Magnetism, an aspect of electromagnetism, one of the fundamental forces of nature. Magnetic forces are produced by the motion of charged particles such as electrons, indicating the close relationship between electricity and magnetism.
Properties of magnets
- Magnetic Materials – magnets only attract strongly certain materials such as iron, steel, nickel, cobalt, which are called ferromagnetics.
- Magnetic Poles – these are the places in a magnet to which magnetic materials are attracted, e.g. iron filings. They are near the ends of a bar magnet and occur in pairs of equal strength.
- North and South Pole – if a magnet is supported so that it can swing in a horizontal plane it comes to rest with one pole, the North-seeking or N pole, always pointing roughly towards the Earth’s north pole. A magnet can therefore be used as a compass.
- Law of magnetic poles- If the N pole of a magnet is brought near the N pole of a suspended magnet repulsion occurs. Two S poles also repel. By contrast N and S poles always attract. The law of magnetic poles summarizes these facts and states: like poles repel, unlike poles attract
Test for a magnet
A permanent magnet causes repulsion with one pole when both poles are, in turn, brought near to a suspended magnet. An unmagnetized magnetic material would give attraction with both poles of the suspended magnet. Repulsion is the only sure test of a magnet.
Magnetic Properties of Iron and Steel
Chains of small iron paper clips and steel pen nibs can be hung from a magnet. Each clip or nib magnetizes the one below it by induction and the unlike poles so formed attract.
If the iron chain is removed by pulling the top clip away from the magnet, the chain collapses, showing that magnetism induced in iron is temporary. When the same is done with the steel chain, it does not collapse: magnetism induced in steel is permanent.
Magnetic material like iron, which magnetize easily but do not keep their magnetism, are said to be soft. Those like steel, which are harder to magnetize than iron but stay magnetized, are ‘hard’. Both types have their uses; very hard ones are used to make permanent magnets.
Theory of Magnetism
If a magnetized thin piece of steel rod is cut into smaller pieces, each piece is a magnet with a N and a S pole. It is therefore reasonable to suppose that a magnet is made up of lots of ‘tiny’ magnets all lined up with their N poles pointing in the same direction. At the ends, the ‘free’ poles of the ‘tiny’ magnets repel each other and fan out so that the poles of the magnet are round the ends. In an unmagnetized bar we can imagine the ‘tiny’ magnets pointing in all directions, the N pole of one being neutralized by the S pole of another. Their magnetic effects cancel out and there are no ‘free’ poles near the ends.