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Homework Help: Group and phase velocity

  1. Oct 21, 2012 #1
    1. The problem statement, all variables and given/known data

    show that the group velocity and phase velocity are related by

    d vgroup = vphase - [itex]\lambda[/itex] ( (d vphase) / (d [itex]\lambda[/itex]) )

    2. Relevant equations
    vphase = [itex]\lambda[/itex]f
    vgroup = d[itex]\omega[/itex]/dk

    3. The attempt at a solution

    dw/dk = [itex]\lambda[/itex]f - [itex]\lambda[/itex](d[itex]\lambda[/itex]f/d[itex]\lambda[/itex])

    dw/dk = [itex]\lambda[/itex]f - [itex]\lambda[/itex]f

    Not really sure where to go with this
  2. jcsd
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