A copper rod of length L and mass m is sliding down a smooth inclined plane of inclination θ with a constant
speed v. A current I is flowing in perpendicular to the plane of diagram inwards. A vertically upward magnetic
field →B exist in this region.The magnitude of the required magnetic field →B is
mgILtanθ
BIL cosθ=mgsinθ or B=mgILsinθcosθ=mgILtanθ