[VCAA Exam Questions] Sound

Sound is best described as a

A. longitudinal pressure wave transmitting air particles from a source to a receiver.
B. transverse pressure wave transmitting wave maxima from a source to a receiver.
C. longitudinal pressure wave transmitting energy from a source to a receiver.
D. transverse pressure wave transmitting energy from a source to a receiver.

A sound engineer, Dan, is setting up for a concert in a large stadium. In order to test the acoustics of the stadium, he sets up a single speaker in the middle of the stage. This speaker transmits sound equally in all directions. Using a signal generator and amplifier attached to the speaker, he sets the frequency of the sound to 500 Hz. Take the speed of sound to be 350 m s^-1.

The wavelength of the signal is closest to

0.07 m
0.70 m
1.43 m
2.34 m

A sound engineer, Dan, is setting up for a concert in a large stadium. In order to test the acoustics of the stadium, he sets up a single speaker in the middle of the stage. This speaker transmits sound equally in all directions. Using a signal generator and amplifier attached to the speaker, he sets the frequency of the sound to 500 Hz. Take the speed of sound to be 350 m s^-1.

Another sound engineer, Limei, investigates the sound intensity level at various points in the stadium. At a distance of 60 m from the speaker, Limei’s sound level meter reads 80 dB.

The sound intensity at this point is closest to

1.0×10^-4Wm^-2
1.0×10⁴Wm^-2
4.0×10^-4Wm^-2
8.0×10⁵Wm^-2

A sound engineer, Dan, is setting up for a concert in a large stadium. In order to test the acoustics of the stadium, he sets up a single speaker in the middle of the stage. This speaker transmits sound equally in all directions. Using a signal generator and amplifier attached to the speaker, he sets the frequency of the sound to 500 Hz. Take the speed of sound to be 350 m s^-1.

Another sound engineer, Limei, investigates the sound intensity level at various points in the stadium. At a distance of 60 m from the speaker, Limei’s sound level meter reads 80 dB.

Limei moves a further 60 m from the speaker.
Her sound level meter will now show a reading closest to

70dB
74dB
77dB
86dB

Which one of the following factors does the loudness (phon) scale specifically take into account?

A. Intensity of sound, as perceived by human hearing, is inversely proportional to distance from the source.
B. The perception of the intensity of sound by human hearing steadily decreases with frequency.
C. There is a very limited range of frequencies that the human ear can hear.
D. The sensitivity of human hearing varies with frequency.

The graph in Figure 1 shows the relationship between sound intensity level (dB), frequency (Hz) and loudness. The sound intensity level of a note of 10 000 Hz is measured by a sound meter to be 60 dB.

Which one of the values below best gives the loudness at the 10 000 Hz, 60 dB point?

80 phon
60 phon
40 phon
20 phon

Yasmin and Paul set up the following experiment in a large open area. They connect two speakers that are facing each other, as shown in Figure 2. Both speakers are connected 10 m apart to the same signal generator and amplifier, which is producing a sound with a wavelength of 1.0 m.

Yasmin stands in the centre, equidistant to speakers A and B. She then moves towards Speaker B and experiences a sequence of loud and quiet regions. She stops at the second region of quietness.

How far is she from Speaker B?

0.75 m
1.25 m
2.75 m
4.25 m

Roger is an instrument-maker who is constructing and testing pipes for a pipe organ. The pipes can be considered to be uniform tubes open at one end and closed at the other. He needs to design a pipe to give a wavelength of 0.325 m.

Which one of the following is closest to the length Roger should make the pipe?

0.081 m
0.325 m
0.650 m
1.35 m

Roger is an instrument-maker who is constructing and testing pipes for a pipe organ. The pipes can be considered to be uniform tubes open at one end and closed at the other. He needs to design a pipe to give a wavelength of 0.325 m.

Roger tests a different pipe by placing a loudspeaker attached to a very precise audio signal generator at the open end of the pipe and gradually increases the frequency.

He finds that in addition to the resonance at 256 Hz, there is a higher resonance (the second harmonic). At which one of the following frequencies will this second harmonic be observed?

128 Hz
512 Hz
768 Hz
1024 Hz

Electret-condenser, crystal and dynamic are three types of microphones.
Which of the following matches each type of microphone to its physical property?

A
B
C
D

Millie and Mikio are testing a loudspeaker. They set it up as shown in Figure 3a.

The sound is not sufficiently loud. They add a large baffle board, as shown in Figure 3b. The intensity of the sound at the sound level meter increases.

What is the best explanation for the increase in the intensity of the sound?

The baffle board prevents interference between waves from the front and back of the loudspeaker.
The baffle board prevents sound travelling out vertically and so more sound reaches the meter.
The baffle board also oscillates with the loudspeaker, thus sending out more sound waves.
There is resonance between the baffle board and the loudspeaker.

