What is the evidence that sound travels as a wa 3vow4d0e3 qcihhj(ac9gs( 3 sve?

What is the evidence that sound is a form of energy* h/ef1 2mo*lxtew(vl?

Children sometimes play with a homemade “telephmc6g:ozr n-p gz6 -e,yone” 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 one cup to the other. ,-r pc-zgny 6ge:moz6

When a sound wave passes from air into water, do you expect the )xn4 z-seig d7(kj e(tfrequency or wavelengtetks-(e7n g4x j)(dzih to change?

What evidence can you give t hq+.w7h 4.gck2qjpy czuz,x: hat the speed of sound in air does not depend significantly o+q c:.,czqh xg2 7 puzkyw4jh.n frequency?

The voice of a person who has inhaled helium sou.x(n biqf2s6c nds very high-pitched. Why?

How will the air temperature in a room affect the pitcho.mcpvd4re+ricj0wc*)xp3 8) whz 5z of organ pipes?

Explain how a tube might be used as a filter to reduce the amplit5(m x/tqo xlmbb 6s+5/mwvqc8ude of sounds in various frequency ranges. (An example is a 8 m+ o5xbqtwv/m6 blq(cm /sx5car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer togethmq975x j hnjt mztk35hk.*sz 4er as you move up the fingerboard toward the bridge? x 5t9 kjt.zz 5s*jmnh3h7kqm4

A noisy truck approaches you from behind a building. Initial b:3s7q040 rdxmjxnbfly you hear it but cannot see it. When it emerges and you do see it, its 3r bxn:q jm0sf7x4db0sound 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 “interf3a)*/mtiyb/ ctpsd9(wp / c dference in space,” whereas beats can be said to be due to “interferf/t( /t/isa cc*wy m 3bdd9p)pence in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered, w:wmdyxj4bnd1 rg8qny1i-* 5n ould the points D and C (where destructive and co w-* 4n nyxydb1dg5r 1qj:n8minstructive interference occur) move farther apart or closer together?

Traditional methods of prot4n bv-g h53inv30l+w7fys nsjecting the 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 thnf4ly+30 sw3nsi7-j gnv5vbhe 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 shown in Fig. 12–31. Each wave s *a(qy 09+weew0i toican 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 frw*a0et+ (0ws 9oqieyiequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and observer move in thed;qy1se z, kkh0ccat l f+y4() same direction, with the same veloc,l(ezc)ycakkd ; f yqt41 +sh0ity? Explain.

If a wind is blowing, will this alter the frequency of the sount .enzx tqtej-5vpc:*a01 o)nd heard by a person at rest with respect to the source? Is the wavelength or velocity cx-): t na *pnee1 otq.05tvjzchanged?

Figure 12–32 shows various positions of a child in motion on a swinb 4sxzi+1lxr5wk c- 3og. 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 5sixo4 -bwlrz+xc3k1 the whistle? Explain your reasoning.

  A hiker determines the length of a lake by listening for the echo of hfvd ej)5;w wvs+,hoh i465slqwaw04 qer shout reflected by a cliff at the far end of the lake. She hears the echo 2.0 s after shouting. Est 5qf s 0lvwiq4d,jww;o5 4+ehw6 vsha)imate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below t a8f p5,tj +ooo2xm-wqhe waterline. He hears the echo of the sound re fq+wjox pa85o t-o,m2flected 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 (Table 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in air at 2 gtzuz1-tq)b kwsw:b:1 ok2e80 $^{\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 n lp3+)yz pfg1 +a*qgeis drifting just above a school of tuna on a foggy day. Without warning, an engine backfire q+p3ea1*+ny)zlgf gp 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 cliff. The splash it make(sxv zste-5 1yte,pw6s when striking the water below is heard 3w6e,y z x -vttp5s1s(e.5 s later. How high is the cliff?    m

  A person, with his ear to the ground, sees axyoe /tjrf4c- 20r dl. 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 a tj.x-oy2f /l40e rrcdway 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-ck.j.fhk*2 q cu7yge6second rule” for estimating the distance from a lightning sfyckce6hk2 ..j qg7* utrike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pain ad531pru w*l9 53 zjeyjgioq 6level 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 leve.d 5tghcjh :4nl of a sound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers proxm20qm ;ca b*oduce a sound level of 95 dB when fired simultaneously at a certain place, what will be the sound level if only one is exploded? [Hint: Add qxc;20ma*b omintensities, not dB’s.]    dB

