Permanent Magnets And Magnetic Behaviour

Permanent Magnets

The magnetic field is produced by objects known as magnets. When these properties of magnetism are not lost throughout time it’s known as a permanent magnet.

Magnetic Behaviour

When imposing a magnetizing field on ferromagnetic substances the domains get arranged to produce magnetism and do not go back to their normal state. When the driving field is zero and even then the domains have not rearranged themselves to normalcy the time the substance takes to demagnetize or remains magnetised for is known as remanence. If we try to put the magnetic property back to zero by applying a field in an opposite direction the amount of that reverse field that’s required to demagnetise that substance is known as coercivity. The lack to retain the magnetic property of a substance is known as hysteresis.

Have you ever noticed that an iron nail which has been attached to a magnet for some time attracts other non-magnetic iron nails for a short span even after it has been detached from the magnet? This is because the domains of the iron nail had been reoriented. This effect is weak and is lost pretty soon. Therefore, an iron nail will not be considered as a permanent magnet.

The main advantage of a permanent magnet over any other type is that it does not need a continuous supply of external energy (in the case of electromagnets, electricity) to exhibit magnetism. For example, permanent magnets are used as compass needles.

Example of Permanent Magnets

An everyday example of a permanent magnet is a refrigerator magnet. The image below shows the magnetic field produced by a bar magnet. The magnetic field is the sphere of influence of the magnet.

This can be visualised by sprinkling iron filings on a bar magnet. The filings will arrange themselves on the magnetic field lines of the magnet used. The strength of different magnets can be seen physically in this way.

This can be visualised by sprinkling iron filings on a bar magnet. The filings will arrange themselves on the magnetic field lines of the magnet used. The strength of different magnets can be seen physically in this way.