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I was just wondering why in photoelectrics, the kinetic energy of an electron released from a certain metal after being struck by a photon follows the classical approach and not the relativistic. For example...

E_photon = (Planck_const)(frequency) = (Work function) + (1/2)(mass_electron)(u^2)

instead of

E_photon = (Planck_const)(frequency) = (Work function) + ((1 - ((u/c)^2)))^(-1)) - 1)(mass_electron)(c^2)

I've read several texts, including my university's text and Serway's text but the answer isn't really there. Thanks in advance!

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# Photoelectrics and kinetic energy

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