A particle of charge -q is at the origin of an x -axis (a) at what location on the acis should a particle of charge -4q1 be placed so that the net electric field is zero at x = 2.0 mm on the axis? (b) if, instead, a particle of charge +4q1 is placed at that location, what is the direction (relative to the positive direction of the x-axis) of the net electric field at x = 2.0 mm?
Please explain and show all work. Thank you!