A magnet is suspended at an angle ` 60^@` in an external magnetic field of ` 5 xx 10^(-4) T `. What is the work done by the magnetic field in bringing it in its direction ? [ The magnetic moment = `20 A-m^(2)`]

Explanation

Work done by the magnetic field,
` W = - MB( cos theta_1 - cos theta_2)`
Here `theta_1 = 60^@ and theta_2 = 0`
`:. W = -20 xx 5 xx 10^(-4) [ cos 60^(@) - cos 0]`
`=-10^(-2)[(1)/(2)-1] = 5 xx 10^(-3) J`.