an apparatus in which a uniformly charged disk of radius r is to produce an electric field. the field magnitude is most important along the central perpendicular axis of the disk, at a point p at distance 1.00r from the disk (fig. a). cost analysis suggests that you switch to a ring of the same outer radius r but with inner radius r/2.00 (fig. b). assume that the ring will have the same surface charge density as the original disk. if you switch to the ring,