1. The problem statement, all variables and given/known data A square coil of side a and consisting of N turns is free to rotate about a vertical axis through the mid-points of two opposite sides. It is situated in a uniform horizontal magnetic field of flux density B so that the plane of the coil makes an angle θ with the field. Draw a diagram of his arrangement as seen from above and show the couple acting on the coil when a current I flows through it. Write down an expression for the magnitude of this couple. Explain how and why this simple arrangement is modified in most moving-coil galvanometers. 2. The attempt at a solution I think this should be the correct representation of the problem: Though I don't quite understand what "couple" means. What does "show the couple acting on the coil" mean?