A level revision

Introduction to electromagnetism

An electromagnet is a magent whose magnetic field (area around magnets which exert forces on magnetic materials) is produced by the flow of current. Because a current is required electromagnets are temporary, stop the current and stop the magnetic field.

Electromagnets are usually made out of a coil of wire which a current passing through it, the magnetic field can be strengthened by using iron cores. Both coiling the wire and using iron cores has the effect of concentrating the magnetic field.

Current-turns

Current-turns is simply the current and number of turns on the coil of an electromagent: where:
is the number of turns
and is the current.

Flux

Magnetic flux (symbol: ) is a measure of the quantity of magnetism. Think of it as an imaginary liquid which flows from the north to the south pole of a magnet. Flux flows along the the field lines.

Factors which affect flux:

Flux can be increased by changing the attributes of the electromagnet involved, to increase the flux you can:

• Increase the turns in the coil
• Increase the crurrent through the coil
• Increase the mass of the material in the core (usually iron)
• Reduce the gap between the core material and the coil

Whilst iron is usually used as the core of an electromagnet other materials such as nickel and cobalt can also be used. Both of these however are not as good as iron and will reduce the flux.

Flux is given the units weber named after the physicist, Wilhelm Eduard Weber.