What is the evidence that sound travels as a wnd clmt99wbu (cyl amv z9lscj; 1):2;ave?

What is the evidence that sound i -wn5msk eb (6(bgh,mos a form of energy?

Children sometimes play with ; 2pfq+qvlnay 0cmj) :a homemade “telephone” 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 qjm)y f+ l0c;pvna 2:qother cup (Fig. 12–29). Explain clearly how the sound wave travels from one cup to the other.

When a sound wave passes from aij/:zddakm:v -r into water, do you expect the frequency or wavelevd:ad mz:/k-j ngth to change?

What evidence can you give that the speed of soundzn c i9s4vma27 in air does not depend significantly on frequencyc9mz4 sva72ni?

The voice of a person who has inhaled helium sounds *t2yriy:s p;olb9psu n-i w40tp-x/x very high-pitched. Why?

How will the air temperature in a room affect the pitdz+: g/u w7ec)ldx-toch of organ pipes?

Explain how a tube might be used as a f 71elvkz:)qgk- 3x1 e1eys wblilter to reduce the amplitude of sounds in wb1yv gl7k) 1e:qeskx 13l-ez various frequency ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer tog(+ upjtoj4g;6s8-rlilz9j uxu*8 tr oether as you move up the fingerboard toward the bridr9zutu oi8x6l -(j4utl8o r*sj ;+jpgge?

A noisy truck approaches you from bf 7g3gusv il,o7fbt 9;ehind a building. Initially you hear it but cannot see it. When it emerges and you do lffbgu7v37i9 t;g,so 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 8wln7ci. h1hu be due to “interference in space,” whereas beats can be said to be due to “interference in time.” E87. i hchnwl1uxplain.

In Fig. 12–16, if the h;hkz+7 lp j1dfrequency of the speakers were lowered, would the points D and C (where destructive+hjph7; 1dz lk and constructive interference occur) move farther apart or closer together?

Traditional methods of protecting toas1ijg6c9 40x xs4wche hearing of people who work in areas with very high noise levels have consisted mainly of efforts to block or reduce noij4x09w s i4soac1 cx6gse 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 levels reaching the ears?

Consider the two waves smcv0gx(6kp dd 4d(by: hown in Fig. 12–31. Each wave can be thought of as a superposition of two sound waves with slig0 y kdg6dpc(b(xm:v4dhtly 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 direct+e xcwi q;q z73i-sv,v+.u kusion, w7xvsz- uke+.i,+qiw3;s cqu vith the same velocity? Explain.

If a wind is blowing, will this alter the frequency of the sound hm0wypew s3 p2irqop4+2)m: ejeard by a person at rest with respect to the source? Is the2 pryqw :)p2ejo0wesm p +3im4 wavelength or velocity changed?

Figure 12–32 shows various positions of a child in motion on a swing. A monitor1 fo+pcf;1s41cwvppd is blowing a wh ow;1pvc1pdf4+fpcs 1 istle 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 your reasoning.

  A hiker determines the length o r8tf ;;ka3frwf 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 s afrr f;wt;f3 a8kter shouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below the watepd86x;2ckwhbb o h4.rrline. 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 sound in seawater is 1560 m/s hk ro4 b2bw6xd8c;hp. (Table 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wa0a/qasb5 n+ ipvelengths 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 schoe 3hh0g20 hxwpol of 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 before the backfire is heard (a) by x0hep 2hwh3g0the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a cliff. The splash it makes when strikingh8o e4vy*/jmy the water below is heard 3.5 s latereo*my v /yj8h4. How high is the cliff?    m

