What is the evidence*gj:s gfok( -5r9nl4ifo qn1u that sound travels as a wave?

What is the evidence that sound is a form vr(ro pn - w3y9ypbb5 d)uv4s,of energy?

Children sometimes play with a homemade “teled3e- tr*y1p/w8 h9nvihlz; et phone” 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 dvw 98i3et yzh* r-h ;nl1/epthow the sound wave travels from one cup to the other.

When a sound wave passescawsum(4lk() from air into water, do you expect the frequency or wavelength toku (4 (m)cslwa change?

What evidence can you give that the speed of sound in air does not depenm :;.,2:yfxo fjagxxwd significax :;f w,x:f mojya2.gxntly on frequency?

The voice of a person who has inhaled helium sounds very high-pitch8pon cfpkv48 w9 b v8l1v;l;f ho)osq:ed. Why?

How will the air temperature in au h4h(wa84o qg.ghfb5 room affect the pitch of organ pipes?

Explain how a tube might be used as a filter to reduce the ak(v esi) bkz +g; u;bnqw8)/jymplitude of sounds in various frequency ranges. (An examp n)b izk;/(gk +b j)euvwyq;8sle is a car muffler.)

Why are the frets on a guitae)g 1nu9q *4mdys:0gexnz wx 4r (Fig. 12–30) spaced closer together as you move up the4zu 0 *1egmxqgn9)ds wn:e4 yx fingerboard toward the bridge?

A noisy truck approaches you from behind a bpkwv91l0 f1f:nr lk.building. Initially you hear it but cannot see it. When it emerges and you do see it, itv f :9 wb1.nkfrk10plls 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 “interference in space,” w*v(qms,0edm t+/mi68fg mq f0jw9d nnhereas beats can be said to b*tv ,i0dq0f/+6m emnjgd98s( qmnmf we due to “interference in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered, would thv+xt4-xn 1 sfo +iu0wre points D and C (where destructive and constructive interference occur) move farther apart or cr4-ivx+otwsx1fn + u0loser together?

Traditional methods of protecting the hearinc;2+bpd0w- bwugy 8wq 1jbk:tg 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 dwbuw:jc21k0+b8 -wtgpb dyq ; etects 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 shown in Fig. 12–31. Each wave can b yqbspkc.4 cbsa- ;c6*e 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 frequencies farther apart? Exp kpscysc .6 -qb4bc;a*lain.
(12-31)
(12-18)

Is there a Doppler shift if the source anu hp 8ki,f6z-2f wej(jd observer move in the same direction, with the same veloci6w jz( uji2-,hfk8pef ty? Explain.

If a wind is blowing, will this alter the frequency of the sound he8x+eh4t1;nwj zuqa il/k :u0ru 7pug-ard by a person at rest l7 ire:+0j;g1 /- tzu4u wnqua h8xkpuwith respect to the source? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a child in motion on a swing. A monitov2 523a/zslb irukdjbea55-or is blowing a whistle in front of the child on the ground. At whbvu3aaj5l ik52e52b/-r oszdich 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 of a lake by listening for the echo of m.(3* hyh6p0ty,bldpxw)kovher shout reflected by a cliff at the far end of the lake. She hears the echo 2.0 s after shouting. Estimate the length of the6tk,v yb hd.3(womx*py)hp0l lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of hq4+uac yhksg6hg;7t +is ship just below the waterline. He hears the echo of the sound reflected from the ocean 7;aug+ tg+hchs 6k4qy 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 (Table 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelev8w *0op4 wp dzq5mtt.ngths 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 onqjcevv ,yjkil/ 981q, 1xm 9by a foggy day. Without warning, an engine backfire liv11q kj/ym 9xj y8v qbc9,,eoccurs 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 cliff. The splash it makes when str.qbnp 7yc54hxn qjol +2us6t 5iking the water below is heard 3.5 s ltn 5j6px 7 os2bh.nlu5cqyq +4ater. How high is the cliff?    m

  A person, with his ear to the gyt,vpzh z/y0ui+ i-v;round, sees a 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,u;-vz+ hp / yt0yiivz 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 milee4ndlv 3lgnj6uecc3w d9/- .+oivs,r of distance by the “5-second rule” for estimating the distance from a lw/jsve,3nulridn .+ gvc3 e 9o-4dcl6 ightning strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensityo)m0;zs lb67cm8e*nzpr q na)n-s j u0 of a sound at the 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 zj:vihpt:7r8 p/f ;yy a sound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level i7b2iv17;f 9 iowynlb of 95 dB when fired simultaneously at a certain place, what will be the sound level if only one is exploded? [Hint: Add intev 1n9if7i;b72yi owbl nsities, not dB’s.]    dB

