A rectangular loop of sides ` 10 cm and 5 cm` carrying a current `1 of 12 A` is placed in different orientations as shown in the figure below:
If there is auniform magnetic field of `0.3 t` in the positive z direction , in which orientations the loop would be in (i) stable equilibrium and (ii) unstable equilibrium ?

Options

A. (i) and (ii) respectively
B. (i) and (iii) respectively
C. (ii) and (iv) respectively
D. (ii) and (iii) respectively

Explanation

Torque on the coil, `tau=IAB sin theta=MB sin theta`
where `theta` is the angle between `vecM` and `vecB`. For equilibrium, torque is zero.
In case of stable equilibrium, `vecM` is parallel to `vecB` and in unstable equilibrium `vecM` is antiparallel to `vecB`. The same is true for figure. (ii) and fig. (iv) respectively.