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Homework Help: Primary cause of the force induced by a current in a magnetic field.

  1. Sep 30, 2012 #1
    Not sure if this is in the right section, but anyway...
    1. The problem statement, all variables and given/known data
    Explain the primary cause of the force experienced by the rod. In your explanation you must
    refer to the magnetic field generated by the current.

    The rod is carrying current perpendicular to the magnetic field created by two magnets.
    2. Relevant equations

    F=QvB, F=BIL

    3. The attempt at a solution
    So the first thing that came to mind was using one of the aforementioned equations as an explanation, saying that since the current is perpendicular to the magnetic field and therefore a force would be produced. However, the answer is as follows:

    Owing to the moving charges of the current in the conducting rod, a magnetic field is
    generated in accordance with the right-hand grip rule. This magnetic field then superimposes
    onto the external magnetic field, resulting in a net magnetic field that has a varying intensity.
    The conductor then experiences a force in the direction of the weaker region of the field and
    the direction is given by the right-hand slap rule.

    I can't wrap my head around this. How does the induced magnetic field interact with the external magnetic field to create a net magnetic field perpendicular to the direction of the external magnetic field? Since the magnetic fields are vectors, surely if a wire did not have an upwards or downwards force on it, how does a magnetic field acting on a wire in equilibirum have an effect perpendicular to it?

    Sorry if this was confusing, and thanks for any answers.
  2. jcsd
  3. Oct 1, 2012 #2


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    Homework Helper

    Well, I think you are right:
    the magnetic field acts with a force F=QvxB on a moving charged particle.
    Current means moving particles, so there is force on a current carrying wire. You can derive how the force can be expressed in terms of current and length of the wire.

    Moving charged particles produce magnetic field and a current produces magnetic field around the wire. The resultant magnetic field around the wire is the sum of the external field and that generated by the current, but the current is not affected by its own magnetic field. Just like the electric field of a charge does not act on the charge itself.

    Last edited: Oct 1, 2012
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