The efficiency of an electrical device depends on:
The more energy a device wastes, the less efficient it is.
To calculate efficiency, use the equation:
This is when:
The energy supplied to a light bulb is 200 J. A total of 28 J of this is usefully transferred. How efficient is the light bulb?
Efficiency can be calculated as a percentage. Multiply by 100 to convert this answer into a percentage:
percentage efficiency = 0.14 × 100
percentage efficiency = 14%
In this example, the light bulb is not very efficient since most of the energy supplied is not transferred usefully. Most of the energy will have been dissipated by infrared radiation. This is because light bulbs become very hot when they are switched on, which increases the thermal store of the surroundings.
Efficient devices use less fuel than less efficient devices. They can operate at a lower power because less of the supplied energy store is wasted.
Efficiency can be improved by: