Q. Monochromatic light of wavelength $3000\mathring{\mathrm{A}}$ is incident on a surface area 4 ${cm}^{2}$. If intensity of light is 150mW$m^{- 2}$, then rate at which photones strike the target is
A) $3 \times 10^{10}\ s^{- 1}$
B) 9 $\times 10^{13}s^{- 1}$
C) $7 \times 10^{15}\ s^{- 1}$
D) $6 \times 10^{19}\ s^{- 1}$
Explanation
(b) $\frac{n}{t} = \frac{IA\lambda}{hc}$
=$\frac{150 \times 10^{- 3} \times 4 \times 10^{- 4} \times 3 \times 10^{- 7}}{6.6 \times 10^{- 34} \times 3 \times 10^{8}} = 9 \times 10^{13}$ s
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.