What is the evidence that sou;n w4e/e eq-thy .v*vlnd travels as a wave?

What is the evidence that sound is a f pql 7xhs-65e*b lha3sorm of energy?

Children sometimes play with a homemade “telepecw 1y sfc 8mxx1e9ek+ 3lj38jhone” by attaching a string to the bottoms of two paper cups. When the string is stretched and a child speaks into one cup, the jj3 ee1 3 +1yx x89slmfce8cwksound 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 into water, do you expect the d2)v6ioldz8ro*o,mpx -lv2lfrequency or wavelength to vv2 idxlol6o*dpzm8- , lr2o)change?

What evidence can you give that the speed of sound in air does not dewbt n j+ aadil71k;jc06y*f,fpend significan;wa6lfi7yt d 1b*j ka+0,jncf tly on frequency?

The voice of a person whuf5utw9g e0w4y ,zd(ll8s)al o has inhaled helium sounds very high-pitched. Why?

How will the air temperature in a ro 9,gx/ tqebtegy4 fo-6om affect the pitch of organ pipes?

Explain how a tube might be l;9gjfalq 4j.8 xcs5uused as a filter to reduce the amplitude of sounds in various frequency ranges. (An example is a car muffler. sl. jjcu;l8g59faxq4)

Why are the frets on a guitar (Fig. 12eq(vo m ,9.f 3eqry,un–30) spaced closer together as you move up the fingerboard t, f.qo(3 euyremvn q9,oward the bridge?

A noisy truck approaches you from behind a building. Initially you hear it but x9 jd)np o z*tos q(rrlx-p5k++;ht9ccannot see it. When it emerges and you do see it, its sound is suddenly “brighter” — you hear more of the high-frequency noise. Explaix9oxt (plz +;dr 9)o5p*njh - tc+rqskn. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due to “interference in space,” wherfwcn4o .v4 9alz a., )d/yzpngeas beats can bevnz4z4.c w/pgy, dl 9na.af) o said to be due to “interference in time.” Explain.

In Fig. 12–16, if the frequency of the l: 2hbpopxj9anv 8s+) speakers were lowered, would the points D an:spnj)lvohxa8b2+ 9 pd C (where destructive and constructive interference occur) move farther apart or closer together?

Traditional methods of protecting the hearing of people.hn u9,urm3y w who work in areas with very yrw.9m ,un3uh 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 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 can be thought of a-l;huo lbx:1 y7 p(+zno,abnm s a superposition of two sound waves with slightly different frequencies, as in Fig. 12–18. In whin bmxa lnu -:, lpz71o(y;+bhoch 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 sg1o/n1bea8-thpmbr 4p c6 ,e bource and observer move in the same direction, with the sameoe-tpa b14/ngc h,meb6p8 1br velocity? Explain.

If a wind is blowing, will t5i s *c bm21ndxj)j2aehis alter the frequency of the sound heard by a person at rest with respect to the source? Is the wavelength or velocity2c*s5deiba1 2jn )x jm changed?

Figure 12–32 shows various3dc 5b*icr6 /e,mxltb positions of a child in motion 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 theb,5m/cltie6x c3 r bd* highest frequency for the sound of the whistle? Explain your reasoning.

  A hiker determines the length of a lake by listening for the echo of her shout r /p-wbk 4f /z-x3l sci;pgai2teflected by a cliff at the far end o3p4c;azf-2txgbw /is/ k-lipf the lake. She hears the echo 2.0 s after shouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the ctvq5a;vd .v.*gtb e, side of his ship just below the waterline. 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 of sound in seawater is 1560 m/s (Table 12–1) and does not vary significanvvtbv,.gtc ;d.5q e*a tly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in air at 20 yaaopb05 i c,2$^{\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 foggy da)j9qktpf; g(qj31f l w3juht- y. Without warning, an engine backfire occurs on another boat 1.0 km away wqu ght393lj-q(t;ff)1kjjp (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 t/rc0:o n8gxse he top of a cliff. The splash it makes when striking the water below iss:/gexrn co80 heard 3.5 s later. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge stone strike the 3/24kw lk 6/evn vfrzitxb/sig(ja0+concrete pavement. A moment later two sounds are heard from the impact: one t(b0+3 axtkk2nvr zlg ej/ f6i /sw/vi4ravels 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 distanck+q, qk /tbt a4nll pl9(0no7b3*tcg yabm-u+e by the “5-second rule” for estimating the distk-0nl pot+b g9 yl 4cbatqtnlka,/ ub7q*(+m3ance 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 of 120 dBmh5oefy5x7* e?    W/$m^2$Compare it to that of a whisper at 20 dB.    $ \times10^{-10 }$W/$m^2$

