Why does the momentum of a matter wave depend on the phase velocity?

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SUMMARY

The discussion centers on the relationship between momentum and phase velocity in matter waves, as described by de Broglie's relations. It establishes that momentum (p) is defined as p = E/vp, where E is energy and vp is phase velocity. The group velocity, defined as dE/dp, is highlighted as the actual velocity of the particle, contrasting with phase velocity. For a particle of mass m, the equations show that phase velocity is p/2m and group velocity is p/m, confirming that group velocity represents the true velocity of the particle.

PREREQUISITES
  • Understanding of de Broglie relations, specifically E = hf and p = h/λ
  • Knowledge of phase velocity and group velocity concepts
  • Familiarity with the relationship between energy, momentum, and mass in quantum mechanics
  • Basic calculus for differentiating energy with respect to momentum
NEXT STEPS
  • Study the implications of de Broglie relations in quantum mechanics
  • Explore the mathematical derivation of group velocity and phase velocity
  • Investigate the role of momentum in wave-particle duality
  • Learn about applications of group velocity in quantum mechanics and optics
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Students and professionals in physics, particularly those focusing on quantum mechanics, wave-particle duality, and the behavior of matter waves.

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de Broglie relations say that E = hf and p = h/λ which implies E/p = λf = ω/κ = vp, or p = E/vp. It seems to me like the momentum of a particle described by a matter wave should relate to the group velocity not the phase velocity, because the group velocity is generally the actual velocity of the particle.
 
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They're all related. The phase velocity is E/p while the group velocity is dE/dp. For a particle of mass m, E = p2/2m. So for this case the phase velocity is p/2m and the group velocity is p/m. Looks like the group velocity is what you want to be the "actual" velocity v.
 

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