I have two identical rods with length 2a with charges +Q. Both rods are on the x axis. One is centered at (0,0) so that it ranges from (-a to a) and then other has a center at (b,0) which ranges from (b-a to b+a). The question asks what is the force exerted by the left rod on the right rod. Now I have an understanding of how to do these types of problems. For example if the left rod was a (0,0) point charge I would have no problem with this question. I determined that F = k(Q^2)/4(a^2) * int[dx dx / x^2] if that is correct? Is this a double integral, and if so, what should my limits of integration be? Is it two integrals from -a to a and b-a to b+a? Or an integral with limits b-2a to b+2a in which case i dont know what to do with the 2nd dx. Thank you.