The human eye has a biological control system that varies

the pupil diameter to maintain constant light intensity to

the retina. As the light intensity increases, the optical nerve

sends a signal to the brain, which commands internal eye

muscles to decrease the pupil's eye diameter. When the

light intensity decreases, the pupil diameter increases.

a$.$ Draw a functional block diagram of the light$-$pupil

system indicating the input, output, and intermediate

signals; the sensor; the controller; and the actuator.

$[$Section $1\mathrm{.}4$: Introduction to a Case Study$]$

b$.$ Under normal conditions the incident light will be

larger than the pupil. If the incident light is smaller

than the diameter of the pupil, the feedback path is

broken $($Bechhoefer$,2005).$ Modify your block diagram

from Part a$.$ to show where the loop is broken. What will

happen if the narrow beam of light varies in intensity,

such as in a sinusoidal fashion?

c$.$ It has been found $($Bechhoefer$,2005)$ that it takes the

pupil about $300$ milliseconds to react to a change in the

incident light. If light shines off center to the retina,

describe the response of the pupil with delay present

and then without delay present.