When a bar magnet is placed at `90^(@)` to a uniform magnetic field, it is acted upon by a couple which is maximum. For the couple to be half of the maximum value, at what angle should the magnet be inclined to the magnetic field `(B)`?

Explanation

We know that, `tau=MBsintheta`
If `theta=90^(@)" then "tau_(max)=MB" "...(1)`
`(tau_(max))/2=MBsintheta" "...(2)`
From equations (1) and (2)
`2=1/(sintheta)orsintheta=1/2ortheta=30^(@)`