Magnetism

Introduction Of Magnetism

The ancient Greeks knew that a type of rock with magnetic properties known as lodestone or magnetite attracted iron. The compass, an important device for navigation, has a suspended magnet which aligns parallel to the magnetic field produced by the Earth and as a result points to the  North Pole. The compass was documented as early as 1040. The Ching Tsung Yao describes how iron can be magnetised by heating and quenching in water. It is known that the Vikings used Lodestone to navigate. By the end of the twelfth century, Europeans were using this simple compass to aid navigation. A steel needle stroked with such a "lodestone" became "magnetic" as well.

In 1600, William Gilbert (also known as Gilberd) of Colchester proposed an explanation in his work De Magnet for the operation of the compass and that The Earth itself was a giant magnet, with its magnetic poles some distance away from its geographic ones (i.e. near the points defining the axis around which the Earth turns). He made an experimental model of the earth by creating a .

Properties of Magnets

William Gilbert also experimented on bar magnets and found the following properties:

A magnet will always have two poles which we call arbitrarily North and South. I the magnet is broken in two this will create two new magnets with North and South poles. If a bar magnet is broken in two, at the fracture new north and south poles are formed at the point of fracture.

• Like pole repel each other. If a N pole is brought close to the north pole of a second magnet a repulsive force will be felt. Similarly if a South pole is brought close to the South pole of another magnet, the two magnets will repel each other.
• Unlike poles attract and will stick together.
• Magnets attract iron rich materials and like poles and the repulsion between like poles can be reduced if a strip of iron is placed between them.