Name Class Date

CHAPTER 22 The Nature of Light

SECTION

3 Interactions of Light Waves

National Science
BEFORE YOU READ Education Standards
After you read this section, you should be able to answer PS 3c
these questions:
• How does reflection affect the way we see objects?
• What happens to light when it passes from one
material into another?
• How do light waves interact with each other?

What Is Reflection?
Light bounces off some objects and passes through oth- STUDY TIP
ers. Reflection happens when light bounces off an object. Organize Concepts As you
Light reflects off objects all around you. You see the objects read, make a Concept Map in
your notebook. Try to include
because the reflected light travels to your eyes. the vocabulary terms and the
You can use the law of reflection to predict where a terms in italics.
light wave will travel after it reflects. The law of reflection
states that the angle of incidence of light is equal to the
angle of reflection. The angle of incidence is the angle at
which a light beam hits an object. The angle of reflection
is the angle at which the light bounces off the object. The
law of reflection states that these two angles are equal. READING CHECK
1. Apply Ideas If a light
The Law of Reflection beam hits a mirror at a
30° angle, what is the angle
A line perpendicular
of incidence?
to the mirror’s surface 

is called the normal.

The beam of The beam of light
light traveling reflected off the 2. Apply Ideas What is the
toward the   mirror is called angle of reflection?
mirror is called the reflected



the incident beam.
beam. 

The angle between The angle between the

the incident beam reflected beam and the
and the normal is normal is called the
called the angle of angle of reflection.
incidence.

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Interactive Textbook 415 The Nature of Light
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SECTION 3 Interactions of Light Waves continued

REGULAR REFLECTION AND DIFFUSE REFLECTION

Light reflects off most objects, such as mirrors and
walls. Why can you see your reflection in a mirror, but
not in a wall? The answer has to do with the surface the
light reflects from. Some objects, such as mirrors, reflect
all the light beams at the same angle. This is called
regular reflection. Regular reflection allows you to see
an image in a mirror or shiny piece of metal.
Some objects, such as walls, reflect the light beams at
many different angles. This is called diffuse reflection.
Diffuse reflection prevents you from seeing images
reflected off walls, furniture, or other rough surfaces.






   












TAKE A LOOK Regular reflection occurs when light

beams are reflected at the same angle.
Diffuse reflection occurs when
light beams reflect at many differ-
3. Identify Circle the image When your eye detects the reflected ent angles. You can’t see a reflection
that shows how light reflects beams, you can see a reflection on because not all of the reflected light
from a mirror. the surface. is directed toward your eyes.

SEEING OBJECTS
You can see some objects because they produce
light. You can see other objects because they reflect
light. Luminous objects are light sources. Flames, light
bulbs, and the sun are examples of luminous objects.
Illuminated objects are visible because they reflect light.
The reflected light travels from the objects to your eyes.
The moon is an illuminated object. You see the moon
READING CHECK because it reflects light from the sun to your eyes.
4. Compare and Contrast
What is the difference
between a luminous object
and an illuminated object?

You can see the body

of a firefly because it is
illuminated.

You can see the tail of

a firefly because it is
luminous.

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Interactive Textbook 416 The Nature of Light
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SECTION 3 Interactions of Light Waves continued

How Is Light Absorbed and Scattered?

When you shine a flashlight, you can observe the light
beam spread out and become dim farther from the flash-
light. The light beam becomes dim because of absorption.
It spreads out because of scattering.

LIGHT ABSORPTION
Absorption is the transfer of light energy into an object
or a particle of matter. Air is full of particles, such as water
droplets or dust. When light shines through the air, these par-
ticles absorb some of the light energy. The farther light travels
from its source, the more its energy is absorbed by particles.
Therefore, light is dimmer farther from its source. READING CHECK
5. Explain What makes
a beam of light become
dimmer as it travels away
from its source?

When light is absorbed by a particle, the light beam loses

energy and becomes dim.

LIGHT SCATTERING
Scattering is the interaction of light with an object that
changes the light’s direction or energy. When light collides
with a particle in the air, the light scatters in all directions.
The scattering of visible light makes the sky look blue.
Light with shorter wavelengths is scattered more than light
with longer wavelengths. Blue light is scattered more by the
atmosphere than red light. The red light passes more easily
through the atmosphere. Therefore, the sky looks blue. READING CHECK
6. Explain Why is the sky
blue?

