Question

Monochromatic light of frequency 6 X 10¹⁴ Hz is produced by a laser. Power emitted is 2W, How many photons per second on an average are emitted by source?

Answer 1

$$\begin{gathered} PoweroflasersemittedP=nh\nu /t \\ orn/t=\frac{P}{h\nu } \\ wearegiven\nu =6\times {10}^{14}Hz,P=2Wandweknowh=6.63\times {10}^{-34}J-s \\ Thereforen/t=\frac{2}{6.63\times {10}^{-34}\times 6\times {10}^{14}}=\frac{1\times {10}^{20}}{19.89}=5.02\times {10}^{18} \\ Thereforenumberofphotonsemittedpersecond=5.02\times {10}^{18}. \end{gathered}$$