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Chapter 18: Light and Optics
Objectives
Summarize the science of optics.
Describe how mirrors and lenses can be
combined to make complex optical tools.
Explain how optical tools are used to
extend natural vision.
Recognize how laser light is made and
used in optical technology
Optics is the science of light and
vision
 Optics is the study of
visible light and the
ways in which visible
light interacts with the
eye to produce vision.
 Mirrors, lenses,
eyeglasses, cameras,
lasers are all optical
tools.
Fiber Optics
Used to transmit
information
efficiently.
EX) Fiber Optic
Cables.
Fiber Optics
 Is Technology based on
the use of light to send
signals through
transparent wires called
optical fibers
 Very important in
communications for
telephones, TV wires,
and broadband internet
connections.
 Medical uses to see
inside a patients body
Lasers
A laser is a device that produces an
intense, concentrated beam of light that is
brighter than sunlight.
A laser is made in a special tube called an
optical cavity in which an energy source
stimulates material to give off light waves.
Laser Beams
A Laser Beam can travel great distances
without spreading because its light waves
are parallel and very concentrated.
The light waves in a laser beam are all
one wavelength and in one phase.
Uses of Lasers
 Surveyors use them
to measure distances
and angles.
 Used to read bar
codes, to scan
images and pages of
text and to create
holograms
Future Uses of Lasers
 Scientist plan to use
them in
nanotechnology—
perform extremely
fine operations.
 New ways of
transferring energy.
 Supply energy for the
spacecraft.
Mirrors and Lenses can be more
Powerful Optical Tools
For example: Mirrors and lenses can be
combined with each other, as they are in
an overhead projector.
Microscopes
 Used to see small
objects.
 A Microscope
enlarges images
using a combination
of convex lens. (2)
 Most microscopes
use a light or mirror to
shine more light on
the object.
 Page 613
Telescopes
A reflection telescope has a CONCAVE
mirror that gathers and focuses light.
Telescopes
Used to see objects to far away to see well
with the naked eye.
2 Types:
Refracting telescope is made by
combining lenses.
Reflection is made by combining lenses
and mirrors.
Refraction
Reflection
Lights, Camera, Action………….
Most film cameras focus images
Like the eyes
Read Page 614
Objectives
Describe how mirrors control reflection.
Describe how mirrors produce images.
Identify how a material medium can refract
light.
Describe how lenses control refraction.
Recognize how lenses produce images.
Mirrors use Regular Reflection
When light waves strike an object, they
either pass through it or they bounce off its
surface.
The law of reflection states that the angle
of reflection equals the angle of incidence.
Regular Reflection
 The reflection of parallel
light rays all in the same
direction is called regular
reflection.
 Surface of the object is
smooth, like a mirror, light
rays that come from the
same direction will
bounce off in the same
new direction.
Diffuse Reflection
 If the surface is not
very smooth, light
rays strike it from the
same direction and
bounce off in many
new directions.
 The reflection of
parallel light rays in
many different
directions is called
diffuse reflection.
 EX) Paper, Cloth
An Image
 When you look in the
mirror, you see an
image of yourself.
 An image is a picture
of an object formed
by waves of light.
 The image of yourself
is reflected off of you,
onto the mirror.
Law of Reflection
States that the
angle of incidence
equals the angle of
reflection
EX) A ray of light
hits a mirror at an
angle of incidence,
the reflection angle
is equal.
Focal Length
The focal length of
a lens is the
distance from the
center of a lens to
its focal point.
Flat Mirrors
 Looks Exactly like you
 Produces an image
that is identical, but
opposite to how you
look
Convex
A Convex mirror or lens is curved outward.
A convex lens brings light rays to a focal point.
The distance from the center of the lens to the focal
point is the focal length.
A convex lens forms a “right-side up” image when
the object is less than one focal length away.
If the object is twice the distance, the image will
appear Upside down & smaller
A convex mirror will produce an image that is right
side up & smaller.
Concave
A Concave mirror or lens is curved inward
towards the center.
Parallel light rays that pass through a
concave mirror are reflected to a focal point
Concave/Convex
Focal Point
The rays striking a concave mirror cross
and then move apart again. The point at
which the rays meet is called the focal
point of the mirror.
P. 597
Light Waves and Refraction
Light Waves
Light Waves move at different speeds
through different Mediums.
A ray of light will slow down when it moves
from air into the denser medium of a pond.
The amount &direction a light ray bends when
it enters a new medium depend on how dense
the medium is.
A light wave enters a new medium at an
angle other than 90º, the wave will turn toward
the normal.
Electromagnetic Waves
Electromagnetic Waves from a star will
travel through empty space, they travel in
straight lines because the medium has not
changed.
A medium can refract light
 Some light rays
reflect off the surface
of glass.
 Refraction occurs
when a wave strikes a
new medium—such
as the window—at an
angle other than 90˚
and keeps going
forward in a slightly
different direction.
Refraction of Light
Page 600
Waves moving at an angle into a denser
medium turns toward the normal.
Waves moving at an angle into a thinner
medium turn away from the normal
Refraction and Rainbows
 Rainbows are caused by
Refraction and reflection of
Light through spherical water
Drops, which acts as prisms.
Only one color reaches
Your eye from each drop.
Red appears at the top of a
Rainbow because it is coming
From higher drops, while violet
Comes from lower drops.
