Question

A magnet of dipole moment $m$ is aligned in equilibrium position in a magnetic field of intensity $B$. The work done to rotate it through an angle $\theta$ in the magnetic field is

• A. $m B \sin \theta$
• B. $m B \cos \theta$
• C. $m B(1-\cos \theta)$
• D. $m B(1-\sin \theta)$

Answer 1

Answer: (C)

Work done $W=\int\limits_{0}^{\theta} m B \sin \theta d \theta=m B(1-\cos \theta)$
$(\text { as } \Delta W=\tau d \theta=m B \sin \theta d \theta)$