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  4×10−6T. Find the pole strength of the magnet.

Magnetic field at the broad side on position (equatorial point).B=μ04πMd2+l23/2       [M=2ml    where m = pole strength]Given :  2l=8 cm⇒l=4 cm    ;   d=3 cm ;  B=4×10−6T∴4×10−6=10−7(m×2l)9×10−4+16×10−43/2 ⇒m=6.25×10−2 Am .