Define the term magnetic susceptibilities of a material. Derive the relation between relative permeability and magnetic susceptibility of a material.

Dear Student,

Magnetic susceptibility is a unit less parameter which symbolises the extent to which a material is susceptible to an external magnetic field. If the material doesn't respond to an external magnetic field by producing any magnetization then its susceptibility must be zero.
 
Magnetic susceptibility of paramagnetic materials is small and positive. For diamagnetic materials it is also small but negative.
 

When a substance is placed in a magnetising field, it becomes magnetised. The total magnetic flux density B with rightwards arrow on top within the substance is the flux density stack B subscript 0 with rightwards arrow on top that would have been produced by the magnetising field in vacuum plus the flux density stack B subscript m with rightwards arrow on top due to the magnetisation of the substance.
So, effective magnetising field is,
B with rightwards arrow on top space equals space stack B subscript 0 with rightwards arrow on top space plus space stack B subscript m with rightwards arrow on top
But, stack B subscript 0 space with rightwards arrow on top space equals space mu subscript 0 H with rightwards arrow on top space a n d space stack B subscript m with rightwards arrow on top space equals space mu subscript 0 I with rightwards arrow on top
Where, I with rightwards arrow on top is the intensity of magnetisation induced in the sample.
Therefore,
stack B subscript 0 space with rightwards arrow on top space equals space mu subscript 0 H with rightwards arrow on top space plus space mu subscript 0 I with rightwards arrow on top space equals space mu subscript 0 open parentheses H with rightwards arrow on top space plus I with rightwards arrow on top close parentheses rightwards double arrow space stack B subscript 0 space with rightwards arrow on top space equals space mu subscript 0 open parentheses H with rightwards arrow on top space space plus space chi subscript m H with rightwards arrow on top space close parentheses space equals space mu subscript 0 space open parentheses 1 plus chi subscript m close parentheses H with rightwards arrow on top
Where, I with rightwards arrow on top space equals space chi subscript m H with rightwards arrow on top and also, B with rightwards arrow on top space equals space mu H with rightwards arrow on top
Therefore,
 mu H with rightwards arrow on top space equals space mu subscript 0 open parentheses 1 plus chi subscript m close parentheses H with rightwards arrow on top space rightwards double arrow space mu space equals space space mu subscript 0 open parentheses 1 plus chi subscript m close parentheses rightwards double arrow space mu over mu subscript 0 space equals space 1 plus chi subscript m space rightwards double arrow space mu subscript r space equals space 1 plus chi subscript m
Where, mu subscript r = relative permeability.

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