CHAPTER 4
Light
Look carefully at the cups. What is
the main difference among them?
Light and Color
• Transparent materials
– Transmit most of the light that strikes it
– See clearly through
• Translucent Materials
– Scatters light as it passes through
– Can see through it w/ fuzzy/blurred details
• Opaque Materials
– Reflects or absorbs all of the light that strikes it
– Light can’t pass through it
Transparent
Translucent
Opaque
If you know how light interacts with
objects…
• You can explain why objects
have different colors
The color of any object…
• Depends on the material of object and color
of light striking it.
Rememeber: Wavelength:
Although light from the sun appears colorless or
"white" it actually contains a range of colors
similar to a rainbow. You can see these colors
using a prism to separate them out.
Color of opaque objects
• They are the color of the light they reflect.
A green object such as a leaf reflects
only those wavelengths that create
the visual effect of green. Other
colors in the light are absorbed by the
leaf.
White objects reflect most of the wavelengths
of light that strike them. When all of these
wavelengths are combined, we see white. On
the other hand, when all of them are
absorbed, and none reflected, we see black.
Color of transparent and
translucent objects
• Only certain colors of light can pass through
• The color of a transparent or translucent
object is the color of the light it transmits
• Color filters
– Piece of glass or plastic that allows light of only a
certain color to pass through it
– Ex: Red color filter only lets red light pass through
– Ex: sunglasses –objects appear to change color
Copy these questions into your notebook!
• Read pg 110 and 111 and answer:
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What are the primary colors of light?
What are 2 ways to make white light?
How do you make different colors of light?
What are the secondary colors of light?
What are complementary colors?
Answer question in figure 5.
What is a pigment?
How is mixing pigments of various colors different than
mixing light of various colors?
– What are the primary colors of pigments?
– What are the secondary colors of pigments?
– Then, do section 1 assessment. You may work with
partner.
DO NOW:
• What are the primary colors (in paint)?
• How are they different from the primary
colors of light?
Combining Colors
• PRIMARY COLORS
– 3 colors that can combine to make ANY other
color
– RED, BLUE, GREEN
• SECONDARY COLORS
– 2 primary colors mixed together
– YELLOW, MAGENTA, CYAN
Primary + secondary color = WHITE
light
Complementary colors
• Any two colors that combine to form white
light
– ex:
• Yellow and blue,
• cyan and red,
• Magenta and green
How does a color TV work?
• It uses only the primary colors of light (R, G, B)
in different ratios/brightness to form all of the
colors.
Mixing Pigments
•What is a pigment?
• Pigment = colored substances used to color
other materials –found in ink, paints, dyes
– They absorb some colors and reflect others
– Whatever color a pigment reflects in the color that
you see!
What are the Primary colors of
PIGMENTS?
Magenta, Cyan, Yellow
What happens when you keep
adding pigments together?
• Fewer colors of light get reflected, so we see
the mixture getting darker and darker
Section 2 – Reflection and Mirrors
Representing Light waves
• You can represent light waves as straight lines
called RAYS.
What does “diffuse” mean?
• Ex:
• John and Jack were in an argument about
who’s a better team—the Cubs or the White
Sox. They started getting very angry at each
other, and other students started getting
involved…. so Mrs. P had to come in and
diffuse the fight.
•
Regular Reflection vs. Diffuse
Reflection
Regular Reflection
– Smooth surface, rays refelect all at the same angle
• Diffuse Reflection
– Rough surface, rays reflect at different angles
How does your reflection wink?
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•
•
•
On a clean sheet of paper:
St. Cassian heading
Title: How does your reflection wink?
Procedure: Answer the two questions within
the procedure using COMPLETE sentences—
restating the question.
• Observing: Answer the questions in complete
sentences, restating the question.
PLANE MIRRORS
• = an everyday mirror
• A flat sheet of glass that has a smooth silver
colored coating on one side (normally the
back)
– Creates a regular reflection and clear image!
Image = copy of an object formed
by reflected or refracted rays of light
DO NOW
• What does virtual mean?
Kind of Image in a Plane Mirror
• You see a virtual image.
= an upright image that forms where light seems
to come from. The image is the same size as the
object, and it is reversed.
• Your image appears to be behind the mirror, but you
cannot reach behind the mirror and touch it
How images form
• Even though the light rays are reflected, your
brain treats them as if they had come from
behind the mirror
When one looks into a
mirror it appears as if you
are looking through it and
seeing the object on the
other side.
Concave Mirrors
• Parallel rays of light reflect so that they meet
at a point.
• Focal point = point at which rays parallel to
the optical axis meet.