When light collides with a particle, it scatters in all directions.

Scattering allows you to see objects outside a beam of light.

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Interactive Textbook 417 The Nature of Light
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SECTION 3 Interactions of Light Waves continued

What Is Refraction?
Refraction happens when a wave bends as it passes
from one material into another. Light travels at different
speeds through different materials. Therefore, passing
from one material to another can change its direction.
Light travels faster in a vacuum than in matter. Light
travels faster in air than in glass or water.

Light bends away from the bound-

ary between the materials here
because light travels more slowly
in glass than in air.

TAKE A LOOK Light in

7. Apply Concepts Which
way will light bend when
it passes from air to water?
Explain your answer.

Light bends toward the boundary between the

materials here because light travels faster in air
than in glass.

OPTICAL ILLUSIONS
Light from a light source or reflected from an object
travels in a straight line through the air to you. Your brain
expects light to always travel in a straight line. However,
when you look at an object under water, the light refracts,
or bends. Because it doesn’t travel in a straight line, you

Critical Thinking
may see an optical illusion, such as the one shown below.

8. Infer What is an optical

illusion?

Air Air
Water Water

Because of refraction, the cat and the fish see optical illusions. To the cat, the
fish appears closer than it really is. To the fish, the cat appears farther away than
it actually is.

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Interactive Textbook 418 The Nature of Light
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SECTION 3 Interactions of Light Waves continued

SEPARATING COLORS
White light contains all of the colors of visible light. Each
color has a different wavelength. Different wavelengths
travel at the same speed in a vacuum, but they travel at
different speeds in glass. Therefore, some colors refract
more than others when they travel through the glass. Colors
with the shortest wavelengths refract the most. Colors with
the longest wavelengths refract the least. READING CHECK
9. Identify What happens to
light when it hits a prism?
Light passing through a prism is refracted twice—
once when it enters and once when it exits.
Violet light has a
shorter wavelength
Red light has than other colors.
a longer wave- Violet light is refracted
length than other the most
colors. Red light
is refracted the
least.

A prism is a piece of glass that uses refraction to separate white light into the
colors of visible light.

What Is Diffraction?
Diffraction happens when waves bend around a barrier
or through an opening. The amount a wave bends depends
on two things: its wavelength and the size of the barrier or Critical Thinking
opening. Waves diffract the most when the barrier or open- 10. Compare and Contrast
ing is the same size as the wavelength or smaller. How are diffraction and
refraction of light alike? How
The wavelength of visible light is very small. It is about are they different?
100 times thinner than a human hair. Therefore, a light
wave won’t bend much unless it passes through a very
narrow opening or around a sharp edge.

DIFFRACTION YOU CAN SEE

You will not often see light waves diffracting around
objects. For example, you can’t see the objects that are
around the corner of a building. However, you can see
some effects of light diffraction. For example, diffraction
makes the edges of a shadow look blurry.

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Interactive Textbook 419 The Nature of Light
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SECTION 3 Interactions of Light Waves continued

This image shows light dif-

fracting. A single wavelength
TAKE A LOOK of light is passing around the
11. Describe Compared to sharp edge of a tiny disk.
the wavelength of the light,
how large is the disk?

What Is Wave Interference?

Interference happens when two or more waves com-
bine to form a single wave. Interference occurs when two
waves overlap. When waves overlap, they can combine by
READING CHECK constructive interference or destructive interference.
12. Identify What are the Constructive interference produces a wave with a larger
two kinds of interference? amplitude than the original waves. Waves that combine by
constructive interference create one wave with a stronger
intensity. For example, light waves that combine by con-
structive interference produce one brighter light wave.
Destructive interference produces a wave with a smaller
amplitude than the original waves. Waves that combine by
destructive interference create one wave with a weaker
intensity. For example, light waves that combine by destruc-
tive interference produce one dimmer light wave.
Constructive and Destructive Interference
1 Light of a single wavelength 2 The light waves diffract as they
passes through two slits. pass through the tiny slits.

TAKE A LOOK
13. Identify What kind of
3 The diffracted light waves 4 The interference can be seen on a
interference produces the combine by both constructive screen as bright and dark bands.
and destructive interference. The bright bands are the result of
dark bands? constructive interference. The dark
bands are the result of destructive
interference.

