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Waves
Table of Contents
Section 1 Types of Waves
Section 2 Characteristics of Waves
Section 3 Interactions of Waves
Chapter 14
Objectives
• Recognize that waves transfer energy.
• Distinguish between mechanical waves and electromagnetic waves.
• Explain the relationship between particle vibration and wave motion.
• Distinguish between transverse waves and longitudinal waves.
Section 1 Types of WavesChapter 14
What Is a Wave?• A wave is a periodic disturbance in a solid, liquid, or
gas as energy is transmitted through a medium.
• Waves carry energy through matter or space.
• Most waves travel through a medium.• The matter through which a wave travels is called the
medium.
• Waves that require a medium are called mechanical waves.
Section 1 Types of WavesChapter 14
Formation and Movement of Ocean Waves
Section 1 Types of WavesChapter 14
What Is a Wave?, continued
• Light does not require a medium.• Light waves consist of changing electric and magnetic
fields in space.
• Light waves are called electromagnetic waves.
• An electromagnetic wave consists of oscillating electric and magnetic fields, which radiate outward at the speed of light.
Section 1 Types of WavesChapter 14
Electromagnetic Waves
Section 1 Types of WavesChapter 14
What Is a Wave?, continued
• Waves transfer energy.
• Energy may spread out as a wave travels.
• When sound waves travel in air, the waves spread out in spheres. As they travel outward, the spherical wave fronts get bigger, so the energy in the waves spreads out over a larger area.
Section 1 Types of WavesChapter 14
Tsunami
Section 1 Types of WavesChapter 14
Vibrations and Waves• Waves are related to vibrations.
• Most waves are caused by a vibrating object. • Electromagnetic waves may be caused by vibrating
charged particles. • In a mechanical wave, the particles in the medium also
vibrate as the wave passes through the medium.
• Vibrations involve transformations of energy.
Section 1 Types of WavesChapter 14
Wave Model
Section 1 Types of WavesChapter 14
Vibrations and Waves, continued
• Whenever a spring is expanded or compressed, it is exerting a force that pushes the mass back almost to the original resting position. • As a result, the mass will continue to bounce up and
down.
• This type of vibration is called simple harmonic motion.
• A wave can pass through a series of vibrating objects.
Section 1 Types of WavesChapter 14
Wave Model
Section 1 Types of WavesChapter 14
Vibrations and Waves, continued
• If the first mass were not connected to the other masses, it would keep vibrating up and down on its own. However, because it transfers its energy to the second mass, it slows down and then returns to its resting position. • A vibration that fades out as energy is transferred from
one object to another is called damped harmonic motion.
• The motion of particles in a medium is like the motion of masses on springs.
Section 1 Types of WavesChapter 14
Transverse and Longitudinal Waves• Particles in a medium can vibrate either up and down
or back and forth.
• Waves are often classified by the direction that the particles in the medium move as a wave passes by.
• Transverse waves have perpendicular motion.
• A transverse wave is a wave in which the particles of the medium move perpendicular to the direction the wave is traveling.
• Light waves are transverse waves.
Section 1 Types of WavesChapter 14
Transverse Wave
Section 1 Types of WavesChapter 14
Transverse and Longitudinal Waves• Longitudinal waves have parallel motion. • A longitudinal wave is a wave in which the particles
of the medium vibrate parallel to the direction of wave motion.• Sound waves are longitudinal waves.
• In a surface wave, particles move in circles.• Surface waves occur at the boundary between two
different mediums, such as between water and air.• The particles move both perpendicularly and parallel to
the direction that the wave travels.
Section 1 Types of WavesChapter 14
Longitudinal Wave
Section 1 Types of WavesChapter 14
Water Wave Motion
Section 1 Types of WavesChapter 14
Objectives
• Identify the crest, trough, amplitude, and wavelength of a wave.
• Define the terms frequency and period.
• Solve problems involving wave speed, frequency, and wavelength.
• Describe the Doppler effect.
Section 2 Characteristics of WavesChapter 14
Wave Properties
Section 2 Characteristics of WavesChapter 14
Wave Properties
• An ideal transverse wave has the shape of a sine curve.
Section 2 Characteristics of WavesChapter 14
• Waves that have the shape of a sine curve are called sine waves.
Wave Properties, continued
• Amplitude measures the amount of particle vibration.• The crest is the highest point of a transverse wave.
• The trough is the lowest point of a transverse wave.
• The amplitude is the maximum distance that the particles of a wave’s medium vibrate from their rest position.
Section 2 Characteristics of WavesChapter 14
Characteristics of a Wave
Section 2 Characteristics of WavesChapter 14
Wave Properties, continued• A longitudinal wave has compressions and rarefactions.
• The crowded areas are called compressions.
• The stretched-out areas are called rarefactions.
• The amplitude of a longitudinal wave is the maximum deviation from the normal density or pressure of the medium.
Section 2 Characteristics of WavesChapter 14
Wave Properties, continued
A. A longitudinal wave has compressions and rarefactions.B. The high and low points of this sine curve correspond to
compressions and rarefactions in the spring.
Section 2 Characteristics of WavesChapter 14
Wave Properties, continued
• Wavelength measures the distance between two equivalent parts of a wave.• The wavelength is the distance from any point on a wave to
an identical point on the next wave.
• Not all waves have a single wavelength that is easy to measure.
• Wavelength is represented by the Greek letter lambda, .
Section 2 Characteristics of WavesChapter 14
Wave Properties, continued• The period measures how long it takes for waves to pass
by.• The period is the time that it takes a complete cycle or wave
oscillation to occur.• The period is represented by the symbol T.
• Frequency measures the rate of vibrations.• The frequency is the number of cycles or vibrations per unit
of time.• The symbol for frequency is f.• The SI unit for measuring frequency is hertz, Hz.
Section 2 Characteristics of WavesChapter 14
Section 2 Characteristics of Waves
Frequency
Chapter 14
Wave Period of Ocean Waves
Section 2 Characteristics of WavesChapter 14
Wave Properties, continued
• The frequency and period of a wave are related.• The frequency is the inverse of the period.
f =
Section 2 Characteristics of WavesChapter 14
Wave Properties, continued
• Light comes in a wide range of frequencies and wavelengths.• Our eyes can detect light with frequencies ranging from
about 4.3 1014 Hz to 7.5 1014 Hz.
• Light in this range is called visible light.
• The full range of light at different frequencies and wavelengths is called the electromagnetic spectrum.
Section 2 Characteristics of WavesChapter 14
Visible Light
Section 2 Characteristics of WavesChapter 14
The Electromagnetic Spectrum
Section 2 Characteristics of WavesChapter 14
Wave Speed• Wave speed equals frequency times wavelength.
Section 2 Characteristics of WavesChapter 14
𝐬𝐩𝐞𝐞𝐝=𝐝𝐢𝐬𝐭𝐚𝐧𝐜𝐞𝐭𝐢𝐦𝐞 𝐯=
𝐝𝐭
𝐬𝐩𝐞𝐞𝐝=𝐰𝐚𝐯𝐞𝐥𝐞𝐧𝐠𝐭𝐡
𝐩𝐞𝐫𝐢𝐨𝐝𝐯=
𝛌𝐓
𝐬𝐩𝐞𝐞𝐝=𝐟𝐫𝐞𝐪𝐮𝐞𝐧𝐜𝐲 ×𝐰𝐚𝐯𝐞𝐥𝐞𝐧𝐠𝐭𝐡 𝐯=𝐟×𝛌
Equation for the Speed of a Wave
Section 2 Characteristics of WavesChapter 14
Math Skills• Wave Speed The string of a piano that produces the
note middle C vibrates with a frequency of 264 Hz. If the sound waves produced by this string have a wavelength in air of 1.30 m, what is the speed of sound in air?
1. List the given and unknown values.Given: frequency, f = 264 Hz
wavelength, = 1.30 m
Unknown: wave speed, = ? m/s
Section 2 Characteristics of WavesChapter 14
Math Skills, continued2. Write the equation for wave speed.
= f
3. Insert the known values into the equation, and solve.
= 264 Hz 1.30 m = 264 s−1 1.30 m
= 343 m/s
Section 2 Characteristics of WavesChapter 14
Wave Speed, continued
• The speed of a wave depends on the medium.• In a given medium, though, the speed of waves is constant;
it does not depend on the frequency of the wave.
• Kinetic theory explains differences in wave speed.• The arrangement of particles in a medium determines how
well waves travel through it.
• In gases, the molecules are far apart and move around randomly. Waves don’t travel as fast in gases.
Section 2 Characteristics of WavesChapter 14
Wave Speed, continued• In liquids, such as water, the molecules are much closer
together. But they are also free to slide past one another.
• In a solid, molecules are not only closer together but also tightly bound to each other. Waves travel very quickly through most solids.
• Light has a finite speed.• All electromagnetic waves in empty space travel at the same
speed, the speed of light, which is: 3.00 108 m/s (186 000 mi/s).
Section 2 Characteristics of WavesChapter 14
• Light travels slower when it has to pass through a medium such as air or water.
Doppler Effect• Pitch is determined by the frequency of sound waves.
• The pitch of a sound, how high or low it is, is determined by the frequency at which sound waves strike the eardrum in your ear.
• A higher-pitched sound is caused by sound waves of higher frequency.
• Frequency changes when the source of waves is moving.• The Doppler effect is an observed change in the frequency
of a wave when the source or observer is moving.
Section 2 Characteristics of WavesChapter 14
Doppler Effect and Sound
Section 2 Characteristics of WavesChapter 14
Objectives• Describe how waves behave when they meet an
obstacle or pass into another medium.
• Explain what happens when two waves interfere.
• Distinguish between constructive interference and destructive interference.
• Explain how standing waves are formed.
Section 3 Wave InteractionsChapter 14
Reflection, Diffraction, and Refraction• Reflection is the bouncing back of a ray of light,
sound, or heat when the ray hits a surface that it does not go through.
• Waves reflect at a free boundary.• The reflected wave is exactly like the original wave
except that the reflected wave is traveling in the opposite direction to the direction of the original wave.
• At a fixed boundary, waves reflect and turn upside down.
Section 3 Wave InteractionsChapter 14
Reflection
Section 3 Wave InteractionsChapter 14
Reflection
Section 3 Wave InteractionsChapter 14
Reflection, Diffraction, and Refraction, continued• Diffraction is the bending of waves around an edge.
• Diffraction is a change in the direction of a wave when the wave finds an obstacle or an edge, such as an opening.
• Waves can also bend by refraction.• Refraction is the bending of a wavefront as the
wavefront passes between two substances in which the speed of the wave differs.
• All waves are refracted when they pass from one medium to another at an angle.
Section 3 Wave InteractionsChapter 14
Diffraction
Section 3 Wave InteractionsChapter 14
RefractionSection 3 Wave InteractionsChapter 14
Interference• Waves in the same place combine to produce a single
wave. • Interference is the combination of two or more waves
of the same frequency that results in a single wave.• The resulting wave can be found by adding the height of the
waves at each point. • Crests are considered positive, and troughs are considered
negative. • This method of adding waves is sometimes known as the
principle of superposition.
Section 3 Wave InteractionsChapter 14
Constructive and Destructive Interference
Section 3 Wave InteractionsChapter 14
Interference, continued• Constructive interference increases amplitude.
• Constructive interference is any interference in which waves combine so that the resulting wave is bigger than the original waves.• The amplitude of the resulting wave is the sum of the
amplitudes of the two individual waves.
• Destructive interference decreases amplitude.• Destructive interference is any interference in which
waves combine so that the resulting wave is smaller than the largest of the original waves.• When destructive interference occurs between two waves
that have the same amplitude, the waves may completely cancel each other out.
Section 3 Wave InteractionsChapter 14
Interference, continued• Interference of light waves creates colorful displays.
• Interference of sound waves produces beats.• When two waves of slightly different frequencies interfere
with each other, they produce beats.
Section 3 Wave InteractionsChapter 14
Standing Waves• Interference can cause standing waves.
• A standing wave is a pattern of vibration that simulates a wave that is standing still.
• Standing waves can form when a wave is reflected at the boundary of a medium.
• Although it appears as if the wave is standing still, in reality waves are traveling in both directions.
Section 3 Wave InteractionsChapter 14
Standing Wave
Section 3 Wave InteractionsChapter 14
Standing Waves, continued
• Standing waves have nodes and antinodes.• Each loop of a standing wave is separated from the next
loop by points that have no vibration, called nodes.• Nodes lie at the points where the crests of the original waves
meet the troughs of the reflected waves, causing complete destructive interference.
• Midway between the nodes lie points of maximum vibration, called antinodes.• Antinodes form where the crests of the original waves line up
with the crests of the reflected waves, causing complete constructive interference.
Section 3 Wave InteractionsChapter 14
Standing Waves, continued
• Standing waves can have only certain wavelengths.• In general, standing waves can exist whenever a multiple
of half-wavelengths will fit exactly in the length of the string.
• It is possible for standing waves of more than one wavelength to exist on a string at the same time.
Section 3 Wave InteractionsChapter 14
Concept Mapping
Section 3 Wave InteractionsChapter 14
Understanding Concepts1. Which of the following waves can be transmitted without a medium?
