What is the evidence that sou kv-.pbxrn7 l.9aa:m bn5.v,i w 8nxydnd travels as a wave?

What is the evidence trcp(*h:betgc q y /x-+hat sound is a form of energy?

Children sometimes play with a homemade “telephone” by attaching a string uhyn*hwo(,ya 5v*pdu pod 0odo6*-7 qto the bottoms of two paper cups. When the stdnhdoay * u6 p*ow5y0u7(-o,vq*dophring is stretched and a child speaks into one cup, the sound can be heard at the other cup (Fig. 12–29). Explain clearly how the sound wave travels from one cup to the other.

When a sound wave passes from air i/b 2h6t 2iqix+7 xxhhinto water, do you expect the frequency or wavel7tixh/b2 +iiqxh 6xh2 ength to change?

What evidence can yoste cyl2s0d-oa70+ d k ja)ax8u give that the speed of sound in air does not depend significantly on fe 70t)xcayao8 l j0d2-sasd+krequency?

The voice of a person who has inhaled helium sounds verk1,p*lpt8fx o r ):4,ruenbl uy high-pitched. Why?

How will the air temperature in a room affect the pitnvosbdda pi0e-1s0+0h a-oo(ch of organ pipes?

Explain how a tube might be u ,o-v buv7 x8.uwzwk+rsed as a filter to reduce the amplitude of sounds iu -xv,uk rzw8+7o. wvbn various frequency ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 1eur6leonw 1q 4wx(o*1 2–30) spaced closer together as you move up the fingerboard wu eerox *4l6n wq1(1otoward the bridge?

A noisy truck approaches you fr e b91qu3 )mae)hqo4y07y bozhom behind a building. Initially you hear it but cannot see it. When it emerges and obm074uhb1e)e o)39yazhqq yyou do see it, its sound is suddenly “brighter” — you hear more of the high-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can bewmxg)cit 5 ewbi,5/) k said to be due to “interference in space,” whereas beats can be said to be due to “interference in time.” Explw / i,5tcxwi)e bk)5gmain.

In Fig. 12–16, if the frequency of the speakers were lowered, would the pe/sf 7* cpcrgnr,rb;0 oints D and C (where destructive and constructive interference occur) move fsg rbpr70/nrf c,;*cearther apart or closer together?

Traditional methods of protecting the h:q ;sot28a2rcf;r wsmearing of people who work in areas with very high noise levels have consisted mainly of efforts to block or reduce 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 sq2fma8 o;:;t2r wrc saddition to the ambient noise. How could adding more noise reduce the sound levels reaching the ears?

Consider the two waves shown jd/l *igq y/39i qy5gtm+qtw5in Fig. 12–31. Each wave can be thought of as a superposition of two sound waves with slightly different frequencies, as in Fig. 12ildygqm/g 5wj qtty35i+9q * /–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 same direction6zlbj-wr2 bgu mwmsp)8d1 ; x-, with the same pj2mb zl1 u8s-xrg-w6md ;b)w velocity? Explain.

If a wind is blowing, will this alter the frequcg* xxjc(tr 1p.d6e3h ency of the sound heard by a person at r*6p gejd(rxxt c 3.h1cest with respect to the source? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a child in motion on a swing. A mh9ebfox; qhd96o to 56onitor is blowing a whistle hft669xe5b9h ; odqooin front of the child on the ground. At which position, A through E, will the child hear the highest frequency for the sound of the whistle? Explain your reasoning.

  A hiker determines theh vmg:au.oo;8 length of a lake by 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 length of the lam ;oau8vo.g h:ke. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below the waterliikm.f7 2lc ss4ne. He hears the echo of the sound reflected from the ocean floor directly below 2.5 s later. How deep is the ocean at this point? Assume the speed o7fic s.k24 slmf sound in seawater is 1560 m/s (Table 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wav) 5om7 qhyb7hjuw4xc9elengths 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 is drifting just above a school of tuna on a foblu,yx(3 ccsk(/ /i wiggy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How much time elapses before the backfire is heard (a) by the fi k3/csbxy ( ,/ui(wclish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a cliff. The s;; t (r2gxhlxn78pi+rx 3vwp y /.snlvplash it makes when striking the water below is heard 3.5 s later. Hh2vlwrx8 x+p;ytgnivp/7 r .n s(l3 x;ow high is the cliff?    m

  A person, with his ear to the ground, sees a huge stone strike the co42b k 3qi4 aneu1f qbzgte*y*2ncrete pavement. A moment later 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? S2nfq* buezqe 12k t4* iag43byee Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent -yg+d o0u n1,/ewfzccerror made over one mile of distance by the “5-second rule”u1y/+cg odcwnez0- f, for estimating the distance from a lightning strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pain level nc *yb3 1 r:zdjkdwm fu2zi*,0of 120 dB?    W/$m^2$Compare it to that of a whisper at 20 dB.    $ \times10^{-10 }$W/$m^2$

