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Homework Help: Proof of Electric Dipole Equations

  1. Jan 22, 2008 #1
    1. The problem statement, all variables and given/known data
    An electric dipole of moment p is placed at a distance r from a point charge +q. The angle between p and r is phi. Show that the energy of interaction between the dipole and the charge is -pqcos(phi)/4[tex]\pi[/tex][tex]\epsilon[/tex]0r^2

    Derive equations for

    a)a radial force on the dipole
    b)a force on the dipole normal to r
    c)a couple on the dipole

    2. Relevant equations

    3. The attempt at a solution

    I have proved the first part of the question using the integral of the torque between [tex]\phi[/tex]0 and [tex]\varphi[/tex] and setting [tex]\varphi[/tex]0 to 90degrees and I believe that questions a, b and c are simple manipulations of the proved equation, but no book I read will give me a proof or an explanation of the 'radial force' and how to prove questions a, b and c could anyone help?
  2. jcsd
  3. Jan 22, 2008 #2
    So you have found the work, or I guess energy of interaction, done to bring the charge to where it is.

    a) How would you find the radial force on a monopole? (Hint: potential)
    b) Similar idea to a), but different dot product
    c) No idea what this means, sorry.
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