What is the evidence that sounpsb)wm hx .b-4e.lvf2d travels as a wave?

What is the evidence thatk: vriyg2 2y9b sound is a form of energy?

Children sometimes play with a homemade “telephone” byj d94e9ity-hu+dkl a/ attaching a string to the bottoms of two paper cups. When the st9 t+k4-e/9yjd hi uadlring 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 aqn41* 7 6ysqfwv; e 8pyckww,iir into water, do you expect the frequency or wavelength to change?6n eiwwfv p8,ycky* 1qs;7 wq4

What evidence can you give that the speed of sound in air does not depend sign(ub : bwryh,e,6kpi5mificantly on frequency(ypbb mr u w,,6h5kie:?

The voice of a person who has inhaled helium sounds very halp7jf:k8 qusxu+tnx2 fe kz:ly, ;* )igh-pitched. Why?

How will the air temperature in a room affect the pitch of oftyw- 5m)g3dgu+)n vgrgan pipes?

Explain how a tube might be used wf*o9(d pcf f+ rcb7)has a filter to reduce the amplitude of sounds in various frequency ranges. (An example isb(d p9) +ff7oh *fccrw a car muffler.)

Why are the frets on a guitar (Fig. 12–30) svc*9j1o p7*jbv p yel;paced closer together as you move up the fingerboard toward the bp 71jp9ejov;y vl *c*bridge?

A noisy truck approaches you from behind a bct6.kdl- lew1tk5f 0 h; mckq,uilding. 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 fhc0 lw ectkk5t16km qld;-,.the high-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due to “interference in space,” whe )cvvzybda(5 tp9/4jqreas beats can be said cb 45jyt pdv /va()q9zto be due to “interference in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered, would tho vv)u6asvcyf741s *um5/ imbe points D and C (where destructubv4im7 ss)yamc1 uo65v/* vf ive and constructive interference occur) move farther apart or closer together?

Traditional methods of protecting the hearing of people who wor;d; o( zt5jz ykl)2uh(h v4ew wy0lyy/k 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 t/k;;h yle4 y w(w02zdyh5(zlvj)y uoreduce the sound levels reaching the ears?

Consider the two waves shown in Fig. 12–31. Each wave can be ty:.1poy vk5zyj ;bf; psmp2 z.hought of as a superposition of two sound waves wit .;1p o;mzbzyyp:y5s2v jpf.kh 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 movw7n7(i qu4x )lrshw9byn7v 3ne in the same direction, with the same veloci) uy4 l7nqn(r3nbx7hvww7s9i ty? Explain.

If a wind is blowing, will this5k383vuzry pwfr8. e m alter the frequency of the sound heard by a person at rest wit.8rrup5e vwf 83myz k3h respect to the source? Is the wavelength or velocity changed?

Figure 12–32 shows various pm.nedi5d dq*rr:vw y*xc.: +z/wej /xositions 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 the highest frequency for the sound of thnw d/drjdi.yc:*. q:e5/mx v*ex +zrwe whistle? Explain your reasoning.

  A hiker determines the length of a lake by listening for the echo of her shki4q e. ( lfcts7glbv- 9l;l *ww,mt3eout reflected by a cliff at the far end of the lake. She hears the echo 2.0 s7e wgl 3kifbllqs;*c4 lt,mw(9v te.- after shouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship jusclbr1 hy ;kdmi6fe x6 a3k76c0t 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 616e bla ichy3krm dx 7;c0f6ksound in seawater is 1560 m/s (Table 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelength rxhz0:xhynr81: 5 pe62pfcxx s 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 sco w +;*kp a3yki*ofsv+hool of tuna on a foggy day. Without warni+ k;y*vwfpoa*i+3 skong, an engine backfire occurs on another boat 1.0 km away (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 clif7wlc(3 r0g;cg3n l eko um5nd-f. The splash it makes when striking the water below is heard 3.5 s later. How high is the clifm3kdnul- ;cco nge 7 l0rwg(53f?    m

