Intensity of Electric field

n0_3sc

Can anyone explain how to go from:

[tex]I_s = \frac{nc\epsilon}{2} |E|^2 [/tex]
to
[tex]I_s = \frac{nc}{8\pi} |E|^2 [/tex]

That means [tex] \epsilon [/tex] is [tex] \frac{1}{4\pi} [/tex]....I can't find that anywhere.

dynamicsolo

Is your source using something like statcoulombs as units? I think the units are defined so that [tex]\epsilon_{0}[/tex] is set to 1...

n0_3sc

It says its using "cgs" units.
By the way [tex]\epsilon[/tex] I quoted, is the same as [tex]\epsilon_0[/tex].

pam

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.

n0_3sc

Ahh ok - thanks a lot pam.