I am trying to answer a question that states: There is a sphere of radius R centred at the origin with a polarisation P = C(xi+yi+zk), where C is a constant, at the surface. What is the total charge in the sphere if there is no net charge? I know that P= Nqd where N is the number of charges, q is the charge on each one, and d is the separation distance in the dipoles. But I do not see how to relate this to the sphere in the question. I do not know of any individual charges in the sphere or of any dipoles, or should I be taking these as atoms? Any pointers in the right direction would be much appreciated. Thanks.