Question

A $160$watt light source is radiating light of wavelength $6200\stackrel{o}{A}$ uniformly in all directions. The photon flux at a distance of $1.8$m is of the order of (Plank's constant $6.63\times {10}^{-34}J-s$).

• A. ${10}^2{m}^{-2}{s}^{-1}$
• B. ${10}^{12}{m}^{-2}{s}^{-1}$
• C. ${10}^{19}{m}^{-2}{s}^{-1}$
• D. ${10}^{25}{m}^{-2}{s}^{-1}$

Answer 1

Answer: (C)

${10}^{19}{m}^{-2}{s}^{-1}$

Intensity of light $I=\frac{160}{4\pi (1.8{)}^2}$

Photon flux =$\frac{I}{hc/\lambda }=1.22\times {10}^{19}$