# Gaussian Units: Electric Field

1. Oct 13, 2009

### soupdejour

I am stuck with Gaussian units. If the field in vacuum is

$$E = \frac{Q}{r^2}$$

Is the field in a dielectric

$$E = \frac{Q}{\epsilon_r r^2}$$

, or is it unchanged?

2. Oct 13, 2009

### Born2bwire

The latter is the correct equation. In gaussian units, free-space epsilon is unity, this is why I prefer MKS units since all the unities in natural units sometimes hide these kind of relationships.