  What is the sound levn- fa0(y*y.*x vajdw zel of a sound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired simultane t;,* r;c+7v egigsix5pqgcg ci-jg-6ously at a certain place, what will be the sound level if only one is exploded? [Hint: Add intensities, nog;qscjv g5*t;xg,gci7i+ icp g6e --rt dB’s.]    dB

  A person standing a certm: 8ck9axin6f47 x w 2shlo3cwain distance from an airplane with four equally noisy jet engines is experiencing a sound level oh2axi4 wwmx k:8 ls9cn63c7fbordering on pain, 120 dB. What sound level would this person 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, whd) vnx5go.+k dereas for a CD player it is 95 dB. What is the ratio of intensities of the signal and the background noise fn.kx5dgdv o+) or each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sowe2-gkv le04h t)3h9tt9/dp caafq, vund from a person speaking in normal conversation. Use Table 12–2. Assume )avfpl/e3k2t40, vtwceahg - d99tqhthe sound spreads 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 e-/m7lw/mlr ,pnae0 lx;r/83yrr u w wjardrum whose 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 modes ef//(( b befqf-rdv9it amplifier 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 connected in turn tof(f9vbf/b-e( qrie d/ 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 registered 130 dB when placed 2.8 m in front 8z8w6fcmn.p e-q)kquof a loudspeaker on the stage. k)8eqm 86u ncf.-pw zq
(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 typically)qp9od f ,g-v:1r8g8a hy xodu detect a difference in sound level of 2.0 dB. What is theh , ag r918voy:ogpxq)dd u-8f ratio of the amplitudes of two sounds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripd92ww5msv ;rvled, (a) by what factor will the intensity increase? Increase by a factorvr;vs95ww2 dm of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacemea, tk wi ycsb6.em+e(,nt amplitudes, but one has twice the frequency of the other. What is the ratio of tyw(a+ceb, m, .tesk6 iheir intensities?   

  What would be the sound level (in dB) of a sound m) m, lg9hxe+hwave in air that corresponds to a displacement amplitude of vibrating air molecules of 0.13 mmh9,)lmm+g x eh at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud as a 100-Hz ba5t1+ *s aeyytone that has a 50-dB sound level? (See Fig. 12–61s by5te* aay+.)    dB

What are the lowest and highest frequencies that an ear can detect when twtjl +r8 ny34xv cv8igezugs,5 9)5amhe sound level is 30 lmt8g 3+5ns4ac9g )r uxvjzw8ei5,vy dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of sound levels. W xhc6hkm 2zm9(pby *9/ hea q/s9vo.rqhat is the ratio oozq 9m69 xh r ashmb./(hkc* 2py/q9evf 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. The length usa0f6sy;a8j hiq-u : of the vibrating portio 8;0ah:- qsisufauy6jn is 32 cm, and it has a mass of 0.35 g. Under what tension must the string be placed?    N

  An organ pipe is 112 cm long. What are the f6mwwiz5k,w5e y47cp k i0s x:tundamental and first three audible overy6k4:ckxzis07 wi pwtm5 ew 5,tones if the pipe is
(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 opz6:mixf(3ihu hhbc9r -(z1 expect from blowing across the top of an empty soda bottle that is 18 cm deep, if you assumed o u3chi-6x(9zb hpz imh1:rf (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-tube pipes spanning the range of hu. eha;tk- 9u0ujioh b7man hearing (20 Hz to 20 kHz), what woul9h jh iab0uk;.t7o-ued 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 third harmonic. What ox8 tm5t43menz*kan6))i xfq will be its fundamental freqm*3)5xxq6ekon )atfz8nm4 t iuency if it is fingered at a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned tn)+vcvd fyczk01.g6so, kqfa*w2 i b4o play E above middle C (330 6c)vyw*q,z+igcad sfv 2fk1nk.40o b Hz).
(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 emits middle C (262 bmzz196 qaj8a Hz) when the temperz8jqa9m6ba1 zature 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 at 20s6z zvw;r, ,us (rt7j nl2wd2r $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flute in Example 1af9hcw2 +cm ap) 5jcmx--, hhb2–10 should the hole be that must be uncovered to play D above middle C atm5c -w a bampcch-hh)x9j2,+f 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 pipe can resonate at 264 Hz, 440 Hz, anv;l ti 8yccv 2ja,l s8r7)vsh9d 616 Hz, but not at any other frequencies in between. (a) Show why this is an open or 2c 7trs c,8l;j8yvha v9ivl)sa 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. It resom0kuf vsnc (623lc, n4i+r apgnates at two successive harmonics of frequencies 275 Hz agnu(a cm+vp640, ni 3 c2kflrsnd 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 e.+ *-wreljfdcj- ,4 hcym j5v$^{\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 f-zgj(no7pdp 6or a 2.14-m-long organ pipe ap6(gzo p-7jdnt 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm long. It is open tw9az sj+ p,rc)e -zs:lo the outside and is clo,z s+: a9 -)slwcpejrzsed 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 d0wk6;k7 b2 gpola jj*0z+ wnsto adjust two strings, one of which is sounding 440 Hz. How fa0wzn 6 bsoj*7akkj gdp l2;+w0r off in frequency is the other string? ±    Hz

