申論題

五 題組

(a) A conducting bar of length L has one end connected to a pivot, and the other end is connected to a conducting ring around the pivot. A magnetic field is directed perpendicular into the ring and varies with the distance r to the pivot by B(r) = 2r. If the rod rotates with a constant angular speed ω about the pivot, what is the induced motional electromotive force between the ring and the pivot?