Magnet and Magnetism

Magnets and magnetism are essential for operating various electrical machines, so understanding them is crucial. Magnetism is defined as the property of a magnet that allows it to attract certain materials. A magnet can attract iron, cobalt, steel, and nickel. If a magnet is free to rotate, it will always align along the north and south.

Magnetic Poles

The magnetic strength of a magnet is strongest near its ends, called magnetic poles. Each magnet has a north pole and a south pole. When a magnet is hung freely, one pole will face north and the other south. These are called the north pole (N) and south pole (S).

Magnetic Materials

Ferro Magnetic Materials: These materials are strongly attracted to magnets. Examples include iron, steel, nickel, cobalt, and some metallic alloys. They have very high relative permeability.
Para Magnetic Materials: These materials are attracted to magnets but not very strongly. Examples include aluminum, tin, platinum, magnesium, and manganese. Their relative permeability is slightly more than one.
Dia Magnetic Materials: These materials are not attracted to magnets. They have a relative permeability of less than one. Examples include zinc, mercury, lead, sulfur, copper, and silver.

Properties of Magnets

1. Magnet always attracts magnetic materials.
2. Magnet always tries to align along north and south.
3. Similar magnetic poles repulse each other.
4. If a magnet is heated, or hammered the magnet can lose its magnetism.
5. If a magnet is divided into many pieces each of the pieces behaves as a complete magnet.

Types of Magnets

Magnets are of two types – natural magnet and artificial magnet. Once at Magnesium area of Asia Minor, some black stone like substances were found which could attract iron and faced along north and south. These black stones were used on those days as the direction indicator. These stones were named as loadstone. These stones were actually magnets and the magnets naturally available in mine are called natural magnet.
The magnet can also be produced artificially. Artificial magnets are of two types – permanent magnet and temporary magnet. A permanent magnet can be produced from allayed steel. An iron piece can be made permanent magnet by directional rubbing of another magnet on it. An iron piece can also be made magnet by winding conductor around the iron piece and by supplying current through the conductor.

Applications of Permanent Magnet

Permanent bar magnets are used in laboratories for various scientific experiments. U shaped magnets and ring magnets are used in different instruments like electrical energy meters, protection relays, watches, meggers, loudspeakers etc. Needle magnets are used to detect the polarity of different electrical machines.

Differences between Permanent Magnets and Temporary Magnets

1. The magnetic strength of a permanent magnet is fixed whereas the strength of a temporary magnet or electromagnet can be changed as per requirements.
2. The polarities of a permanent magnet are fixed but the polarities of the electromagnet can be altered as per requirement.
3. A permanent magnet does not lose its magnetism instantaneously but after switching off the supply the magnetism of the electromagnet suddenly vanishes.
4. A permanent magnet is not a very strong magnet but the strength of an electromagnet can be increased much higher than a same sized permanent magnet by increasing supply current.
5. By heating or hammering the magnetism of a permanent magnet can be destroyed. The magnetism of electromagnet can be lost by interrupting supply current.