HIGH SCHOOL SCIENCE
Physical
Science 6:
Waves
WILLMAR PUBLIC SCHOOL
2013-2014 EDITION
C HAPTER 6
Waves
In this chapter you will:
1. Describe frequency, period, wavelength, and wave
speed for different kinds of waves.
2. Describe how to measure amplitude and relate amplitude to the energy of a wave.
3. Describe the properties of sound waves and explain
how sound is produced.
4. Explain how relative motion determines the frequency of sound an observer hears.
5. Analyze the functions of the main regions of the human ear.
6. Rank and classify electromagnetic waves based on
their frequencies and wavelengths.
7. Describe the uses for different waves of the electromagnetic spectrum.
S ECTION 6.1
Waves
O BJECTIVES :
1. Describe frequency, period, wavelength, and
wave speed for different kinds of waves.
2. Describe how to measure amplitude and relate
amplitude to the energy of a wave.
Vocabulary:
periodic motion
cycle
period
mechanical wave
medium
transverse wave
longitudinal wave
surface waves
frequency
wavelength
amplitude
How do surfers know when the next wave is coming? If they
count the time between two successive crests, the next crest
usually will come after this same time interval. Any motion
that repeats at regular time intervals is called periodic
motion. A cycle is a complete motion that returns to its
starting point. The time required for one cycle is called the
period.
A mechanical wave is a disturbance in matter that transfers
energy through the matter. A mechanical wave starts when
matter is disturbed. A source of energy is needed to disturb
matter and start a mechanical wave.
The energy of a mechanical wave can travel only through
matter. The matter through which the wave travels is called
the medium or media.
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There are three types of mechanical waves: transverse,
longitudinal, and surface waves. They differ in how particles
of the medium move. A transverse wave is a wave in which
the vibration is at right angles to the direction in which the
wave travels. In a transverse wave, particles of the medium
vibrate up and down perpendicular to the direction of the
wave. A longitudinal wave is a wave in which the vibration
parallel to the direction the wave travels. In a longitudinal
wave, particles of the medium vibrate back and forth parallel
to the direction of the wave. A surface wave is a mechanical
wave that propagates along the interface between differing
media. In a surface wave, particles of the medium vibrate both
up and down and back and forth, so they end up moving in a
circle.
A transverse wave can be characterized by the high and low
points reached by particles of the medium as the wave passes
through. The high points are called crests, and the low points
are called troughs.
Any periodic motion has a frequency, which is the number of
complete cycles in a given time. For a wave, the frequency is
the number of wave cycles that pass a point in a given time.
Frequency is measured in cycles per second, or hertz (Hz).
Wavelength is the distance between a point on one wave
and the same point on the next cycle of the wave. A transverse
wave is characterized by the high and low points reached by
particles of the medium as the wave passes through. The high
points are called crests, and the low points are called troughs.
For a transverse wave, wavelength is measured between
adjacent crests or between adjacent troughs. For a
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longitudinal wave, wavelength is the distance between
adjacent compressions or rarefactions.
energy of the disturbance to pass from particle to particle
through the medium.
The amplitude of a wave is the maximum displacement of
the medium from its rest position. The more energy a wave
has, the greater is its amplitude.
The amplitude of a transverse wave is the distance from the
rest position to a crest or a trough. It takes more energy to
produce a wave with higher crests and deeper troughs.
Increasing the frequency of a wave decreases its wavelength.
You can calculate the speed of a wave by dividing its
wavelength by its period. You can also calculate wave speed by
multiplying wavelength by frequency.
In order to measure the amplitude of a longitudinal wave, you
look at the maximum displacement of a point from its rest
position. The more energy the wave has, the more the medium
will be compressed or displaced.
Short-wavelength waves have more energy than longwavelength waves of the same amplitude. A higher-frequency
wave has more energy than a lower-frequency wave with the
same amplitude
The speed of a wave can change if it enters a new medium or if
variables such as pressure and temperature change. However,
for many kinds of waves, the speed of the waves is roughly
constant for a range of different frequencies. The speed of
most waves depends on the medium, or the matter through
which the waves are traveling. Generally, waves travel fastest
through solids and slowest through gases. That’s because
particles are closest together in solids and farthest apart in
gases. When particles are farther apart, it takes longer for the
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Section Review:
1. What is period in respects to waves?
2. How do you think surface waves are related to transverse
and longitudinal waves?
1. What unit is used to measure frequency?
2.In the diagram, which wave has a greater frequency?
