What is the evidence that sxwd3cjs1 ,n:mhh w1g5 ound travels as a wave?

What is the evidence that sound is a form o: q9ht fs52ezbf energy?

Children sometimes play with a homemade “te9nuw7ee i 47/db h(kinlephone” by attaching a string to the bottoms of two paper 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 oni7w4niek /bhe9(d7 u ne cup to the other.

When a sound wave passes from air into water, do you expect the frequencybcyr8 3o; u ya5x;dp7o or wavo ;d73oar xyyp58ucb ;elength to change?

What evidence can you 0,lwwlbk/ x+mgive that the speed of sound in air does not depend significantly on frequenc/lwl,+0xk b wmy?

The voice of a persom94ij-bw n:zyhm ed3na*d05h n who has inhaled helium sounds very high-pitched. Why?

How will the air temperature ing8;6 m1k2 gsxwgg9r gv a room affect the pitch of organ pipes?

Explain how a tube might be used as a filter to d36 i:lsvoa kcg45m4creduce the amplitude of sounds in various frequency 6lcd:mgc i4 54 sov3akranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closerbow-7 .y0no ug together as you move up the fingerb7 .ngwu-ooby0 oard toward the bridge?

A noisy truck approacr5.nwlzd6 b*nx: a5-ertic 2dhes you from behind a building. Initially you hear it but cannot see it. When it emerges and you do see i *-edid 5:at5r.cnrbnlwz2 6x t, its sound is suddenly “brighter” — you hear more of the high-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be5f(ucb2 yf5isne o g-4x- f6jw said to be due to “interference in space,” whereas beats c-ci5jf ff xuo4n- be( 65wys2gan be said to be due to “interference in time.” Explain.

In Fig. 12–16, if the frequency of the speakers scobj.hj.(3 q were lowered, would the points D and C (where destructive and constructs obh3(c .qj.jive interference occur) move farther apart or closer together?

Traditional methods of protecting vfyk52l*8 5h 7sk jkvm1x+gfrthe 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 sougvfmkx7f hs8ykjv2rl1k5* 5+ nd levels reaching the ears?

Consider the two waves shown in Fig. 12–31. Each wave can be tosjlhx,5l d9vl +ix3p we*l-, hought of as a superposition of two sound waves with slightly different frequencies, asl*vpxie dj5,3 wlx,o+-l s lh9 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 sourcd 32v3fvwt *due and observer move in the same direction, widv ud3vtfw 32*th the same velocity? Explain.

If a wind is blowing, will this alter the frequency .-:k9 hler9nag-3cav ts*qkd of the sound heard by a person at rest with respect to the source? Is the wavelength or v-9k.c:rls*n9 ta3ed gaq-vkh elocity changed?

Figure 12–32 shows various plbw (/.gi ( 1)o zlum,znthb/sositions of a child in motion on a swing. A monitor is blowing a whistle in front of the child on the ground. At which p,()b1zut/nllbw/hzs. og i( m osition, A through E, will the child hear the highest frequency for the sound of the whistle? Explain your reasoning.

  A hiker determines the leq l2kw77 tr5d44k wr sc vpiq6c;8m;kvngth 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 w7r4skd6w4 ;tc vkqp5 l7rvick2m8q; s after shouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his -g-mporkh1jyb0q4 8 zship just below the waterline. He hears the echo of the sound reflected from the ocean floor directly below 2.5 s later. How deep ipok-z0-brh4 y qj8m1gs 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 wavelengths in air aii4(dxv6 saukbhps s ac9* z;48tah,5t 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 oysqi ib9t -4xm4k--vv f tuna on a foggy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How much time elapses beforsv 4q-mv-b-ik4 ix9 yte 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 sp5 g:qnlxj7aexumu42: lash it makes when striking the xagx524mu n:u7jq:el water below is 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 concre3av qrx7z-/;74 wgp,zxlkei+g.cem qte 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 wxlkiv, /+-ez7qcqega7 gx;r4mz3.paway did the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one mile of distance by the “5-secowmifa;+ wl8 p/nd rule” for estimating the distlmw a;p8f/+wi ance 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 dB? -teblg4 cm:2 x   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 whzq1x(ht d 7p7wose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound leveayhnjae.ea69+g 7 p h-l of 95 dB when fired simultaneously at a certain place, what will be the sound level if only one is exploded? [Hint: Add intensities, noty 6 g9-pa.anheah +7je dB’s.]    dB