  A person, with his ear to the ground, sees a 9jaenl,6+t:zi,ze6*ks v war 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. How far away did the impact o er+sjev*9lakzz6, :n 6taw, iccur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one mile of distance by the “5-second rt3f n0l7ggoc ,bby 5w+ule” for estimating the distance from a lightning strike if thewcony0 l,+g73f bbtg 5 temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the paop3w* es b8o-onb4kb1in level of 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 soun 4ei gwi2aurwop+m70 ujd4 9u7rlf89nd whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired simunk,(ypt cs 8 4-naogr9tcm8 r2ltaneously at a certain place, what will be the sound level io8s t, yrn(a mnc482k9trgc-pf only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an kl 9;b(lw gbnj38p gr3airplane with four equally noisy jet engines is experiencing a sound level bordewgk; nb9(l plrjbg833ring on pain, 120 dB. What sound level would this person experience if the captain shut down all but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to have r- wcq1rghv hl1r(,wnlte( : 1 h2x*ara signal-to-noise ratio of 58 dB, whereas for a CD p, 1:ql*1r1agvwchre2nh -lh (r(rt xwlayer it is 95 dB. What 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 sound from a person speaking in normal conve1odt(*m, 2dk rkt-yagt( , zw ku+lt3jrsation. Use Table 12–2. Assume the sound spreads roughly uniformly ovettt(,d duyz(1lw-j k+atg2 *o ,kkr3mr 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 anbf35; cb4fedj0oqn 6qbna/ p8 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 amplifier B 9 0xeex b,wki3is rated at 40 W. (a) Estimate the sound lev ib0x3xew ek9,el 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(ggkg w3d vc31 130 dB when placed 2.8 m in front of a loudspeaker on the sta3vgk3gg1(w c dge.
(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 lem) nb :-a2 w3t);xxlktfgku 4nvel of 2.0 dB. What is the ratio o) mb :fn3nwt4g kxka utlx-)2;f the amplitudes of two sounds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a soundjkuet h. 5 5d(mk27zlm wave is tripled, (a) by what factor will the intensity mk2lk5d ht7j 5umz .(eincrease? Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displace61l 83opce4i bnfk-mz36mi q wment amplitudes, but one has twice the frequency of 4 pbi8ce6m klzf- 6q3om1 3iwnthe other. What is the ratio of their intensities?   

  What would be the sound level (in dB) ju0lqp j*;ymre k0u4t,r+uc3 of a sound wave in air that corresponds to a displacement amplitlj4e,3 y*rqjcu+u0ru; p t0mkude of vibrating air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have wh vg a8;7quel 0g6gb;hsat sound level to seem as loud as a 100-Hz tone that has a 50-dB sound levsve ;g b;ul78gh gqa60el? (See Fig. 12–6.)    dB

What are the lowest and highj 1e.ws71 sh,erd+m4yvx +auoest frequencies that an ear can detect when the sound level is 30 +1.xse erya mdvj4,u soh1 w7+dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of sound levenib; giuq tc(1w3 w5;lls. What is the ratio of highest to lowest intensity at 13gliw;5(q ucb t;iw n
(a) 100 Hz,$ \times10^{ a }$ a =   
(b) 5000 Hz? $ \times10^{ a }$ a =   
(See Fig. 12–6.)

  The A string on a violin has a fundamentnw1,ld :i +v4kx4p chzal frequency of 440 Hz. The length of the vibrating portion is 32 cm, and it has a masscx4,l1w kd phiz4:nv+ of 0.35 g. Under what tension must the string be placed?    N

  An organ pipe is 112 a7di o3bqxz 9jquvp72/;p)tlcm long. What are the fundamental and first three audible overtones if the pipe is 9zb/p;qi7adp2ql xot3 j)7v u
(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 blo5lvr m) rlk9 .hg+tps/wing across the top of an empty soda bottle that is 18 cm deepv5m./tklh 9gs )r rl+p, 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 the range of h1g(m c w(uxnv2uman hearing (20 Hz to 20 kHz), what would be the rang 2vmwxungc1(( e of the lengths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a freques 0mll2)nbxp9cm i)1 vncy of 540 Hz as its third harmonic. What will be its fundamental frequency if it is fingered at v)p1) sn9mlc2lim bx0 a length of only 60% of its original length?   Hz

