The walls of a house consists of L=0.02 m thick plywood backed by insulation with the same thickness. The temperature of the inside surface of the wall (the insulation side) is T2=25 oC, while the temperature at the outside surface (the plywood side) is T1= -15 oC, both being constant. The thermal conductivities of the plywood and insulation are, respectively k1=0.09 J/(s m oC) and k2=0.03 J/(s m oC). a) Find the temperature T at the plywood – insulation interface. b) If the total surface area of the walls is 70 m2, find the amount of heat the house looses in 24 hours. (Assuming all the heat losses are due to the thermal conductivity of the walls). c) Does the entropy of the house change? If it does, by how much?
Energy transfer
The flow of energy from one region to another region is referred to as energy transfer. Since energy is quantitative; it must be transferred to a body or a material to work or to heat the system.
Molar Specific Heat
Heat capacity is the amount of heat energy absorbed or released by a chemical substance per the change in temperature of that substance. The change in heat is also called enthalpy. The SI unit of heat capacity is Joules per Kelvin, which is (J K-1)
Thermal Properties of Matter
Thermal energy is described as one of the form of heat energy which flows from one body of higher temperature to the other with the lower temperature when these two bodies are placed in contact to each other. Heat is described as the form of energy which is transferred between the two systems or in between the systems and their surrounding by the virtue of difference in temperature. Calorimetry is that branch of science which helps in measuring the changes which are taking place in the heat energy of a given body.
The walls of a house consists of L=0.02 m thick plywood backed by
insulation with the same thickness. The temperature of the inside surface of the wall (the insulation side) is T2=25 oC, while the temperature at the outside surface (the plywood side) is T1= -15 oC, both being constant. The thermal conductivities of the plywood and insulation are, respectively k1=0.09 J/(s m oC) and k2=0.03 J/(s m oC).
a) Find the temperature T at the plywood – insulation interface.
b) If the total surface area of the walls is 70 m2, find the amount of heat the house looses in 24 hours. (Assuming all the heat losses are due to the thermal
c) Does the entropy of the house change? If it does, by how much?
d) Does the entropy of the Universe change? If it does, by how much?
e) If the cost of electric power is $0.15 per kilowatt hour, how much one has to pay to keep the house warm for 24 hours?
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