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 = 12 A-m Magnetic length is `2l = 10 cm or l = 0.05 m` Distance from the magnet is `d = 20 cm = 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`