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12/6/2016
1
CHAPTER 10 WAVES
Section 10.1 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
moves Examples: 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 10.2 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
l
◦ 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, l
wavelength, l
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.
1frequency , 1/
per
ior
odf T
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 10
4 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 Addition Amplitude ~ 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