Abdelhady (2011)1explains that Einstein presented his hypothesis that light may behave as a particle in order to find a plausible explanation of the photoelectric effect. A key piece of evidence Einstein cited was the existence of a measured cutoff frequency of light — a threshold below which light would not eject electrons from metal surfaces in photocells, regardless of how much light is shone on the surface — which he found as proof of his hypothesis1
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Comments on Einstein’s Explanation of Electrons, Photons, and the Photo-Electric EffectSalama Abdelhady2011Applied Physics Research
Qian (2023)2notes that Planck and Einstein empirically obtained a statistical relationship between the energy of a light quantum and the frequency of light, a foundational result of the quantum theory they helped create while explaining the photoelectric effect2
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On the Physical Process and Essence of the Photoelectric EffectWeihong Qian2023Journal of Applied Mathematics and Physics
Historical Reception and Experimental Confirmation
Níaz et al. (2010) reconstruct six key historical aspects of the photoelectric effect, including: Einstein's quantum hypothesis, the lack of acceptance of that hypothesis within the scientific community, and ultimately Millikan's experimental determination of both the Einstein photoelectric equation and Planck's constant h . Their analysis of 103 university textbooks found that these historical elements are largely ignored or distorted .
Limitations of the Evidence
The retrieved evidence only partially covers this topic. I cannot provide a full quantitative description of the photoelectric equation (e.g., KE = hf − φ) from these sources alone, as none of the evidence blocks state it verbatim.
