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Homework Help: Expressions for the group velocity

  1. Mar 5, 2010 #1


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    1. The problem statement, all variables and given/known data
    Okay so I've been deriving various expressions for the group velocity starting with


    then g=v+kdv/dk

    also g=v-lambda dv/dlambda (*)

    then finally g=c/u(1+lambda/u (du/dlambda))

    Ok so finally im asked to use equn (*) to derive the following expression

    g=v[1-1/(1+(v/lambda')(d lambda'/dv))

    where lambda' is the wavlength in vacuum..

    not sure how to do it..any help would be great thanks

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Mar 5, 2010 #2


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    Any ideas?
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