  A person standing a certain distance from an airplane with ff .j-ba:yafez7z 3p:kour equally noisy jet engines is experiencing a sound level bordering on pajz:7k:z-y e3.a fbfpain, 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 a signal-to-noise rattb*onm+elt52 q1 s6unio of 58 dB, whereas for a CD player it is 95 dB. What is the ratio of intensities of the signal and the background noise for each devosunt nlb6 5+me1q2*tice? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from a person speaak 8l/cb.8 xs8o k)n 5ief0me .ndkqk8king in normal conversation. Use Table 12–2qbs knike8n.a/f) x8ko5d .8 mc0kel8. Assume 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 strikes20q +b rkog ed*5nrj.a 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, while the moozkrch 9/m+hb+ kv98 yre 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 loudspeaker con8b hk/mh+zk9+ vc 9roynected 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-a /g:j l *fk0lsk t6l,zait-g dB when placed 2.8 m in front of a loud kl -,flz gats:60-ga*jk/ tlispeaker 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 typically detecn+ahm 0f+d 5q0fp l8iyr; fmep/:u4vzt a difference in sound level of 2.0 dB. What is the ratio of the amplitudes of two sounds whose levels differ by this amount? [Hint: See Section 11–9584 0imn e;r0 pa lfmfdzpyu+ q+fv:/h.]$\approx$   

  If the amplitude of a sound28) slag7odna kka .vl 2/dck9 wave is tripled, (a) by what factor will the intensity inc8.nd 9d7o2 2 lclka/kaksavg)rease? Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but one has twice ta nos84k tn1.bhe frequency of the other. What is the r k tan14osn.b8atio of their intensities?   

  What would be the souu5/ebuxrin s:ol-: 1zo l/wzf v*d(1ond level (in dB) of a sound wave in air that corresponds to a displacem * vndio/b 1z ulxzfou/ow:r 1se5-:(lent amplitude of vibrating air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have whbkdi:p5x:o am urj.5i)py96 vat sound level to seem as loud as a 100-Hz tone that has a 50-dB sound level? (See Fig. 12–6x:5a 9bkydo6rpu jp.v im)5i:.)    dB

What are the lowest and highest frequencies that an ear can dete tai i*(gf bjuybir)(8 ;;./yiyunos0ct when the sound u/fit ni.* 0yyuy i(sr;(i;aogbbj)8 level is 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of sound levels. What )o+uuursclcwl j9qpf8 +184j is the ratio of highest top f+uluul89j8rc oq1c4w )+sj 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. Tpy6o;y. v j)dm)ubh- mhe length of the vibrap. 6d yhm );)ojvymbu-ting portion is 32 cm, and it has a mass of 0.35 g. Under what tension must the string be placed?    N

  An organ pipe is 112 cm long: w qsiis.;y pph+kx39. What are the fundamental and first three audible overtones if the pipei hwsp:q y ipk9x+.s3; 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 frequenc, 0 ty+1trud-z3eblwf y would you expect from blowing across the top of an empty soda bottle that is 18 cm deep, if you assumed it was a closed tbl+u zwdr-y1te f03, 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 0t8ogryso 30wa am;/(t ccw;/1rvcmp pipes spanning the range of human hearing (20 Hz to 20 kHz), what would be the range of the lengths of pipeop 3;80 mv/;c/rwwacs cg(ry tam0t 1os required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a frequency of 540 Hz as its third harmonihyb2hw) o2-s +yr8zlk c. What will be its fundamental frequency if it is fi)2w2yb+r-lkysh 8zh ongered at a length of only 60% of its original length?   Hz

