Magnets and their properties

A magnet is an object that attracts certain materials, chiefly iron. The story goes that a shepherd in ancient Greece found the iron tip of his stick clinging to a dark rock. That rock was a natural magnet, later called lodestone or magnetite. Today most magnets are made in factories from iron, steel and special alloys, in the shapes of bars, horseshoes, rings and discs.

Magnetic and non-magnetic materials

Materials that are attracted by a magnet are called magnetic materials. Iron, nickel and cobalt, and steel which contains iron, are magnetic. Materials that are not attracted are non-magnetic: wood, plastic, rubber, glass, paper, copper, aluminium, gold and silver. Notice that not all metals are magnetic.

Properties of a magnet

• It has two poles. The pull of a magnet is strongest near its two ends, called the poles. Dip a bar magnet in iron filings and most of them cling to the ends.
• It points north-south. A freely hanging magnet always comes to rest in the north-south direction. The end that points north is the north pole (N); the other is the south pole (S). This happens because the earth itself behaves like a huge magnet.
• Like poles repel, unlike poles attract. Bring two north poles together and they push each other away. Bring a north pole near a south pole and they pull together.
• Poles always come in pairs. Break a magnet in two, and each piece becomes a complete magnet with its own north and south pole. A single pole cannot be separated.

Repulsion is the sure test of a magnet. A magnet attracts a piece of plain iron as well as another magnet, but only two magnets can repel each other.

The compass

A magnetic compass is a small magnetised needle that turns freely on a pivot inside a box. Since it always points north-south, sailors, soldiers and trekkers have used it for centuries to find directions.

Making a magnet

Take an iron nail or a steel needle. Stroke it with one pole of a bar magnet from one end to the other, lift the magnet, bring it back and stroke again, thirty or forty times, always in the same direction. The nail becomes a weak magnet. A current flowing through a coil of wire wound around an iron nail also makes a magnet, called an electromagnet. It works only while the current flows. Cranes in scrap yards and electric bells use electromagnets.

Uses and care

Magnets are found in refrigerator doors, speakers, motors, fans, pencil boxes and toys. A magnet loses its power if it is heated, hammered or dropped. Bar magnets should be stored in pairs, with unlike poles side by side and a piece of soft iron, called a keeper, across each end. Keep magnets away from phones, computers and bank cards.