What is the evidence that sound travelxrl t8 g19qx;ns as a wave?

What is the evidence that sound is a form oft(2 dibv1eg)uyuv.8w-o lz6y7 7 cvb v energy?

Children sometimes play with a homemade “telep t8u*8iu-v7lgll 9qr phone” by attaching a string to the bottoms of two paper cups. When the s -9l7 vll8tp*uqgir 8utring 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 int6- 6kc/o6ftg r7xood sc*z2kho water, do you expect the frequency or wavelenkocz rs6ohg76*c dtk2-/fo6x gth to change?

What evidence can you give that the speed of sound in air do s3(bbepe3 o+7jhyz3w7y( j scyy x-x-es not depend significantly on frequenc3y x b+bjyessp-wz(7yhx-ec 7 jy3(o3 y?

The voice of a person l2 uinuvzh ljb./lq uh657ovi3*3 f(gwho has inhaled helium sounds very high-pitched. Why?

How will the air temperature i mkcs/c7htjfpv n/,r7rh5l41mx0n3 i n a room affect the pitch of organ pipes?

Explain how a tube mig1 )rfj ,/q9 v.sbrgbopht be used as a filter to reduce the amplitude of sounds in various frequency ranges. (An example is a car muffler.)r orgp)sb9qfv /b,j .1

Why are the frets on a guitar (Fig. 12–30) spaced closer together tjwit+1tc5t7xye: qws72u+e:gj 5 ro as you move up the fingerboard toward tht7+ereotquy1:g:j7j wic2 w +tsx55t e bridge?

A noisy truck approapkf 3;.8b7vteehr-8 oq1w z sfches you from behind a building. Initially you hear it but cestq8bfek 7p f3.ov -r1wz;h8 annot 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 11–15 on diffraction.]

Standing waves can be said to be due to “interference in spfn)4xnl rs couc6ho 8-c r4 jy7qvjs8qn5b0+; ace,” whereas beats can be said to be due to “interferench+sly0n; qnv6 8j57rc8u j4 os)-fnbcroxq4ce in time.” Explain.

In Fig. 12–16, if th *l((md:9;oi, ddemfvi f x2+kekn*sve frequency of the speakers were lowered, would the points D and C (where destructive and ;fod ,l dmekks(v x9v(e *i+:f*i mdn2constructive interference occur) move farther apart or closer together?

Traditional methods of protecting thez zv2*s.)v dbp hearing 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 addition to the ambient noise. How could adding more noise reduce the sound levez2dv*p z)s. vbls reaching the ears?

Consider the two waves shown in Fig. 12–31. Each wave can be thought of as a o4 t x;*(sxzozsuperposition of two sound waves with slightly different frequencies, as in Fig. 12–18. In which of the waves, (a) or (b), are the two component frequencz; 4o(oxsz*x ties farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and observer m4cf01 i yj +ghqj3l)lxove in the same direction, wig0x c1 +jjy4q3fi)llh th the same velocity? Explain.

If a wind is blowing, will thisx aid6m 0sf*3vjaed/7 b; ddlvc, s1a7 alter the frequency of the sound heard by a person a,7cf1 vlsbv;e 6 axid0m/a7ad *djds3t rest with respect to the source? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a child in motion on a swing9lu 1h87xhm z pts8yf+. A monitor is blowing a whistle in 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 8fz+1ut7 xmp sh8hy9lyour reasoning.

  A hiker determines the length of a lake by listening for the echo of her2x b ;pqo/i 94lyni5oiv3del4 shout reflected by a cliff at the far end of tie5idb;vp2i34 ol l9y /qo4xn he lake. She hears the echo 2.0 s after shouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below t 0m8u,obkcr hp*p5(rz he waterline. He hears the echo of the sound reflectkh8rz b uc0o ppr(5m,*ed 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 significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wa,vy,)e3b561 s wm rvucl .himwvelengths 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 twlmpwf1 d2a -)1lv c1puna on a foggy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How much t1 2 d1 vafw)c-lmwppl1ime 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 striking8 4d z7yswkptw)m*)sp the water below is heard 3.57 w8ptd)yp kzsmsw) *4 s later. How high is the cliff?    m

