A conducting sphere of radius R is placed in a uniform electric field E, directed along axis. The electric potential for outside points is given by +z V=-E (1-(R/r)')r cose, where r is the distance from the center and is the polar angle. The charge density on the surface of the sphere is (a) 3 E cos 0 (b) E E cos (c) -3, E cos 0 (d), E cos