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Group and phase velocities

  1. Nov 4, 2013 #1
    Hello
    1. The problem statement, all variables and given/known data
    I have this tab
    http://img18.imageshack.us/img18/3317/eyph.png [Broken]

    Anf I have to find the group and phase velocities for a wavelength λ=550nm
    2. Relevant equations
    v(phase)= c/n

    v(group)=dw/dk

    v(phase)*v(group)=c²/n²


    3. The attempt at a solution
    I don't know how I can determine n for the wavelength of 550nm using the tab ?
    I was absent the day of this course
    Can I use the relation v(phase)*v(group)=c²/n² ?

    Thanks !
     
    Last edited by a moderator: May 6, 2017
  2. jcsd
  3. Nov 4, 2013 #2

    mfb

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    2016 Award

    Staff: Mentor

    Where do those two formulas come from? Where are they valid? Can you use them here?

    Do an interpolation.
    Interpolation is a much more general concept you should know.
     
  4. Nov 4, 2013 #3
    The formulas come from my book, for electromagnetic waves.
    Why can't I use them ?
    OK, so I'll do an interpolation !
    Thanks
     
  5. Nov 5, 2013 #4

    mfb

    User Avatar
    2016 Award

    Staff: Mentor

    Those equations would give v(phase)=v(group) everywhere, which is not true.
    Please check how they got defined, and where they are applicable.
     
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