A cylindrical steel rod of length 0.1 m and thermal conductivity 50 Wm ⁻¹ ~K ⁻¹ is welded end to end to a copper rod of thermal conductivity 400 Wm ⁻¹ ~K ⁻¹ and of the same area of cross section but 0.2 m long. One end of the copper rod is maintained at 0^ C . The free end of the steel rod is maintained at a temperature of 200^ C . Assuming that the rods are perfectly insulated, the temperature of the junction is