Question

A monochromatic source of light emits photons of frequency $ 6 \times 10^{14}\, Hz $ . The power emitted by the source is $ 8 \times 10^{-3}W $ . Calculate the number of photons emitted per second (Take $ h = 6.63\times 10^{-34}\,J- s $ )

• A. $ 6 \times 10^{14} $
• B. $ 4 \times 10^{15} $
• C. $ 2 \times 10^{16} $
• D. $ 1 \times 10^{17} $

Answer 1

Answer: (C)

The number of photons emitted per second from a source of monochromatic radiation of wavelength $\lambda$ and power $P$ is given by
$ n =\frac{P}{hv}$
$ = \frac{8 \times 10^{-3}}{6.63 \times 10^{-34} \times 6 \times 10^{14}}$
$ = 2\times 10^{16}$