"A parallel beam of light of wavelength $900 \mathrm{~nm}$ and intensity $100 \,\mathrm{Wm}^{-2}$ is incident on a surface perpendicular to the beam. The number of photons crossing $1 \mathrm{~cm}^{2}$ area perpendicular to the beam in one second is :"

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Accepted Answer

"

$\lambda$ = 900 nm

I = 100 W/m²

A = 10^$-$4

$\Rightarrow$ P = 10^$-$2 W

$\Rightarrow$ Number of photons incident per second

$= {{{{10}^{ - 2}}\lambda } \over {hc}}$

$$ = {{9 \times {{10}^{ - 11}} \times {{10}^2}} \over {6.63 \times {{10}^{ - 34}} \times 3 \times {{10}^8}}} \simeq 4.5 \times {10^{16}}$$

"

A parallel beam of light of wavelength $900 \mathrm{~nm}$ and intensity $100 \,\mathrm{Wm}^{-2}$ is incident on a surface perpendicular to the beam. The number of photons crossing $1 \mathrm{~cm}^{2}$ area perpendicular to the beam in one second is :

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A parallel beam of light of wavelength $900 \mathrm{~nm}$ and intensity $100 \,\mathrm{Wm}^{-2}$ is incident on a surface perpendicular to the beam. The number of photons crossing $1 \mathrm{~cm}^{2}$ area perpendicular to the beam in one second is :

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