What is the evidence that souw:dsp4*y4f-lb (ohr/t h2 qd bnd travels as a wave?

What is the evidence that sound is a b;pa 1t49v , 1ns bzbfuh/pmr1form of energy?

Children sometimes play with a homemade “telephone” by attaching a stk0jq4r3 .hlphring to the bottoms of two paper cups. When the string is strlqrh 3j4.0ph ketched 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 pabig hk9 :.5uqmsses from air into water, do you expect the frequency or wavelength u:g5.b9hqim k to change?

What evidence can you give that ko a3:ecdgqih1-s o/ 8the speed of sound in air does not depend significantly ai hk csqo- 3g1/:deo8on frequency?

The voice of a person who has inhaled helium sounds very high-pitcs b0ijd3j4( xehed. Why?

How will the air temperature in a room affect the pitch of organ z4l o ; x:dx6ksw7)pee(m)oyipipes?

Explain how a tube might be used as a filter to redug*n9 a.m oapg5acz;br5/i m/ kce the amplitude of sounds in various frequency ranorba kz ; c/5/5ngg*pmmia a9.ges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closeuv 8ky70; upmmr together as you move up the fingerboard8muv;7myp ku0 toward the bridge?

A noisy truck approaches you from behind a building. Initimm.gj18p.rpx*ia/ox( qq i4 kally you hear it but cannot see it. When jp(14i.p g/8.irqq x* kamxomit 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 space,” where4(cbuk:h( z6/exzazy8ucwc a kq/)mw(p,pk 4 as beats can be said t4k(hm/ukbzc:pywuazc(wc(4) ,pka6 x/ ze 8 qo be due to “interference in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered, would the 2vs 9r2dgi/fe points D and C (where destructivie9v2rf g2d/s e and constructive interference occur) move farther apart or closer together?

Traditional methods of protecting the hear0 ppdp+pv f0; l-*fzfxing 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, thp0vfppl-*zdpxf 0; f +en 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 t 4tczdds;39q+;ur wo 0hi m3zas a superposi03qdtidtz;93+ro shuz c 4 m;wtion 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 frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and observer move in the samowr *b.uo bgqwq2 8ok//i)j2oe direction, with the same velocityr o2*w j/bqgibow2u k qo)8./o? Explain.

If a wind is blowing,:66hx9rofx6 0z jd4o2qljgi 9 wy*urx will this alter the frequency of the sound heard by a person at rest with respect to the source? Is the wavelelx6wjgr o*q4 jrfhu9 x0ziod69yx26: ngth or velocity changed?

Figure 12–32 shows various positions of a child in motion oo grj6de.m tly-w1+,.aup 5ldn 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 the highest frequency for the sound of the whistle? Ex+t5 eud1,6 orjd.a-mlgl.wy p plain your reasoning.

  A hiker determines the length izo/h/kt n6 z7of a lake by listening for the echo of her shout reflected by a cliff at the h/6oi/zn zt7k far end of 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 side o 5hjzyve(xly 1c/lu,ic* 46 jkf his ship just below the waterline. He hears the echo of the sound reflected from the ocean floor directly below 2.5 s later. Hoc/l 5v4k1elyu*, chz xjijy(6w 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 wav;m6ls+*uyy v helengths 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 ju:s ji xl+vdq( b7:f r()cz2fepst above a school of tuna on a foggy day. Without warning, an engine backfire occurs on another boat 1.0 km awayf +rzq sj7b(ep2dx::c(vl)fi (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 spla y2 c6d5,owtqa *+fqlfw62jdmsh it makes when striking the water below is heard 3.5 s lad5 moqat+*6 w2q ,ydfc f2lj6wter. How high is the cliff?    m

