Rankers Physics

Magnetic Properties of Matter: Practice Problem & Solution

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

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 $vec{M}$ and $vec{B}$ is $theta = 0^{circ}$. The potential energy is $U = -MB cos 0^{circ} = -0.4 times 0.16 = -0.064 text{ J}$.

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