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Interactive Textbook 420 The Nature of Light
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SECTION 3 Interactions of Light Waves continued

LIGHT INTERFERENCE YOU CAN SEE

The experiment shown in the last figure used only one
wavelength of light. However, the light you see around you
every day is white light. White light contains many differ-
ent wavelengths. The many waves don’t usually combine in
total destructive or constructive interference. This is why
you do not usually see the effects of interference. READING CHECK
14. Explain Why do we
Light Wave Interaction not usually see the effects of
constructive and destructive
light interference?
,IGHT GETS INTERFERENCE
BRIGHTER
)NTERFERENCE
.OT SEEN
,IGHT GETS

$ESTRUCTIVE

,IGHT
INTERACTS "LURRY SHADOW
WITH EDGES

,IGHT BENDS
AROUND OR
THROUGH OBJECTS /PTICAL ILLUSIONS

,IGHT PASSES
,IGHT BETWEEN
WAVES MATERIALS

,IGHT INTERACTS
WITH BEAM
!BSORPTION 3PREAD OUT BEAM
SCATTERING

,IGHT
BOUNCES TAKE A LOOK
BACK 15. Describe Complete
6ISIBLE OBJECTS
the Flow Chart with the
-IRROR REFLECTION information from this section.

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Interactive Textbook 421 The Nature of Light
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Section 3 Review NSES PS 3c

SECTION VOCABULARY
absorption in optics, the transfer of light energy reflection the bouncing back of a ray of light,
to particles of matter sound, or heat when the ray hits a surface that
diffraction a change in the direction of a wave it does not go through
when the wave finds an obstacle or an edge, refraction the bending of a wavefront as the
such as an opening wavefront passes between two substances in
interference the combination of two or more which the speed of the wave differs
waves that results in a single wave scattering an interaction of light with matter
that causes light to change its energy, direction
of motion, or both

1. Explain Why is a beam of light wider and dimmer when it hits a wall than when it
leaves the flashlight?

2. Describe Use the vocabulary words to name the type of wave interaction that
causes each condition.

Condition Wave Interaction

A log is sticking up from the water. It looks
as if its top and bottom are not attached.
The edge of a shadow is blurry.

You can see your image in the mirror.

A beam of light becomes dimmer farther

away from its source.

3. Apply Ideas In a dark room, you can see the image on the screen of a television.
However, you cannot see the table the television is sitting on. Why can you see
the image but not the table?

4. Explain Why can you see your reflection in the bowl of a spoon but not in a piece
of cloth?

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Interactive Textbook 422 The Nature of Light
 Physical Science Answer Key continued

Review 13. Wavelength Type of wave Uses

1. When an electrically charged particle Longer than radio waves radio and TV
vibrates, the electric field around it vibrates. 30 cm
This creates a magnetic field. An electric 0.1 cm to 30 cm microwaves microwave
field and a magnetic field vibrating together ovens, cell
produce an electromagnetic wave. phones,
communication
2. Ocean waves are slow; light waves are faster satellites, radar
than anything else known. Ocean waves 700 nm to1 mm infrared waves night
involve water, a medium; light waves can binoculars, heat
travel through a vacuum. photographs
400 nm to visible light human sight
3. Radiation of sunlight is the transfer of 700 nm
energy from the sun as EM waves.
60 nm to ultraviolet light making vitamin
4. Energy from the sun travels in the form of 400 nm D, killing
EM waves. These waves must travel through bacteria
space, which is almost a vacuum, to reach 0.001 nm to X rays medical X rays,
Earth. 60 nm security

