# Surface charge density

1. Jul 11, 2010

### pat666

1. The problem statement, all variables and given/known data
A large plane having uniform charge density has an electric field just outside the plane that points directly toward the plane with magnitude 1.50×10^4 N/C .

What is the surface charge density?

2. Relevant equations

I am not sure how to start this, the relevant equations would probably be enough to get me through this questions.

3. The attempt at a solution
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Jul 11, 2010

### aim1732

Right. By Gauss Law electric field of an infinitely large plane non-conducting sheet is σ/2ε where σ is charge density and ε is permittivity of free space.

3. Jul 11, 2010

### pat666

thanks for that, what is the permittivity of free space????? also is this meant to be an easy question?

4. Jul 12, 2010

### aim1732

Permittivity constant accounts the dielectric properties of the medium and for air(or vacuum) it is 8.854×10−12 Fm-1.
Remember the constant in the Coulomb's Law? It is actually 1/4πε .
As for the question itself if you are familiar with Gauss law it shouldn't be difficult and the result is used as a standard formula in many texts.