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Quiz13_solutions

Quiz13_solutions - Physics 222 Name Section Quiz 13A Fall...

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Physics 222 Fall 2011 Name:_______________ Section:______________ Quiz 13A 1) A photon strikes a metal surface and releases an electron through the photoelectric effect. The work function of the metal surface is 8.00×10 -19 J. If the electron has energy of 5.00×10 -19 J, what is the largest wavelength the photon could have had? Solution Minimum photon frequency is related to other parameters by eV 0 = hf - φ , so f = (eV 0 + φ)/h . Using λ = c/f , then, the maximum wavelength is λ = ch/(eV 0 + φ) = (3.00×10 8 m/s)(6.63×10 -34 Js)/(5.00×10 -19 J + 8.00×10 -19 J) = 153 nm 2) If you chill an object to half its original temperature, at what fraction of its former intensity does it emit blackbody radiation? Solution Total blackbody radiation intensity is given by I = σT 4 . Let the initial temperature and intensity be T 0 and I 0 ; then I 0 = σT 0 4 . If the new temperature is T , then T = T 0 /2 , and I = σT 4 = σ(T 0 /2) 4 = (1/16)σT 0 4 = (1/16)I 0

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Physics 222 Fall 2011 Name:_______________ Section:______________ Quiz 13B 1) The threshold wavelength of a metal surface is 300 nm; that is, photons above that
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Quiz13_solutions - Physics 222 Name Section Quiz 13A Fall...

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