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A thin nonconducting rod with a uniform distribution of positive charge Q is bent into a circle of radius R (see the figure). The central perpendicular axis through the ring is a z axis, with the origin at the center of the ring. What is the magnitude of the electric field due to the rod at (a) z = 0 and (b) z = ? (c) In terms of R, at what positive value of z is that magnitude maximum? (d) If R - 2.29 cm and Q = 4.04 JC, what is the maximum magnitude? R