Magnetics 4 Question 7
8. A current carrying loop is placed in a uniform magnetic field in four different orientations, I, II, III and IV. Arrange them in the decreasing order of potential energy.
(2003, 2M)
(III)
(IV)
(a) I $>$ III $>$ II $>$ IV
(b) I $>$ II $>$ III $>$ IV
(c) I $>$ IV $>$ II $>$ III
(d) III $>$ IV $>$ I $>$ II
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Answer:
Correct Answer: 8. (c)
Solution:
- $U=-\mathbf{M B}=-M B \cos \theta$
Here, $\mathbf{M}=$ magnetic moment of the loop $\boldsymbol{\theta}=$ angle between $\mathbf{M}$ and $\mathbf{B}$
$U$ is maximum when $\theta=180^{\circ}$ and minimum when $\theta=0^{\circ}$. So, as $\theta$ decreases from $180^{\circ}$ to $0^{\circ}$, its PE also decreases.
