Homework Help: Conducting rod through a magnetic field

1. Jun 11, 2010

thereddevils

There is this conducting rod being moved to the right a constant speed v by a mechanical force F along 2 parallel , smooth, and horizontal conductors in a uniform vertical magnetic field of flux density B.

The question is why is the speed constant although its being moved by a force ,F.

Well let me answer that first :

Since the conducting rod is being moved through a magnetic field , there is a change in the magnetic flux , hence an emf/current is being induced in the conductor. Now , from Fleming's left hand rule , there exist a magnetic force acting in opposite direction as the mechanical force but are of the same magnitude since the rod moves in Constant velocity.

Another thought came to me , since F=Fm , the conducting rod should be in equalibrium and shouldn't be moving so how did it move with constant velocity according to the question?

2. Jun 11, 2010

RoyalCat

Remember Newton's First and Second Laws:

$$\Sigma \vec F = \frac{d\vec p}{dt}$$

If $$\frac{d\vec p}{dt}=0$$, what does that tell us about the momentum, $$\vec p=m\vec v$$ ? Does it mean that the velocity is 0, or something else?

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