
A heater is placed inside a hollow sphere of surface area and emissivity . This sphere is enclosed by another hollow sphere of surface area and emissivity . The bigger sphere is surrounded by vaccuum. If temperature of smaller sphere in steady state is then (Take : ):



Important Questions on Kinetic Theory of Gases and Radiation


The filament of a light bulb has surface area The filament can be considered as a black body at temperature emitting radiation like a point source when viewed from far. At night the light bulb is observed from a distance of . Assume the pupil of the eyes of the observer to be circular with radius . Then:
(Take Stefan-Boltzmann constant Wiens' displacement constant , Planck's constant , speed of light in vacuum )



Two black bodies and have equal surface areas and are maintained at temperatures and respectively. What will be the ratio of the thermal energy radiated per second by to that by




A black coloured solid sphere of radius and mass is inside a cavity with a vacuum inside. The walls of the cavity are maintained at temperature . The initial temperature of the sphere is . If the specific heat of the material of the sphere varies as per unit mass with the temperature of the sphere, where is a constant, then the time taken for the sphere to cool down to temperature will be
( is Stefan Boltzmann constant)











