Fa07-MT1-Huang-Exam

Fa07-MT1-Huang-Exam - University of California, Berkeley...

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University of California, Berkeley Physics 7B, Fall 2007 ( Xiaosheng Huang ) Midterm 1 Tuesday, 10/2/2007 6:00-8:00 PM Fundamental Constants: Avogadro's number, N A : 6.02×10 23 Gas Constant, R : 8.315 J/mol·K Boltmann's Constant, k B : 1.38×10 -23 J/K Stefan-Boltzmann Constant, σ : 5.67×10 -8 W/m 2 ·K 4 1) (20 pts.) The density of atoms, mostly hydrogen, in interstellar space is about one per cubic centimeter. The temperature of this gas is ~3000 K. The diameter of a hydrogen atom is approximately 10 -10 m. Assume that the ideal gas law holds. a ) Estimate the pressure of this gas and express the pressure in torr. (1 atm=760 torr=1.01x10 5 Pa) b ) Estimate the mean free path. (You do not have to derive the expression for the mean free path.) 2) (30 pts.) A real heat engine working between heat reservoirs at T L =350K and T H =900K produces 700J of work per cycle for a heat input of 1800J. a
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This note was uploaded on 02/04/2010 for the course PHYSICS 7B taught by Professor Packard during the Spring '08 term at Berkeley.

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Fa07-MT1-Huang-Exam - University of California, Berkeley...

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