A sphere and cube made of same material and having same surface area are heated to the same temperature and kept in the same surrounding. The ratio of their initial rates of cooling will be

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

A spherical body of emissitivity $e = 0.6$ placed inside a perfect black body is maintained at temperature $T$, then the energy radiated per second will be

Two rods $A$ and $B$ of same cross-sectional are $A$ and length $l$ connected in series between a source $(T_1 = 100^o C)$ and a sink $(T_2 = 0^o C)$ as shown in figure. The rod is laterally insulated The ratio of the thermal resistance of the rod 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 ....... $^oC$

Six wires each of cross-sectional area $A$ and length $l$ are combined as shown in the figure. The thermal conductivities of copper and iron are $K_1$ and $K_2$ respectively. The equivalent thermal resistance between points $A$ and $C$ is