Does the Equation E=mc² Apply to Photons?

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Discussion Overview

The discussion centers around the applicability of the equation E=mc² to photons, exploring the relationship between energy, mass, and momentum in the context of light. Participants examine theoretical implications and mathematical formulations relevant to photons and their properties.

Discussion Character

  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant suggests that if the energy of a photon is given by Ephoton = hν, then it could be related to mass through E=mc², leading to the equation m = h/λc.
  • Several participants argue that E=mc² applies only to massive particles at rest and that the full equation E² = m²c⁴ + p²c² should be used for photons.
  • Another participant points out that setting m=0 in the full equation leads to E = pc, which can be used to determine the momentum of photons.
  • One participant acknowledges the clarification regarding the momentum of photons after it is presented.
  • A later reply mentions that this topic has been addressed in the forum's FAQ section.

Areas of Agreement / Disagreement

Participants generally disagree on the applicability of E=mc² to photons, with some asserting it does not apply while others explore its implications under certain conditions. The discussion remains unresolved regarding the interpretation of mass in the context of photons.

Contextual Notes

There are limitations regarding the assumptions made about mass and energy in the context of photons, as well as the dependence on definitions of momentum and energy in relativistic contexts.

Phys_Boi
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If the energy of a photon: Ephoton = hν, where h = Planck's constant,
and E = mc2, then does hv = mc2

And if so, if c=vλ: Ephoton = hc/λ = mc2

Thus mass: m = h/λc ?
 
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##E=mc^2## only applies to massive particles at rest, not photons. You need to use the full equation which is
##E^2 = m^2c^4 + p^2 c^2##
 
Khashishi said:
##E=mc^2## only applies to massive particles at rest, not photons. You need to use the full equation which is
##E^2 = m^2c^4 + p^2 c^2##
So what is the momentum of photons since gravitation is applied?
 
Set m=0 and you get ##E = pc##. You can solve for the momentum of the photon.
 
Khashishi said:
Set m=0 and you get ##E = pc##. You can solve for the momentum of the photon.
Ah. Thank you
 
Please note that this has been covered and answered in one of our FAQ.

Zz.
 
Last edited:

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