Magnetism

Magnets

The natural magnets used in the primitive compasses were called as lodestones or leading stones, which is a form of iron ore called as magnetite.

        The Earth is another natural magnet with massive magnetic properties being generated by its moving molten core. The parts where the attractive forces are concentrated are called poles. Every magnet has North Pole and South Pole that are on opposite sides of each other. The magnetic effect of electric current and magnetic materials is known as a magnetic field, which has both magnitude and direction.

        As shown in the following figure of the earth’s magnetic field, the North Pole of the compass needle will point to the top direction and the South Pole at the bottom. As the geographic poles are always on the spin axis, they are different from the magnetic poles.

FIGURE

        If we suspend a compass needle to rotate vertically and laterally, it will align itself with the earth’s magnetic field. The angle between the direction of the earth’s magnetic flux lines and the horizontal is known as the angle of dip. This angle is larger at the poles and least at the magnetic equator.

        The earth’s polarity is unstable, which would have detrimental effects on animal species. The effect would be severe on magnetic compasses and related detection systems.

        Apart from lodestones and the earth, all other magnets are artificial magnets. They can be made in any shape by magnetising in various ways. The bar magnet and the horse-show magnet are the two common types of magnets that are in wide use.

Properties of a Magnet

• A magnet attracts magnetic materials.
• A magnet always have two poles. If a magnet is cut into two pieces, each piece behave as an independent magnet and will have North and South poles.
• The like poles of a magnet repel each other.
• The unlike poles of a magnet attracts each other.
• The magnetic field is greater at the poles of a magnet than at the middle of the magnet.
• A freely suspended magnet always align in the North-South direction.