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The average intensity of the sunlight is 900 W/m². then what is the value of radiation pressure on a black body

 

Option: 1

13 \times 10^{-6} Nm^{-2}


Option: 2

 4.5 \times 10^{-6} Nm^{-2}


Option: 3

3 \times 10^{-6} Nm^{-2}


Option: 4

None of the above 


Answers (1)

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For a black body, we get 100 % absorption or a=1

i.e for this surface 100% of the photon will be absorbed

so | \Delta p|=|0-p_i|=\frac{h}{\lambda }

So Force is given as F=n(\Delta p)=\frac{P\lambda }{hc}*\frac{h}{\lambda }=\frac{P}{c}

where P=Power

As I=\frac{P}{A}\Rightarrow P=IA

So Force is given as F=\frac{P}{c}=\frac{IA}{c}

 

 and radiation pressure is given as Pressure=\frac{F}{A}=\frac{I}{c}

So  Pressure= \frac{900}{3*10^8}=3*10^{-6} \ N/m^2

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