Shape determines how lenses from images
Just as a curved mirrors distort images,
certain transparent mediums called lenses
alter what you see through them.
A lens is a clear optical tool that refracts
light. Different lenses refract light in
different ways and form images useful for
a variety of purposes.
Convex & Concave Lenses
 A convex lens causes
parallel light rays to
meet at a focal point
 A concave lens
causes parallel light
rays to spread out.
 Page 601 & 602
Images Formed by Lenses
Notice the distance between the penguin
and the lens in the illustration on page
602.
The distance is measured in terms of a
focal length, which is the distance from
the center of the lens to the lens’s focal
point.
To summarize
If you look at an object through a concave
lens, you’ll see an image of the object that
is right side up and smaller than the object
normally appears.
If you look at an object through a convex
lens, the image could be formed upside
down and larger if two focal lengths away.
Or it will appear right side up and larger if
one focal length away.
How does a camera lens form an image
 A camera lens uses refraction to focus light on
the film, or in a digital camera.
 When a ray of light passes from a less dense to
a more dense medium (such as from air to
glass) it slows down. If it strikes the glass
surface at an angle, it is also bent a little, and
this is called refraction. When it passes back into
air, it speeds up again, and is again refracted if
the surface is at an angle.
18.3
The Eye is a Natural Optical Tool
Objectives
Recognize how the eye depends on
natural lenses.
Explain how artificial lenses can be used
to correct vision problems.
Eyes gathers and focuses light
Eyes transmit light, refract light, and
respond to different wavelengths of light.
Eyes contain natural lenses that focus
images of objects and then sends signals
to the brains.
The brain interprets these signals as
shape, brightness, and color.
How Light Travels
through the Human Eye
1. Light enters the eye
through the cornea,
a transparent
membrane that
covers the eye.
 The two parts of the
eye that refract light
are the CORNEA
AND LENS
Retina
The retina detects
an image and send
signals to the brain
The CORNEA acts
like a convex lens
The lens adjusts to
focus an image on
the retina
How Light Travels
through the Human Eye
2. Light continues
through the pupil, a
circular opening that
controls how much
light enters the eye.
 The pupil is
surrounded by the
iris, which opens
and closes to
change the size of
the pupil.
How Light Travels
through the Human Eye
3. Next, the light passes through the lens.
It refracts light to make fine adjustments
for near or far objects.
The lens is connected to tiny muscles
that contract and relax to control the
amount of refraction that occurs and to
move the focal point.
How Light Travels
through the Human Eye
4. The light then
passes through he
clear center of the
eye and strikes the
retina. The retina
contains specialized
cells that respond to
light. Some of these
cells sends signals
through the optic
nerve to the brain.
How the Eye Forms Images
For a complete image to be formed in the
eye and communicated to the brain. The
Retina plays a very important role.
Retina: Rod Cells
 Rod cells distinguish
between white and
black and shades of
gray. Help in night
vision.
Retina: Cone Cells
 Cone cells- respond
to different
wavelength of light so
they detect color.
There are three types:
Red, Blue, and
Green. They respond
to other colors by
using a combination
of the three.
Cameras
Just like our eyes
have to focus on
an image, we must
move the lens of a
camera to focus an
image onto film
Corrective Lenses can Improve Vision
 How many of you wear
contacts or glasses?
 About 36 million wear
contact lenses
 When the image formed
by the lens of the eye
does not fall exactly on
the retina. A blurry image
is formed. Artifical lenses
are used to correct this
problem.
Farsighted
 Objects are clearer to a
farsighted person when
the objects are farther
away. It occurs when
the lens of the eye
focuses an object’s
image behind the
retina.This can be
caused by aging.
 A person who is
farsighted can be
helped by a convex
lens, that make light
rays converge farther
towards the retina.
Corrective Lenses
 Nearsighted cannot see
objects clearly unless
they are near. It occurs
when the lens of the eye
focuses the image in
front of the retina.
 A person who is
nearsighted wears
glasses to spread light
out so that the image is
focused on the retina.
Surgery
Doctors can use surgical procedures to
shape the cornea.
To correct nearsightedness, surgeons
remove tissue from the center of the
cornea.
To correct farsightedness, surgeons
remove tissue from around the edge of the
cornea.
http://www.youtube.com/watch?v=dZZguJ
NitnU
Contacts
 Contact lenses also
correct vision by
changing the way the
cornea refracts light.
 CONTACTS work
with the cornea and
tears to act as a
single lens.
 This is only a
temporary fix.
Objectives









Identify sources of EM waves
Recognize how EM waves transfer energy
Describe how different EM waves are used
Observe how to detect visible light
Explain how visible light is produced
Describe bioluminescence
Identify types of artificial light
Recognize how light waves interact with materials
Recognize why objects have color & how colors are
produced
Visible Light Spectrum
Electromagnetic Waves
Electromagnetic
waves can be
converted into
useful forms
(Microwave ovens)
Incandescence & Bioluminescence
Incandescence
is the
production of
light by
materials at
high
temperatures.
 Some organisms
can produce their
own light, this is
called
bioluminescence.
Artificial Lighting
There are many
types of artificial
lighting (Textbook
Page 571-572)
Light Waves
Light can be transmitted, reflected,
absorbed or scattered.
A prism is a tool that uses refraction to
spread out different wave lengths of light
Polarization
Polarization is a quality of light in which all
of its waves vibrate in the same direction