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Electric fields equalling zero

  1. Jan 14, 2007 #1
    Trying to work this one out.
    If you have two charges Q1 and Q2 separated by a distance of x then how do you show what distance from the charge Q1 is the total electric from the two charges zero.

    I know that Enet =E1 +E2 and if i use coulombs law i get:
    KQ1/x^2 +KQ2/x^2
    the K cancles and you get Q1/x^2 + Q2/x^2 = 0 but that doest seeem right. anyone with any ideas?
  2. jcsd
  3. Jan 14, 2007 #2
    Are the charges like or opposite in sign? If theyre like in sign, the point will be inbetween them, but if theyre opposite in sign, the point will be outside and closer to the weaker charge.

    Lets say the charges are like. That means that the distance from the spot to one charge + the distance from the spot to the other charge = x. The trick is to write one distance in terms of the other. The point will not be rigt inbetween the 2 unless the charges are equal, and then its not much of a question.

    Now lets say the charges are opposite, one charge will be a distance r from the point and the second charge will be a distance r + x
  4. Jan 14, 2007 #3
    both charges are positive
  5. Jan 14, 2007 #4


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    You didn't add forces here: you merely added their magnitudes.
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