2. The retina of a human eye can detect light when radiant energy incident on it is at least 4.0X10-17 J. For light of 600-nm wavelength, how many photons does this correspond to?

Question

2.	The retina of a human eye can detect light when radiant energy incident on it is at least 4.0X10-17 J. For light of 600-nm wavelength, how many photons does this correspond to?

drwls · Answer

Photon energy = h*c/(wavelength) = 6.62*10^-34 J*s * (3*10^8 m/s)/600*10^-9 m = 3.3*10^-19 J 4*10^-17 J corresponds to 120 photons of that color (orange) light