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Derivation of group velocity.

  1. Sep 10, 2013 #1
    I was reading the derivation on Wikipedia:


    Why is the first part before the integral sign ignored when calculating the velocity? Surely it would also cause a phase shift in some time interval and make the waves move forward (or backward)?
  2. jcsd
  3. Sep 10, 2013 #2


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    Staff: Mentor

    Group velocity cares about the speed of the amplitude, phases are not relevant for the group velocity.
  4. Sep 11, 2013 #3
    Ok, but when calculating the velocity by dividing the terms in front of t by those in front of k, why can some of the terms in front of t be ignored?
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