Question

A current carrying circular loop is placed in a uniform magnetic field $B$, the potential energy is minimum when the magnetic moment of the loop is

• A. $\text{Parallel to}B$
• B. $\text{Perpendicular to}B$
• C. $\text{Inclined at an angle of}{45}^{\circ }\text{to}B$
• D. $\text{Anti-parallel to}B$

Answer 1

The correct option is A $\text{Parallel to}B$

Potential energy of a current carrying loop placed in a uniform magnetic filed is given by $$U=\overrightarrow{\mu }.\overrightarrow{B}=-\mu B\cos \theta$$ Where, $\mu$ is magnetic moment.

So, $U$ will be minimum for $\theta =0^{\circ }$i.e, when $\overrightarrow{\mu }$ and $\overrightarrow{B}$ are parallel to each other.

$\Rightarrow U=U_{min}=-\mu B\cos 0^{\circ }=-\mu B$

Hence, option (a) is the correct answer.