Question

The number of photons of light having wavelength $100nm$ which can provide $1J$ energy is nearly:

• A. ${10}^7$ photons
• B. $5\times {10}^{18}$ photons
• C. $5\times {10}^{17}$ photons
• D. $5\times {10}^7$ photons

Answer 1

Answer: (C)

$5\times {10}^{17}$ photons

$E=\frac{nhc}{\lambda }$

$n=\frac{E\lambda }{hc}$

$=\frac{1\times 100\times {10}^{-9}}{6.626\times {10}^{-34}\times 3\times {10}^8}$

$=5\times {10}^{17}$.

Hence, $5\times {10}^{17}$ photons of light having wavelength 100nm can provide 1J energy

Hence, the correct option is $C$