Physics - Heat & Thermo Question with Solution | TestHub

Two cylindrical rods of lengths $l_1$ and $l_2$, radii $r_1$ and $r_2$ have thermal conductivities $k_1$ and $k_2$ respectively. The ends of the rods are maintained at the same temperature difference. If $l_1=2l_2$ and $r_1=\frac{r_2}{2}$, the rates of heat flow in them will be the same if $\frac{k_1}{k_2}$ is: