The diagram shows four slabs of different materials with equal thickness, placed side by side. Heat flows from left to right and the steady-state temperatures of the interfaces are given. Rank the materials according to their thermal conductivities, smallest to largest.

Question

Quizplus · Accepted Answer

The thermal conductivity is proportional to the rate of heat transfer through a material for a given temperature gradient. As heat is flowing from left to right, the higher the temperature difference between the left and right interfaces of a material, the higher its thermal conductivity. 
From the diagram, we can see that the temperature difference between interface 1 and 2 is the smallest, indicating that material 1 has the lowest thermal conductivity. The temperature difference between interface 3 and 4 is the largest, indicating that material 4 has the highest thermal conductivity. 
Between materials 2 and 3, the temperature difference between interfaces 2 and 3 is smaller than that between interfaces 3 and 4, indicating that material 2 has a lower thermal conductivity than material 3. 
Therefore, the ranking according to thermal conductivities from smallest to largest is 1, 2, 3, 4, leading to choice D as the answer.

The Diagram Shows Four Slabs of Different Materials with Equal