What is the evidence that sound travels as a wave:nf:l ecs. 1sp0l1xt t?

What is the evidence that sound is a form of energy?xl/ncn rrh-; 6

Children sometimes play sf)sn .,dt*t71wn w pzw,h.fiwith a homemade “telephone” by attaching a string to the bottoms of two paper,nz iswt w1)whsd* pff7 t.,n. 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 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 frece7pp+2)3zht ;yaf dx quency or wavela e3 p;zf2p+xcty 7)hdength to change?

What evidence can you give that the speed of sound iry 1i k1o99iy0e:bp fon air does not depend significantly on ie9 fk19opo:bi y1y0r frequency?

The voice of a person whcerb ax /r*z6n2vy(r f9o bxc*.ru/n6o has inhaled helium sounds very high-pitched. Why?

How will the air temperaturj(q y ttx5i(k4e in a room affect the pitch of organ pipes?

Explain how a tube might be used as a filter to reduce the .+asf(,bq* wsvw m wi)*rg0ggamplitude of sounds in various*ws)q, a(sf rwbig mwvg.+*0 g frequency ranges. (An example is a car muffler.)

Why are the frets onjk2xx lzpelz.2+z8w vzqi53; a guitar (Fig. 12–30) spaced closer together as you move up the fingerboard toward3e2+iqwk.x2lx p zzzzl v5;j8 the bridge?

A noisy truck approaches you from be6new6: v 5amzchind a building. Initially you hear it but cannot 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: zwcm6e6: n5av See Section 11–15 on diffraction.]

Standing waves can be said to be due to “interference in spack4 9c l7ja(vrge,” whereas beats can be said to be due to4k(j97 ac rvgl “interference in time.” Explain.

In Fig. 12–16, if th *a )arfe4p,lhgt*,3pn vtd y0e frequency of the speakers were lowered, would the points D and C (where destructive and constructive interference occurehvtygpnr f *0)4,* a dtpal3,) move farther apart or closer together?

Traditional methods of protecting the hearinth)3;b a.hd; hs*k) r0lb1ddfx)mihwg 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 feedl;1m 3)rdfiwhba*)x. dkh hsh;td 0)bs 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 wifkz0cwn:j3 1ave can be thought of as a superposition wc3 0kij:z1fn 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 same direction,oi*w6aqcu cy, a-oxrrexa.a +/3g.z 7 with the same c,63-o zuo7+ .eyag c awaaxxi/q*rr.velocity? Explain.

If a wind is blowing, will this 98r yrk7fqzj,9g uii-alter the frequency of the sound heard by a person at ru-ii 7jyfq k,rzgr998est with respect to the source? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a child in motion on a nqtdtu2n / 1lgg q*c38wjt 2o1swing. 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 frdo 813/ctjqt n*1tql2gnugw2 equency for the sound of the whistle? Explain your reasoning.

