## Intensity of Electric field

Can anyone explain how to go from:

$$I_s = \frac{nc\epsilon}{2} |E|^2$$
to
$$I_s = \frac{nc}{8\pi} |E|^2$$

That means $$\epsilon$$ is $$\frac{1}{4\pi}$$....I can't find that anywhere.

Recognitions:
Homework Help
 Quote by n0_3sc Can anyone explain how to go from: $$I_s = \frac{nc\epsilon}{2} |E|^2$$ to $$I_s = \frac{nc}{8\pi} |E|^2$$ That means $$\epsilon$$ is $$\frac{1}{4\pi}$$....I can't find that anywhere.
Is your source using something like statcoulombs as units? I think the units are defined so that $$\epsilon_{0}$$ is set to 1...
 It says its using "cgs" units. By the way $$\epsilon$$ I quoted, is the same as $$\epsilon_0$$.

## Intensity of Electric field

Your first equation is in SI units. The epsilon there is epsilonzero.
The second equation is in cgs gaussian units.
To go from SI to gaussian, let 4piepsilonzero-->1.
 Ahh ok - thanks a lot pam.