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1. Physics of the Human Eye
How is the eye similar to a camera?

2. Camera Human Eye
The camera, a boxlike device for
taking pictures modelled after
the human eye.
1. Shutter – little door behind
an aperture or hole, opens and
closes(eyelid) and
aperture(pupil)
2. Diaphragm – controls the
amount of light that enters the
camera by changing the size of
the aperture(iris)
Eye, spherical in shape with
about 2.5 cm in diameter.
1. Cornea – front part of
the eye covered with a clear
membrane
2. Retina – back part
with light sensitive cells(lens)
3. Pupil – part of the eye
that looks black
4. Iris – ring muscle that
controls the opening and
regulates the amount of light
that enters the eye.

3. Vision Defects Causes How is it
corrected?
Myopia
(nearsightedness/sh
ort-sightedness)
Long eyeball;
image of distant
objects falls in
front of the retina
Concave lenses
bring the point of
focus backward
and on the retina
Hyperopia
(farsightedness/long
-sightedness)
Short eyeball;
image of distant
objects falls
behind retina
Convex lenses
bring the point of
focus forward and
on the retina
Presbyopia Lack of
accomodation
Bifocal Lenses

5. How are images reflected and
Refracted by Mirrors and Lenses?
Chapter 20

6. Essential Questions:
• What is the secret behind one –way mirror?
• How can lenses be used to correct eye defects?

7. Mirror are smooth reflecting surfaces, usually made up of
polished metal or glass that been coated with some
metallic substances
Flat mirror/ Plane
mirror
Curved Mirror(either
convex or concave)
Image formed by plane
mirror:
Same as the size of the
object, as far behind the
mirror as the object is in
front, virtual and upright
but laterally inverted
Maybe virtual and real
images. Depends upon the
position of the object.
Due to lateral inversions of image in plane mirrors, the word
ambulance is written backwards in front of the hospital cars to appear
in the proper orientation when seen in a rearview mirror

9. Virtual and Real images are produced when light is reflected or
refracted.
Virtual Image Real Image
•Right-upside
•Appears because light rays
Seem to meet at a point but
do not actually do so.
•Cannot be projected on
screen
•Upside down
•When reflected rays meet
at a point
•Can be projected in the
screen

10. Multiple reflections
 A single mirror gives one image.
 If you add one more mirror, more
images will be formed.
 Two mirrors facing each other will
give you an infinite number of
images depending on the angle
between them.

11. Reflections on Curved Mirrors (spherical mirror)
Concave Mirror Convex Mirror
•Curves inward like a cave
•Turns parallel rays into
convergent rays
•Used as magnifying glass
for shaving and applying
make-up , as reflecting
telescopes, as beam of
lights in flashlights and car
headlights
•Curves outward
•Reflect parallel rays that
meet at a
point(diverging/spread-out)
•Used in cars as passenger-
side rear view mirror

12. Lens is a curved piece of glass or some other transparent
material that is used to refract light
Convex
Lenses*converging
Concave
Lenses*diverging
•Thicker at the center than
at the edges
•Parallel rays are refracted
inwards
•Thinner at the center than
at the edges
•Parallel rays are refracted
outward
CHROMATIC ABERRATION – is a lens defect caused by dispersion
of different wavelengths of light as they pass through the lens
ACHROMATIC lens – used in all precision optical instruments that
joins both converging and diverging lens to eliminate CHROMATIC
ABERRATION

13. Ray diagramming

14. Essential Questions
• How are images formed by a mirror or lens?
• How do we locate the position of an image?

15. Steps to follow in Ray diagramming:
1. Draw a horizontal line to represent the principal axis intersecting a circular
arc representing the mirror or lenses
2. Mark the positions of F and C on the principal axis. 2f=R
3. Draw the object. The distance between the object and the mirror is the
OBJECT DISTANCE
4. Draw rays with arrow to indicate directions from the tip of the object
(a) RAY 1 – a ray parallel to the principal axis is reflected so that it appears to
come from the principal axis
(b) RAY 2 – a ray directed toward the principal focus is reflected parallel to the
principal axis
(c) RAY 3 – a ray directed toward the center of curvature is reflected along its
own path
5. Draw the image of the arrow with its tail on the principal axis. (used dashed
lines when extending rays backwards)
6. Find the Nature of the object: whether the image is VIRTUAL or REAL,
INVERTED or UPRIGHT, ENLARGED or REDUCED or THE SAME SIZE.

16. Plane mirror
Image formed by plane mirror:
Same as the size of the object, as far behind the mirror as
the object is in front, virtual and upright but laterally
inverted
Reflections on Mirrors

17. Concave Mirror(Virtual
and Real)
Convex Mirror
Always virtual images of
reduced size
Object
Position
Image
position
Nature of
Image
Between F and
the mirror
Behind the
mirror
Virtual, Erect
and magnified
At F - No Image
Between C and
F
At infinity Real, inverted
and magnified
At C At C Real, inverted
and same size
Beyond C Between C and
F
Real, Inverted
and Reduced
At infinity At F Real, inverted
and reduced

18. Refractions on Lenses
Concave Lenses (Virtual
and Real)
Convex Lenses
Always produced virtual
images of reduced size
Object Position Image position Nature of
Image
Between F’ and
the lens
Same side of the
lens as object
Virtual, Erect and
magnified
At F’ - No Image
Between F’ and
2F’
Beyond 2F Real, inverted
and magnified
At 2F’ At 2F Real, inverted
and same size
Outside 2F’ Between F and
2F’
Real, Inverted
and Reduced
At infinity At F Real, inverted
and reduced