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consider two surfaces at different temperatures, one cold at Tc and one hot at T

ID: 2013818 • Letter: C

Question

consider two surfaces at different temperatures, one cold at Tc and one hot at Th. Two rods of different materials and different cross-sectional areas, but the same length, are placed in contact with the walls, and they conduct heat from one to the other. One rod is copper with kCu= 397J/s m degree C, and the second is iron with kFe= 79.5J/s m degree C. If both rods transfer energy at the rate P, determine the area AFe of the iron rod if the copper one has ACu= 0.3m^2. (note both rods have same length.)

Explanation / Answer

Data: Let Temperature of cold surface = Tc Temperature of hot surface = Th Length of each rod = L kCu= 397 J/s m degree C kFe= 79.5 J/s m degree C Area of cu rod, Acu = 0.3 m^2 Area of iron rod, AFe = ? Solution: Power, P = Q / t                  = k A (Th - Tc) / L Here, the constant quantities are:
P, L, and (Th - Tc) for both rods.
So,   kcu * Acu = kFe   * AFe          397 * 0.3 = 79.5 * AFe                     AFe = 1.498 m^2 Ans: AFe = 1.498 m^2 (or) 1.5 m^2