Use the following method to show that the torque on an irregularly shaped planar loop is given by Eq. (19- 13a). The irregular loop of current in part
(a) Of the figure carries current I. There is a perpendicular magnetic field B. To find the torque on the irregular loop, sum up the torques on each of the smaller loops shown in part

(b) Of the figure. The pairs of imaginary currents flowing across carry equal currents in opposite directions, so the magnetic forces on them would be equal and opposite; they would therefore contribute nothing to the net torque. Now generalize this argument to a loop of any shape.

4a 3 40 4a