Field and Wave Electromagnetics 2nd Edition by David Cheng

Exercise 32

A toroidal iron core of relative permeability 3000 has a mean radius R = 80 (mm) and a circular cross section with radius b = 25 (mm). An air gap l g = 3 (mm) exists, and a current I flows in a 500-turn winding to produce a magnetic flux of 10 - 5 (Wb). (See Figure.) Neglecting flux leakage and using mean path length, find
a) the reluctances of the air gap and of the iron core,
b) B g and H g in the air gap, and B c and H c in the iron core,
c) the required current I.
Figure: A toroidal iron core with air gap