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 strength is `m=120 CGS units =12A-m`
Magnetic length is `2l=10vm ` 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)(T-m)/A)(4xx(12A-m)xx(0.05m)xx(0.2m))/[(0.2m^(2))-(0.05m^(2))]^(2)`
`=3.4xx10^(-5) T`.