  A person, with his ear to the,r r f*e/tvq p;j8.hno ground, sees a huge stone strike the concrete 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/jrt q8f .;vr ,n*ophe. How far away did the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one milxjmxeou a7:q /)p(ugg7t a*d, e of distance by the “5-second rule” for estimating the distance from a lightning strike if the temperature is (aqgu ma/o,a(: 7tj xpge *7x)ud) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pain level of 120 d/zy4ke ruy. 9vB?    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 p54m al::qhei qio,j- sound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound l0q.v4q n:ci8p x ,qyskt6k z,qevel of 95 dB when fired simultaneously at a certain place, what will be the sound level if only one is exploded? [Hintkq,i,6sx qzy8pt c 4.nqk0q:v : Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane with four equallyvz bd+v9i466y a xv)db noisy jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would this person expei6 zb+)vv4 9dvdybxa 6rience 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-noisi7qd n m4/2dw)lo 2buse ratio of 58 dB, whereas for a CD player it is 95 dB. What is the ratio of intensities of the signal and the bac nwu qb7omsi2l/d2d4 )kground noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of v90lqft c +m.hz.g r,ksound from a person speaking in normal conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphh, qtc.0grvkf.l+zm9 ere 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 area i5sfje +m: mof2s $5 \times10^{ -5} m^2$ (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 atcepvc((1mh;fz* k-3 3lw/mk nice(dk 250 W, while the more modest amplifier B is rated at 40 W. (a) Estimate the souk(c f3e/ dc c((mniplz*k- ke3mw;1hv nd level in decibels you would expect at a point 3.5 m 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 registered 130 dB when placed 2.8 m i9u)o5mbfka2 og)p2lp n front of a loudspeaker on thp5o )2b9 pgkoa)mf2l ue 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 dBnkc ;d3p2vqbjt9 j -*j. What is the ratio of the amplitudes of two sounds whose levels differ by this amount? [Hintjjp9- bt2c *;vkjqd3n: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a 047d tvj2biov) by what factor will the intensity increase? Increase0vtdvoj 2 4bi7 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 9b8sw*0vx4yy r7ql.ylmrgs9 frequency of the l9.r r b0y8*x74l9svymw s qygother. What is the ratio of their intensities?   

  What would be the sound level (in dB) of a sonyihmpf5ogd (*f bd1z8(6 p) gund wave in air that corresponds to a displacement amplitude of vibrating air molecules of 0.13 mm18h z gdn*56pfyig(o (dbfp)m at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud as a 100-Hz tosw. hl ptf c-fn344.d;dcfeo 5ne that has a 50-dfwd.-;4l5p c4 .df hf3 cnotseB sound level? (See Fig. 12–6.)    dB

What are the lowest and highe6tt ei3gs+ c, qx*go3dst frequencies that an ear can detect when the sound level i6g3*tg xiq+oets ,dc 3s 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of sound l 56fgr 0wk) vu71 rfahqc6zj4fevels. What is the ratio of highest to lowest intensity at qwv6a16rk4j)5z7 ffcfgrhu 0
(a) 100 Hz,$ \times10^{ a }$ a =   
(b) 5000 Hz? $ \times10^{ a }$ a =   
(See Fig. 12–6.)

  The A string on a violgkhvrjs,xe((c)*n hr/e d95cin has a fundamental frequency of 440 Hz. The length of the vibrating portion is 32 cm, and it has a mas9hn(vr,herx( sc dkcj/g 5*)es of 0.35 g. Under what tension must the string be placed?    N

  An organ pipe is 112 cm long. What are the fundamental and firstmrvs qk:2y:,f4gw 9nq3 bhuk+ three audible overtones ifqhvnk3b9y+2 g : rk4mw :suqf, 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 expect from blowing across the ig6 y1qr9k)zx ictn)k82 0rptap y-;wtop of an empty soda bottle that is 18 cm deep, if you asir9qi8 t0))k-nc;zw trgxypy1kp a6 2sumed 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 ramg d;0) 9l 1czjfw fa6dou.qm0nge of human hearing (20 Hz to 20 kHz), what would be the range of the lengths j0m6za0);wo mudql 9.gffd 1cof 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+ f1y a/nd9obnrzb 76e will be its fundamental frequency if it is fingered at a length 67+ /e 1yabbodnfn9z rof only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is t ew* 0 z2iawej/ih.6bp,fn4o1pc wtt6uned to play E above middle C (330 wi htet2i*,pa oc 64fj6w0enp/ zb1.wHz).
(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 leodwo+ 0 rkpj,bx5,t- v 8wv-mfk1w/ npngth of an open organ pipe that emits middle C (262 Hz) when the temperature iwn1,kw,vbo tfr05 op/+ -px8d-wk mjvs 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 a:;h pui-ua+ b9vl-yz -ix3ihet 20 $^{\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 should the holeigistvq9h d) 5v+7n o, be that must be uncovered to play donh9)7q tsi+5g ivv, 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 at aj: se5 fsc;6knny other frequencies in between. (a) Show why this is an open or a closj;6sk fcn:es5 ed 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 two sur adq lea.8qf )h):4jfccessive harmonics of frequencies 275.:j)qf )aerh lf 8da4q 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 6v irl /4cr5/r-uysla+i qw2 c$^{\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 *ot jbp0a wtnds :zgw8j4.d06ba e t c,rk5m.3range for a 2.14-m-long organ pipeg8o cj0ett.m:bkbd*,z4prn3dw s 5aa6 tw .j0 at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm lonp-n f7:-n)cu4 m,/egi kkdokwg. It is open to the outside and is 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 relation-,f u-ne wokkkg)7cp 4dn: i/mship 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, svx 0.zs8lhk5.ttha - one of which is sounding 440 Hz. How far off in frequency is the othzh.txtkh-av5s .08sl er string? ±    Hz

