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Ferromagnetic Substances
Those substances which when placed in a magnetic field are strongly magnetized in the direction of the applied field are called ferromagnetic substance. E.g iron, nickel, cobalt etc.
Since the strong induced magnetic field is in the direction of the applied field, the resultant magnetic field inside the ferromagnetic material is very large; often thousand times greater than the magnetizing field. Hence the magnetic susceptibility is very large; often thousand times greater than the magnetizing field. Hence, the magnetic susceptibility of a ferromagnetic material is positive having a very high value, e.g. about 8000 for soft iron.
It is clear that relative permeability r for such substances will be very high of the order of several thousands. It is clear that a substance whose relative permeability is very high is a ferromagnetic substance. It may be noted that in some ferromagnetic substances, the magnetism persists even when the external magnetic field is removed.
Some properties of ferromagnetic substances are :
A ferromagnetic substance is strongly attracted by a magnet.
When a rod of ferromagnetic substance is suspended freely in a uniform magnetic field, it quickly aligns itself in the direction of the applied field.
When a ferromagnetic substance is placed in a non-uniform magnetic field, it movers from weaker to stronger regions of magnetic field.
When a ferromagnetic substance is placed in a magnetic field, it is strongly magnetized in the direction of the applied field.
When a ferromagnetic substance is placed in a magnetic field, the magnetic field lines tend to crowd into the substance.
The magnetic susceptibility of a ferromagnetic substance is positive having a very high value.
The relative permeability ( r ) of a ferromagnetic substance is very high.
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