What is Magnetism ?
The property due to which a magnetic substance attracts other magnetic substances like iron pieces towards it , is called magnetism.
The substance which possesses the property of magnetism is called a magnet.
Type of magnets :
1. Permanent magnets : there are two types of permanent magnets :
Natural magnets :
Definition: Pieces of naturally occurring substance like lodestone are called natural magnets.
Properties :
(i) Attractive property: They attract small iron pieces towards them.
(ii) Directive property: when suspended freely , a magnets aligns itself in the geographical North - South direction for this reason , the suspended piece is called Lodestone or leading stone.
Limitation:
(1) They may have irregular shape.
(2) They generally have weak magnetic properties.
Artificial magnets :
Artificial magnets are made of steel or special alloys like Alnico. These magnets have many small 'Atomic' magnets.
Ordinarily the atomic magnets are oriented in random directions . In this case the substance is unmagnetised.
When such a piece is placed in the North - South direction and hammered , the atomic magnets align themselves in the direction of the earth's magnetic field. They retain this alignment and the piece develops a North (N) and south (S) pole near it's ends.
Advantage :
They may be given a desired regular shape.
They are strong in magnetic properties.
Temporary magnets ( Electromagnets ) :
Electromagnets are based on the magnetic effect of electric current. An electromagnet is usually made by placing a soft iron core .
An electromagnet exhibits magnetic properties only as long as the electric current flows through the solenoid. Hence, Electromagnets are temporary magnets.