What is the evidence that sound travels d9bl2* nfdrzp1 bd1hzh53.plne7 8 d kas a wave?

What is the evidence thagdc4 h* . yi4s jv4zik(*bdlb x-odb)-t sound is a form of energy?

Children sometimes play with a homemade *bp)oh-b po)r“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 (Fig. 12–29). Explain clearly how the sound wave travels from one chb)-p* o)pb orup to the other.

When a sound wave passes from air into water, do you exdq l: qxx ba278vg:)fi*s c va6rl+8dupect the frequency or wavele l8gqaacfi6b +:*x7l)ds:qdxv8v ru2 ngth to change?

What evidence can you give that the speed ki0 f-hkiql,p3m 4fp :of sound in air does not depend significantlyh4mf, p 3pk:kq0lii- f on frequency?

The voice of a person who has inhaled helium soun,,uhv)k+ff jg ds very high-pitched. Why?

How will the air temperaoi9a- i 1q:37r/,rlil.wxya :xb smi)xg cpt7ture in a room affect the pitch of organ pipes?

Explain how a tube might iv,ogit pxlc+o13no4/co l0. be used as a filter to reduce the amplitude of sounds in +vxiocn4 l oo0g/1io tl3,pc.various frequency ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer ;sri9 m)wmbi )together as you move up the fingerboard towabrm;9i) smi)wrd the bridge?

A noisy truck approaches you from bjjr.5 t v;/s)j1o6vg 2cwkx-hopf sv -ehind a building. Initially you hear it but cannot see it. When it emerges and you do sxf)-crh5 ;pjst.ko/w16 sj-v ov2gvj ee 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 be due to “interference in space,” whereas beats num461mh 5fweecva ;9can be said to be due to “interference in ti mvhefmwuc5 e9an1 64;me.” Explain.

In Fig. 12–16, if the frequencyc kfjqu74y;bn6 g2;fx(o-shh of the speakers were lowered, would the points D and C (where destructive and constructive interference bu(n;;h fg x4j-f7cskyq 6 oh2occur) move farther apart or closer together?

Traditional methods of protecting the h0z7 1wfcxsqs-1u7d9g)7b )xu )wa3f skvvhbuearing 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 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 eauzavc3s0 w)) 7x 9xg771sd1vb ubh qf-wfk)us rs?

Consider the two waves shown in Fig. 12–31. Eachx 9k:yq- ol-rr w;j6 awss1ms,ph:t9n 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 o :w 1x,s;sp:9tlh a-mn6w-qj 9rkyr swaves, (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 dire/ h jg7yvm vd-o;qrd/bmkl cb 2c9*71hction, with the same velocity? Eh rvqcc1/2g hd vld7*yb/kmm ;97b-jo xplain.

If a wind is blowing, tppkjeb.8w9.aze zaj0t*y1e7 +y.ie will this alter the frequency of the sound heard by a person at rest pey9e*+.. jtb aiejp8z.e70k1tawyzwith respect to the source? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a child in mothccz h*m,xw l-* ap4(ch wqied1k;+f1ion on a swing. A monitor is blowing a whistle in front of the child on the ground. At which position, A through E,xca i+zcfhl* 11c(*ehp-kh w,q4;w dm 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 2g;: .,j :xbfvd,og-sj 0mludovbk 3tfor 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. Est; :xobkl-vofm , j3,dgtg sdb:2u0.vjimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship j- ha34c(tr) 4qyarjxa ust below the waterline. He hears the echo of the qx3aarr44-( )yhct aj 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 (Table 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in a rp4onpm*h2jf/ h)9eeu9d y1rir 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 on a itkgc.dv6cdxoiw u d 47-)7u1foggy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How much time elapsg1 ktcu) .4dio-i7v7xc ddu6wes before the backfire is heard (a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top o0 3mlddw6 m3pru:-( ccxj4 amof a cliff. The splash it makes when striking the water below is heard 3.5 s later. H0-dc wupxm(mar c3l6:m 34jodow high is the cliff?    m

