Expressions for the group velocity

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SUMMARY

The discussion focuses on deriving expressions for group velocity, specifically starting from the fundamental equation g = dw/dk. The user presents several transformations, including g = v + k(dv/dk) and g = v - λ(dv/dλ). The final goal is to derive the expression g = v[1 - 1/(1 + (v/λ')(dλ'/dv))], where λ' represents the wavelength in a vacuum. The user seeks assistance in completing this derivation.

PREREQUISITES
  • Understanding of group velocity and its mathematical representation.
  • Familiarity with calculus, particularly derivatives and their applications in physics.
  • Knowledge of wave properties, including wavelength and frequency relationships.
  • Basic grasp of the concepts of phase velocity and its relation to group velocity.
NEXT STEPS
  • Study the derivation of group velocity from first principles in wave mechanics.
  • Explore the relationship between phase velocity and group velocity in different media.
  • Investigate the implications of varying wavelength on group velocity using calculus.
  • Learn about applications of group velocity in optics and wave propagation.
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Students and professionals in physics, particularly those studying wave mechanics, as well as educators looking to clarify concepts related to group velocity and its derivations.

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Homework Statement


Okay so I've been deriving various expressions for the group velocity starting with

g=dw/dk

then g=v+kdv/dk

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

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

Ok so finally I am 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

Homework Equations





The Attempt at a Solution

 
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