- 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)
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)
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.
- 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
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
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)
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?