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

Explanation

We know that , `tau = MB sin theta `
If ` theta = 90^(@) " then " tau_("max")=MB`........... (1)
From equation (1) and (2)
`2 = (1) sin theta or sin theta = (1)/(2) or theta = 30^(@)`