# Charge Density from E-field

1. Apr 4, 2014

1. The problem statement, all variables and given/known data
I have a function for an E-field $$E(x,y,z,t)=E_o\cos(k(x-ct))\hat j$$ and I need to find the charge density....
2. Relevant equations

$$\vec \nabla \cdot\vec E=\frac{\rho}{\epsilon_o}$$

3. The attempt at a solution

When I compute the dot product of gradient operator with the E-field I get zero since the only "term" in the factor is in the y direction, but it also does not have any variation with y so is the charge density in this region of space just zero?

2. Apr 4, 2014

### Dick

I would agree with that.