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Chapter: Sound and Light
Table of Contents
Section 1: Sound
Section 2: Reflection and Refraction
of Light
Section 3: Mirrors, Lenses, and
the Eye
Section 4: Light and Color
• When an object vibrates, it creates sound waves.
• Sound waves are compressional waves.
Sound
Sound
1
• 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.
• 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
Sound
1
• 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
Sound
1
• 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.
Amplitude and Energy of Sound Waves
Sound
1
• 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.
Intensity and Loudness
Sound
1
• Each unit on the scale for sound intensity is called a decibel.
Intensity and Loudness
Sound
1
• Pitch is the human perception of the frequency of sound waves.
Pitch and Frequency
Sound
1
• Frequency is a measure of how many wavelengths pass a particular point each second.
• Frequency is measured in hertz (Hz).
Pitch and Frequency
Sound
1
• 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.
• The change in pitch or frequency due to the relative motion of a wave source is called the Doppler effect.
Doppler Effect
Sound
1
A Moving Listener
Sound
1
• 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.
Using Sound
Sound
1
• 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.
1
Section Check
Question 1
Sound frequencies above 20,000 Hz are called
__________ waves.
A. infrasonic
B. infrared
C. subsonic
D. ultrasonic
1
Section Check
The answer is D. Subsonic and infrasonic
are waves with frequencies below 20 Hz.
Answer
1
Section Check
Question 2
Describe the Doppler effect.
Answer
The Doppler effect is the change in pitch due
to a moving wave source.
1
Section Check
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
1
Section Check
Answer
The answer is C. Sound waves require a medium
through which to travel. So, sound waves cannot
travel through empty space.
The Interaction of Light and Matter
Reflection and Refraction of Light
2
• The opaquematerial in this candleholder only absorbs and reflects light—no light passes through it.
Absorption, Transmission, and Reflection
• Materials that allow some light to pass through them, like the material of thiscandleholder are described as translucent.
Absorption, Transmission, and Reflection
Reflection and Refraction of Light
2
Absorption, Transmission, and Reflection
Reflection and Refraction of Light
2
• Transparent materials, such as this candleholder transmit almost all the lightstriking them, so you can see objects clearly through them.
Reflection of Light
Reflection and Refraction of Light
2
• A smooth, even surface such as a pane of glass produces a sharp image by reflecting parallel light waves in only one direction.
Regular and Diffuse Reflection
• 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.
Regular and Diffuse Reflection
Reflection and Refraction of Light
2
• 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 of light from a rough surface is diffuse reflection.
Refraction of Light
Reflection and Refraction of Light
2
• Refraction is caused by a change in the speed of a wave when it passes from one material to another.
Refraction of Light
Reflection and Refraction of Light
2
• 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.
Refraction of Light
Reflection and Refraction of Light
2
• 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.
Refraction of Light
Reflection and Refraction of Light
2
• 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.
Mirages
Reflection and Refraction of Light
2
• Mirages result when the air at ground level is much warmer or cooler than the air above.
Mirages
Reflection and Refraction of Light
2
• 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.
2
Section Check
Question 1
What happens to light waves that strike
an object?
Answer
Light waves that strike objects can be
absorbed, reflected, or transmitted.
2
Section Check
Question 2
What is the difference between refraction
and reflection?
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.
Answer
2
Section Check
Question 3
__________ material only absorbs and reflects
light; no light passes through.
A. Transparent
B. Translucent
C. Opaque
D. Mirage
2
Section Check
Answer
The answer is C. Transparent and translucent
materials both allow some light to pass through.
• A mirror is any surface that produces a regular reflection.
• A flat smooth mirror is a plane mirror.
Light Rays
Mirrors, Lenses, and the Eye
3
Mirrors
Plane Mirrors
Plane Mirrors
Mirrors, Lenses, and the Eye
3
• 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.
• Light rays from a light source strike you.
Virtual and Real Images
Mirrors, Lenses, and the Eye
3
• 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.
• Plane mirrors always form virtual images.
Virtual and Real Images
Mirrors, Lenses, and the Eye
3
• The image formed by a concave mirror depends on the location of the object relative to the focal point.
Virtual and Real Images
Mirrors, Lenses, and the Eye
3
• 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.
Convex Mirrors
Mirrors, Lenses, and the Eye
3
• A mirror that curves outward like the back of a spoon is called a convex mirror.
• The image also is upright and smaller than the actual object is.
so a convex mirror forms only a virtual image.
• Reflected rays diverge and never meet,
• A lens is a transparent object with at least one curved surface that causes light rays to refract.
• A convex lens is thicker in the middle than at the edges.
Lenses
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.
Convex Lenses
Mirrors, Lenses, and the Eye
3
Convex Lenses
Mirrors, Lenses, and the Eye
3
• Lenses with flatter sides have longer focal lengths.
• 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.
Concave Lenses
Mirrors, Lenses, and the Eye
3
• 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.
The Human Eye
Mirrors, Lenses, and the Eye
3
• Light then passes through the pupil.
The Human Eye
Mirrors, Lenses, and the Eye
3
• Behind the pupil is a flexible convex lens.
containing light sensitive cells that convert an image into electrical signals.
• The retina is the inner lining of your eye,
• 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 and Intensity
Mirrors, Lenses, and the Eye
3
• Brightness is the human perception of light intensity.
• Eyes respond to bright light by decreasing the size of your pupil.
• If you can see distant objects clearly but can’t bring nearby objects into focus, then you are farsighted.
Correcting Vision Problems
Mirrors, Lenses, and the Eye
3
Correcting Vision Problems
Mirrors, Lenses, and the Eye
3
• The eyeball might be too short or the lens isn’t curved enough to form a sharp image of nearby objects on the retina.
• Eyes cannot form a sharp image on the retina of an object that is far away.
Nearsightedness
Mirrors, Lenses, and the Eye
3
• The image is formed in front of the retina.
3
Section Check
Question 1
A __________ mirror curves inward.
A. concave
B. convex
C. obtuse
D. plane
3
Section Check
The answer is A. A concave mirror curves
inward and forms a real image. A convex
mirror curves outward and forms a virtual
image.
Answer
3
Section Check
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.
3
Section Check
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
3
Section Check
Answer
The answer is C. The image forms in front of
the retina and a concave lens corrects it.
Why Objects Have Color
Light and Color
4
• White light is a blend of all colors of visible light.
• Black is the absence of visible light.
Colored Filters
Light and Color
4
• 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.
Seeing Color
Light and Color
4
• 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.
Cones and Rods
Light and Color
4
• Your eyes have three types of cones.
• Red cones respond to mostly red and yellow light.
• Green cones respond to mostly yellow and green.
Cones and Rods
Light and Color
4
• 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.
Color Blindness
Light and Color
4
• 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.
Mixing Colors
Light and Color
4
• 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.
Mixing Pigments
Light and Color
4
• 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.
Mixing Pigments
Light and Color
4
• The area where the colors overlap appears to be black because the three blended primary pigments absorb all the primary colors of light.
4
Section Check
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.
4
Section Check
Question 2
What are the two types of light-detecting cells
in the eye?
The two types of light-detecting cells that
make up the retina are the rods and cones.
Answer
4
Section Check
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
4
Section Check
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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