Question

A current carrying rectangular coil is placed in a uniform magnetic field. In which orientation, the coil will not tend to rotate

• A. The magnetic field is parallel to the plane of the coil
• B. The magnetic field is perpendicular to the plane of the coil
• C. The magnetic field is at $45^{\circ }$ with the plane of the coil
• D. Always in any orientation

Answer 1

Answer: (B)

According to the definition
$\tau =\mathrm{MB}\sin \theta$ and $U=-MB\cos \theta$
If $\theta =0,\tau =0$ and $Q_{\min }=-MB$