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Table of Contents
Chapter: Sound and Light
Section 1: Sound
Section 2: Reflection and Refraction
of Light
Section 3: Mirrors, Lenses, and
the Eye
Section 4: Light and Color
Sound
1
Sound
• When an object vibrates, it creates sound
waves.
• Sound waves are compressional waves.
• The compression moves away as these
molecules collide with other molecules in air.
• A rarefaction is formed where the molecules
are farther apart.
• This series of compressions and rarefactions
is the sound wave that you hear.
Sound
1
Sound
• The material in which a sound
wave moves is called a medium.
• Sound waves travel in solids, liquids, and
other gases as a vibrating object transfers
energy to the particles in the material.
Sound
1
Sound
• The speed of a sound
wave in a medium
depends on the type
of substance and
whether it is a solid,
liquid, or gas.
• Sound travels
slowest in gases
and fastest in
solids.
Sound
1
Amplitude and Energy of Sound
Waves
• The amount of energy a wave carries
corresponds to its amplitude.
• More energy is transferred to the medium
when the particles of the medium are
forced closer together in the compressions
and spread farther apart in the rarefactions.
Sound
1
Amplitude and Energy of Sound
Waves
Sound
1
Intensity and Loudness
• The amount of energy transferred by a sound
wave through a certain area each second is
the intensity of the sound wave.
• Loudness is the human perception of sound
intensity.
Sound
1
Intensity and Loudness
• Each unit on the scale for sound intensity is
called a decibel.
Sound
1
Pitch and Frequency
• Pitch is the human perception of the
frequency of sound waves.
• Frequency is
a measure of
how many
wavelengths
pass a
particular
point each
second.
Sound
1
Pitch and Frequency
• Frequency is measured in hertz (Hz).
• A healthy human ear can hear sound
waves with frequencies from about 20
Hz to 20,000 Hz.
• Sound frequencies above 20,000 Hz
are called ultrasonic waves.
• Infrasonic, or subsonic, waves have
frequencies below 20 Hz.
Sound
1
Doppler Effect
• The change in pitch or frequency due
to the relative motion of a wave
source is called the Doppler effect.
Sound
1
A Moving Source of Sound
Sound
1
A Moving Listener
• You also can hear the Doppler effect
when you are moving past a sound
source that is standing still.
• The Doppler effect happens any time
the source of a sound is changing
position relative to the listener.
Sound
1
Using Sound
• Echolocation is the process of locating
objects by emitting sounds and detecting
the sound waves that reflect back.
• Sonar is a system that uses the reflection of
underwater sound waves to detect objects.
• Reflected ultrasonic waves are used
to examine different body parts.
Section Check
1
Question 1
Sound frequencies above 20,000 Hz are called
__________ waves.
A. infrasonic
B. infrared
C. subsonic
D. ultrasonic
Section Check
1
Answer
The answer is D. Subsonic and infrasonic
are waves with frequencies below 20 Hz.
Section Check
1
Question 2
Describe the Doppler effect.
Answer
The Doppler effect is the change in pitch due
to a moving wave source.
Section Check
1
Question 3
In which of the following environments would
sound waves not travel?
A. at altitudes of 10,000 – 15,000 m
B. in solid aluminum
C. on the Moon
D. under water
Section Check
1
Answer
The answer is C. Sound waves require a medium
through which to travel. So, sound waves cannot
travel through empty space.
Reflection and Refraction of Light
2
The Interaction of
Light and Matter
Absorption, Transmission,
and Reflection
• The opaque
material in this
candleholder only
absorbs and reflects
light—no light
passes through it.
Reflection and Refraction of Light
2
Absorption, Transmission,
and Reflection
• Materials that allow some light to pass
through them, like the material of this
candleholder are
described as
translucent.
Reflection and Refraction of Light
2
Absorption, Transmission,
and Reflection
• Transparent materials, such as this
candleholder transmit almost all the light
striking them,
so you can see
objects clearly
through them.
Reflection and Refraction of Light
2
Reflection of Light
Regular and Diffuse Reflection
• A smooth, even surface such as a pane of glass
produces a sharp image by reflecting parallel
light waves in only one direction.
• Reflection of light waves from a
smooth surface is regular reflection.
• To cause a regular reflection, the
roughness of a surface must be less
than the wavelengths it reflects.
