Q.State Coulomb's inverse law.

Coulomb's law for magnetism is the direct magnetic analogue of Coulomb's law for electric charges: the force between two magnetic poles is directly proportional to the product of their pole strengths and inversely proportional to the square of the distance between them,

$\vec F = k\,\frac{q_{mA}q_{mB}}{r^2}\,\hat r, \qquad k=\frac{\mu_0}{4\pi}\approx10^{-7}\ \text{H m}^{-1}\ (\text{free space})$ …