Two spheres of the same material have radii 1 m and 4 m and temperatures 4000 K and 2000 K respectively. The energy radiated per second by the first sphere is
The energy radiated per second E, by a body of surface area A, at temperature TK is given by
[Stefan's law)
where k = relative emissivity
E1 = energy radiated per second by
first sphere
Similarly,