A current loop in a magnetic field (a) can be in equilibrium in two orientations, both the equilibrium states are unstable. (b) can be in equilibrium in two orientations, one stable while the other is unstable. (c) experiences a torque whether the field is uniform or non uniform in all orientations. (d) can be in equilibrium in one orientation.

Answer: (b). τ = mBsin θ = 0 at θ = 0° and θ = 180°: two equilibrium positions. U = -mBcos θ is minimum at 0° (stable) and maximum at 180° (unstable). So the answer is (b).

A current loop in a magnetic field | NEET 2013

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Field of a Magnet & Magnet in a Uniform Field

A current loop in a magnetic field

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Answer: (b)

$\tau = mB\sin\theta = 0$ at $\theta = 0^\circ$ and $\theta = 180^\circ$ : two equilibrium positions.
$U = -mB\cos\theta$ is minimum at $0^\circ$ (stable) and maximum at $180^\circ$ (unstable).
So the answer is (b).

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