Question

The figure shows three different arrangements of materials 1, 2 and 3 (identical in shape) to form a wall. The thermal conductivities are $K_1$, $K_2$ and $K_3$, respectively, and $K_1>K_2>K_3$. The left side of the wall is ${20}^{\circ }C$ higher than the right side.

• A. In steady state, the rate of energy conduction through the wall (III) is greatest.
  
• B. In steady state, the rate of energy conduction through all the walls (I), (II) and (III) are same.
• C. In steady state, temperature difference across material 1 is greatest in wall (II).
• D. In steady state, temperature difference across material 1 is same in all the walls.

Answer 1

Answer: (B), (D)

The correct options are
B In steady state, the rate of energy conduction through all the walls (I), (II) and (III) are same.
D In steady state, temperature difference across material 1 is same in all the walls.

Rate of heat flow, $q=\frac{-KA\Delta T}{L}$

$K_{eq}$ is same in all three cases.
All other parameters (area, thickness and net temperature difference) being same, net rate of energy conduction is same in all three cases.
Similarly, temperature difference across any material in any wall is also same.