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Methods of magnetization
Magnetization process basically involves making the dipoles to be aligned in one direction as seen above. Suitable methods of magnetization are therefore those which enable us to achieve such alignment easily.
(a) Induction method
Activity 1.4: To demonstrate magnetic induction
Click on the play button to observe the effect of magnetization by induction.
The pins are observed to attract and hold onto each other, showing that they have also acquired some magnetism. The process by which they have acquired magnetism is called induction. Induction is the method by which a magnetic material acquires magnetism when placed close to a magnet. What happens to the dipoles during the induction process? Click on the button to observe the effect on magnetic dipoles, of moving a magnet closer to a magnetic material such as iron bar.
The magnetic dipoles in the iron bar are observed to align themselves in the direction of the magnet and finally the iron bar moves towards the magnet. The alignment of magnetic dipoles causes the iron bar to become magnetized. This is what happens during the induction process.
(b) Electrical method
In this method, the material to be magnetized is placed in a solenoid connected to a direct current source (Fig.1.5). When a direct current (d.c) flows round a magnetic material, the material gets magnetized. Observe the behaviour of magnetic dipoles when the switch is closed and again when it is open.
On closing the switch, current flows and magnetic dipoles are urged to align themselves in one direction, causing the iron bar to become magnetized and attract the steel needle. The end Y becomes a North pole and X, a South pole. When the switch is opened, current stops flowing, the iron bar loses magnetism; so the falls off.
(c) Stroking method
In this method, the iron bar is stroked several times using a bar magnet as demonstrated in ANIMATION 1.6. Click on the button and take observations.
ANIM 1.6: Single stroke
During the process, the dipoles in the iron bar get more and more aligned with each successive stroking; so it gradually becomes magnetized. Finally the attraction becomes strong enough to move the pin.