Three materials A, B and C of equal thickness and of thermal conductivity of 20, 40 & 60 kcal/hr. m. °C respectively are joined together. The temperature outside of A and C are 30°C and 100°C respectively. The interface between B and C will be at a temperature of __________ °C.
A)40
B)95
C)70
D)50

Question

Quizplus · Accepted Answer

The temperature at the interface between B and C can be found using the concept of thermal resistance in series. Since the materials are of equal thickness and their thermal conductivities are given, the temperature drop across each material is inversely proportional to its thermal conductivity. The total temperature difference (100°C - 30°C = 70°C) is distributed among A, B, and C in inverse proportion to their thermal conductivities. Material C, having the highest thermal conductivity, will have the least temperature drop, and the interface between B and C will be closer to the higher temperature of 100°C. By calculating the exact distribution, we find that the interface temperature is 70°C.

Three Materials A, B and C of Equal Thickness and of Thermal