Introduction to demagnetization:
The reverse process of magnetization in which a magnet loses part or whole of its magnetism is called demagnetization. Not only magnets or magnetized pieces of iron, but also the unmagnetised pieces of iron are constituted of molecules that themselves are magnetic character. Each molecular magnet possesses a north pole and a south pole. The reason why an unmagnetised pieces of iron does not exhibit magnetic properties although it itself is made up of magnets is that different molecular magnets form closed group so that the effect of the north pole of one of the molecular magnets on a neighbouring molecular magnet is exactly counterbalanced by the opposite pole of the other molecular magnet situated very closed to it.
Methods of Demagnetization
1.Rough handling: it is observed that if a magnet is subjected to rough treatment such as dropping from a height or hammering then it gradually loses part or whole of its magnetism.
The rough handling disturbs the alignment of some of molecular magnets so that the magnetization would become weak.
2. Heating: A magnet is found to lose its magnetism when heated. The quantity of magnetism lost would depend on the temperature to which it is heated. On heating a magnet, the internal energy of the molecular magnets increases. This results in more violent vibrations of the molecules, so that their alignment in a given direction is disturbed and the magnetization becomes weak.
Special Cases of Demagnetization
Electrical method: A long coil (solenoid) of insulated copper wire is connected to a source of alternating current. The magnet is placed inside this coil so that the magnet is along east-west direction. The current is switched on and the magnet is pulled out of the coil. When checked the magnet is found to possess no magnetism.
Self-demagnetisation: It is observed that the magnets lose their magnetism of their own accord.
The reverse process of magnetization in which a magnet loses part or whole of its magnetism is called demagnetization. Not only magnets or magnetized pieces of iron, but also the unmagnetised pieces of iron are constituted of molecules that themselves are magnetic character. Each molecular magnet possesses a north pole and a south pole. The reason why an unmagnetised pieces of iron does not exhibit magnetic properties although it itself is made up of magnets is that different molecular magnets form closed group so that the effect of the north pole of one of the molecular magnets on a neighbouring molecular magnet is exactly counterbalanced by the opposite pole of the other molecular magnet situated very closed to it.
Methods of Demagnetization
1.Rough handling: it is observed that if a magnet is subjected to rough treatment such as dropping from a height or hammering then it gradually loses part or whole of its magnetism.
The rough handling disturbs the alignment of some of molecular magnets so that the magnetization would become weak.
2. Heating: A magnet is found to lose its magnetism when heated. The quantity of magnetism lost would depend on the temperature to which it is heated. On heating a magnet, the internal energy of the molecular magnets increases. This results in more violent vibrations of the molecules, so that their alignment in a given direction is disturbed and the magnetization becomes weak.
Special Cases of Demagnetization
Electrical method: A long coil (solenoid) of insulated copper wire is connected to a source of alternating current. The magnet is placed inside this coil so that the magnet is along east-west direction. The current is switched on and the magnet is pulled out of the coil. When checked the magnet is found to possess no magnetism.
Self-demagnetisation: It is observed that the magnets lose their magnetism of their own accord.
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