Three narrow concentric rings of radii 50 mm, 70 mm and 90 mm are centered at the origin, with the axis of symmetry oriented along the y-axis. The total charge on the inner ring is 1.0mC, that on the middle ring is -2.0 mC and the charge on the outer ring is 1.0 mC. Discover the electric field at a position (0, 100 mm, 0). What single point charge Q should be placed on the y-axis at (0, -100 mm, 0) to make the electric field equal zero at (0, 100 mm, 0)? Would the field then be zero elsewhere on the y-axis?