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Methods of Magnetisation

Artificial magnets are generally prepared by any one of the following methods:
  1. Mechanical method.
  2. Electrical method.
Mechanical Method
Single Touch Method Take a soft iron piece which is to be magnetised and place it on a table. Rub the soft iron piece with any one end say, north pole of a bar magnet. Repeat this many times without changing the pole or direction of rubbing as shown in Figure. The soft iron piece gets magnetised.

This process of magnetising by rubbing with a magnet is called single touch method (mechanical method).
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Single Touch Method
Double Touch Method Take an iron piece and place it on the table. Take two bar magnets and place them at the centre of the iron piece with their unlike poles pointing at each other. Rub the iron piece with them several times without changing the poles and direction as shown in Figure. This iron piece when brought near the iron filings attracts them showing that it is magnetised.
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Double Touch Method

Electrical Method

In this method, electric current is used for magnetising a steel rod or a rod of soft iron. These types of magnets are called electromagnets.
Wind a good length of copper wire around a steel bar which is to be magnetised. Connect the ends of the wire to a switch and terminals of a battery. When the electric current passes through the copper wire, in a short time the steel bar gets magnetised permanently. If a soft iron bar is used, it becomes a strong magnet temporarily. It loses its magnetism as soon as the current in the coil is switched off. Such temporary magnets are called electromagnets.


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Electrical Method


Uses of Electromagnets
  1. Electromagnets are used in electric motors which are used in fans, washing machines, etc.
  2. Electromagnets are used in electric bells.
  3. Electromagnets are used for lifting scrap iron objects in a scrap yard.
  4. Electromagnets are used by surgeons for removing iron bits from wounds.
  5. Electromagnets are used in telephone, telegraph, radio, television, loudspeaker, etc.
  6. Electromagnets are used as cranes to lift heavy iron and steel articles in factories.
Uses of Magnets
  1. Magnets are used in magnetic compass to find the direction.
  2. Magnets are used in refrigerator doors to keep them shut tightly.
  3. Ceramic magnets are used in large computers and electric motors.
  4. Magnets are used in bicycle dynamos.
  5. Magnets are used in toys to give a magical effect.
  6. Magnetic levitation (maglev) trains have come into existence in some advanced countries, where the train is able to float without touching the rails due to magnetic repulsion.
  7. Magnetic resonance imaging uses principle of magnetism. MRI provides images of organs of human body to diagnose diseases.

Demagnetising a Magnet

The magnetic property of a magnet gets destroyed when
  1. a magnet is heated red hot,
  2. dropped from a considerable height several times,
  3. hammered several times,
  4. magnets are kept in disarray, i.e., when like poles are tied together.
Care and Storing Magnets Magnets must be kept in a specific manner to ensure retention of magnetism for a long time. Some of these techniques are shown in Figure.


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Storing Magnets


First, keep two bar magnets with a wooden piece in between them so that the opposite poles point the same direction. Then join the opposite poles at each end with soft iron pieces. These are called magnetic keepers.
Similarly, horseshoe magnet or U-shaped magnets are also preserved by using keeper as shown in the figure.

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