User:Johnjbarton/sandbox/introduction to quantum mechanics: Difference between revisions
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His revolutionary proposal started by reanalyzing Planck blackbody theory, arriving at the same conclusions by using the new "energy quanta". Einstein then showed how energy quanta connected to JJ Thomson's electron. In 1902, [[Philipp Lenard]] directed light from an arc lamp onto freshly cleaned metal plates housed in an evacuated glass tube. He measured the electric current coming off the metal plate, for higher and lower intensity of light and for different metals. This is the [[photoelectric effect]]. Lenard showed that amount of current – the number of electrons – depended on the intensity of the light, but that the velocity of these electrons did not depend on intensity. The continuous wave theories of the time would predict that more light intensity would accelerate the same amount of current to higher velocity contrary to experiment. Einstein's energy quanta explained the volume increase: one electron is ejected for each quanta: more quanta mean more electrons.
Einstein then predicted that the electron velocity would increase in direct proportion to the light frequency above a fixed value that depended upon the metal. Here the idea is that energy in energy-quanta depends upon the light frequency; the energy transferred to the electron comes in proportion to the light frequency. The type of metal gives a [[work function | barrier]], the fixed value, that the electrons must climb over to exit their atoms, to be emitted from the metal surface and be measured.
Ten years elapsed before Millikan's definitive experiment<ref>{{Cite journal |last=Millikan |first=R. A. |date=1916-03-01 |title=A Direct Photoelectric Determination of Planck's " h " |url=https://link.aps.org/doi/10.1103/PhysRev.7.355 |journal=Physical Review |language=en |volume=7 |issue=3 |pages=355–388 |doi=10.1103/PhysRev.7.355 |issn=0031-899X}}</ref> verified Einstein's prediction. During that time many scientists rejected the revolutionary idea of quanta.<ref name=pais>{{Cite journal |last=Pais |first=A. |date=1979-10-01 |title=Einstein and the quantum theory |url=https://link.aps.org/doi/10.1103/RevModPhys.51.863 |journal=Reviews of Modern Physics |language=en |volume=51 |issue=4 |pages=863–914 |doi=10.1103/RevModPhys.51.863 |issn=0034-6861}}</ref> But Planck's and Einstein's concept was in the air and soon affected other theories.
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