Science glossary film: Efficiency

The proportion of energy supplied to a device or process that is converted into a useful form. It is calculated by dividing the useful energy output by the total energy input. This can then be multiplied by 100 to get a percentage. These loudspeakers have an efficiency of around 3 per cent. That's how much of the electrical energy supplied to the speakers is converted into sound. The rest – around 97 per cent – is converted into non-useful forms, such as heat. The human body is very efficient at converting fuel, in the form of food, into useful energy. A sprinter is four times more efficient than a motorbike.

It is calculated by dividing the useful energy output by the total energy input. This can then be multiplied by 100 to get a percentage. These loudspeakers have an efficiency of around 3 per cent. That's how much of the electrical energy supplied to the speakers is converted into sound. The rest – around 97 per cent – is converted into non-useful forms, such as heat. The human body is very efficient at converting fuel, in the form of food, into useful energy. A sprinter is four times more efficient than a motorbike.