What is the evidence th i1*dwytj su6.at sound travels as a wave?

What is the evidence2va6y w7 fcun5 that sound is a form of energy?

Children sometimes playk7hav6 f5 .mepij :v s5sg/ur2juv(l 7 with 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 other cup (F kf7g5 u:p u hjj6e avlrs7vvi5s/(.m2ig. 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 y+ae i9co/qd,nf 8 kc4//aghis ou expect the frequency or wavelength tca8k, /nica9oe4hd is f/ q/+go change?

What evidence can you )* 2xo uf0ajq dm-ftsy s*)uj;give that the speed of sound in air does not depend significantly on frequenc ufd uxj* )ayt-j)s20omq;f*s y?

The voice of a person who has inhaled helium sounds very high- 1 cz6;ofr zllwfc-)-ypitched. Why?

How will the air temperature in a room affelwe rg 1os6sui n1*z)th5:-h ict the pitch of organ pipes?

Explain how a tube might be used as a filter to reduce t 0h:* u2-.n(cfpaylkqm.fjp b he amplitude of sounds in var.q2m.kch(:f0a yb-fju npp *l ious frequency ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced c3+y qpn4x+ku86zovh dloser together as you move up the fingerbou68 xp zo+yv +h43dknqard toward the bridge?

A noisy truck approaches you from behind a building.,nsc ct .wz1u4 Initially you hear it but cannot see it. When it emerges and you do see it, its sound is suddenly “brightcc14uwn t,z. ser” — 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, t ox3j h/8fdhp)(s9kz” whereas beats can be said to be due to “interference in ti(hdfp/kt 3xh8 jo9 )zsme.” Explain.

In Fig. 12–16, if the frequency of the speakers were lo(0g.(al,x e8x fqfzgxwered, would the points D and C (where destructive and constructive interference occur) move farther apart or closer tog (fa0 ,zfxe gq8lx.gx(ether?

Traditional methods of protecting the hearing of peo+)s qx qfpj,5zple 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. Insxz q5 )qfj+p,stead, 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 wgvz )e .e3q*klave can be thought of as a superposition of two sound waves with slightly different frequencies, as in Fig. 12–18. In which of the wav*kq gle3 .evz)es, (a) or (b), are the two component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the sourc ,9thttvsb 6qg45wde3o)1;u xukwt9je and observer move in the same direction, with the same velocity? Expl 1sttodu)wth 99 w4k v6ju qe;3xb,tg5ain.

If a wind is blowing, will this alter the frequency ou 1k/lgat69 kknn8,5i,jar 1sx vv 8jcf the sound heard by a person at rest with respect to the source? k j1g,6u 8srxkki/9 a5vj1ntanvl,8cIs the wavelength or velocity changed?

Figure 12–32 shows various posiv 2bnikcu)u ( +.rt,dph,u 2u-qh4scdtions 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 t, 4dvhcu(rb) u s.+p,q 22tc hnkuiu-dhe whistle? Explain your reasoning.

  A hiker determines the length of a lake by liq 15)l tmy9gucstening 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 th5l)ucmy9t1 g qe length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below the waterline. He hears th y(exis z7(qm/di xv pgi-f 54s.t)63iv cvz2ie echo of the sound reflected from the f(6zyic4dp sqm x.(xit)v/vs - i2g53 i7ze viocean 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 ;cqdmv:1h mq2 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 on a foggy hh7t+9u c j4zwday. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How much time elapses before the backfire is hetc7j z hwu4+9hard (a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a 1ufg097xjig xcliff. The splash it makes when striking the water below is heard 3. 7uxig0g1f 9xj5 s later. How high is the cliff?    m

  A person, with his ear to the grpn v 49dnaz qsj:x3f:*ound, 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 1:*dz 9p qn:x4n3afsvj.1 s apart. How far away did the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent e)mi.cq,v-a7np(f,z )cl w dqq rror made over one mile of distance by the “5-second rule” for estimating the disczfip(v q 7cm ,q.),nwda l-q)tance from a lightning strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pab*a: ;lxd2aee2y e/qd in 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 in +bwf w ap-mbtbkib52zyxj***,9j mi 2tensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers provcxqg;7r r,n/ m 9*pjoduce a sound level of 95 dB when fired simultaneously at a certain place, what will be thrx c;*n7/,9ojq mrvgpe sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from jk/ozp)d9bq ( 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 if the captain shut down all but one engine? [Hint: Add intensities, not dB’/9kjo d(pq z)bs.]    dB

