KVPY SX SB Exam 2012 Question Paper

A cylindrical steel rod of length 0.10 m and thermal conductivity $50\mathit{W}{\mathit{m}}^{-1}{\mathit{K}}^{-1}$ is welded end to end to copper rod of thermal conductivity $400\mathit{W}{\mathit{m}}^{-1}{\mathit{K}}^{-1}$ and of the same area of cross section but 0.20 m long. The free end of the steel rod is maintained at 100°C and that of the copper rod at 0°C. Assuming that the rods are perfectly insulated from the surrounding, the temperature at the junction of the two rods is