2 A parallel bearn of monochromatic light of wavelength 660nm has an intensity of 0.25 mW m^-2,
The beam is incident normally on a surface where the light is absorbed totally
Calculate, for a cross-sectional area of 1.2 cm^2 of the beam:
a. the number of photons passing per second through the area,
b. the momentum of a photon of the light,
c. the force exerted on the surface by the light.
(Planck constant h = 6.63 x 10^-34 Js; speed of light c = 3.00 x 10^8 ms^-1.)