  A person, with his ear to the ground, sees a huge stone strikegmuk26.gl a kc;wq49t the concrete pavement. A moment later tw 2g ;gwqkatl64u.9c kmo 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 :.q.jtrc w86tiwk;d):b7id3fn obc d over one mile of distance by the “5-second rule” for estimating the distance from a lightning8b3iw7 ckd6d ) .ndf: tjc qriwbt.o:; 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 ab* h1, +2 at gxa56goryb5zfpof 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 of a sound ,7 v./tfa)jm cljq* axpgp9aoc1*wk4whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired simultaneousd*r-g:g mbl9 gly at a certa *b-rlggd9gm: in place, what will be the sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certv/:-8j zg3-vas o zgtzain 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-a/g- s v8zvzzgotj: 3 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 ratio of 58 dB, whereas forn ( e3wnrf zrzu. b/);6tgxl)w a CD player it is 95 dB. What/r;)feuzt.z 3 (6wxg)w rl bnn is the 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 6e h3n t7mpx-t jw(xq3sound from a person speaking in normal conversation. Use Table 12–2. Assume the sound h mt7 e6q33xpjtn-(xw 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 j4 j.e6nkhzrf q)1xun7; oev: 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 250 W, while the more modest iyv vub-kelsc 3l0 ; dq+3e;5lamplifier B is rated at 40 W. (a) Estimate the sound level in decibels you would exvv uc;kqd53b- 0l y+3s; illeepect 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 d3 0q7scixz;j+; pbwu yB when placed 2.8 m in front of a loudspeaker on the s ;zqu+bx0jiw cy;p37 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 level4a 6jdz;jhia6 of 2.0 dB. What is the ratio of the amplitudes of two sounds whose levels differ by this amount? [6z h;4jai6da jHint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tr4 k;b 3o0konbtn,bj 4v h, z48/xdrbrcipled, (a) by what factor will the intensity increase? Increase by a fac;/,d8 norz0nbvb 4htbjk4 ox 34c br,ktor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have 1xn5r,r3imp( *hay y uequal displacement amplitudes, but one has twice the frequency hya3p1 xy5*ri,u (rnmof the other. What is the ratio of their intensities?   

  What would be the sound level (in dB) oy,) pb yan: 6huc s, 7vanp5z owclgwjt)6)e:6f a sound wave in air that corresponds to a displacement amplitudep,zgcbc) 7ny)n)ay6:j, h6we wouasp:t65vl 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-Hz toneq/ygs5bzo2o sp ;c+3 j-qz6ec that has a 50-dB sound level? ( ecz +oqo;y/g6 -p css2bj53zqSee Fig. 12–6.)    dB

What are the lowest and highest frequencies that an ear can l8ll- .:u3t*e ppcp trdetect when the sound level is 30 dB? (See Fig. 12–6.) 8lt-lcr3 :ptuep* p.l

  Your auditory system can accommodate a huge ran)kg up bz)r lq*+ cgak-4h1:mvge of sound levels. What is the ratio of highest to lowest inta c*g)1q+4-kgvu :brkz )m lphensity 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 440 Hz.acp/n no-3(x 4spbp7p uj -*gp The length of the vibrating portion is 32 cm, and it has a mass of 0.35 g. Under what tension must the string be placesxoaucg47p p pnnbj --p3*(/pd?    N

  An organ pipe is 112 cm long. What are the fundamental aco-lhk7kv6 nc)-o rktcz 3,4ayk5 u1 znd first three audible overtones if7oc -lcvrkyzc4a 1)k 36o5h n ,kku-zt 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 freqk fhq l/h0bh3-nw t:i-0l md7cuency would you expect from blowing across the top of an empty 7c -fhw0k3nid/lhm0-q hl :btsoda bottle that 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 pipesm6vj un-j6fmp f,3h7c spanning the range of human hearing (20 Hz to 20 kHz), what would be the range of the hjm ,pcjf6 6n3fuvm7- lengths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a h+*i0) .qjvpqo 1cqznfrequency 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 lennpv) *+jqih. 0zoqqc1 gth?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to plv411sm:pnhsw/s(uv tg6 r iw+hpu. 2 zay E above middle C (330 th1 w us.1hrui mg2sp4zs(+p 6wvn/:vHz).
(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 middletld gbrb*yej0;,j*xe;*c6 lt C (262 Hz) when the temperature is 21 g;xj*rj*b6yl;te, * bedcl t0$^{\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 acz80ifpd.*4 xdm oco r/6c 0bgt 20 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiec8g2*/ mue-qj qqhh2e te of the flute in Example 12–10 should the hole be that mugeq2um8/ *jtqq2 hhe -st 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 ::d*ap nb,h xgresonate at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in bb:hg,*dna: pxetween. (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 at both ends.u s5o33a,xc:.p/ elpydv m7q f It resonates at two successive harmonics of f/xuld f .qvp53spoc 73:meya,requencies 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 fq2wx yzws 83wbs-2d j d6-qkh2m:5w 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 rangkuc15d.fo:v)e nnv j. e for a 2.14-m-long organ pikej)u 1o.fn :vcvdn5.pe at 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 22x8 7eas8eb8n5 alnjj b o1p 0a9qjqaoutside and is closed at the other end by the eardrum. Estimate the frequenci l j epba882qnb9qaajsxa7j528en0 1oes (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 adjust two strings, oc wyoo+sen8eo5b,8 s*d m5d f1ne of which is sounding 440 Hz. Howc 5o8sd+ e5e* dyw n8b,o1osmf far off in frequency is the other string? ±    Hz

