Deck 15: Sound

Question 1

How many times louder is the sound of busy traffic (80 dB) than the sound of normal conversation (40 dB)?

A)2
B)20
C)200
D)10000

Answer 1

10000

Question 2

How do we perceive the sounds of 40 Hz and 3 kHz, both at 100 dB?

A)We perceive 40 Hz sound as louder than 3 kHz sound.
B)We perceive 3 kHz sound as louder than 40 Hz sound.
C)We perceive both sounds as equally loud, they are both 100 dB.
D)There is not enough information to conclude the answer.

Answer 2

We perceive 3 kHz sound as louder than 40 Hz sound.

Question 3

Which of the following statements accurately describes a wave in a closed tube (incoming wave) and a reflected wave making a standing wave?

A)The phase of a reflected wave is shifted by a half wavelength compared to an incoming wave.
B)The phase of a reflected wave is shifted by a whole wavelength compared to an incoming wave.
C)The phase of a reflected wave is shifted by a phase difference 2ð compared to an incoming wave.
D)The amplitude term has the same sign for both waves.

Answer 3

The phase of a reflected wave is shifted by a half wavelength compared to an incoming wave.

Question 4

The tube in Fig. 15.1 is filled with helium. What is the fundamental frequency of the tube if the ë in the figure is 65.55 cm? The speed of sound in helium is 1007 m/s.

A)2640.4 Hz
B)1320.2 Hz
C)38.4 Hz
D)15.4 Hz

Question 5

If the distance from the source of sound is doubled, how will the intensity of the sound change?

A)increase by 2 times
B)increase by 4 times
C)decrease by 2 times
D)decrease by 4 times

Question 6

Consider an organ pipe that is open at one end and closed at the other. What is the relationship between the wavelengths of the harmonics and the length of the pipe?

A)The length of the pipe is equal to an odd number of halves of wavelengths.
B)The length of the pipe is equal to an even number of halves of wavelengths.
C)The length of the pipe is equal to an odd number of quarters of wavelengths.
D)The length of the pipe is equal to an even number of quarters of wavelengths.

Question 7

An ideal isothermal gas is in a horizontal container. From an equilibrium position, it is compressed by a piston. Which of these statements best describes the behaviour of the piston once it is released to move freely?

A)The piston restores directly to the equilibrium position.
B)The piston is held in the same position by the atmospheric pressure acting on the outside.
C)The piston oscillates around the equilibrium position.
D)The gas responds by ejecting the piston.

Question 8

A sound wave is established in the air. Which of these statements accurately describes the motion of the individual air molecules?

A)back and forth around equilibrium positions in the direction of the sound wave
B)back and forth around equilibrium positions perpendicular to the direction of the sound wave
C)continuous motion in the direction of the sound wave
D)molecules not moving; sound moving between them

Question 9

What is the amplitude of a gas element, at 20°C, when a sound wave of frequency 4 kHz propagates, and the pressure variation is 28 ìP, at the threshold of human hearing?

A)2.7 × 10^-12 m
B)1.7 × 10^-11 m
C)1.7 × 10^-9 m
D)2.7 × 10^-3 m

Question 10

Which statement describes a sound wave?

A)It is a transverse wave.
B)It is a pressure wave produced when particles of medium are moved from the source of the sound to the receiver.
C)It is a longitudinal wave.
D)The medium's particles oscillate perpendicular to the direction of the wave.

Question 11

Figure 15.1 The figure shows a standing wave in a closed tube.
The tube in Fig. 15.1 is filled with air. What is the fundamental frequency of the tube if ë in the figure is 65.55 cm? The speed of sound in air is 343 m/s.

A)523.3 Hz
B)261.6 Hz
C)130.8 Hz
D)65.4 Hz

Question 12

Which of these relationships accurately compares the lengths of one tube that is open at both ends and another tube that is open at one end when both tubes have the same fundamental frequency?

A)The tube that is closed at one end is half the length of open tube.
B)Because the fundamental frequency is the same, the length has to be the same for both tubes.
C)The tube that is open at both ends is half the length of the tube open at one end.
D)The tube that is closed at one end is 1.5 times the length of the open tube.

Question 13

Consider the human outer ear auditory canal as a tube open at one end and as a 2.5-cm-long resonator with rigid walls. What is the resonant frequency of the auditory canal? The speed of sound is 343 m/s.

A)34.3 Hz
B)3430 Hz
C)6860 Hz
D)13720 Hz

Question 14

For the wave in Fig. 15.2, what is the frequency of the second harmonic if the distance between two pressure nodes is 30 cm? The speed of sound in air is 343 m/s.

