How many photons of a radiation of wavelength λ= 5 x 10-7 m must fall per second on a blackened plate in order to produce a force of 6.62 x 10-5 N?

The momentum of photon=h/λIf n is the number of photons falling per second on the plate, then total momentum per second of the incident photons isp=n×hλSince the plate is blackened, all photons are absorbed by it.ΔpΔt=nhλ Since F=ΔpΔt=nhλ∴ n=Fλh=6.62×10−5×5×10−76.62×10−34=5×1022