Q. A bar magnet is placed in the position of stable equilibrium in a uniform magnetic field of induction B. If it is rotated through an angle $180{^\circ},$ then the work done is ($M = \ $Magnetic dipole moment of bar magnet)
A) MB
B) 2MB
C) $\frac{MB}{2}$
D) Zero
Explanation
(b) $W = MB(1 - \cos\theta)$
$\ \ \ \ \ \ = MB\left( 1 - \cos{180{^\circ}} \right) = 2MB$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.