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Homework Help: Intensity of Electric field

  1. Mar 17, 2008 #1
    Can anyone explain how to go from:

    [tex]I_s = \frac{nc\epsilon}{2} |E|^2 [/tex]
    [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.
  2. jcsd
  3. Mar 17, 2008 #2


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    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...
  4. Mar 17, 2008 #3
    It says its using "cgs" units.
    By the way [tex]\epsilon[/tex] I quoted, is the same as [tex]\epsilon_0[/tex].
  5. Mar 18, 2008 #4


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    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.
  6. Mar 19, 2008 #5
    Ahh ok - thanks a lot pam.
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