CH301H_Fall_2007_Sample_Exam_3

CH301H_Fall_2007_Sample_Exam_3 - CH 301H Fall 2007 CH 301H...

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CH 301H Fall 2007 Professor Alan Campion CH 301H Sample Exam 3 1. Professor Campion’s laser pointer is a quantum well laser whose energy levels are described by the one-dimensional particle in a box model. The length of the laser cavity (the box) is 0.421 mm. Assume that the light is emitted when an electron makes a transition from the first excited state (n = 2) to the ground state (n = 1). Calculate the energy and the wavelength of the emitted photons. Is the wavelength you get consistent with the color you observe? 2. Emission between the n = 2 and n = 1 states of the Li 2+ ion is a promising source of radiation for printing very small features (< 32 nm) in silicon for future generations of microprocessors. What is the wavelength of this radiation and in which portion of the electromagnetic spectrum does it fall? 3. We discussed a number of experiments whose results could not be explained by classical physics. They divide roughly into two classes, which stimulated the discovery of two important, and revolutionary, concepts in quantum mechanics. What are the two concepts and what were the key results of the experiments that forced physicists to accept these new conclusions? 4. What is the longest wavelength of light that would cause electrons to be emitted from the surface of chromium? The work function Φ for Cr is 7.21 x 10 -19 J. Would Cr be a good material to detect visible light, say in a video camera? 5. Electrons in a cathode ray television tube (the clunky, old fashioned kind) are accelerated to a voltage of 10,000 eV (1.6 x 10 -15 J). Assume that the uncertainty in the momentum of the electrons is 1% of the momentum itself ( p = 0.01p). Use the uncertainty principle to calculate the uncertainty in the position of the electrons as they strike the television screen. Does the uncertainty principle limit the resolution of high definition television? 6. Sketch the first three quantum mechanical wavefunctions and probability distributions for a
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CH301H_Fall_2007_Sample_Exam_3 - CH 301H Fall 2007 CH 301H...

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