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CUET · PHYSICS · PYQ PAPER 2023

A short bar magnet of magnetic moment \(m =0.45 J / T\) is placed in a uniform magnetic field of 0.22 T . If the bar is free to rotate in the plane of the field, what is the potential energy of the magnet in stable and unstable equilibrium respectively?

  1. A \(-9.8 \times 10^{-2} J\) (Unstable); Zero (Stable)
  2. B Zero (Unstable); \(9.8 \times 10^{-2} J\), (Stable)
  3. C \(-9.8 \times 10^{-2} J\) (Unstable); \(9.8 \times 10^{-2} J\), (Stable)
  4. D \(9.8 \times 10^{-2} J\) (Unstable); \(-9.8 \times 10^{-2} J\), (Stable)
Verified Solution

Answer & Solution

Correct Answer

(D) \(9.8 \times 10^{-2} J\) (Unstable); \(-9.8 \times 10^{-2} J\), (Stable)

Step-by-step Solution

Detailed explanation

\(U = -mB \cos\theta\) \(U_{stable} = -(0.45)(0.22) \cos 0^\circ = -0.099 J\) \(U_{unstable} = -(0.45)(0.22) \cos 180^\circ = 0.099 J\)
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