Download Chapter 18: Light and Optics

Chapter 18: Light and Optics
Objectives
Summarize the science of optics.
Describe how mirrors control reflection.
Describe how mirrors produce images.
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.
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
 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.
 The reflection of parallel
light rays all in the same
direction is called regular
reflection.
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.
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.
Flat Mirrors
 Looks Exactly like you
 But, if you raise your
right hand, in the
mirror it appears that
your raising your left
hand.
Concave & Convex Mirrors
A convex mirror is curved outward, like the
bottom of a spoon. In a convex mirror,
parallel light rays move away from each
other.
A concave mirror is curved inward toward
the center, like the inside of a spoon.
Parallel light rays reflecting off a concave
mirror move toward each other.
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
Review
 Explain the term optics in your own words?
 Optics is the study of light and vision.
 How is diffuse reflection similar to regular
reflection? Different?
 Diffuse reflection and regular reflection both
obey the law of reflection sends parallel light
rays in many different directions; regular
reflection sends parallel rays in the same
direction.
Review
Describe the path that light rays take when
they form an image of your smile when
you look into a flat mirror?
Light rays reflected from your smile strike
the mirror, bounce off, and enter your eye.
18.2
Lenses form images by refracting light
Objectives
Identify how a material medium can refract
light.
Describe how lenses control refraction.
Recognize how lenses produce images.
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.
Review
What quality of a material affects how
much it refracts light?
The speed of light in the material.
How does the curve in a lens cause it to
refract light differently from a flat piece of
glass?
Because the angle at which light strikes a
curved surface varies across the surface,
the amount of refraction for different light
rays varies also.
Review
How does a camera lens form an image?
A camera lens refracts light waves inward
toward a focal point.
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 cornea acts as
a convex lens and
does most of the
refracting in the eye.
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.
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.
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.
 Can be corrected with
glasses with concave
lenses. They spread
out the rays of light
before they enter the
eye.
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. Can be
corrected by convex
lenses.
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.
 They fit directly over
the cornea and float
on a thin layer of
tears.
 This is only a
temporary fix.
Review
1. Where are images focused in an eye
with perfect vision?
 On the Retina
2. What causes people with
nearsightedness to see blurry images of
objects at a distance.
 The eye focuses the image in front retina
Review
What kind of lens is used for correcting
farsightedness? Why?
Convex lens; it bends light inward, which
moves the focal point of the image forward
toward the retina.
18.4 Optical Technology makes
use of Light Waves
Objectives
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
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.
 Uses a combination
of convex lenses- the
eyepiece and the
objective lenses.
 Most microscopes
use a light or mirror to
shine more light on
the object.
 Page 613
Telescopes
The objective lens gathers and focuses
light from a distant object to form an image
of the object. The eyepiece enlarges the
image.
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
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.
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
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
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.