Question

A wall has two layers A and B, each made of different material. Both the layers have the same thickness. The thermal conductivity for A is twice that of B. Under steady state. the temperature difference across the whole wall is ${36}^{\circ }$C. Then the temperature difference across the layer A is.

• A. $6^{\circ }C$
• B. ${12}^{\circ }C$
• C. ${18}^{\circ }C$
• D. ${24}^{\circ }C$

Answer 1

The correct option is B ${12}^{\circ }C$

The correct answer is option(B).

In thermal equilibrium, the rate of flow across the two layers is the same.

$\frac{2K\left(\Delta T_1\right)A}{l}=\frac{K\left(\Delta T_2\right)A}{l}⟹\frac{\Delta T_1}{\Delta T_2}=\frac{1}{2}⟹\frac{\Delta T_1}{36-\Delta T_1}=\frac{1}{2}⟹\Delta T_1=12°C$

The temperature difference across the layer A is $12°C$