The outer faces of a rectangular slab made of equal thickness of iron and brass are maintained at $100^{\circ} C$ and $0^{\circ} C$ respectively. The temperature at the interface is ........... $^{\circ} C$ (Thermal conductivity of iron and brass are $0.2$ and $0.3$ respectively.)

Two rectangular blocks, having identical dimensions, can be arranged either in configuration $I$ or in configuration $II$ as shown in the figure. One of the blocks has thermal conductivity $k$ and the other $2k$. The temperature difference between the ends along the $x-$ axis is the same in both the configurations. It takes $9s$ to transport a certain amount of heat from the hot end to the cold end in the configuration $I$. The time to transport the same amount of heat in the configuration $II$ is .......... $\sec$

The temperature of the two outer surfaces of a composite slab, consisting of two materials having coefficients of thermal conductivity $K$ and $2K$ and thickness $x$ and $4x$ , respectively are $T_2$ and $T_1$ ($T_2$ > $T_1$). The rate of heat transfer through the slab, in a steady state is $\left( {\frac{{A({T_2} - {T_1})K}}{x}} \right)f$, with $f $ which equal to

In a steady state, the temperature at the end $A$ and $B$ of $20\,cm$ long rod $AB$ are $100\,^oC$ and $0\,^oC$ respectively. The temperature of a point $9\,cm$ from $A$ is....... $^oC$

Two rods of same length and material transfer a given amount of heat in $12$ seconds, when they are joined end to end. But when they are joined lengthwise, then they will transfer same heat in same conditions in ....... $\sec$

Two identical square rods of metal are welded end to end as shown in figure $(a)$. Assume that $10\, cal$ of heat flows through the rods in $2\, min$. Now the rods are welded as shown in figure, $(b)$. The time it would take for $10$ cal to flow through the rods now, is ........ $\min$