Six identical rods are arranged as shown in the figure. The temperature of the junction $B$ will be……… $^oC$

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

If the wavelengths of maximum intensity of radiations emitted by the sun and the moon are $0.5\times10^{-6}\, m$ and $10^{-4}\,m$ respectively. The ratio of their temperatures is

The radiant energy from sun incident normally at the surface of earth is $20\, k\,cal/m^2- min$. What would have been the radiant energy incident normally on the earth if the sun had a temp. twice of the present one ? ……….. $k\,cal/m^2- min$

Two spheres of the same material have radii $1\ m$ and $4\ m$ and temperatures $4000\ K$ and $2000\ K$ respectively. The ratio of the energy radiated per second by the first sphere to that by the second is