Q.A magnetising field of 360 A m$^{-1}$ produces a magnetic flux density $B=0.6$ T in a ferromagnetic material. What is its permeability, in T m A$^{-1}$? (A) 1/300 (B) 300 (C) 1/600 (D) 600

Magnetization M is defined as the net atomic magnetic dipole moment of a material per unit volume, $M=\dfrac{m_{net}}{V}$; it is a vector quantity with SI unit A m$^{-1}$. When a material rod is placed inside a current-carrying solenoid (n turns per unit length, current I), the field produced by the solenoid ALONE is $B_0=\mu_0nI$, and the material contributes an additional field $B_m=\mu_0M$ proportional to its magnetization, so the total field is $B=\mu_0(nI+M)$. …