Magnet and Magnetism are utilized for operating all kinds of electrical machines. Hence we should have a deep concept of magnets and magnetism. The property of a magnet is called magnetism. The magnet is an element which can attract magnetic materials. Normally a magnet can attract iron, cobalt, steel, nickel. If a magnetic piece is made free to rotate, it will always align along north and south.
Magnetic Poles
The magnetic strength of a magnet is maximum at a point nearer to the ends of the magnet. These points of a magnet are called magnetic poles. Each magnet does have two poles and these are the north pole and south pole. If we hang a magnet freely one magnetic pole will face towards the north and another pole will face towards the south. The pole faces north is called the north pole and the pole faces south is known as the south pole. Generally, the north pole and south pole are denoted by N and S respectively.
Magnetic Materials
Ferro Magnetic Materials: these materials are strongly attracted by a magnet. The examples of Ferromagnetic materials are iron, steel, nickel, cobalt, some metallic alloys. The relative permeability of these materials is very high.
Para Magnetic Materials: these materials are attracted by a magnet but not very strongly. The examples of paramagnetic materials are aluminum, tin, platinum, magnesium, manganese etc. The relative permeability of these materials is slightly more than one.
Dia Magnetic Materials: these materials are not at all attracted by any magnet. The relative permeability of these materials is less than one. The examples of diamagnetic materials are zinc, mercury, lead, sulfur, copper, silver etc.
Properties of Magnets
- Magnet always attracts magnetic materials.
- Magnet always tries to align along north and south.
- Similar magnetic poles repulse each other.
- If a magnet is heated, or hammered the magnet can lose its magnetism.
- 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.
