What is the evidence that soo m 6qynshu52xdkme/2s3w4d . und travels as a wave?

What is the evidence that sound isj kp* m;0jz 12.hgq xjgs2dal4 a form of energy?

Children sometimes play with a homemade “telephone” by attaching a strinerqroic .3 ,ph968 breg to the bottoms of two paper cups. When the string is stretched and a child speaks into one cup, the sound can be heard at the other cup (Fig. 12–29). Explain.,e3r bq rreoi86h9p c clearly how the sound wave travels from one cup to the other.

When a sound wave passes from air into water, do you expect the frequency or),jp/ c 1ubdhc wavelength to/,dbh) pc ucj1 change?

What evidence can you give that the speed or z76wfty (w5ef sound in air does not depend significantl7w6f (yet zwr5y on frequency?

The voice of a person who has inhaled helium sounds very high-pitched. Wha540afaa ujo11 ph w2sy?

How will the air temperature in a room affect the pitch o(yra5+ hn9fm5 sydldu g5 m+7kf organ pipes?

Explain how a tube might be used as a filter to reduce the amplitude of9 0.2my/fzbns c3cbit sounds in various frequency ranges. (An example is a car mufflericf t/3y. sm90 bzbcn2.)

Why are the frets on a guitar (Fig. 12+8gigc5b he7ot f2uh3 –30) spaced closer together as you move up the fingerboard tg cg2i3+hobfh5 t7eu8oward the bridge?

A noisy truck approaches you from behind a building. Initially you hear it but h2)q9n 6v,vdkll -oedcannot see it. When it emerges and you do see it, its sound is suddenly “brighter” — you hear more of the high-frequency noise. Explain. [Hint: See Section 1llq26ho9dev, n-vk )d1–15 on diffraction.]

Standing waves can be said to be due to “interference in space,” whereaslunhjl5; ck de4ro,l; gc,9;n beats can be said to be due to “interference in l eunld, ;kng ;4,5lcrjc;o9h time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered, would6fad5 vy/c s7f the points D and C (where destructive and constructive interf /7safc6dy fv5erence occur) move farther apart or closer together?

Traditional methods of protecting the hearing ofl c8* ;+4xg(odlukca-/ge yrc people who work in areas with very high noise levels have consisted mainly of efforts to block or redua 8 rcoyxl;gc d+(*ek4culg /-ce noise levels. With a relatively new technology, headphones are worn that do not block the ambient noise. Instead, a device is used which detects the noise, inverts it electronically, then feeds it to the headphones in addition to the ambient noise. How could adding more noise reduce the sound levels reaching the ears?

Consider the two waves shown in Fig. 12–31. Each wave cq:ln/nwcp a2 n*e/j 1uan be thought of as a superposition of two sound waves with slightly different freenncp*:nu1/ /wjq al2quencies, as in Fig. 12–18. In which of the waves, (a) or (b), are the two component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and observer move in the 88n7; fj 90quste)w;tzz spov same direction, with the same vqstn;z j 98s; o f7upv80)tzewelocity? Explain.

If a wind is blowing, will this alter the frequency of the sound heard by a perl. flz7t cq52tz7j*jfson at rest with respect to the so tfz5fz. l7qj2 j*tlc7urce? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a child in ,ttl7h3l a2,)v kjprsmotion on a swing. A monitor is blowing a whistle in front of the child on the ground. At which position, A through E, will the child hear 7h 2aj p ,r3ks)l,vlttthe highest frequency for the sound of the whistle? Explain your reasoning.

  A hiker determines the length of a lake by 92za zo-zurwykt+c1 .listening for the echo of her shout reflected by a cliff at the far end of the lake. She hears the echo 2.0 s after shouting. Estimate the lengthu+. 1-ytowrk z2zcaz9 of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side ogn pye 7l-bl-yuo /e-1 3py l8giw)ic1f his ship just below the waterline. He hears the echo of the sound reflected from the ocean floor directly bly1 /yelw i-cn po)-up8l ggi- 137beyelow 2.5 s later. How deep is the ocean at this point? Assume the speed of sound in seawater is 1560 m/s (Table 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavea oax:lp;q* 3elengths in air at 20 $^{\circ} $ C for sounds in the maximum range of human hearing, 20 Hz to 20,000 Hz. $\lambda_{20Hz}$ =    m $\lambda_{20kHz}$ =    $ \times10^{-2 }$ m(b) What is the wavelength of a 10-MHz ultrasonic wave?    $ \times10^{ -5}$m

