# P1a 2 (AQA Core Physics)

Summary notes for AQA Core Physics Unit 2 (using energy)
(notes adapted from the Nelson Thornes text book and revision guide)

• Created by: ;)
• Created on: 14-01-12 16:00

## Unit summary

• Energy cannot be created or destroyed; just transformed from one form to another or transferred from one place to another
• when energy is transformed not all is useful some is always wasted
• energy will eventually be transferred to its surroundings, usually increasing the heat of the surroundings
• efficiency = (useful energy transferred) ÷ (total energy)
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## P1a 2.1 Forms of energy

• energy exists in different forma
• energy can be transformed from one for to another

these are the forms of energy with examples:

• Light - lamp
• sound - speaker
• kinetic (movement) - cog
• nuclear - nuclear reactions
• electrical - circuit
• gravitational potential - bird in the air
• elastic potential - spring
• chemical - batteries

(the last three forms are stored energy)

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## P1a 2.2 Conservation of energy

Energy cannot be created or destroyed, it can only be transformed from one type to another, or transformed from one place to another.

example:

• electrical energy in the mains is transferred to a computer
• it is them transformed to useful light and sound energy and wasted heat energy
• the heat energy is transferred to its surroundings
• it transforms to kinetic energy of particles
• the energy can be followed forever because it will never  be destroyed
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## P1a 2.3 Useful energy

• when energy is put into a device (e.g. computer) it is called input energy
• the input energy is transferred by the device into useful energy and wasted energy
• so, total (input) energy = useful energy + wasted energy

wasted energy is transferred to its surroundings, usually as heat energy

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## P1a 2.4 Energy and efficiency

Energy is measured in joules (J)

efficiency = (useful energy) ÷ (total energy)

e.g. 6J ÷ 10J = 0.6 or (x 100) 60%

answers can be written as a decimal of percentage

nothing can be 100% efficient (except heaters which convert all energy into heat)

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## P1a 2 Summary questions

1.       Which three forms of energy are stored?

2.       Why is the only 100% efficient device a heater?

3.       What is the efficiency of a kettle when it uses 720 000 J and is supplied with 750 000 J?

4.       What happens to the rest of the energy in the above question?

5.       What is the energy in a stretched spring?

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