  A person, with his ear to the ground, sees a 6iibopmi4 i4iiah *,5huge stone strike the concrete pavement. A moment later two4i5i6o ,4 *ipbii iham 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 33. ,m)hy5jpngwq kg bby the “5-second rule” for estimating the distaqp3gmwh bjynk3 )g 5.,nce 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 og,;ad gyd; *wvf 120 dB?    W/$m^2$Compare it to that of a whisper at 20 dB.    $ \times10^{-10 }$W/$m^2$

  What is the sound level ,fjjgn6 0*,p6t8+on8+lh gh dwdkyvh 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 simultaneousl3+g 5c qf-i/ohnrx7m+h dznrkw2/,e qy at a certain place, what will be the sound level if only of hgernc /+ mkzwn i7o5xhd/ q-q23,r+ne is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane with t2zc,yjhg : -e32ayn vfour equally noisy jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would this person experience if the capvhj-3yz t2ng ,ec2ay:tain shut down all but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to have a signal-to-nono7gqud : *olmo.id4(ise ratio of 58 dB, whereas for a CD player it is 95 dB. What is the ratiun gqd. o:4 ldm*oi(7oo 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 person s/ )t(qyywnq1e xv; 7lhpeaking in normal conversation. Use Table 12–2. Assume tq ly1(n e)h;yvtq x7/whe 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 atfdq 98j qdn6i9s k*0jrea 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, whilbz 8 lda6(+yqwjeu9s 1e the more modest 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 lobsewdu1y9 a(j lq8z6 +udspeaker 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 registered 130 dB when placed 2.8 m in front gbg it;lh;t(tsz3*g l9a(m;s of a loudsp9 gb(m(t t lis *3zglh;ast;g;eaker on 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 typically detect a difference in sound level of 2.0 dB.su4wctky rdzmq y1fx 2-n1*3z36/prx What is the ratio of thwzzx3u 6y12/ - 3 rpmrndyc*q1ts4fxke amplitudes of two sounds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound w q lhm9 wo/f-z9hq2b6zave is tripled, (a) by what factor will the intensity increase? Increase by a factor ofm hzh/2l obqfz96w9q-    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but one has twice the fktslsw d/;64f ;p rcm; ld*+rprequency of the other. Wrmp csw+/sd4t;6dl;pf;* lrkhat is the ratio of their intensities?   

  What would be the sound level (in dB) of a sound i acwk2phns8 ;q:qx6-wave in air that corresponds to a displacement amplitude of vibrating air molecules of 0.13 mmhkxpq csni;6 2:q a8-w at 300 Hz?    dB

  A 6000-Hz tone must ha.;ctdquyo,6 c75o c peve what sound level to seem as loud as a 100-Hz tone that has a oeopu .c ; tdcy6,7cq550-dB sound level? (See Fig. 12–6.)    dB

What are the lowest and highest frequencies that an ear can detect when the /;(lthjlr8 bv nl,xi, sound leveil/jtnblhx rv (8,l, ;l is 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a hugedce8 s th9+-i ws44fow range of sound levels. What is the ratswotwsh8 +-4cef4 9id io 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 rxoqo:g rulkf* + wx 92qf-6p8of 440 Hz. The length of the vibrating portion is 32 cm, and it has a mass of 0.35 g. Undepkl:9w*f +2u- xqr fox g86rqor what tension must the string be placed?    N

  An organ pipe is 112 cm long. What are the fundamental and first thr3 v/huok04i jdee audible overtones if the pip43uid0 j/kovh e 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 fre d;;raoozi/u6 quency would you expect from blowing across the top of an empty soda bottle th6 u;aordz; o/iat 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 spannin )w-ckl5id7ou dkc 2o17;il5ejp 9kntg the range of human hearing 5 ne2o)iulo 5p dw-kc1jd;9kl77tc ik(20 Hz to 20 kHz), what would 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 a wqg2.q.5gp zock.qr1s its third harmonic. What will be its fundamentalpq1g.g k q25.o cwzqr. frequency if it is fingered at a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0.7otz 4)hj*-zl r3 m long and is tuned to play E above middle C (33-j* ortz)zh4l0 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 pipeqq co59 jjw .49ayvbt0 that emits middle C (262 Hz) when the temperaqjoj 5.awq40 yv99 tcbture 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 20sjnu(g px(k43 $^{\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 shop0l;n5hrgtme ywy5v4 6qm;+p6(rs ev uld the hole be that must be uncovered to plae6yrep(5pms;+56 wtv0 4v q ;rmyhlgny 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, bu: 6fxi f5abdc,t not at any other frequencies in between. (a) Show why this is an open or fdb5 ixa,:f c6a 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 resonates at t fl8i-n5 i:h oqkocb:vx ,4 3q))m8ynzmu2iqgwo successive harmonics of cq3: x z5gmuinf8,y i-imq 2koo hv)n84)q:blfrequencies 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 th(7p 7bnzec/cp +ma- $^{\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 2.14-m-long ny7uxqx,7i. hknx5ii5 i9q (q organ pi7hqxx5qniqix, ii ku.(9n7 y5pe at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximate6oqzh *x f85py/-ru(bsrh1j sly 2.5 cm long. It is open to the outside and is closed at the other end by the eardrum. Estimate the frequencies (in the audible rango*rphhxsz ju- 8q5y/1sfb(r 6 e) 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 adju+d(2tv7i3v:joco)*n4hs uvkv nc)q 16vvcjast two strings, one of which is sounding 440 Hz. How far off in frequency is the other string? )2 +co6*ihv janqc)oudv jvk1:csv4v3n vt(7±    Hz

