A toroidal iron ring has a uniform cross-sectional area of 50, and a mean magnetic path length of 100mm. the ring has an air-gap of 1mm, the ring is excited with a dc current of 1 A through a coil of 100 turns wound uniformly along its length. The iron may be assumed to be perfect magnetic material. The effect of fringing at the gap may be assumed to increase the effective area of magnetic flux at the gap by 10%.

Evaluate
(a) The exciting mmf of the coil
(b) The effective reluctance of magnetic circuit
(c) The inductance of the coil
(d) The energy stored in the magnetic field under the above excitation.