$A$ situation of population inversion is related to

$A$ laser produces a beam of light of frequency $5 \times 10^{14} \,Hz$ with an output power of $33 \,mW$. The average number of photons emitted by the laser per second is (Planck's constant $h = 6.6 \times 10^{-34} \,J \,s$)

Calculate the number of photons entering the eye of a duck per second,corresponding to the minimum intensity of white light $(\sim 10^{-10} \ W/m^2)$. Take the area of the duck's eye as $0.4 \ cm^2$ and the average frequency of white light as $6 \times 10^{14} \ Hz$.

When a photon enters glass from air,which one of the following quantities does not change?

In pair annihilation,an electron and a positron destroy each other to produce gamma radiation. How is the momentum conserved?

If the momentum of a photon is $p$,then its frequency is: