試題詳解

18. A heat conducting rod, 0.90m long, is made of an aluminum section that is 0.10 m long, and a copper section that is 0.8 m long. Both sections have cross-sectional areas of 0.0004 m². The aluminum end is maintained at a temperature of 40℃ and the copper end is at 150 ℃ . The thermal conductivity of aluminum is 205 W/m•K and of copper is 385 W/m•K. Steady state has been reached, and no heat is lost through the well-insulated sides of the rod. The temperature of the aluminum-copper junction in the rod is closest to
(A) 61℃ .
(B) 48℃ .
(C) 56℃ .
(D) 34℃ .
(E) 70℃ .