Chapter 17 - Waves II

Chapt Chapter er 17: 17:

WAVES VES – II

1. The speed of of a sound wav wavee is determined determined by: by: A. its amplitu amplitude de B. its inten intensit sity y C. its its pitc pitch h D. number number of harmonics harmonics present present E. the transmittin transmitting g medium medium ans: E 2. Take ake the speed speed of sou sound nd to be 340 340 m /s. A thund thunder er clap clap is heard heard about 3 s after after the lightnin lightningg is seen. The source of both light and sound is: A. mov moving ing overhe overhead ad faster faster than the speed of sound sound B. emitting emitting a much higher higher freque frequency ncy than than is heard C. emitting emitting a much much lower lower frequency frequency than than is heard D. about about 10 1000m 00m aw awa ay E. much much mor moree than than 10 1000 00 m away away ans: D 3. A soun sound d wave has has a wavelen elengt gth h of 3. 3 .0 m. The The dist distan ance ce from from a comp compre ress ssio ion n cen center ter to the adjacent rarefaction center is: A. 0.75 m B. 1.5 m C. 3.0 m D. need need to know know wa wave speed speed E. need need to kno know freque frequency ncy ans: B 4. A fire whist whistle le emits emits a tone tone of 17 170 0 Hz Hz.. Take ake the the speed speed of sound sound in air to be 340 m /s. The wavelength of this sound is about: A. 0.5 m B. 1.0 m C. 2.0 m D. 3.0 m E. 340 m ans: C 5. During During a time interv interval al of exactly one period of vibration vibration of a tuning fork, fork, the emitted emitted sound travels a distance: A. equal equal to the length length of the the tuning tuning fork fork B. equal equal to twice twice the length length of the tunin tuning g fork fork C. of abou aboutt 3330m 30m D. which which decr decreas eases es with time time E. of one one wave wavelen length gth in air air ans: E

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6. At points points in a sound sound wave wave where the gas gas is maximally maximally compresse compressed, d, the pressure pressure A. is a max maxim imum um B. is a mini minimu mum m C. is equal equal to the amb ambien ientt value value D. is greater greater than the ambient ambient value value but less than than the maximum maximum E. is less than the ambien ambientt value value but greater greater than the minimum minimum ans: A 7. You are listening listening to an “A” note played played on a violin violin string. string. Let the subscript subscript “s” “s” refer to the violin string and “a” refer to the air. Then: A. f s = f a but λs = λa B. f s = f a and λs = λa C. λs = λa but f but f s = f a D. λs = λa and f and f s = f a E. linear linear density density of string = volume volume densit density y of air ans: A

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8. “Beats “Beats” ” in sound sound refe referr to: A. interfer interference ence of two two waves waves of the same frequency frequency B. com combinat bination ion of two two waves waves of slightly slightly diff erent erent frequency C. revers reversal al of phas phasee of re re flected wave relative to incident wave D. two two media having having sligh slightly tly diff erent erent sound velocities E. eff ect ect of relative motion of source and observer ans: B 9. To produce beats it is necessary necessary to use two waves waves:: A. travel traveling ing in opposite opposite directions directions B. of slig sligh htly tly diff erent erent frequencies C. of equal equal wavel wavelength engthss D. of equa equall am ampli plitud tudes es E. whose whose ratio of frequ frequencie enciess is an integer integer ans: B 10. In order for two two sound waves waves to produce audible audible beats, it is essential essential that the two two waves waves have: have: A. the same same ampl amplitu itude de B. the same same frequ frequenc ency y C. the same same number number of harmoni harmonics cs D. sligh slightly tly diff erent erent amplitudes E. sligh slightly tly diff erent erent frequencies ans: E