3. How is wavelength measured in a transverse wave?
4.How is wavelength measured in a longitudinal wave?
5. What happens to the wavelength as you increase the
frequency?
6.What is the equation for the speed of waves?
7. How can the speed of a wave change?
8.How is energy related to amplitude?
9.In a transverse wave, how is amplitude measured?
10.In a longitudinal wave, how is amplitude measured?
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S ECTION 6.2
Wave Interactions
O BJECTIVES :
1. Identify ways that waves can interact with
matter.
Waves interact with matter in several ways. The interactions
occur when waves pass from one medium to another. The
types of interactions are reflection, refraction, and diffraction.
An echo is an example of wave reflection. Reflection occurs
when waves bounce back from a surface they cannot pass
through. Reflection can happen with any type of waves, not
just sound waves. For example, light waves can also be
reflected. In fact, that’s how we see most objects. Light from a
light source, such as the sun or a light bulb, shines on the
object and some of the light is reflected. When the reflected
light enters our eyes, we can see the object.
2. Define and give examples of wave reflection,
refraction, and diffraction.
Vocabulary:
reflection
angle of reflection
refraction
diffraction
Reflected waves have the same speed and frequency as the
original waves before they were reflected. However, the
direction of the reflected waves is different. When waves
strike an obstacle head on, the reflected waves bounce straight
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back in the direction they came from. When waves strike an
obstacle at any other angle, they bounce back at the same
angle but in a different direction. The waves are reflected at
the same angle, called the angle of reflection, but in a
different direction. Notice that both angles are measured
relative to a line that is perpendicular to the wall.
Refraction is another way that waves interact with matter.
Refraction occurs when waves bend as they enter a new
medium at an angle. You can see an example of refraction in
the picture below. Light bends when it passes from air to
water or from water to air. The bending of the light traveling
from the fish to the man’s eyes causes the fish to appear to be
in a different place from where it actually is. Waves bend as
they enter a new medium because they start traveling at a
different speed in the new medium. For example, light travels
more slowly in water than in air. This causes it to refract when
it passes from air to water or from water to air.
Did you ever notice that you can hear sounds around the
corners of buildings even though you can’t see around them?
As you can see from the figure, sound waves spread out and
travel around obstacles. Diffraction is the bending or
turning of a wave when it encounters an obstacle. It also
occurs when waves pass through an opening in an obstacle.
All waves may be diffracted, but it is more pronounced in
some types of waves than others. For example, sound waves
bend around corners much more than light does. That’s why
you can hear but not see around corners.
For a given type of waves, such as sound waves, how much the
waves diffract depends on the size of the obstacle (or opening
in the obstacle) and the wavelength of the waves. The Figure
5.65 shows how the amount of diffraction is affected by the
size of the opening in a barrier. Note that the wavelength of
the wave is the distance between the vertical lines.
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Section Review:
1. What happens if waves strike a reflective surface at an
angle other than 90 °?
2. Why does refraction occur?
3. Where would the fish appear to be if the man looked
down at it from straight above its actual location?
4. When does diffraction occur?
5. How is wavelength related to diffraction?
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S ECTION 6.3
In science, sound is defined as the transfer of energy from a
vibrating object in waves that travel through matter. Most
people commonly use the term sound to mean what they hear
when sound waves enter their ears. The tree above generated
sound waves when it fell to the ground, so it made sound
according to the scientific definition. But the sound wasn’t
detected by a person’s ears if there was nobody in the forest.
Sound
O BJECTIVES :
1. Describe the properties of sound waves and
explain how sound is produced.
2. Explain how relative motion determines the
frequency of sound an observer hears.
3. Analyze the functions of the main regions of
the human ear.
Vocabulary:
sound waves
speed of sound
intensity
loudness
wave frequency
pitch
infrasound
ultrasound
Doppler effect
outer ear
middle ear
inner ear
All sound waves begin with vibrating matter. Sound waves
are longitudinal waves—compressions and rarefactions that
travel through a medium. Most of the sounds we hear reach
our ears through the air, but sounds can also travel through
liquids and solids. If you swim underwater—or even submerge
your ears in bathwater—any sounds you hear have traveled to
your ears through the water. Some solids, including glass and
metals, are very good at transmitting sounds. Foam rubber
and heavy fabrics, on the other hand, tend to muffle sounds.
They absorb rather than pass on the sound energy.
Many behaviors of sound can be explained using a few
properties—speed, intensity, loudness, frequency and pitch.
