Physics Help Forum Amplitude and Intensity

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 Mar 25th 2012, 12:42 PM #1 Junior Member   Join Date: Sep 2011 Posts: 3 Amplitude and Intensity My professor posted this: $\displaystyle I = \langle \left| A(t) \right|^2 \rangle = \int\limits_t \left| A(t) \right|^2 \, dt$ Since LaTeX doesn't seem to be working: I = <|A(t)|^2> = Integral over t of |A(t)|^2 dt OK, I can accept this relation between intensity and amplitude. But isn't there a 1/t factor missing to convert the integral sum to a mean average? Or am I not understanding this? thanks! Last edited by pramoda; Mar 25th 2012 at 01:03 PM.
 Mar 26th 2012, 10:55 AM #2 Physics Team     Join Date: Jun 2010 Location: Morristown, NJ USA Posts: 2,347 You're on the right track. The power of the wave is the average of the amplitude squared, or: P = (1/T) Int (from 0 to 2 pi/w) A^2 dt where T = period of the wave. For a sine wave this works out to P = 1/2 A^2 As for intensity - that is usually defined as power per unit area, so if you are d meters away from a source that radiates in all directions then intensity = (1/2) A^2/(4 pi d^2)

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