Question

A bar magnet has a length of 8 cm. The magnetic field at a point at a distance 3 cm from the centre in the broadside-on position is found to be 4 $\times {10}^{-6}$ T. Find the pole strength of the magnet.

Answer 1

Magnetic field at the broadside on position :

Here 2l = 8 cm, d = 3 cm

B = $\frac{{\mu }_{0}M2l}{4\pi (d^2+l^2{)}^{\frac{3}{2}}}$

$\Rightarrow 4\times {10}^{-6}=\frac{M\times 8\times {10}^{-9}}{(25{)}^{\frac{3}{2}}+({10}^{-4}{)}^{\frac{3}{2}}}$

M = $\frac{4\times {10}^{-6}\times 125\times {10}^{-6}}{8\times {10}^{-9}}$

= 6.25 $\times$ 10-2 A-m