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

Magnetic field at the broad side on position (equatorial point).
$B=\frac{{\mu }_0}{4\pi }\frac{M}{{\left(d^2+l^2\right)}^{3/2}}$       [M=2ml    where m = pole strength]

Given :  $2l=8cm\Rightarrow l=4cm\text{\hspace{0.33em} ; }d=3cm$ ;  $B=4\times {10}^{-6}T$
$\therefore 4\times {10}^{-6}=\frac{{10}^{-7}(m\times 2l)}{{\left(9\times {10}^{-4}+16\times {10}^{-4}\right)}^{3/2}}$ 
$\Rightarrow m=6.25\times {10}^{-2}Am$ .