Radiating power of a black body =E0=σ(T4−T04)A where σ is known as the Stefan-Boltzmann constant, A is the surface area of a black body, T is the temperature of the black body and T0 is the temperature of the surrounding. ∴60=σ(10004−5004) ...(i) [T=727°C=727+273=1000K, T0=227°C=500K] In the second case, T=1227°C=1500K and let E′ be the radiating power. ∴E′=σ(15004−5004) ...(ii) From (i) and (ii) we have