The power emitted is 9 42 mW (a) Find the energy and momentum of each photon in the light beam,
(b) 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), and
(c) How fast does a hydrogen atom have to travel in order to have
the same momentum as that of the photon