Energy and Efficiency

S Thompson

Mr S Thompson

Forms of

EnergySound

Light Thermal

Kinetic

Gravitational

Chemical

Nuclear

Energy changesTo describe an energy change for a light bulb we need to do 3 steps:

Electricity Light + heat

1) Write down the starting energy:

3) Write down what energy types are given out:

2) Draw an arrow

Conservation of EnergyIn any energy change there is ALWAYS some “waste” energy:

e.g. a light bulb:

In this example HEAT is wasted and it is transferred to the surroundings, becoming very difficult to use.

Electricity Light + heat

EfficiencyEfficiency is a measure of how much USEFUL energy you get out of an object from the energy you put IN.For example, consider a TV:

Electrical Energy (200J)

Light (80J)

Sound (40J)

Heat (80J)

Efficiency = Useful energy out

Energy in

x100%

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:

100W electrical energy

“Input” energy “Output” energy

80W heat energy (given

to the surroundings)

20W light energy

More ExamplesConsider a kettle:

600W Sound

energy

400W Wasted heat

1000W Heat to water

2000W electrical energy

Consider a computer:

150W electrical energy

10W wasted sound

20W wasted heat

120W Useful light and sound