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Paramagnetic Substances
Those substances which when placed in a magnetic field are weakly magnetized in the direction of the applied field are called paramagnetic substances e.g. aluminum, antimony, copper, sulphate etc.
Since the weak induced magnetic field is in the direction of the applied field, the resultant magnetic field in the paramagnetic substance is slightly more than the external field. Hence, the magnetic susceptibility of a paramagnetic substance is positive having a small value, e.g. +0.00001 for a typical paramagnetic substance.
It is clear that relative permeability r (= 1 + xm) for such substances will be slightly more than 1. This shows that paramagnetism is a weak form of magnetism.
It follows that a substance whose relative permeability is slightly greater than 1 is paramagnetic substance. It may be noted that paramagnetic substance loses its magnetism as soon as the external magnetic field is removed.
In a paramagnetic substance, the individual atom / molecule / ion has small net magnetic moment.
Some important properties of paramagnetic substances are :
A paramagnetic substance is feebly attracted by a strong magnet.
When a rod of paramagnetic substance is suspended freely in a uniform magnetic field, the rod comes to rest with its axis parallel to the applied field.
In a paramagnetic substance, the external magnetic field induces a magnetic field that is directed in the same direction as the applied field. For this reason, a paramagnetic substance on being placed in a non-uniform magnetic field begins to move form weaker to stronger regions of the magnetic field.
When a paramagnetic substance is placed in a magnetic field, it is feebly magnetized in the direction of the applied field.
When a paramagnetic substance is placed in a magnetic field, the magnetic field lines prefer to pass through the paramagnetic substance rather than air.
The magnetic susceptibility (xm) of paramagnetic substance has a small positive value.
The relative permeability (r) of paramagnetic substance is slightly more than 1.
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