Sound Waves
If sound B is 10x the intensity of sound A, then its decibel level is _______ higher.
10 dB
How many times more intense is a 30 dB sound is a 20 dB sound?
10 or 10^1
How many times more intense is a 40 dB sound is a 20 dB sound?
100 or 10^2
How many times more intense is a 80 dB sound is a 50 dB sound?
1000 or 10^3
How many times more intense is a 80 dB sound is a 20 dB sound?
1000000 or 10^6
A change of 30 dB means that the sound is ________ louder.
1000x louder Ex: going from 70 dB to 100 dB
A change by 20 dB means that the sound is _______ louder.
100x Ex: going from 50 dB to 70 dB
A change by 10 dB means that a sound is ______ louder.
10x Ex: going from 110 dB to 120 dB
If sound B is 100x the intensity of sound A, then its decibel level is _______ higher.
20 dB
If sound B is 1000x the intensity of sound A, then its decibel level is _______ higher.
30 dB
What is the speed of sound in air when the temperature is 20ºC?
343.3 m/s
If sound B is 10000x the intensity of sound A, then its decibel level is _______ higher.
40 dB
When the scientific notation increases or decreases, you have to...
Add or subtract a 0 depending on the exponent
Doppler shift is seen with ______ waves.
All, including sound, and light (visible, UV, x-rays, radio, and electromagnetic)
What is a sound wave?
An object vibrates and affects the air molecules close to it, causing a sound
If there is an echo in the problem and the problem says, "If the sound wave returns to a camera x seconds seconds after leaving the camera, how far away is the object?" what do you have to do?
Divide the time by 2
Decibel increase
Ex: 10x louder, 100x louder, 1000x louder
Decibel levels
Ex: 70 to 80 to 90
T of F: As the teacher balks, students hear the voice because particles of air move from the mouth of the teacher to the ear of the student.
False
T or F: Does the sound get louder when the Doppler Effect is happening?
False The sound isn't actually getting louder; the frequency is just increasing because the sound is moving closer, and the sound waves are bunched up.
What does pitch depend on?
Frequency
What pitch does a high frequency wave cause?
High pitch
What is the amplitude of the wave?
How far the particles vibrate away from their resting position
What is the wavelength of the wave?
How long the wave is
What is the period of the wave?
How much time it takes the particles to complete a vibrational cycle
What is the frequency of the wave?
How often the particles vibrate about their fixed position
What type of waves are sound waves?
Longitudinal and mechanical waves (sometimes called pressure waves)
What pitch does a low frequency wave cause?
Low pitch
Where are rarefactions located relative to wave fronts?
Midway between wave fronts
When an object vibrates to the left, what happens to the air molecules on the right, density, and air pressure?
Molecules on the right are pulled farther apart Lower molecular density Lower air pressure *Rarefactions are formed
When an object vibrates to the right, what happens to the air molecules on the right, density, and air pressure?
Molecules on the right are pushed closer together Higher molecular density Higher air pressure *Compressions are formed
If there is an echo in the problem and the problem says, "Determine the time elapsed between when a person yells and when the echo is heard?" what do you have to do?
Multiply the distance by 2
Sound waves can be translated into a ______ curve.
Sine
Do particles travel the fastest in solids, liquids, or gases?
Solids; the particles are the closest
What is the Doppler Shift?
The apparent (observed) change in the frequency of a sound when there is relative motion between the source of the waves and an observer The difference between the frequency at which sound waves are produced and the frequency at which they are observed by the hearer. Motion between the source of sound and observer
What would the compression be in a wave drawing?
The circles
What would a rarefaction be in a wave drawing?
The spaces in between the circles
How do the wave fronts near the source compare to the ones far away?
They are more circular
Tosh is holding one end of a slinky; the opposite end is attached to a wall. Which way must he move his hand to create a longitudinal wave?
Toward the wall and then away
T of F: A sound wave does not consist of crests and troughs.
True
T of F: All sound waves are produced by a vibrating object.
True
T of F: Speed is constant.
True
Understanding the Doppler Effect has allowed us to...
Use doppler radars to see how fast storms are moving toward or away from us Use doppler blood flow to see how blood moves to and from the heart
What is the equation for velocity?
