The figure shows a wire sliding on two parallel conducting rails placed at a separation \( I \)....

The figure shows a wire sliding on two parallel conducting rails placed at a separation \( I \). A magnetic field \( B \) exists in a direction perpendicular to the plane of the rails. The force required to keep the wire moving at a constant velocity \( v \) will be
(a) \( e v B \)
(b) \( \frac{\mu_{0} B v}{4 \pi I} \)
(c) BIv