Electro-Magnets

A wire which has a current flowing through it has a magnetic field around it. This can be shown using plotting compasses or non filings.

If you reverse the current you reverse the polarity of the field.

A coil of wire with electricity flowing through it acts as a bar magnet. However, you can control magnetism, you can turn it on and off by using a switch to turn the current and off. You can also reverse the chaining the connections battery. Placing a piece of iron into the coil induces a magnetic effect in the iron when the current is flowing in the coil and so turning it into an electro-magnet to the polarity by on

The strength of the electro-magnet can be improved by the following:

• increasing number of coils
• increasing the current
• using an iron core (iron magnetises and demagnetises quickly, whereas steel takes time to magnetise and demagnetise)

Use of electro-magnets

• Electric generators
• Electric Motors
• Loudspeakers
• Telephones
• Tapes - flexible magnets

Beware - if you try and put too much current (ie more than 4-6v) through the coil it may get hot! It is suggested that you do not use Labpak mains voltage reducing devices to investigate electro-magnetism - it can cause a short circuit and may overheat.
Having made an electro-magnet it can now be used to produce movement.
Iron or steel can be attracted towards the end of the electro-magnet when it is switched on.
Bar magnets and other electro-magnets may be repelled away the nearest pole is the same (like poles repel ...... etc).
Metal may also spring back when the current is turned off.
One final bit of theory - and the reverse of the initial electro-mag theory - if a magnet or magnetic field is moved near a wire then an electric current flows in the wire. This is important to understanding why many things work.