- #1

offscene

- 7

- 2

- Homework Statement
- Griffith's E&M, problem 4.7: Show that the energy of an ideal dipole p in an electric field E is given by $$U=-p \cdot E$$

- Relevant Equations
- $$W=qV$$

$$V(r) = -\int_{\textrm{reference (take as infinity)}}^{r} E \cdot dl$$

Griffith's E&M problem 4.7 asks to calculate the energy of a dipole in a uniform electric field and I ended up getting a different answer than the one given. I thought that calculating the energy/work done to construct the dipole is the same as dragging two point charges where one is d apart from the other (please correct me if I am wrong) under the effect of a constant electric field. This should be done by just being able to drag the first with just the constant E-field acting on it and then dragging in the second charge (opposite sign) which has both the contribution from the constant E-field as well as the other charge that has already been placed. However, the answer does not come out to be correct if I include the contribution of the field from the already placed charge and I am confused as to why we can ignore this. (Essentially, I am getting the same answer as stated but with an additional term due to the potential of the other charge itself)