Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

B Group velocity and phase velocity

  1. Aug 12, 2016 #1
    Could you please explain the derivation of
    group velocity = dw/dk

    I read ut here https://en.m.wikipedia.org/wiki/Group_velocity

    Is it approximation, if so under what circumstances
     
  2. jcsd
  3. Aug 12, 2016 #2

    blue_leaf77

    User Avatar
    Science Advisor
    Homework Helper

    Isn't the derivation already available in that link? The group velocity is defined to be the velocity at which the envelope of a wave travels. It's an approximation in the sense that it was derived involving approximating the phase in first order of ##k##.
     
  4. Aug 12, 2016 #3
    How did they put the linearization equation?
    Was there approximate and then it could really be applied for wavefunction approaching delta functions
     
  5. Aug 12, 2016 #4

    blue_leaf77

    User Avatar
    Science Advisor
    Homework Helper

    Yes, the linearization is an approximation which only applies to cases where ##A(k)## is sharply peaked. If this is not the case, higher orders of the phase must be included in the calculation and they usually lead to the modification of the shape of the pulse (so-called "chirping").
     
  6. Aug 12, 2016 #5
    If i add two sine wave functions (real parts) envelopes are formed. So group velocity must not be dw/dk. Asking coz my proff said that which i feel is wrong
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Group velocity and phase velocity
Loading...