Chapter 14

Tripling the power output from a speaker emitting a single frequency will result in what increase in loudness?

c. 4.8 dB

In which part of the ear is the cochlea?

C. inner ear

The density of a certain metal solid is 7.2 × 103 kg/m3, and its Young's modulus is 10 × 1010 N/m2. What is the speed of sound in this metal?

c. 3 700 m/s

What sound level change corresponds to a factor of two change in intensity?

c. 3 dB

What is the lowest frequency that will resonate in an organ pipe 2.00 m in length, closed at one end? The speed of sound in air is 340 m/s.

a. 42.5 Hz

A child sits on a swing supported by ropes of length 3.0 m. With what frequency will she need to apply the driving force to maintain swinging?

a. 0.29 Hz

If I triple the mass per unit length of guitar string, its natural frequency changes by what factor?

a. 0.58

A 100-m-long high-voltage cable is suspended between two towers. The mass of the 100-m cable is 150 kg. If the tension in the cable is 30 000 N, what is the lowest frequency at which this cable can oscillate?

a. 0.71 Hz

What is the intensity of sound from a band with a sound level of 120 dB? (I0 = 10−12 W/m2)

a. 1 W/m2

I stretch a rubber band and "plunk" it to make it vibrate in its fundamental frequency. I then stretch it to twice its length and make it vibrate in the fundamental frequency once again. The rubber band is made so that doubling its length doubles the tension and reduces the mass per unit length by a factor of 2. The new frequency will be related to the old by a factor of:

a. 1.0.

The frequency separating audible waves and ultrasonic waves is considered to be 20 kHz. What wavelength in air at room temperature is associated with this frequency? (Assume the speed of sound to be 340 m/s.)

a. 1.7 cm

Tripling the distance between sound source and a listener will change the intensity, as detected by the listener, by what factor?

a. 1/9

A plane is traveling at Mach 0.950 through air at a temperature of 0°C. What is the plane's speed? (Speed of sound at 0oC is 331 m/s.)

a. 314 m/s

The speed of sound at 0°C is 331 m/s. What is the speed of sound at 25°C? (0°C = 273 K)

a. 346 m/s

A 1.5-m string is held fixed at both ends. When driven by a 180-Hz source, the string vibrates in 4 distinct segments. What is the natural fundamental frequency of the string?

a. 45 Hz

A bat, flying at 5.00 m/s toward a wall, emits a chirp at 50.0 kHz. If the wall reflects this sound pulse, what is the frequency of the echo received by the bat? (vsound = 340 m/s)

a. 51.5 kHz

8. Assuming that the wave speed varies little when sound waves are traveling though a material that suddenly changes density by 10%, what percentage of the incident wave intensity is reflected?

a. < 1 %

The air in a tube open at both ends is sent into its fundamental resonance. One end of the tube is then closed and the air column is again set into its fundamental resonance. The resonant frequency _______________ after the end is closed.

a. halves

An airplane flying with a constant speed flies from a warm air mass into a cold air mass. The Mach number will:

a. increase.

Which of the following ranges corresponds to the longest wavelengths?

a. infrasonic

When I stand halfway between two speakers, with one on my left and one on my right, a musical note from the speakers gives me constructive interference. How far to my left should I move to obtain destructive interference?

a. one-fourth of a wavelength

72. The number of overtones, and their relative intensities, is associated with what property of the tone generated by a musical instrument?

a. quality

Two loudspeakers are placed side by side and driven by the same source at 500 Hz. A listener is positioned in front of the two speakers and on the line separating them, thus creating a constructive interference at the listener's ear. If one of the speakers is gradually pushed toward the listener, how far must it be moved to repeat the condition of constructive interference at the listener's ear? (The speed of sound = 340 m/s.)

b. 0.68 m

A tuning fork is sounded above a resonating tube (one end closed), which resonates at a length of 0.20 m and again at 0.60 m. If the tube length were extended further, at what point will the tuning fork again create a resonance condition?

b. 1.0 m

The Doppler shift of ultrasonic waves can measure the speed of blood in an artery. If the frequency of the stationary source is 100 kHz and the reflected sound has a Doppler shift of 200 Hz, what is the blood flow speed? (The speed of sound inside the body is 1 500 m/s.)

