A current loop in a magnetic field

Options

A. can be in equilibrium in one orientation
B. can be in equilibrium in two orientations, both the equilibrium states are unstable
C. can be in equilibrium in two orientations, one stable while the other is unstable
D. experiences a torque whether the field is uniform or non uniform in all orientations.

Answer

C

Explanation

Torque acting on a current loop in external magnetic field is given by :
` vac tau = vec M xx vec B rArr tau = MB sin alpha `
Where `alpha ` is the angle between magnetic moment of loop `vec M ` and external magnetic field `vec B ` .
`alpha = 0^(@)` corresponds to stable equilibrium.
` alpha = 180^(@)` corresponds to unstable equilibrium .