Reflection and Refraction of Light
2
Regular and Diffuse Reflection
• Reflection of light from a rough surface
is diffuse reflection.
• Diffuse reflection is a type of scattering
that occurs when light waves traveling in
one direction are made to travel in many
different directions.
Reflection and Refraction of Light
2
Refraction of Light
• Refraction is
caused by a
change in the
speed of a
wave when it
passes from
one material
to another.
Reflection and Refraction of Light
2
Refraction of Light
• Index of refraction is the ratio of the speed
of light in a vacuum to the speed of light in
the material.
• The index of refraction indicates how much
the speed of light is reduced in the material
compared to its speed in empty space.
• The larger the index of refraction, the
more light is slowed down in the material.
Reflection and Refraction of Light
2
Refraction of Light
• White light, such as sunlight, is made up
of light waves with range of wavelengths.
• Prism refracts the
light twice—once
when it enters the
prism and again
when it leaves the
prism.
Reflection and Refraction of Light
2
Refraction of Light
• The longer wavelengths of light are slowed
less and are bent the least.
• As a result, the
different colors
are separated
when they emerge
from the prism.
Reflection and Refraction of Light
2
Mirages
• Mirages result when the air at ground level is
much warmer or cooler than the air above.
Reflection and Refraction of Light
2
Mirages
• The density of air increases as air cools
and light waves move slower in cooler
air than in warmer air.
• Light waves are refracted as they pass through
air layers with different temperatures.
Section Check
2
Question 1
What happens to light waves that strike
an object?
Answer
Light waves that strike objects can be
absorbed, reflected, or transmitted.
Section Check
2
Question 2
What is the difference between refraction
and reflection?
Answer
Refraction occurs if a light wave changes speed
in moving from one material to another.
Reflection occurs when light waves are returned
or thrown back from a surface.
Section Check
2
Question 3
__________ material only absorbs and reflects
light; no light passes through.
A. Transparent
B. Translucent
C. Opaque
D. Mirage
Section Check
2
Answer
The answer is C. Transparent and translucent
materials both allow some light to pass through.
Mirrors, Lenses, and the Eye
3
Light Rays
Mirrors
• A mirror is any surface that produces a
regular reflection.
Plane Mirrors
• A flat smooth mirror is a plane mirror.
Mirrors, Lenses, and the Eye
3
Plane Mirrors
• Light rays from a light
source strike you.
• Every point that is struck
by the light rays reflects
these rays so they travel
outward in all directions.
• Light rays are reflected
from the mirror back to
your eyes.
Mirrors, Lenses, and the Eye
3
Virtual and Real Images
• Plane mirrors always form virtual images.
• If light rays from an object pass through
the location of the image, the image is
called the real image.
• If the surface of a
mirror is curved
inward, it is called a
concave mirror.
Mirrors, Lenses, and the Eye
3
Virtual and Real Images
• The image formed by a concave mirror
depends on the location of the object relative
to the focal point.
Mirrors, Lenses, and the Eye
3
Virtual and Real Images
• An object between one and two focal lengths
from a concave mirror is real, inverted, and
larger than the object.
• An object closer than one focal length from a
concave mirror produces a virtual image that
is upright and larger than the object.
Mirrors, Lenses, and the Eye
3
Convex Mirrors
• A mirror that curves outward like the back
of a spoon is called a convex mirror.
• Reflected rays diverge and never meet,
so a convex mirror
forms only a
virtual image.
• The image also
is upright and
smaller than the
actual object is.
Mirrors, Lenses, and the Eye
3
Lenses
• A lens is a transparent object with at
least one curved surface that causes
light rays to refract.
Convex Lenses
• A convex lens is thicker in the middle
than at the edges.
Mirrors, Lenses, and the Eye
3
Convex Lenses
• Light rays are refracted toward
the center of the lens.
• All light rays
are refracted
so they pass
through a
single point,
which is the
focal point of
the lens.
Mirrors, Lenses, and the Eye
3
Convex Lenses
• Lenses with flatter sides have longer focal
lengths.
Mirrors, Lenses, and the Eye
3
Concave Lenses
• A concave lens is thinner in the middle
and thicker at the edges.
• Light rays that pass through a concave
lens bend away from the optical axis.