b. 1.5 m/s

f the distance between a point sound source and a dB detector is increased by a factor of 4, what will be the reduction in intensity level?

b. 12 dB

What is the intensity of a sound with a measured intensity level of 84 dB? (I0 = 10−12 W/m2)

b. 2.5 × 10−4 W/m2

If I0 = 10−12 W/m2 is the threshold of hearing, a sound with intensity I1 = 10−11 W/m2 will give a certain decibel level. Suppose a new sound has an intensity I2 = I12/I0. What is the new decibel level?

b. 20

A tuning fork is sounded above a resonating tube (one end closed), which resonates at a length of 0.200 m and again at 0.600 m. What is the frequency of the fork when the speed of sound is taken to be 340 m/s?

b. 425 Hz

A 500-Hz whistle is moved toward a listener at a speed of 10.0 m/s. At the same time, the listener moves at a speed of 20.0 m/s in a direction away from the whistle. What is the apparent frequency heard by the listener? (The speed of sound is 340 m/s.)

b. 485 Hz

A train station bell gives off a fundamental tone of 500 Hz as the train approaches the station at a speed of 20 m/s. If the speed of sound in air is 335 m/s, what will be the apparent frequency of the bell to an observer riding the train?

b. 530 Hz

The term "timbre" refers to which of the following?

b. The quality of sound from instruments due to the mixture of harmonics.

When a sine wave is used to represent a sound wave, the crest corresponds to:

b. condensation.

As a train starts from rest and then accelerates down the track, coming toward me faster and faster, the speed of the sound waves coming toward me will be:

b. equal to the normal speed of sound in air.

Consider a vibrating string that makes a sound wave that moves through the air. As the guitar string moves up and down, the air molecules that are a certain horizontal distance from the string will move:

b. toward and away from the guitar string.

Two loudspeakers are placed next to each other and driven by the same source at 500 Hz. A listener is positioned in front of the two speakers and on the line separating them, thus creating a constructive interference at the listener's ear. What minimum distance would one of the speakers be moved back away from the listener to produce destructive interference at the listener's ear? (The speed of sound = 340 m/s.)

c. 0.34 m

Doubling the tension in a guitar string will change its natural frequency by what factor?

c. 1.4

A 2.50-m-long organ pipe is open at one end and closed at the other. Its fundamental tone has wavelength:

c. 10.0 m.

What is the first overtone frequency for an organ pipe 2.00 m in length, closed at one end? The speed of sound in air is 340 m/s.

c. 128 Hz

A sound wave in air has a frequency of 500 Hz and a wavelength of 0.68 m. What is the air temperature?

c. 15°C

A sound wave coming from a tuba has a wavelength of 1.50 m and travels to your ears at a speed of 345 m/s. What is the frequency of the sound you hear?

c. 230 Hz

Two tuning forks sounding together result in a beat frequency of 3 Hz. If the frequency of one of the forks is 256 Hz, what is the frequency of the other?

c. 259 Hz or 253 Hz

If the tension on a guitar string is increased by a factor of 3, the fundamental frequency at which it vibrates is changed by what factor?

c. 3

A phase difference of 270° corresponds to what wavelength difference?

c. 3 /4

Of the frequencies listed below, to which one is the human ear most sensitive?

c. 3 300 Hz

When two sound waves are out of phase by _______, destructive interference will occur.

c. 540°

A C note (f = 256 Hz) is sounded on a piano. If the length of the piano wire is 1.00 m and its mass density is 2.50 g/m, what is the tension in the wire?

c. 655 N

A very loud train whistle has an acoustic power output of 100 W. If the sound energy spreads out spherically, what is the intensity level in dB at a distance of 100 meters from the train? (I0 = 10−12 W/m2)

c. 89.0 dB

When the standing wave pattern in a pipe is NANA, the pipe has which of the following set of properties? (N stands for node, A for antinode.)

c. It is open at one end and closed at the other end.

The speed of sound in air is a function of which one of the following

c. temperature

For a standing wave on a string the wavelength must equal:

c. twice the distance between adjacent nodes.

