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# The intensity of direct sunlight before it passes through the earth's atmosphere is $\;1.4 KW/m^2\;.$ If it is completely obsorved than the corresponding radiation pressure :

$(a)\;4.7 \times10^{-6} Nm^{-2}\qquad(b)\;4.7 \times10^{-7} Nm^{-2}\qquad(c)\;4.7 \times10^{-5} Nm^{-2}\qquad(d)\;4.7 \times10^{-8} Nm^{-2}$

Answer : (a) $\;4.7 \times10^{-6} Nm^{-2}$
Explanation :
For completely absorbing surface
$pressure=\large\frac{I}{c}=\large\frac{1.4\times10^{3}}{3\times10^{8}}$
$=4.7\times10^{-6}\;Nm^{-2}\;.$

edited Nov 11, 2014