1. The problem statement, all variables and given/known data Calculate the Electric Field vector at the surface of a proton. 2. Relevant equations F = qE --> E = F/q F = [k(q1)(q2)] / (r^2) 3. The attempt at a solution Well basically I'm not sure... I know it's a really simple question (it's not really even a homework exercise, just something that was put up in a lecture) but I'm having trouble understanding how to use these equations since Coulomb's law describes the force caused on one charge by another (ie involves two charges). But this question is asking to find an intrinsic electric field held by one isolated charge. If you sub F = [k(q1)(q2)] / (r^2) into E = F/q I can see that you could end up with E = (kq) / (r^2) but that's just by cancelling out the q's without really understanding what they represent. I assume either (q1) or (q2) is going to have to be e = 1.6*(10E-19), but as for the other? And even the value 'r'... at the surface, shouldn't the distance be 0? Eh, I'm sure it's really simple, but any help would be great. Thanks.