An apparatus for measuring thermal conductivity employs an electrical heater sandwiched between two identical samples of diameter 25 mm and length 60 mm, which are pressed between plates maintained at a uniform temperature To = 77°C by a circulating fluid. A conducting grease is placed between all the surfaces to ensure good thermal contact. Differential thermocouples are imbedded in the samples with a spacing of 15 mm. The lateral sides of the samples are insulated to ensure one-dimensional heat transfer through the samples. Required:

a. What is the thermal conductivity of the stainless steel sample material?

b. What is the average temperature of the samples?