1. Energy efficiency Some might: all must: most should :
By the end of this lesson...
all must:
Identify useful and waste energy types
Recall the 8 common types of energy
most should :
Apply the conservation of energy to a range of appliances
Calculate the efficiency of a range of devices
Some might:
Compare efficient and inefficient devices
Energy efficiency

2. Energy types Recall the 8 common types of energy
Sound energy
Heat energy
Chemical energy
Light energy
Gravitational potential
energy
Elastic potential energy
Electrical energy
Kinetic energy
Key word
Pronunciation
Definition
Conservation of energy
kon-ser-vey-shuh
Energy can neither be created or destroyed during a transfer of energy.
Recall the 8 common types of energy
All
Learning objectives
Apply the conservation of energy to a range of appliances
Most

3. Calculating efficiency
Example
25 J
light
100 J
electrical
75 J
Heat
Identify useful and waste energy types
All
Learning objectives
Calculate the efficiency of a range of devices
Most

4. Sankey Diagrams
Sankey diagrams summarise all the energy transfers taking place in a process. The thicker the line or arrow, the greater the amount of energy involved.
The Sankey diagram for an electric lamp below shows that most of the electrical energy is transferred as heat rather than light.

5. Efficiency?
How do the Sankey diagrams show which light bulb is more efficient? Describe two devices and diagrams which explain this point.
Ordinary electric lamps contain a thin metal filament that glows when electricity passes through it. However, most of the electrical energy is transferred as heat energy instead of light energy.
Modern energy-saving lamps work in a different way. They transfer a greater proportion of electrical energy as light energy.

6. Sankey diagrams 7 squares = 7 joules 10 Joules electrical energy
1 square is 1 joule of energy

7. Sankey Diagrams How to draw you Sankey Diagram… GET GRAPH PAPER
GLUE IT INTO YOUR BOOK!
Step 1) start with a blank piece of graph paper.

8. Sankey Diagrams
The height of the box represents the amount of energy that is put in.
Step 2) Draw a box to represent the input energy. Emphasise that it doesn’t matter how long the box is.

9. Sankey Diagrams
The height of the next box represents the amount of useful energy.
Step 3) Draw a second box to represent the useful energy.

10. Sankey Diagrams
The height of the final box represents the amount of wasted energy.
Step 4) We draw another box to represent the wasted energy, however, we rotate it around to show it is wasted. I liken this to a toilet, our waste goes downwards.
But we rotate it to show that it is wasted energy.

11. Sankey Diagrams Useful Output Energy Input Energy
Finally we add arrows to our boxes and label the diagram.
Step 5) Complete the arrows and add labels.
Wasted Output Energy

12. Energy Transfers Light Energy 8 Joules Input Useful Wasted
Now for an example, an energy efficient light bulb.
Electrical Energy
10 Joules
Light
Energy
8 Joules
Heat Energy
2 Joules
Input
Useful
Wasted
Now compare with a real example.
There is still 10 joules of energy available, but it now appears differently.

13. What about energy? Light Energy Electrical Energy 8 joules 10 joules
An energy efficient light bulb with an input energy of 10 joules, useful output of 8 joules and a wasted output of 2 joules.
Again I asked students where they think the boxes should go.
Heat Energy
2 joules

14. What makes a good sankey?
Arrows are labelled with input and output energies.
Light Energy
8 joules
Electrical Energy
10 joules
Boxes are the correct width.
Straight lines, drawn with a ruler.
Emphasise what makes a good sankey and what you would expect from their work.
The wasted energy is labelled.
Heat Energy
2 joules

15. What is wrong?
0:29
0:30
0:32
0:28
0:31
0:26
0:23
0:24
0:25
0:33
0:27
0:34
0:40
0:41
0:42
0:43
0:39
0:38
0:35
0:36
0:37
0:22
0:21
0:05
0:06
0:07
0:08
0:04
0:03
1:30
End
0:01
0:02
0:09
0:10
0:17
0:18
0:19
0:20
0:16
0:15
0:11
0:12
0:13
0:14
0:44
0:45
1:16
1:17
1:18
1:19
1:15
1:14
1:10
1:11
1:12
1:13
1:20
1:21
1:27
1:28
1:29
1:30
1:26
1:25
1:22
1:23
1:24
1:09
1:08
0:53
0:54
0:55
0:56
0:52
0:51
0:47
0:48
0:49
0:50
0:46
0:57
1:04
1:05
1:06
1:07
0:58
1:03
0:59
1:02
1:00
1:01
Mistakes: no units, not drawn with a ruler, drawn in pen rather than pencil, incorrect title, if this was for a light bulb then the wasted energy is in the wrong place, arrow sizes are incorrect, labels are not fully completed.

16. Arrows are labelled with input and output energies.
Boxes are the correct width.
Straight lines, drawn with a ruler.
An example of a good sankey. Show this slide and emphasise that sankey diagrams don’t have to be coloured in. I would also leave this slide up whilst students work on their sankey diagrams, as a reference point.
The wasted energy is labelled.

17. 1. Draw 3 Sankey diagrams for any of the objects that you calculated energy efficiency for.
Complete the questions on the next slide in your bookss

18. Sankey Diagrams
This diagram represents energy transfer by the drill motor. The manufacturer claims the drill motor has an efficiency of The drill motor is supplied with 3000 J of electrical energy when the hole is drilled.
What form of energy does A represent?
What does B represent and what forms of energy are included in it?
What is the useful energy transferred by the drill motor used for?
What is the useful energy from the drill motor?
What is the energy wasted by the drill?
(1-0.35) x 3000J = 1950J
0.35x 3000J = 1050J
Kinetic
wasted thermal / sound
Electrical