Explanation
For a temporary magnet the hysteresis loop should be long and narrow.
Magnetism of a magnet falls with rise of temperature and becomes practically, zero above curie temperature.
For a diamagnetic substance χ is small, negative and independent of temperature.
Susceptibility of a paramagnetic substance is independent of magnetising field.
In the given figure OQ refers to retentivity while OR refers to coercivity. For permanents both retentivity and coercivity should be high.
Intensity of magnetisation of diamagnetic substance is very small and negative.
For paramagnetic substance magnetization M is proportional to magnetising field H, and M is positive.
It is quite clear that magnetic poles always exist in pairs. Since, one can imagine magnetic field configuration with three poles. When north poles or south poles of two magnets are glued together. They provide a three pole field configuration. It is also known that a bar magnet does not exert a torque on itself due to own its field.
As we know every atom of a magnet acts as a dipole, so poles cannot be separated. When magnet is broken into two equal pieces, magnetic moment of each part will be half of the original magnet.
In case of the electric field of an electric dipole, the electric lines of force originate from positive charge and end at negative charge. Where as isolated magnetic lines are closed continuous loops extending through out the body of the magnet.
In an atom, electrons revolve around the nucleus and as such the circular orbits of electrons may be considered as the small current loops. In addition to orbital motion, an electron has got spin motion also. So the total magnetic moment of electron is the vector sum of its magnetic moments due to orbital and spin motion. Charge particles at rest do not produce magnetic field.
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