05_vacuum

5 1019 10 high 10 6 very high 10 ultrahigh 10 vacuum

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Unformatted text preview: Very high 10 Ultrahigh 10 Vacuum • The “proper” unit of measure for pressure is Pascals proper” (Pa), or N·m-2 • Most vacuum systems use Torr instead M.F.P. (m) 8 – based on mm of Hg • Atmospheric pressure is: – – – – 760 Torr 101325 Pa 1013 mbar 14.7 psi • So 1 Torr is 133 Pa, 1.33 mbar; roughly one milliroughly one atmosphere Winter 2008 Lecture 5 3 Winter 2008 4 1 Vacuum Systems 01/24/2008 UCSD: Physics 121; 2008 UCSD: Physics 121; 2008 Kinetic Theory Mean Free Path • The particles of gas are moving randomly, each with a unique velocity, but following the Maxwell Boltzmann distribution: • The mean free path is the typical distance traveled before colliding with another air molecule • Treat molecules as spheres with radius, r • If (the center of) another molecule comes within 2r of of the path of a select molecule: • Each molecule sweeps out cylinder of volume: • The average speed is: V = 4 r2vt – in time t at velocity v • If the volume density of air molecu...
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This note was uploaded on 01/30/2014 for the course PHYS 121 taught by Professor Staff during the Winter '08 term at UCSD.

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