Q. Magnetic moment of bar magnet is M. The work done to turn the magnet by $90{^\circ}$ of magnet in direction of magnetic field B will be
A) Zero
B) $\frac{1}{2}MB$
C) 2 $MB$
D) MB
Explanation
(d) Work done, $W = MB\left( 1 - \cos\theta \right)$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \theta = 90{^\circ}$
$\therefore\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ W = MB$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.