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
$\tau=\operatorname{MB} \sin \theta$ and $U=-M B \cos \theta$
If $\theta=0, \tau=0$ and $Q_{\min }=- MB$