  A hiker determines the t ,56hjj7 pl+0yfemlx length of a lake by listening for the echo of her shout reflected by a cliff at the far hxl mft056,ej l7jy+p 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 of his ship just below the waterl)4fya *vos 4/ruiplzg25t2 vsine. He hears the echo of the sound reflected from the ocean floor directly below 2.5 s later. How deep s *vtu2si4 opz4a rvf/52 lg)yis 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 wavelzp)qidfo 15va ox+h*3 n:w,vlengths 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 foggy day. Wi/)(;klf4 uotmf* gqqfthout warning, an engine backfire occurs on another boat 1.0 km away (Fig. 124)go /l;(t*fmuq kfqf–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 spd3s/gzen d4 h-lash it makes when striking the water below is heard 3.54z-hsd d3e/gn s later. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge stone sta)68ae,4deu* nw)dw zm2qt rkrike the concrete pavement. A moment later two sounds are heard from the impact: one travels in the air and the other in the concrete, at6 k4a,zwer a 8*)) 2uqemdnwdnd 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 milulc7e0 *) zexk 2ogysy,/ 1y, kz( brrdd)is+re of distance by the “5-second rule” for estimating the distance from a lightning strike if the temperature i yyzlseke) rkui x)byg 0 od,+7 (s*zrc1d2r,/s (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pain level of 120 dB? nh/m/ s7c6q 7rfo1ndm   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 inten q o+ypzjzel0hnk54)5 sity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of b 74/:/+pgpgiaje iyu 95 dB when fired simultaneously at a certain place, what will be the soun+: a/4 / 7upieggipbyjd level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a x xx*m vdy16(n 9 7yikdjfy9+hcertain distance from an airplane with four equally noisy jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would this person experience if the captain shut i+d9v1j( nyk hxx *x9y y7fm6ddown all but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to have a signaj0hvv8s r7zw )29h .*qjnt vdjl-to-noise ratio of 58 dB, whereas for a CD player it is 95 dB. What is 7s j jvn tq08j*.dr)zvh2vh9wthe 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 person speakind04e,6u)mvk ,q jayp ngwh ,vh59i6stg in normal conversation. Use Tabvs ahm5p0g , 9e, i)n46yw,qvj6ukht dle 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 whosvc8;x*,xc ;nivee 3 lwe 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 2n+b:d)vw /4uqu bf3 gt 3,ogrh50 W, while 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 u,ghwq rnut3b3:+gofb/4 v )dloudspeaker 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 iulef,-il 6mzb+t5hq;s h0j3m 45rj bun front of a loudspeakehqfiu- 5j3bt+6 m, rejl4blz;m 50suhr 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 lvij5- v4h8at8p ckjw;evel of 2.0 dB. What is the ratio of the amplitudes of two sounds whose levels differ by this amount? [Hint: 8c-j85p4vj a;wiv t khSee Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by 58elu4n*y jpwags nv.82rn .zwhat factor will the intensity increase? Increase by a facto2n848vr yw j..zu5ngsa peln*r of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplituqk ldmp;3b*7e des, but one has twice the frequency of thebm3q*k ; delp7 other. What is the ratio of their intensities?   

  What would be the sound l) syqqlq,,9wc. qr.v level (in dB) of a sound wave in air that corresponds to a displacement amplitude of vibrating air molecules of 0.13 mm at .,r q9cvsl ,qylq)q.w300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as l7xi/ ze4*trgpe2p ; paoud as a 100-Hz tone that has a 50-dB sound gpx4ai 2 p/rze*p7;etlevel? (See Fig. 12–6.)    dB

What are the lowest and highest frequencies that an ear can detect when th,(ifm wfcu.yg n o9:j3e sound level is 9i ,f3:c(gjy uno wfm.30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of sound levels. What i snlsvh8*,mc7s the ratio of highest to lowest intensity at h*n 8m,l sv7cs
(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 lengx nxbfsf69oy+;c+ p((tq kj -sth of the vibratt x 6 +fq;yos(c(9jnxsfbk+-ping portion 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 fundamental and first tsxxj ebc*h067 ti .4jmhree audible overtonc s*xxjhm76 e04 tij.bes 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 expect from blowing across the top jxw7kr7 7 r8rv(- jo b-ukbgd2of an empty soda bottle that-j727v u gj7b8 rwkkodbxr-r ( 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 buildsj-r/a:l n)z5km ku -k a pipe organ with open-tube pipes spanning the range of human hearing (2/l)-s kknj :5 rmkau-z0 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 frequ yj ee9y8;tai,2drbq lep:2ogz u571sency of 540 Hz as its third harmonic. What will be its fundd 9:lb;quzg2y2yae15t j7 eri,8 o pseamental frequency if it is fingered at a length of only 60% of its original length?   Hz

