Light from a source travels out with a velocity $c$. If the source moves away from the observer with a velocity $v$,then the relative velocity of light with respect to the observer is

The momentum of a photon with frequency $1.5 \times 10^{13} \ Hz$ is .......

The number of photons emitted from a photocell by a source placed at a distance of $0.5 \ m$ is how many times the number of photons emitted by the same source placed at a distance of $1 \ m$?

Write the equation for the energy of a photon.

Number of photons of equal energy emitted per second by a $6 \ mW$ laser source operating at $663 \ nm$ is . . . . . . . (Given: $h=6.63\times10^{-34} \ J.s$ and $c=3\times10^{8} \ m/s$)

In the Compton scattering process,the incident $X$-radiation is scattered at an angle of $60^{\circ}$. The wavelength of the scattered radiation is $0.22 \ \text{Å}$. The wavelength of the incident $X$-radiation in $\text{Å}$ units is: