A magnet is 10cm long and its pole strength is 120 CGS units (1 CGS unit of pole strength `= 0.1 A m)`. Find the magnitude of the magnetic field `B` at a point on its axis at a distance 20cm from it.

Explanation

The pole stength is `m = 120 CGS units = 12 A m`.
Magnetic length is `2l = 10cm` or ` l = 0.05 m`
Distance from the magnet is `d = 20cm = 0.2 m`. The field `B at a point in end-on position is
`B= (mu_0)/(4pi) (2Md)/((d^2 - l^2)^2)`
= (mu_0)/(4pi) (4mld)/((d^2 - l^2)^2)`
= (10^(-7) Tm)/A) (4 xx (12 Am) xx (0.05 m) xx (0.2))/([(0.2 m)^2 - (0.05 m)^2]^2)`
`=3.4 xx 10^(-5) T`.