Question

A current carrying loop is placed in a uniform magnetic field in four different orientations I, II, III & IV. Arrange them in the decreasing order of potential Energy.

• A. $I>III>II>IV$
• B. $I>II>III>IV$
• C. $I>IV>II>III$
• D. $III>IV>I>II$

Answer 1

The correct option is C $I>IV>II>III$

The potential energy is given by:

$U=-\overrightarrow{M}.\overrightarrow{B}=-MBcos\theta$

In case I:

$\theta ={180}^o$

So, $U=\pm MB$

In case II:

$\theta ={90}^o$

So, $U=0$

In case III:

$\theta$ is acute,

So, $U=-ve$

In case IV:

$\theta$ is obtuse

So, $U=+ve$

$\therefore I>IV>II>III$