Rankers Physics

Magnetic Properties of Matter: Practice Problem & Solution

9. A short bar magnet of magnetic moment $0.4$ J T$^{-1}$ is placed in a uniform magnetic field of $0.16$ T. The magnet is in stable equilibrium when the potential energy is: (2011 Mains)
$-0.064$ J
Zero
$-0.082$ J
$0.064$ J

Solution Explained:

To solve this problem, we apply the core principles of Magnetic Properties of Matter. Understanding the underlying formula is key to arriving at the correct answer below:

For stable equilibrium, the angle between $M$ and $B$ is $0^{\circ}$.
Potential energy $U = -MB \cos 0^{\circ} = - (0.4)(0.16)(1) = -0.064$ J.

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