Current I is carried in a wire of length ' L '. If wire is bent into a circular coil of single turn, the maximum torque in a given magnetic field B is

Step-by-step solution

The maximum torque _ max on a current-carrying coil in a magnetic field B is _ max = NIAB , where N is the number of turns, I the current, A the area. For a single-turn coil with wire length L bent into a circle, the circumference is L = 2 r , so r = L 2 . The area follows as A = r^2 = ( L 2 )^2 = L^2 4 . Substituting into the torque equation gives _ max = I L^2 4 B = L^2IB 4 , which corresponds to option B .