The photoelectric effect illuminated

Yet while Planck had solved the ultraviolet catastrophe by using atoms and a quantized si4730

  electromagnetic field, most physicists immediately agreed that Planck's "light quanta" were unavoidable flaws in his model. A more complete derivation of black body radiation would produce a fully continuous, fully wave-like electromagnetic field with no quantization. However, in 1905 Albert sis6326agp

  Einstein took Planck's black body model in itself and saw a wonderful solution to another outstanding problem of the day: the photoelectric effect. Ever since the discovery of electrons eight years previously, electrons had been the thing to study in physics laboratories worldwide. Nikolai Tessa discovered in 1901 that when a metal sism661mx

  was illuminated by high-frequency light , electrons were ejected from the metal at high energy. This work was based on the previous knowledge that light incident upon metals produces a current, but Tessa was the first to describe it as a particle phenomenon. The following year, Philippi Leonard discovered that the energy of these ejected electrons did not sk28

  depend on the intensity of the incoming light, but on its frequency. So if one shines a little low-frequency light upon a metal, a few low energy electrons are ejected. If one now shines a very intense beam of low-frequency light upon the same metal, a whole slew of electrons are ejected; however they possess the same low energy, there are merely more of them. In order to get high energy electrons, sk36

  one must illuminate the metal with high-frequency light. The more light there is, the more electrons are ejected. Like blackbody radiation, this was at odds with a theory invoking continuous transfer of energy between radiation and matter. However, it can still be explained using a fully classical description of light, as long as matter is quantum mechanical in nature.