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11. The largest largest number number of beats per second will be heard from from which pair pair of tuning forks? forks? A. 200 200 and and 201 201 Hz B. 256 256 and and 260 260 Hz C. 534 534 and and 540 540 Hz D. 763 763 and and 774 774 Hz E. 84 8420 20 and and 842 8422 2 Hz ans: D 12. Two stationa stationary ry tuning forks forks (350 and 352 Hz) are struck simultan simultaneous eously ly.. The resulting resulting sound is observed to: A. beat with with a frequ frequenc ency y of 2 beats beats/s B. beat with with a freque frequency ncy of 351 351 beats beats /s C. be loud loud but but not not beat beat D. be Doppl Doppler er shifte shifted d by by 2 Hz E. have have a freque frequency ncy of 702 702 Hz ans: A 13. When listening listening to tuning tuning forks forks of frequency frequency 256 256 Hz and 260 Hz, one hears hears the following following number number of beats per second: A. zero zero B. 2 C. 4 D. 8 E. 258 ans: C 14. Two iden identical tical tuning tuning forks forks vibrate vibrate at 256 Hz. One of them them is then loaded loaded with a drop drop of wax, wax, after after which 6 beats/s beats/s are heard. The period of the loaded tuning fork fork is: A. 0.006s B. 0.005s C. 0.004s D. 0.003s E. none none of thes thesee ans: C 15. Which Which of the following following properties properties of a sound sound wave wave determine determine its “pitch”? “pitch”? A. Amplitu Amplitude de B. Distance Distance from from source source to to detector detector C. Frequen requency cy D. Phas Phasee E. Spee Speed d ans: C

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16. Two notes notes are an “octav “octave” e” apart. The ratio ratio of their frequenc frequencies ies is: A. 8 B. 10 C. 8 D. 2 E. 2 ans: D

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17. Consider Consider two two imaginary imaginary spherical spherical surface surfacess with di ff erent erent radii, each centered on a point sound source source emittin emitting g spheri spherical cal wave waves. s. The power power transm transmitt itted ed across across the larger larger sphere sphere is the power transmitted across the smaller and the intensity at a point on the larger sphere is the intensity at a point on the smaller. A. greate greaterr than, than, the the same same as B. greater greater than, than, greater greater than than C. great greater er than, than, less less than than D. the same same as, less less than than E. the same same as, the same same as ans: D 18. 18. The soun sound d inten intensit sity y 5. 5.0 m from a point point source source is 0. 0 .50 W/m2 . The power power output of the source is: A. 39 W B. 160W C. 266W D. 320W E. 390 W ans: B 19. The standar standard d reference reference sound sound leve levell is about: A. the thresh threshold old of of human human heari hearing ng at 1000 1000 Hz B. the thresh threshold old of pain pain for huma human n hearing hearing at 1000 1000 Hz C. the level level of sound sound produce produced d when the 1 kg standar standard d mass is dropped dropped 1 m onto a concrete concrete floor D. the level level of normal normal conv conversa ersation tion E. the level level of sound sound emitted emitted by a standar standard d 60 Hz tuning fork fork ans: A 20. The intensit intensity y of sound wave wave A is 100 times that of sound wave wave B. Relative Relative to wave wave B the sound level of wave A is: A. 2 db B. +2db C. +10 db D. +20 db E. +100db ans: D

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21. The intensit intensity y of a certain sound sound wav wavee is 6 µW/cm2 . If its intensit intensity y is raised by 10 db, the new 2 intensity (in µ (in µW/cm W/cm ) is: A. 60 B. 6.6 C. 6.06 D. 600 E. 12 ans: A 22. If the sound level level is increased increased by 10 db the intensit intensity y increases increases by a factor of: A. 2 B. 5 C. 10 D. 20 E. 100 ans: C 23. The sound sound level level at a point point P is 14 db below below the sound sound level level at a point 1. 1.0 m from a point source. source. The distance from the source to point P is: A. 4.0 cm B. 20 2m C. 2.0 m D. 5.0 m E. 25 m ans: D 24. To A. B. C. D. E.

