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Electromagnetic question

  1. Oct 7, 2015 #1
    1. The problem statement, all variables and given/known data
    . A charge 2Q is located at the origin while a second charge -Q is located at x = 1m. Find the position x where a third charge should be placed so that the net force on this charge is zero?

    2. Relevant equations


    3. The attempt at a solution
    I know that the charge must be placed further away from the origin than -Q and net force of 0=k*2Q*Q3/(r1)2 + k*-Q*Q3/(r2)2
    where
    k=8.99x109
    r1=distance from 2Q to Q3
    r2= distance from -Q to Q3

    and also r1=r2+1m

    Thanks for any help
     
  2. jcsd
  3. Oct 7, 2015 #2
    quick question, I have tried again, does the distance between the origin and the third charge equal 3.41m
     
  4. Oct 7, 2015 #3

    RUber

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    Are you to assume that the third charge is also a -Q?
    In that case, letting x denote the position of the third charge, your guiding equation simplifies to:
    ## 0 = \frac{-2Q^2}{(x^2)} + \frac{Q^2}{(1-x)^2}##
     
  5. Oct 7, 2015 #4
    I don't really know.

    by solving that equation does that mean x=~2.41m?
     
  6. Oct 7, 2015 #5

    ehild

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    That is correct for the distance of the third charge from the origin. But show your work in detail.
     
  7. Oct 7, 2015 #6

    RUber

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    That (2.41) doesn't seem to solve the equation. I get about 1 instead of zero when I plug that in. 3.41 is good.
     
  8. Oct 7, 2015 #7

    ehild

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    No need to assume anything about the third charge.
     
  9. Oct 7, 2015 #8

    RUber

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    Got it. It can factor out just like k.
    Thanks.
     
  10. Oct 7, 2015 #9
    Thank you all very much :)
     
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