De broglie vs classical wavelength

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Discussion Overview

The discussion centers on the comparison between the de Broglie wavelength and classical wavelength, particularly in the context of quantum particles like electrons and photons. Participants explore whether the de Broglie wavelength can be treated similarly to classical wavelengths in wave equations and the implications of this for understanding energy and momentum in quantum mechanics.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants question whether the de Broglie wavelength, defined as h/p, can be used interchangeably with classical wavelength in wave equations.
  • One participant suggests that the de Broglie wavelength is viewed as a characteristic size of a quantum particle and may not be relevant for classical wave equations.
  • Another participant notes that while the relationship for photons is straightforward (E=pc), the situation for electrons is more complex due to the need to account for rest mass.
  • It is mentioned that to find the frequency of the wave using E=hf, one must consider the total energy, which includes both kinetic and rest energy for particles with mass.
  • A participant raises a question about the apparent contradiction in the relationships between velocity and wavelength for different contexts, suggesting confusion over the implications of these relationships.
  • Some participants clarify that the wave relationship holds for massless particles, while discussing the distinction between phase velocity and group velocity in wave packets.

Areas of Agreement / Disagreement

Participants express differing views on the applicability of the de Broglie wavelength in classical contexts, with some asserting its limited relevance and others exploring its implications for particles with mass. The discussion remains unresolved regarding the interchangeability of the de Broglie wavelength with classical wavelengths.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about the relationships between velocity, wavelength, and energy, particularly in the context of massless versus massive particles. The mathematical steps involved in deriving these relationships are not fully resolved.

xiankai
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since it is defined (from what i can tell) as h/p,

is it interchangeable with the classical wavelength in equations involving waves in general? or is it a special separate case for matter?

that is,

for photons we have the following equation:
E = hf
E = hc/λ

can the same equation be used to find the wavelength/energy of electrons?
 
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The de Broglie wavelength is now kinda viewed as the characteristic "size" of a quantum particle. It's not really a super-relevant physical quantity anymore, nor can you just put it into classical wave equations to get anything physical.
 
xiankai said:
since it is defined (from what i can tell) as h/p,

is it interchangeable with the classical wavelength in equations involving waves in general? or is it a special separate case for matter?

that is,

for photons we have the following equation:
E = hf
E = hc/λ

can the same equation be used to find the wavelength/energy of electrons?
For a photon E=pc, so the dB wavelength for a given energy is simple.
For an electron p=\sqrt[{E^2/c^2-m^2}, so the dB wave length in terms of energy is more complicated,.
 
Meir Achuz said:
For a photon E=pc, so the dB wavelength for a given energy is simple.
For an electron p=\sqrt[{E^2/c^2-m^2}, so the dB wave length in terms of energy is more complicated,.

we must include the rest mass of the electron?
 
Yes. And to get the frequency of the wave via E = hf, you must use the total energy (kinetic energy plus rest energy).
 
According to de broglie relation lambda=h/mv ...which implies that velocity is inversely proportional to wavelength. But According to the reletion

V=n lambda ... velocity is directly proportional to wavelength... How That diffenence is Causesd ? Am i going wrong Somowhere ?
 
Note that the wave relationship only holds for massless particles.
 
The V in V=\nu\lambda is the phase velocity of the traveling wave packet.
This V also = E/p=h\nu/p, which is consistent.
The phase velocity is >c, but the group velocity v_G=p/E is less than c.
 

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