Sections
Chapter Review

# Chapter Review

### Concept Items

#### 14.1Speed of Sound, Frequency, and Wavelength

1.

What is the amplitude of a sound wave perceived by the human ear?

1. loudness
2. pitch
3. intensity
4. timbre
2.
The compressibility of air and hydrogen is almost the same. Which factor is the reason that sound travels faster in hydrogen than in air?
1. Hydrogen is more dense than air.
2. Hydrogen is less dense than air.
3. Hydrogen atoms are heavier than air molecules.
4. Hydrogen atoms are at a higher temperature than air molecules.

#### 14.1Speed of Sound, Frequency, and Wavelength

3.
A bat produces a sound at $17,250Hz$ and wavelength $0.019m$. What is the speed of the sound?
1. $1.7×106m/s$
2. $8.6×105m/s$
3. $1.15×10−6m/s$
4. $3.28×102m/s$
4.
A sound wave with frequency of $80Hz$ is traveling through air at $0∘C$. By how much will its wavelength change when it enters aluminum?
1. $68m$
2. $64m$
3. $4m$
4. $60m$

#### 14.2Sound Intensity and Sound Level

5.

What is the mathematical relationship between intensity, power, and area?

1. $I=PA2I=PA2$
2. $I=PAI=PA$
3. $I=API=AP$
4. $I=PAI=PA$
6.

How does the "decibel" get its name?

1. The meaning of deci is “hundred” and the number of decibels is one-hundredth of the logarithm to base 10 of the ratio of two sound intensities.
2. The meaning of deci is "ten" and the number of decibels is one-tenth of the logarithm to base 10 of the ratio of two sound intensities.
3. The meaning of deci is “one-hundredth” and the number of decibels is hundred times the logarithm to base 10 of the ratio of two sound intensities.
4. The meaning of deci is “one-tenth” and the number of decibels is ten times the logarithm to base 10 of the ratio of two sound intensities.
7.
What is “timbre” of sound?
1. Timbre is the quality of the sound that distinguishes it from other sound
2. Timbre is the loudness of the sound that distinguishes it from other sound.
3. Timbre is the pitch of the sound that distinguishes it from other sound.
4. Timbre is the wavelength of the sound that distinguishes it from other sound.

#### 14.3Doppler Effect and Sonic Booms

8.

Two sources of sound producing the same frequency are moving towards you at different speeds. Which one would sound more high-pitched?

1. the one moving slower
2. the one moving faster
9.
When the speed of the source matches the speed of sound, what happens to the amplitude of the sound wave? Why?
1. It approaches zero. This is because all wave crests are superimposed on one another through constructive interference.
2. It approaches infinity. This is because all wave crests are superimposed on one another through constructive interference.
3. It approaches zero, because all wave crests are superimposed on one another through destructive interference.
4. It approaches infinity, because all wave crests are superimposed on one another through destructive interference.
10.
What is the mathematical expression for the frequency perceived by the observer in the case of a stationary observer and a moving source?
1. $fobs=fs(vwvs±vw)$
2. $fobs=fs(vw±vsvw)$
3. $fobs=fs(vs±vwvw)$
4. $fobs=fs(vwvw±vs)$

#### 14.4Sound Interference and Resonance

11.
When does a yo-yo travel the farthest from the finger?
1. when the amplitude of the finger moving up and down is greater than the amplitude of the yo-yo
2. when the amplitude of the finger moving up and down is less than the amplitude of the yo-yo
3. when the frequency of the finger moving up and down is equal to the resonant frequency of the yo-yo
4. when the frequency of the finger moving up and down is different from the resonant frequency of the yo-yo
12.
What is the difference between harmonics and overtones?
1. Harmonics are all multiples of the fundamental frequency. The first overtone is actually the first harmonic.
2. Harmonics are all multiples of the fundamental frequency. The first overtone is actually the second harmonic.
3. Harmonics are all multiples of the fundamental frequency. The second overtone is actually the first harmonic.
4. Harmonics are all multiples of the fundamental frequency. The third overtone is actually the second harmonic.
13.

What kind of waves form in pipe resonators?

1. damped waves
2. propagating waves
3. high-frequency waves
4. standing waves
14.
What is the natural frequency of a system?
1. The natural frequency is the frequency at which a system oscillates when it undergoes forced vibration.
2. The natural frequency is the frequency at which a system oscillates when it undergoes damped oscillation.
3. The natural frequency is the frequency at which a system oscillates when it undergoes free vibration without a driving force or damping.
4. The natural frequency is the frequency at which a system oscillates when it undergoes forced vibration with damping.

### Critical Thinking Items

#### 14.1Speed of Sound, Frequency, and Wavelength

15.
What can be said about the frequency of a monotonous sound?
1. It decreases with time.
2. It decreases with distance.
3. It increases with distance.
4. It remains constant.
16.
A scientist notices that a sound travels faster through a solid material than through the air. Which of the following can explain this?
1. Solid materials are denser than air.
2. Solid materials are less dense than air.
3. A solid is more rigid than air.
4. A solid is easier to compress than air.