  An unfingered guitar string / y ekczvxpww/0:-umj0h*g/rf) x sa(8qjj+ eis 0.73 m long and is tuned to play E above middle C (330 Hz) q*x/g(e j8f kw+0es)jp- zxyrj:ma w/h v0c/u.
(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 (26 okf l/(e-p5gf2 Hz) when the temperature is /ge(fkpofl- 5 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 4ni,h kz*ipwd4lp - oa,(qan220 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of jh0r/ ko8j i9qthe flute in Example 12–10 should the hole be that must be uncovered to play D abovq krjihj9/0 8oe 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 ca xi* b)gwur3xo);jrx+n resonate at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (a) Show why thw rbu)ji *r xx3;oxg)+is 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 at both ends. It resonates a p6 aupwuol60795rimlt two successive harmonics of frequencies 275 Hz and 330 Hz. W uwa76p0rm9l p6ouli5 hat 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 c (stgkskn/h2/p 21kc$^{\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 presezv2oss:fly9 g2v 71if nt within the audible range for a 2.14-m-long organ pgolfv 7 2sf 2is9:1zvyipe at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is ap,k/kvdw*4l kfproximately 2.5 cm long. It is open to the outside and is closed at the other end by the eardrum. Estimate tlfw 4 v/,k*kkdhe 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 cvj;wy (4 dj;a2fir1dadjust two strings, one of which is sounding j; v 1w4diad(frc;y2j440 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency o)34taprhnu vp5 pb(1fi c*j;gj57bh if middle 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 operates atvgu)vuqw1 f.e5: x b(r 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 operating frequencu xeg vv:(51wf.ur bq)y of brand X.    kHz

  A guitar string produces 4 yfk zrkrn11 (;g5ec 9bbeats/s when sounded with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency yk 1 fe;rgcr5b (1kz9nof the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequenm1hlp yk 81/h* ;twtoswa yr+3cy, 294 Hz. The tension in one string is then decreased by 2.0%. What will be the beat frequency heard when the two strings are played together? [Hint 31*h8+tywp1m syokw/r;lta h: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identical flutes enw,lw/l3gm7eig2 i- i: azci1ach try to play middle C (262 Hz), but one is at 5.0°Clliw/ii w3a-e2n7 cz:gm,ig1 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 441v*4* jfyu ofl*d v9x(o 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 49xfj(*v *ylovdu *fo 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 oei :)t36fxct ge wa0j)ne speaker and 3.50 m from the other. wfcx6 t te):03)aeigj
(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 Hz4oj-iwvo/g0s :w osvga- 7x z;f7wo5e, but a piano tuner heario0-f-7w;s jswez 5/vo 7vw:ooag xg 4s three 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 wavelengths 2.64 m and 2.76 m in air. How many beats pi0+ 1r2bbu piwtw66wmb tv p/*er second will be heard?6uwibppb/mr6 +wt vi1b2 t0*w (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s siren is 1550((gprb rv4s6nfp h . y67c9yvz Hz when at rest. What 6vyybgh7s 6zf(r.n vcp94 (prfrequency do you detect 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 f t84ocr:o27ty2ndu eb ire engine whose siren emits at 1550 Hz moves at a speed of 32 m/s 4y:t28dc72orn teuob
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequer3 * k*zuuz/(m bw*eurncy if a 2000-Hz source is moving toward you at 15 m/s versus you moving toward it at 15 m/s Are tz(*wuue/rk* zmb3 r*uhe 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 hxb*yo6i8ge3 y mu(2b6vw5g n lorn. When one is at rest and the other is moving toward the first at 15 m/s the driver at rest hears a beat fr6v(5yywb8g 3i xg6*ln o e2mubequency 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 receives them p*oh1p:44z d/aqi* to-6yaba3g yykhreturned from an object moving directh ka6*o *-pa1zh4d:biqo 34ty/ gpyay ly away from it at 25 m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a 6. ibyigmq9au)m,:lmwall at a speed of 5 m/s As it flies, the bat emits an ultrasonic sound wav 9, uim6).bamq:lg miye with frequency 30.0 kHz. What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a t k/ sf ac6e4nz3woq)5euba 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 car appron6 3ak czow e4e5f/qs)ached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultraszv7ncaiz5,z qs;u 1w2ound 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 frequency if blood is flowing in largeniauv zz21s;7,w5zc q leg arteries at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using ultrasonic s62w2kxja2 p sb stiymdup45ixd7sk5rz)3- 0 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 frequencyibuch63 -6: pwb+vip; ej3xiu 570 Hz. When the wind velocity is 12 m/s from the north, what frequency will:b6 jv ip;e+u33cihxwui-6 bp 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 speed icop2(-db9 gj 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 (wj geuiq2t;8m/s (a) What is the angle the shock wave ma(teiqguw;j8 2 kes 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 so)9 2pifim q22zl,y susund is oy9 i mp2f)u i2,z2lqssnly about 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} $