Question

A coil of N turns is wrapped around an iron ring of radius ‘d’ and cross-section
‘A’ (d > > A). Assuming a constant permeability, mu > > 1 for the iron.
Find the following :
(i) the magnetic flux as a function of the current ‘i’, and
(ii) the magnetic flux if a gap of width delta ^2 < < A) is cut in the ring.