#### 14.2Sound Intensity and Sound Level

17.
Which property of the wave is related to its intensity? How?
1. The frequency of the wave is related to the intensity of the sound. The larger-frequency oscillations indicate greater pressure maxima and minima, and the pressure is higher in greater-intensity sound.
2. The wavelength of the wave is related to the intensity of the sound. The longer-wavelength oscillations indicate greater pressure maxima and minima, and the pressure is higher in greater-intensity sound.
3. The amplitude of the wave is related to the intensity of the sound. The larger-amplitude oscillations indicate greater pressure maxima and minima, and the pressure is higher in greater-intensity sound.
4. The speed of the wave is related to the intensity of the sound. The higher-speed oscillations indicate greater pressure maxima and minima, and the pressure is higher in greater-intensity sound.
18.
Why is decibel (dB) used to describe loudness of sound?
1. Because, human ears have an inverse response to the amplitude of sound.
2. Because, human ears have an inverse response to the intensity of sound.
3. Because, the way our ears perceive sound can be more accurately described by the amplitude of a sound rather than the intensity of a sound directly.
4. Because, the way our ears perceive sound can be more accurately described by the logarithm of the intensity of a sound rather than the intensity of a sound directly.
19.
How can humming while shooting a gun reduce ear damage?
1. Humming can trigger those two muscles in the outer ear that react to intense sound produced while shooting and reduce the force transmitted to the cochlea.
2. Humming can trigger those three muscles in the outer ear that react to intense sound produced while shooting and reduce the force transmitted to the cochlea.
3. Humming can trigger those two muscles in the middle ear that react to intense sound produced while shooting and reduce the force transmitted to the cochlea.
4. Humming can trigger those three muscles in the middle ear that react to intense sound produced while shooting and reduce the force transmitted to the cochlea.
20.
A particular sound, S1, has an intensity $3$ times that of another sound, S2. What is the difference in sound intensity levels measured in decibels?
1. $9.54dB$
2. $6.02dB$
3. $3.01dB$
4. $4.77dB$

#### 14.3Doppler Effect and Sonic Booms

21.

When the source of sound is moving through the air, does the speed of sound change with respect to a stationary person standing nearby??

1. Yes
2. No
22.
Why is no sound heard by the observer when an object approaches him at a speed faster than that of sound?
1. If the source exceeds the speed of sound, then destructive interference occurs and no sound is heard by the observer when an object approaches him.
2. If the source exceeds the speed of sound, the frequency of sound produced is beyond the audible range of sound.
3. If the source exceeds the speed of sound, all the sound waves produced approach minimum intensity and no sound is heard by the observer when an object approaches him.
4. If the source exceeds the speed of sound, all the sound waves produced are behind the source. Hence, the observer hears the sound only after the source has passed.
23.
Does the Doppler effect occur when the source and observer are both moving towards each other? If so, how would this affect the perceived frequency?
1. Yes, the perceived frequency will be even lower in this case than if only one of the two were moving.
2. No, the Doppler effect occurs only when an observer is moving towards a source.
3. No, the Doppler effect occurs only when a source is moving towards an observer.
4. Yes, the perceived frequency will be even higher in this case than if only one of the two were moving.

#### 14.4Sound Interference and Resonance

24.

When does the amplitude of an oscillating system become maximum?

1. When two sound waves interfere destructively.
2. When the driving force produces a transverse wave in the system.
3. When the driving force of the oscillator to the oscillating system is at a maximum amplitude.
4. When the frequency of the oscillator equals the natural frequency of the oscillating system.
25.
How can a standing wave be formed with the help of a tuning fork and a closed-end tube of appropriate length?
1. If the tube is just the right length, the reflected sound arrives back at the tuning fork exactly half a cycle later, and it interferes constructively with the continuing sound produced by the tuning fork.
2. If the tube is just the right length, the reflected sound arrives back at the tuning fork exactly half a cycle later, and it interferes destructively with the continuing sound produced by the tuning fork.
3. If the tube is just the right length, the reflected sound arrives back at the tuning fork exactly one full cycle later, and it interferes constructively with the continuing sound produced by the tuning fork.
4. If the tube is just the right length, the reflected sound arrives back at the tuning fork exactly one full cycle later, and it interferes destructively with the continuing sound produced by the tuning fork.
26.
A tube open at both ends has a fundamental frequency of $500Hz$. What will the frequency be if one end is closed?
1. $1000Hz$
2. $500Hz$
3. $125Hz$
4. $250Hz$

### Problems

#### 14.2Sound Intensity and Sound Level

27.

Calculate the sound intensity for a sound wave traveling through air at 15° C and having a pressure amplitude of 0.80 Pa. (Hint—Speed of sound in air at 15° C is 340 m/s .)

1. 9.6×10−3 W / m2
2. 7.7×10−3 W / m2
3. 9.6×10−4 W / m2
4. 7.7×10−4 W / m2
28.
The sound level in dB of a sound traveling through air at $0∘C$ is $97dB$. Calculate its pressure amplitude.
1. $4.3Pa$
2. $0.20Pa$
3. $0.04Pa$
4. $2.1Pa$

#### 14.3Doppler Effect and Sonic Booms

29.
An ambulance is moving away from you. You are standing still and you hear its siren at a frequency of $101Hz$. You know that the actual frequency of the siren is $105Hz$. What is the speed of the ambulance? (Assume the speed of sound to be $331m/s$.)
1. $17.07m/s$
2. $16.55m/s$
3. $14.59m/s$
4. $13.1m/s$
30.
An ambulance passes you at a speed of $15.0m/s$. If its siren has a frequency of $995Hz$, what is difference in the frequencies you perceive before and after it passes you? (Assume the speed of sound in air is $331m/s$.)
1. $47.0Hz$
2. $43.0Hz$
3. $94.9Hz$
4. $90.0Hz$

#### 14.4Sound Interference and Resonance

31.
What is the length of an open-pipe resonator with a fundamental frequency of $400.0Hz$? (Assume the speed of sound is $331m/s$.)
1. $165.1cm$
2. $82.22cm$
3. $20.25cm$
4. $41.38cm$
32.
An open-pipe resonator has a fundamental frequency of $250Hz$. By how much would its length have to be changed to get a fundamental frequency of $300.0Hz$? (Assume the speed of sound is $331m/s$.)
1. $77.32cm$
2. $44.09cm$
3. $32.16cm$
4. $11.03cm$