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Making electricity.

Extracts from this document...

Introduction

Making electricity

You can make an electric current in a wire if a wire is at right angles to a magnetic field and the magnetic field is changing. We say that the electric current has been induced.

You can change the magnetism by moving the wire past the magnet, or moving the magnet past the wire. It will show up better on a meter if you use a coil of wire.

A current is generated only when the magnet is moving.

The current stops if the magnet stops moving - even if it is inside the coil.

The current goes the other way if the magnet moves in the opposite direction

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Middle

If you keep the magnet still and move the wire, you induce a current in exactly the same way.

Generators

Generators induce a current by moving a magnet inside a coil of wire, or by moving a coil of wire inside a magnetic field. One example of a generator is a bicycle dynamo.

Bicycles sometimes have dynamos which rub against the back tyre. As the bike moves, a wheel on the top of the dynamo turns a magnet inside a coil.

Generators from motors

Simple electric motors generate electric currents when you spin them. Instead of using electric current to turn a coil, turning the coil produces an electric current.

Transformers

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Conclusion

Voltage across coil 1/voltage across coil 2 = number of turns in coil 1/number of turns in coil 2

Transformers in real life

Transformers are not 100% efficient. As the current flows through the coils some heat will be produced. The output of a real transformer will be less than predicted by this calculation, so sometimes you will be asked for the percentage efficiency of a transformer.

The National Grid

Electricity is carried around the country by the National Grid. There is less energy loss at high voltages, so the electricity is sent through the wires at 275kV and 400kV. Power stations usually work at 25kV, so they use transformers to increase the voltage. Transformers are also used at the other end to bring the voltage down to 240V.

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