Question

A $160watt$ infrared source is radiating light of wavelength $50000\stackrel{\circ }{A}$ uniformly in all directions. The photon flux at a distance of $1.8m$ is of the order of.

• A. $10m^2{s}^{-1}$
• B. ${10}^{10}{m}^{-2}{s}^{-1}$
• C. ${10}^{15}{m}^{-2}{s}^{-1}$
• D. ${10}^{20}{m}^{-2}{s}^{-1}$

Answer 1

Answer: (D)

${10}^{20}{m}^{-2}{s}^{-1}$

Photon flux is given by

$N=\frac{I\lambda }{hC}=\frac{P\lambda }{\left(4\pi R^2\right)hc}$

On putting the given values we will get $N={10}^{20}{m}^{-2}{s}^{-1}$