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Induced voltage and magnetic force

  1. Jun 19, 2015 #1
    Hey all!

    I have a question about induced voltage and magnetic force "acting together". What I mean is that I know that when there is a perpendicular magnetic field acting on a wire that has current going through it, it will produce a magnetic force perpendicular to both magnetic field and current/wire as according to Ampere/Lorentz law.

    But at the same time I know that a changing magnetic field acting on a perpendicular wire will produce a current in it accroding to Faraday's law. So my question is that if there is a wire with some current I going through it and there is a changing magnetic field B acting on it, then what will happen? Will it generate just induced voltage and the wire will stay motionless or will it move because of the force acting upon it and there will be no induced voltage generated? Or will it be somekind of a mix of both- that the magnetic field will generate some current as well as some movement.

    Maybe the answer to this is obvious and I have some opinion what should happen, but I'm not so sure about it at the moment.

  2. jcsd
  3. Jun 19, 2015 #2


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    Say that you have a (x,y,z) system of coordinates with a wire conducting a DC-current along the x-axis, and a electromagnet with AC-current producing a magnetic field parallel to the y-axis.

    1) A changing force will act upon the wire in the z-direction. The wire will vibrate in this direction due to ineraction between the DC-current and the changing magnetic field.

    2) A circulation voltage and thus a circulation (eddy)current will be induced inside the wire ( not along ). This eddy current will interact with the magnetic field so that the wire will also vibrate ( a small amount ) in the y-direction.
  4. Jun 19, 2015 #3
    Just to make sure I get it right - so besides circular (eddy) current there won't be any voltage and current produced alongside the wire (x-axis)?
    Even if the wire would be fixed and could not oscillate in the diestcion of z-axis?

    Thank you so much for answering!
  5. Jun 19, 2015 #4


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    The current flowing inside (along) the wire, must of course have a path wherein the current can return, forming a circulation loop. You cannot have a current flowing, without flowing somehow in a closed loop ( a consequence of Kirchhoffs current law ).

    If the shape of this circulation-loop includes an amount of flux from the electromagnet ≠ 0, there will be induced ac-voltage in the loop, but you don't know.

    If, for example, the return path runs straight below or straight above the wire, no flux will be included in the current-loop ( say that the flux direction is straight up/down ), thus no voltage will be induced. Contrary, if the return path includes a (flat) coil with 1000 turns lying in the x-z plane, the closed loop will include a lot of flux.
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