Question

A current carrying circular coil, suspended freely in a uniform external magnetic field orients to a position of stable equilibrium. In this state

• A. the plane of the coil is normal to the external magnetic field
• B. the plane of the coil is parallel to the external magnetic field
• C. flux through the coil is minimum
• D. torque on the coil is maximum

Answer 1

The correct option is A the plane of the coil is normal to the external magnetic field

In equilibrium torque is zero.
$\overrightarrow{\tau }=0=\overrightarrow{M}\times \overrightarrow{B}$
$=ni\overrightarrow{A}\times \overrightarrow{B}$
$=niAB\sin \theta$
So, $\sin \theta =0\Rightarrow \theta =0^0$
So, the plane of the coil is normal to the field.