  An ocean fishing boat isil, ,9yaww du+9rhgn7 drifting just above a school of tuna on a foggy day. Without warning, an engine backfire occurs on another boat 1.0 km awa9ri7u+g,aw,h9yl ndw y (Fig. 12–33). How much time elapses before the backfire is heard (a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a cliff. The splash it makes when strikingg2;sxf3 d f/fx the water below is heard 3.5 s later. Howxff/dxg 3 f2;s high is the cliff?    m

  A person, with his ear to6 gdg8(i )hx y2yi1+* t(a c naeexb0p42xlfgp the ground, sees a huge stone strike the concrete pavement. A moment la fe )y2t(2gxblei60dc g*gyxx48p1in aa h+(pter two sounds are heard from the impact: one travels in the air and the other in the concrete, and they are 1.1 s apart. How far away did the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one mile of distance by the “5-secox6)5w)owv-pc uk hsi 2 *ytgg ja-(w,bnd rule” for estimating the distance from a lightning strike if vw*kt),2c wh56s-jgi py bo) au(g-x wthe temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pain level of 4nx usq/* d2xk120 dB?    W/$m^2$Compare it to that of a whisper at 20 dB.    $ \times10^{-10 }$W/$m^2$

  What is the sound level of 4t+isg ug :k mx*qz.fk1gy23na sound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound levely-i;fck+wh /f of 95 dB when fired simultaneously at a certain placf/h;ky+f-i wce, what will be the sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane wi+y7-+t.:vzme ,/x hstwlddf c th four equally noisy jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would this person xd +-e f+lm,tt/ydwcv.hs:z7 experience if the captain shut down all but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to have a signal-to-noise ratio of 58 dB, whereas rwh:lyoy; rwp6 * :k(ba7-+ls kge- lpfor a CD player:wpo*phk 7- w;r la( 6yy+-g sl:ekblr it is 95 dB. What is the ratio of intensities of the signal and the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from a pergvr+c09w *.3 mm bq/dlqkk.xnson speaking in normal conversation. Use Table 12–2. Assume the sound spreadscwd0kv/gqq mxm.r.kbln +*3 9 roughly uniformly over a sphere centered on the mouth. $\approx$    $ \times10^{ -6}$W(Round to the nearest integer)
(b) How many people would it take to produce a total sound output of 100 W of ordinary conversation? [Hint: Add intensities, not dB’s.]$\approx$    $ \times10^{7}$people

  A 50-dB sound wave strikes an eardrum whog t5y+jgj m- fkhdt8,;se area is $5 \times10^{ -5} m^2$ (a) How much energy is absorbed by the eardrum per second?    $ \times10^{-12}$W (b) At this rate, how long would it take your eardrum to receive a total energy of 1.0 J?   $ \times10^{ 3}$yr

  Expensive amplifier A is rated at 250 W, while the more modest ampbqui0nz uk -x7/n,g,olifier B is rated at 40 W. (a) Estimate the sound level in decibels you would expect at a point 3.5 m from a loudspeaker cou-q kn g,0n7,oz/ibuxnnected in turn to each amp.$I_{250}$ =    dB $I_{40}$ =    dB (b) Will the expensive amp sound twice as loud as the cheaper one?

  At a rock concert, a dB meter registereda;ku)f3nw hd5 130 dB when placed 2.8 m in front of a loudspeaker n hkdw)a53 f;uon the stage.
(a) What was the power output of the speaker, assuming uniform spherical spreading of the sound and neglecting absorption in the air?$\approx$    $ \times10^{2 }$W(“Round to one decimal place)
(b) How far away would the sound level be a somewhat reasonable 90 dB?   $ \times10^{2}$m

  Human beings can type4g tg-,pnf izt+) jarw:/;vtically detect a difference in sound level of 2.0 dB. What is the ratio of the amplitudes of two sounds whose levels differ by this amount? [Hint: Se/;ggezfvwti4atjp ,n :) r+ t-e Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factor will the intensi - ndfzwn6x1 tui: 4:gdzla 5v9-s+qpatya6s :5-:p4 wdgvf-zluzn+x9ain t qd1 increase? Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have mru69 31 m en1pg tzfjv*rrq45equal displacement amplitudes, but one has twice the frequency of the other. What is the ration5 1reqz4um1 9v pf*mr6gjrt3 of their intensities?   

