Question

A monochromatic light of frequency $ 3\times 10^{14}\,\,Hz $ is produced by a Laser, emits the power of $ 3\times 10^{-3}W $ . Find, how many number of photons are emitted per second

• A. $ 1.5\times 10^{16} $
• B. $ 2.5\times 10^{16} $
• C. $ 4.5\times 10^{16} $
• D. $ 8.5\times 10^{16} $

Answer 1

Answer: (A)

Power $=$ Energy emitted per unit time
$=3 \times 10^{-3} J / s$
$\Rightarrow $ Energy of one photon $= hv$
$=6.64 \times 10^{-34} \times 3 \times 10^{14}$
$\Rightarrow S$ o number of photons emitted per second
$=\frac{3 \times 10^{-3}}{6.64 \times 10^{-34} \times 3 \times 10^{14}}$
$=\frac{1}{6.64} \times 10^{17}$
$=0.15 \times 10^{17}$
$=1.5 \times 10^{16}$