  An unfingered guitar stsj l.1 d7,wxx1q c5uisring is 0.73 m long and is tuned to play E above middle C (330 Hzdq7jsi 11 ul5s,.wxcx).
(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 2/i.b*os skhhtm3qmb1 tt-;o2 Hz) when the teoto st s mh-/kb3*i12h;b.mqtmperature 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 20 0a nv)6 zwcce(hk :-bi$^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouvs 13 8j u9xin.zp trnipgi4;0thpiece of the flute in Example 12–10 should the hole be thanjin3gz1rit. p p48v9s;xu i0t must 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 resonate at 4( mno v:ne uui+t8:dg264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in g4n:n(oe u: miv8 udt+between. (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. It rudynn (8v8rodb-mz;: esonates at two successive harmondmn(o 8y:zrv8;b -udnics of frequencies 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 vjmnd0 */nx9 u 1e :n86rryydx$^{\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 ran8kn;zm3hde t/ge for a 2.14-m-long organ pipe at3zk/tedh8m; n 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm long. Iv7 i4p +feq hb/g+ftj 6z,,2b5y pczewt is open to the outside and is closed at the other end by the eardrum. Estimate the frequencies (in the2t, 7e h54wbebpqzv/ i++6,ffjg z pyc 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 beatb9*uhk 7.g,n2j t71g h )awjnsd, kxlw every 2.0 s when trying to adjust two strings, one of which is sounding 440 Hz. How far ofsb 7ha n1n j.w* g9w72 t,)x,gjukhldkf in frequency is the other string? ±    Hz

  What is the beat frequency ikhhmg4l49wh8pb) ic hh7fh 7+f 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 f-qvp4ho5 v/x operates at 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 ov4of -q vp/h5xccurs when they are played simultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces ;xu2 yw+v6v tj4 beats/s when sounded with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is twjv ;u 6yt+vx2he vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz. The tens,0n6(kk-btc uw3 u8*izk ocenion in one st-u k w0 n*(un,kz6ict3okcb8ering is 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 z 1zjea 8;jtt)(f4o pnto play middle C (262 Hz), but one is at 5.0°C and the other at 25.0 tea48n pz o z(;t)jjf1$^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, cozpfvh 3:5y5 3d g*zdand 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 aregyo*p3zdfv3:z 5c d5h 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 m from one speaker anz6 */nhralz*pd 3.50 m from the*hr*/za6pzl n 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, bu f:- 5xz7nq ugyf 0zu+a)m1duo3hn sb7t a piano tuner hears three beats every 2.0 s whqfu0zxaf-d 15n7s)3+gzh myn obu7 u:en 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 y)uc+a )fahm: of wavelengths 2.64 m and 2.76 m in air. How many beats per second will be heard? (Assume T = + ucamh:a))y f20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s siren is 1550 zdtgfkfxt d9qa0 3mb ,6m7 -k9Hz when at rest. What frequency do you dete kt7x-fz,mdg9ta 3q96k0fb mdct 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 frequetudsw8 xmunz4 :* qf95ncy do you detect if a fire engine whose siren emits at 1550 Hz moves at a speed o* qunws t4x z:f89um5df 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 tolvm)p:/t /db+y m:ao -3/cmadezo1u u ward you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencieomae3 bd/+:ul1py/ m-)c/ : vzou tdams 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 one is *5v8f:qhe uxykd j3 (wat rest and the other is moving toward the first at 15 m/s the driver :uv 3 d(khxf*85w yqjeat 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)mxa4gxdv7 - vlki3/j9k 8zc d kHz and receives them returned from an object moving directly away from it at 25 m/s What is the receivedm /gckxa)ijz4-97d vk3ld vx8 sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As it fliehd(k-5)hq jq cs, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency does the bat hear in the reflected wakq5)c-dj(q hh ve?    $ \times10^{4}$ Hz

  In one of the original Doppler e(f 14kf wjhkx;g/ ph5kxperiments, 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 bef ;xk5jk(4fk/ hpg1hwat frequency was heard if the train car approached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter fuvd*i *wnle ,7st8;d uses ultrasound 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 large leg arteries at 2 cm/s directlts*d nuwe;d 7ilv, *8fy away from the sound source?   Hz

  The Doppler effect using ultrasonic wave1 m,o;qo6obtg-i2snks 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:9vq,nej i, (eul ,gib velocity is 12 m/s from the north, what frequenc:qnieveil(,jg9 bu, ,y 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 speed at 209tpkqm2y* wgtj +-+rk $^{\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 y swv vq)i3q59Mach 2.3 where the speed of sound is 310 m/s (a) What is the angle the shock wave makes wit9v)3yq5qi ws vh 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 plkxq3o- 7j pi5-f0w6j ,eugei)prk vf 6anet where the speed of sound is only about 35 e, gi orj)j kk0ip-xf76e-wpv q56fu 3m/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} $