  What would be the sound level (in dB) of a sound wave iaimfw. fd 2k-2n air that corresponds to a displacement amplitude of vibrating k-.d2 w mfaif2air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud as a 100-q -y.e s 3.(mrzyge,q1fxtp2xbz ,x4qHz tone that has a 50-dB sound lex41gyq(.qb-ptx z zf. 3ye m,e2s x,rqvel? (See Fig. 12–6.)    dB

What are the lowest and highest frequencies thn 3il (9yng ue)z )rzkwkf 5//+nkxl6hn 7a-wiat an ear can detect when the sounle)k/nu5lkz 9a6fig hwnx+n(i /)w7 yk nrz-3d level is 30 dB? (See Fig. 12–6.)

  Your auditory system can sacvh ;sv/te92vpun1shvo ,g+9:o9p accommodate a huge range of sound levels. What is the ratio9chg1ve+ pvta vo/np;:vs 9,s u2s9ho of highest to lowest intensity at
(a) 100 Hz,$ \times10^{ a }$ a =   
(b) 5000 Hz? $ \times10^{ a }$ a =   
(See Fig. 12–6.)

  The A string on a violin has a fundamental frequency of 440 Hz. x.:b 0hpugah-i mpnlj( spw :h 0n*h4;The length of the vibrating portion is 32 cm, and it has a mass of 0.35 g. Under what tension must the string be placed? n:b0; h i:s.pahhu*wp4(xhm- glj0pn    N

  An organ pipe is 112 cm long. What are the fut:el6: cbkk+tyg zp t*:8)ooqndamental and first three audible overtones if the pipe iso:kt 6 : gk otz*cy+l8tb:q)ep
(a) closed at one end, $f_{1}$ =    Hz $f_{3}$ =    Hz $f_{5}$ =    Hz $f_{7}$ =    Hz
(b) open at both ends?$f_{1}$ =    Hz $f_{2}$ =    Hz $f_{3}$ =    Hz $f_{4}$ =    Hz

  (a) What resonant frequency would you expect from blowing a jt .d27etfl71 3dkycbcross the top of an empty soda bottle that is 18 cm deep, if you assumf71det .c3kb 2 7jytdled it was a closed tube?    Hz (b) How would that change if it was one-third full of soda?   Hz

  If you were to build a pipe organ with open-;nup ta-c*y 05bc0cbjtube pipes spanning the range of human hearing (20 Hz to 20 kHz), what would;tby*0jcc-5a cp bn 0u be the range of the lengths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a frequency of 540 Hz as its thir:dxil3 yz8bbdu5,c6r sf4x5 j d harmonic. What will be its fundamental frequency if it is fingered at a length of only 60% of its origin dxs,8f4bz 565uxcr:yj3l id bal length?   Hz

  An unfingered guitar string is ak c* z9vw51tund g4c50.73 m long and is tuned to play E above middle C (330 Hz)u49dkgccat zn*vw 155 .
(a) How far from the end of this string must the finger be placed to play A above middle C (440 Hz)?$\approx$    m
(b) What is the wavelength on the string of this 440-Hz wave? $\approx$    m
(c) What are the frequency and wavelength of the sound wave produced in air at 20°C by this fingered string?    Hz    m

  (a) Determine the length of an open organ pipe that emiy3* gm6ngm r f7zu4z-9 rolw7bts middle C (262 Hz) when thg96b y73fm-7znz ourmr w4*lg e temperature is 21 $^{\circ} $ C.    m
(b) What are the wavelength and frequency of the fundamental standing wave in the tube?    Hz    m
(c) What are $\lambda$ and $f$in the traveling sound wave produced in the outside air?    Hz    m

  An organ is in tune ata+iwh g1f2*+ib s bmz5 20 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flx nbm8pp:r8 n7)2br jnute in Example 12–10 should the hole be that must be uncovere b )mbj8p:8nxpnrr2n7d to play D above middle C at 294 Hz?    m

  (a) At T = 20 $^{\circ} $C how long must an open organ pipe be to have a fundamental frequency of 294 Hz?    m
(b) If this pipe is filled with helium, what is its fundamental frequency?   Hz

  A particular organ pipei1q4v9dco h7g can resonate at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (a) Show why this is an ope7hq9d ci vo1g4n or a closed pipe. ----待选择----closedopen  (b) What is the fundamental frequency of this pipe?   Hz

