1121_Physics ProblemsTechnical Physics

1121_Physics ProblemsTechnical Physics - 462 Introduction...

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Unformatted text preview: 462 Introduction to Quantum Physics Q40.7 Wave theory predicts that the photoelectric effect should occur at any frequency, provided the light intensity is high enough. However, as seen in the photoelectric experiments, the light must have a sufficiently high frequency for the effect to occur. Q40.8 The stopping voltage measures the kinetic energy of the most energetic photoelectrons. Each of them has gotten its energy from a single photon. According to Planck’s E hf = , the photon energy depends on the frequency of the light. The intensity controls only the number of photons reaching a unit area in a unit time. Q40.9 Let’s do some quick calculations and see: 1.62 MHz is the highest frequency in the commercial AM band. From the relationship between the energy and the frequency, E hf = , the energy available from such a wave would be 1 07 10 27 . × − J, or 6.68 neV. That is 9 orders of magnitude too small to eject electrons from the metal. The only thing this student could gain from this experiment is a heftyeject electrons from the metal....
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