Question

A composite cylinder is made of two different materials A and B of thermal conductivities K_A and K_B. The dimensions of the cylinder are as shown in the figure. The thermal resistance of the cylinder between the two end faces is –

• A. $\frac{\mathcal{l}}{\pi r^{2}(K_{A} + 3K_{B})}$
• B. $\frac{\mathcal{l}}{\pi r^{2}}\left( \frac{1}{K_{A}} + \frac{3}{K_{B}} \right)$
• C. $\frac{\mathcal{l}}{\pi r^{2}}\left( \frac{1}{K_{A}} + \frac{4}{K_{B}} \right)$
• D. $\frac{\mathcal{l}}{\pi r^{2}(K_{A} + 4K_{B})}$

Answer 1

Answer: (A)

$\frac{\mathcal{l}}{\pi r^{2}(K_{A} + 3K_{B})}$

Answer 2

R_eq = $\frac{R_{1}R_{2}}{R_{1} + R_{2}}$