lec26 - MIT OpenCourseWare http://ocw.mit.edu 8.044...

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Unformatted text preview: MIT OpenCourseWare http://ocw.mit.edu 8.044 Statistical Physics I Spring 2008 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms . Thermal Radiation Radiation in thermal equilibrium with its surroundings k E 0 B 0 E = E 0 e i ( r t ) k = c | k | k B = B 0 e i ( r t ) B = 1 k E 0 /c 8.044 L26B1 1 2 Time average energy density u = 2 | E | Time average energy ux j E = ( cu ) 1 k Time average pressure ( to k ) P = u Thermal radiation has a continuous distribution of frequencies. u( ,T) Peaks near h = 3 k B T ( h/k B 5 10 11 K-sec) 8.044 L26B2 Spectral Region (Hz) T (K) Thermal Rad. Radio 10 6 5 10 5 Microwave 10 10 . 5 cosmic background Infrared 10 13 5 10 2 room temp. Visible 1 2 10 15 2 10 4 suns surface Ultraviolet 10 16 5 10 5 X ray 10 18 5 10 7 black holes ray 10 21 5 10 10 8.044 L26B3 ENERGY ABSORBED ABSORPTIVITY ( ,T) ENERGY INCIDENT ISOTROPIC ENERGY EMITTED EMISSIVE POWER e ( ,T) AREA ISOTROPIC 8.044 L26B4 THERMAL RADIATION: PROPERTIES...
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lec26 - MIT OpenCourseWare http://ocw.mit.edu 8.044...

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