1000 turns per meter are wound over a Rowland ring of ferromagnetic material. On passing a current of 2 ampere in the coil, a magnetic field of 10 Wb/m2 is produced in it.

The relative permeability of the material will be :

3.98 x 10³

$\mu_r = 1+ \chi = 1+ \frac{I}{H} = 1+ \frac{7.96\times 10^6}{2\times 10^3} = 3.98\times 10^3$