lecture19 101102 - Photo-Electric/Plancks Constant Lab...

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1 Photo-Electric/Planck’s Constant Lab Photo-Electric Facts No electrons are emitted if the incident light frequency is below some cutoff frequency that is characteristic of the material being illuminated The maximum kinetic energy of the photoelectrons is independent of the light intensity The maximum kinetic energy of the photoelectrons increases with increasing light frequency Electrons are emitted from the surface almost instantaneously, even at low intensities Einstein’s Explanation A tiny packet of light energy, called a photon , would be emitted when a quantized oscillator jumped from one energy level to the next lower one The photon’s energy would be E = hƒ Each photon can give all its energy to one electron in the metal Max Planck 1858 – 1947 Introduced a “quantum of action,” h Awarded Nobel Prize in 1918 for discovering the quantized nature of energy Arthur Holly Compton 1892 – 1962 Discovered the Compton effect Worked with cosmic rays Director of the lab at U of Chicago Shared Nobel Prize in 1927 Compton Scattering Compton assumed the photons acted like other particles in collisions Energy and momentum were conserved The shift in wavelength is (1 cos ) o e h mc     Louis de Broglie 1892 – 1987 Discovered the wave nature of electrons Awarded Nobel Prize in 1929
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2 Quick Quiz What is the value of Planck’s Constant? A. 1.6 x 10 -19 Coulombs B. 6.6 x 10 -34 Joule-sec C. 340 m/sec D.
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lecture19 101102 - Photo-Electric/Plancks Constant Lab...

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