I came across the following expression about the electric dipole moment:
$\vec p=\int_V \rho(\vec {r}')\vec r'$
But I don't understand it. What is $\vec r'$ supposed to represent and the density? Are we observing some region with a charge distribution and we take a small infinitesimal volume $dV$ and also the charge density there?
The expression I know for the dipole moment is: $\vec p= q\vec a$. Here $q$ is the charge value, and $\vec a$ a vector from the negative charge to the positive.
How does the above formula resembles to the last one?