Three rods of the same dimensions have thermal conductivities $3K, 2K$ and $K$. They are arranged as shown in the figure with their ends at $100\,^{\circ}C, 50\,^{\circ}C$ and $20\,^{\circ}C$. The temperature of their junction is....... $^{\circ}C$

Dimensional formula for thermal conductivity is (here $K$ denotes the temperature)

If the ratio of the coefficient of thermal conductivity of silver and copper is $10 : 9$,then the ratio of the lengths up to which wax will melt in the Ingen Hausz experiment will be:

The figure shows a system of two concentric spheres of radii $r_1$ and $r_2$ kept at temperatures $T_1$ and $T_2$,respectively. The radial rate of flow of heat in a substance between the two concentric spheres is proportional to

In a steady state, the graph between temperature $(\theta)$ and distance $(x)$ from the hot end is:

Two identical rods of copper and iron are coated with wax uniformly. When one end of each is kept at the temperature of boiling water,the lengths up to which wax melts are $8.4 \ cm$ and $4.2 \ cm$ respectively. If the thermal conductivity of copper is $0.92$,then the thermal conductivity of iron is: