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 B in the core for a magnetising current of 1.2 A?
Radius of ring (r) = 15cm = 0.15m
Number of turns in the ring (n) = 3500
Relative permeability of the ferromagnetic core (μr) = 800
Current in the Rowland ring (I) = 1.2A
Magnetic Field due to circular coil (B) = 
Where, μ0 = Permeability of free space = 4π × 10-7TmA-1
∴ B = 
= 4.48T
24