  A person standing a certain distance from an airplane -*u us2;k1 wsnl3j bvmpq -0tpwith 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 down all but one engine? [Hint: Add qunpsus-pmtjl3 wb01 v*2;k- intensities, not dB’s.]    dB

  A cassette player is said to havbhu*j6t1+/ c)w1 (jhlcqhvu ee a signal-to-noise ratio of 58 dB, whereas for a CD player it is 95 dB. What is the ratio of inte /*6qthcbuj ce1(hv+hu )wj1lnsities of the signal and the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the powiy/ufz wg-z1-c8 e,o qer output of sound from a person speaking in normal conversation. Use Table 12–2. Assume t 1-wizu- 8o,cyeq /zfghe 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 st r*1/ 7 fph1o2lrwirxarikes 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 250 W, 8 q-toz(dc;ml/ du -gawhile the more modest amplifier B is rated at 40 W. (a) E/c8oa ;d g(-dz-lmuqtstimate the sound level 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 1 r7d.kfo ixs5h7w:xy8 wh3wat9 s;3sn30 dB when placed 2.8 m in front of a loudspeakery75sh3;dws3o x w.: x8taw7inrf k 9sh 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 typicallx9yyqg36ox nci::f z- y detect a difference in sound level of 2.0 dB. What is the ratio of the amplitudes of two sounds whose level xg9oyi3-6xf : cqy:zns differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) r:ua3hk k.iezk 8s ki3)tuewfq(+/+ cby what factor will the intensity increase? Increwu/cihk:kkf(ar 3e8eks+ z+tiq 3 u. )ase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displak.zez ll;t) 5+jr zo)lcu4a,qcement amplitudes, but one has twice the frequet;ejl4,)r.+5c zzlqzk a o)l uncy of the other. What is the ratio of their intensities?   

  What would be the sound level (in dB) of a sound waveff ;s3mb efna:39v bj( in air that corresponds to a displacement amplitude of vibrating air molecules of 0.13 mm a:n3b a 9( sf3e;mbfvjft 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud as a 100-Hz to+ 28 ecn/op:qu(g qibkne that has a 50-dB sound l n (8 ucoqe+b2gki/q:pevel? (See Fig. 12–6.)    dB

What are the lowest and highest frequencies-i,yi1-k g rgw that an ear can detect when the sound lei1 kir--,y wggvel is 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of soisr6u t9px0yyr, /yu/ und levels. What is the ratyp/u0r iy 69x,uyst/ rio of highest to lowest 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 440 Hz. The length of th-:eyzaed x((*)de2w a hmqh b34wxq p5e vibrating portion is 32 cm, and it has a mass of 0.35 g. Under what tension must the(d*2w(ax3 4max-eyqbqe) wdhe z p h:5 string be placed?    N

  An organ pipe is 112 cm long. Wha(z). luspm xyqmbc-/*t are the fundamental and first three audible overtones if the pipe is *ms(x .-m)bcplz/yq 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 blowing acrossz.t xo3jo(1oj51zj l-yy :vkm the top of an empty soda bottle that y-zk1lj:otv jojx zy m 5(3o1.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 pipb(j4;o7i86ivt ohe s2mem,yy e organ with open-tube pipes spanning the range of human hearing (20 Hz to 20 kHz), what would be the i;t,sy64ee y o mjimho2v87b( 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 as ilrl,3ayl3wp8((2 p m j qndrv9ts third harmonic. What will be its fundamental frequency if it is fingered at a length of only 60% of its original le(l v ,8ydq9p3mjaw(2 prnlrl 3ngth?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to play +eomm+mmd/, v E above middle C (33/omd m+,mvem+0 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 len(7thtpl+a1 geu dk z/5gth of an open organ pipe that emits middle C (262 Hz) when the temperature is 2/zea(+ 1 57tpukdtghl1 $^{\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 2xkvad(gc /8)d 0 $^{\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 shoulde pwr ;8ud4c(h the hole be that must be uncovered to play (84hruw cpe;dD 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 264 l/hg 5b.mq9c+8 xhz ogHz, 440 Hz, and 616 Hz, but not at a xq l895 ghch+.zmgo/bny other frequencies 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 long is open at both ends. Itis1- zq f j;hkmn/n:-f resonates at two successive harmonics of frequencies 275 Hz and 330 Hz. W snjinz qm:f/fk h1--;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 nx:y z(513b)ap pvxwu$^{\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 range for a 2.14-m-long orga-emet+umt p)m 3 e,iz:n pipe at 20 u+:z ime3p,)m-mtete $^{\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 outow80 7 aez+aps bl4o9aside and is closed at the other end by the eardrum. Estimate the frequencies (in the audible range) of the standing waves in za+7 l49we osb0p aoa8the 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 p +(vnx7oxlt ly:lu8: 2.0 s when trying to adjust two strings, one of which is sounding 440 Hz. Howpx7: :+y8oxnl vllt(u far off in frequency is the other string? ±    Hz

