1. Energy can change forms as it is transferred. A light bulb takes in electrical energy and outputs light energy and heat energy. 2. Not all energy input is useful output - some is always wasted. For a light bulb, heat is wasted energy transferred to the surroundings. 3. Efficiency measures useful energy out versus energy in as a percentage. A light bulb that outputs 80J of light from 100J of electrical input has an efficiency of 80%.

1. Energy and EfficiencyS ThompsonMr S Thompson

2. KineticNuclearThermalForms of EnergyLightChemicalSoundGravitational

3. Energy changes3) Write down what energy types are given out:1) Write down the starting energy:2) Draw an arrowElectricity Light + heatTo describe an energy change for a light bulb we need to do 3 steps:

4. Conservation of EnergyElectricity Light + heatIn this example HEAT is wasted and it is transferred to the surroundings, becoming very difficult to use.In any energy change there is ALWAYS some “waste” energy:e.g. a light bulb:

5. EfficiencyEfficiency = Useful energy out Energy inx100%Efficiency is a measure of how much USEFUL energy you get out of an object from the energy you put IN.Light (80J)For example, consider a TV:Electrical Energy (200J)Sound (40J)Heat (80J)

6. Energy Transfer diagramsFor a light bulb: Let’s say that the bulb runs on 100 Watts and transfers 20 Watts into light and the rest into heat. Draw this as a diagram:“Input” energy“Output” energy20W light energy100W electrical energy80W heat energy (given to the surroundings)

7. More ExamplesConsider a kettle:Consider a computer:2000W electrical energy150W electrical energy20W wasted heat400W Wasted heat1000W Heat to water120W Useful light and sound600W Sound energy10W wasted sound