Question

The figure represents four positions of a current carrying coil in a magnetic field directed towards right. $\hat{n}$ represents the direction of area vector of the coil. The correct order of potential energy is:-

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

Answer 1

Answer: (A)

$\because U=-BE\cos \theta$
(i) $\theta =180^{\circ }$
$\therefore U_I=+BE$
(ii) $\theta =90^{\circ }$
$\therefore U_{II}=0$
(iii) $90^{\circ }<\theta <180^{\circ }0<U_{III}<+BE$
(iv) $0^{\circ }<\theta <90^{\circ }-BE<U_{IV}<0$
$\therefore I>III>II>IV$