Question 1

The wavelength of ultrasound at 1 million Hz in air where the speed of sound is 340 m/s is
A) 0.00000034 m.
B) 0.0000034 m.
C) 0.00034 m.
D) 0.34 m.
E) 340,000,000 m.

Accepted Answer

The formula for calculating the wavelength of a sound wave is:
wavelength = speed of sound / frequency
Substituting the given values:
wavelength = 340 / 1,000,000 = 0.00034 m or 0.34 mm
Therefore, the answer is choice C.

Question 2

A source emits sound at a fixed constant frequency f . If the source moves away from you faster than the speed of sound in air, the frequency that you hear is
A) the same as f.
B) higher than f.
C) lower than f.
D) unrelated to f.

Accepted Answer

The answer of A source emits sound at a fixed...

Question 3

A source emits sound at a fixed constant frequency f . If you run towards the source, the frequency you hear is
A) the same as f.
B) higher than f.
C) lower than f.
D) unrelated to f.

Accepted Answer

When running towards the source, you are approaching the sound waves being emitted. Therefore, the relative velocity between you and the waves increases, causing the wavelength to decrease and the frequency to increase (according to the equation v=fλ, where v is the speed of sound). This means that the frequency you hear will be higher than the original frequency f.

Question 4

A source emits sound at a fixed constant frequency f . If the source moves away from you, and at the same time you run away from the source, the frequency you hear is
A) the same as f.
B) higher than f.
C) lower than f.
D) unrelated to f.

Accepted Answer

When the source moves away from the observer, the frequency of the sound waves emitted by the source is lengthened, which leads to a lower frequency (as the speed of sound remains constant). And when the observer runs away from the source, the observed frequency is further reduced. Therefore, the frequency heard by the observer is lower than the frequency emitted by the source, making choice C the correct answer.

Question 5

Which of the following is not one of the ways sound can be used?
A) to circulate the refrigerant in a refrigerator
B) to relay information to orbiting satellites
C) to form images of internal organs
D) to measure the air temperature aloft
E) to make a bubble in water produce light

Accepted Answer

The answer of Which of the following is not one...

Question 6

Choose the correct statement.
A) The perceived pitch of a sound usually doesn't depend on the sound's frequency.
B) The frequency of each musical note is 10 Hz higher than that of the next lower note.
C) The decibel is the standard measure of tone quality.
D) The perceived loudness of a sound depends somewhat on frequency.

Accepted Answer

The perceived loudness of a sound does depend on frequency, as different frequencies will activate different parts of the cochlea in the ear. Option A is incorrect, as the perceived pitch is directly related to the frequency of the sound. Option B is incorrect, as the frequency difference between each musical note depends on the musical scale being used. Option C is incorrect, as the decibel is a measure of loudness or sound pressure level, not tone quality.

Question 7

As you move farther away from a source emitting a pure tone, the ___________ of the sound you hear decreases.
A) frequency
B) period
C) wavelength
D) amplitude
E) none of the above

Accepted Answer

As you move farther away from a source of sound, the amplitude of the sound decreases, which is perceived as a decrease in volume. The frequency, period, and wavelength of the sound wave do not change with distance from the source.

Question 8

You listen to a live orchestra concert from a cheap seat far away, high up in the balcony. The music seems to be a little out of sync with the conductor's beat. Why?
A) The musicians are paying no attention to the conductor.
B) You are noticing a time lag due to the finite speed of sound.
C) The orchestra is not very good.
D) The viola section is dragging.

Accepted Answer

The sound takes time to travel from the orchestra to your ears, so there will be a slight time lag between what you see and what you hear. This can make it seem like the music is out of sync with the conductor, even if the musicians are playing perfectly in time with each other.

Question 9

The figure shows a 'snapshot' of four different waves in identical ropes stretched with the same force.  The wave where the speed is greatest is
A) I.
B) II.
C) III.
D) IV.
E) all of the above.

Accepted Answer

The answer of The figure shows a 'snapshot' of four...

Question 10

A source emits sound at a fixed constant frequency f . If the source moves away from you, the frequency you hear is
A) the same as f.
B) higher than f.
C) lower than f.
D) unrelated to f.

Accepted Answer

When a source moves away from you, the frequency of the sound waves reaching you decreases, resulting in a lower perceived frequency (known as a Doppler shift). This is shown by the Doppler equation: f' = f(v +-vd)/(v +-vs), where f' is the perceived frequency, f is the emitted frequency, v is the speed of sound, vd is the velocity of the detector, and vs is the velocity of the source. Since the source is moving away from the detector, vs is positive, and the denominator becomes v + vs, which is greater than v - vs. Therefore, f' must be less than f, and the answer is C.

Question 11

In ultrasound the _____________ of the sound is much greater than in normal sound.
A) frequency
B) period
C) wavelength
D) amplitude
E) speed

Accepted Answer

The frequency of ultrasound is much greater than that of normal sound, typically above 20 kHz, which is the upper limit of human hearing.

Question 12

Two speakers in a stereo emit identical pure tones. As you move around in front of the speakers, you hear the sound alternating between loud and zero. This occurs because of
A) interference.
B) changing sound level.
C) diffraction.
D) the Doppler effect.
E) shock waves.

Accepted Answer

This phenomenon is known as constructive and destructive interference, where the waves from the two speakers interfere with each other either constructively (adding up and creating a loud sound) or destructively (canceling each other out and creating no sound).