  A uniform narrow tube 1.80 m long is open at both ends.wkln2 ad m6 dtd: -b.qmo0z:r4 It resonates at two succesmd0: -4w.on d a qzm6lk:r2bdtsive harmonics of frequencies 275 Hz and 330 Hz. What is
(a) the fundamental frequency,    Hz
(b) the speed of sound in the gas in the tube?$\approx$    $ \times10^{2 }$ m/s

  A pipe in air at 20 r)ddu-t/kpvuu0 / b. d:7o; yl.wyha: w 9harm$^{\circ} $ C is to be designed to produce two successive harmonics at 240 Hz and 280 Hz. How long must the pipe be, and is it open or closed?  ----待选择----closedopen  f =    m

  How many overtones are present within the audible range for a 2bow25, 6v wvgh.14-m-long organ pipe at , w2who6 bvg5v20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm long. It fud 5b6hwvjuikt68st8:, /* pl 1vnev is open to the outside and iewv5lv*kj phf 68:8 6 nt/bvsud1,tuis closed at the other end by the eardrum. Estimate the frequencies (in the audible range) of the standing waves in the ear canal. What is the relationship of your answer to the information in the graph of Fig. 12–6? $f_1$ =    Hz $f_3$ =    Hz $f_5$ =    Hz

  A piano tuner hears one beat every 2.0 s when trying to adjust two strings, f ppuyr k,2c 4ne /fck.*ia85yone of which is soundif uk 5kcec.*ynpf8iyr42p /a,ng 440 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency if middle C (7ke-eqs8 a+o y5( sv/ta cod)v262 Hz) and $C^＃$ (277 Hz) are played together?    Hz What if each is played two octaves lower (each frequency reduced by a factor of 4)? $\approx$    Hz

  A certain dog whistle operates at 23.5 kHz, while another (brand X) operates3d9h flg+a/eh26bbv n at an unknown frequency. If neither whistle can be heard by humans when played separately, but a shrill whine of frequency 5000 Hz occurs when they are played simultaneously, estimate the o9hd /n3fel26+g avbhb perating frequency of brand X.    kHz

  A guitar string produces 4 beats/s when soundekzqgiw; d6t+3(bt jp: d with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuningbk3w zd(t;qi+j g:pt 6 fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency,s4 i*8t1 l-(1wgmlesq.bhbwo 294 Hz. The tension in one string is then decreased by 2.0%. What will be the beat frequency heard when the two strings i1b.hbel*q-4(l wwt 1gom8ss are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identical flutes eac1uui oq)cic383qup ym5x,zzoxa 9 q5*h try to play middle C (262 Hz)pqyu i5m 5aoc *9cxu 3xqi8z)3qz,1 ou, but one is at 5.0°C and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a frequesr w):mgmdtetliz934 n/5ck- ncy of 441 Hz; when A and B are sounded together, a beat frequency of 3 Hz is heard. When B and C are sounded together, the beat frequency is 4 Hz. What are the possible frequencies of A and C? What beat frequencie /k5:t-sedwznmlri)4 c9t g3m s are possible when A and C are sounded together?$f_A$ =    Hz or    Hz
$f_C$ =    Hz or    Hz
|$f_A$-$f_C$|    Hz or    Hz

  Two loudspeakers are 1.80 m apart. A person stands 3.00 m from one slk)b8.1ozmb 4is yp1r peaker and 3.50 oiy8r z1km4l bs1)bp.m from the other.
(a) What is the lowest frequency at which destructive interference will occur at this point? f =    Hz
(b) Calculate two other frequencies that also result in destructive interference at this point (give the next two highest). Let T = 20 $^{\circ} $C $\approx$    Hz $\approx$    Hz

  Two piano strings are supposed/q+z:hfsi (w :wvq bo- to be vibrating at 132 Hz, but a piano tuner hears three beats every 2.0 s when they are p wsvqozqf+hiw/b(-: :layed together. (a) If one is vibrating at 132 Hz, what must be the frequency of the other ?   Hz    Hz
(b) By how much (in percent) must the tension be increased or decreased to bring them in tune?   % increase    %decrease

