Question

Monochromatic light of wavelength $3000\stackrel{\circ }{A}$ is incident on a surface area $4c{m}^2$. If intensity of light is $150mW/m^2$, then rate at which photons strike the target is

• A. $3\times {10}^{10}/s$
• B. $9\times {10}^{13}/s$
• C. $7\times {10}^{15}/s$
• D. $6\times {10}^{19}/s$

Answer 1

Answer: (B)

$9\times {10}^{13}/s$

$\frac{n}{t}=\frac{lA\lambda }{hc}$
$=\frac{150\times {10}^{-3}\times 4\times {10}^{-3}\times 3\times {10}^{-7}}{6.6\times {10}^{-34}\times 3\times {10}^8}$
$=9\times {10}^{13}/s$.