1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Force on electric dipole

  1. Jan 18, 2009 #1
    1. The problem statement, all variables and given/known data

    Show that a line of charge density [tex]\lambda[/tex] exerts an attractive force on an electric dipole with magnitude F = [tex]\frac{2\lambda p}{4\pi\epsilon_{0}r^{2}}[/tex]. Assume that r is much larger than the charge separation in the dipole.


    2. Relevant equations

    I need to show that the magnitude, F = [tex]\frac{2\lambda p}{4\pi\epsilon_{0}r^{2}}[/tex]

    p = qs => assume s is very small at end of calculations

    F = Fon -q + Fon +q = 0

    Fon -q = -qE
    Fon +q = +qE

    3. The attempt at a solution

    I am not sure if I am doing this correct?

    F = Fon -q + Fon +q
    F = -qE + +qE

    = [tex]\frac{pE}{s} + \frac{pE}{s}[/tex]

    = [tex]\frac{p}{s}\frac{1}{4\pi\epsilon_{0}}\frac{2\lambda}{r} + \frac{p}{s}\frac{1}{4\pi\epsilon_{0}}\frac{2\lambda}{r}[/tex]
  2. jcsd
  3. Jan 19, 2009 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    There are 2 problems here:

    • A "-" sign got lost from the -qE term, when you went on to the next step.
    • The distance to the +q charge is not r.

    Hope that helps. :smile:
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Force on electric dipole