Ok i been reviewing my fields and waves notes and have come across something i am not quite sure of.

It was proved that the electric field intensity

**E**at a point p (in space above the plane) due to a uniform charge density ρs on an infinite plane is equal to ρs/2ε where ρs = surface charge density and ε is equal to the permittivity of the medium that p is in.

In this derivation there is no criterion required that states that the plane is a conductor or not as this is not required.

Reading over the boundary conditions it states that the normal component of the electric flux density vector

**D**n is equal to ρs when the Flux is coming out of a conductor. This is due to the fact that the tangential components of the electric field vector at the interface between two different media are equal. In a conductor, there is no tangential component so this is indirectly why D out of the conductor is normal.

So if

**D**n is = ρs then

**E**n is =

**E**n/ε

When this was stated there was no criteria given as to the dimensions of the conducting surface.

So looking back at the first example mentioned, if we assume that the infinite plane is a conductor, then is

**D**= ρs/2 or ρs?