A loudspeaker emits a sound of frequency 30 Hz. The speed of sound in air in these conditions is 330 m s^-1. Which one of the following best gives the wavelength of the sound?

30 m
11 m
3.3 m
0.091 m

Consider an air particle initially at rest 5.0 m in front of a loudspeaker, as shown in Figure 1. The speed of sound in air in these conditions is 330 m s^-1.

Which one of the following best describes the subsequent motion of this particle when the loudspeaker is emitting a sound of frequency 30 Hz

It moves in direction Z at a constant speed of 330 m s^-1.
It oscillates about its rest position in direction WX 30 times per second.
It oscillates about its rest position in direction YZ 30 times per second.
It oscillates about its rest position in direction YZ at an average speed of 330 m s^-1.

A loudspeaker emits a sound of frequency 300 Hz equally in all directions. Emily is standing 4.0 m from the loudspeaker and measures the sound intensity level as 80 dB.

Which one of the following best gives the sound intensity (in W m^-2) at the point where Emily is standing?

8.0 × 10^-5 W m^-2
1.0 × 10^-4 W m^-2
8.0 × 10^-4 W m^-2
3.0 × 10² W m^-2

Emily walks away from the loudspeaker until she is 8 m from it.
Which one of the following best gives the sound intensity level (in dB) she will now hear?

77 dB
74 dB
16 dB
4.0 dB

Students conduct an experiment to observe standing waves in air columns. They use a hollow tube immersed in water, so the length of the air column in the tube can be varied, as shown in Figure 2.

The speed of sound in air under the conditions during their experiment is 320 m s^-1. The end of the tube nearest the speaker acts as an open end and the end of the tube away from the speaker acts as a closed end.

The students set the signal generator to 200 Hz. They begin with the tube at a length of 0.30 m and then raise the tube until they hear the first resonance.

Which one of the following is the best estimate of the length of the air column at which they hear the first resonance?

0.40 m
0.80 m
1.6 m
3.2 m

Students conduct an experiment to observe standing waves in air columns. They use a hollow tube immersed in water, so the length of the air column in the tube can be varied, as shown in Figure 2.

The speed of sound in air under the conditions during their experiment is 320 m s^-1. The end of the tube nearest the speaker acts as an open end and the end of the tube away from the speaker acts as a closed end.

The students set the signal generator to 200 Hz. They begin with the tube at a length of 0.30 m and then raise the tube until they hear the first resonance.

Which one of the following is the best estimate of the length of the air column at which they hear the next resonance?

0.40 m
0.60 m
1.2 m
1.6 m

Curves of equal phon value are shown in the graph below.

Richard is listening to sound of frequency 50 Hz. He hears it at a loudness of 60 phon.
Without changing the sound level of the speaker in decibels, the frequency is increased to 2000 Hz. Which one of the following best gives the loudness at which Richard will now hear the sound?

100 phon
80 phon
52 phon
40 phon

Curves of equal phon value are shown in the graph below.

Which one of the following statements explains why the phon curves have the shapes shown in Figure 3?

The speed of sound in air is different for different frequencies.
The sensitivity of the human ear increases linearly as the frequency increases.
The frequency sensitivity of the human ear is different to that of many animals.
The sensitivity of the human ear increases until a particular frequency and then decreases again.

Curves of equal phon value are shown in the graph below.

Roger is listening for a distant sound of frequency 100 Hz. He has normal hearing; that is, as in the phon graph. The distant sound is measured by a sound meter as 20 dB.

Which one of the following best describes what Roger will hear?

He will hear it at less than 20 dB.
He will hear it at 20 phon.
He will hear it at 20 dB.
He will not hear it at all.

A group of students is conducting experiments to study the diffraction of sound.
The first experiment is conducted on the school oval. The arrangement is shown in Figure 4.

The frequency is 1200 Hz. The width of the gap between the two barriers is 0.5 m.
At some distance from the gap, the students note that the edge of the diffraction pattern is 1.5 m off the centre line.

The students increase the frequency to 3000 Hz.
Which one of the following is most likely to be observed?

The edge of the pattern will still be approximately 1.5 m off the centre line.
The edge of the pattern will be closer to the centre line.
The edge of the pattern will be further out than 1.5 m.
There will now be no edge of the pattern.

A group of students is conducting experiments to study the diffraction of sound.
The first experiment is conducted on the school oval. The arrangement is shown in Figure 4.

The frequency is 1200 Hz. The width of the gap between the two barriers is 0.5 m.
At some distance from the gap, the students note that the edge of the diffraction pattern is 1.5 m off the centre line.

The students now repeat the experiment in their classroom, but do not observe such a clear edge to the pattern. Which one of the following is the most likely reason for this?

The room is too big for the wavelength.
The room is too small for the wavelength.
The doorway allowed a proportion of the sound to escape and so destructive interference did not occur completely.
Reflection off the walls and ceiling of the classroom meant that destructive interference did not occur completely.

[VCAA Exam Questions] Sound

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