A rectangular loop with a current is allowed to rotate about

A rectangular loop with a current is allowed to rotate about axis O (which is perpendicular to the page). In the indicated orientation, the loop itself is perpendicular to the page and you are seeing only its top edge. It can be wired so that the current flows up on that top edge or down on that top edge (as indicated in the diagram). Additionally, the net torque on the loop is zero and the net force on the loop is zero in that orientation. Thus, the loop is in equilibrium! Before you continue with the question, you should make sure you understand why they are zero. If the current flows up across the top of the rectangular loop, is that equilibrium stable or unstable? Explain. If the current flows down across the top of the rectangular loop, is that equilibrium stable or unstable? Explain.

Solution

a: when the current flows up the magnetic moment is to the left , when it flows down the magentic moment is to the right.

Diagram is not provided as stated in the problem, It is assumed there is a maganeitc field B to the right.

When the current flows up any tilt of th loop form this postion, the torque restores to this position and hence it is stable equlibrium.

When the current flows down the top edge and if the loop is tilted a little from this equilibrium position it will resotr to the opposite position where the current flows up the top edge.

Thsi is true with the assumptio that the Magnetic field B is to the right. If the magnetic field is to theleft intead, then above statement get reversed.