B.4 Uniformly charged rod near a metal surface. An infinite, thin, uniformly charged rod (line charge density A) is placed parallel to a horizontal grounded metal plate a distance d above it. Point M lies on the plate vertically below the rod. Point P lies on the plate a distance from point M, where line PM is perpendicular to the plane defined by the rod and point M. Use the result obtained in Problem A.4(b) 2 to calculate the electic field at P as a function of r.