A composite wall is made of two layers of thickness d1 and d2 having thermal conductive K and 2K and equal surface areas normal to the direction of heat flow. The outer surfaces of the composite wall are at 100°C and 200°C respectively. The heat transfer takes place only by conduction and the required surface temperature at the junction is 150° C. What will be the ratio of their thicknesses (IES-04)
d1 : d2?
a. 1 : 1 b. 2 : 1
c. 1 : 2 d. 2 : 3