445lec27 - PHYS 445 Lecture 27 Black-body radiation II...

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PHYS 445 Lecture 27 - Black-body radiation II 27 - 1 © 2001 by David Boal, Simon Fraser University. All rights reserved; further resale or copying is strictly prohibited. Lecture 27 - Black-body radiation II What's Important: radiation pressure radiative power Text : Reif Radiation pressure The general definition of the mean force for a change in its conjugate variable h is ß = ln Z h (27.1) which for the mean pressure implies ß p = ln Z V . (27.2) For a photon gas, we determined that ln Z = - ln1 - e - ß i ( 29 i so Eq. (27.2) implies ß p = V - ln1 - e - ß i ( 29 i = - i V i ln1 - e - ß i ( 29 i = - i V ( - 1) ( - ß i ) e - ß i 1 - e - ß i ( 29 i = - ß i V i e - ß i 1 - e - ß i ( 29 i (27.3) Now, how does a photon energy change with volume? Consider a specific quantum state n i in a cubic cavity of volume V = L 3 . From the usual standing wave condition, the wavelength i is i = 2 L / n i so
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This note was uploaded on 09/07/2009 for the course PHYS 445 taught by Professor Davidboal during the Spring '08 term at Simon Fraser.

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445lec27 - PHYS 445 Lecture 27 Black-body radiation II...

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