Question

A magnet of magnetic moment $20\, CGS$ units is freely suspended in a uniform magnetic field of intensity $0.3\, CGS$ units. The amount of work done in deflecting it by an angle of $30^\circ$ in $CGS$ units is

• A. $6$
• B. $3 \, \bar{3}$
• C. $3(2 - \bar{3})$
• D. $3$

Answer 1

Answer: (C)

$3(2 - \bar{3})$

Answer 2

Work done, $W =-MB_{\mu} (1 - \cos \, \theta)$
$= 20 \times 0.3 (1- \cos \, 30^{\circ})$
$= 6 \, 1 - \frac{\bar{3}}{2} = 3 \, 2 - \bar{3}$