Does the Equation E=mc² Apply to Photons?

Phys_Boi · Nov 10, 2015

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

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

Thus mass: m = h/λc ?

Khashishi · Nov 10, 2015

##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##

Phys_Boi · Nov 10, 2015

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?

Khashishi · Nov 10, 2015

Set m=0 and you get ##E = pc##. You can solve for the momentum of the photon.

Phys_Boi · Nov 10, 2015

Khashishi said:

Set m=0 and you get ##E = pc##. You can solve for the momentum of the photon.

Ah. Thank you

ZapperZ · Nov 10, 2015

Please note that this has been covered and answered in one of our FAQ.

Zz.

Does the Equation E=mc² Apply to Photons?

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