What will be the power incident normally on unit area of spherical surface which is at distance R from the outermost surface of Sun of radius r at `t^(@)C` ? `sigma=` Stefan - Boltzmann's constant

Options

A. `(r^(2)sigma(t+273^(4)))/(4piR^(2))`
B. `(16pi^(2)r^(2)sigmat^(4))/(R^(2))`
C. `(r^(2)sigma(t+273)^(4))/(R^(2))`
D. `(4pir^(2)sigmat^(4))/(R^(2))`

Answer

C

Explanation

From Stefan - Boltzmann law,
`P=AesigmaT^(4)`
`:.P=4pir^(2)sigmaT^(4)" "[becauseA=4pir^(2),e=1]`
Power incident per unit area,
`=(P)/(4piR^(2))=(4pir^(2)sigmaT^(4))/(4piR^(2))=(r^(2)sigma(t+273)^(4))/(R^(2))`