4. In order for the human eye to detect the visible light, its optical nerves must be exposed to a minimum energy of 5.31 x 1015 J. (a) Calculate the number of photons of red light needed to achieve this (2 = 740nm). (b) Determine the number of photons of yellow light (1 = 570 nm) that will be required to excite the optical nerves? (4 points)