5.24 A Rowland ring of mean radius 15 cm has 3500 turns of wire wound on a ferromagnetic core of relative permeability 800. What is the magnetic field in the core for a magnetizing current of 1.2 A?

Mean radius of Rowland ring, r= 15 cm =0.15 m
Number of turns on a feromagnetic core, N= 3500
Relative perme ability of the core material, μr=800
Magnetising curent, I=1.2 A
The magnetic field is given by the relation: B=μrμ0IN2πr
Where, μ0=Permeability of free space=4π×10-7T m A-1
B=800×4π×10-7×1.2×35002π×0.15=4.48 T
Therefore, the magnetic field in the core is 4.48 T.