Electromagnetic Induction: The Electric Generator

Electricity can be generated by rotating a coil of wire in a magnetic field or by rotating a magnet inside a coil of wire.

This is how a generator works.

If a wire, or coil of wire, cuts through a magnetic field, or vice-versa, a voltage (potential difference) is produced between the ends of the wire. This induced voltage causes a current to flow if the wire is part of a complete circuit. This is called the generator effect,

The size of the induced voltage increases when:

the speed of the movement increases;

the strength of the magnetic field is increased;

the number of turns on the coil is increased;

the area of the coil is greater.

A changing magnetic field will also produce an induced voltage in a coil.

The direction of the induced current is reversed if either the direction of the movement or the direction of the magnetic field is reversed.

It can be found using Fleming's Right Hand Dynamo Rule.

The right hand rule predicts the direction of an induced current and RIGHT has an I in it - the symbol for current!

Consider the example below:

Hold up your right hand with the fingers mutually at right angles.

The Field is going from N to S (make this your First finger)
The wire is being Moved upwards (make this your thuMb)
This results in the Current flowing into the page (away from you - indicated by the cross in the diagram) - your seCond finger shows the direction of this

Try these examples (mouseover for the solution!):

At GCSE level you should be able, when provided with a diagram, to explain how an a.c. generator works, including the purposes of the slip rings and brushes

Here are the links for interactive demonstrations of generators:

AC generator

DC generator

Here is a page that explains how a simple a.c. generator works.

Try the electromagnetic induction wordsearch: click here

A metal detector works using electromagnetic induction. Click here to see how it works.

Regenerative braking converts kinteic energy into electrical energy rather than kinetic energy into heat - less energy wasted - increasing efficiency.

A 'shaking flashlight' works using electromagnetic induction.

One of the best ways to check you understand a topic is to try some past paper questions.

The link on the right takes you through to some sample questions on this topic.

The solutions do not just give you the 'answer required' but also have comments to explain why the examiner looks for particular words or phrases in an answer.