# Permittivity and conductivity

1. Mar 10, 2009

### thefireman

I have an relation between permittivity and conductivity as follows:

$$\epsilon(\omega) = 1 + \frac{4\pi\iota\sigma(\omega)}{\omega}$$

Yet am unclear as to how it was derived. Does this relationship have a name and/or derivation to follow through somewhere? also, I believe it is cgs units, what is the SI equivalent?

Thanks

2. Mar 11, 2009

### tiny-tim

Hi thefireman!

(i think you just leave out the 4π … or is it 4πe0 ? … to get SI units)

this looks a bit like like the "complex permittivity" definition …

$$\hat{\epsilon}(\omega)\ =\ \epsilon(\omega) + \frac{\iota\sigma(\omega)}{\omega}$$ is the "complex permittivity"

… but with a different notation