A steel ring has a mean diameter of 20 cm, a cross-section of 25 cm2 and a radial air-gap of 0.8 mm cut across it. When excited by a current of 1 A through a coil of 1000 turns wound on the ring core, it produces an airgap flux of 1 m Wb. Neglecting leakage and fringing, calculate
(a) relative permeability of steel, and
(b) total reluctance of the magnetic circuit.