1. The problem statement, all variables and given/known data The figure shows a charge q placed at the centre of a hemisphere. A second charge Q is placed at one of the positions A,B,C and D .in which position(s) of this second charge , the flux of the electric field through the hemisphere remains unchanged ? 2. Relevant Point: My textbook says "if the vector E line from a charge cuts the surface once -there will be net contribution to the electric flux." 3. The attempt at a solution In the following cases Obviously from points A and E all the straight lines cut the surface twice as shown below.So if we happen to bring another charge Q at any of these two points the value of electric flux would not change because these will not contribute in it.But what about other points B,C & D?I am unable to figure out for these points.How to sketch the diagrams for these points?Any help would be greatly appreciated!