Mirrors, Lenses, and the Eye
3
The Human Eye
• Light enters your eye through a transparent
covering on your eyeball called the cornea.
• The cornea
causes light
rays to bend
so that they
converge.
• Light then
passes through
the pupil.
Mirrors, Lenses, and the Eye
3
The Human Eye
• Behind the pupil is a flexible convex lens.
• The retina is the inner lining of your eye,
containing
light sensitive
cells that
convert an
image into
electrical
signals.
Mirrors, Lenses, and the Eye
3
Brightness and Intensity
• The human eye can adjust to the brightness
of the light that strikes it.
• Light intensity is the amount of light energy
that strikes a certain area each second.
• Brightness is the human perception of light
intensity.
• Eyes respond to bright light by decreasing the
size of your pupil.
Mirrors, Lenses, and the Eye
3
Correcting Vision Problems
• If you can see distant objects clearly but can’t
bring nearby objects into focus, then you are
farsighted.
Mirrors, Lenses, and the Eye
3
Correcting Vision Problems
• The eyeball might be too short or the lens
isn’t curved enough to form a sharp image
of nearby objects on the retina.
Mirrors, Lenses, and the Eye
3
Nearsightedness
• Eyes cannot form a sharp image on the
retina of an object that is far away.
• The image is formed in front of the retina.
Section Check
3
Question 1
A __________ mirror curves inward.
A. concave
B. convex
C. obtuse
D. plane
Section Check
3
Answer
The answer is A. A concave mirror curves
inward and forms a real image. A convex
mirror curves outward and forms a virtual
image.
Section Check
3
Question 2
What type of lens refracts light rays away from
the optical axis?
Answer
Concave lenses are thicker at the edges and
refract light rays away from the optical axis.
Section Check
3
Question 3
In nearsightedness, the image forms _______
the retina and a _______ lens can be used to
correct it.
A. behind, concave
B. behind, convex
C. in front of, concave
D. in front of, convex
Section Check
3
Answer
The answer is C. The image forms in front of
the retina and a concave lens corrects it.
Light and Color
4
Why Objects Have Color
• White light is a blend of all colors of visible
light.
• Black is the absence of visible light.
Light and Color
4
Colored Filters
• A filter is a transparent material that transmits
one or more colors of light but absorbs all
others.
• The color
of a filter is
the color of
the light
that it
transmits.
Light and Color
4
Seeing Color
• The retina is made up of two types of cells
that absorb light.
• A cone enables you to distinguish colors and
detailed shapes of objects.
Light and Color
4
Cones and Rods
• Your eyes have three types of cones.
• Red cones respond to mostly red and yellow
light.
• Green cones respond to mostly yellow and
green.
Light and Color
4
Cones and Rods
• Blue cones respond to mostly blue and violet
light.
• A rod is sensitive to dim light and enables
you to see at night.
• Rod cells do not enable you to see colors.
Light and Color
4
Color Blindness
• If cone cells do not function properly, you
might not be able to distinguish certain
colors.
• This condition is called
color blindness.
• The most common form
of color blindness makes
it difficult to distinguish
between red and green.
Light and Color
4
Mixing Colors
• A pigment is a colored material that is used
to change the color of other substances.
• Red, green, and blue are the primary colors
of light.
• Mixing the primary colors in different
proportions can produce the colors you see.
Light and Color
4
Mixing Pigments
• You can make any pigment color by mixing
different amounts of the three primary
pigments—magenta, cyan, and yellow.
• Pigments both
absorb and reflect
a range of colors.
Light and Color
4
Mixing Pigments
• The area where the colors overlap appears
to be black because the three blended
primary pigments absorb all the primary
colors of light.
Section Check
4
Question 1
An object’s color depends on the __________
it reflects.
Answer
An object’s color depends on the wavelengths
of light it reflects. If an object absorbs all
wavelengths of visible light except green, the
object appears green.
Section Check
4
Question 2
What are the two types of light-detecting cells
in the eye?
Answer
The two types of light-detecting cells that
make up the retina are the rods and cones.
Section Check
4
Question 3
What is the appearance of the three primary
colors of pigment when they are mixed?
A. black
B. brown
C. gray
D. white
Section Check
4
Answer
The answer is A. The three primary colors of
pigment are magenta, cyan and yellow, and
appear black when they are mixed.
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