raise the pitch pitch of a certain certain piano string string,, the piano tuner: tuner: loosens loosens the string string tight tightens ens the the stri string ng shorte shortens ns the the stri string ng length lengthens ens the string string remo removes ves some some ma mass ss ans: B

25. A piano piano wire wire has has leng length th L and mass M mass M .. If its fundamental frequency is f , f , its tension is: A. 2Lf/m B. 4M Lf C. 2M f 2 /L D. 4f 2 L3 /M E. 4LMf LM f 2 ans: E

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26. If the length of a piano wire (of given given density) density) is increased increased by 5%, what appro approximat ximatee change change in tension is necessary to keep its fundamental frequency unchanged? A. Decrea Decrease se of of 10% 10% B. Decrea Decrease se of 5% C. Increa Increase se of 5% D. Increa Increase se of 10% 10% E. Increa Increase se of 20% ans: C 27 27.. A piano piano wire wire has has a leng length th of 81 cm and and a ma mass ss of 2. 2 .0 g. If its fundame fundament ntal al frequen frequency cy is to be 394 Hz, its tension must must be: A. 0.32 N B. 63 N C. 130N D. 250N E. none none of thes thesee ans: B 28. A stretc stretched hed wire wire of lengt length h 1. 1 .0 m is clamped at both b oth ends. ends. It is plucked plucked at its center as shown. shown. The three longest wavelengths in the wire are (in meters): . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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..... .................. ................................... . . . . . . . . . . . . . . . . ................... .. ............. ................. •........... •

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A. B. C. D. E.

4, 2, 1 2, 1, 0.5 2, 0.67, 0. 0.4 1, 0.5, 0.33 1, 0.67, 0. 0.5 ans: C

29. Two identi identical cal strings, strings, A and B, have have nearly the same same tension. tension. When they they both vibrate vibrate in their funda fundamen mental tal resona resonant nt modes, there is a beat frequen frequency cy of 3 Hz. When When string string B is tigh tightened tened slightly slightly,, to increase the tension, tension, the beat frequenc frequency y becom b ecomes es 6 Hz. This means: means: A. that that before before tighten tightening ing A had a higher higher freque frequency ncy than B, but after after tighten tightening ing,, B has a higher frequency than A B. that that before before tighten tightening ing B had had a higher higher freque frequency ncy than A, but after after tighten tightening ing,, A has has a higher frequency than B C. that before before and after after tightening tightening A has a higher higher frequen frequency cy than B D. that before before and after after tightening tightening B has a higher higher frequen frequency cy than A E. none none of the abov above ans: D


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30. 30. Two Two pipes are each each open open at one end and closed closed at the other. other. Pipe A has length length L and pipe B has length 2L 2L. Which harmonic of pipe B matches in frequency the fundamental of pipe A? A. The funda fundamen mental tal B. The The seco second nd C. The The thir third d D. The The four fourth th E. There There are are none none ans: E 31. 31. A column column of argon argon is open at one one end and closed closed at the other. other. The shorte shortest st length length of such such a column column that will resona resonate te with a 200 200 Hz tuning tuning fork fork is 42 42..5 cm. The speed speed of sound sound in argon argon must be: A. 85.0 m/s B. 170m 0m/ /s C. 340m 0m/ /s D. 470m 0m/ /s E. 940 m/s ans: C 32. A tuning tuning fork produces produces sound sound wav waves of wavele waveleng ngth th λ in air. air. This This sound sound is used used to cause cause resonanc resonancee in an air column, closed closed at one end and open at the other. The length length of this column column CANNOT be: A. λ/4 B. 2λ/4 C. 3λ/4 D. 5λ/4 E. 7λ/4 ans: B 33. A 1024 Hz tuning fork fork is used to obtain a series of resonanc resonancee levels levels in a gas column of varia variable ble length length,, with with one end closed closed and and the other other open. open. The length length of the column column change changess by 20 cm from resonance to resonance. From this data, the speed of sound in this gas is: A. 20 cm/s B. 51cm 1cm/ /s C. 102 cm/s D. 205m 5m/ /s E. 410 m/s ans: E 34. A vibrating vibrating tuning fork fork is held over over a water column column with one end closed and the other other open. As the water water level is allowed allowed to fall, a loud sound is heard heard for water levels levels separated separated by 17 cm. If the speed of sound sound in air is 340m 340m/ /s, the frequency of the tuning fork is: A. 500 Hz B. 100 000 0 Hz C. 2000 Hz D. 578 780 0 Hz E. 578, 00 000 0 Hz ans: B 262


