Two spheres of the same material have radii 1 m and 4 m and temperature 4000 K and 2000 K respectively. The energy radiated per second by the first sphere is

The energy radiated per second, P, by a body of surface area A, at temperature T kelvin, is given by   E = eσAT4Hence,        E1 = eσ4π(1)2 × (4000)4                       = eσπ×1024×1012 Jand       E2 = eσ[4π(4)2](2000)4                   = eσπ×1024×1012JSo, E1 = E2