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L/O/G/O Chapter 2 Vacuum Technology for Applied Surface Science 講義下載： .tw/FacultyWeb/LeeYL Kinetic theory of gases: Explain the macroscopic properties of gases (P, T, V..) by microscopic behavior of the molecules. 1 2 1 2 p 3  C or p 3 nm C (1) 2 kT C 3 (2) m ρ: gas density , n=number density of particles, (m-3), C2 :mean square velocity m: mass of a molecule -1 k: Boltzmann constant, (JK ). T: Absolute temperature,(K). Collision rate (Z): the average number of collisions per second between particles. c 8kT z (3) , c (4)  pm λ: mean free path - the mean path which each particle makes between collision. 3 1 5 10     cm 2   (5)   P torr 2n 2r for air  2 The quantity  2r is called the collision cross-section of the molecule and is often denoted by the symbol  . Chapter 2 Vacuum Technology  Vacuum( 真空): A defined space where the pressure is significantly smaller than the atmosphere. concept ： 宇宙內沒有絕對的真空(無任