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35. 35. An organ organ pipe with one end open and the other other closed closed is operatin operating g at one of its resonan resonantt frequencies. The open and closed ends are respectively: A. pressure pressure node, press pressure ure node B. pressure pressure node, node, displace displacemen mentt node C. displaceme displacement nt antinode, antinode, pressu pressure re node D. displacemen displacementt node, displac displacemen ementt node E. pressure pressure antinode, antinode, press pressure ure node node ans: B 36. An organ organ pipe with one one end closed closed and the the other open has has length length L L.. Its fundamental frequency is proportiona proportionall to: A. L B. 1/L C. 1/L2 D. L2 E. L ans: B

√

37. Five Five organ pipes are described below. below. Which Which one has the highest highest frequency frequency fundamen fundamental? tal? A. A 2.3-m pipe with one end open and the other closed B. A 3.3-m pipe with one end open and the other closed C. A 1.6-m pipe with both ends open D. A 3.0-m pipe with both ends open E. A pipe in which which the the displace displacemen mentt nodes are are 5 m apart apart ans: C 38. If the the speed speed of soun sound d is 340 340 m/s, the length length of the shortest shortest closed pipe that resonates resonates at 218 Hz is: A. 23 cm B. 17cm C. 39cm D. 78cm E. 1.56cm ans: C 39. The lowes lowestt tone produced produced by a certain certain organ organ comes comes from a 3. 3 .0-m pipe with both ends open. If the speed speed of sound sound is 340 m/s, the frequency of this tone is approximately: A. 7 Hz Hz B. 14 Hz C. 28Hz D. 57 Hz E. 70Hz ans: D


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40 40.. The The speed speed of of sound sound in air air is 340 340 m/s. The length of the shortest pipe, closed at one end, that will respond to a 512 Hz tuning fork is approximate approximately: ly: A. 4.2 cm B. 9.4 cm C. 17cm D. 33cm E. 66cm ans: C 41 41.. If the the speed speed of of soun sound d is 340 340 m/s, the two lowest frequencies of an 0. 0 .5-m organ pipe, closed at one end, are approximately: A. 170 170 and and 340 340 Hz B. 170 170 and and 510 510 Hz C. 340 340 and and 680 680 Hz D. 34 340 0 and and 10 1020 20 Hz E. 57 and and 170 170 Hz ans: B 42. Organ Organ pipe Y (open at both ends) ends) is half as long as organ organ pipe pipe X (open at one end) as shown shown.. The ratio of their fundamental frequencies f X :f Y Y is: X Y A. B. C. D. E.

1:1 1:2 2:1 1:4 4:1 ans: A

43. 43. A 200 200-cm -cm organ organ pipe with one end open is in resonanc resonancee with with a sound sound wave wave of wave wavelen length gth 270 270 cm. The pipe is operatin operating g in its: A. fundamen fundamental tal frequency frequency B. second second harmon harmonic ic C. third third harmon harmonic ic D. fourth fourth harmon harmonic ic E. fifth harmonic ans: B

