Monochromatic light of wavelength 632.8 nm is produced by a helium-neon laser. The power emitted is 9.42 mW.
How fast does a hydrogen atom have to travel in order to have the same momentum as that of the photon ?

Monochromatic light of wavelength 632.8 nm is produced by a helium-neon laser. The power emitted is 9.42 mW. Find the energy and momentum of each photon in the light beam .

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 an average , arrive at a target irradiated by this beam ? (Assume the beam to have uniform cross-section which is less than the target area)