Figure shows a wire sliding on two parallel, conducting rails placed at a separation ℓ. A magnetic field B exists in a direction perpendicular to the plane of the rails. What force is necessary to keep the wire moving at a constant velocity v?



Given:


Velocity of wire=v


Separation between rail=l



We know that,


Force experienced by a wire of length l carrying current I in a magnetic field B and placed perpendicular to magnetic field is given by



Now since here there is no formation of closed circuit the circuit is open and the current flowing in the wire =0


Therefore, force experienced by wire due to magnetic field =0


Hence net force on wire becomes zero and it moves with constant velocity v


Therefore, no external force is needed to move the wire with velocity v


1