Chapter 6 - Sound and Doppler Effect Flashcards
How do pressure pulses of air travel down a closed pipe?
It travels down to the closed end and is reflected back toward the origin. It reaches the open-end origin, where it is reflected back toward the closed end. It has changed phase (decreased). It is reflected again at the closed end and once it reaches the open-end origin, it changes phase (increases). It continues this cycle.
What is the wave interference at an antinode?
constructive
Equation: frequency of standing waves in a closed pipe
fn = nv/4L
n = odd numbers (1, 3, 5, …)
Equation: harmonic frequency of a standing wave of a string in terms of fundamental frequency
fn = nf1
n = harmonic number
Equation: sound intensity level (β)
β = 10 x log (I/I0)
I0 = reference sound intensity
How far are nodes from each other in a standing wave?
1/2 wavelength
What is a standing wave?
a wave that does not appear to move in either direction along the length of a string
Equation: speed of sound in ideal gas
v = √γP/ρ = √γRT/M
ρ = gas density
P = gas pressure
γ = Cp/Cv (molar heat capacity at pressure/molar heat capacity at volume)
R = ideal gas constant
T = temperature (K)
M = gas mass
Equation: Doppler effect
fL = [(v +/- vL)/(v +/- vs)] x fs
fL = frequency encountered by listener
fs = frequency emitted by source
vL = speed of the listener relative to the still air (moving toward source = +, moving away from source = -)
vs = speed of the source relative to the still air (moving toward listener = -, moving away from listener = +)
v = speed of wave in air
What is a rarefraction?
an area in a sound wave that has low density
How does the fundamental frequency for a closed pipe compare to that of an open pipe?
It is 1/2 the fundamental frequency of an open pipe.
If distance increases by a factor of 3.2, how does the intensity of a sound change?
It drops by a factor of 10.
What type of wave are sound waves?
longitudinal
How do pressure pulses of air travel down an open pipe?
Since it is open on both ends, it travels down to one end, some of it continues out, but the rest is reflected back in. It tracks back toward the origin and some of it continues out, but the rest is reflected back in. It continues this cycle.
What is displacement of a string at a node?
0
In an open pipe, where are the antinodes of a wave?
at each open end
Equation: wavelength of a harmonic wave on a string
λn = 2L/n
What are harmonics?
frequencies that are integer multiples of the fundamental frequency (f1)
What is displacement of a string at an antinode?
maximum amplitude
What is γ for a monatomic gas, diatomic gas, and polyatomic gas?
monatomic = 1.67
diatomic = 1.40
polyatomic = 1.33
In a closed pipe, where are the nodes and antinodes of a wave?
The antinode will be at the opening of the pipe, while the node wll be at the closed end of the pipe.
What is the order for sound speed in different mediums?
Vsolid > vliquid >vgas
How does speed of sound in a monatomic gas compare to the speed of sound in a polyatomic gas?
speed of sound is faster in a monatomic gas
How far are antinodes from each other in a standing wave?
1/2 wavelength
What is the intensity of the reference sound for humans?
10-12 W/m2
How far are nodes and antinodes from each other in standing waves?
1/4 wavelength
What are overtones?
frequencies greater than the fundamental frequency (f1)
ex: first overtone = second harmonic
How does intensity change with distance?
Intensity decreases with increased distance by a squared factor.
Do waves travel faster in warm or cold air?
warm air
Equation: wavelength of standing waves in an open pipe
λn = 2L/n
Equation: beat frequency
fbeat = If1 - f2I
High frequency sounds are generated by nerves closest/farthest from the oval window?
closest
What determines the speed of sound of an object?
The strength of the forces between the molecules in a given medium determines the speed of sound. If the restoring forces are greater, than sound will travel faster.
Equation: frequency of harmonic wave on a string
fn = nv/2L
Equation: frequency of standing waves in an open pipe
fn = nv/2L
What is the speed of sound in air at room temerature?
~340m/s
For every drop in intensity by a factor of 10, how does this affect the decibel level?
Decibel level decreases by 10.
What are the units of sound intensity?
J/(m2s) = W/m2
What is the wave interference at a node?
destructive
What is the Doppler effect?
the change in pitch of a sound (or any wave) from a high frequency as it approaches an observer to a low frequency as it moves away from the observer
What affects sound loudness/intensity?
amplitude (higher amplitude = louder)
What are the units of intensity level?
decibel (dB)
How do you solve for an echo problem?
plug into the Doppler equation twice (you may need to change signs based on who is the source/listener)
Equation: wavelength of standing waves in a closed pipe
λn = 4L/n
n = odd numbers (1, 3, 5, …)
Equation: intensity of sound in terms of power and energy
I = Power/Area = Energy/(Area x Time)
What affects sound pitch?
frequency (higher frequency = higher pitch)
Consecutive harmonics differ by how much in frequency?
the fundamental frequency
