under controlled darened conditions in the laboratory, a light receptor cell on the retina of a person's eye can detect a single photon of light of wavelength 506nm and having an energy of 3.94*10^-19J. We shall assume that this energy is abosred by a single cell during one period of the wave. Cells of this kind are called rods and have a diameter of approx 2.0*10^-3mm
What is the intensity in W/m^2 deleivered to a rod.