Is the Speed of Light (c) Always 3x10^8 m/s in E=hc/λ?

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Discussion Overview

The discussion centers around the interpretation of the speed of light (c) in the equation E=hc/λ, particularly in the context of refraction and phase velocity changes in different media. Participants explore whether c always represents the speed of light in a vacuum or if it can refer to the speed in a medium, and how this affects the relationship between wavelength and energy.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant questions whether c in E=hc/λ is always 3x10^8 m/s or if it refers to the speed of light in a medium.
  • Another participant asserts that c in the equation is always the speed of light in vacuum and that the refractive index would account for changes in a medium.
  • A participant raises the question of whether a decrease in wavelength in a refractive medium implies an increase in energy.
  • Another participant clarifies that the relationship regarding energy is different in quantum mechanics compared to electromagnetic wave descriptions.
  • There is a suggestion that the interpretation of λ is crucial, as it may refer to wavelength in vacuum or in the medium, and that E=hf is a more universally applicable formula.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of c in the equation, with some asserting it always refers to the speed in vacuum while others suggest it may vary depending on the context. The discussion remains unresolved regarding the implications of wavelength changes in a medium on energy.

Contextual Notes

There are unresolved questions regarding the definitions of wavelength in different contexts and the implications of using different models (quantum vs. wave) for understanding energy relationships.

sorax123
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I was thinking about refraction and phase velocity change, when i thought about whether the c in e=hc/lambda is always 3x10^8 or does it refer to the speed in the medium?
Thanks
 
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in ##E=hc/\lambda## ##c## is always the speed of light in vacuum.
if the speed in the medium is important, it will show up in equations as a refractive index.
as far as the photon is concerned, the "medium" is an array of atoms with empty space in between.
 
So if wavelength decreases in a refractive medium, does that mean energy increases?
 
sorax123 said:
I was thinking about refraction and phase velocity change, when i thought about whether the c in e=hc/lambda is always 3x10^8 or does it refer to the speed in the medium?
Thanks

It depends on what do you mean by λ. It is the wavelength in vacuum or in the medium?
Anyway, you should have the formula getting back to E=hf which is valid in vacuum and media as well.
 
Cheers folks. I now see that the qm and wave models must be evaluated differently and that E=hf is a more useful formula to employ :).
 

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