Answer: The minimum number of photons that must strike the receptor is

Step-by-step explanation:
The relation between energy and wavelength of light is given by Planck's equation, which is:

where,
E = energy of the light =

N= Number of photons = ?
h = Planck's constant =

c = speed of light =

= wavelength of light =

Thus the minimum number of photons that must strike the receptor is