5. People eat plants (fruits and vegetables) and Shorter than gamma rays killing cancer
0.1 nm cells, killing
animals (meat). Plants use the sun’s energy bacteria in food
to store sugars. When we eat plants or ani-
mals that eat plants, we gain energy from Review
the sun. 1. 1) The three types of waves have different
6. Light travels faster than sound. wavelength regions in the EM spectrum.
2) You can see visible light, but not infrared
SECTION 2 THE ELECTROMAGNETIC or ultraviolet light.
SPECTRUM 3) Ultraviolet light can burn your skin.
1. violet 2. Description Region of EM spectrum
2. No, they send out radio waves that carry Used by police officers to microwaves
sound information. detect the speed of cars
by radar
3. AM because AM radio waves travel farther.
Energy from the sun that UV light
4. to broadcast radio and TV can cause sunburn
5. Microwaves can get through only the out- Used in a device that X rays
side of the food. You need to stir it to even takes images of bones
out the heat. Carry television signals to radio waves
your home
6. traffic controller, ship navigator, police
officer Can produce rainbows visible light
when there are water
7. The mouse is warmer than the grass, so it droplets in the sky
gives off more infrared waves.
3. Helpful: 1) Treat cancer; 2) kill bacteria in food.
8. visible light
Harmful: 1) can kill normal cells in your body.
9. There should be a stick figure with a hat and
4. UV light must be able to travel through
shoes. The hat should be colored red with
clouds. Then, it does not need to be sunny
“700 nm” written in red next to it, and the
and warm for you to get a sunburn.
shoes should be violet with “400 nm” in
violet next to them.
SECTION 3 INTERACTIONS OF LIGHT WAVES
10. No, visible light is part of sunlight, which
also includes ultraviolet light and the other 1. 30°
ranges of the EM spectrum. 2. 30°
11. Too much X-ray exposure hurts or kills cells. 3. The left-hand image should be circled.
X rays can’t get through lead. 4. A luminous object is a light source. An illu-
12. X rays pass through muscles and skin but minated object reflects light from
not bones. The X rays show the shapes of somewhere else.
the bones when they hit the film.

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Interactive Textbook Answer Key 96 Physical Science
 Physical Science Answer Key continued

5. Its energy is absorbed by particles it inter- 3. allows light to pass through unimpeded
acts with. 4. Rain is transparent, fog is translucent, and
6. scattering of blue light snow is opaque.
7. It will bend away from the boundary. Light 5. 700 nm, 700 nm
travels more slowly through water than air. 6. the colors of light that reflect from it
8. something you think you see that isn’t really 7. The black hairs absorb all the colors of light
there energy, so they feel warmer.
9. It refracts. 8. red, blue, and green
10. They are both the bending of light. 9. Combine a red light and a green light.
Diffraction is light bending around things;
10. They absorb some colors of light and reflect
refraction is light bending when it moves
others.
from one material to another.
11. Yellow is a primary pigment. Pigments don’t
11. the same size or smaller
combine the same way light does.
12. constructive interference, destructive
12. yellow, cyan, and magenta
interference
13. destructive Review
14. Most light we see is made of many different 1. When white light shines on the grass, only
wavelengths, which don’t usually combine in green light is reflected. All the other colors
total destructive or constructive of light are absorbed. Thus, the grass looks
interference. green.
15. Left to right and top to bottom: Light inter- 2. Possible answers: Tissue paper and gauze
acts with light; light gets dimmer; light are translucent; cardboard and metal are
interacts with particles; constructive inter- opaque.
ference, destructive interference, diffraction, 3. Colors of light combine by color addition
refraction, reflection, rainbow, dimmer beam because you see all the light. Pigments com-
bine by color subtraction because you see the
Review
remaining colors after the others are absorbed.
1. The beam of light is wider because of scat-
4. the colors of light that it transmits
tering that causes light to change directions.
The beam of light is dimmer because of both 5. cyan, magenta, yellow
scattering and absorption.
2. Condition Wave interaction
Chapter 23 Light and Our
A log is sticking up from refraction World
the water. It looks as if its
top and bottom are not SECTION 1 MIRRORS AND LENSES
attached.
1. a straight line
The edge of a shadow is diffraction
blurry. 2. It bends.
You can see your image in (regular) reflection 3. by shape
the mirror.
4. The image is reversed left to right.
A beam of light becomes absorption
dimmer farther away from 5. virtual images
its source. 6. a mirror that curves inward
3. The television is a light source, so you can 7. The focal point is the point through which
see it. The table must be illuminated for you light rays reflect. The focal length is the dis-
to see it. tance between the mirror’s surface and the
4. The spoon produces regular reflection, but focal point.
the cloth produces diffuse reflection. 8. A right-side-up, virtual image will form.
9. in front of the mirror
SECTION 4 LIGHT AND COLOR 10. The real image is smaller and is upside-
1. No, transmission of light is what lets you see down. The virtual image is larger and is
what’s on the other side. right-side-up.
2. reflection, absorption, transmission 11. virtual
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Interactive Textbook Answer Key 97 Physical Science