Question

Potential energy of a bar magnet of magnetic moment $m$ placed in a magnetic field of induction $B$ such that, it makes an angle $\theta$ with the direction of $B$ is

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

Answer 1

Answer: (B)

Potential energy $P E=-m B\left(\cos \theta_{2}-\cos \theta_{1}\right)$
When $\theta_{1}=90^{\circ}$ (position of zero PE), $\theta_{2}=\theta$
$PE =-m B \cos \theta$