9. Concave Lens
It is thin at the middle
and thick at the edges.
Lens such that a parallel
beam of light passing
through it is caused to
diverge or spread out.
11. Myopia
(nearsightedness) This is a defect of
vision in which far objects appear
blurred but near objects are seen
clearly. The image is focused in front
of the retina rather than on it usually
because the eyeball is too long or the
refractive power of the eye’s lens too
strong. Myopia can be corrected by
wearing glasses/contacts with
concave lenses these help to focus
the image on the retina.
14. Hyperopia
(farsightedness) This is a defect of
vision in which there is difficulty with
near vision but far objects can be seen
easily. The image is focused behind
the retina rather than upon it. This
occurs when the eyeball is too short or
the refractive power of the lens is too
weak. Hyperopia can be corrected by
wearing glasses/contacts that contain
convex lenses.
17. Astigmatism
This defect is when the light rays do not all
come to a single focal point on the retina,
instead some focus on the retina and some
focus in front of or behind it. This is usually
caused by a non-uniform curvature of the
cornea. A typical symptom of astigmatism is if
you are looking at a pattern of lines placed at
various angles and the lines running in one
direction appear sharp whilst those in other
directions appear blurred. Astigmatism can
usually be corrected by using a special
spherical cylindrical lens; this is placed in the
out-of-focus axis.
19. Presbyopia
Presbyopia is part of aging. When
someone gets into their forties, and is
caused by the hardening of the
crystalline lenses in the eye. People
with this will find that their arms are
“getting shorter” as they have to hold
reading material farther and farther
away.
21. Strabismus
Strabismus, more commonly known
as crossed-eyes, is when the two eyes
do not look toward the same object
together. One eye is normal, while the
other one points in some other
direction. Strabismus can be corrected
with prisms. The prisms bend the light
so the light goes to the correct spot.
23. Cataract
A cataract is when the lens of the eye
or its capsule is opaque. It is the
leading cause of blindness in the
world. The word “cataract” means
waterfall. For someone with a serious
cataract, it's like seeing through a
waterfall to them.
25. Sample Problem #1
A 4.00-cm tall light bulb is placed
a distance of 45.7 cm from a
double convex lens having a focal
length of 15.2 cm. Determine the
image distance and the image
size. Like all problems in physics,
begin by the identification of the
unknown information.
26. ho = 4.00 cmdo = 45.7 cmf = 15.2
cmNext identify the unknown
quantities that you wish to solve for.
di = ???hi = ???To determine the image
distance, the lens equation must be
used. The following lines represent the
solution to the image distance;
substitutions and algebraic steps are
shown.