Question

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

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

Answer 1

Answer: (C)

I > IV > II > III

Answer 2

U = - MB = -$Mcos \theta$
Here, M = magnetic moment of the loop 9 = angle between M and 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.