  What is the beat freq e8ud9 ov:-koduency 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 at 23.5 kHz, wnhc;9b yal6ksnqi jt89l-424mvt g s5 hile 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 a;ky 4-s68c bjl 92gsnih4ltt a5mv q9nre played simultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces dws0iw:ql++1*vb n1r,1 i.tjdcqi sx 4 beats/s when sounded with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hzswci,0qbixt*jidlwv s+qr1d +1 1: .n tuning fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to u4za93gyg3(fgy. /qk m lab1g the same frequency, 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: Recall.fg3/z3( 1ayy9agk4qgugmb l Eq. 11–13.]    Hz

  How many beats will be heard ifpvq397 xh)duftel7 k6hg jc1 7 two identical flutes each try to play middle C (262 Hzl6ej37f1h) pt 7xvh9kdcq7g u), but one 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 j0uhqf6 7/fv+uz9dzp 3y gy ,ax)u1km 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 are the possible freq hag9zfypu,+u)z0u3 7 vj1m6yfqdx k/uencies 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 pers;q. --eo l 9fbj3wzirton stands 3.00 m from one speaker and 3.-3i 9robe wz-;fqt.lj 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 to be vibrating at 132 Hz, but a pimaq+mw h po)d2:0msi/ano tuner hears three beats every 2.0 s when they are played together. (a) If one is v)som2 :wm/ dq+m pai0hibrating 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.rwzw,j0t 5rl8+q m8(zl-rxbj 76 m in air. How many beats per second will be heard? (Assumqrmw8x( r,t+r zbj85 0-z wljle T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequencyht 7fi6)x8nr v9;z3m(nea7 yqn0 nxtm of a certain fire engine’s siren is 1550 Hz when at rest. What frequency do you detect if you move with a str v 6nnif;t8hy77zqxx)(mn0 39ea mnpeed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequency do you 2l :or3uioa i0detect if a fire engine whose siren emits at 1550 Hz mou 23or:iiol a0ves at a speed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency i.iivrgy5j vuup .r/8.f a 2000-Hz source is moving toward you at 15 m/s versus you moving towa /i g 58.vv.jpryi.uurrd 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 frequency horn. When ln7 u-y.2 ovmnone is at rest and the other is moving toward the first at 15 m/s the drin-.7ln yvom2uver 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 sogxid m wl:2gbh;qvd9 22l*o:kund waves at 50.0 kHz and receives them returned from an object moving directly away from it at 25 m/s What is the received sound frequenckg2 bw2d*l x:qlim2hov:d9;g y?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As it flies, the bat4mu8 jrko5c 8r emits an ultrasonic sound wave with frequency 30.0 kHz. What frequencyom8rj8 k4rcu 5 does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments8vm2(xmwr 2eql 8kbw,, a tuba was played on a moving flat train car at a frequ2qmb( l x,82mwkev w8rency 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 speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measuri66l*sjyrrf: e blood-flow speeds. Suppose the device emits sound at 3.5 MHz, and the slr 6jri s*6fy:peed 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 usi rvrd2yh9s8ty0o +) o; ( jdv)nnj.uosng ultrasonic 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 e4ptwyo n5:e:. When the wind velocity is 12 m/s from the north, what froneey5 p:t4 w:equency 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 o21, p(k ykic9vdsaz*olx5.hm7y u0w hn land if 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 ist k nq5wx. bobx/xl132 310 m/s (a) What is the anglelkoqn/xx 152b.b x3t w the 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 atmosphp2l57 now/d xsere of a planet where the speed of sound is2ldnxso wp7 /5 only 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} $