  A cassette player is said to have a signal-to-noise ratio of 58 dp 1,63; r7uffxmfzimpB, whereas for a CD player it is 95 dB. What is the ratizi 76p f3;pm1 xrfumf,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 from a personrvqe xr4 0 ad/x2e n3)e+iwfb, speaking in normal conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a q i)v xa ,/few 4r23drnb0ex+esphere 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 eardrum whose mzff.z nf0,kx hfo) ,4area 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 amplifie qlivlup1d ky7 c-,;ap9.)j ipr B is rated at 40 W.lyil-d) 1 k7q p ij.vc,u;p9ap (a) Estimate 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 130 dB when placed 2.8 m in f;d,fav5 idn:m ront of a loudspeake ,dvim f5n;a:dr 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 detect a difference in sound level of 2.0 dB. What -l4/d* llzpq,p-nkyvb /b i5,c;resh0,yz q bis the ratio of the ampliti /;4dy-s5pez hbblpvc,n0 r/, yqb -* zqlkl,udes of two sounds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tk m2v ,o2if4ieripled, (a) by what factor will the intensity increase? 2e,24i vkfimo Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacementp(l /3ncsc7 p q7;8bd3oo elhj amplitudes, but one has twice the frequency 3nq8dbs3;c7c( ll jpeph7 oo/of the other. What is the ratio of their intensities?   

  What would be the sound level (in dB) of a sound wave in air that cor oj5pynr/ps67i ncf:s+x05x jresponds to a displacement amplitude of vibrating air molecules of 0.13 mm at 300 Hz+ 7ofsx:ppr5/jcx5ns6in 0yj ?    dB

  A 6000-Hz tone must have wl5k vhja ;;gx+vfl.d90k* euyhat sound level to seem as loud as a 100-Hz tone that vje9fdaglv*. ; xh5;y0 k+luk has a 50-dB sound level? (See Fig. 12–6.)    dB

What are the lowest and highest frequencies that an ear d oam1q0u. we9can detect when the sound level is 30 dB? (See Fig. 1u1.woa0md9qe 2–6.)

  Your auditory system can accommodknk,m ji7-v:l3k/xt v(k:opdizgc- 4ate a huge range of sound levels. What is the ratio of highest to lopnd7v,o j/i-c (ikkl:t4z mvx:3-kgkwest 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 2n pt 1) x:cuva89ctllof 440 Hz. The length of the vibrating portion is 32 cm, and it has a mass of 0.35 g. Under what tension must the stri1ltv p9cn:82c al)tx ung be placed?    N

  An organ pipe is 112 cm long. Wh8m1 :8:l 1gt *byazeypip(mozat are the fundamental and first three audible overtones i:peb:myg* 8p1a1i l8zy ozmt (f 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 blowing across the toy)x* (oed ::e8wjaeno.v )kan p of an empty soda bottle that is 18 cm deep, if you assumed it was)e*.awj::vo kond )ya( 8exe n 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 span nkmdkt 7h,t pny20vyg ln*w ;-cf:a)+ning the range of human hearing (20 Hz to 20 kHz), what would be the range of the lengths of pipesah2y0+mdfkvw , ; nl- 7ygn: ctn*k)pt required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a frequency of 540 Hz as its third harmonic. Wpz c4w49vt4w bx q:d-jhat will be its fundamental z4c:t- v4q dwb x4jp9wfrequency if it is fingered at a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73v69zrh 2+rxu,vj t iq( m long and is tuned to play E above middle C zj+th26 ri x9u( rqv,v(330 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 length of an open organ pipei q*btqni75 1f that emits middle C (262 Hz) when * i q5q7intb1fthe temperature 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 2xm- . pbw 9oln/dx;n*p0 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece ofl.eh;+erf 1y1o8szvw-rsb4 d; h;pvt the flute in Example 12–10 should the hole be that must be uncovered to play D above middle C ato 1;1wvt+ybhr8 ds.4elpe z -h ;vrs;f 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 resonatsr0rrp g*m46 ikf-l0ue at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies im kgpir0r0*u f4-s6rln 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. xstupo9s:zbz1 s :;5 qIt resonates at two successive harmoni5ut:x;p9:z zbs q1soscs 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 d 9 rhun4fdugtyz;ki,*6 v(n/ $^{\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 audiblxbsf5kwi a m5m:*ce*+lw1)ft 9(cq yme range for a 2.14-m-long organ pmqicm5yx(w+k:fs*1)wfec5 b tlma9*ipe at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.a6 )*i1 oq.aiut ,hswr5 cm long. It is open to the outside and is closed at the qai.h t6)siw1a*o ,u rother end by the eardrum. Estimate the 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 every 2.0 s when tryingi. jifia7ii2 2jv- 3ai to adjust two strings, one of which is sounding 440 Hz. How far off in frequency is the other string?27j-3 ij.iiiaafi2v i ±    Hz

