Question

The number of photons of wavelength $13.2$ $A^0$ in $6$ $J$ of energy is:

($h$=$6.6\times {10}^{-34}$ $Js$)

• A. $2\times {10}^{12}$
• B. $4\times {10}^{16}$
• C. $6\times {10}^{20}$
• D. $4\times {10}^{24}$

Answer 1

The correct option is B $4\times {10}^{16}$

The energy of one photon of wavelength $13.2A$ is

$E=\frac{hc}{\lambda }=\frac{6.64\times {10}^{-34}\times 3\times {10}^8}{13.2\times {10}^{-10}}=1.509\times {10}^{-16}J$

Hence 6J of energy must contain $\frac{6}{1.509\times {10}^{-16}}$ photons $=4\times {10}^{16}$ photons

So, the answer is option (B).