  What is the beat frequency if middle C (262 Hz) an r5jgzkfg;o50 d $C^＃$ (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 2xj(u8v(esusw /d6+ lsb ,2rpz.u j(ni3.5 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, estinxej d/ s s8i(lr,jv.uz2(+psuuw (b6mate the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded with a 350-Hz tuning forti 1xi;vp6 q 3qal9:er q*iw7ak and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrati7x:iarq6w;q 391eali*pi tvq onal frequency of the string? Explain your reasoning.    Hz

  Two violin strings a7y e3p7 pi8zvvre tuned to the same frequency, 294 Hz. The tension in one string is then decreased by 2.3 7pv8vey7izp0%. 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 flf+p*i o s*ns-kutes each try to play middle C (262 Hz), but f *s-iopks +*none 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 frequency of 441 Hz; ff0rq lao0(ff(n i*e4 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 frequencies are possible when A and C are *frl0n(oa4f(i 0fqfesounded 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 pzalkmvz r;*,, ) a9gchrdr0 ;person stands 3.00 m from one speaker and 3. *ahd0;lg c,,z zar9mkvp;rr )50 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 t8l5hpm,al 6w oo 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 1aw56, lhm8l op32 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 wavelengths 2.64 m and 2.7o/wfes kz o2gg:g rz6*;lo(4w6 m in air. How many beats per second will be heard? l* z;fo2wsgzg w kr6e4:g(/oo(Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain firergc kta s ;0nu5 4a0b7bs);sas engine’s siren is 1550 Hz when at rest. What frequency do you detect if you move with a speed of 05;7n ca tk 0bsgu)srs asab4;30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What f pjs.2e*pu-bx requency do you detect if a fire engine whose siren emits at 1550 Hz moves-buj.x2es p p* at a speed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequencq s),897ak4 vx:s c(twpawgqcy if a 2000-Hz source is moving toward you at 15 m/s versus youvt8xw w7( )c9qs g,kcaaqps :4 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 frequcyi:zs55u5 er ency horn. When one is at rest and the other is moving toward the first at 15 m/seiy5u5r :sz5 c 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 kHz and v)xw,-t4 gchj4y8v df receives them returned from an object moving directly away from it at 25 m/s -gwj h)xc8d yftv4 4v,What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall a,uy lhx+ ws8(ul3kmvbu01xn rhv.) 8kt a speed of 5 m/s As it flies, the bat emits an ultrasonic sound wave with frequency 30.m83kyw vx . 8) 0l,blnr(uhuuvx +skh10 kHz. What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was played on a moving f0f2ejqowe+h9j 03.az osdc,rlat train car at a frequency of 75dr9,2jje.+afz hs30 e wc0oqo 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 car approached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measure zp8v7yuy 2+h8ae + frvv5kvv3 blood-flow speeds. Suppose the device emits sound atyuv 5hvy +8k7r8+3 vvfe2vapz 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 away from the sound source?   Hz

  The Doppler effect using ultrasonic waves of fr-.jbd0qyb3f)d i ige; , hgybe*h/a:aequency $2.25 \times10^{ 6}$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 kh) y2uv: -owetwa76n wind velocity is 12 m/s from the north, what frequency will observersu6k7e)hotw y: 2av wn- 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 .vz1)dje5wr* fg )iop +en-t tspeed 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 2f; ce*er0og nam3qo74 moa l7d,/wouspeed of sound is 310 m/s (a) What is the angle the shock wavd gu0m;e,w o37r/laeac*4fm27 q n oooe 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 speed of sounacm 4puz9-yz g;7w*y sd is only abouta*u4y9czmz p gw7;ys- 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} $