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Homework Help: Electric Fields and charges of equal magnitude

  1. Sep 28, 2010 #1
    1. Two point charges of equal magnitude are 8.4 cm apart. At the midpoint of the line connecting them, their combined electric field has a magnitude of 45 N/C.

    Find the magnitude of the charges.

    2. E=k(q)/r^2

    3. I've tried 45= 8.99x10^9(q)/(.084)^2 and got q to equal 35 pC, but that isn't correct :(
  2. jcsd
  3. Sep 30, 2010 #2


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    Homework Helper

    Hi mli273,

    The quantity 8.99x10^9(q)/(.084)^2 gives the magnitude of the electric field from one charge q at a distance 8.4 cm away from that charge. Do you see why that is wrong for this problem, and what to do now?
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