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Homework Help: How do ı can find r'?

  1. Oct 29, 2016 #1
    1. The problem statement, all variables and given/known data

    Calculate the electric field at a given position due to two point charges +q and -q located on the z axis with a separation d.
    q=10^-8 c
    P(1 1 1)
    2. Relevant equations
    p'=q*d' (d<<r)
    3. The attempt at a solution
    I think +q charge on the positive z axis and -q charge on the negative z axis so r'=p-(0 0 0). Is that wrong ?
    The charges on the z axis with separation d so happy mean d/2 on the z direction. Can ı write r'=p-(0 0 d/2) ?
    Which one ı choose ?
    Last edited by a moderator: Oct 29, 2016
  2. jcsd
  3. Oct 29, 2016 #2


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    Science Advisor
    Homework Helper
    Gold Member

    It doesn't matter as long as you state your coordinate system. I would set the origin at the midpoint since it will yield a symmetric form.
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