A natural discovery
Long ago, people found that certain rocks attract pieces of iron. These natural magnets are called lodestone, and they contain an iron ore called magnetite. Today almost all the magnets we use are made artificially, in shapes such as bar magnets, horseshoe (U-shaped) magnets, ring magnets and cylindrical magnets.
Magnetic and non-magnetic materials
Magnetic materials (attracted by a magnet) | Non-magnetic materials (not attracted) |
|---|---|
iron | wood |
nickel | plastic |
cobalt | rubber |
steel (an iron alloy) | glass, paper, cloth |
A common misconception is that a magnet attracts all metals. It does not. Aluminium, copper, gold and silver are metals, but they are not attracted by a magnet.
Poles of a magnet
Dip a bar magnet into iron filings and lift it out. Most of the filings cling to the two ends and very few stick to the middle. The ends, where the magnetic attraction is strongest, are called the poles of the magnet.
Every magnet has two poles: a north pole (N) and a south pole (S). If you break a magnet into two pieces, each piece becomes a complete magnet with both a north and a south pole. You can never get a magnet with only one pole.
Finding directions
Hang a bar magnet freely from a thread so that it can turn. It always comes to rest pointing in the north–south direction. The end that points north is the north-seeking pole, or simply the north pole.
A magnetic compass uses this property. It has a small magnetised needle that can turn freely, inside a box with directions marked on its dial. Travellers, sailors and pilots use compasses to find their way.
Attraction and repulsion
Bring two bar magnets close together:
Unlike poles attract: N and S pull towards each other.
Like poles repel: N and N, or S and S, push each other away.
Repulsion is the surest test for a magnet. An iron bar is attracted to both poles of a magnet, but only another magnet can be pushed away (repelled) by a magnet.
Making a simple magnet
Place an iron nail on a table. Stroke it with one pole of a bar magnet, from one end of the nail to the other, always in the same direction, lifting the magnet away at the end of each stroke. After 30 to 40 strokes, the nail becomes a weak magnet and can pick up pins.
Taking care of magnets
Magnets lose their magnetism if they are:
heated strongly,
hammered or dropped repeatedly,
stored carelessly.
Bar magnets should be stored in pairs, with unlike poles on the same side and a piece of wood between them, and two pieces of soft iron placed across the ends. Keep magnets away from mobile phones, computers, credit cards and other electronic devices, because the magnetic field can damage them.
Summary
Magnets attract iron, nickel and cobalt, but not all metals.
Every magnet has a north and a south pole, and its attraction is strongest there.
A freely hanging magnet points north–south. A compass uses this.
Like poles repel and unlike poles attract. Repulsion is the true test of a magnet.