  A person standing a certain distance from an airplane with four equallyvk(6 ex.k l n-9z crrl)zx:uj6 noisy jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would this pers)6l6ke9zl(u:. n-rz jv xckrxon 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 ral 5-kd 5(8,honm a syl )cii06uge8zcdtio of 58 dB, whereas for a CD player it is 95 dB. What is the ratio of intensities of thll58iadys5,z 68(e- gh n)kc m0 uiocde signal and the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sou;dwhi h66 xu3jv)/tnbnd from a person speaking in normal conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphere centered on the mou)vb3id6j h xnw;t/hu 6th. $\approx$    $ \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 striker 9bvw7teq3z 8s an eardrum 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 9pwp 8+.7 gaidxy6mwn250 W, while the more modest amplifier B is rated at 40 W. (a) Estimate the sound level in decibels you would expecpy+ m6n ww87paig9.dxt 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 in front of r e8q8 kry r8z5ry9dg(a loudspeaker on thezr(e8qd85 r8r9ky ryg 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 differencey..))on s2 1txlt vwqw in sound level of 2.0 dB. What is the ratio of the amplitudes.tx)1wl.nwt q ysv)2o of two sounds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is trd,bt ly nxyhu1a*)2njc/a ( ;tipled, (a) by what factor will the intensity incr 2cna)yyu ,(xa1 dl;tt*b/nhj ease? Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudea/,f)kl y)o 0of y3hkcs, but one has twice the frequency of the other. What is the ratio of t3yfo/ako, ) lkfy c0)hheir intensities?   

  What would be the sound level (in dB) of a sound wave in air that correspondst iax1-piu0kg 7 .8ker to a displacement amplitu-t kier ax7i.g1 0up8kde of vibrating air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud as a 100+xmk o1jc:v28/dk,zy r+zb ei-Hz tone that has a 50-dB sound level? (See Fig. 12– mv :b,z xy8o+rki1jez +c/k2d6.)    dB

What are the lowest ru1y 0c zdlm76vjz-c+and highest frequencies that an ear can detect when the sound level7vyc0 61m+zcrudj - zl is 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range :hbw yavm3 e6f0+/dxeof sound levels. What is the ratio of highest to l0dexvfm3w:yb+/h 6ae owest 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 4ipc;b az*p9720h r fx0yz2gta40 Hz. The length of the vibrating portion is 32 cm, and it has a bczg;f*pahx2 p0 y29 tz07raimass 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 ol7zlm-p0.jv first three audible overtoo0j7m-vp. llznes 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 y 41faw p*:ghcrfm3y3tosw z ;)ou expect from blowing across the top of an empty soda bottle that is g3*a 3 twyhcrp4fw:z)f;so1m18 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 spanning thimnj,qf +t :2kf/bxl:fe, -y xe range of human hea:f lq ,jkf: m+t b,neiyxf/-x2ring (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 frequenn+zwsgre 4/8ug6jkav7w: bg , cy of 540 Hz as its third harmonic. What will be its fundamental frequency if it is fingered at a length of only 60% of its original l6wezvn,:jg8 ag74srb/ k + guwength?   Hz

