# Homework Help: Magnitude of dipole moment

1. Jan 25, 2010

### nothingatall

1. The problem statement, all variables and given/known data
A certain electric dipole is placed in a uniform electric field E of magnitude 20 N/C. Figure 22-59 gives the potential energy U of the dipole versus the angle θ between E and the dipole moment P. What is the magnitude of P?

2. Relevant equations
U=p(dot)E

3. The attempt at a solution
Somehow there is an integral needed to solve this but I don't know where to start. there is also a graph with this question.

2. Jan 25, 2010

### minimark1234

i thought...
$$U=-\vec{p} \cdot \vec{E}$$
but idk if that really changes much.

3. Jan 26, 2010

### nothingatall

It does, i was just forgetting to multiply it by the factor of 10^-26 hehe. Thanks.

4. Feb 10, 2011

### slamin27

can't you just take Us to be the maximum, and the angle of 180 to be the angle that corresponds to the maximum potential, and plug these into U=-pEcos(theta), along with the magnitude of E?