1. All of the energy going into a device is either transferred or stored.
Some gets wasted in every transfer. There are unwanted energy transfers to the surroundings.
Explore 1

2. Have a look at these appliances and work out the missing numbers.
Input
Output
Electricity
200 W x 20 min =
120 kJ
Light = 15 J
Sound = ?
Heating = 100 J
Television
Input
Output
Electricity
1500 W x 4 min =
3600 J
Movement = 500 J
Heating = ?
Sound = 100 J
Hair dryer
Input
Output
Electricity
500 W x 10 min =
300 kJ
Movement = 50 kJ
Heating = 240 kJ
Sound = ? kJ
Vacuum cleaner
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3. Air conditioner Electric drill Washing machine SS1 Input Output
Electricity
4000 W x 24 min =
5000 kJ
Movement ?
Heating 4000 kJ
Sound 50 kJ
Input
Output
Electricity
600 W x 2 min = 72 kJ
Movement = 60 kJ
Sound = 3 kJ
Heating = ?
Electric drill
Input
Output
Electricity
3000 W x 100 min = kJ
Heating = kJ
Sound = 1000 kJ
Movement = ?
Washing machine
SS1
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4. The more energy transferred that is useful energy, the
more efficient the device is.
On the previous slides the RED numbers show wasted energy transfers.
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5. Rate the devices on their efficiency.
You might have seen energy efficiency ratings on a new fridge or washing machine.
Rate the devices on their efficiency.
Explore
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6. Sankey diagrams makes things much clearer.
Energy output
Transferred by heating
100 kJ
Energy input (transferred electrically)
2 kJ
Transferred by light 15 kJ
Sankey diagram for a television.
Transferred by sound 5 kJ
Explain

7. You can see that the largest arrow is heating. This is wasted energy.
Transferred by heating 100 kJ
Energy input (transferred electrically)
2 kJ
Transferred by light 15 kJ
This television is not very energy
efficient. What percentage of the energy input gets wasted?
Transferred by sound 5 kJ
Explain 7 7

8. Let’s look at the different types of light bulb
Let’s look at the different types of light bulb. Draw Sankey diagrams for each one and calculate their efficiency.
Output energy
Normal light bulb –
20 W for 10 min
Energy transferred by light = 2 kJ
Input energy (transferred electrically) = 12 kJ
Energy transferred by heat= ?kJ
Output energy
LED light bulb
Energy transferred by light= 11 kJ
Input energy (transferred electrically) 12 kJ
Energy transferred by heat= ?kJ
Elaborate
SS2