  An unfingered guitar strin34h6fstae oou/ 3p * imz 4:d, vh1eoipv:eht.g is 0.73 m long and is tuned to play E above middle C (z4fese /313mph,opv ia ui6:hh :tot.o4*d ve 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 middle C (262 Hz) whenqsw)rpu +*u 9u 43jvoq the temperature is 21u)+pqosj ur349w v*u q $^{\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 ,9p,rw m, hmnhg /x8ilpcw20 fat 20 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece opuw 4d.9ub.vw5g6i rof the flute in Example 12–10 should the hole be that must be uncovered to play D aboveui.rbvg4 u w69wodp.5 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 Hg )kby/*ql;ne z, but not at any other frequencies in between. (a) Show why this is an open ok;n yg bl*e/)qr 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 reshxnd)* t.yjjtf:* (l conates at two successive harmonics of fdj*nt:t h.c( )xjfy* lrequencies 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 cpjb:u 22 f-zo8ga4isei 31smy p3ue/ $^{\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 lf7iddat2fw q5, e ,9xpresent within the audible range for a 2.14-m-long organ pipe at 20 qa,edxitf59l, f7wd 2 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approx m3ejqxz .ga+.imately 2.5 cm long. It is open to the outside and is clos.x +e mqz3.jgaed 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 eve* rx:cxoi 5qa.ry 2.0 s when trying to adjust two strings, one of which is sounding 44:iox .*c 5qxra0 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency if middle 36b-asikytv tb4l j+ak +6e8m 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 at ;(ulplw - sjt jfog07123.5 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 thewjfsu;l01( -tj7 opgly are played simultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded with a 350-Hz tuning fo*uz rouq: *1kuuawjoad4e w9/ob-u3,)g a4xp rk and 9 beats/s when sounde,xpwa*)oo az a3: o* u1qdw4gj/u kbe4uru- u9d with 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 oirsmc3n-sho 58+ d;h 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: Recall Eq. 11–1r;os o 3cds mi-5h+hn83.]    Hz

  How many beats will be heard if two identical f fg2*ydvfk*gy. hn17 - pveufsn9, aj(lutes each try to play middle C (262 Hz), but one is at 5.0°C and the o1v fkyj2-d as7v.g ufh(*nf,e p9*ygnther at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has lebug, /; :rkna frequency of 441 Hz; when A and B are sounded together, a beat frequency of 3 Hz is heard. Whneulg;rk: ,b/ en 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 l.t uuimb7 y0r50 xcb; oti8.rm from one speaker and 3.50.r; 8 orxiu m 5biuct0.lt7yb0 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 to be vibrating at 132 Hz, but a piano tuner heb7m*g idr4i96(w iokr ars three beats every 2.0 s when they are played together. (a) If one is vibratiirg 4*w(6rm ok79ii bdng 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 beadjv)mc2: 6q iknmv z68ts per secon2d8nqjz 6mckvvi: )6m d will be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a ce32urmr-z gi2(pj b z1v --fiogrtain fire engine’s siren is 1550 Hz when at rest. What frequency do you detect if you mp- ij-bu voz2ig- rgm z(f2r13ove 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 fir(uwbqij +v5c:2)4d6szof ) qbw 7 hpbte engine whose siren emits at 1550 Hz moves at a speed of 32 m/s 6fc 4p5: )o h7+i u(wbbswqq2dztj)vb
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz source is mov2vqfl aklgen7d..d ,-. yuzt (ing toward you at 15 m/s versus you moving toward it at .tzvld- , uenfqa. dlg. (ky7215 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 frequenc;.y4t:y l-4: kyqd lqr8.ofbi g bw(xpy 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 frequency of 5.5 Hz. What is the frequen o by(xqywiy44:qp . d. fltk:l8rg-;bcy the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at 50.0 kHz and recj bm.;qa085 2*ulfi-sc,w nklq;tqsdeives them returned from an object moving directly away from i 2ltfjs wlusi ;,;b8n 5qa-kc0 qm*d.qt at 25 m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a/ +m ( ly4b.0divtsfj4oa e;rw speed of 5 m/s As it flies, the bat emits an ultrasonic sound wave with frequency 30.t(/ vsyj . 4;0blw4+adoefmr i0 kHz. What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba wa 0qzsv :1 d*;irzwadso -5of+ds 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 approached the station at a speeo f0+d ;o5z i-q dzv1rs:d*wsad of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound wa:):ood mf qwhr(vf 7z7ves 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 Whawfoh7fq)( r:z: md v7ot 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 frequenc/;za8 g7v9kuhom)wwboy(z s 4y $2.25 \times10^{ 6}$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 s+/cz t.n usk+bkz3c)4xkkwc gud9 0( tound of frequency 570 Hz. When the wind velocity is 12 m/s from the north, what frequency will ob(gd9z+4cwnc.t+3uc/ bkz)t0 kkskux servers 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 i/ij z9h .h:-lp 53k kzfib4jhff 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) What i+ q; 5gnokkyc+s the angle the shock wave makes with the direction of the airplany cn;qo+k+kg5 e’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 7aw b64bt18t hydrj( sof sound is only awb1(d ahbj7r68ty 4s tbout 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} $