Ewing’s molecular theory of magnetism, Other Engineering

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Ewing’s molecular theory of magnetism

Every molecule of a magnetic substance behaves as a tiny magnet called molecular magnet.
In an unmagnetized state the molecular magnets in the iron- bar are randomly distributed as N and S poles pointing in all possible directions so that the net orientation becomes zero.
When the iron bar is magnetized with the help of a magnet, the molecular magnets arrange themselves in an orderly way. The order is due to the pointing of all the N- poles of individual in one direction and all S-poles in the opposite direction. This state of magnetisation is shown in the fig.
In side the magnetized iron bar the N- Poles of each elementary magnet is coupled to S-pole of the next magnet and so on. However there are free N-poles at one end and free S-poles at the other end. These free poles make the iron bar as a whole magnet with two (N-S) poles. These two poles are the points where N and S poles of the molecular magnets are left free or uncoupled.
Repetition of the process of magnetisation only allows the maximum alignment among the molecular magnets. This means the magnetisation of the iron bar cannot be increased further. This limit of magnetisation of a substance is called magnetic saturation.
When the magnetized iron bar is cut into number of smaller and smaller pieces, each piece continues to act as a magnet. By extension of this logic, this means that the smallest possible piece is also a magnet.
Magnetic poles always exists in pairs, two poles have equal strength. since any magnet consists of two poles, a magnet is also called magnetic dipole.
Magnetism of a magnet can be destroyed by tapping, hammering, heating etc.

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