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Homework Help: Size of Force between two Point Charges

  1. Apr 17, 2010 #1
    1. The problem statement, all variables and given/known data
    A point charge of +2.0 microC is separated from a second point charge of -0.35 microC by a distance of 4.0 x10-4 m. Calculate the size of the force that each charge exerts on the other and its direction. (Assume 1/4 pi ε0 = 9.0 x109 m F-1)

    2. Relevant equations

    F = 1/(4 pi ε0) x (q1 x q2 / r-squared)

    3. The attempt at a solution

    I get an answer of -3.9 x 10 (power of 4) N

    The question asks for the direction. So by stating the -'ve before the 3.9 am I indicating the direction?

    Or should I state the answer is +3.9 x 10 (power of 4) N in a particular direction?

    Thank you
  2. jcsd
  3. Apr 17, 2010 #2
    You've got the size of the force down. As for the direction: you have opposite charges, which means they attract one another. So your first answer (the negative one) is the one you should use.
  4. Apr 17, 2010 #3
    Ok, thanks very much for the help Cryxic. It's very much appreciated. :smile:
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