  An unfingered guitar 95 ukzq s :.1he1/aqxj cdotx7string is 0.73 m long and is tuned to play E above middle C (330 H:j1t9u/ h zqqxx.ksc75a deo1 z).
(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 emithu , oytlc5.y+s middle C (262 Hz) when the temperalh5o.,cy tuy +ture 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 fun,if 5t y;(m$^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flute in Exaoecdj ;,fwam*0 nba,gi5i b8 1mple 12–10 should the hole be that must be uncovered to play D above midd1,0em ;g*jw ,bcni iab 8d5ofale 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 resonated a+f*txw.81.xhf lko at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (a) Show why this is an open or a closed+t.lhdok1f8* .x fx wa 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 bo c4kdk.m(v d6 s83uitkth ends. It resonates at two successive harmonics of frequencies 275 Hz andks uk4m i(c td86kd3v. 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 4cjj93 +m8 v6z7macl5vvgs av4 8 ap(8z ztuhj$^{\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 j9x lki0-z/t lrange for a 2.14-m-long organ pipe a/j 0 xt-lzikl9t 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm lhb hrx*c:)31 w .ilox kkbyz0,ong. It is open to the outside and is closed 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 y*0): hio b,zcywklrh.1xkb3x our 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.x;cjzz)-5r gol)od 5gi k5gzc x u6;gs:tpg / s when trying to adjust two strings, one of which is sounding 440 Hz. How far off in frequency is the 5rc5xto):gsg ;upzg;g6 5/idj -xzog.)kc zl other string? ±    Hz

  What is the beat frequency if middle C (262 Hz)vbgna1wa+ iqj5 . ,uh( 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 another (brand X)eh( *ln5+lodc(8c sjw(du:pcfr1)ol operates at an unkno jcocporcw* fse l:1+)ll5hdd8(nu ((wn 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 frequency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded with a 350-Hz tuning fork r )xwv*t9uke4 and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of the string? 9e4vk*u)twrx Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz. The+ 4 bbnrxz+z.c tension in one string is then decreased by 2.0%. What will be the beat frequency heard when t4+zrbcnz. +xbhe two strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identical flutes each try to play middlea,ja5vg m -lol0i) j0x C (262 Hz), but one is at 5.0°C and the other ma i0o-g)lj,xj l 50vaat 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C.6 v ka0b* pa pid24cu;.mrtie/ 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 are sounded together,pi./ u 6 04atdkp2 r;v*maiecb 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 per2ofp+ve d1t k/son stands 3.00 m from one speaker and 3.50 m frofk+d1ovp2/t e m 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 vibratin1oqr7d c 8al0mg 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 dc o8q70arm l1132 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 waveleng2 j)+qsw;xl6 i tafr)qe1y /ffrq j1s7ths 2.64 m and 2.76 m in air. How many beats per second will be heard? (Assume T = 20 f1l qjqjt26f1fseq/+; ix7wyarr s ))$^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain.r; 2u*n z yd hf.ikx 0)qx8op(gxuoalhq 3x3, fire engine’s siren is 1550 Hz when at rest. Whatl*xxo(3 )3rhq.i 2y u,p xga.k;fznuqox8 hd 0 frequency 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 d) mcp-hj9am :jwtcfr(;6q he-o you detect if a fire engine whose siren emits at 1550 Hz moves at a speed of 32 m/cw6t-9c a)rehp:-jmf( j; mqh s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequenp*-+; x6jeawr r4db mzcy 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 exactly the same? Are they close?z6;r bap * rx+jmew-d4 $f'_{source\,movine}$    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 samxh h4ok)m(mf.e 5p-fge 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 of 5.5 Hz. What is the frequency the horns emit? ef )fo (xk4pgm5. h-mhAssume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at 50.0 kHz and receives th:fke :c jaeb*tadd(cy8p 5))g em returned from an object moving directly away from it at 25 m/s What is the receiva :pk*bfc:5(gdeyt)8)ajcd eed sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As it flies, the bat ,zph ,scu vgix3:rker03se 93 emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency does the bat hear in 3k, rzhr,se:vus 3x9pcge03ithe reflected wave?    $ \times10^{4}$ Hz

  In one of the original Dopwh)hvz/ j-4hppler experiments, 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 beat freh/jhh- vwpz) 4quency 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 measu3 ,plz ((0r zynwxyl6p-jl ar6re blood-flow speeds. Suppose the device emits sound at 3.5 MHz, and the speed j3apz(p l (l-yrn y6zrw,x l06of 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 using ultrasonic waves ,z 72ih qvx wohq:,oj*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 winddg b386(uemf 72 i96qvrpog ll velocity is 12 m/s from the north, what frequency will observers hear who are lq836 oel7gg l vudmr(b62if9 pocated, 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 object3y(vmr34: dtqrm o1.)svfqlc moving on 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 is 310 m/s (a) What islz s19g(mg6 us the angle the shock wave makes with the direction of the m1g us6glsz(9 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 sox n(sarfpe: 7 y4dc7*lund is only abouldsacrenp77(xf *4:y t 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} $