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Derive energy of electric dipole in electric field

  1. Nov 29, 2014 #1
    Hello there,

    I want to derive ##U(\theta) ## for electric dipole placed in uniforum electric field $\vec{E} = E\vec{e}_x$ where E is constant. I define the dipole moment as $p = qd$, where $d$ is the distance from the two

    I write $\mathm{d}W = p\,E\sin\theta \mathrm{d}\theta = \tau\mathrm{d}\theta$, but how do I determine what the sign should be? Should it be $\tau\mathrm{d}\theta$ or $-\tau\mathrm{d}\theta$?

    I dont understand how to work it out. What determines what the sign should be?

    Thank you for your time.

    Kind regards,
  2. jcsd
  3. Nov 29, 2014 #2


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    2017 Award

    Staff: Mentor

    How did you define theta?
    Just consider the energy for different values of theta, that should give the answer.
  4. Nov 29, 2014 #3
    Let theta be the angle between ##\vec{p}## and ##\vec{E}##.
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