Question

Work done in displacing a magnetic dipole of magnetic moment $ M $ (bar magnet) in uniform magnetic field $ B $ from an angle $ \theta_1 $ to $ \theta_2 $ is

• A. $ W=B\left(cos\theta_{1}-cos\theta_{2}\right)/M $
• B. $ W=M\left(cos\theta_{1}-cos\theta_{2}\right)/B $
• C. $ W=M\,B\left(cos\theta_{1}+cos\theta_{2}\right) $
• D. $ W=M\,B\left(cos\theta_{1}-cos\theta_{2}\right) $

Answer 1

Answer: (D)

Work done = Change in potential energy
$=U_{f}-U_{i}$
$=-MB \, cos \,\theta_{2}-(-MB\,cos \, \theta_{1})$
$=MB (cos \theta_{1}-cos \theta_{2})$