Sound Flashcards
Explain the Doppler Effect
The observed wavelength of a sound changes due to relative motion.
True or false:
As the object moves away from the observer, the wavelength of sound reflected & perceived by the observer increases.
True
If a block is moving towards a laser sensor at constant speed, how does the wavelength of the perceived signal change?
The wavelength of the perceived signal decreases by a constant value.
*Note that constant speed also translates to a constant change in wavelength (whether increasing or decreasing)
When an object moves towards a sensor, how is frequency affected?
When an object moves away from a sensor, how if frequency affect?
Towards = higher freq. in reflected light
Away = lower freq. in reflected light
Doppler Effect equation
TOP PART OF EQUATION:
*Towards the object/source: + sign
*Away from object/source: − sign
BOTTOM PART:
Use same rules as top part, but just flip the sign after.
Differentiate transverse & longitudinal waves
Transverse - wave particles oscillating perpendicular to direction of propagation
Longitudinal - wave particles oscillating parallel to direction of propagation causing periods of compression and rarefaction
Sound is a (transverse/longitudinal) wave.
longitudinal wave
Calculating propagation speed/velocity for a wave
v = fλ
Question applying relationship between frequency and velocity of wave source
Points I and III; velocity is 0, therefore frequency of the doppler doesn’t change
Wavelength
Distance from 1 maximum crest to another
Frequency
The # of wavelengths passing a fixed point per second. (Cycles per second)
Measured in Hz
Period (T)
seconds per cycle
T = 1/f
Amplitude
Maximum displacement from the equilibrium position to the crest or trough
Crest vs trough
Crest -top curved part of the wave
Trough - bottom part of the wave
constructive interference
Waves are perfectly in phase w/ each other, troughs and crests line up
0˚ or 360˚ phase difference
destructive interference
Waves are out of phase w/ each other
180˚ phase difference
Adding identical waves 270˚ out of phase produces what type of interference?
Both constructive and destructive
What are the frequencies that young adults are able to detect?
Between 20 Hz and 20,000 Hz
High frequency hearing declines with ______.
age
What is damping or attenuation?
A decrease in amplitude of a wave caused by an applied or nonconservative force. Happens when you are moving from one medium to another as well.
Damping changes all aspects of a sound wave except _______.
Frequency
What is sound?
A longitudinal wave transmitted by the oscillation of particles in a deformable medium.
Sound can’t travel through a vacuum.
How is speed of sound affected by density and phase of the medium?
Sound has fastest speed when traveling in solid & low density medium.
Question relating speed of sound wave and medium change
Speed of sound equation
v =
Infrasonic waves and ultrasonic waves
Infrasonic - sound waves w/ frequencies below 20 Hz
Ultrasonic - sound waves w/ frequencies above 20,000 Hz
What is pitch of a sound?
Our perception of the frequency of sound
Shock wave
What is loudness of a sound?
Our perception of the intensity of the sound; loudness is subjective
What is intensity of a sound?
Objective measure; the average rate of energy transfer per area across a surface that is perpendicular to the wave
(Power transported per unit area)
Intensity of a wave is also referred to as “energy” of the wave. Therefore energy and amplitude are directly related.
TRUE; energy is proportional to A^2
Calculating intensity
I = Power/Area
SI units: Watts/m^2
How are amplitude and intensity related?
Intensity is proportional to the square of amplitude.
Doubling amplitude = x4 intensity
Relationship between intensity and distance from the sound wave source
Inversely proportional to the square of the distance from the source
How is intensity affected when sound waves travel through various mediums?
As a sound wave travels through different mediums (since the refractive indexes are different); the sound waves are partially reflected at these interfaces which causes the intensity of the waves to decrease.
How frequency changes along the basilar membrane:
Base
Apex
The base records high frequency sounds, the apex records low frequency sounds
A from apex and lo from low “Alo”
Units for sound level
dB (decibels)
Define loudness and pitch
Our perception of intensity of a sound.
Our perception of frequency of a sound.
Calculating sound level of a sound
β = 10*log(I/I0)
I0 is the threshold of hearing = (1 x 10^-12 W/m^2)
I is the intensity of the sound wave
Calculating sound level when its intensity is changed by some factor
βfinal = βinitial + 10log(I final/ I initial)
*I is intensity
β is sound level
Relationship between intensity and sound level
As intensity increases by a factor of 10 each time, the sound level increases by +10 dB.
True or false:
The sound of 90 dB is 100 times as intense as a sound of 70 dB.
True
When does a standing wave form?
When 2 waves of the same frequency traveling in opposite directions interfere w/ one another as they travel through the same medium.
It exhibits no net transport of energy and doesn’t itself propagate, although it “appears” to propagate as shown in the image.
Nodes vs antinodes
Nodes - closed/fixed ends, point of minimum displacement/amplitude
Antinodes - open ends, point of max displacement/amplitude
Generic equation for determining harmonic for a string & open pipe
λ = 2L/n
n is a positive integer.
Determining harmonic for string attached at both ends
Use equation: λ = 2L/n
count the number antinodes which will be “n”
Determining harmonic for open pipe
Use equation λ = 2L/n
for n value count the number of NODES
L = λ/2
Generic equation for determining harmonic for closed pipe (at one or both ends)
λ = 4L/n
n is only an odd integer and is counted by each half wavelength
L = λ/4
True or false:
Higher harmonics correspond w/ shorter wavelengths.
True; harmonic # and wavelength are inversely proportional to each other.
n is the harmonic number
The fundamental frequency is 300 Hz. What is the 3rd harmonic?
EQUATION TO USE:
n * fundamental freq
n is the harmonic #
What is the 1st overtone? 2nd overtone?
1st overtone is the 2nd harmonic. NOT the 1st harmonic.
2nd overtone is the 3rd harmonic, etc.
When a sonic boom reflects off the Earth’s surface, which property of the wave changes?
-The intensity because some of the sound wave is transmitted into the ground, before reflecting.
Fundamental frequency of open tube, when closed tube fundamental freq. is f.
2f
f is fundamental freq of closed tube and its equal to 1/4L.
In order to get 1/2L which is what the fundamental frequency of an open tube is equal to
When a sound when travels from one medium to another, which aspects of the wave change:
Wavelength
Frequency
Velocity
Intensity
Wavelength, velocity, and intensity change
NOT frequency