V = λ • f velocity = wavelength • frequency V = d / t velocity = distance over time
What are the units for power?
W Watts
What are the units for intensity?
Watts / m^2 Watts per square meter
When does the Doppler Shift occur?
When there is a difference in motion between the source of the sound and an observer Either the sound is moving (an ambulance moving down the street) or the observer is moving (driving past a fire station when their siren is blaring)
What is a decibel?
a dimensionless unit that describes the ratio of two intensities of a sound, the threshold of hearing is commonly used as the reference intensity
What is pitch?
a measure of how high or low a sound is perceived to be, depending on the frequency NOT loudness
If a person yells (as opposed to whispering) then it will cause...
air molecules to vibrate with greater amplitude
Sound waves travel in ____ directions.
all
Loud sounds have a high...
amplitude
What is a plane wave?
any small portion of a spherical wave that is far from the source
20 Hz < f < 20,000 Hz
audible sound
The sound source is located in the __________, creating a sound.
center
What is a wave front?
circle representing compressions of waves
When an object vibrates, it causes a continuous cycle of...
compressions and rarefactions
The speed of the wave stays ___________ because the medium is ___________.
constant; the constant
As the frequency of a sound increases, the wavelength _______ and the period _______.
decreases; decreases
Intensity ________ as the distance from the source ________.
decreases; increases
Everyone's ears are...
different
What is the equation for frequency?
f = 1 / T frequency = 1 / period
Solids transmit sounds the ________ while gases transmit sounds the _________.
fastest; slowest Exception: If the solid is elastic Ex: playdough
A sound wave is described as being 384 waves/s. This quantity describes the wave's...
frequency
High-pitched sounds have a high...
frequency
What does audible sound depend on?
frequency and intensity
High pitched sounds have relatively large _____ and small _____.
frequency; wavelength
Mediums could be ___________, ___________, and ___________.
gases (air), liquid, or solids
When sound waves are translated into a sine curve, what pressure do crests have?
high
The _______ the temperature, the _______ the sound travels.
higher; faster Molecules are moving faster at higher temperatures so it is easier for the energy to transmit through the wave (most important for gases).
What is the speed of the wave?
how fast the wave moves through the medium
f < 20 Hz
infrasonic waves
What is the equation for intensity?
intensity = power / area (of a sphere) intensity = P / (4πr^2) Only r is squared; r = distance from source
Pitch is only an _________________ of the frequency.
interpretation
The decibel scale
logarithmic varies by powers of 10
In the Doppler Shift, the waves that get "stretched out" behind the moving object have a __________ wavelength, which then causes the frequency to be _________.
longer; lower
When sound waves are translated into a sine curve, what pressure do troughs have?
low
When the person is far away from the sound, the wavelength and frequency are...
low
What are the units for r?
m meters
What is decibel level?
measure of loudness
Frequency can be...
measured
Sound waves are ___________ waves.
mechanical
Sound waves require a _________ in order to move their _________ from a source to an observer.
medium; energy
"Stretched out" =
object moves away from observer
The speed of a sound wave depends upon the...
properties of the medium through which it moves
What is a ray?
radial line from the source perpendicular to the wave front
Sound travels fastest when the particles are...
rigid and less easy to compress
"Bunched up" =
running into own sound waves; object moves toward observer
In the Doppler Shift, the waves that get "bunched up" in front of the moving object have a __________ wavelength, which then causes the frequency to be _________.
shorter; higher
When the person is close to the sound, the wavelength is _______ and the frequency is _______.
small; high
The spacing of particles for solids, liquids, and gases
solids = close liquids = moving gases = far
What shape are sound waves from the sound source?
spherical
The speed of the sound also depends on the...
temperature
If a person yells (as opposed to whispering) then it will cause...
the loudness of the sound to be louder
What is loudness?
the perceived intensity by your ear, measured in decibels (dB)
What is intensity?
the rate at which energy flows through a unit area perpendicular to the direction of wave motion
1000 Hz and 1.0 x 10^-12 W/m^2
threshold of hearing
1.0 W/m^2
threshold of pain
f > 20,000 Hz
ultrasonic waves
Sound cannot travel in a __________.
vacuum