It takes time for sound to travel from place to place, thus they
have speed. The speed of sound is the distance that sound
waves travel in a given amount of time. In general, sound
waves travel fastest in solids, slower in liquids, and slowest in
gases. This is partly due to the fact that particles in a solid
tend to be closer together than particles in a liquid or a gas.
The speed of sound depends on many factors, including the
density of the medium and how elastic the medium is. The
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speed of sound also depends on the temperature of the
medium. For a given medium, sound has a slower speed at
lower temperatures.
Intensity is the rate at which a wave's energy flows through a
given area. Sound intensity depends on both the wave's
amplitude and the distance from the sound source. Sound
intensity levels are measured in units called decibels.
can hear, and ultrasound is sound at frequencies higher
than most people can hear.
The Doppler effect is a change in sound frequencies caused
by the motion of the sound source, motion of the listener, or
both. As a source of sound approaches, you hear a higher
frequency. When the sound source moves away, you hear a
lower frequency.
Unlike intensity, loudness is subjective—it is subject to a
person's interpretation. Loudness is a physical response to
the intensity of sound, modified by physical factors. The
loudness you hear depends, of course, on sound intensity. As
intensity increases, loudness increases. But loudness also
depends on factors such as the health of your ears and how
your brain interprets the information in sound waves.
Wave frequency is the number of waves that pass a fixed
point in a given amount of time. High-pitched sounds, like the
sounds of the piccolo, have high-frequency waves. Lowpitched sounds, like the sounds of the tuba, have lowfrequency waves. The frequency of a sound wave depends on
how fast the source of the sound is vibrating.
Pitch is the frequency of a sound as you perceive it. Pitch
does depend upon a wave's frequency. High-frequency sounds
have a high pitch, and low-frequency sounds have a low pitch.
Most people hear sounds between 20 hertz and 20,000 hertz.
Infrasound is sound at frequencies lower than most people
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The Anatomy of the Ear: The outer ear gathers and focuses
sound into the middle ear, which receives and amplifies the
vibrations. The inner ear uses nerve endings to sense
vibrations and send signals to the brain.
The outer ear is the part of the ear you can see funnels sound
waves down the ear canal, a tunnel about 2.5 cm long. There,
sound waves strike the eardrum, a tightly stretched
membrane between the outer and middle ear. The eardrum
vibrates at the same frequency as the sound waves striking it.
The middle ear contains three tiny bones (Auditory Bones)—
the hammer, the anvil, and the stirrup. When the eardrum
vibrates, the hammer vibrates at the same frequency. The
hammer strikes the anvil, which in turn moves the stirrup
back and forth. The three bones act as a lever system to
amplify the motion of the eardrum.
Section Review:
1. What properties describe the behaviors of sound?
2. In general, how does that state of matter (solids, liquids,
& gases) affect the speed of sound?
3. What does the sound intensity depend on?
4. How is intensity different than loudness?
5. What is the normal range people hear?
6. What happens to the sound as the source approaches
you?
7. What happens to the sound as the source moves away
from you?
8. Describe how the ear works.
The inner ear is the innermost part of the ear consisting of
the cochlea and semicircular canals. In the inner ear,
vibrations from the stirrup travel into the cochlea, a spiralshaped canal filled with fluid. The inside of the cochlea is
lined with thousands of nerve cells with tiny hair-like
projections. As the fluid in the cochlea vibrates, the
projections sway back and forth and send electrical impulses
to the brain.
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S ECTION 6.4
Light
O BJECTIVE
Electromagnetic waves are waves that consist of vibrating
electric and magnetic fields. Like other waves, electromagnetic waves transfer energy from one place to another.
The transfer of energy by electromagnetic waves is called
electromagnetic radiation. Electromagnetic waves can
transfer energy through matter or across empty space.
1. Rank and classify electromagnetic waves based
on their frequencies and wavelengths.
2. Describe the uses for different waves of the
electromagnetic spectrum.
Vocabulary:
electromagnetic waves
electromagnetic radiation
electromagnetic spectrum
radio waves
infrared rays
visible light
ultraviolet rays
X-rays
gamma rays
The full range of frequencies of electromagnetic radiation is
called the electromagnetic spectrum. Electromagnetic
waves vary in their wavelengths, frequencies, and energy
levels. Electromagnetic waves with shorter wavelengths have
higher frequencies and more energy. The full range of
electro- magnetic waves makes up the electromagnetic
spectrum. The electromagnetic spectrum includes radio
waves, infrared rays, visible light, ultraviolet rays, X-rays, and
gamma rays.
