100 J of energy
transferred from the fuel, only 25 J ends up in the moving car. The rest is
transferred to the surroundings by heating (70 J) and sound (5 J).
Task N Grid
Handout 5.13
| Strengthening teaching and learning of energy in Key Stage 3 science | Session 5
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A fire lighter stores 200 kJ of energy. When it burns, 190 kJ is transferred to the
surroundings by heating and 10 kJ by light.
2
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1
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Handout 5.14
Task N Energy tokens
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Some participants may make their diagrams by sticking their tokens onto the
squared paper, as in the example on slide 5.10. Others may limit the number of
tokens so that they have to move the tokens across the diagram and hence model
the transfer process. Some participants may label the tokens with a value – say
10 J.
As participants complete this task, circulate among them and prime an appropriate
pair to demonstrate each of the aspects identified on slide 5.15 for task O.
Additional guidance
T
You may need to model the process for participants if they are not familiar with
Sankey diagrams.
How useful are Sankey diagrams when used in this way?
Slide 5.15
130
Allow participants a few minutes to discuss the usefulness of using Sankey
diagrams with blocks or tokens when they teach about energy conservation. Have
slide 5.15 on display and use it to provide a context for discussion if necessary.
| Strengthening teaching and learning of energy in Key Stage 3 science | Session 5
| Notes for tutors
© Crown copyright 2003
The usefulness of Sankey diagrams
Slide 5.15
How does using blocks or tokens with Sankey diagrams help pupils to understand:
• transfer of energy;
• conservation of energy;
• dissipation of energy (as energy is transferred it becomes more spread out
and less useful);
• energy efficiency?
What are the limitations of using Sankey diagrams in this way?
Task O
Demonstrating the use of Sankey diagrams
15 minutes
Ask the pairs you primed during task N to demonstrate one of the following
(selected from slide 5.15) using their Sankey diagrams:
•
transfer of energy;
•
conservation of energy;
•
dissipation of energy;
•
energy efficiency.
Take feedback on the strengths and limitations of using Sankey diagrams in this
way.
Additional guidance
T
•
Transfer of energy. Any of the energy stories except 3 and 6 should provide
an opportunity to demonstrate this. Pick a pair who have moved counters
across the diagram to show the transfer process, rather than a pair who stuck
different counters down at all stages of the transfer.
•
Conservation of energy. Any of the stories should provide the opportunity to
show this.
•
Dissipation of energy. Energy stories 4 and (possibly) 6 will provide an
opportunity to exemplify dissipation. In story 4 the concentrated energy
transferred to the hairdryer by the electric current is ‘spread out’ into several
smaller, and therefore less useful, quantities in other places.
•
Energy efficiency. This is the most challenging idea. Aim to prime one pair to
provide this feedback during the task. Ask them to show how the efficiency can
be calculated from their diagram. You may need to prompt them with the
formula:
efficiency =
useful energy transferred
total energy transferred
Participants could do this using numbers of tokens or in joules if they have
assigned a value to each token. If appropriate, discuss why the answer will be
the same in a given story irrespective of whether participants use tokens or
joules.
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If you have a small group, it may be necessary to model one or more of the
aspects identified in task O yourself.
Points that may arise include:
•
Moving the tokens across the diagram reinforces the idea of a transfer from one
place to another.
•
Having to account for all the tokens encourages pupils to look for where the
energy has gone and challenges the misconception that it simply disappears
(you are not allowed to throw any tokens away).
•
A lot of energy in one place at the start gradually gets broken down into smaller
and smaller amounts with each successive transfer.
•
Efficiency can be calculated by comparing the number of tokens (or the value of
those tokens in joules) that end up in the desired location with the total number
transferred.
•
Dissipation can be introduced by looking at the smaller amounts of energy
located in a number of different places at the end of the transfer process
compared with the concentrated store of energy in one place at the start.
Limitations include:
•
Sticking down tokens at each stage results in a proliferation of tokens, which
may reinforce the misconception about creating and destroying energy.
•
Energy is not a real thing like a token. The model may encourage pupils to think
of energy as a substance. This is particularly problematic when dealing with
heating.
•
Energy does not come in finite packets. It may be quantised into packets in
some circumstances, but there is no standard-sized energy packet.
