The photoelectric effect is a phenomenon in which electrons are emitted from a material (typically a metal) when it is exposed to electromagnetic radiation, such as light. The effect was first observed by Heinrich Hertz in 1887 and was later explained by Albert Einstein in 1905, which contributed to the development of quantum theory.
No matter how hight the wave intensity, if it the frequency is small, no photons are removed from the material.
This is different from classic waves where energy is proportional to intensity, and coherent with the existence of photons and the Planck-Einstein relation.
Photoelectric effect by UCSB Physics Lecture Demonstrations (2021)
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