# Mastering Physics 13

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question
Propagation of pressure fluctuations in a medium
Based on the information presented in the introduction of this problem, what is a sound wave? Propagation of sound particles that are different from the particles that comprise the medium Propagation of energy that does not require a medium Propagation of pressure fluctuations in a medium Propagation of energy that passes through empty spaces between the particles that comprise the medium
question
Pressure fluctuations travel along the direction of propagation of the sound wave.
Having established that a sound wave corresponds to pressure fluctuations in the medium, what can you conclude about the direction in which such pressure fluctuations travel? The direction of motion of pressure fluctuations is independent of the direction of motion of the sound wave. Pressure fluctuations travel perpendicularly to the direction of propagation of the sound wave. Pressure fluctuations travel along the direction of propagation of the sound wave.
question
yes
Does air play a role in the propagation of the human voice from one end of a lecture hall to the other? yes no
question B, C
The graphs shown in (Figure 1) represent pressure variation versus time recorded by a microphone. Which could correspond to a sound wave?
question f, λ = 1000,0.344 Hz,m
The next graph in (Figure 2) shows a sound wave consisting of a sinusoidal displacement of air particles versus time, as recorded at a fixed location. For sinusoidal waves, it is possible to identify a specific frequency (rate of oscillation) and wavelength (distance in space corresponding to one complete cycle). Taking the speed of sound in air to be 344 m/s, what are the frequency f and the wavelength λ of the sound wave shown in the graph?
question
It is perceived as louder.
A certain sound is recorded by a microphone. The same microphone then detects a second sound, which is identical to the first one except that the amplitude of the pressure fluctuations is larger. In addition to the larger amplitude, what distinguishes the second sound from the first one? It is perceived as higher in pitch. It is perceived as louder. It has a higher frequency. It has a longer wavelength.
question
It is perceived as higher in pitch.
A certain sound is recorded by a microphone. The same microphone then detects a second sound, which is identical to the first one except that it has twice the frequency. In addition to the higher frequency, what distinguishes the second sound from the first one? It is perceived as higher in pitch. It is perceived as louder. It has a higher amplitude. It has a longer wavelength.
question the harmonic content
What varies between two tones that are different in timbre, that is, two tones that have the same fundamental frequency but are produced, say, by different musical instruments? Note that the graphs B and C in (Figure 1) could represent tones with different timbre. the pitch the harmonic content nothing
question 4000 Hz
There is no simple mathematical formula for converting phons into decibels. The relationship between these two measures of intensity has been determined by experiment. The graph (Figure 1) displays the perceived loudness of sound waves of different intensities (vertical axis) and frequencies (horizontal axis). Each individual curve represents a sound that is perceived by the human ear to be equivalent to a specific phon level. To practice reading this graph, note that a sound wave of intensity 70 dB that vibrates with a frequency of 50 Hz is perceived by the human ear as a 40-phon sound. The lowest curve, labeled 0 phons, forms the true lower limit to human sound perception. (Actually, even this statement is not completely true owing to variations in sound perception in the general population.) At approximately what frequency do most people perceive the least intense sounds?
question 35 dB
For a sound at 100 Hz, what is the decibel level necessary for human perception?
question 103.5 (≈5000) times more intense
How many times more intense is the least intense perceptible sound at 100 Hz compared to the least intense perceptible sound at 1000 Hz? Specifically, you are looking for the ratio I100Hz/I1000Hz. 10^35 times more intense 10^3.5 (≈5000) times more intense 35 times more intense 3.5 times more intense equally intense
question 101.2 (≈15.8) times more intense
Normal conversation has a sound level of about 60 dB. How many times more intense must a 100-Hz sound be compared to a 1000-Hz sound to be perceived as equal to 60 phons of loudness? 10^12 times more intense 10^1.2 (≈15.8) times more intense equally intense
question 10^1.0 (≈10) times more intense
Normal conversation has a sound level of about 60 dB. How many times more intense must a 10,000-Hz sound be compared to a 1000-Hz sound to be perceived as equal to 60 phons of loudness? 10^10 times more intense 10^1.0 (≈10) times more intense equally intense
question β = 10 dB
What is the sound intensity level β, in decibels, of a sound wave whose intensity is 10 times the reference intensity (i.e., I=10I0)? Express the sound intensity numerically to the nearest integer
question β = 20 dB
What is the sound intensity level β, in decibels, of a sound wave whose intensity is 100 times the reference intensity (i.e. I=100I0)?
question Δβ2, Δβ4, Δβ8 = 3,6,9 dB
Calculate the change in decibels ( Δβ2, Δβ4, and Δβ8) corresponding to m=2, m=4, and m=8.
question 2f0
If the organ pipe is cut in half, what is the new fundamental frequency? 4f0 2f0 f0 f0/2 f0/4
question f0
After being cut in half in Part A, the organ pipe is closed off at one end. What is the new fundamental frequency? 4f0 2f0 f0 f0/2 f0/4
question 3f0
The air from the pipe in Part B (i.e., the original pipe after being cut in half and closed off at one end) is replaced with helium. (The speed of sound in helium is about three times faster than in air.). What is the approximate new fundamental frequency? 3f0 2f0 f0 f0/2 f0/3
question
f = 214 Hz
Throughout the problem, take the speed of sound in air to be 343 m/s .Consider a pipe of length 80.0 cm open at both ends. What is the lowest frequency f of the sound wave produced when you blow into the pipe?
question
higher than before.
A hole is now drilled through the side of the pipe and air is blown again into the pipe through the same opening. The fundamental frequency of the sound wave generated in the pipe is now: ( f before = 214 Hz) the same as before. lower than before. higher than before.
question
f′ = 429Hz
f you take the original pipe in Part A and drill a hole at a position half the length of the pipe, what is the fundamental frequency f′ of the sound that can be produced in the pipe? ( f before = 214 Hz)
question
Only the even multiples of the fundamental frequency
What frequencies, in terms of the fundamental frequency of the original pipe in Part A, can you create when blowing air into the pipe that has a hole halfway down its length?( f before = 214 Hz) Only the odd multiples of the fundamental frequency Only the even multiples of the fundamental frequency All integer multiples of the fundamental frequency
question
Half the length of the open-open pipe
What length of open-closed pipe would you need to achieve the same fundamental frequency f as the open-open pipe discussed in Part A? ( f before = 214 Hz) Half the length of the open-open pipe Twice the length of the open-open pipe One-fourth the length of the open-open pipe Four times the length of the open-open pipe The same as the length of the open-open pipe
question
f′′ = 643 Hz
What is the frequency f′′ of the first possible harmonic after the fundamental frequency in the open-closed pipe described in Part E? (length is Half the length of the open-open pipe)
question
The loudness of a sound is related it its amplitude. The pitch of a sound is determined by its frequency.
Which of the following statements are true? Check all that apply. The speed of sound is constant. The loudness of a sound is related it its amplitude. Sound is a transverse wave. Sound can travel through a vacuum. The pitch of a sound is determined by its frequency.
question
open at one end and closed at the other end.
A pipe that is 120 cm long resonates to produce sound of wavelengths 480 cm, 160 cm, and 96 cm but does not resonate at any wavelengths longer than these. This pipe is open at one end and closed at the other end. open at both ends. closed at both ends. We cannot tell because we do not know the frequency of the sound.
question
2L, L, 2L/3
Consider a pipe of length L that is open at both ends. What are the wavelengths of the three lowest-pitch tones produced by this pipe? 2L, L, L/3 2L, L, L/2 2L, L, 2L/3 4L, 4L/3, 4L/5 4L, 2L, L
question
900 Hz 