  A source emits sound-v yg gar2)f3s of wavelengths 2.64 m and 2.76 m in air. How many beats per second gsa 2-gr3v)yfwill be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engi7o5,:o,gj2hahba*wj ogv+ur ne’s siren is 1550 Hz when at rest. What frequency do you detect if yob :ggoa2 h,owa5 *7vur+j,joh u move with a speed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequency do you detect *g .bas;g(ular46ny l if a fire engine whose siren emits at 1550 Hz mov;.sgy(rg l6* aaunl4b es at a speed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz source is moving towv:l qb f1v/;y:k4 /1sq3g xsutrxi1 irard you at 15 m/svxqx;1g3u: 4ty/l1krqif si1:rb v/s versus you moving toward it at 15 m/s Are the two frequencies exactly the same? Are they close? $f'_{source\,movine}$    Hz
$f'_{observe\,movine}$    Hz
(b) Repeat the calculation for 150 m/s and then again
$f'_{source\,movine}$    $ \times10^{ 3}$Hz
$f'_{observer\,movine}$    $ \times10^{ 3}$Hz
(c) for 300 m/s What can you conclude about the asymmetry of the Doppler formulas?$f'_{source\,movine}$    $ \times10^{ 3}$Hz
$f'_{observer\,movine}$    $ \times10^{ 3}$Hz

  Two automobiles are equipped with the same single frequency hos u y53jqd2hqn*l v3vfzj w-/( (.qsofv,b0hprn. When one is at rest and the other is moving toward the first at 15 m/s the driver at rest hears a beat frequency of 5.5 Hz. What is the frqo 5/v hy3-j2(fbdv0fzv pw.ls(u*j,3hsnq qequency the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ul/k:.udy11t; e7;vn4r rf2rni iqsz yvtrasonic sound waves at 50.0 kHz and receives them returne1q1 vi. /ndry s7 i;yk ve;ru2rfn:4tzd from an object moving directly away from it at 25 m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As it fliesrhcy t rovstc76+/(f9j )w/ui , the bat emits an ultrasonic sound wave wittjc 7f/ s(9w 6ct +u/vhyio)rrh frequency 30.0 kHz. What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doe;wy blx*/ .:i crg s4zsi54qlppler experiments, a tuba was played on a moving flat train car at a frequency of 75 Hz, and a second identical tuba played the same tone while at rest in the railway station. What beat frequency was heard if the train .x qlgcy*b l wi;/5i:44zsse rcar approached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses usz -u 5q7(srkultrasound waves to measure blood-flow speeds. Suppose the device emits sound at 3.5 MHz, and the speed of sound in human tissue is taken to be 1540 m/s What is the expected beat fq5(uzs7 u-ksrrequency if blood is flowing in large leg arteries at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using u weqcg ,bb(jntg9o) 4 3sn-zs2ltrasonic waves of frequency $2.25 \times10^{ 6}$Hz is used to monitor the heartbeat of a fetus. A (maximum) beat frequency of 500 Hz is observed. Assuming that the speed of sound in tissue is $1.54 \times10^{3 }$ m/s calculate the maximum velocity of the surface of the beating heart.    m/s

  A factory whistle emits sound of frequency 570 Hz. Woo4(g m:t1tlq7*fwn r hen the wind velocity is 12 m/s from the north, what freq fgr7 (o4tqlm:now*t1uency will observers hear who are located, at rest,
(a) due north,   Hz
(b) due south,   Hz
(c) due east,    Hz
(d) due west, of the whistle? What frequency is heard by a cyclist heading    Hz
(e) north    Hz
(f) west, toward the whistle at 15 m/s?   Hz
Assume T = 20 $^{\circ} $C

  How fast is an object moving on land if its spee 7wo sn9y rjfq/,l/f/b4t3 lyzd at 20 $^{\circ} $C is Mach 0.33?    m/s
(b) A high-flying jet cruising at 3000 km/h displays a Mach number of 3.2 on a screen. What is the speed of sound at that altitude?    m/s

  An airplane travels at Mach 2.3 where the speed of sound;3snk) z20wy1ez qw kq is 310 m/s (a) What is the angle the shock wave makesnkwqek23z 0sq)1ywz; with the direction of the airplane’s motion?    $^{\circ} $
(b) If the plane is flying at a height of 7100 m, how long after it is directly overhead will a person on the ground hear the shock wave? $\approx$    s (Round to the nearest integer)

  A space probe enters the thin atmosphere of a planet where the speedx1bpu q49 trhzyf1a 1ci8rzi 6iz+n; : of sound is only a1cy4;81q +z i6pt: xai1bhnz9urr fzibout 35 m/s
(a) What is the probe’s Mach number if its initial speed is 15000 km/h$\approx$    (Round to the nearest integer)
(b) What is the angle of the shock wave relative to the direction of motion?    $^{\circ} $