Question

A steel rod is joined by a copper rod as shown in figure. Both the rods have same cross sectional area. The thermal conductivity of steel and copper are $5\text{watt/m-K}$ and $10\text{watt/m-K}$ respectively. If thermal resistance of steel rod is $60\text{K/watt}$ then for copper rod it will be (in $\text{K/watt)}$.

Answer 1

Thermal resistance is defined as $R=\frac{l}{kA}$
$\frac{R_s}{R_c}=\frac{l_s}{l_c}\times \frac{k_c}{k_s}$
$\frac{60}{R_c}=\frac{2}{3}\times \frac{10}{5}$
$R_c=45\text{K/watt}$