The rectangular toroid of Fig. 3-7 in Example 3-4 consists of a material whose relative permeability can be assumed to be infi- nite. The other parameters are as given in Example

3-4. An air gap of 0.05 mm length is introduced. Calculate (a) the coil induc- tance L, assuming that the core is unsaturated and (b) the max- imum current beyond which the flux density in the core will exceed 0.3 T.