Motional EMF (direction of moving bar)

[sandy.bridge]

Homework Statement

Can someone please explain to me how to determine the direction of the veloicty of a bar that is conducting and inducing a current.

Fb=q(VxB)?

 

[WatermelonPig]

Use F = IL x B instead.

 

[sandy.bridge]

Consider a conducting wire attached to a small weight. Fg acts to the right, and Fb (due to magnetic field perpendicular) is directed to the left. Say Fb>Fg. If the system is allowed to reach "steady state" why is the motional emf not Fb-Fg and directed to the right?

 

[sandy.bridge]

The only reason I am asking is that I read that the magnetic force that develops due to a velocity always has to oppose it... Which doesn't seem like it would always be the case. Especially if there is a current passing through the wire such that it is that force giving it the acceleration.