An 'iron ring has a cross sectional area of 5 cm? and a mean diameter of 30 cm. An air gap of 0.5 mm is cut across the section of

the ring. The magneto-motive force (mmf) produced by the winding on the ring is 500A-turns and it is found that the flux produced in the ring is 0.3 mWb. Find the relative permeability of the iron.