  What is the sound level of a sound whose inc *fk8 2wjw6gotensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired simultaneously;e *;aecqi+d/g(- -j ff sbl2 fzion2r at a certain place, what will be the sound level if onijf eol*sf ;(-aqb zd2g+ie;f/c2n r-ly one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane wi7vcmi9 v5 z *ohhc7- b nptrkf*7h2ta1th four equally noisy jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would this person vh9kf7trmch 2np hao1c7-v*7b zt 5i* experience if the captain shut down all but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to have xg(ae;ovj 3dj xu:6awva7(0oa signal-to-noise ratio of 58 dB, whereas for a CD player it is 95 dB. What is the ratia xja 7oe : a(u3;g6(wjodvvx0o 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 frop4gw62w /hjerm a person speaking in normal conversatwhrw g2e 46p/jion. Use Table 12–2. Assume the 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 eardrum whose jg-tf;+2bn*xb xyef m1 um,v/ 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 amplifier 3-7yp*hf8lfyqrc3 ux B is rated at 40 W. (a) Estimate the sound level in decibels you would expect at a point 3.5 mf *-cyq huxyfr83 pl37 from a loudspeaker connected 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 registergp;r;(sky8z8g4fp3 9. 8 smqs rgltz sed 130 dB when placed 2.8 m in front of a loudspeaker on the stage. r(g s883p;8zps4 9ftkgsy.gr; z qsml
(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 detect a difference in sound level of 2.0 dB. What i48hcdxw2+sl q -jm ,mcs the ratio of the amplitudes of two sounds whose levels differ by this amount? [Hint: Seeshc,8-4+ ql mmwdcj2x Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factor will the intensfen96 9szxziaqf3 5 0gity increase? Increas56qa9snx eiz0gf39 f ze by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but one has twice the frequzxihhw3l. b83ency of the other. What is the 3 xlh.i3hbw8zratio of their intensities?   

  What would be the sound level (in dB) of a sound wave in ai0m 8i.ff+2plyf8yqq4;azfz sr that corresponds to a displacement amplitude of vibrating air moleculezqf.lf 0 8q8zys;2amifp+ yf4s of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud as a -ipfq e 9 1tovqxqeul8 --c*p2100-Hz tone that has a 50-dB sound level? (See Fig. 12–6c v*q918ptqqi2-f-pl uox-e e .)    dB

What are the lowest and highest frequencies that an earz(nsm7 u.d uz+ can detect when the soundd7mu+nz(.us z level is 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of sound levels. What i igf.dda2 c/e+/jqx 27lb5np rs the ratio of highest to lowest intensity at /qd2 crdg/ +b2al f7nex.ji5p
(a) 100 Hz,$ \times10^{ a }$ a =   
(b) 5000 Hz? $ \times10^{ a }$ a =   
(See Fig. 12–6.)

  The A string on a violin has a fundame7ozu; h.36 es gacnvz,ntal frequency of 440 Hz. The length of the vibrating portion is 32 cm, and it has a mass of 0.35 g. Under what tension must th36aeg nuh,z v.s ;czo7e string be placed?    N

