Solving for Wavelength: What Did I Do Wrong?

  • Context: Graduate 
  • Thread starter Thread starter Isaac0427
  • Start date Start date
  • Tags Tags
    Wavelength
Click For Summary

Discussion Overview

The discussion revolves around the application of De Broglie's postulate in calculating wavelength and the implications of using the equation E=pc for different types of particles. Participants explore the conditions under which these equations are valid and the potential errors in reasoning regarding the speed of matter waves.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant states that De Broglie's postulate leads to the conclusion that matter waves cannot travel at the speed of light, raising a question about the validity of their calculations.
  • Another participant points out that the equation E=pc is applicable only to massless particles, suggesting that the original reasoning is flawed because it assumes this equation applies to all particles.
  • A later reply questions whether the mass-energy equivalence mc² should be considered in the calculations, indicating a need for clarification on the treatment of massive versus massless particles.
  • Some participants provide a link to external resources for further exploration of the topic, indicating a willingness to assist in understanding the concepts involved.

Areas of Agreement / Disagreement

Participants generally agree that E=pc is specific to massless particles, but there is no consensus on how to correctly incorporate mass into the calculations or whether the initial reasoning was fundamentally flawed.

Contextual Notes

The discussion highlights the need for clarity regarding the conditions under which different equations apply, particularly the distinction between massless and massive particles, and the implications of using E=pc without considering mc².

Isaac0427
Insights Author
Gold Member
Messages
718
Reaction score
163
De Broglie's postulate states that λ=h/p and ƒ=E/h. If you plug in E=pc, then you get λ=c/ƒ. Using the equation for wavelength λ=v/ƒ, I found that v=c, but this can't be true, because the matter waves would be traveling a c. What did I do wrong? Thanks!
 
Physics news on Phys.org
E=pc holds only for massless particles. You have obtained that massless particles propagate at the speed of light. But that is obvious.
 
dextercioby said:
E=pc holds only for massless particles. You have obtained that massless particles propagate at the speed of light. But that is obvious.
So do I need to factor in mc^2 too?
 

Similar threads

Undergrad De Broglie Wavelength at rest: λ = h/p = h/0 when v=0?
  • · Replies 5 ·
Replies
5
Views
2K
Graduate Why is deBroglie λ for electrons the same as λ for photons?
  • · Replies 3 ·
Replies
3
Views
2K
High School Does Wavelength Affect Uncertainty in Macroscopic Objects?
  • · Replies 11 ·
Replies
11
Views
2K
Graduate Wavelength associated with the body - What does it mean?
  • · Replies 2 ·
Replies
2
Views
2K
Undergrad Where did I go wrong in deriving quantized energy?
  • · Replies 3 ·
Replies
3
Views
1K
Calculating the Planck Length
  • · Replies 3 ·
Replies
3
Views
1K
Graduate Wavelength of matter waves at speed equal to zero.
  • · Replies 14 ·
Replies
14
Views
8K
Undergrad Please help me understand quantum tunneling conceptually?
  • · Replies 13 ·
Replies
13
Views
3K
Undergrad E=hf for massive particles, but which Energy exactly?
  • · Replies 5 ·
Replies
5
Views
2K
Compton Scattering- finding photon wavelength
  • · Replies 5 ·
Replies
5
Views
2K