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

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

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

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 in series, then they will transfer same heat in same conditions in…….. $\sec$

A long metallic bar is carrying heat from one of its ends to the other end under steady-state. The variation of temperature $\theta$  along the length $x$ of the bar from its hot end is best described by which of the following figures ?