The rate of dissipation of heat by a black body at temperature $T$ is $Q$. What will be  the rate of dissipation of heat by another body at temperature $2\,T$ and emissivity $0.25$ ?

A cylinder of radius $R$ made of a material of thermal conductivity $K_1$ is surrounded by a cylindrical shell of inner radius $R$ and outer radius $2R$ made of material of thermal conductivity $K_2$ . The two ends of the combined system are maintained at two different temperatures. There is no loss of heat across the cylindrical surface and the system is in steady state. The effective thermal conductivity of the system is

A wall has two layer $A$ and $B$ each made of different material, both the layers have the same thickness. The thermal conductivity of the material $A$ is twice that of $B$. Under thermal equilibrium the temperature difference across the wall $B$ is $36^o C$. The temperature difference across the wall $A$ is ……. $^oC$

A cylindrical metallic rod, in thermal contact with two reservoirs of heat at its two ends, conducts an amount of heat $Q$ in time $t.$ The metallic rod is melted and the  material is formed into a rod of half the radius of the original rod. Amount of heat  conducted by the new rod, when placed in thermal contact with same two reservoirs in  time $t$ , is

Certain quantity of water cools from $70\,^oC$ to $60\,^oC$ in first $10\, minutes$ and to $54\,^oC$ in the next $10\, minutes$. The temperature of the surrounding is  ……… $^oC$