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Homework Help: Electric Dipole Moment and electric field

  1. Feb 8, 2010 #1
    1. The problem statement, all variables and given/known data
    Two dipoles are oriented as shown in the diagram below. Each dipole consists of two charges +q and -q, held apart by a rod of length s, and the center of each dipole is a distance d from location A. If q = 6 nC, s = 1 mm, and d = 6 cm, what is the electric field at location A?


    2. Relevant equations

    E(axis) = qk x (r-s/2)^2 - (r+s/2)^2)^-1

    E(axis) = 2qks/d^3 when d>>s

    k=8.99E9 N^2 m / C^2

    3. The attempt at a solution

    Since d>>s, the x-axis dipole's angle can be considered linear, and thus, the E-field for the x component is 0.

    For the y-axis dipole, d>>s allows us to use the second equation, E(axis) = 2qks/d^3.

    E = 2 (8.99E9) (6E-9) (0.001) / (0.06^3) = 500.

    My answer would be <0,500,0>. I got the x and z components correct, but the y component is not. Why is that? Did I get the x component right for the wrong reasons or something?
  2. jcsd
  3. Feb 8, 2010 #2


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    Homework Helper

    The y component of the electric field arising from the x-axis dipole is not 0.

  4. Feb 9, 2010 #3
    Oh, whoops. You're right.

    With the Y component for the x-axis, it would be E(y) = kqs/y^3 = (8.99E9 * 6E-9 * 0.001) / (0.06^3) = 250.

    250 + 500 = 750; <0,750,0>

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