Monochromatic light of wavelength 667 nm is produced by a helium neon laser. The power emitted is 9 mW. The number of photons arriving per second on the average at a target irradiated by this beam is :

Q. A) Monochromatic light of wavelength $632.8\text{nm}$ is produced by a helium-neon laser. The power emitted is $9.42\text{mW}$ .Find the energy and momentum of each photon in the light beam.

B) Monochromatic light of wavelength $632.8\text{nm}$ is produced by a helium-neon laser. The power emitted is $9.42\text{mW}$. How many photons per second, on the average, arrive at a target irradiated by this beam? (Assume the beam to have uniform cross-section which is less than the target area).

C) Monochromatic light of wavelength $632.8\text{nm}$ is produced by a helium − neon laser. The power emitted is $9.42\text{mW}$. How fast does a hydrogen atom have to travel in order to have the same momentum as that of the photon?"

Q. Monochromatic light of wavelength 632.8 nm is produced by a helium-neon laser. The power emitted is 9.42 mW.
How many photons per second, on average, arrive at a target irradiated by this beam? (Assume the beam to have a uniform cross-section which is less than the target area).