  What is the beat frequency if middlb 99kid7 3n/pzou gq.)ac m7qne C (262 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 otkr5ofxme9gqdn + ,rs45w0j +perates at 23.5 kHz, while another (brand X) operates at an unknown frequency. If neither whistle can 05m4f9xjk,r5t q dr nos+wg+ebe heard by humans when played separately, but a shrill whine of frequency 5000 Hz occurs when they are played simultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string producesu/esz)uz;j /f- 4 ii ci/jbyk, 4 beats/s when sounded with a 350-Hz tuning fork and 9 beats/s when sounded with /jckb,) juy-/ s;e if/iz4uiz a 355-Hz tuning fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz. The t2b, s6:64 rnhzj e lzybudo-y-qx9 ;0zd9uzucension in one string is then decreased by 2.0%. What will be n:6qju ozxs hz2- 4ucy 6d,;99ru0zbzedl-yb the beat frequency heard when the two strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identical flutesi5pe -koh 5esvs7(e y+3gvrd- each try to play middle C (262 Hz), but one is at 5.0°C and the other at 25. rp3svi57es-y(ekg-d 5vho e+0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a frequency ot zh+ci h-2ujfq 53aop)yri)(f 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 poss )f jy)-i3o( u+2c irqhat5phzible frequencies of A and C? What beat frequencies 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 apary b)f+s9 bne )ygtvz63t. A person stands 3.00 m from one speaker and 3.50 m from the othefzvbb)t+ng69y s)y 3 er.
(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 ar537 cuy1xvbzn+ 9 5pntujc 1l98q vzdle supposed to be vibrating at 132 Hz, but a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibrating at 132 Hz, what must be the frequt7vz 9nun8x35+y1jlqc z5 u 9 1pldcvbency 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 of wavelengths 2.64 m and 2.76 m in air. Howz8h :1n2sdc i qpe0mu;x 8rx6v many beats per second will m2:n0v8u rdxz6 ;xhsc1eq8pi be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s sirky o.* zfxb3488 tvo-kxo ptx.en is 1550 Hz when at rest. What frequency do you detect* kf4ok.o3 tz8pbx8-yv oxx.t if you move with a speed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequencynegq/ycu:w- - g.vk naf,xv p+wi5;0i do you detect if a fire engine whose siren e+cqv y;v . gin:wpf 0--5ag ,ekxui/wnmits at 1550 Hz moves at a speed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequencyhgww4/o 6hm e8 8gvcc- if a 2000-Hz source is moving toward you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exactly the same? Are thv c ce6ohwg/g-w8m84 hey 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 s apr4t)8xcl7same single frequency horn. When one is at rest and the other is moving towardr48 7)pslta xc the first at 15 m/s the driver at rest hears a beat frequency of 5.5 Hz. What is the frequency the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at 50.0 52xy*1+ p0foucfmtw bkHz and receives them returned from an object moving directly away f5c+f12wt*um of 0ybxprom it at 25 m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall aet iyx8 mm/kc7dra 49/t a speed of 5 m/s As it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency doesyt/r ek c8ai/xd7m9m 4 the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was played on a mouy/etnao0z2 a g)z:r1ving flat train car at a frequency of 75 Hz, and a second identical tuba played rz)o/:2yt0un ze a1ag the same tone while at rest in the railway station. What beat frequency was heard if the train car approached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to -0bkr-mytqo;;9 bc w smeasure blood-flow speeds. Suppose the device emits sound at 3.5 MHz, and the speed of sound in human tissumqw -cs kbr;0-9tyo ;be is taken to be 1540 m/s What is the expected beat frequency if blood is flowing in large leg arteries at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using ultrason4n7evs rp6 ji*ic 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 (2bd -5k(moo6h rmdwwk n0wh*570 Hz. When the wind velocity is 12 m/s from the no(bnmk5 m(d*o k6w-rh0wwohd 2rth, what frequency 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 objecuu2 -c1z 0q.obn.jx6 ltrfilrl3k4/k t moving on land if its speed 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 is 310 m/s (a) nfb 1ybu;o w8jgxg 7(dgm-1e8What is the angle the shock wave makes with the direction of the airplane’s motiondg ;b egfx1bon8(m w871 jyg-u?    $^{\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 spewm+it.zsw eu( l,;k v:ed of sound is only ,;:s+l m(we. ikuwz vtabout 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} $