Field and Wave Electromagnetics 2nd Edition by David Cheng

Exercise 14

A small circular turn of wire of radius r 1 that carries a steady current I 1 is placed at the center of a much larger turn of wire of radius r 2 ( r 2 r 1 that carries a steady current I 2 in the same direction. The angle between the normals of the two circuits is and the small circular wire is free to turn about its diameter. Determine the magnitude and the direction of the torque on the small circular wire.