$A$ composite slab is made of two different materials of equal thickness,having thermal conductivities $K$ and $2K$ respectively. The equivalent thermal conductivity of the slab is ........

$A$ temperature difference of $120\,^oC$ is maintained between the two ends of a uniform rod $AB$ of length $2L$. Another bent rod $PQ$,of the same cross-section as $AB$ and length $\frac{3L}{2}$,is connected across $AB$ as shown in the figure. In the steady state,the temperature difference between $P$ and $Q$ will be close to .......... $^oC$.

Two identical metal wires of thermal conductivities $K_{1}$ and $K_{2}$ respectively are connected in series. The effective thermal conductivity of the combination is

For the shown figure,calculate the equivalent thermal resistance if the bricks are made of the same material of thermal conductivity $K$.

Two metal plates of equal thickness have thermal conductivities $K_1$ and $K_2$ respectively. They are joined together to form a single plate. The equivalent thermal conductivity of this composite plate is ..........

Why do people prefer to give a layer of sand or foam insulation on ceilings made of concrete?