phys 369 09 hw 12 - filament resistance with temperature....

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Phys. 369, Fall 2009 Homework #12 Due Fri. Dec. 4, beginning of class 100 points total 1. (12 points) Schroeder, problem 7.19 2. (20 points) Schroeder, problem 7.23 (a) through (e) (Skip (f), (g)) 3. (10 points) Schroeder, problem 7.25 4. (20 points) Schroeder, problem 7.29 5. (18 points) A furnace has a volume V = 5.0 m 3 , and a temperature T = 1700 K. a) Find the energy U of the photons in the furnace. b) Show that the total number of photons in the furnace is = 0 2 3 1 8 dx e x hc kT V N x π Find the value of the integral (using math tables or a computer program), and use your result to calculate the number of photons in the furnace. c) What is the entropy of the photon gas, per photon, in units of k ? 6. (20 points) A tungsten filament of resistance R = 800 Ω and area A = 10 mm 2 is connected to the V = 120 V line voltage. Its emissivity is η = 0.4. Assume the filament is in the form of a thin flat sheet; i.e. it has two surfaces both of area A , and that you can neglect the change in the
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Unformatted text preview: filament resistance with temperature. a) Calculate the temperature of the filament, assuming that the only source of energy loss is its blackbody radiation. b) Find the total power P BB radiated by the filament as blackbody radiation. c) Make a sketch of the spectrum of the radiation (power per unit photon energy interval). At what photon energy is the spectral intensity the highest? What wavelength photon does this correspond to? Compare this to the value of the peak emission wavelength obtained from Wiens displacement law max T = 2.90 10 3 m K d) What fraction of the emitted radiation is contained in the visible part of the spectrum (wavelengths 400 nm to 700 nm)? (You will have to do the integral numerically.) e) What fraction of the electrical power drawn by the filament is converted into blackbody radiation? What fraction is converted into visible radiation?...
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This note was uploaded on 11/06/2010 for the course PHY 369 taught by Professor Staff during the Fall '08 term at University of Texas at Austin.

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