Q.A bar magnet of magnetic moment 10 Am² has a cross-sectional area of 2.5×10⁻⁴ m². If the intensity of magnetisation of magnet is 10⁶ A/m, the length of the bar magnet is ______.

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 $B=\mu_0(nI+M)$. …