# Homework Help: Dielectric image charges

1. Mar 27, 2010

### asdfgh333

1. The problem statement, all variables and given/known data

A point charge q is a distance d from a dielectric half-space (z < 0). We will
solve for the potential outside of the dielectric, in the region z > 0.

(a) Away from the point charge, what equation does V satisfy? Find the bound-
ary conditions at the dielectric surface.

(b) Find an image charge in the dielectric slab that allows you to satisfy the
boundary conditions. What is the potential V outside the dielectric?

(Hint: as epsilon-naught approaches infinity, you should recover the result for a charge next to an infinite
conducting half-space.)

2. Relevant equations

$$\sigma$$= P dot n = Pz= epsilon-naught*Chi*E

F = 1/(4*pi*ep-naught)*q*qb/(2d)^2=-1/4*pi*ep-naught*(Chi/(Chi+2))*q^2/(4*d^2))

3. The attempt at a solution

I know how to get the potential in the dielectric (Z<0) but I cannot get the potential above Z.

Any help would be greatly appreciated.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Mar 27, 2010

### gabbagabbahey

Okay, well how about you start by showing us that then....What does that mean the potential will be at $z=0$?