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44. An organ organ pipe with with both ends open is 0.85 m long. Assuming Assuming that that the speed of sound sound is 340 340 m/s, the frequency of the third harmonic of this pipe is: A. 200 Hz B. 300 Hz C. 400 Hz D. 600 Hz E. none none of thes thesee ans: D 45. 45. The “A” on a trumpet trumpet and a clarin clarinet et have have the same pitch, pitch, but the two two are clearly clearly distindistinguishable. Which property is most important in enabling one to distinguish between these two instruments? A. Inten Intensit sity y B. Fundamen undamental tal frequen frequency cy C. Displacem Displacement ent amplitude amplitude D. Pressure Pressure amplitude amplitude E. Harmonic Harmonic conten contentt ans: E 46. The valv valves es of a trumpet and the slide of a trombone trombone are for the purpose of: of: A. playing playing short short (staccato (staccato)) notes B. tuning tuning the instrumen instruments ts C. changi changing ng the harmoni harmonicc conten contentt D. chang changing ing the the length length of the air colum column n E. producing producing gradation gradationss in loudnes loudnesss ans: D 47. Two small small identical identical speakers speakers are connected connected (in phase) to the same source. source. The speakers speakers are 3 m apart apart and at ear level. level. An observ observer er stands stands at X, 4 m in front front of one speaker speaker as shown. shown. If the amplitudes are not changed, the sound he hears will be most intense if the wavelength is:

↑|

...... ................. .... ..... ..... ..... .... .......................................

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| 3 m speakers | | ... ...... ............................. .... .... ..........................................

↓

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• X

←−−−−−−−−−−− 4 m −−−−−−−−−−−→ A. B. C. D. E.

1m 2m 3m 4m 5m ans: A


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48. Two small small identical identical speakers speakers are connected connected (in phase) to the same source. source. The speakers speakers are 3 m apart and at ear level. level. An observe observerr stands at X, 4 m in front of one speaker speaker as shown. shown. The sound she hears will be most intense if the wavelength is: ...... ........... .... ............................... .... .................................. | | 3 m speakers | | ...... ........... .... ................. .... • X ................................................ 4m

↑ ↓

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←−−−−−−−−−−−

A. B. C. D. E.

−−−−−−−−−−−→

5m 4m 3m 2m 1m ans: E

49. The rise in pitch pitch of an approaching approaching siren siren is an apparent apparent increase increase in its: A. spee speed d B. am ampl plitu itude de C. frequ frequenc ency y D. wavel wavelengt ength h E. number number of harmonics harmonics ans: C 50. The diagram diagram shows shows four situations situations in which which a source source of sound S with variable variable frequency frequency and and a detector D are either moving or stationary. The arrows indicate the directions of motion. The speeds are are all the same. Detector Detector 3 is stationary stationary. The frequency frequency detecte detected d is the same. Rank the situations according to the frequency of the source, lowest to highest. • S

• D

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1 A. B. C. D. E.

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• D

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2

1, 2, 2, 3, 3, 4 4, 3, 3, 2, 2, 1 1, 3, 3, 4, 4, 2 2, 1, 1, 2, 2, 3 None No ne of of the the above above ans: B


• S

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• S

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• D

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4

51. A station stationary ary source source gener generates ates 5 .0 Hz water waves waves whose speed is 2. 2.0 m/s. A boat is approaching the source source at 10 m/s. The frequency of these waves, as observed by a person in the boat, is: A. 5.0 Hz B. 15 Hz C. 20Hz D. 25 Hz E. 30Hz ans: E 52. A stationary stationary source source S generates generates circular circular outgoing outgoing waves waves on a lake. The wave wave speed is 5 .0 m/s and the crest-to-crest distance is 2. 2 .0 m. A person person in a motor boat boat heads direct directly ly toward toward S at 3.0 m/s. To this person, the frequency of these waves is: A. 1.0 Hz B. 1.5 Hz C. 2.0 Hz D. 4.0 Hz E. 8.0 Hz ans: D 53. A statio stationar nary y source source emits a sound sound wave wave of freque frequency ncy f . f . If it were were poss possib ible le for for a man to travel toward the source at the speed of sound, he would observe the emitted sound to have a frequency of: A. zero zero B. f /2 C. 2f /3 D. 2f E. infinity ans: D 54. A source source emits sound sound with a frequenc frequency y of 1000 Hz. It and an observ observer er are moving moving in the same same direct direction ion with the same speed, 100 m/s. If the the speed speed of sound sound is 340 340 m/s, the observer hears sound with a frequency of: A. 294 Hz B. 545 Hz C. 1000 Hz D. 183 830 0 Hz E. 3400 Hz ans: C 55. A source source emits sound with with a frequency frequency of 1000 1000 Hz. It and an observ observer er are moving moving towar toward d each other, other, each with a speed of 100 m/s. If the speed speed of sound sound is 340 340 m/s, the observer hears sound with a frequency of: A. 294 Hz B. 545 Hz C. 1000 Hz D. 183 830 0 Hz E. 3400 Hz ans: D Chapt Chapter er 17: 17:

