Derivation of the photon energy

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Discussion Overview

The discussion centers on the derivation of the photon energy formula, specifically the relationship between energy and frequency multiplied by Planck's constant. Participants explore whether this formula can be derived from fundamental physical principles or if it was primarily established through experimental observations related to phenomena like the photoelectric effect and black body radiation.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • One participant suggests that all theories are based on observations and that special relativity implies energy is proportional to frequency, leading to the conclusion that E/f = constant, identified as Planck's constant.
  • Another participant requests specific textbooks that demonstrate how to derive E/f = constant.
  • A different participant asserts that the relationship cannot be derived and is merely an experimental observation.
  • One participant argues that it can be derived under certain assumptions, particularly those of special relativity, noting that Lorentz transformations necessitate that energy and frequency scale similarly.
  • This participant also clarifies that special relativity does not rely on the quantization of light, despite both concepts being introduced in the same year.

Areas of Agreement / Disagreement

Participants express differing views on whether the photon energy formula can be derived from fundamental principles or if it is solely an empirical observation. No consensus is reached on this matter.

Contextual Notes

The discussion highlights the dependence on specific assumptions regarding special relativity and the nature of experimental observations. There is also an acknowledgment of the historical context in which these concepts were developed.

shaiyefet
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Hi everyone,

Anybody knows if the photon energy (frequency * Planck's constant) can be derived from more basic physical principles or this formula was "invented" to explain the photo-electric effect or black body radiation?

If you know a way to derive it, please share.

Thanks a lot !
 
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Everything is fundamentally based on observations. Our theories are made based on those observations, and have to agree with them.
Special relativity would not work if energy would not be proportional to frequency. From the observation that physics, and in particular the speed of light, is the same for all observers, and quantization from quantum mechanics, you can derive E/f = constant. This constant is then called Planck constant.
 
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Thanks for your comment,
Do you know any specific textbook that shows how to derive E/f=const. ?
Thanks
 
You can't really derive it, it was (and is) an experimental observation.
 
Well, you can derive it based on other assumptions (in particular, those of special relativity). Lorentz transformations require that both E and f scale in the same way. Otherwise you would not get the same invariant mass of systems of two photons or photon plus massive particle.

Special relativity is not based on quantized light, although both were introduced in the same year by the same person. Lorentz transformations are actually a bit older.
 
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