An ice box made of styrofoam (thermal conductivity $=0.01 {\mathrm{Jm}}^{-1}{ \mathrm{s}}^{-1}{ \mathrm{K}}^{-1}$) is used to keep liquids cool. Its total wall area including lid is$0.8{ \mathrm{m}}^2$ and the thickness of the wall is $2.0 \mathrm{cm}$ . A bottle of water is placed in the box and filled with ice. If the temperature outside the box is $30°\mathrm{C}$, then the rate of flow of heat into the box is (in ${\mathrm{Js}}^{-1}$)

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

A composite block is made of slabs $A, B, C, D$ and $E$ of different thermal conductivities (given in terms of a constant $K$) and sizes (given in terms of length $L$ ) as shown in Fig. All slabs are of the same width. Heat $Q$ flows only from left to right through the blocks. Then in steady state.

The graph, shown in the figure represents the variation of temperature $\left(T\right)$ of two bodies, $x$ and $y$ having the same surface area, with time $\left(t\right)$ due to emission of radiation. Find the correct relation between the emissivity and absorptive power of the two bodies.