Representing How images form
• Use a ray diagram to see where focused image
forms.
• See figure 10
• Concave mirrors can form either virtual images or real images
• Virtual Image
– If object is between mirror and focal point
– Appears behind the mirror and is upright
– Always larger than object
• Real Image
– When rays actually meet
– It is upside down
– Might be larger or smaller than object
– Occurs when object is farther away from mirror than the
focal point
Convex Mirrors
• Mirror with a surface that curves outward.
Convex Mirrors
• The rays appear to come from a focal point
behind the mirror.
• The rays appear to come together but they
never actually meet.
• The image formed will be virtual and smaller
than the object.
• What is refraction?????????????
When light rays enter a medium
at an angle, the change in speed
causes the rays to bend, or
change direction
Section 3 – Refraction and
Lenses
• When you are looking at fish in a
tank, what are the three mediums
the light is passing through?
Water, glass, air
Refraction in Different Mediums
• Light bends more in some mediums than in
others.
• When light passes
– from airwater, it slows.
– From water  glass, it slows down more.
– Glass air it ____________
• The glass causes the light to bend the most, so
it has a high index of refraction.
• Index of refraction = measure of how much a
ray of light bends when it enters the material
– The higher the index, the more it bends light
Prisms and Rainbows
• When white light enters a prism, each
wavelength of light is refracted by a different
amount
– Red has longest wavelength and is reflected least
– Violet has shortest wavelength and is reflected
most
– Same thing happens with water droplets in the air.
Mirages
• An image of a distant object caused by
refraction of light
• See page 121.
DO NOW
• Where are places you see lenses everyday?
• What do you know about lenses?
Lenses
Lens = a curved piece of glass or other
transparent material that is used to refract
light
– It forms an image by refracting light rays that pass through it
– Type of image depends on
• 1. shape of lens
• 2. position of object
There are 2 types of Lenses
• 1. Convex
• 2. Concave
• Make 2 columns and compare and contrast
Convex and concave lenses.
Cow’s Eye Dissection-- Virtual
• http://www.exploratorium.edu/learning_studi
o/cow_eye/how.html
DO NOW
• What is needed to see?
• What parts of the eye do you know already?
DO Now, cont’d
• Do Activity page 26. Answer the questions.
The Human Eye
• You see objects when a process occurs that
involves both your eyes and your brain
1st. Light Enters the Eye
• 1.) Through the transparent cornea.
– Protects eye and acts as lens to focus light rays
• 2.) Through the pupil
– Black center of eye – an opening that becomes
larger to let in more light in the dark
IRIS
• Ring of muscle that contracts and expands to
change the size of the pupil.
• Colored
2nd An Image Forms
• 1.) Light Passes through LENS
– Convex
– Refracts light to form image on lining of your
eyeball
– Ciliary muscles hold lens in place.
An Image Forms, Cont’d
• 2.) Ciliary muscles relax to focus on distant
objects, and contract to focus on nearby
An Image Forms, cont’d
• 3. ) Upside-down image forms on retina
(layer of cells lining inside of eyeball)
– a.) Rods
• Cells with a pigment that responds to low light.
They help you see in dim light.
– B.) Cones
• Cells that respond to color and respond best in
bright light
Rods and Cones
Third: A Signal Goes to the Brain
• Rods and cones send signals to the brain along
a short, thick never called the optic nerve.
• It combines image from each of your eyes into
a single 3D image.
Correcting Vision
• If your eyeball is slightly too long or too short,
the image on retina is out of focus.
• Contacts and Glasses
• Concave lenses correct nearsightedness.
• Convex lenses to correct farsightedness
Nearsightedness
• Person can see nearby things clearly but
faraway objects are blurred
• Need concave lens
Farsightedness
• Can see distant objects clearly, but nearby
objects appear blurry
• Need convex lens
DO NOW
• Can you think of 3 common types of optical or
light-using instruments ?
SECTION 5 – USING LIGHT
3 Common Optical Instruments
• 1. Telescope
• 2. Microscope
• 3. Camera
• What do you know about telescopes???
TELESCOPES
• Use lenses or mirrors to collect and focus light
from distant objects
• Make distant objects look bigger
2 Types of Telescopes
• 1. refracting
– Uses 2 lenses to focus light
• 2. reflecting
– Uses a lens and a mirror to focus light
Microscopes
• What do you already know about
microscopes?
Microscopes
• Use a combination of lenses to focus light and
produce and magnify an image
• Makes small, nearby images look bigger.
Camera
• Uses a lens to focus light and form a real,
upside-down image on film in the back of the
camera
• Forms images on film as “pictures”
5. Using Light