## 12 Af Essay

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Part A TRUE/FALSE 1. Which of the following statements are TRUE of sound waves Identify all that apply. A sound wave is a mechanical wave. A sound wave is a means of transporting energy without transporting matter. Sound can travel through a vacuum. A sound wave is a pressure wave they can be thought of as fluctuations in pressure with respect to time. A sound wave is a transverse wave. To hear the sound of a tuning fork, the tines of the fork must move air from the fork to ones ear. Most (but not all) sound waves are created by a vibrating object of some type. To be heard, a sound wave must cause a relatively large displacement of air (for instance, at least a cm or more) around an observers ear. 2. Which of the following statements are TRUE of sound intensity and decibel levels Identify all that apply. The intensity of a sound wave has units of Watts/meter. When a sound wave is said to be intense, it means that the particles are vibrating back and forth at a high frequency. Intense sounds are characterized by particles of the medium vibrating back and forth with a relatively large amplitude. Intense sounds are usually perceived as loud sounds. The ability of an observer to hear a sound wave depends solely upon the intensity of the sound wave. From the least intense to the most intense, humans have a rather narrow range of intensity over which sound waves can be heard. The intensity of sound which corresponds to the threshold of pain is one trillion times more intense than the sound which corresponds to the threshold of hearing. Two sounds which have a ratio of decibel ratings equal to 2.0. This means that the second sound is twice as intense as the first sound. Sound A is 20 times more intense than sound B. So if Sound B is rated at 30 dB, then sound A is rated at 50 dB. Sound C is 1000 times more intense than sound D. So if sound D is rated at 80 dB, sound C is rated at 110 dB. A machine produces a sound which is rated at 60 dB. If two of the machines were used at the same time, the decibel rating would be 120 dB. Intensity of a sound at a given location varies directly with the distance from that location to the source of the sound. If the distance from the source of sound is doubled then the intensity of the sound will be quadrupled. If the distance from the source of sound tripled, then the intensity of the sound will be increased by a factor of 6. 3. Which of the following statements are TRUE of the speed of sound Identify all that apply. The speed of a sound wave depends upon its frequency and its wavelength. In general, sound waves travel fastest in solids and slowest in gases. Sound waves travel fastest in solids (compared to liquids and gases) because solids are more dense. The fastest which sound can move is when it is moving through a vacuum. If all other factors are equal, a sound wave will travel fastest in the most dense materials. A highly elastic material has a strong tendency to return to its original shape if stressed, stretched, plucked or somehow disturbed. A more rigid material such as steel has a higher elasticity and therefore sound tends to move through it at high speeds. The speed of sound moving through air is largely dependent upon the frequency and intensity of the sound wave. A loud shout will move faster through air than a faint whisper. Sound waves would travel faster on a warm day than a cool day. The speed of a sound wave would be dependent solely upon the properties of the medium through which it moves. A shout in a canyon produces an echo off a cliff located 127 m away. If the echo is heard 0.720 seconds after the shout, then the speed of sound through the canyon is 176 m/s. The speed of a wave within a guitar string varies inversely with the tension in the string. The speed of a wave within a guitar string varies inversely with the mass per unit length of the string. The speed of a wave within a guitar string will be doubled if the tension of the string is doubled. An increase in the tension of a guitar string by a factor of four will increase the speed of a wave in the string by a factor of two. An increase in the linear mass density of a guitar string by a factor of four will increase the speed of a wave in the string by a factor of two. 4. Which of the following statements are TRUE of the frequency of sound and the perception of pitch Identify all that apply. A high pitched sound has a low wavelength. A low-pitched sound is a sound whose pressure fluctuations occur with a low period. If an object vibrates at a relatively high frequency, then the pitch of the sound will be low. The frequency of a sound will not necessarily be the same as the frequency