Sun light falls normally on a surface of area 36 cm 2 and exerts an average force of 7 . 2 × 10 - 9 N within a time period of 20 minutes. Considering a case of complete absorption, the energy flux of

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Sun light falls normally on a surface of area 36 cm 2 and exerts an average force of 7 . 2 × 10 - 9 N within a time period of 20 minutes. Considering a case of complete absorption, the energy flux of incident light is

TestHub · Accepted Answer

The radiation pressure in case of complete absorption is given by,
$P = \frac{I}{c}$ .
Therefore, the force will be,
$F = \frac{I}{c} \times A \Rightarrow I = \frac{F c}{A}$
$\Rightarrow I = \frac{7.2 \times 10^{- 9} \times 3 \times 10^{8}}{36 \times 10^{- 4}} = 600 W m^{- 2} \Rightarrow I = 0.06 W {cm}^{- 2}$

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