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) 

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  • 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
  • Thermal (heat) - radiator 
  • 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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