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Two charges located along x. Find all values?

  1. Apr 18, 2015 #1
    1. The problem statement, all variables and given/known data
    The first one has charge Q is at "-a" from origin the second is at "+3a" which is an unknown charge.What are the values for unknown charge if at the origin the net electric field they produce with magnitude 2Ke(Q/a2)
    2. Relevant equations
    Ke (Q/a2)i - Ke(q/9a2)=2Ke(Q/a2)i
    if charge is negative
    or
    if the charge is positive
    Ke (Q/a2)i - Ke(q/9a2)=-2Ke(Q/a2)i
    3. The attempt at a solution
    The question is how to choose signs for equation.
    Attempt:
    Assuming charge one is pointed towards the origin along x axis so the sign will be "+i" and the second charge is pointed towards the origin in the negative x direction so tthe sign will be "-i".
    Two possible values are at the origin: "+" or "-" 2Ke(Q/a2) .
    If you choose "+" at the origin the answer will be -9Q. And for case chosen "-" sign in the origin, the answer will be 27Q so the particle has positive charge.
    I wondering if this is the explanation?
     
  2. jcsd
  3. Apr 18, 2015 #2

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    Correct.
     
  4. Apr 18, 2015 #3
    Thanks
     
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