# Help with Dielectrics

1. Jan 4, 2009

### rbtqwt

Hi. I have a problem in trying to find the field $$\vec E$$ in the following situation:
I have an infinite charged plane, with charge density $$\sigma$$, and two dielectrics, like in picture:
http://img53.imageshack.us/img53/2301/testrb0.jpg [Broken]
Now, if i think of $$\vec D$$ being orthogonal to the charged plane, using Gauss law i get $$\vec D = \frac{\sigma}{2} \vec k$$, then i get the fields $$\vec E$$in the dielectrics: $$\vec E_1 = \frac{\sigma}{2\varepsilon_0 k_1} \vec k$$ and $$\vec E_2 = \frac{\sigma}{2\varepsilon_0 k_2} \vec k$$.. but, because of $$\oint \vec E \cdot d\vec x = 0$$, I obtain $$E_{t_1} = E_{t_2}$$ , where $$E_{t_i}$$ is the tangential (to the contact surface of dielectrics) component of $$\vec E$$ in dielectric $$i$$. But $$E_{t_1} = \|\vec E_1}\| \ne \|\vec E_2\| = E_{t_2}$$.

What is wrong?

Last edited by a moderator: May 3, 2017
2. Jan 4, 2009

### clem

Re: Dielectrics

The basic equation is E1=E2. Then find D1 and D2. There will be a sigma1 and silgma2.

3. Jan 4, 2009

### rbtqwt

Re: Dielectrics

In the problem $$\sigma$$ is fixed :shy: