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CHAPTER 15 WAVES

Section 15.1 Types of Waves

◦What does a wave carry?

◦How are waves generated?

◦What is the difference between a transverse wave and a longitudinal waves?

◦How do the particles in ocean waves move?

Intro to Waves Clip

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What is a wave?

◦ Wave- a disturbance that transmits energy through matter or space

◦ Energy may spread out as a wave travels.

◦ Waves are all around us:

◦ light from the stoplight

◦ ripples in a puddle of

◦ electricity flowing in wires

◦ radio and television and cell phone transmissions

Waves

◦Medium- the matter through which a wave travels◦ Water

◦ Air

◦ Earth-seismic waves

◦Mechanical wave- a wave that requires a medium through which to travel

◦ sound waves (air)◦water waves◦waves in a spring

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Waves

◦ Electromagnetic wave-a wave caused by a disturbance in electric and magnetic fields◦Does not require a medium◦Also called a light wave◦ can transfer energy through a vacuum ◦ can also transfer energy through a material medium

Example: light

waves through

space, through air,

through glass

Waves transfer Energy

◦ A wave caused by dropping a stone in a pond might carry enough energy to move a leaf up and down several centimeters

◦ A tsunami is a huge ocean wave caused by earthquakes.◦ A tsunami can carry enough energy to damage coastal dwellings.

Animation

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Vibrations and Waves

◦Most waves are caused by vibrating objects.

◦Electromagnetic waves may be caused by vibrating charged particles.

◦Mechanical waves are caused by the vibration of particles within the medium.

Vibrations and Waves

◦ Vibrations involve

transformations of

energy A wave can pass

through a series of

vibrating objects.The disturbance travels

down the row as energy is

transferred from one mass

to another.

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Waves

Transverse wave

◦ Particles oscillate up and down about their equilibrium positions, perpendicular to the direction of wave propagation

◦ its oscillations perpendicular to

the direction the wave moves

Longitudinal wave

◦ Particles oscillate back and forth about their equilibrium positions, parallel to the direction of wave motion

◦ oscillations in the same

direction as the wave

movesExamples: light waves, water

waves, all waves belonging to

the electromagnetic spectrum Example: Sound waves

transverse wave

longitudinal wave

Clip

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Waves Properties

◦ Waves have crests and

troughs or compressions

and rarefactions.

◦ compressions: the

crowded areas of a

longitudinal wave

◦ rarefactions: the

stretched-out areas

of a longitudinal

wave

Do longitudinal wave have

crest and troughs?

Surface Waves

◦ In a surface wave, particles move in circles.

◦Water waves are an example of surface waves.

◦ Surface waves occur at the boundary between two different media

◦ Ex: water and air

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Section 15.2 Characteristics of Waves

What are some ways to measure

and compare waves?

How can you calculate the speed

of a wave?

Why does the pitch of an

ambulance siren change as the

ambulance rushes past you?

Wave Properties

◦ Crest-the highest point of a transverse wave

◦ Trough-the lowest point of a transverse wave

◦ Amplitude-the greatest distance that particles in a medium

move from their normal position when a wave passes

Rest

position

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Wavelength

◦Wavelength-the distance between any two successive identical parts of a wave

◦ represented by the symbol

λ

◦ expressed in the SI unit meters (m)

Amplitude and wavelength tell you about

energy.

• larger amplitude = more energy

• shorter wavelength = more energy

A Longitudinal Waveform

◦A cycle consists of one compression and one expansion of the particles of the medium.

◦Particles of medium then return to their equilibrium positions

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A Transverse Waveform

amplitude

crest

trough

wavelength, λλλλ

wavelength, λλλλ

equilibrium

position

A cycle consists of one crest and one trough.

Your Turn

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Period

◦ the time that it takes a complete cycle or wave oscillation to occur

◦ represented by the symbol T

◦ expressed in the SI unit seconds (s)

•Period-the time required for one full wavelength to pass a certain point

Frequency

◦ frequency: the number of cycles or vibrations per unit of time;

• also the number of waves

produced in a given

amount of time

• represented by the symbol

f

• expressed in the SI unit

hertz (Hz), which equals

1/s

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Frequency

◦ The frequency and period of a wave are related.

◦ The frequency is the inverse of the period.

What is the frequency in

the diagram?

What is the formula if you’re

looking for period?

Period= 1/frequency

f = 0.5 Hz

Calculating Wave Speed

◦Wave speed-the speed at which a wave passes through a medium

Wave speed equals frequency times

wavelength.

Wave speed= frequency x wavelength

V= f x ����V

f ����

Period= T

f= 1

T

Frequency= f

Wavelength = ����

Wave speed = v

T= 1

f

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1. The musical note A above middle has a frequency of 440 Hz.

If the speed of sound is known to be 350 m/s, what is the

wavelength of this note? `

Practice Problem: Wave Speed

f = 440 Hz

v = 350m/s���� = ?

���� = v/f ���� = 350 m/s

440 Hz

���� = 0.80 m

2. A certain FM radio station broadcasts electromagnetic

waves at a frequency of 9.05 x 107 Hz. These radio waves

travel at a speed of 3.00 x 108 m/s. What is the wavelength of

these radio waves?

f = 9.05 x 107 Hz

v = 3.00 x 108 m/s���� = ?

���� = v/f

���� = 3.00 x 108 m/s

9.05 x 107 Hz

���� = 3.31 m

Practice Problem: Wave Speed

3. The average wavelength in a series of ocean waves is 15.0

m. A wave crest arrives at the shore on average every 10.0 s,

so the frequency is 0.100 Hz. What is the average speed of the

wave?

4. Yellow light with a wavelength of 5.89 x 10-7 m travels trough

quartz glass with a speed of 1.94 x 108 m/s. What is the

frequency of the light?

f = .100Hz

v = ?���� = 15.0 m

v =���� x f

v = 15.0 m x .100 Hz

v =1.5 m

f = ?

v = 1.94 x 108 m/s���� = 5.89 x 10-7 m

What is the period?

What is the period?

f = v/ ���� f = 1.94 x 108 m/s / 5.89 x 10-7 m

f = 3.29 x 1014 Hz

T= 1/f T= 1/(.100Hz) T= 10 s

T= 1/f T= 1/(3.29 x 1014 Hz) T=3.04 x 10-15 s

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Practice Problems: Wave Speed

5. Waves in a lake are 6 m apart and pass a person on a raft

every 2 s. What is the frequency?

What is the speed of the wave?

6. A drum is struck, producing a wave with a wavelength of 1.1m

and a speed of 2.42 x 104 m/s. What is the frequency of the

wave?

What is the period?

f = ?

t= 2s

f = 0.5 Hz

v = ?���� = 6 m

f = 1/ T f = 1/ 2 f = 0.5 Hz

v = 6 m x 0.5 Hz v = 3 m/s

f = ?

v = 2.42 x 104 m/s ���� = 1.1m

f = v/ ����f = (2.42 x 104 m/s) / 1.1m

f= 22000 Hz

T= 1/f T= 1/22000 Hz T= 4.55 x 10-5 s

Wave Speed

◦ The speed of a wave depends on the medium

◦ Greatest in solids and least in gases

◦Kinetic theory explains differences in wave speed

◦ Light has a finite speed

◦ Speed of light: c = 3 x108 m/s

◦ 3 x108 m/s or 186,000 mi/s

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Wave Speed

◦ Ranges of waves from lowest to highest are: radio waves, microwaves, infrared waves, visible light, ultraviolet light, X-rays, and gamma rays

◦ The full range of light frequencies is called the electromagnetic spectrum

Doppler Effect

◦ Pitch is determined by the frequency of sound waves.

• The pitch of a sound =how high or low it is

• A higher-pitched sound is caused by sound waves of higher frequency.

◦ Frequency changes when the source of waves is moving◦ Ex. Siren moving toward you sounds different than a siren

moving away from you

◦ Doppler effect occurs for light and other type of waves as well

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Doppler Effect

◦ Doppler effect-an observed change in the frequency of a

wave when the source or observer is moving

◦ A sound wave frequency change is noticed as a change in

pitch.

◦ The Doppler effect occurs for many types of waves,

including sound waves and light waves.

Video Clip

Section 15.3 Wave Interactions

◦ How do waves behave when they hit a boundary, when they

pass around an edge or opening, and when they pass from

one medium to another?

◦ What happens when two or more waves are in the same

location?

◦ How does a standing wave affect the medium in which it

travels?

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R

Reflection Diffraction Refraction

Wave Interactions

Wave Interactions

◦Waves bend when they pass from one medium to another at an angle.

◦Waves will experience :

◦ Reflection

◦ Diffraction

◦ Refraction

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Reflection

◦ Reflection – the bouncing back of a wave as it meets a surface or

boundary

◦ Examples:

◦ The reflection of light waves in a lake can create a mirror image of a

landscape.

◦ Water waves are reflected when they hit the side of a boat.

Diffraction

◦Diffraction – the bending of a wave as it passes an edge or an opening

◦Examples:

◦Water waves diffract around a block in a tank of water.

◦ Sound waves passing through a door diffract.

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Refraction

◦ Refraction – the bending of waves as they pass from one

medium to another

◦ All waves are refracted when they pass from one medium to

another at an angle.

Interference

◦ Interference- the combination of two or more waves that exist in the same place at the same time

◦ Two types

◦ Constructive interference

◦Destructive interference

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Constructive Interference

◦Waves combine without any phase difference

◦Waves combine to form a bigger wave

◦ Increases amplitude

Wave AdditionAmplitude ~ Intensity

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Destructive Interference

◦ Waves combine differing by multiples of 1/2 wavelength

◦ waves combine to form a wave smaller than the largest of

the original waves

◦ Decreases amplitude

Wave Subtraction

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Interference

◦ Interference of light waves creates colorful displays

◦ Ex. Rainbows, oil in water, soap bubbles

Interference

◦ Interference of sound waves produces beats

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Standing Waves

◦ Standing waves-wave caused by

interference that shows some regions

of no vibrations

◦ Does not move along the medium

◦ Standing waves have nodes and antinodes

◦ Nodes

◦ Each loop of a standing wave is separated by a point

◦ Nodes have no vibrations

◦ Nodes are where the crests of the original waves meet the troughs of the reflected wave (destructive interference)

Standing Waves ◦ Antinodes

◦ lie midway between the nodes

◦ point of maximum vibration

◦ form where the crests of the original waves line up with the crests of the reflected waves (constructive interference)

◦ Standing waves can have only certain wavelengths

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nbc