![]() ![]() ![]() Light from a white light source was directed through a coloured filter and a ring shaped electrode in a vacuum chamber to illuminate a photoelectric target which in response emitted a stream of electrons. This enabled him to devise a simpler, more accurate experiment for determining Planck's constant based on photo-electric emissions. Where e is the electric charge on an electron and V is the voltage of the corresponding electrical field, so that eV is the electrical energy of the emitted electrons. Millikan used instead the electrical equivalent of the energy namely: Einstein expressed the energy in terms of the kinetic energy of the emitted electrons, but since this was difficult to measure, no accurate value of Planck's constant had yet been determined. Where E is the energy of the electrons emitted from a metal due to photoelectric emission, h is Planck's constant, f is the frequency of the incident light, and W is the work function, in Millikan's words, "the work necessary to get the electron out of the metal". In 1905 Einstein had incorporated Planck's Law into his photoelectric theory with the equation: In 1916 Robert Millikan devised an experiment based on photo-electric emissions to determine the value of Planck's constant. Millikan's Determination of Planck's Constant Millikan's Determination of Planck's Constant. ![]()
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