Step-by-step solution
We first compute the energy of a single incident photon, answering the first part of the question above.
Next we calculate the power of the sunlight entering your pupil. To do so, we use the intensity equation above, the given intensity of the light
and the area of the pupil.
We have determined the power of the light entering your pupil and the energy of a single photon. Now we will relate these two values to find
the number of photons per second that enter your eye.
Note that N is a very large number of photons per second. Sensors in the eye’s retina can actually respond to just a single photon. A single
molecule in one “rod” cell in your eye can absorb one photon, triggering a chemical reaction that sends a signal to the optic nerve. However,
neural filters only let a signal go to the brain if approximately five to nine photons arrive every 100 ms. This limit prevents the visual fuzziness or
“noise” that would exist under conditions of low intensity light if the eyes were too sensitive.