# Homework Help: Dielectric between Grounded Plates

1. Nov 1, 2009

### jmtome2

1. The problem statement, all variables and given/known data
"When a block of insulating material such as Lucite is bombarded with high-energy electrons, the electrons penetrate into the material and remain trapped inside. In one particular instance a 0.1 mA beam bombarded an area of 25cm$$^{2}$$ of Lucite (Class A: $$\epsilon_r$$=3.2) for 1 second, and essentially all the electrons were trapped about 6mm below the surface in a region about 2mm thick. The block is 12mm thick. In the following calculations neglect edge effects and assume a uniform density for the trapped electrons. Assume also that both faces of the Lucite are in contact with grounded conducting plates. Lucite is a Class-A dielectric. What is the bound charge density in the charged region?"

2. Relevant equations

Gauss' Law

3. The attempt at a solution

Just curious how the grounded plates affect the E field? Can this configuration be treated as a typical parallel capacitor?

Last edited: Nov 1, 2009
2. Nov 1, 2009

### jmtome2

Haven't really dealt with grounded conductors before... this means that extra charge rolls off of these plates leaving them with Q=0, meaning that they don't contribute to the E field?

3. Nov 1, 2009