Q. If air core is replaced by an iron core in an inductor, its self-inductance is increased from to . The relative permeability of iron is

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Solution:

Inductance of a solenoid coil of length , total number of turns and cross-sectional area , is given as

where, is the permeability in vacuum (or air).
If air core is replaced by iron core, inductance will be given as

On dividing Eq. (ii) by Eq (i). we get


where, is the relative permeability of iron. Given,