$A$ wall consists of two layers $A$ and $B$. The two layers have the same thickness but are made of different materials. The thermal conductivity of $A$ is twice that of $B$. Under steady-state conditions,the temperature difference between the two ends is $36 ^\circ C$. The temperature difference across the two surfaces of $A$ is .......... $^\circ C$.

The two ends of a rod of length $x$ and uniform cross-sectional area $A$ are kept at temperatures $T_1$ and $T_2$ respectively $(T_1 > T_2)$. If the rate of heat transfer through the rod in steady state is $Q/t$,then the coefficient of thermal conductivity $K$ is:

The ends $Q$ and $R$ of two thin wires,$PQ$ and $RS$,are soldered (joined) together. Initially,each of the wires has a length of $1 \,m$ at $10^{\circ} C$. Now,the end $P$ is maintained at $10^{\circ} C$,while the end $S$ is heated and maintained at $400^{\circ} C$. The system is thermally insulated from its surroundings. If the thermal conductivity of wire $PQ$ is twice that of the wire $RS$ and the coefficient of linear thermal expansion of $PQ$ is $1.2 \times 10^{-5} \,K^{-1}$,the change in length of the wire $PQ$ is (in $\,mm$)

For cooking the food,which of the following type of utensil is most suitable?

The ratio of the diameters of two metallic rods of the same material is $2 : 1$ and their lengths are in the ratio $1 : 4$. If the temperature difference between their ends is equal,the rate of flow of heat in them will be in the ratio: (in $:1$)

$A$ composite slab is prepared with two different materials $A$ and $B$. The relation between their coefficients of thermal conductivity and thickness is given as $K_A = \frac{K_B}{2}$ and $X_A = 2 X_B$, respectively. If the temperatures of the outer faces of $A$ and $B$ are $75^{\circ} C$ and $50^{\circ} C$ respectively, what will be the temperature of the common surface (in $^{\circ} C$)?