# Sphere near a plane(electrostatics(dipole))

1. Nov 3, 2008

### Zipi

Greetings,

i have the following question:

a sphere with the polarization density of P vector (constant) and radius R is placed next to an infinate grounded plane , and is touching it.
_ <-- infinate grounded plane
O <--- sphere
and in the question data im given is that the field inside the sphere is E= -P/3e
and im told to find the field in the middle of the sphere and at the touching point.

anyways what i ask is , since P is constant , there is no volume charge density. now , the area charge density is should be Pn that is 2RP. now my question is , would it be right to say that the field inside the sphere is as is said above by the question data and the sphere outside would be E=(8pie(R^3)P)/(r^2) and if that would be the case i'd be also looking at the mirror charge behind the plane and that would bring me to my solution ? also another question , about the grounded plane , what diffrence does it make in the case when i work with image charges if the plane is grounded or ungrounded?

btw , the reason i've posted this here is because its more a theoretical question and im not asking to solve the problam.
also if you cant understand what i wrote formula wise please say so and i'll try to draw it :P