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Chapter3_18 - the electric field within the light If the...

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PHY3063 R. D. Field Department of Physics Chapter3_18.doc University of Florida Photon Basic quantum of light! The Photoelectric Effect (1) When light is incident on a metal surface ( visible or ultraviolet ), electrons will be ejected from the surface. In 1916 experiments by Milliken showed that the kinetic energy of the ejected electrons is independent of the intensity of the light, but does depend in a simple way on the frequency of the light. The kinetic energy of the emitted electrons varies linearly with the frequency of the light. The higher the frequency the larger the kinetic energy. Increasing the intensity of the light increases the number of emitted electrons per second but does not affect their energy. This is very difficult to understand classically since the intensity is proportional to the amplitude of the electromagnetic oscillations squared and the larger the amplitude the larger
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Unformatted text preview: the electric field within the light. If the electric field is larger than it can accelerate the electron to a higher speed and hence more kinetic energy. Einstein: A beam of light comes in parcels with energy of magnitude E = hf which can be absorbed by an electron, where h is a fundamental constant. Thus, the kinetic energy of the emitted electron is W hf KE − = , where W is the amount of work required to remove the electron from the metal ( i.e. binding energy of the electron to the metal). W is called the “work function” and is a property of the metal ( independent of f ). (Note that the intensity of light determines the number of photons per second striking the surface of the metal.) Einstein did not use the term photon . V 1 V 2 electrons Incident Light photocathode collector x-axis y-axis z-axis E B Direction of Propagation...
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