The retina of the human eye can detect light when radiant energy incident on it at least 4.0 x 10^-17 J. For light of 585-nm wavelength, how many photons does this energy respond to?

Question

The retina of the human eye can detect light when radiant energy incident on it at least 4.0 x 10^-17 J.  For light of 585-nm wavelength, how many photons does this energy respond to?

anonymous · Answer

use E=hv, with h being the planck's constant and v being the frequency of the photon (careful of the units; if the unit of the constant is joules per meter then convert your frequency to meter) and figure out what energy one photon should have.

After that divide the total energy by the energy that one photon has, that'll give you the total number of photons