What is the evidence that sound en0*;2gw pitkmxqf.peo8 ; f;- si+nntravels as a wave?

What is the evidence that sound is a form of enb2mjbv1d/bz.ik5) z :p2n5c qh xfm:eergy?

Children sometimes play with a homemade “telephone” by f,1pqa5 j)y-cwux1 h rattaching 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 othp1f a y,urh5 1-q)jcwxer 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 f k7x / w rg:gro*9/4iccbpnc.1m6aepl requency or wavelength tp.i 46gc1roln*r9 //:pk cceb7mw gxao change?

What evidence can you give thrq joz-:8kw/ cat the speed of sound in air does not depend significaw8roqc:/kjz- ntly on frequency?

The voice of a person who has inhaled helium sounds very high-pitched.edva23 oco+z 0 Why?

How will the air temperature in a room affect the pitch of organ pipjg-yv /yxd v46tl4 3kges?

Explain how a tube might be used as a filter to reduce the ampw( lkpiwh-0 y-litude of sounds in various fr(0l p-wywh ik-equency ranges. (An example is a car muffler.)

Why are the frets on a m. hu3m y xg,s/.;bvffguitar (Fig. 12–30) spaced closer together as you move up the fingerboard toward t.fgy3v; .s / mfhumb,xhe bridge?

A noisy truck approaches you ;k fyw0i x r e2a0qh3b60(lu/-wlfaes from behind a building. Initially you hear it but cannot see it. When it emerges and you do see it, it2el a (qfaw3l06kbwh/e0 fxu0i- ;syrs 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 wbqj/foifp3;/jxe3 *u lld 8)zvi 20b“interference in space,” whereas beats can be said to be due to “interfere v0 o2x*w iizpff ueq/b;jjl3/3 8d)lbnce in time.” Explain.

In Fig. 12–16, if the frequency of the speakers wer i;npyh tt0dz+9qb,t 1y/eyy3e lowered, would the points D and C (where destructive and constructive interference occur) movy tp+,3 e/;ytdn yibtz109yhq e farther apart or closer together?

Traditional methods of protecting the hearing j )*qfyjj ig1f572iy aof 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 tyqii*g2j fafj 17 yj)5he sound levels reaching the ears?

Consider the two waves shown in Fig. 12–31. Eachktxm 8r1 :)dpi wave can be thought of as a superposition 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 frequenciestk )1:iprxm8d farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and observer move in the same dir813mmrnu c21 3gktspqection, with the same velocityk3mc 2pn1smut1q38 rg? Explain.

If a wind is blowing, willt1 xydfrxvsk0oq* i)25 p0n )cxp tb.3 this alter the frequency of the sound heard by a person at rest with respect to the source? Is the wavelength o)0ki.5 o0xsxfxn2* p1cpyv) qbd 3ttr r velocity changed?

Figure 12–32 shows various positions of a child in motion on a swing. A monim yst (*w6kty6tor is blowing ayktm(6t ys *w6 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? Explain your reasoning.

  A hiker determines the .xxv5bfsr vc)a 6p*5vlength 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 s after shouting. Estimate the laxrvvx5vc .f6)5p b*s ength of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the sidg3g 5sbpe g5*de of his ship just below the waterline. He hears the echo of the sound reflected from the ocean floor directly below b p*5gs35ged g2.5 s later. How 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 wavelmltpg g7: y,0z(y9gf9mu v+k xengths 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 sch1u9hxzw82ej6 ey/r goool of tuna on a foggy day. Without warning, an engine backfire occurs on anothe8e2hu 9/r xe61zowygjr 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 cliff. The splash mlec;e +y, ,rw5 *o1cgz+cacoit makes when striking the water below is heard 3.5e, +a,ow1lc*o5yz;rgecccm + s later. How high is the cliff?    m

  A person, with his ear to the gih2927ke4xv i ps b35clh6smr round, sees a huge stone strike the concrete pavement.5x6mvsiek2 37sp 9r 2l4hbchi 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 occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over/: (qw/8 f(flbzrv8p2fidb mb one mile of distance by the “5-second rule” for estimating the distance from a lightning strike if the temm/ 88qf:fb f(rvp/(b zbd2wilperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the mv afovog)/94 pain 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 sound whose intensity is;:w:hpv -to(dopz8*njh wb e * $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound l4s kzdd) y 9tjq(9 vbt-a)3wuxevel of 95 dB when fired simultaneously at a certain place, what will be the sound level if only one is exploded? [Hint: Add intensities, not dB-y(k tjqwdxu3b4)sta9z )v d9’s.]    dB

