MAGNETISM AND SOME DETAILS

Sailors used magnetic compasses to find their way on the world's oceans at least 1000 years ago, but the true nature of magnetism puzzled people for many centuries. Magnetism is an invisible force that comes from objects called magnets. The region around a magnet in which its magnetism acts is called a magnetic field.

Magnetic Earth

The earth itself act like a giant bar magnet, with a magnetic field and two magnetic poles. These poles are found near the earth's geographical north and south poles. The earth's magnetism is probably caused by the movement of  molten iron at the earth's core.

The earth's magnetic field stretches more than 60,000km (37,000 miles) out into space. In addition to affecting objects on the planet's surface, the earth's magnetism also affects electrically charged particles such as electrons and protons emitted by the sun. The other planets in the solar system also have magnetic fields, as does the sun itself.

Aurora:

The earth's magnetic poles pull electrically charged particles from the sun into the atmosphere. As the particles strike atoms or molecules in the air, coloured light is emmited in a dazzling display called an aurora.

Magnetic materials

When placed within a magnet's force field, some materials turn into magnets themselves-either briefly or permanently. These materials are said to be magnetic.

Inside a magnetic material, there are tine regions of magnetism called domains, all pointing in different directions. Their effects cancel out, so there is no overall magnetism.

In a magnet, the domains all point the same way. Their effects combine to give a strong magnetism.

Placing a bar magnet near a magnetic material causes the material's domains to line up and point in the same direction, turning it into a magnet. This is magnetic induction. This effect is usually temporary, but some material such as steel, stay permanently magnetized.

Magnetic forces

When two magnets are placed pole to pole, a force act between them. Different poles (a north and a south) pull each other together. This is attraction. Similar poles (two north or two south) push (repel) each other apart. This is repulsion.