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The cost of electricity

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Electric motors transfer electrical energy into kinetic energy, using magnets and coils of wire. There is a relationship between electrical power, voltage and current (power = voltage × current).

Whenever useful energy is transferred, some energy that is not useful is also transferred – we say such energy is 'wasted'. When you measure the efficiency of a device, you measure how much of the energy supplied is useful.

The cost of electricity depends upon the amount of electrical power used, the amount of time it is used for, and the charge made for each unit of electricity. It is possible to reduce heat losses from homes using insulation, and this saves money, but some methods of insulation are more cost-effective than others.

# Electric motors

If you are given information such as a diagram, you should be able to explain how an electric motor works.

## The electric motor

A simple electric motor can be built using a coil of wire that is free to rotate between two opposite magnetic poles. When an electric current flows through the coil, the coil experiences a force and moves.

The direction of the current must be reversed every half turn, otherwise the coil comes to a halt again. This is achieved using a conducting ring split in two, called a split ring or commutator. A coil of wire is used with lots of turns to increase the effect of the magnetic field.

The animation shows a simple electric motor, with the arrow heads showing the direction of the current.

Explore this activity to find out more about how the electric motor works.

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