Using the relation for potential energy of a current carrying planar loop in a uniform magnetic field, obtain expression for work done in moving the planar loop from its unstable equilibrium position to the stable position.

Explanation

Potential energy of a current loop when its dipole moment `vecM` makes angle `theta` with the field `vecB` is given by `U=-MB cos theta`
Work done in turning the loop from orientation
`theta_1` to `theta_2` is `W=-MB(cos theta_2-cos theta_1)`
In unstable equilibrium, `theta_1=180^@`, and in stable equilibrium `theta_2=0^@`
`:. W=-MB(cos 0^@-cos 180^@)=-MB(1+1)`
`=-2MB=-2(NIA)B`