JEE MAIN - Physics (2022 - 28th July Evening Shift - No. 15)
Sun light falls normally on a surface of area $$36 \mathrm{~cm}^{2}$$ and exerts an average force of $$7.2 \times 10^{-9} \mathrm{~N}$$ within a time period of 20 minutes. Considering a case of complete absorption, the energy flux of incident light is
$$25.92 \times 10^{2} \mathrm{~W} / \mathrm{cm}^{2}$$
$$8.64 \times 10^{-6} \mathrm{~W} / \mathrm{cm}^{2}$$
$$6.0 \mathrm{~W} / \mathrm{cm}^{2}$$
$$0.06\mathrm{~W} / \mathrm{cm}^{2}$$
Explanation
Pressure $$ = {l \over c}$$
$$ \Rightarrow {F \over A} = {l \over c}$$
$$ \Rightarrow l = {{7.2 \times {{10}^{ - 9}} \times 3 \times {{10}^8}} \over {36 \times {{10}^{ - 4}}}}$$ W/m2
$$ = 600$$ W/m2
$$ \Rightarrow l = 0.06$$ W/cm2
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