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Homework Help: Conducting rod through a magnetic field

  1. Jun 11, 2010 #1
    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. jcsd
  3. Jun 11, 2010 #2
    Remember Newton's First and Second Laws:

    [tex]\Sigma \vec F = \frac{d\vec p}{dt}[/tex]

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