•
Energy is not red.
Plenary
Slide 5.16
20 minutes
Show slide 5.16, which gives the expected outcomes for the session.
Plenary for session 5
Slide 5.16
Objectives for session 5
• To describe how conservation of energy can be used as an accounting system
during energy transfers
• To provide one possible teaching strategy to develop pupils’ understanding of
conservation of energy
By the end of this session participants should:
• be able to show pupils how energy conservation can be used as an accounting
system in science
• know how to use the conservation of energy to explain efficiency and dissipation
of energy
• be able to use blocks or tokens with Sankey diagrams to illustrate conservation of
energy
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Handout 5.7
Dennis the Menace
Imagine Dennis who has blocks that are absolutely indestructible and cannot
be divided into pieces. Each is the same as the other. Let us suppose he has 28.
His mother puts him with his 28 blocks into a room at the beginning of the day.
At the end of each day, being curious she counts them and discovers a
phenomenal law. No matter what he does with the blocks, there are always
28 remaining.
This continues for some time until one day she only counts 27, but with a little
searching she finds one under a rug. She realises she must be careful to look
everywhere.
One day later she can only find 26. She looks everywhere in the room, but cannot
find them. Then she realises the window is open and the two blocks are found
outside in the garden.
Another day, careful counts show there are 33 blocks. This causes considerable
dismay until it is realised that Bruce came to visit bringing his blocks with him and
left a few.
She removes the five extra blocks and gives them back to Bruce and all returns to
normal.
We can think of energy like this except there are no blocks.
We can use this idea to track energy transfers during changes. We need to be
careful to look everywhere to ensure that we can account for all the energy.
Adapted from Richard Feynman
141
| Strengthening teaching and learning of energy in Key Stage 3 science | Session 5
| Notes for tutors
© Crown copyright 2003
Handout 5.12
Task N Energy stories
Choose one of the energy stories below.
Use the squared paper and tokens to draw a Sankey diagram to represent the
energy transfers in your chosen story.
142
1
A fire lighter stores 200 kJ of energy. When it burns, 190 kJ is transferred to the
surroundings by heating and 10 kJ by light.
2
Jayesh eats a chocolate bar at break time. The label says there is 1000 kJ of
energy stored in the chocolate. As he runs around he transfers 600 kJ to the
surroundings by heating and 5 kJ by sound (that’s a lot of shouting!). How
much of the energy from the chocolate bar is left to be stored by Jayesh’s body
at the end of break?
3
A ‘low-energy’ light bulb typically transfers about 80% of its energy to the
surroundings by light and the rest by heating.
4
Of every 1000 J of energy transferred to a hairdryer by the electric current, the
hairdryer typically transfers about 800 J to the warm air by heating and moving
it, about 190 J through the case to the person’s hands and about 10 J to the
surroundings by sound.
5
For every 50 J of energy transferred to the surroundings by sound, a portable
CD player transfers another 300 J by heating.
6
The journey to the seaside uses 40 l of petrol. Janice has read that each litre of
petrol stores 40 000 kJ of energy. She is curious to know where this energy has
been transferred to by the time the car stops. She wants to know how much of
the energy is transferred to the moving car. Charlie says if all she wants to know
is where the energy is at the end, she doesn’t need to know anything about the
car at all!
7
Chris finds that a toy bow and arrow can store 20 J of energy when it is fully
pulled back. When it is released, the bow transfers 10 J to the arrow, 6 J to the
surrounding air by heating, 3 J to the elastic of the bow itself by heating and
1 J to the surroundings by sound.
8
A car engine is typically only 25% efficient. For every 100 J of energy
transferred from the fuel, only 25 J ends up in the moving car. The rest is
transferred to the surroundings by heating (70 J) and sound (5 J).
| Strengthening teaching and learning of energy in Key Stage 3 science | Session 5
| Notes for tutors
© Crown copyright 2003
Handout 5.13
Task N Grid
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| Strengthening teaching and learning of energy in Key Stage 3 science | Session 5
| Notes for tutors
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Handout 5.14
Task N Energy tokens
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| Strengthening teaching and learning of energy in Key Stage 3 science | Session 5
| Notes for tutors
© Crown copyright 2003