Matter Waves: Phase vs Group Velocity Equation

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SUMMARY

The discussion focuses on the relationship between phase velocity (vp) and group velocity (vg) in wave mechanics, specifically in a substance where phase velocity is inversely proportional to wavelength. The valid equation derived from the analysis is vg = 2 vp, confirming that group velocity is twice the phase velocity. The participant initially suggested vg = vp but corrected this after further calculations. The key equations utilized include the definitions of phase and group velocities in terms of angular frequency and wave number.

PREREQUISITES
  • Understanding of wave mechanics and properties of waves
  • Familiarity with the concepts of phase velocity and group velocity
  • Knowledge of mathematical relationships involving angular frequency and wave number
  • Ability to manipulate equations involving wavelengths and velocities
NEXT STEPS
  • Study the derivation of the group velocity equation in wave mechanics
  • Explore the implications of phase and group velocities in different media
  • Learn about the dispersion relation and its effect on wave propagation
  • Investigate applications of phase and group velocity in optics and quantum mechanics
USEFUL FOR

Students and professionals in physics, particularly those studying wave mechanics, as well as educators looking to clarify the concepts of phase and group velocities in their teaching materials.

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Homework Statement



In a particular substance the phase velocity of the waves is proportional to the reciprocal of the wavelength. If vp represents the central phase velocity of a wave group and vg represents the group velocity, which of the following equations is valid?


Homework Equations



(A) vg = 1/vp
(B) vg = ½ vp
(C) vg = vp
(D) vg = 2 vp
(E) vg = 4 vp


The Attempt at a Solution



I'm having a hard time finding relevant information on this question. I believe the answer is C. If anyone can help me to further understand this problem, I would appreciate the help.
 
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I think that
[tex] v_p=\frac{w}{k}=a \frac{1}{\lambda}.[/tex]

We get from this
[tex] w=a \frac{k}{\lambda}=a \frac{k^2}{2 \pi}.[/tex]

Then
[tex] v_g=\frac{dw}{dk}=2a \frac{k}{2 \pi}=2a \frac{1}{\lambda}.[/tex]

[tex] v_g=2 v_p.[/tex]
 

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