Electric dipole in electric field.

[dalarev]

Homework Statement

An electric dipole moment, vector P, is initially pointing in the directio of a uniform electric field, vector E (say, in the positive x direction). How much external work is needed to turn the dipole by 90 degrees?

Homework Equations

vector P is directly proportional to E. It will tend to point in the same direction as E.

The Attempt at a Solution

The only relevant equation I can gather is the torque N = p X E.

 

[borgwal]

What's the energy of a dipole in an electric field? That equation should be right next to the equation you mention!

 

[dalarev]

E of a dipole in an electric field = k * P/r^3

Wouldn't I need a force, as in F*d to find work?