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Simple charge question

  1. Jun 22, 2005 #1
    Hello everyone, I've been having the hardest time getting the hang of coulobs law. I got a physics book, physics for complete morons. The question is simple enough:

    Consider a line of charges, q1 = 8.0 micro C at the orginin, q2 = -12 micro C at 2.0 cm, and q3 = 10 micro C at 4.0cm. What is the force on q3 due to the ohter two charges?

    So you find F31 and u find the F32 and then add up the two forces to find your answer. But to find F31 they used a distance of .04m which confuses me. If the charges are as follows:

    .02m .04m

    Why wouldn't the distance from q1 to q3 be .06m? :bugeye:

  2. jcsd
  3. Jun 22, 2005 #2
    Yeah it is 0.06m, maybe you are misunderstanding what they are trying to do. What did they use for F32?
  4. Jun 22, 2005 #3

    Doc Al

    User Avatar

    Staff: Mentor

    I suspect that those are the positions of the charges (their coordinates along the axis), not the distances between them. Calling it the x-axis, the charges are at:
    x1 = 0m
    x2 = 0.02m
    x3 = 0.04m

    Make sense?

    And welcome to PF, by the way!
  5. Jun 23, 2005 #4
    ahhh, how simple. Thanks Doc you were right!
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