Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

What is the electric dipole moment of the charge distribution with $q$ at $(0,0,1)$, $q$ at $(0,0,-1)$ and $-2q$ at $(0,0,0)$? I would think that it is $\vec{0}$ by the definition $\vec{p}=\sum\limits_i \vec{r_i}q_i$. So would it follow that the potential field due to it be $0$? Since $V=k {\vec{p}\cdot \hat{r}\over r^2}$ where $\vec{r}$ is the position vector of a point at which we wish to evaluate the potential.

share|improve this question
add comment

1 Answer

up vote 2 down vote accepted

That formula only works for short dipoles. Here, you need to use the fudamental potential formula, $\frac{kq_1}{r}$. By this formula, we get potential due to $q$ as $\frac{kq}{2}$, and potential due to $-2q$ as $-2kq$. Net potential is $-\frac{3kq}{2}$.

When we say a short dipole, we mean that the distance between the charges should be negligible with respect to the surroundings.

share|improve this answer
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.