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Homework Help: Electrostatic Force diagram

  1. Apr 7, 2010 #1
    Two positive point charges, each of which
    has a charge of 1.5 × 10−9 C, are located at
    y = +0.50 m and y = −0.50 m.
    The Coulomb constant is 8.98755 ×
    10^9 N · m2/C2.
    a) Find the magnitude of the resultant elec-
    trical force on a charge of 1.0×10−9 C located
    at x = 0.55 m.
    Answer in units of N.

    So I drew out a force diagram and thought that the equation would be:
    Fel=kc(Q1*q/d1^2)+kc(Q2*q/d2^2) where the q is the 1.0e-9C charge.
    so Fel=5.404757e-6

    Apparently that was the wrong answer. Does anybody know or want to explain how I should now re-examine the problem?
  2. jcsd
  3. Apr 7, 2010 #2

    Doc Al

    User Avatar

    Staff: Mentor

    The force from each charge is a vector. You have to add them like vectors, not numbers--the direction matters. Hint: What happens to the y-components?

    Also: What's the distance between the charges?
  4. Apr 7, 2010 #3
    yeah...I missed the fact that q was on the x axis. makes sense now. Thank you for your help!
  5. Jun 2, 2010 #4
    I have a question about the operation of the electrostatic force. I solved the Maxwell's equations in a pure static electric conditions and the result I got does not look like a wave equation. If that is the case, then what is the speed of electrostatic interaction in free space? And what is the messenger particle?
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