I was going through my textbook, Introduction to Electrodynamics, and I came across this question that puzzled me. The book is really great by the way, I would highly recommend it. No, this isn't a homework question, it just got me thinking. For a finite line of charge (like a rod, for example), there should be a general relationship for the direction of the electric field no matter where point X is located with respect to the finite line of charge. What do you think this general relationship is? Lets assume it’s a finite line of positive charge. I think of the electric field (E-field) always pointing outwards. So if you take a point X directly above the finite line of charge, say centered, it’s going to point up. But what relationship can we use to describe this? I know you can take a bunch of little dq's and add them up, and the direction each one of those points as X can be added up as the direction of the E-field. Can we incorporate the right-hand-rule with this? No rush to answer I was just curious.