Homework #7 Mirrors and Eyeballs Please answer all questions completely. If calculations are required, show enough steps so that I can follow your reasoning.
1. Briefly describe the optical function of each of these parts of the eye:
a) rodsb) cones
c) iris
d) lens
e) optic nerve
f) cornea
2.) A concave mirror has a focal length of 20 cm. What type of image (real/virtual, upright/inverted) is formed for each of the object distances below? (Note: You don't have to do any calculations!)
a. object is 30 cm in front of the mirrorb. object is 10 cm in front of the mirror.
3.) Can a convex mirror ever form a real image? Why or why not?
4.) The "normal" far point for a human eye is infinity- you can see objects as far away as you wish. A myopic person has a far point that is much closer. The eyeglasses for a myopic person take an object very far away (at "infinity") and form an image at the person's own far point.
Suppose a myopic person has a far point of 2 meters (she can't see anything clearly beyond 2 meters). Use the thin lens equation to determine the focal length of her eyeglasses.
Hint #1: the object distance do is
infinite, and 1/an infinitely large number = 0
Hint #2: the image will be a virtual image (she looks through
the lens of the glasses) so the image distance is
negative.
What is the power of these corrective lenses in diopters?
5.) The "normal" near point for a (young adult) human eye is about 25 cm. (Actually, very young children are comfortable holding reading material very much closer than that, while most folks over 40 need to hold print at arms length or more.) A hyperopic or presbyopic person has a near point considerbly more than 25 cm. The corrective lenses for these conditions form an image at the person's own near point when the object is held at a comforable 25 cm distance.
Suppose a presbyopic person has a near point of 1 meter. Use the thin lens equation to determine the focal length of reading glasses that will allow him to hold a book 25 cm from his eye.
Hint #1: the object is the book, at a distance
of (negative) 25 cm
Hint #2: the image will be virtual (he looks through the lens
of the glasses) so the image distance is negative
What is the power of these corrective lenses in diopters?
Of course, the challenge comes when the near point and far point are both about a meter or two! Fortunately, line-less bifocals are available!