1. KS4 Physics
Energy Transfers

2. Energy Transfers Useful energy Conservation of energy Wasted energy
Contents
Energy Transfers
Useful energy
Conservation of energy
Wasted energy
Efficiency
Summary activities

3. Useful energy transfer
Many everyday objects are designed to transfer energy from one form into another useful form.
What energy transfer is an electric fan designed to carry out?
electrical
energy
kinetic
energy

4. What is the useful energy transfer?
What energy transfer is a speaker designed to carry out?
electrical
energy
sound
energy

5. What is the useful energy transfer?
What energy transfer is a wind farm designed to carry out?
Acknowledgement
© Energy Northwest/DOE/NREL
Turbine installation at the Nine Canyon Wind Project; largest wind farm to be built in Washington State.
kinetic
energy
electrical
energy

6. What is the useful energy transfer?
What energy transfer is a hydroelectric power station designed to carry out?
gravitational
energy
electrical
energy

7. Useful energy transfers
Complete the input and useful output energies for the devices in this table.
Device
Input
energy
Output energy
kettle
solar cell
catapult
coal fire
electrical
heat
light
electrical
elastic
kinetic
chemical
heat

8. Energy Transfers Useful energy Conservation of energy Wasted energy
Contents
Energy Transfers
Useful energy
Conservation of energy
Wasted energy
Efficiency
Summary activities

9. Law of conservation of energy
All energy transfers follow the law of conservation of energy:
Energy cannot be created or destroyed,
just changed in form.
This means that energy never just ‘disappears’.
The total amount of energy always stays the same,
i.e. the total input energy = total output energy.
In most energy transfers, the energy is transferred to several different forms, which may be useful or not useful.
The energy which is transferred to unwanted forms of energy is wasted.

10. Energy transfer in a television
An energy transfer diagram shows the input energy and the output energies for a device. This includes all the useful and wasted forms of energy.
For example, in a television:
light
electrical
sound
heat

11. Energy transfer in a radio
What are the main energy transfers in a radio?
(Don’t forget the wasted energy.)
sound
electrical
heat

12. Energy transfer in a car engine
What are the main energy transfers in a car engine?
(Don’t forget the wasted energy.)
kinetic
chemical
sound
heat

13. Identifying energy transfers
Question 1: An electric light bulb
Input: electrical
Output: light, heat
Question 2: A girl cycling along a road
Input: chemical
Output: kinetic, heat, sound
Question 3: A solar panel
Input: light
Output: electrical
Question 4: Firing a catapult
Input: elastic
Output: kinetic, sound
Question 5: An aeroplane taking off
Output: kinetic, sound, heat, gravitational
Question 6: Winding up a clockwork toy
Input: kinetic
Output: elastic, sound

14. Falling objects
When an object falls in a gravitational field:
Gravitational potential energy (GPE) at the top
equals the kinetic energy (KE) of the object
just before it hits the ground.
If a diver has J of GPE at the top of a cliff,
how much KE will she have just before she hits the sea?
_________
4 000 J
Assuming no energy is lost by air resistance!!!

15. Gerald the Human Cannonball

16. Energy Transfers Useful energy Conservation of energy Wasted energy
Contents
Energy Transfers
Useful energy
Conservation of energy
Wasted energy
Efficiency
Summary activities

17. Wasted energy
Whenever energy is changed from one form to another, some energy is always wasted.
Energy is usually wasted as:
heat energy;
sound energy.
All electrical devices produce a small amount of heat energy which is normally wasted.

18. car engine hairdryer jet engine washing machine
Wasted sound energy
If you can hear a device that is not designed to make noise then energy is wasted as sound.
Examples of devices which waste energy as sound include:
car engine
hairdryer
jet engine
washing machine

19. car engine television mobile phone charger radio
Wasted heat energy
If a device gets warm and it is not designed to get warm then energy is wasted as heat.
Examples of devices which waste energy as heat include:
car engine
television
mobile phone charger
radio

20. Which type of energy is wasted?

21. What happens to wasted energy?
What happens to the wasted energy produced whenever energy is changed from one form to another?
(Remember energy cannot be created or destroyed.)
Wasted energy spreads out into the surroundings – this is called dissipated energy.
This dissipated energy is too spread out to do useful work and so cannot be re-used.
This is why it is important to reduce the amount of energy that is wasted.

22. Energy Transfers Useful energy Conservation of energy Wasted energy
Contents
Energy Transfers
Useful energy
Conservation of energy
Wasted energy
Efficiency
Summary activities

23. Energy efficiency
Efficiency is a measure of how good a device is at changing energy from one form to another.
All devices waste energy, so the efficiency of a device is never 100%.
The more efficient a device
is the less energy is wasted.
Energy efficient light bulbs are more efficient than normal light bulbs because they w____ less energy. More of the e_______ energy that they are supplied with is converted into l____ energy and not h___.
aste
lectrical
ight
eat

24. Calculating efficiency
The efficiency of a device can be calculated using this formula :
efficiency =
useful energy out
total energy in
Useful energy is measured in joules (J).
Total energy is measured in Joules (J).
This means that efficiency does not have any units.
It is a number between 0 and 1 or a percentage.

25. Efficiency of a bulb
This filament bulb is supplied with 100 J of electrical energy which it converts to 45 J of light energy.
Wasted energy = Total – Useful
= 100 J – 45 J
= 55 J
How much energy
is wasted?
In what form is the energy wasted?
What is the efficiency
of the bulb?
55 J
heat
Efficiency = Useful
Total
= 45 J
100 J
= 0.45 or 45%
0.45 or 45%

26. Efficiency of a radio
This radio is supplied with 300J of electrical energy which it converts to 96J of sound energy.
Wasted energy = Total – Useful
= 300 J – 96 J
= 204 J
How much energy
is wasted?
In what form is the energy wasted?
What is the efficiency of the radio?
204 J
heat
Efficiency = Useful
Total
= 96 J
300J
= 0.32 or 32%
0.32 or 32%

27. Efficiency of a television
This television converts
2 000J of electrical energy into useful energy at an efficiency of 65%.
What useful energy does a television produce?
How much useful
energy is produced?
light and sound
Efficiency = Useful
Total
Useful = Efficiency x Total
= 0.65 x J
= J
1 300 J

28. Efficiency questions

29. Energy Transfers Useful energy Conservation of energy Wasted energy
Contents
Energy Transfers
Useful energy
Conservation of energy
Wasted energy
Efficiency
Summary activities

30. dissipated – Energy that spreads out into its surroundings
Glossary
dissipated – Energy that spreads out into its surroundings
so that it is no longer useful.
efficiency – A measure of how good a device is at changing energy from one form to another.
energy transfer – The process of changing energy from
one form into another.
input energy – The energy going into a device.
output energy – The forms of energy produced by a device.
useful energy– Energy in a form which is wanted.
wasted energy – Energy in a form which is not wanted or
is not used.

31. Anagrams

32. Energy transfers – summary

33. Multiple-choice quiz