Permaent magnets

Permanent magnets are found in nature. Magnetite, which is also known as lodestone, is naturally magnetic and ancient mariners used it as an aid to navigation. Modern permanent magnets are made from alloys. One particular permanent (hard) magnetic material named alnico , is an alloy of iron, aluminium, nickel, cobalt and a small amount of copper. The magnetism that it contains arises from the structure of the atoms of the metals that are alloyed together.

Magnetic force is a natural phenomenon. To deal with magnetism, rules about its behaviour have been established. The rules that are important to our study are related to the behaviour of magnets and the main rules that concern us are:

• Magnets have North and South poles;

• Magnets have magnetic fields;

• Magnetic fields are made up from lines of magnetic force;

• Magnetic fields flow from North to South.

If two bar magnets are placed close to each other, so that the north pole of one is close to the south pole of the other, the magnets will be drawn together. If the north pole of one magnet is placed next to the north pole of the other, the magnets will be pushed apart. This tells us that like poles repel each other and unlike poles attract each other.

Electromagnetism