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  • Sun light falls normally on a surface of area and exerts an average force

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
 

Option: 1

25.92 \times 10^{2} \mathrm{~W} / \mathrm{cm}^{2}


Option: 2

8.64 \times 10^{-6} \mathrm{~W} / \mathrm{cm}^{2}


Option: 3

6.0 \mathrm{~W} / \mathrm{cm}^{2}


Option: 4

0.06 \mathrm{~W} / \mathrm{cm}^{2}


Answers (1)

best_answer

\mathrm{ A=36 \times 10^{-4} \mathrm{~m}^2=36 \mathrm{~cm}^2}

\mathrm{F=7.2 \times 10^{-9} \mathrm{~N}}

\mathrm{\Delta t=20 \mathrm{~min}=1200 \mathrm{~s}}

\mathrm{\text { Energy } f lu x=\frac{\text { Energy }}{\text { (time) (Area) }}}

\mathrm{=(\text { Radiation pressure) }}

\mathrm{=\frac{F C}{A}}

=\frac{7.2\times 10^{-9}\times 3\times 10^{8}}{36}

=0.6\times 10^{-1}\mathrm{\frac{w}{cm^{2}}}

\mathrm{Energy \: flux=0.06}

Hence 4 is correct option.






 

Posted by

Ritika Harsh

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