  A person, with his ear to the ground, sees a huge xrql 76vry9oz f39;rmstone 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 1rv;9l xf7qr 6m3yr9o z.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 mile of distance by the “5-se ;cs(7bhob8fz n1qav+ 5o/hs pcond rule” for estimating the distance from a lightns;bq1+8 s(/hoozpc 7v5a bhf ning strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pain level of 1202:wqi( efhe o9,q k:um 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 sounr9ewct-w-x mq1vt z, 6dxc.8rd whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of su3q:;8 c6exgabwaln3)- ltp 95 dB when fired simultaneously at a certq;)cbp 3la-3lawxn u g68s:etain place, what will be the sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain d 0skcvdoi1 -j7istance from 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 enginejks-vo0ic7d 1 ? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said toif 4+tqudt-;fp 1l4ae have a signal-to-noise ratio of 58 dB, whereas for a CD player it a+41 4u; -pltf eitfdqis 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 n:z 0fw-,rvqa-eba+q/ hpwll+ *p o x/oormal conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphere ce:l-o, + e/w-qqx+ bawp o*vf/zpl0harntered 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 whtffqx3ww2+de2l0 q0z ose 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 Ah: 4lt7jppkg: i7o u6j 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 poilp:jg7 oikp47jh :ut6 nt 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, aziv )hbtdcdp4 2p ::i1 dB meter registered 130 dB when placed 2.8 m in front of a loudspeake ih4 :2pcibtv 1z:dd)pr 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 8td9afg fmd .wyl 78y,in sound level of 2.0 dB. What is the ratio of the amplitudes of two sounds whose lev87y f ld,md8ty9gf. awels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what3 hm,;lsf62nd rm rne, factor will the intensity increase? Increase by a factor osr,nfmh m,ler236; nd f    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displac0(w04yh )bvec nyh3 wsy-88bmtpj4bt ct/ih 3 ement amplitudes, but one has twice the frequency of the othyv3b8hbb tw-y p mt8e/(iyc 03h 4 h4)n0tjscwer. What is the ratio of their intensities?   

  What would be the sojm 8k5/uk pu:3 vot7zv. *uugjund level (in dB) of a sound wave in air that corresponds to a displacement amplitude uvmt8uju5k3z:*vk7/. ogjup of vibrating air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level tr95gmkmiwdzd+cok ,b;ue :: 6 o seem as loud as a 100-Hz tone that has a 50-dB sound level? (See Fig. 12crwd ,k; :mdbeg : oi+5mk69zu–6.)    dB

What are the lowest and highest frequencies that an ear+9e*qk(v9j 9six xdjq can detect when the sound leved q9 qjj(9i+xe s9*xkvl is 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of sound levels. 6 y-l jh7g;cmtWhat is the ratio of highest toy-t6lc hj;7gm 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 fundament ejqwq(e1lc a0)pg8.ugzba /.al frequency of 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 string be placeda1j weae.q8g.) cu p qzlg/0b(?    N

