Question

Figure (38-E11) shows a wire sliding on two parallel,
conducting rails placed at a separation 1. 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 ?
Х
X
X
X
X
x x
X
X
Х
X
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Figure 38-E11​

Answer 1

Answer:

Because the force exerted by the magnetic field on the rod is given by Fmagnetic = ilB, the direction of this force is opposite to that of the motion of the rod.

Now, let the external force on it be F.

Because the velocity is constant, the net force acting on the wire must be zero.

Thus, F = Fmagnetic = ilB is acting in the direction of the velocity.