Question

A magnetic dipole with magnetic moment M is placed at right angles to a magnetic field B. If it is rotated by an angle of ${180}^0$, the total work done is

• A. Zero
• B. 2MB
• C. -2MB
• D. MB

Answer 1

The correct option is A Zero

Workdone, $dw={\int }_{{\theta }_1}^{{\theta }_2}\tau d\theta$

$={\int }_{90}^{270}MB\sin \theta d\theta$

$=MB(-\cos \theta {)}_{90}^{270}$

$=MB\left[0\right]=0$