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Dropping two magnets through a copper tube

  1. Apr 25, 2012 #1

    In class we were discussing the effects of a two bar magnets being dropped through a copper tube at around the same time, with the same pole facing towards each other, so that the two magnets repel - would the magnets fall through the tube faster or slower than if only one was dropped through?

    At a guess I think the magnets will fall slightly faster, the field density between the two magnets should be decreased as the lines are pointing in opposite directions, this means that flux is cut at a lesser rate so the strength of the eddy currents should be decreased.

    (The experiment was attempted once, and the effect was seen to be small, however it was quite a unreliable set-up).
  2. jcsd
  3. Apr 25, 2012 #2


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    Staff: Mentor

    I think the lower one would fall quicker, the upper one would fall slower, as both are repelling and therefore accelerating away from each other ;).

    Considering eddy currents: I don't know the relative sizes of your setup parts. However, the field lines are mainly parallel to the direction of movement, right? In that case, I wouldn't expect a large effect from eddy currents.
  4. Apr 26, 2012 #3
    Thanks, that makes sense, will try the experiment again if time and equipment allowsl
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