  An organ pipe is 112 cn3wlsu/s4k 8- dedy( vm long. What are the fundamental and first three audible overtones if the - nkvleu3s swy(48/dd 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 fr *o-ojfobgo fo )18um7equency would you expect from blowing across the top of an empty soda bottle thatoo1-)ofjg f*7b uoom8 is 18 cm deep, if you assumed 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 s 4(usof 477pxn qvvf.qrj9o6qpanning the range of human hearing (20 Hz to 20 kHz), what would be the range of the lengths of pipes r .7v(f7fo 94vopqnus6j4 qqxr equired? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a frequency of 540 Hz as its third harmonic. Whatoi n11yr ,f2cc will be its fundamental frequency if it is fingered at a length of only 62,c11 ync iofr0% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and nzvk pe* (cv17is tuned to play E above middle C (*zcn1v7pvk e(330 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 xxp73bfr .:2yuui 3aw middle C (262 Hz) when the temperature is 21 3f .b2u7wxxiu:pay3r$^{\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 2b78z h7f7x :uju(pm ks0 $^{\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 12–10 sdd3b:g6ft1y5glm 9*oiwq *gphould the hole be that *td 3w 6 ggy1l*dq:gfbmo9p5imust be uncovered 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 pipe can resonate at 264 Hz, 440 Hz, and 616 Hz, but not a3)x6j99 c al4 dia(nyo4oxdhtt any other frequenhaj 9too 4dlxnxcdy(a43 i)9 6cies in between. (a) Show why this is an open 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 a99 l eguw..p.0tt i98ajye agxt both ends. It resonates at two successive harmonics of frequencies 275 Hz and 33e9 ejpa a0 wui9.xy8gg9t t..l0 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 f:xmg-3 qr*kfjxi40o4vsn w)$^{\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 ari-la 4 fn y,-w,(o3*xugndcvde present within the audible range for a 2.14-m-long organ pipe a nwdcfu*lx 4y ,(ogia-3vdn-, t 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 to the outside and qddaz;4 .uu p c mcn.0lw0q.)o xl.vv rukm4)3is closed at the other end by the eardrum. Estimate the frequencies (in .nd0dqmqmo.xvl.uwl 3c z u ru)0c;4av4k ).pthe 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 beafjkd0 bje8 7 aixt3a-d/1h6 wgt every 2.0 s when trying to adjust two strings, one of which isk3dib g/a 16 d8ft- ajje07whx sounding 440 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency if middle C (26e3uw 0i78 arcfk77nvn2 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 operate3b 6 no7mhcxy:s at 23.5 kHz, while another (brand X) operates 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 y:bm6 oh3xn7c operating frequency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded with a 350-Hzk16c nuqm07tc tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibq0 nc7kcm6u1t rational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to t3q888 z.eq jw rc(ajlghe same frequency, 294 Hz. The tension in one string is then decreased by 2.0%. What will be the beat freque zj8(q38q j c.egl8arwncy heard when the two strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be h 0mr295n7(w wcxgourmei .jj *c -dov7eard if two identical flutes each try to play middle C (262 Hz), but one is at 5.0°*7orwcc9m.rgjxn5v ( wi0e- mjo7d2 uC and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning fork6dls :k0 n;wozs, A, B, and C. Fork B has a frequency of 441 Hz; when A and B are soundel z;wod6n 0sk:d 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 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 apart. A person stands 3.00 m 1-/ j- uzc )duckk.sgrfrom one speaker and 3.50 m f.- -sz1jckkuud)/ rcg rom 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 to be vibrating at 132 Hz, but a piano tuner henwpp7dun w(i:jlo, qr+18m2nx7 i p)qars three beats every 2.0 s when they are playnri7p (87qq, w muod: l1njp2 )wixn+ped 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 oh :je6,/ 0fv /*rtrv1zjuohb.; nfquzf wavelengths 2.64 m and 2.76 m in air. How many beats per second will be heard? (Assume T r et 6nh0.v :/;qoj u z,rf*/vhfuj1zb= 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain firc syrd*,1pw7d 1hh lm0cp, r;ke engine’s siren is 1550 Hz when at rest. What frequency do you detect if you move with a sp;pc,p dr*w7h,ydc1mhk0 l1 sreed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequency do you gyqg6flyz9t2 fg gk /5:sj7ih7e, 4hi)lrqo+detect if a fire engine whose siren emits at 1550 Hz moves at a2z y9gfi hsi/f6lqq,+yj )el5r:tkgh7g47 go speed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequencyoby . u0i3lx dqcch-7- if a 2000-Hz source is moving toward you at 15 m/s versus you moving toward it at 15 m/s A-l c3uoi 0qc7y x-b.hdre 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 wi)rq ar-p0/narth the same single frequency horn. When one is at rest and the other is moving toward the first at 15 m/s the driver at rest hears a beat /anpr0r a rq)-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 sount5jabm py9+ k/d waves at 50.0 kHz and receives them returned from an object moving directly awaytmpy/abk9+5j 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 s 0i80vod4ed ,p +o2byln wgg+5 m/s As it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. Wh4+l2 ondsow 8 +bp 0edgig0,yvat frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was played on atcvb-3 u5z,v o 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 frequ5vc -ob3vzut ,ency 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 measure blood-flow spgg o)ikxny o9l8yu337/ggqd7zi h 59 aeeds. 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 frequency if blood is flowing in large leg arteries at 2 cm/s directly ogd k x8ln/7579iq3ig zg9og3ay yu h)away from the sound source?   Hz

  The Doppler effect using ulix0o2mo 4w39 -klyg fatrasonic 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. When ze e- woy 6dlbs5kd. :4c:si56w, vllvthe wind velocity is 12 m/s from the north, what frequency will observersc5vl6s5vw4l:i6s de d eyz owkb:-l., 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 spepsplja emlt,.md- 3 :u9l 3ao,ed 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 c5k puuf ys7,s41i*dy ol0/yfm/s (a) What is the angle the shock wave makes with the opy,7f yfdyi0slu cs*k u5/4 1direction 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 speed of sound is*c kx ijm.q up+enz++57: whbs only about 35 m/s k n xs.7+iej+mh*q :wzc+p5ub
(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} $