Ch. 17 Flashcards
Does the principle of linear superposition imply that two sound waves, passing through the same place at the same time, always create a louder sound than is created by either wave alone?
No, because if the two sound waves have the same amplitude and frequency, they might cancel and no sound will be heard.
Suppose that you are sitting at the overlap point between two speakers. Because of destructive interference, you hear no sound, even though both speakers are emitting identical sound waves. One of the speakers is suddenly shut off. Will you now hear a sound?
Yes
Starting at the overlap point, you walk along a straight path that is perpendicular to the line between the speakers and passes through the midpoint of that line. As you walk, the loudness of the sound..
Does not change
Starting at the overlap point, you walk along a path that is parallel to the line between the speakers. As you walk, the loudness of the sound..
Changes from loud to faint to loud
At an open air rock concert you are standing directly in front of a speaker. You hear the high frequency sounds of a female vocalist as well as the low frequency sounds of the rhythmic bass. As you walk to one side of the speaker, the sounds of the vocalist ___, and those of the rhythmic bass ___.
Drop off noticeably; drop off only slightly
Which type of radio, AM or FM, diffracts more readily around a given obstacle?
AM, because it has a greater wavelength
A tuning fork has a frequency of 440Hz. The string of a violin and this tuning fork, when sounded together, produce a frequency of 1Hz. From these two pieces of information alone, is it possible to determine the exact frequency of the violin string?
No, because the frequency of the violin string could be either 439 or 441Hz
When the regions of constructive and destructive interference move past a listeners ear, a beat frequency of 2Hz is heard. Suppose that the tuning forks are sounded underwater and that the listener is also underwater. The forks vibrate at 438 and 440Hz, just as they do in air. However, sound travels four times faster in water than in air. The beat frequency heard by the underwater listen is ___.
2Hz
A standing wave that corresponds to the 4th harmonic is set up on a string that is fixed at both ends.
How many loops are in this standing wave?
4
A standing wave that corresponds to the 4th harmonic is set up on a string that is fixed at both ends.
How many nodes (excluding the nodes at the ends of the string) does this standing wave have?
3
A standing wave that corresponds to the 4th harmonic is set up on a string that is fixed at both ends.
Is there a node or an antinode at the midpoint of the string?
Node
A standing wave that corresponds to the 4th harmonic is set up on a string that is fixed at both ends.
If the frequency of this standing wave is 440Hz, what is the frequency of the lowest-frequency standing wave that could be set up on this string?
110Hz
The tension in a guitar string is doubled. By what factor does the frequency of the vibrating string change?
It increases by a factor of sqrt(2)
A string is vibrating back and forth. The tension in the string is decreased by a factor of 4, with the frequency and length of the spring remaining the same. A new standing wave pattern develops on the string. How many loops are in this new pattern?
2
A rope is hanging vertically straight down. The top end is being vibrated back and forth, and a standing wave with many loops develops on the rope, analogous to a standing wave in a horizontal rope. The rope has mass. The separation between successive nodes is..
Greater near the top of the rope than near the bottom
A cylindrical bottle, partially filled with water, is open at the top. When you blow across the top of the bottle a standing wave is set up inside it.
Is there a node or an antinode at the top of the bottle?
Antinode
A cylindrical bottle, partially filled with water, is open at the top. When you blow across the top of the bottle a standing wave is set up inside it.
Is there a node or an antinode at the surface of the water?
Node
A cylindrical bottle, partially filled with water, is open at the top. When you blow across the top of the bottle a standing wave is set up inside it.
If the standing wave is vibrating at its fundamental frequency, what is the distance between the top of the bottle and the surface of the water? Express your answer in terms of the wavelength of the standing wave.
(1/4)wavelength
A cylindrical bottle, partially filled with water, is open at the top. When you blow across the top of the bottle a standing wave is set up inside it.
If you take a sip from the bottle, is the fundamental frequency of the standing wave raised, lowered, or does it remain the same?
Lowered
Both tubes are filled with air, in which the speed of sound is vair.
Frequency fork next to vair has “frequency = f”. Suppose, instead, the tube near the tuning fork labeled “Frequency = 2f” is filled not with air, but with another gas in which the speed of sound is vgas. The frequency of each tuning fork remains unchanged. How should vgas compare with vair in order that the standing wave pattern in each tube has the same appearance?
vgas = 2vair
Standing waves can ruin the acoustics of a concert hall if there is an excessive reflection of the sound waves that the performers generate. For example, suppose that a performer generates a 2093Hz tone. If a large-amplitude standing wave is present, it is possible for a listener to move a distance of only 4.1cm and hear the loudness of the time change from loud to faint. What does the distance or 4.1cm represent?
One-fourth the wavelength of the sound
A wind instrument is brought into a warm house from the cold outdoors. What happens to the natural frequencies of the instrument? Neglect any change in the length of the instrument.
They increase
Two cellists, one seated directly behind the other in an orchestra, play the same note for the conductor, who is directly in front of them. Because of the separation between the cellists, destructive interference occurs at the conductor. This separation is the smallest that produces destructive interference. Would this separation increase, decrease, or remain the same if the cellists produced a note with a higher frequency?
The separation would decrease because the wavelength of the sound is smaller.
As the frequency does up, the wavelength goes down, so the separation between the cellists decreases.
A loudspeaker is producing sound of a certain wavelength. Which combination of the wavelength lambda (expressed as a multiple of lambda0) and the speakers diameter D (expressed as a multiple of D0) would exhibit the greatest amount of diffraction when the sound leaves the speaker and enters the room?
Lambda = 2lambda0 D = D0
