Q. A bar magnet of magnetic moment $200\ A$-$m^{2}$ is suspended in a magnetic field of intensity $0.25\ N/A$-$m$. The couple required to deflect it through $30{^\circ}$ is
A) 50 $N$-$m$
B) 25 $N$-$m$
C) 20 $N$-$m$
D) 15 $N$-$m$
Explanation
(b) $\tau = MB\sin\theta$
$\tau = 200 \times 0.25 \times \sin{30{^\circ}} = 25\ N \times m$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.