of the vibrating object since sound speed will be altered as the sound is transmitted from the object to the air and ultimately to your ear. Two different guitar strings are used to produce a sound. The strings are identical in terms of material, thickness and the tension to which they are pulled. Yet string A is shorter than string B. Therefore, string A will produce a lower pitch. Both low- and high-pitched sounds will travel through air at the same speed. Doubling the frequency of a sound wave will halve the wavelength but not alter the speed of the wave. Tripling the frequency of a sound wave will decrease the wavelength by a factor of 6 and alter the speed of the wave. Humans can pretty much hear a low-frequency sound as easily as a high-frequency sound. Ultrasound waves are those sound waves with frequencies less than 20 Hz. 5. Which of the following statements are TRUE of standing wave patterns Identify all that apply. A standing wave pattern is formed as a result of the interference of two or more waves. When a standing wave pattern is established, there are portions of the medium which are not disturbed. A standing wave is really not a wave at all it is a pattern resulting from the interference of two or more waves which are traveling through the same medium. A standing wave pattern is a regular and repeating vibrational pattern established within a medium it is always characterized by the presence of nodes and antinodes. An antinode on a standing wave pattern is a point which is stationary it does not undergo any displacement from its rest position. For every node on a standing wave pattern, there is a corresponding antinode there are always the same number of each. When a standing wave pattern is established in a medium, there are alternating nodes and antinodes, equally spaced apart across the medium. 6. Which of the following statements are TRUE of the concept of resonance Identify all that apply. A musical instrument can play any frequency imaginable. All musical instruments have a natural frequency or set of natural frequencies at which they will vibrate each frequency corresponds to a unique standing wave pattern. The result of two objects vibrating in resonance with each other is a vibration of larger amplitude. Objects which share the same natural frequency will often set each other into vibrational motion when one is plucked, strummed, hit or otherwise disturbed. This phenomenon is known as a forced resonance vibration. A vibrating tuning fork can set a second tuning fork into resonant motion. The resonant frequencies of a musical instrument are related by whole number ratios. 7. Which of the following statements are TRUE of the harmonics and standing wave patterns in guitar strings Identify all that apply. The fundamental frequency of a guitar string is the highest frequency at which the string vibrates. The fundamental frequency of a guitar string corresponds to the standing wave pattern in which there is a complete wavelength within the length of the string. The wavelength for the fundamental frequency of a guitar string is 2.0 m. The wavelength for the second harmonic played by a guitar string is two times the wavelength of the first harmonic. The standing wave pattern for the fundamental played by a guitar string is characterized by the pattern with the longest possible wavelength. If the fundamental frequency of a guitar string is 200 Hz, then the frequency of the second harmonic is 400 Hz. If the frequency of the fifth harmonic of a guitar string is 1200 Hz, then the fundamental frequency of the same string is 6000 Hz. As the frequency of a standing wave pattern is tripled, its wavelength is tripled. If the speed of sound in a guitar string is 300 m/s and the length of the string is 0.60 m, then the fundamental frequency will be 180 Hz. As the tension of a guitar string is increased, the fundamental frequency produced by that string is decreased. As the tension of a guitar string is increased by a factor of 2, the fundamental frequency produced by that string is decreased by a factor of 2. As the linear density of a guitar string is increased, the fundamental frequency produced by the string is decreased. As the linear density of a guitar string is increased by a factor 4, the fundamental frequency produced by the string is decreased by a factor of 2. 