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56. 56. A source source emits emits sound sound with with a freque frequency ncy of of 1000 1000 Hz. It is movin moving g at 20 m /s toward a stationary reflecting ecting wall. wall. If the speed of sound sound is 340m 340m/ /s an observer at rest directly behind the source hears a beat frequency of: A. 11 Hz B. 86 Hz C. 97Hz D. 118 Hz E. 183 Hz ans: D 57. 57. In each each of the followin following g two two situat situation ionss a source source emits sound sound with a freque frequency ncy of 1000 1000 Hz. In situat situation ion I the source source is mo movin ving g at 100 m/s towa toward rd an observ observer er at rest. rest. In situatio situation n II the observ observer er is mov moving ing at 100 m /s toward toward the source, which which is stationar stationary y. The speed of sound is 340m/ 340m /s. The frequencies heard by the observers in the two situations are: A. I: 14 1417 17 Hz; II: 12 1294 94 Hz B. I: 141 1417 7 Hz Hz;; II: 1417Hz 1417Hz C. I: 12 1294Hz; 94Hz; II: II: 129 1294 4 Hz D. I: 773 773 Hz Hz;; II: II: 706Hz 706Hz E. I: 773 773 Hz Hz;; II: II: 773Hz 773Hz ans: A 58. The Doppler Doppler shift formu formula la for the frequency frequency detected detected is 

f = f

v ± v ± vD , v vS

∓

where f where f is the frequency emitted, v is the speed of sound, v D is the speed of the detector, and vS is the speed of the source. source. Suppose Suppose the source source is traveling traveling at 5 m/s away from the detector, the detector detector is trave travelin ling g at 7 m/s toward the source, and there is a 3-m/s wind blowing from the source toward toward the detector. detector. The values values that should should be b e substituted substituted into into the Doppler shift equation are: A. vD = 7 m/s and v and v S = 5 m/s B. vD = 110 0 m/s and vS = 8 m/s C. vD = 4 m/s and v and v S = 2 m/s D. vD = 110 0 m/s and vS = 2 m/s E. vD = 4 m/s and v and v S = 8 m/s ans: B 

59. 59. A plane plane produces produces a sonic sonic boom only only when: when: A. it emits sound wav waves es of very long wav waveleng elength th B. it emits sound sound wav waves es of high frequen frequency cy C. it flys at high altitudes D. it flys on a curved path E. it flys faster than the speed of sound ans: E

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60. 60. If the the speed speed of soun sound d is 340 340 m/s a plane flying ying at 400 m/s creates a conical shock wave with an apex half angle of: A. 0 (no (no shock shock wave wave)) B. 32 C. 40 D. 50 E. 58 ans: E ◦ ◦ ◦ ◦

61. 61. The speed speed of of sound sound is 340 340 m/s. A plane flys horizontally at an altitude of 10, 10 , 00 0000 m and a speed of 400m/ 400m/s. When When an observ observer er on the ground ground hears hears the sonic sonic boom the horiz horizon ontal tal distance distance from the point on its path directly above the observer to the plane is: A. 5800 m B. 6200 m C. 8400 m D. 12, 000m E. 16, 000m ans: B


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Chapter 17 - Waves II

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