The earth receives at its surface radiation from the sun at the rate of 1400 W/m2. The distance of the centre of the sun from the surface of the earth is 1.5 x 1011 m and the radius of the sun is 7.0 x 108 m. Treating the sun as a black body it follows from the above data that its surface temperature is

Let TK be the temperature of sun.Energy E radiated per unit area per second =σT4(Stefan's law).Total surface area of sun =4πRs2∴Total energy radiated per unit solid angle =σT4Rs2Now intensity of radiation at earth =σT4Rs2/Res2where Res= distance between earth and sun.Substituting the given values, we get 1400=5⋅67×10−8T47⋅0×1081⋅5×10112Solving, we get T = 5803 K.