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Homework Help: Electric dipole

  1. Jun 25, 2009 #1
    The problem statement, all variables and given/known data
    Two point charges likes those in the figure below are called an electric dipole. Show that the electric field at a distant point along the x-axis is given by [tex]E_{x}=\frac{4k_{e}qa}{x^3} [/tex]
    Figure: http://img300.imageshack.us/my.php?image=58ag9.png

    2. Relevant equations
    Electric field equation: [tex] E=\frac{k_{e}q}{r^2}[/tex]

    3. The attempt at a solution

    I know that the total electric field at some point equals the vector sum of the electric fields of both charges. So...


    From the solutions it puts in x-a and x+a for r values (x+a was orignally x-(-a)). I want to know why its subtracting the vector.
  2. jcsd
  3. Jun 25, 2009 #2


    User Avatar

    Staff: Mentor

    Did you check the signs on the q's?
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