1. Efficiency Ashfield Direct Learning Verity Payne Ks4 Energy

2. Efficiency of Energy Transfer  When devices transfer energy, only a part of it is ‘usefully’ transferred to where it is wanted and in the way it is wanted.  What is left is used in a non- useful way and so is ‘wasted’. This wasted energy is transferred to the surroundings which become warmer.

3. Example Calculation 1. Tungsten filament light bulb. Electrical Heat 100 joules/sec 80 joules/sec (wasted Light 20 joules/sec (useful) Efficiency = useful energy transferred by device Total energy supplied by device So for light bulb – efficiency – 20 100 x 100 =20%

4. Efficiency of Devices  The greater the proportion of energy supplied to a device, that is used usefully, the more efficient we say the device is.  For example: a car engine is 20% efficient- a lot more energy is wasted than is usefully transferred.  a microwave oven is 60% efficient- more energy is usefully transferred than is wasted.