A spherical body of area A and emissivity e = 0 .6 is placed inside a perfectly black body' The heat radiated by the body at temperature T is

When a non-black body is placed inside a hollow enclosure, the total radiation from the body is sum of what it would emit in the open (with e < 1) and the part of the incident radiation from the walls reflected by it. The two add up to a black body radiation. In this way, the total radiation emitted by the body is 1⋅0 σAT4.