A square metal plate of edge length 8.0 cm and negligible thickness has a total charge of 6.0 x 10-6 C.

(a) Estimate the magnitude E of the electric field just off the center of the plate (at, say, a distance of 0.50 mm from the center) by assuming that the charge is spread uniformly over the two faces of the plate.

(b) Estimate E at a distance of 30 m (large relative to the plate size) by assuming that the plate is a point charge.