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Current density question

  1. Mar 7, 2006 #1
    http://higgs.phys.washington.edu/phy121b/HW/light speed changes.pdf

    Above is what I need to do. So essentially, I have to show that in the new reference frame, that the new magnetic force will counter the old electric force. So then I have to use the equation of attraction due to a wire, and then some lorentz contraction. buit then i think i'm lost...Thanks!
    Last edited by a moderator: Apr 22, 2017
  2. jcsd
  3. Mar 7, 2006 #2


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    Homework Helper

    So, in the new frame, are the + charges closer together or farther apart?
    Are the - charges closer together or farther apart?

    The "old" Electric Force was zero, as measured in frame S.
    The electric Force in frame S' is not zero. (recall Gauss to find E).
    The magnetic Force due to the (moving) + charges in frame S' is not zero.
    (recall Ampere to find B).
    Do they cancel?
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