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Help visualizing E-field between moving magnets

  1. Jan 10, 2015 #1
    I'm doing my best at learning electricity & magnetism for the first time and I could use some help. Let's say I have two horizontal bar magnets moving horizontally towards each other at constant velocity. The changing B field should induce an electric field gradient in the perpendicular direction, but I can't quite figure out what this would look like. And what happens when the magnets stop and reverse direction?

    to make things more complicated, what if I turn the magnets at 90 degrees relative to their motion. Does this double the E field? Any help (or references to go to) is appreciated.
  2. jcsd
  3. Jan 11, 2015 #2

    Stephen Tashi

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    To figure this out, I think we'd have to know how the N and S poles of the two magnets are oriented relative to each other. As we push the two magnets together, are they repelling or attracting each other?
  4. Jan 11, 2015 #3
    I'm actually curious about both cases but let's just say they are attracting each other.
  5. Jan 11, 2015 #4

    Stephen Tashi

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    For visualizing, we can start by drawing (in 2-D) the magnetic field between two attracing magnets. (e.g. as show in http://en.wikipedia.org/wiki/Force_between_magnets). Do this in one position and another position where they are a little closer.

    I don't know how much math you want to use in this. One could develop the equations for the fields and then plot a representation.
  6. Jan 11, 2015 #5


    Staff: Mentor

    The easiest way to do this will be to write down the field for the magnet at rest and then use the Lorentz transform to calculate the field for the moving magnet.
  7. Jan 12, 2015 #6
    Thanks for the direction. I'm wanting to do some example problems and calculations to get a feel for the magnitudes of the fields relative to a source I'm familiar with. What got me interested in this was an experiment with a generator with no load connected. It seems to me that if dB/dt was large enough the resulting electric field could cause electrical breakdown in the motor. Does this happen? My thought was to check this myself by seeing what what value of B or what velocity would be needed to cause kV level fields. Does this make sense?
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