A silicon iron ring is wound with 800 turns, the ring having a mean diameter of 120mm and a cross-sectional area of 400mm2.
If when carrying a current of 0.5 A the relative permeability is found to be 3000, calculate
(a) the self inductance of the coil,
(b) the induced e.m.f. if the current is reduced to zero in 80ms.