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 numbers 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

The correct option is A $1.5\times {10}^{16}$

Energy of a photon, $E=h\nu$
$E=(6.63\times {10}^{-34}Js)(3\times {10}^{14}Hz)=19.89\times {10}^{-20}J$
Power of the source, $P=3\times {10}^{-3}W$
Number of photons emitted per second,
$N=\frac{P}{E}=\frac{3\times {10}^{-3}W}{19.89\times {10}^{-20}J}=1.5\times {10}^{16}$