1. The problem statement, all variables and given/known data Problem # 4: A thin semicircular rod has a total charge +Q uniformly distributed along it. A negative point charge -Q is placed as shown. A test charge +q is placed at point C. (Point C is equidistant from -Q and from all points on the rod.) http://imgur.com/AeVfddb Let FP and FR represent the force on the test Charge due to the point charge and the rod respectively. Part C: A second negative point charge -Q is placed as shown. http://imgur.com/eYEOkPc Is the magnitude of the net electric force on +q greater than, less than, or equal to the magnitude of the net electric force on +q in part b? Explain. Whole Problem http://imgur.com/VbAtlg5 2. Relevant equations F = kq1q2/r2 Also basic knowledge of electric forces based on vector math and x/y - components. 3. The attempt at a solution So I solved part b (hopefully correct), but I want to say that the magnitude of the net electric force on +q will be less than the one found in part b since the -Q charges would cancel out as they are the same distance thus same magnitude, but opposite directions. However, I am confused on how the semicircular rod affects this as it is right there between it and the -Q charge.