  What is the beat frequency if middle C (26pv./dwdw 9d(s2 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, whi1- k terh38xuv1mcbfa9v)n7 ile another (brand X) operates at an unknown frequency. If neither whistle can be heard by humans when played separately, but a)7nx hvk f9ue1vitb1c38 a-rm shrill whine of frequency 5000 Hz occurs when they are played simultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/z6dx 2o4nec c2d a:sg:s when sounded with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is thag 4oce n:2d6d:cszx 2e vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same freqziy-9apu * tj6uency, 294 Hz. The tension in one string isy j *tiu9-pz6a then decreased by 2.0%. What will be 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 flutes each try to plh8p1 .q:dow4m3kqc h fay middle C (26mp:wqo k13ch48 qdh.f2 Hz), but one is at 5.0°C and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning f febn hci(2at-:k7uz ,orks, A, B, and C. Fork B has a frequency 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 2-(e7nb h zu:k f,aitcare 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 from one speak*nuqzk 0w1x(-g p 0gvyer and 3.50 m from the o-zpk wqgxng yu1(*00 vther.
(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 heal bpp d*2g,7tl-adl s.rs t2l7 lat p.,dl d*s-gbphree beats every 2.0 s when they are played 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 of wave-3kz79 hmoo rhlengths 2.64 m and 2.76 m in air. How many beats per sech 3k7oh-mzr9o ond will be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s siren is 1550 Hz when at re/,n tswrr1tn8/;pm pjst. What frequency do you /sp / ntm8 jpt,1rnr;wdetect 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 frequency do you detect if a fire engi mgy. z6wfp3y()l4fc o - l;siqtnun-8ne whose sirew8p);ti.ymn-( f yz lqo3gul-n 46cfsn emits 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 frequency if a 2000-Hz source is moving toward7ve *7qepq1uh you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exactueh q p771ev*qly 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 tat -3ted u,/hkb5ft:eh)z5l, sg1)wgmw7lo xhe same single frequency horn. When one is at rest and the other is moving tod,kl )u,aegs57hhtwwo g)3 b: xt-mz/et5lf1 ward 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 ulv prz/9c. 9w3 hrm5ryutrasonic sound waves at 50.0 kHz and receives them returned from an object moving directly away from it at 25rwv9ym/3c. hu9 rp5z r m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a walucrdf(*ov9y. l at a speed of 5 m/s As it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHzf*ru(v9od y c.. What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experimuz6kl)zy* :qh ents, 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 hkuzzq) l:yh6 *eard if the train car approached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measu( k2 vbw*)8r8xdc dcn1ujg kq+. qd*irre blood-flow speeds. Suppose the device emits sound at 3.5 MHz, and the speed of sound in human tissue is taken to be 1540gn*+cb) qv 8irw* ( x.kdjdudcqr281k 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 ultrasonic wavesjp,t: m2yeci()1 ubhr 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 the wind velo,r6vluih1o x. city is 12 m/s from the north, what1xi6hu lor,. v 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 object moving on land if its spe,f,ny57yvt il 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 o1/0 he1e f)vld(a. z-cestqd kf sound is 310 m/s (a) What is the angle the-.fq1/cd1(z0aeh) td lve esk shock wave makes 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 sg* a: 6psf0x imw2vy,:v qto8dpeed of sound is only about 35 8*qv xv6y:dow a pi02:sgf,tm 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} $