Year 10 AQA unit P1a

1. Energy and Efficiency S Thompson Mr S Thompson

2. Kinetic Nuclear Thermal Forms of Energy Light Chemical Sound Gravitational

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

4. Conservation of Energy Electricity Light + heat In 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. Efficiency Efficiency = Useful energy out Energy in x100% 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 diagrams For 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” energy 20W light energy 100W electrical energy 80W heat energy (given to the surroundings)

7. More Examples Consider a kettle: Consider a computer: 2000W electrical energy 150W electrical energy 20W wasted heat 400W Wasted heat 1000W Heat to water 120W Useful light and sound 600W Sound energy 10W wasted sound