How do generators work?

A motor turns electricity into movement. A generator does the opposite, we provide the motion and it produces electricity.

Michael Faraday discovered that when a conductor is made to move through a magnetic field then a potential difference(voltage) is induced (made to happen) across its ends. You should imagine the conductor "cutting" through the magnetic field lines. When a conductor cuts field lines we get an induced p.d.

If this conductor is part of a complete circuit then a current will also be induced. Reversing the direction of the motion or the magnetic field reverses the potential difference and the induced current.

If a magnet is moved into a coil then a potential difference is induced across the terminals of the coil. If the magnet is pulled out of the same coil then the potential difference and so also the current is reversed.

To induce a potential difference you can either move the magnet or the coil. It doesn’t matter as long as they move relative to each other.

How do a.c. generators work?

A generator contains a coil or copper wire and a magnetic field. Usually the coil rotates and the field doesn't and so a p.d. is induced across the ends of the coil. Rotating the coil is a bit like moving the magnet in and out of the coil in the diagram above so an alternating p.d. is produced which produces an alternating current.

The slip rings and brushes allow the coil to rotate freely. If there were just wires they would very quickly get tangled up.

What affects how big the induced potential difference is?

When a conductor cuts field lines a potential difference is induced. The more field lines are cut every second the greater the induced p.d.

We can get a bigger p.d. therefore if we do any of the following;

a) increase the speed of the conductor relative to the field (e.g. spin the coil faster)

b) have a stronger magnetic field

c) use a coil with more turns

d) use a coil with a bigger area

___________________________________________________________________________________________________________________________________

Revision Questions

1. If you took a bicycle dynamo to pieces what would you find inside?

2. One design of a byclcle dynamo does not produce a big enough voltage. How could it be increased?

3. Why do you travel slower when you turn your byclcle dynamo on?

4. Explain why generators need slip rings and brushes?

5. What makes the generators in a power station turn around?