Main Menu Table of Contents Back Chapter 15 Review Vocabulary review Match the following terms with the correct definition. There is one extra definition in the list that will not match any of the terms. !"#$%&" 1. pitch 2. pressure 3. decibels 4. acoustics 5. microphone !"#$'() a. Unit for measuring the loudness of sound b. Device used to change sound energy to an electrical signal c. Characteristic we hear as proportional to frequency d. The science and technology of sound e. Oscillation of this quantity in the air is what carries a sound wave f. Device used to change an electric signal to sound energy 1. Doppler effect 2. longitudinal 3. spectrum 4. reverberation 5. Fourier's theorem a. Complex waves are the sum of single frequency waves b. Graph showing amplitude versus frequency c. Causes the sonic “boom” of high speed airplanes d. Sound is a wave of this type e. Shift in the frequency of sound caused by motion of the source of sound f. Sound made from multiple echoes !"#$'*+"" 1. sonogram 2. octave 3. musical scale 4. consonance a. Separation between two notes where the frequency of one is twice the frequency of the other b. Unpleasant combination of sounds c. Graph showing the frequency and loudness of a sound versus time d. Set of notes related to one another by specific frequency ratios e. Combination of sounds considered pleasant 305 Main Menu Table of Contents Back You don't have to write the question. I should be able to tell what the question was by reading your answer. Concept review 1. Sound travels faster in a liquid or a solid than in a gas. Why? 2. If a small piece of space debris were to strike a space station, workers on the inside might hear the sound made by the collision, but workers outside the station would not. Explain. 3. How are pitch and frequency of a sound related? 4. Your parents complain that the “rap” you are listening to is not music. Based upon the information in this section, what thoughts can you offer to support your choice of music? 5. As you tune your clarinet, you hear an oscillating sound your instructor calls beats. What causes them and how can you use them to tune your instrument? 6. Why does an “A” played on a piano not sound exactly like an “A” produced by a guitar? 7. A steel string does not produce a loud sound by itself. Explain how an acoustic guitar produces a loud sound when a string is “plucked.” 8. How does an electric guitar pickup produce an amplified sound? 9. The decibel scale is used to measure the “loudness” of a sound. How is loudness (the decibel scale) of a sound related to the amplitude of the sound wave? 16. As the temperature increases, the fundamental frequency produced by a flute changes slightly. Does it increase or decrease? Give an explanation for your answer. 17. What causes consonance and dissonance? Problems You don't have to write the statement of the problem. In a calculation, follow the steps shown in class (list of given quantities, expression, algebra if needed, substitute given values, write final answer with the correct units). 1. Students in a physics class prepare “musical instruments” to play in lab. They cut tubes of !-inch PVC pipe to various lengths. When students blow across the open end and cover the bottom with a thumb, fundamentals of the scale are produced. Approximately what length of tube will produce the fundamental frequency of 264 hertz, “middle C”? (Assume the speed of sound is 340 m/s.) 2. On a day when the speed of sound is 344 m/s, Tom hollers and hears an echo 2.4 seconds later. How far away is the object that caused the echo? 3. A pipe closed on one end is 2.46 m long. On a day when the speed of sound 345m/s, what is the fundamental frequency of this pipe? 4. Human hearing depends upon both the frequency and the intensity of the sound. Answer the questions below based upon the graph of Decibel Level as a function of Frequency. 10. Most people know that sound is a wave. List at least three pieces of evidence to support the idea that sound is a wave. 11. How is the wavelength of sound produced by a musical wind instrument related to the size of the instrument? 12. A patron at a concert claims that she cannot hear clearly certain notes being played unless she moves her head slightly to one side or the other. Explain how this could happen. 13. Parents are concerned for the hearing of their children who wear stereo headsets adjusted to high volume settings. Using Table 15.1, explain why on Pg 288 their concerns are justified. 14. When an astronomer observes the sun, she notices that the light from one edge is slightly shifted toward the red end of the visible spectrum while the opposite edge is slightly shifted toward violet. What causes this shift? 15. While scuba diving, Roy and his partner become separated. Roy taps on his scuba tank to help his partner locate him. Why is this technique not as useful underwater as it might be at the surface? 306 a. b. c. d. At which frequency is the threshold of pain lowest? What is the approximate range of frequencies for speech? What is the decibel range for most speech? At what frequency are our ears most receptive? Main Menu Table of Contents Back You don't have to write the statement of the problem. In a calculation, follow the steps shown in class (list of given quantities, expression, algebra if needed, substitute given values, write final answer with the correct units). 5. The diagram represents wave fronts produced by a source moving at constant velocity through air. Answer the following questions based upon the diagram and your knowledge of the Doppler Effect. a. b. c. 8. Which pair of component waves would most likely produce the complex wave pattern shown below? Assume the times axis is horizontal and the same for all graphs. In which direction is the source moving? If this were a sound source, at which point would the pitch be highest? If the source were to accelerate, what would happen to the wavelength immediately behind the source? 6. A sonar signal requires 1.31 seconds to travel to the bottom of the ocean and back to the ship’s depth finder in water 1,000 meters deep. What is the speed of the sound signal? 7. The speed of sound in air at 20°C is about 343 m/s. A 1.2 m tube closed on one end has a fundamental frequency measured to be 80 hz. Is the temperature higher or lower than 20°C? Justify your answer with an explanation/calculation. 307 Main Menu 9. Table of Contents Examine the diagram which illustrates two waves of different frequencies (50 hz and 55 hz) and the sum of these two waves. a. b. c. Back 11. The graph below on the left shows the wave amplitude of the fundamental harmonic produced by a tuning fork with a frequency of 264 hz. The graph on the right shows the spectrum of wave amplitudes produced by a musical instrument playing the same fundamental note. What is represented at t = 0.00 sec, t = 0.10 sec, t = 0.20 sec and t = 0.30 sec on the diagram representing the sum of the two waves? What is the period between beats? (Hint: The time between two louder or “softer” sounds) What is the beat frequency? (Hint: The reciprocal of the period) 10. Examine the diagrams of 4 objects whose velocities differ with respect to the sound they emit. a. b. a. b. 308 Indicate the speed of each object relative to the speed of sound. Indicate for which objects the Doppler effect occurs and for which a shock wave occurs. What frequencies does the instrument produce? List the frequencies produced in order of intensity from greatest to least. Applying your knowledge 1. Wrap the ends a 24 to 30 inch piece of thread around your index fingers. Hang a metal hanger from the thread. Have a partner tap the hanger. Put your fingers in your ears and again, have a partner tap the hanger with a pencil. Describe what you hear and explain any difference. 2. Older people seem generally less tolerant of loud music than younger people. Is there any reason that this should be so? Research online to answer this question and write a short report on your findings. 3. Why does the pitch of a person's voice change when they speak after inhaling helium? Would this happen if the air in the room consisted entirely of helium (assuming you could survive this)?
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