Radio waves have the longest wavelengths in the
electromagnetic spectrum, from 1 millimeter to as much as
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thousands of kilometers or longer. Because they are the
longest waves, radio waves also have the lowest frequencies in
the spectrum—300,000 megahertz (MHz) or less. Radio
waves are used in radio and television technologies, as well as
in microwave ovens and radar. In radio broadcasts, sounds
are encoded in radio waves by changing either the amplitude
(AM) or frequency (FM) of the waves. The encoded waves are
broadcast from a tower and changed back to sounds by radio
receivers. In television broadcasts, sounds and pictures are
encoded in radio waves, broadcast from a tower, and changed
back to sounds and pictures by television sets. A cell phone
encodes the sounds of the caller’s voice in microwaves by
changing the frequency of the waves. The encoded
microwaves then travel through the air to a cell tower and
eventually to the receiver of the person being called. The
receiver decodes the microwaves and changes them back to
sounds. Radar stands for radio detection and ranging. It is the
use of reflected microwaves to determine vehicle speeds, track
storms, or detect air traffic.
Electromagnetic waves that are commonly called light fall
roughly in the middle of the electromagnetic spectrum. Light
includes infrared light, visible light, and ultraviolet light.
Infrared rays have higher frequencies than radio waves and
lower frequencies than red light. Infrared wavelengths vary
from about 1 millimeter to about 750 nanometers. (A
nanometer is 10−9 meters, or one millionth of a millimeter.)
Infrared rays are used as a source of heat and to discover
areas of heat differences. The sun gives off infrared light as
do flames and living things. You can’t see infrared light waves,
but you can feel them as heat. But infrared cameras and night
vision goggles can detect infrared light waves and convert
them to visible images.
The visible part of the electromagnetic spectrum is visible
light that the human eye can see. Each wavelength in the
visible spectrum corresponds to a specific frequency and has a
particular color. The colors include red, orange, yellow,
green, blue, indigo and violet. These colors combine to form
white light. Visible light is used for seeing and everyday use.
The wavelengths of ultraviolet rays vary from about
400 nanometers to about 4 nanometers. Ultraviolet radiation
has higher frequencies than violet light. Ultraviolet rays have
applications in health and medicine, and in agriculture.
Ultraviolet light also has more energy, which makes it useful
for killing germs. Too much exposure to ultraviolet light can
damage the skin.
X-rays have very short wavelengths, from about
12 nanometers to about 0.005 nanometers. They have higher
frequencies than ultraviolet rays. X-rays have high energy and
can penetrate matter that light cannot. X-rays are used in
medicine, industry, and transportation to make pictures of the
inside of solid objects. X-rays have enough energy to pass
through soft tissues such as skin, although not enough to pass
through bones and teeth, which are very dense. The bright
areas in the skull X-ray shows where X-rays were absorbed by
teeth and bones. X-rays are used not only for medical and
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dental purposes but also to screen luggage at airports. X-rays
can penetrate the body, damage cells, and cause cancer.
Gamma rays have the shortest wavelengths in the
electromagnetic spectrum, about 0.005 nanometer or less.
They have the highest frequencies and therefore the most
energy and the greatest penetrating ability of all the
electromagnetic waves. Sources of gamma rays include
radioactive atoms, nuclear explosions, and stars. Gamma rays
from space are absorbed by Earth’s atmosphere. Exposure to
tiny amounts of gamma rays are tolerable, but overexposure
can be deadly. Gamma rays can destroy living cells, produce
mutations, and cause cancer. Gamma rays are used in the
medical field to kill cancer cells and make pictures of the
brain, and in industrial situations as an inspection tool. They
can be used to treat cancer by focusing the deadly rays on
cancer cells.
Section Review:
1. Describe the relationship between the wavelength and
frequency of electromagnetic waves.
2. What is included in the electromagnetic spectrum?
3. What is range of wavelength for each of the
electromagnetic spectrum?
4. Describe how each part of the electromagnetic spectrum
is used.
5. The composition of the ionosphere changes somewhat
from day to night. The changes make the nighttime
ionosphere even better at reflecting AM radio waves.
How do you think this might affect the distance AM
radio waves travel at night?
6. You should apply sunscreen even on cloudy days.
Explain why it is important?
7. What do the dark areas in an X-ray image represent?
8. Predict how gamma rays might affect living things on
Earth if they weren’t absorbed by the atmosphere.
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