The laser pulse in this question has a wavelength of [tex]\lambda=524 nm=525\times 10^{-9}m[/tex]. To solve this problem, we first have to calculate the energy of a single photon in the laser pulse. The equation for calculating the energy of a single photon of an electromagnetic wave is [tex]E=\frac{hc}{\lambda}[/tex] where [tex]c[/tex] is the speed of light, [tex]h[/tex] is planks constant and [tex]\lambda[/tex] is the wave length of the photons.
For this problem, [tex]c=3.0\times 10^8m/s[/tex], [tex]h=6.63\times10^{-34}J.s[/tex] and [tex]\lambda=525\times 10^{-9}m[/tex]. We use these values to calculate the energy of the photon as shown below,
[tex]E=\frac{hc}{\lambda} \\E=\frac{(6.63\times 10^{32}Js)\times(3.0\times10^8m/s)}{525\times 10^{-9}m} \\E=3.79\times 10 ^{-19}J.[/tex]
Now that we know the energy for a single photon, we will divide the total energy given by the energy of one photon to get the number of photons in the pulse. The number of photons [tex]n[/tex] is calculated as shown below,
[tex]n=\frac{4.4\times 10^{-3}J}{3.79\times10^{-19}J} =1.16\times 10^{16}[/tex]. There are [tex]1.16\times 10^{16}[/tex] photons.