A. electromagnetic
B. longitudinal
C. mechanical
D. transverse
Standardized Test PrepChapter 14
Understanding Concepts1. Which of the following waves can be transmitted without a medium?
A. electromagnetic
B. longitudinal
C. mechanical
D. transverse
Standardized Test PrepChapter 14
Understanding Concepts2. How do longitudinal waves carry energy from a source?
F. Particles vibrate outward from the source of the wave.
G. Particles vibrate parallel to the direction of the wave.
H. Particles vibrate perpendicular to the direction of the wave.I. Particles vibrate both parallel and perpendicular
to the direction of the wave.
Standardized Test PrepChapter 14
Understanding Concepts2. How do longitudinal waves carry energy from a source?
F. Particles vibrate outward from the source of the wave.
G. Particles vibrate parallel to the direction of the wave.
H. Particles vibrate perpendicular to the direction of the wave.I. Particles vibrate both parallel and perpendicular
to the direction of the wave.
Standardized Test PrepChapter 14
Understanding Concepts3. What is measured by the amplitude of a wave?
A. the amount of vibration of particles
B. the direction of vibration of particles
C. the rate of vibration of particles
D. the wavelength of vibration of particles
Standardized Test PrepChapter 14
Understanding Concepts3. What is measured by the amplitude of a wave?
A. the amount of vibration of particles
B. the direction of vibration of particles
C. the rate of vibration of particles
D. the wavelength of vibration of particles
Standardized Test PrepChapter 14
Understanding Concepts4. Which combination of wave interactions can cause a standing wave?
F. diffraction and interference
G. diffraction and reflection
H. reflection and interference
I. reflection and refraction
Standardized Test PrepChapter 14
Understanding Concepts4. Which combination of wave interactions can cause a standing wave?
F. diffraction and interference
G. diffraction and reflection
H. reflection and interference
I. reflection and refraction
Standardized Test PrepChapter 14
Understanding Concepts5. Why do astronauts on the moon need a radio transmitter
to carry on a conversation with each other?
Standardized Test PrepChapter 14
Understanding Concepts5. Why do astronauts on the moon need a radio transmitter to carry on a conversation with each other?
Answer: Sound waves require a medium to carry energy from one place to another. On the moon, there is no air to carry the vibrations.
Standardized Test PrepChapter 14
Reading Skills
The Doppler Effect applies to light as well as sound. Astronomers have used this fact to measure the speed of objects in space as they move away from Earth. They know the frequency and wavelength of the light as it leaves a star because the energy transitions in atoms are the same throughout the universe. When the light reaches Earth, it has a different frequency from when it left the star.
6. Assess how the knowledge that light always travels at the same speed is essential for determining the speed at which a distant galaxy and Earth are moving apart.
Standardized Test PrepChapter 14
Reading Skills
6. Assess how the knowledge that light always travels at the same speed is essential for determining the speed at which a distant galaxy and Earth are moving apart.
Answer: Using the change in frequency of light and the fact that the speed of light is constant, astronomers can calculate how fast the objects are moving away from one another.
Standardized Test PrepChapter 14
Reading Skills
7. Astronomers have observed that the wavelength of light reaching Earth from one edge of the sun is slightly different than from the other edge. What can be concluded about the sun based on this observation?
Standardized Test PrepChapter 14
The Doppler Effect applies to light as well as sound. Astronomers have used this fact to measure the speed of objects in space as they move away from Earth. They know the frequency and wavelength of the light as it leaves a star because the energy transitions in atoms are the same throughout the universe. When the light reaches Earth, it has a different frequency from when it left the star.
Reading Skills
7. Astronomers have observed that the wavelength of light reaching Earth from one edge of the sun is slightly different than from the other edge. What can be concluded about the sun based on this observation?
Answer: The observation indicates that the sun is rotating. The light from one edge is shifted to a shorter wavelength, and light from the other edge is shifted to a longer wavelength.
Standardized Test PrepChapter 14
Interpreting Graphics
8. What wave phenomenon is demonstrated in this illustration?A. diffraction C. reflectionB. Interference D. refraction
Standardized Test PrepChapter 14
Interpreting Graphics
8. What wave phenomenon is demonstrated in this illustration?A. diffraction C. reflectionB. Interference D. refraction
Standardized Test PrepChapter 14
Interpreting Graphics
9. Which of the points on the illustration indicates an antinode?F. W H. YG. X I. Z
Standardized Test PrepChapter 14
Interpreting Graphics
9. Which of the points on the illustration indicates an antinode?F. W H. YG. X I. Z
Standardized Test PrepChapter 14