  What is the beat frequency rpjlw:*a2yf3 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, while anot uz+bo g+*am,wei, d+ov-so;jher (brand X) operates at an unknown frequency. If neither whistle can be heard by humans when played separatelywe+zis+-o jo , +*m v,dabuog;, but a shrill whine of frequency 5000 Hz occurs when they are played simultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/s v +6p* rgdp k:tn)9v/yrkzixt27c 4cr 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 ofpx26t+7vgkdvzrn)ci* /4k r rpy: 9ct the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz. The tension in on6hf;gy1-*tm t q,ebak e string gk t*et;fmy-qa 61,hbis 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 flute;dq 2s h1,xc/lwotyf-dv 5 (lts each try to play middle C (262 Hz), but one is at 5.0°C and the otwdh-ql1/x5 c ;vtf(,dyts l2oher at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B fr zhcy))bah8b e4q/6has a frequency of 441 Hz; when A and B8hy)zh qb6rf 4e/ ac)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 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 fr wkt ji xv+gc1w:.f.we k,2eb)om one speaker and 3.50 m from the owk,):c b.k.2eivjgew 1 xwtf+ ther.
(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 vibra*dkfuyy;ur5cq5 yd 1sl: 2mh +ting at 132 Hz, but a piano tuner hears 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 u r f:ymcy+u*kd;5l1qsd25yhother ?   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 )7p nogp9i4t oof wavelengths 2.64 m and 2.76 m in air. How many beats per second will be heard? (Assume T 9g itn7)p4o op= 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequencywq3xf/ zcfc:a o3b(n +2zp0yh;/ged o of a certain fire engine’s siren is 1550 Hz when at rest. What frequency do you detect if you move with a speed ofo(:cbz3wcf/dha o; 3xepf 2z+0qn /y g 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 whose sirn*+ k zbm)w/st72ox)w,pdnggen emits at 15+/wnkd o g)p2 )bz,gmnwxt*7s 50 Hz moves at a speed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequencyx.i6hfskn5t+ i.2r xh if a 2000-Hz source is moving toward you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exr5hk26ti.xi+ nxsh. factly 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 tft/0vk6 u;j ,cg wdw,qhe same single frequency 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 ,t gkq fv ,cuj0;dw/6wof 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 50.0eg77 3uwi;lsj sr-af0 kHz and receives them returned from an ojs7fw 7esi;r-g 0lau3bject moving directly away from it at 25 m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As it flies, the ba br/jtiwk ou)3.:su (tt emits an ultrasonic sound wave with frequency 30.0 kHz. Wha j/itw ku):3u.s(r tbot frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was played oo v6rk78 ohp3dn a moving flat train car at a frequency of 75 Hz, and a second identical t hd6o3rk o7vp8uba 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 toluymm y;g2h o5221pvi :; owrb 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 vy12 ;yr m5gu oh:obi 2w2lp;mexpected beat frequency if blood is flowing in large leg arteries at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect usingzm4rdzwun z6w7 e6b j5- ,i2hj 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 5 lxnnpk1 +cjxthr*e d 4m;(7+k70 Hz. When the wind velocity is 12 mlkx+1( nj dtex+;n*mk4r pc7h/s from the 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 lb *j1a+ rcv)fpo8o qw(and 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 is 310 m/s (a m63qn izpqe-;ll za(;) What is the angle the shock wave makes with the direc3zai-qmnp6lqzl e;;(tion 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 hp ejfz)i.et( m94,cuplanet where the speed of sound is only aboefeimu, tc z) (ph9.4jut 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} $