1. The problem statement, all variables and given/known data This picture shows two points charges, q1 = +5 nC, and q2 (unknown), fixed in place on the x axis. At the location marked P, the net electric field due to both charges is zero: EP = 0 N/C. Based on the information shown in the picture, what can you conclude about the magnitude and sign of the charge q2? Explain your reasoning without calculations. I've attached a pic. 2. Relevant equations 3. The attempt at a solution E1 = -E2 at P because the two fields must point in opposite directions at that position and have equal magnitudes at that position. (as discussed in the tutorial) Also E1 is pointing left from P and E2 is pointing to the right from P. Finally, q2 is definately a positive charge because E2 is pointing in the opposite direction (to the right) while E1 is pointing left, like charges repel. after looking at it again i'm not so sure i'm correct. Why must they be equal in magnitude and opposite in direction? the fields are equal and opposite just describes the equation E1 = -E2, but i'm not sure why its true at P and looking at q1, which is a positive charge. Therefore, the field E1 created by q1 at the point directly away from q1. ..I don't seem to be understanding whats with the diagram. I just can't put it into words I guess. I think I see whats happening just can't explain it, can someone please break this down simply and clearly, i think i must be over thinking it.