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Relation between Group velocity and Phase velocity

  1. Jun 7, 2007 #1
    Is there any unconventional method to find out the relation between group velocity and phase velocity? know there is a method employing Fourier tarnsforms and another easier method as well
     
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  3. Jun 7, 2007 #2

    Meir Achuz

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    Phase and group velocities only have meaning using a Fourier transform.
    w/k and dk/dw are in terms of Fourier variables.
     
  4. Jun 9, 2007 #3
    one thing to notice is that, for a group velocity to be meaningful, the wave packet has to be merely composed of wavenumber in a narrow range.
     
  5. Jun 9, 2007 #4

    Meir Achuz

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    That is a very good point. The equation v_g=dk/dw comes from keeping only the first term of a Taylor expansion. Many of the papers claiming funny group velocities for light miss the point you mention.
     
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