12â75 the emissivity of a tungsten filament can be approximated to be 0.5 for radiation at wavelengths less than 1 mm and 0.15 for radiation at greater than 1 mm. determine the average emissivity of the filament at (a) 2000 k and (b) 3000 k. also, determine the absorptivity and reflectivity of the filament at both temperatures

To save energy, the air supply to a 2000 ft office has been shut off overnight and the room temperature has dropped to 40°f. in the morning, the thermostat is reset to 70°f and warm air at 120 f begins to flov in at 200ft'/min. the air is well mixed within the room, and an equal mass flow of air at room temperature (changing with time) is withdrawn through a return duct. the air pressure is nearly 1 atm everywhere. ignoring heat transfer with the surroundings and kinetic and potential energy effects, estimate how long it takes for the room temperature to reach 70°f. plot the room temperature as a function of time.