The toroidal (circular cross section) core shown below is made from cast steel. The coil has 312 turns and the inner radius (r) of the toroid is 10 cm and its outer radius (d) is 15 cm. If a 3.2-mm-wide air gap is made in the toroid (across A−A'), determine the new coil current required to maintain a core flux density of 1.2 tesla. Ignore the effects of fringing.