Question 269 of 276

A uniform magnetic field $B$ of $0.3T$ is along the positive $\text{Z}$ -direction. A rectangular loop ($abcd$) of sides $10cm\times 5cm$ carries a current $I$ of $12A$. Out of the following different orientations which one corresponds to stable equilibrium?

ABCD

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Answer: (C)

$U=-\vec{M}\cdot \vec{B}=-MB\cos \theta$

For stable equilibrium potential energy should be minimum and $\tau =0$

${U}_{min}=-MBwhen\theta =0^{\circ}$
$\Rightarrow \cos ⁡\theta = 1$

$\Rightarrow$$\vec{M}and\vec{B}$ are on same direction.