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Homework Help: How to find magnitude of Q1 and Q2?

  1. Mar 12, 2012 #1
    1. The problem statement, all variables and given/known data
    Two point charges, Q1 and Q2 are 6m apart. The electric field intensity a point A, midway between the two charges is 5 N/C directed toward Q2, and the potential at the same point is 45V. Find:
    a) the magnitude of Q1
    b) the magnitude of Q2

    2. Relevant equations

    3. The attempt at a solution

    This is what I got so far.
    VA = k [(Q1+Q2)/r]
    45 V = 9x109 [(Q1+Q2)/3]

    Then I'm stuck at what to do next and what to do with E = 5 N/C
  2. jcsd
  3. Mar 12, 2012 #2


    User Avatar

    Staff: Mentor

    5 N/C is the field intensity at the same point for which you've written an expression for the potential. You're also given the net field direction there. You'll want to write an expression for the field in terms of Q1, Q2, and their distances from that point. That will give you two equations and two unknowns...
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