Thermal Properties Of Matter

A planet having average surface temperature at an average distance from the sun. Assuming that the planet receives radiant energy from the sun only and it loses radiant energy only from the surface and neglecting all other atmospheric effects we conclude

According to Newton's law of cooling, the rate of cooling of a body is proportional to , where is the difference of the temperature of the body and the surroundings, and is equal to

A solid cylinder of radius made of a material of thermal conductivity is surrounded by a cylindrical shell of inner radius and outer radius made of a material of thermal conductivity . The two ends of the combined system are maintained at two different temperatures. Then 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