Discussion Forum : Heat Transfer
Question -


The earth receives solar radiation at a rate of 8.2 J/cm2 - minute. Assuming that the sun radiates like a blackbody, calculate the surface temperature of the sun. The angle subtended by the sun on the earth is 0.53 and the Stefan constant σ=5.67×108W/m2 - K4.

Options:
A .   6800 K
B .   5800 K
C .   7800 K
D .   7800 K
Answer: Option B
:
B

Let the diameter of the sun be D and its distance from the earth be R. From the question,


DR0.53×π180


=9.25×103                                 . ...(i)


The radiation emitted by the surface fo the sun per unit time is


At distance R, this radiation falls on an area 4πR2 in unit time. The radiation received at the earth's surface per unit time per unit area is, therefore,



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