Question 13

You can hear sound through an open window from sources that are not in your line of sight because of
A) interference.
B) diffraction.
C) the sound level.
D) the Doppler effect.
E) none of the above.

Accepted Answer

The sound waves diffract or bend around obstacles like walls, trees, buildings or other objects. This bending of sound waves allows us to hear sound from sources that are not directly in our line of sight, like a car horn or a distant train whistle, even if there are obstacles in between.

Question 14

A source emits sound at a fixed constant frequency f . If the temperature of the air rises, the frequency you hear is
A) the same as f.
B) higher than f.
C) lower than f.
D) unrelated to f.

Accepted Answer

The frequency of the sound as heard by an observer does not change with temperature; what changes is the speed of sound in the air, not its frequency.

Question 15

Which of these waves will diffract the most when passing through a 20 cm wide opening in a barrier?
A) a wave with a wavelength of 25 cm
B) a wave with a wavelength of 2 cm
C) a wave with a wavelength of 0.05 cm
D) none of these waves will diffract at all

Accepted Answer

The degree of diffraction is directly proportional to the size of the opening and inversely proportional to the wavelength of the wave. Therefore, the wave with the longest wavelength (option A) will diffract the most through the 20 cm wide opening.

Question 16

A wave moves in a rope with a certain wavelength. A second wave is made to move in the same rope with twice the wavelength of the first wave. The frequency of the second wave is _______________ the frequency of the first wave.
A) 1/2
B) the same as
C) 2 times
D) unrelated to

Accepted Answer

The frequency of a wave is inversely proportional to its wavelength, meaning that as wavelength increases, frequency decreases. Since the second wave has twice the wavelength of the first wave, its frequency must be half of the frequency of the first wave. Therefore, the answer is choice A) 1/2.

Question 17

When two identical waves arrive at the same place in phase, there is
A) constructive interference.
B) destructive interference.
C) diffraction.
D) a Doppler effect.
E) a shock wave.

Accepted Answer

When two identical waves arrive in phase, the peaks and troughs of the waves align, resulting in constructive interference, which leads to an increase in the amplitude of the resultant wave.

Question 18

Ultrasound is used
A) to form images of internal organs.
B) by bats to navigate.
C) in automatic focus cameras.
D) to control insects.
E) all of the above

Accepted Answer

All of the options are correct. Ultrasound is used to form images of internal organs in medical diagnosis, by bats to navigate in the dark, in automatic focus cameras for precision focusing, and also for controlling insects in some agricultural applications.

Question 19

A source emits sound at a fixed constant frequency f . If the source moves, the wavelength of the sound in front of the direction of motion is ____________ the wavelength behind the direction of motion.
A) the same as
B) larger than
C) smaller than
D) unrelated to

Accepted Answer

According to the Doppler effect, when a sound source moves towards an observer, the frequency of the sound waves increases and the wavelength decreases. Conversely, when the sound source moves away from an observer, the frequency of the sound waves decreases and the wavelength increases. Therefore, in front of the direction of motion, the wavelength will be smaller than the wavelength behind the direction of motion.

Question 20

You shout at a cliff, and hear your echo in 2 seconds. If the speed of sound in the air is 340 m/s, the distance of the cliff from you is
A) 85 m.
B) 170 m.
C) 340 m.
D) 680 m.
E) none of the above.

Accepted Answer

The answer of You shout at a cliff, and hear...

Quiz 6: Waves and Sound

The wavelength of ultrasound at 1 million Hz in air where the speed of sound is 340 m/s is

A source emits sound at a fixed constant frequency f . If the source moves away from you faster than the speed of sound in air, the frequency that you hear is

A source emits sound at a fixed constant frequency f . If you run towards the source, the frequency you hear is

A source emits sound at a fixed constant frequency f . If the source moves away from you, and at the same time you run away from the source, the frequency you hear is

Which of the following is not one of the ways sound can be used?

Choose the correct statement.

As you move farther away from a source emitting a pure tone, the ___________ of the sound you hear decreases.

You listen to a live orchestra concert from a cheap seat far away, high up in the balcony. The music seems to be a little out of sync with the conductor's beat. Why?

The figure shows a 'snapshot' of four different waves in identical ropes stretched with the same force. The wave where the speed is greatest is

A source emits sound at a fixed constant frequency f . If the source moves away from you, the frequency you hear is

In ultrasound the _____________ of the sound is much greater than in normal sound.

Two speakers in a stereo emit identical pure tones. As you move around in front of the speakers, you hear the sound alternating between loud and zero. This occurs because of

You can hear sound through an open window from sources that are not in your line of sight because of

A source emits sound at a fixed constant frequency f . If the temperature of the air rises, the frequency you hear is

Which of these waves will diffract the most when passing through a 20 cm wide opening in a barrier?

A wave moves in a rope with a certain wavelength. A second wave is made to move in the same rope with twice the wavelength of the first wave. The frequency of the second wave is _______________ the frequency of the first wave.

When two identical waves arrive at the same place in phase, there is

Ultrasound is used

A source emits sound at a fixed constant frequency f . If the source moves, the wavelength of the sound in front of the direction of motion is ____________ the wavelength behind the direction of motion.

You shout at a cliff, and hear your echo in 2 seconds. If the speed of sound in the air is 340 m/s, the distance of the cliff from you is