PHYSICS · Subjective · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
A rectangular loop of N turns, each of length l and breadth b, carries a steady current I. The loop is placed in a uniform magnetic field B making an angle θ with the normal to the plane of the loop.
(i) Starting from the expression for the magnetic force on a straight current element, show that the net translational force on the loop is zero.
(ii) Hence derive an expression for the moment of the couple acting on the loop.
(iii) Rewrite the result obtained in vector form using magnetic dipole moment and explain the physical meaning of the vector product that appears.
(iv) Discuss the conditions for stable and unstable equilibrium of the loop in the field.