1. Find the electrostatic energy of a neoprene sphere or ratio R, charged with Q if: a) Q is uniformly distributed in surface 3. The attempt at a solution So, I can calculate the displacement field (so that I can use the expresion U= [tex]\int \vec{D}.\vec{E} dV[/tex]), but only for those points in space where r>R. Then, given that D=[tex]\epsilon[/tex]E, I can find the electric field for r>R. But I don't know how to get the electric field inside the sphere, since D=0 there because there're no free charges inside. It could also happen that E doesn't exist inside the sphere either, but I woundn't know the reason why. Any ideas? Thanks.
How are you calculating the displacement field? And why can't you calculate it for [itex]r\leq R[/itex]? doesn't [itex]\epsilon=\epsilon_0[/itex] for [itex]r>R[/itex]? You've already given the reason why.....just assume that neoprene is a linear dielectric, then you know [itex]\textbf{D}=\epsilon\textbf{E}[/itex], so if [itex]\textbf{D}=0[/itex], then so does the electric field!