Question

A magnet of magnetic moment M is freely suspended in a constant uniform magnetic field of intensity H. Calculate work done in deflecting the magnet through an angle $\theta$ from the direction of H.

• A. MH
• B. $MH\cos \theta$
• C. $MH(1-\cos \theta )$
• D. $MH(1-\sin \theta )$

Answer 1

Answer: (C)

Relation for work done, W = - MH (cos ${\theta }_2$ - cos ${\theta }_1$)
Here ${\theta }_1$ = 0 and ${\theta }_2=\theta$
$\therefore$ W = MH (cos $\theta$ - cos 0) = - MH(cos $\theta$ - 1) = MH (1 - cos $\theta$)