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Amplitude Squared Proportional to Intensity?

  1. Dec 6, 2009 #1
    [tex]A^{2}[/tex] [tex]\propto[/tex] [tex]I[/tex]

    When is it appropriate to use this formula?

    I don't understand how to use a proportionality. Say I have an amplitude A and I make it 2A can I use the equation to determine the intensity will increase by a factor of 4?

    I guess I don't know why it is a proportionality as opposed to an equation.
  2. jcsd
  3. Dec 6, 2009 #2
    It would be appropriate to use it if you're given an equation for some EM wave. Then the constant in front squared would represent the intensity of the wave.
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