  What is the beat frequency if midd1ph;nh97nbmf le 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 kj cl*. brr un8;2q(wx k0;smriHz, 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 play 0.ck m2uriwl( jr;s*xb8nq r;ed simultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded witzfr 0d7 qy4uxe75)vxv h a 350-Hz tuning fork and 9 beats/s whezv)q0x 4rvfy5eu 7 dx7n sounded with a 355-Hz tuning fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tunwa ;1hl 4d;p0zldvi l9ed to the same frequency, 294 Hz. The tension in one stringpwl0dd;4 l1 alzhv;9 i 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 idenr5su6 hs--hhre )y- tttical flutes each try to play middle C (262 Hz), but one is -u ttyrh6s -5er-hs)h at 5.0°C and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks,hhhg d.oirngc g6zo:hm38yx1 /q1 -u , A, B, and 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 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 sougdg1oqgm :chhn3x1/yhz r,-i 6 h. o8unded 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 sk14g y raiv*r 3.jsj.ufwv,*apeaker and 3.50 m from thek**u13a.wv s,jg4rvy . faijr 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(jq6tr nvpjs;jjq(/ lpnj l8(3.q,by be vibrating 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 thr jpnl/ y((( bn. qs3p6jqqjtjlv,;j8e 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 ykvpc*yi ,8g1of wavelengths 2.64 m and 2.76 m in air. How many beats per second will be heard pg*yik8cv1 y,? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s siren is 1550 Hz when at rd*k rr2 i.j5mce52jird *.kr cmst. What 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 do you de.v hmm5bgtb) *tect if a fire engine whose siren emitmbg.)5m bv*hts 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 movin r: hli nflk:nmm/1m5e9jb(;hg toward you at 15 m/s versus you moving towa(kfl mr5bj;hm/m nn: :he19 ilrd 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 3brz 8un0gc v7zm2z0q equipped with the 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 of 5.5 Hz. What is the frequency the horns emit? Assume T = 20 83 2mz07u cvrgzqz 0nb$^{\circ} $C    Hz

  A bat at rest sends o0flz6 0d6,7t xwnixve ut ultrasonic sound waves at 50.0 kHz and receives them returned from an object7t n0wxxe0d6li6vf, z 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 bat emitao*+(6 bt xjlki:w9g6+ziumi s an ultrasonic sound wave with frequency 30.0 kHz. What frequency does thi: aj+ibulwi6+omk9gx*t 6 (ze bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, ard3 - dauzqc aw1vfn;z- qu -vt+66yfr;0jz*q tuba was played on a moving flat train car at a frequency of 75 Hz, and a second identical tuba played -udaz afq; qd1zyf 6 czwr -;*6urvj+- qvnt03the 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 measure blood-flow speeds. Suppfb eoj:gp jkmwo 2h/mma:hs(;l09* j8ose 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 directly away from (/ml :k;hejg:ps *8m2mjj fab9howo0the sound source?   Hz

  The Doppler effect using ultrasoam yr4hlg)hz ,.mv: 1tnic 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. When the wind e 0a47t 1dtwrgvelocity is 12 m/s from the north, what frequency will observers hear adgwe14 7rtt0who 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 j )f3mm)b/uxy 2izzaf.:*pxf 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 th) cdva 7ycp :se8w9qm4e speed of sound is 310 m/s (a) What is the angle the shock wave makes with the dirqs4:v dp )87 yawmecc9ection 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 sound is w-uim8l .tm9kkdt.. u only about 35 m/si-mwuul. 8.kk9dt mt.
(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} $