1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Derive group velocity

  1. Oct 25, 2009 #1
    1. The problem statement, all variables and given/known data

    Starting from: vg=vp+k(dvp/dk) show that the group velocity can also be expressed by vg=vp-λ(dvp/dλ).

    2. Relevant equations

    I'm told that vg=vp+k(dvp/dk) with vg=group velocity and vp=phase velocity. I also know that k=(2π)/λ and ω=2πf.

    3. The attempt at a solution

    I tried to start with the equation ω=kvp and take the derivative with respect to λ but it doesn't work out.
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Oct 25, 2009 #2

    Redbelly98

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    (Moved to Advanced Physics.)

    Welcome to Physics Forums :smile:

    What rule from calculus would allow you to relate

    dvp/dk & dvp/dλ?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook