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Homework Help: Were is the electric field zero?

  1. Mar 15, 2010 #1
    1. The problem statement, all variables and given/known data

    What is the net electric field intensity at the origin due to two charges Q1= 2[tex]\mu[/tex]C at (x=3,y=4) and Q2 = -10[tex]\mu[/tex]C at (x=6,y=-8). And where should a third charge of magnitude 5 [tex]\mu[/tex]C be placed so the net electric field at the origin is zero?

    2. Relevant equations
    E=KQ/R[tex]^{2}[/tex] [tex]\widehat{r}[/tex]

    3. The attempt at a solution

    I have found the first part of the question to be E= 3236[tex]\widehat{i}[/tex]-10069[tex]\widehat{j}[/tex] but I am not sure how you would find out were to place the third charge. Please help
  2. jcsd
  3. Mar 15, 2010 #2


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    Hi blackblanx! :smile:

    (have a mu: µ :wink:)
    The third charge will have to supply a field of minus E. :wink:
  4. Mar 15, 2010 #3
    but what are the coordinates of where that charge should be placed?
  5. Mar 15, 2010 #4
    oh wait never mind i think i got it know thanks it would just be the negative of the electric field vector divided by k(5[tex]\mu[/tex]C)
  6. Mar 15, 2010 #5
    Forget I realized that does not work any ideas of how to find the coordinates?
  7. Mar 16, 2010 #6


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    It'll be on the line in the direction of E, at the distance appropriate to the given strength. :smile:
  8. Mar 18, 2010 #7
    ok thanks
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