  A person standing a certain distance from p 9ofzd;nn55k54pmf khh/ y3p an airplane with four equally noisy jet engines is experiencing a sound level bordering on pain, 1204khpp9np55;/d3 hfyf5 nkm oz 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 s/yg pniqu.hw h0yq)e9f6+/vc aid to have a signal-to-noise ratio of 58 dB, whereas for a CD player it is 95 dB. What is the rati9wev /n/g 6uyy+ .0qhphfci q)o 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 fr d k.j8gjs;th:p fer7/om a person speaking in normal conversation. Use Table 12–2. Assu:j7t /hdke8fgsjr.;pme 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 eho0 tm.j c6/weardrum 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+ qj ln. yvlj924i+czt is rated at 250 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 louds.lq24jij9ln ++ ztyc vpeaker 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 metp6f: 4egm urrobryl z/* od:0:er registered 130 dB when placed 2.8 m in front of a loudspeaker on the stag:rz/ b* 6y:0 lfge4du:po rrmoe.
(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 m 8 75kqxwomkoqog-nuq4*isc 3)1( llsound level of 2.0 dB. What is the ratio of the amplitudes of two sounds whose lekqmw )u i4oql csn5go71xqok- l8m3*(vels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) bisxcyv*0)m n5x i(hf*xxi e b/c q2h6(y what factor will the intensity increase? Incr2qm(cx0)c (h*yx5 ib /fxi*sv xin6 ehease by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplit6p 4u7 m/m)nt6 jysvgtudes, but one has twice the frequency of the other. What is the ratio of their intensities?7vtt 46u/j )g 6mypmns   

  What would be the sound level (in dB) km:wr) t1rg8)wqct t8 bk2cx 0of a sound wave in air that corresponds to a displacement amplituwtx:r 18kg28mrwb0qctc ) kt )de of vibrating air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what s1dndf9y(g3 fas (9 l sxlh6r3oib ;s8hound level to seem as loud as a 100-Hz tone that has a 50-dB sound lev(f9dlf xgosihrdh y3n9b(l; a3s861sel? (See Fig. 12–6.)    dB

What are the lowest ,mv+sjp l:s4 -9 uj 4jwzywgp;and highest frequencies that an ear can detect when the sound level is 30 dB? (See Fig. 12–6.)w:lsm4wgzv4+,y;9pu jp j sj-

  Your auditory system can accommodate a huge range of sound levels. What is thejul;: . 9*h)nq /fhkqokpi)iw ratio of highest to lowest i9fk) ).; i*/k:jphhqnqiowlu ntensity 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 * vriy64wyq;e(y :xzm of 440 Hz. The length of the vibrating portion is 32 cm, and it has ;ve *ixy6 qzwmry4:(y 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)7ckm5xb41w dhf (jqp and first three audible overqkd5f)px (jm bh47wc 1tones 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 blow; f7lgxi cppcs )*uq(8ing across the top of an empty soda bottle that is 18 cm deep, if yous;(c7* lpxu pqc f8i)g 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 rang:x.38 oidewlp e of human hearing (20 Hz to 20 kwo3i8:lx p d.eHz), 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 frequency of 540 Hz aj;nv9/p n0u9q z;5f45svq:eb kqlxcns its third harmonic. What will be its fundamental frequency if it is fingered at a length of only 60% onf5;n94vqxcv z9u:bkp eq l0j q/n5;sf its original length?   Hz

