Electrical appliances

There are many electrical appliances that are used in the home to transfer electrical energy to other useful forms.

ApplianceUseful energyWasted energy
Electric kettleEnergy that heats the water.Internal (thermal) energy heating the kettle. Infrared radiation lost to the surroundings.
HairdryerInternal (thermal) energy heating the air. Kinetic energy of the fan that blows the air.Sound energy. Internal (thermal) energy heating the body of the hairdryer. Infrared radiation lost to the surroundings.
Battery operated torchLight radiation given out by the hot filament of the bulb.Infrared radiation lost to the surroundings.
Battery operated analogue wall clockThe kinetic energy of the hands moving around.The sound energy of the ticking noise.

The greater the amount of the supplied electrical energy that the appliance transfers to useful energy stores, the more efficient the device will be. This can be shown in an energy transfer diagram.


A kettle will transfer the supplied electrical energy to both useful and wasted energy stores. The useful energy store will heat the water and the wasted energy stores will be dissipated to the surroundings.

Energy transfer diagram of water with figures.

As efficiency is calculated using the equation:

efficiency = \frac{useful \: power \: transferred}{total \: power \: supplied}

efficiency = \frac{180,000}{200,000}

efficiency = 0.9

As a percentage, this is (0.9 x 100)% = 90%.


What are the useful and wasted stores of energy for a washing machine?

Useful stores - kinetic energy of the drum, internal (thermal) energy of the water. Wasted stores - sound energy and infrared radiation dissipated to the surroundings.