# Proof of Electric Dipole Equations

1. Jan 22, 2008

### Cheetox

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$$\pi$$$$\epsilon$$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 $$\phi$$0 and $$\varphi$$ and setting $$\varphi$$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. Jan 22, 2008

### Mindscrape

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.