8. Which of the following statements are TRUE of the harmonics and standing wave patterns in air columns Identify all that apply. The speed of the waves for the various harmonics of open-end air columns are whole number multiples of the speed of the wave for the fundamental frequency. Longer air columns will produce lower frequencies. The pitch of a sound can be increased by shortening the length of the air resonating inside of an air column. An open end of an air column allows air to vibrate a maximum amount whereas a closed end forces air particles to behave as nodes. Open-end air columns have antinodes positioned at each end while closed-end air columns have nodes positioned at each end. Closed-end air columns can only produce odd-numbered harmonics. Open-end air columns can only produce even-numbered harmonics. A closed-end air column that can play a fundamental frequency of 250 Hz cannot play 500 Hz. An open-end air column that can play a fundamental frequency of 250 Hz cannot play 750 Hz. A closed-end air column has a length of 20 cm. The wavelength of the first harmonic is 5 cm. An open-end air column has a length of 20 cm. The wavelength of the first harmonic is 10 cm. Air column A is a closed-end air column. Air column B is an open-end air column. Air column A would be capable of playing lower pitches than air column B. The speed of sound in air is 340 m/s. An open-end air column has a length of 40 cm. The fundamental frequency of this air column is approximately 213 Hz. The speed of sound in air is 340 m/s. A closed-end air column has a length of 40 cm. The fundamental frequency of this air column is approximately 213 Hz. If an open-end air column has a fundamental frequency of 250 Hz, then the frequency of the fourth harmonic is 1000 Hz. If a closed-end air column has a fundamental frequency of 200 Hz, then the frequency of the fourth harmonic is 800 Hz. 9. Which of the following statements are TRUE of sound interference and beats Identify all that apply. Beats result when two sounds of slightly different frequencies interfere. Beats are characterized by a sound whose frequency is rapidly fluctuating between a high and a low pitch. Two sounds with a frequency ratio of 21 would produce beats with a beat frequency of 2 Hz. Two tuning forks are sounding out at slightly different frequencies - 252 Hz and 257 Hz. A beat frequency of 5 Hz will be heard. A piano tuner is using a 262 Hz tuning fork in an effort to tune a piano string. She plucks the string and the tuning fork and observes a beat frequency of 2 Hz. Therefore, she must lower the frequency of the piano string by 2 Hz. Part B Multiple Choice 10. What type of wave is produced when the particles of the medium are vibrating to and fro in the same direction of wave propagation a. longitudinal wave.b. sound wave.c. standing wave.d. transverse wave. 11. When the particles of a medium are vibrating at right angles to the direction of energy transport, the type of wave is described as a _____ wave. a. longitudinalb. soundc. standingd. transverse 12. A transverse wave is traveling through a medium. See diagram below. The particles of the medium are moving. INCLUDEPICTURE http//www.physicsclassroom.com/reviews/sound/q12.gif MERGEFORMATINET a. parallel to the line joining AD.b. along the line joining CI.c. perpendicular to the line joining AD.d. at various angles to the line CI.e. along the curve CAEJGBI. 13. If the energy in a longitudinal wave travels from south to north, the particles of the medium ____. a. move from north to south, only.b. vibrate both north and south.c. move from east to west, only.d. vibrate both east and west. 14. The main factor which effects the speed of a sound wave is the ____. a. amplitude of the sound waveb. intensity of the sound wavec. loudness of the sound waved. properties of the mediume. pitch of the sound wave 15. As a wave travels into a medium in which its speed increases, its wavelength ____. a. decreasesb. increasesc. remains the same 16. As a wave passes across a boundary into a new medium, which characteristic of the wave would NOT change a. speedb. frequencyc. wavelength 17. The ____ is defined as the number of cycles of a periodic wave occurring per unit time. a. wavelengthb. periodc. amplituded. frequency 18. Many wave properties are dependent upon other wave properties. Yet, one wave property is independent of all other wave properties. Which one of the following properties of a wave is independent of all the others a. wavelengthb. frequencyc. periodd. velocity 19. Consider the motion of waves in a wire. Waves will travel fastest in a ____ wire. a. tight and heavyb. tight and lightc. loose and heavyd. loose and light 20. TRUE or FALSE The SI unit for frequency is hertz. a. Trueb. False 21. TRUE or FALSE Doubling the frequency of a sound source doubles the speed of the sound waves which it produces. a. Trueb. False 22. A sound wave has a wavelength of 3.0 m. The distance between the center of a compression and the center of the next adjacent refraction is ____. a. 0.75 m.b. 1.5 m.c. 3.0 m. d. 6.0 m.e. impossible to calculate wi...