A)f = 190.6 Hz
B)f = 381.1 Hz
C)f = 571.7 Hz
D)f = 1143.3 Hz

Question 15

Consider three types of tubes filled with air: closed, open, and half-closed. Assume that an external force is used to move (oscillate) a piston harmonically back and forth with an angular frequency, ù_ext, similar to the frequency of the first harmonic of the standing wave forming in the tube, ù_standing. Which tube will experience resonance (increase of amplitude of oscillations)?

A)only the closed and the half-closed pipes
B)only the closed pipe
C)only the half-closed pipe
D)all three pipes

Question 16

Figure 15.3 The figure shows the anatomy of the human ear.
Where in the ear does the sound get amplified?

A)in the middle ear
B)in the inner ear
C)in the ear canal
D)on the eardrum

Question 17

Figure 15.2
The figure shows pressure nodes in a tube that is open on both ends.
For the wave in Fig. 15.2, what is the fundamental frequency if the distance between two pressure nodes is 30 cm? The speed of sound in air is 343 m/s.

A)f = 190.6 Hz
B)f = 381.1 Hz
C)f = 571.7 Hz
D)f = 1143.3 Hz

Question 18

We compare two sound waves in air at room temperature. Wave 2 has a 2 times longer wavelength than wave 1. Which of the following relations holds between their speeds?

A)v₁ = v₂
B)v₁ > v₂
C)v₁ < v₂
D)We cannot draw a conclusion without knowing their frequencies.

Question 19

Where in the ear does the sound get analyzed and identified by frequencies? Refer to Fig 15.3.

A)in the middle ear
B)in the inner ear
C)in the ear canal
D)on the eardrum

Question 20

In which of these media does sound propagate the fastest?

A)vacuum
B)air
C)water
D)brick

Question 21

If the intensity of a sound under water at a distance of 3 m from the source is 4.5 × 10^-2 W/m², what is the intensity when you move to a position 10 m from the source?

Question 22

Humans hear due only to vibration of the eardrum.

Question 23

If an object is vibrating, and another object acts on it with an external vibration close to the original frequency, the result is a dramatic increase in amplitude.

Question 24

A sound wave is a wave that propagates through a medium: the more elastic the medium, the bigger the resistance to the sound and therefore the slower the speed of the sound.

Question 25

A clarinet and a flute have nearly cylindrical bores with similar length and diameter, yet they are quite different in tone quality and range of pitch. Discuss those differences and explain the reasons.

Question 26

A dolphin emits an ultrasound pulse, which bounces off a small fish about 50 m away. How much time is required for the dolphin to notice the fish? The density of seawater is 1028 kg/m³, and the bulk modulus of water is 2.34 × 10⁹ Pa.

Question 27

For sound to be heard by the human ear, the displacement of air by the sound wave has to be significant, at least a few centimetres.

Question 28

In music, a one octave interval corresponds to a factor of 2 in frequency. How will the sound of a wind instrument change if you alter it (for example, by sliding a pipe, or closing holes) in such a way that the tube gets longer by a factor of 4? The speed of sound in air is 343 m/s.

Question 29

What is the fifth harmonic frequency of a 3.4 m organ pipe open at one end and closed at the other end? The speed of sound in air is 343 m/s.

Question 30

The speed of sound depends only on the density of the medium that it travels through.

Question 31

A sound wave is a longitudinal wave.

Question 32

If one sound is 70 dB and another sound is 100 dB, the difference in intensity between the two sounds is 1000 times.

Question 33

What fraction of atmospheric pressure (P_atm = 1.0 × 10⁵ Pa) is produced by a sound wave of frequency 1600 Hz and displacement amplitude D = 1.8 × 10^-11 m? The speed of sound in the air is 343 m/s, and the density of air is 1.2 kg/m³ at 20°C.

Question 34

A louder sound moves faster through air than a sound that is less loud.

Question 35

Figure 15.4 The figure shows an overview of a cochlea.
In Fig. 15.4, what is the order of frequencies exciting the membrane from the oval window on the left toward the right in the basilar membrane?

Question 36

The 100 dB sounds of 40 Hz and 3 kHz are equally loud, because the loudness expressed in decibels is the same.

Question 37

In music, a 1 octave interval corresponds to a factor of 2 in frequency. The lowest C on a piano, C1, has a frequency of 32.7 Hz, and the highest C, C8, is 7 octaves higher. What is the ratio of lengths of organ tubes that would produce C1 and C8 frequencies? The speed of sound in air is 343 m/s.

Question 38

If the amplitude of a sound wave is 0.001 atm, what is the maximum net force it produces on an eardrum that has an area of about 1 cm²? Is this a loud or a soft sound?

Question 39

Calculate the speed of sound for a winter temperature of -30°C. Is it slower or faster than the speed of sound at +30°C?

Question 40

You compress an ideal isothermal gas in a horizontal container with a piston. When you release the piston, the system restores directly to the state of equilibrium.