Question

A photosensitive surface is receiving light of wavelength $5000A^0$ at the rate of ${10}^{-7}J/s$. The number of photons received per second is

• A. $2.5\times {10}^{12}$
• B. $2.5\times {10}^{11}$
• C. $252\times {10}^3$
• D. $2.5\times {10}^9$

Answer 1

The correct option is C $252\times {10}^3$

Wavelength of the photon,

$\lambda =5000A^0=5000\times {10}^{-10}m$

Rate at which the photon are emitted $={10}^{-8}J/s$

So, number of photon emitted, $n$

$n=\frac{E}{nc/\lambda }=\frac{{10}^{-8}}{6.6\times {10}^{-34}\times 3\times {10}^8/5000\times {10}^{-10}}$

$n=252\times {10}^{3}photons$