1. The problem statement, all variables and given/known data http://imgur.com/EiCFIDe [Broken] 2. Relevant equations E = kq/r2 λ = dq/dx Q = λa 3. The attempt at a solution Here is the book solution: http://imgur.com/aKSeKo0 [Broken] I need help with part (a). I understand everything in the solution except for the distance they used for between (r2 in the equation above). It seems they used (a+r-x) and they say that is the distance between a segment at x and the charge q. What does q have to do with the problem at all? Part (a) asks for the electric field due to the charge distribution Q where x > a. So shouldn't the distance be between dx(a segment on the charge distribution) and x?