Question

Monochromatic light of frequency of $6\times {10}^{14}Hz$ is produced by a laser. Power emitted is $2\times {10}^{-3}W.$ Approximately how many photons per second are emitted by the source?

• A. $5\times {10}^{13}$
• B. $5\times {10}^{14}$
• C. $5\times {10}^{15}$
• D. $5\times {10}^{16}$

Answer 1

The correct option is C $5\times {10}^{15}$

Power emitted is given by
$P=nh\nu$

Therefore, no. of photons emitted per second
$n=\frac{P}{h\nu }=\frac{2\times {10}^{-3}}{6.6\times {10}^{-34}\times 6\times {10}^{14}}$
$=5\times {10}^{15}$