  An unfingered guitar string is 0.73 m long anvw8hr:6wfy- f d is tuned to play E above middle C (330 Hff-r8 6ywhv:wz).
(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 tg1t 1g-d m;sschat emits middle C (262 Hz) when the temperature issd;mggsct1 -1 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 a9vwyudo :e+t /t 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 h: gj/8:z kzwhvole be that must be uncovered to play D above middle C w8:z/kvh:zj gat 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 atrm5)btywy pu+o1)ut* any other frequencip)o tyryt5u)1+b u m*wes in 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 lonu(q* : lninslh2vnq1 ,e5gt, y 7sep5xg is open at both ends. It resonates at two successive harmonics of frequencies 275 Hz and 330 Hz1hxs2eys7n gtnq 5 ieq,:( *u vn5ll,p. 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 (vl;w0sptwl am **8o b$^{\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 audvnh-o)yf(ph . ible range for a 2.14-m-long organ pi.f)h(hvpo-y n pe at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approxim6nm5vh t yimmti ( 9q;x/h oh2(zid1+mately 2.5 cm long. It is open to the outside and is closed at the other end by the eardrum. Estimate q t o mymxihd91z/(2 v6m5(;nihi mt+hthe 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 everewbmx.lqz;) w l-0)wul:* jdsy 2.0 s when trying to adjust two strings, one of whichqlsl.ww)e0l u-m:;d* b)jw xz is sounding 440 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency if middle ao t4cc tvcvqo0q7782; e7he4jjy rs+ 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 6demiv1d q:.vx x*yk+:gm h)tkHz, 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 fqd e:y+1*:ivg 6x k.tm)mxvh drequency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded withqp9:sm vo(t ;o a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of the string? Explai o 9m:o(pqv;tsn your reasoning.    Hz

  Two violin strings are tuned to turfjnv 2k;f p6ecb0ma:6l1,(x .k fpohe same frequency, 294 Hz. The tension in one string is then2e0po;u6fr( fk.k vx6:a 1pf, ljnbcm 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 hearln u (wqp3xd,7d if two identical flutes each try to play middle C (262 Hz), but one is at 5.0°C and the q ,lpdwn7 ux3(other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a frequency of 441 Hatqa mw 5,(9gwz; 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 sounded to m(awwtaq,5g 9gether?$f_A$ =    Hz or    Hz
$f_C$ =    Hz or    Hz
|$f_A$-$f_C$|    Hz or    Hz

  Two loudspeakers are 1.80 m apart. A pert47jzp i .,qw.uuul3qson stands 3.00 m from one speaker and 3.50 m f.4upu uj 7iqtl3wq z,.rom 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 :vmcr+a: adr 3kv1)f1zu m9esvibrating at 132 Hz, but a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibrating acvd re:mas)mk1a+u f1:vrz 93 t 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 be9-p3lhbhr ,reats per second will be heard? (Abp3e r-9hrh,lssume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s siren is 1550 Hz wld*sm6qm fq y/v5(* szhen at rest. What freq/*6lq msvd f(m q5y*szuency 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 fire engine wh 8gj)a)3 r:rt (gxlolmose siren emiar: )lj)(xlgrom 83gtts at 1550 Hz moves at a speed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz source is movi6tei::qu k;+id2+l tvjpj,l jng toward you at 15 m/s versus you mo j2tld q6klu j+:i;+tp,i:jveving 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 freq7p p gzwk++rs+i+0rhm:kx3g f uency horn. When one is at rest and the other is moving tzxp g+h+7sf+ gkpirr :m3w+ 0koward the first at 15 m/s 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 receives e) shi2b-yhkd6 v dp6:qx 4;muthem returned from an object moving directly away from it at 25 m/s What is t y pqbm)hd:x; u2i -e4dshv6k6he received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at ja/vyj/)p9 sqxihoem)0tq,9a speed of 5 m/s As it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency does the bat hear in the rhjm/ov/as)p9)eq90j, tyi xq eflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was played on a moving fkmf9,/ crrwolsb 7w:( lat tra ww,k(rm7l bc:9f/r osin 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 speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasmjwqy.k q4 z8(ound waves to measure blood-flow speeds. Suppose the device emits sound at 3.5 MHz, and the speed of sound in h(z k4m qyjq8.wuman 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 frequency 1de*v4 9(k uz 0wp-kdlcvfd2 lheaa24:tkgn / $2.25 \times10^{ 6}$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 freo3kdqi cw+1 si6;iz3aiea+ c:quency 570 Hz. When the wind velocity is 12 m/s from tzaic; 3 i: o1eaii+d+ ck3sw6qhe north, what frequency 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 lan9 rnv swiz0o0sf3 xsraj0 c07k*n.n/jd 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 ish,axhvlrg;d0(g/l 2 b 310 m/s (a) What is the angle thex0a ghlh rb lv;dg(/2, 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 atmosphere of a planet where the speed of so5 lq.s t8ybz;bund is on8s5qyblbt ;.zly 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} $