midterm1 - Name: _ 2.57 Midterm Exam No. 1 November 2, 2004...

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Name: ____________________ 2.57 Midterm Exam No. 1 November 2, 2004 * Mass of one proton : 1.67 µ 10 -27 kg. You should remember other constants needed. 1. Answer the following ten short questions. Briefly explain your answer ( 60 Points ). (1) Estimate the average velocity of helium atoms in helium gas maintained at 300 K. (2) Air molecules at 1 atm have a mean free path approximately 70 nm. Estimate the mean free path at 1 torr, i.e., 1/760 of 1 atm. (3) Light is incident from a medium of refractive index 2 towards an interface with vacuum. What is the reflectivity if the angle of incidence is 65 o .
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Name: ____________________ (4) Silicon crystals are fcc structures with two atoms as the basis. The lattice constant of the conventional cubic unit cell is 5.4 Å. What is the phonon specific heat of silicon per unit volume at high temperatures? What is the specific heat per unit mass at the same temperatures? (5) A quantum dot has a cubic shape of 20x20x20 Å 3 . The potential barriers surrounding the quantum dot is infinitely high. The electron effective mass equals that of the free electron.
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midterm1 - Name: _ 2.57 Midterm Exam No. 1 November 2, 2004...

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