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
$=\frac{3\times 10^{-3}}{6.64\times 10^{-34}\times 3\times 10^{14}}$
$=\frac{1}{6.64}\times 10^{17}$
$=0.15\times 10^{17}$
$=1.5\times 10^{16}$