A constant electric field exists in a region of Space. The field has a magnitude of 1600N/C and points due north. A point charge of +4.0 * 10^-9 C is then placed in this electric field. What is the magnitude and direction of the net electric field at a spot 13 cm due east of the charge? http://img135.imageshack.us/img135/3221/46204214bm6.png [Broken] My question is, how do we know that the origin starts off positive? Thanks.