Question

The Sun shines with a blackbody temperature of 5780 K and a total power output of 3.8 x 1026 w. The Sun has been doing this for 4.5 x 10 yr, during which time the surface temperature has increased by a few percent and the luminosity by 20%, ie. they have remained roughly constant. (a) (5 marks) Use the heat-flow formula for entropy change to calculate the total entropy in all the sunlight the Sun has ever emitted. (b) (3 marks) Estimate the number of photons the Sun has radiated to date, and hence find the entropy of the solar photon gas Hint: Use the Wien displacement law. Your entropy from heat flow and entropy from counting photons should approximately agree. c) ( mark) Where is most of this sunlight now?

Answer 1

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2 1.38x10 -19 S규 80 C) et i the Snlight a uuiu be at maximum