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Photons, Electrons, and Atoms

Photons, Electrons, and Atoms. Visible and non-visable light. Frequencies around 10 15 Hz Much higher than electric circuits Theory was about vibrating charge in the atom This lead to the “quantum” theory of light

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Photons, Electrons, and Atoms

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  1. Photons, Electrons, and Atoms

  2. Visible and non-visable light • Frequencies around 1015 Hz • Much higher than electric circuits • Theory was about vibrating charge in the atom • This lead to the “quantum” theory of light • It states that some of the properties of EM radiation resemble those of particles • Where KE is proportional to f

  3. The Photoelectric Effect • It is caused by an element absorbing certain wavelength of light which causes electrons to be ejected from the surface • This “potential energy barrier” can be found with the work function f • Classic mechanics predicted that the amplitude of the wave, not its frequency, would cause more electrons to be emitted

  4. Photoelectric cont. • It was found that the amplitude, no matter how bright, would not cause the electrons to leave. • Only when critical or threshold frequency was reached, would the electrons move • For most metals it’s in the ultraviolet range • At frequencies higher than ft, the stopping potential would completely stop the flow of electrons from the surface

  5. Equations • Stopping potential • Energy of a photon • Planck’s constant h = 6.6260755 x10-34 j.s

  6. The eV • The electron volts relates electrons and energy • 1 eV = 1.602 x 10-19 J • Ex: If Vo = 5V then eV = 5eV • Example 41-1 • Photon energy • p = momentum

  7. EM Spectrum

  8. Line spectra • Line spectra phenomenon vs spectrum • Each line is an image of the spectrograph slit, deviated at an angle that depends on the frequency of the light • Each element emits a “signature” • Certain wavelengths of light unique to its atomic structure • Classical mechanics could not explain this

  9. Energy • Bohr proposed the idea of energy levels • All atoms of an element have the same energy levels, with no electrons existing in “intermediate” levels • The electrons can “jump” from a higher to a lower level by emitting a photon • hf = Ei - Ef

  10. Balmer Series • Trial and error resulted in the formula • R = 1.097 x 107 m-1 • Substituting in for l we get En ( energy levels

  11. Emission spectra

  12. Sources • http://cwx.prenhall.com/bookbind/pubbooks/hillchem3/medialib/media_portfolio/07.html

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