Lect24-Phys172s09-(11.8-12.4-Maxwell-Gas_law)

Lect24-Phys172s09-(11.8-12.4-Maxwell-Gas_law) - Spring 2009...

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Unformatted text preview: Spring 2009 PHYS 172: Modern Mechanics Lecture 24 – Maxwell-Boltzmann, Gas laws Read 11.8 – 12.4 EXAM 3 Multiple choice scores posted on CHIP, Average: 43.4/70 (62%) Hand-grading in progress Survey points will be entered into CHIP during the last week of classes. Average translational kinetic energy in a gas 2 2 2 2 1 1 1 1 2 2 2 2 trans x y z K Mv Mv Mv Mv = = + + ( ) 2 1 1 2 2 x Mv kT = Each “degree of freedom” contributes ½kT Root mean square (rms) speed: 2 rms v v ≡ Average translational kinetic energy for an ideal gas: 3 2 trans K kT = (high temperature, If kT >> ω ) 2 3 1 2 2 rms Mv kT = Note: rms v v = 0.92 rms v v = 3 rms v kT M = (see book for details) Speed of sound in a gas 3 rms v kT M = Example: N 2 at 293 K v rms = 496 m/s Speed of sound = 344 m/s CLICKER : In which of the gases speed of sound is highest? A) H 2 (2 g/mol) B) N 2 (28 g/mol) C) O 2 (32 g/mol) D) Ar (40 g/mol) E) Xe (131 g/mol) Vibrational energy in a diatomic molecule ( ) trans vib rot K E E Mgy kT kT kT kT x y z P E e dv dv dv e dxdydz e e---- &...
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Lect24-Phys172s09-(11.8-12.4-Maxwell-Gas_law) - Spring 2009...

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