Question

Two rods of equal length and diameter but of thermal conductivities 2 and 3 units respectively are joined in series. The thermal conductivity of the combination is :

• A. 6
• B. 5
• C. 1
• D. none of these

Answer 1

The correct option is D none of these

As we know that both rods are joined in series,so equivalent thermal conductivity will be $K_1+K_2$
Now, we know that $K=\frac{L}{KA}$
So, $\frac{2L}{K_{equivalent}}=\frac{L}{K_1}+\frac{L}{K_2}$
$\frac{2L}{K_{equivalent}}=\frac{L}{2}+\frac{L}{3}$
$K_{equivalent}=\frac{12}{5}=2.4$