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Unformatted text preview: CHEM 356, Lecture 2, Fall 2009 1 2. The Photoelectric Effect: Basic Observations ∙ electrons are emitted when light strikes a clean metal plate in a vacuum ∙ the number of emitted electrons depends upon the light intensity; their kinetic energy does not ∙ the maximum kinetic energy (KE) of the emitted electrons depends only upon ∙ no (measurable) time lag occurs between the time when light initially strikes the surface and when the first electron is emitted Einstein (1905) : pointed out that these observations are readily explained if we assume that the energy associated with light of frequency is itself quantized as = ℎ . Implications : KE of the emitted electrons is given by 1 2 e 2 = ℎ − , with , known as the work function is characteristic of the specific metal. ∙ we note that, as a quantum ℎ of energy is given up to an electron upon collision with a photon, the lack of a time-lag was also explained CHEM 356, Lecture 2, Fall 2009 2 3. Spectroscopic Transitions The very existence of sharp spectral lines was mystifying since, according to classical physics, an accelerated charge continuously emits radiation, with the consequence that an extranuclear electron should lose energy and spiral down...
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