Heating mechanisms
In the problems in this section, clearly identify the system and objects in the environment that interact with the system. Label the work as WEnvironment on System, heating as QEnvironment to System, and the change in internal energy as ΔUint.
Insulating a house You insulate your house using insulation rated as R-12, which will conduct 1/12 Btu/h of thermal energy through each square foot of surface if there is a 1 °F temperature difference across the material (R-12 insulation is said to have a thermal resistance R of 12 h . ft2 . °F/Btu). The conduction rate through a material of area A, across which there is a temperature difference T2 - T1, is
H Conduction = (1/R2) (T2 - T1)
Solar collector You wish to install a solar panel that will run at least five lightbulbs, a TV, and a microwave. How large should the panel be if the average sunlight incident on a photoelectric solar collector on a roof for the 8-h time interval is 700 W/m2 and the radiant energy is converted to electricity with an efficiency of 20%?
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