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26 20 points radiation the spectral hemispherical emissivity of tungsten...

Question: 26 20 points radiation the spectral hemispherical emissivity of tungsten...

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2-6 (20 Points): Radiation The spectral, hemispherical emissivity of tungsten may be approximated by the distribution depicted below. Consider a cylindrical tungsten filament that is of diameter D 0.8 mm and length L20 mm. The filament is enclosed in an evacuated bulb and is heated 0.61-, ε,-0.45 0.4 0.2 a=0.10 0 0 40 I m

by an electrical current to a steady-state temperature of 2900 K. (a) What is the total hemispherical emissivity when the filament temperature is 2900 K? (b) Assuming the surroundings are at 300 K, what is the initial rate of cooling of the filament when the current is switched off?

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