For a standing wave in an air column in a pipe that is open at both ends, there must be at least:

c. two antinodes and one node.

How far away is a lightning strike if you hear the thunderclap 3.00 s after you see the lightning bolt strike? (vsound = 340 m/s, vlight = 3 × 108 m/s)

d. 1 020 m

A sound source of frequency 1 000 Hz moves at 50.0 m/s toward a listener who is at rest. What is the apparent frequency heard by the listener? (speed of sound = 340 m/s)

d. 1 170 Hz

f a guitar string has a fundamental frequency of 500 Hz, what is the frequency of its second overtone?

d. 1 500 Hz

If one-third of the members of a symphony orchestra are absent because of head colds, thus reducing the overall intensity of sound by 33%, what will be the reduction in the decibel level?

d. 1.7 dB

f two adjacent frequencies of an organ pipe closed at one end are 550 Hz and 650 Hz, what is the length of the organ pipe? (vsound = 340 m/s)

d. 1.70 m

A series of ocean waves, 5.0 m between crests, move past at 2.0 waves/s. Find their speed.

d. 10 m/s

The intensity level of sound 20 m from a jet airliner is 120 dB. At what distance from the airplane will the sound intensity level be a tolerable 100 dB? (Assume spherical spreading of sound.)

d. 200 m

While standing at a crosswalk, you hear a frequency of 560 Hz from an approaching police car. After the police car passes, its frequency is 480 Hz. What is the speed of the police car? (speed of sound = 340 m/s)

d. 26.2 m/s

A flute behaves like a tube open at both ends. If its length is 65.3 cm, and the speed of sound is 340 m/s, what is its fundamental frequency in Hz?

d. 260 Hz

What is the intensity level of a sound with intensity of 5.0 × 10−10 W/m2? (I0 = 10−12 W/m2)

d. 27 dB

Two vibrating tuning forks, held side by side, will create a beat frequency of what value if the individual frequencies of the two forks are 342 Hz and 345 Hz, respectively?

d. 3 Hz

You stand by the railroad tracks as a train passes by. You hear a 1 000-Hz frequency when the train approaches, which changes to 800 Hz as it goes away. How fast is the train moving? The speed of sound in air is 340 m/s.

d. 37.8 m/s

The lower A on a piano has a frequency of 27.5 Hz. If the tension in the 2.0-m-long string is 304 N and one-half wavelength occupies the string, what is the mass of the string?

d. 50 g

Two cars, one in front of the other, are traveling down the highway at 25 m/s. The car behind sounds its horn, which has a frequency of 500 Hz. What is the frequency heard by the driver of the lead car? (vsound = 340 m/s)

d. 500 Hz

By what amount does the sound intensity decrease when the distance to the source doubles?

d. 6.0 dB

In the afternoon, the decibel level of a busy freeway is 80 dB with 100 cars passing a given point every minute. Late at night, the traffic flow is only 5 cars per minute. What is the late-night decibel level?

d. 68 dB

A standing wave is set up in a 200-cm string fixed at both ends. The string vibrates in 5 distinct segments when driven by a 120-Hz source. What is the wavelength?

d. 80 cm

When a sound wave moves through a medium such as air, the motion of the molecules of the medium is in what direction (with respect to the motion of the sound wave)?

d. Both choices b and c are valid.

A vibrating guitar string emits a tone simultaneously with one from a 500-Hz tuning fork. If a beat frequency of 5 Hz results, what is the frequency of vibration of the string?

d. Either choice b or c is valid.

A standing wave is set up in a 2.0-m string fixed at both ends. The string vibrates in 5 distinct segments when driven by a 120-Hz source. In how many distinct standing wave segments will the string vibrate if the tension is increased by a factor of 4?

d. No standing wave pattern occurs.

What phenomenon is created by two tuning forks, side by side, emitting frequencies, which differ by only a small amount?

d. beats

Comparing the speed of sound in liquids, gases, and solids, the speed of sound is usually lowest in ________ and highest in ________.

d. gases, solids

f the intensity of a sound is increased by a factor of 100, how is the decibel level changed? The new decibel level will be:

d. twenty units greater.