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Question

(d)

Total photons emitted from source is

$N=\frac{	ext { Power }}{h c / \lambda}$

$=\frac{160 	imes 50000 	imes 10^{-10}}{6.6 	imes 10^{-

Vedclass · Accepted Answer

$10^{20}$

Vedclass · Answer

(d)

Total photons emitted from source is

$N=\frac{	ext { Power }}{h c / \lambda}$

$=\frac{160 	imes 50000 	imes 10^{-10}}{6.6 	imes 10^{-34} 	imes 3 	imes 10^8}$

So, photon flux falling over spherical surface of radius $r=18\,m$ is

$n=\frac{N}{A}=\frac{N}{4 \pi r^2}$

$=\frac{160 	imes 50000 	imes 10^{-6}}{6.6 	imes 10^{-34} 	imes 3 	imes 10^8 	imes 4 \pi 	imes(18)^2}$

$\approx 10^{20} \,m ^{-2} s ^{-1}$

A $160 \,W$ infrared source is radiating light of wavelength $50000 \,\mathring A$ uniformly in all directions. The photon flux at a distance of $1.8 \,m$ is the order of ............. $m^{-2} s ^{-1}$

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