  An organ pipe is 112 cm lon;sto:w8+bgvk 4/griq ,k- farg. What are the fundamental and first three audible overtones if the pipe 4vatwg8 gb/:r kq;o+ r,f-iksis
(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 avt 4rcb 9g2.mtop of an empty soda bottle that is 18 cm deep, if you assumed i4vt.2g9 m bcart 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 ln+gbt u ig//c;ydovy e662h 8open-tube pipes spanning the range of human hearing (20 Hz to 20 kHz), what would be the range of the lengths of pipes requiredycio 6; g+v le/yt8hbng62u/d? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a frequency of 540 Hz as s6spo3.9*7e :tt d0x*hvyizt *z jvh uits third harmonic. What will be its fundamental frequency if it is fingered at a length of o:i6sjy*. vtz hpd u *79t3 osxe*vt0hznly 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to- bqwg /3aoxi7vmdwa0-6i2q x m,d;dj play E above middle C (3 -;dqo,03wiixq2vd6m xw 7a dmb/g-a j30 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 pipe that emits middle C -h akp- c iec36p:pfqj l6(mxabdg*14(262 Hz) when the temperature is 21 lq(m-6b:cca 3 xgp *fi41h-e6kpdapj $^{\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 ; ( /5ab3i5mzgdrqned20 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of l8r;s* ax zz8uthe flute in Example 12–10 should the hole be that must be uncovered to z;8l8 uxzsar *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 vmqcvng4.n:krfbcs-: 83lh ;can resonate at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencb-gh vcq nl;4f :nrm8.v:k sc3ies 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 endr:6m.xnr on g:u 87ufds. It resonates at two successive harmorgux7rm86 : ud.nfon:nics 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 x3 r -8,qfbjonw) cy4k$^{\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 fovk8::ty(js,sfi 0oh ur a 2.14-m-long organ pipe at 20 ,j s:i0oy sthk8fv(u: $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal i-t 8xwjo9vzi l;dz-ndd:7pdji 6b-a 6 s approximately 2.5 cm long. 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 y8zij- v6;6ba idd dn9p x7-: wtzjdol-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 s when tryinh 0szo l4km2wi5o/zwc mjk6:vro4 2 v1g to adjust two strings, one of which is sounding 440 Hz. How far off in frequency is the other w6joso:zclw1h2ovm 2r0v 45zi /kmk4string? ±    Hz

  What is the beat frequency if middleanowmbt:5mah3-k u + . 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 another (brandoc. e5xqca-1q 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 frequenqc1o-x. c5qe acy of brand X.    kHz

  A guitar string produces 4 beats/s when sounded wk oyh+ qx; 7cq,hx1dk;ith a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of the strh,kq7;d1kcx x+yh q ;oing? Explain your reasoning.    Hz

  Two violin strings arhg*m.m al1g;/yo g)aq1lry6we tuned to the same frequency, 294 Hz. The tension in one string is then decreased by 2.0%. What will be the beat frequency heard when the two strings ar ahlgor1a)/;mygl6*1g.mw yq e played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will b xe +th6nbi. x4am7kc3e heard if two identical flutes each try to play middle C (262 Hz), but one is at 5.0°C and the othexi4k c7nxb .a m+6h3etr at 25.0 $^{\circ} $ C?    beats/sec

  You have three tunin+4v3e jo3*: rgxupdi cg forks, 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 sou+ degorj3 ivx3c* p4:unded 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 i0q/o-iqaq)s 7 0 xwuma-rk0 operson stands 3.00 m from one speaker and 3.50 m from the othemarqu0 o0qaii / 0 )w-xsqok7-r.
(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 bcv;k 4-8gjbg ye vibrating at 132 Hz, but a piano tuner hears three beats every 2.0 sv g8bc-gj ;y4k when 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 of wavelengths 2.64 m and 2.76 m in air. Hownsw) , b8i pemxz/n(5c many beats per secondis)epmnwbx5z/ c(8,n will be heard? (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 jrt() 9wd k jst4-skq-when at rest. What frequency do you detect ksd 9k--wjsj rt)q 4(tif you move with a speed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing stibj6.xeujde /wev(,fz x *,e,oll. What frequency do you detect if a fire engine whose siren emits at 1550 Hz moves at a s be(d,. ju6xwe,o*/e,zvj exf peed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency rdy3*f o+th gn/ p/j*i)2cgmy if a 2000-Hz source is moving toward you at 15 m/s versus you moving toward it at 15 m/s Are the t)of* ncmhyi* y td/3/g2+pjgrwo 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 frequency horn. When one is n )db pn2y5uv:at rest and the other is moving toward the first at 15 m/s the driver at rest hears a beat frequency of 5.5dp5: yu n2)vbn Hz. What is the frequency the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at 50.0cgz,bdk/n +4v kHz and receives them returne/z4n vbc, k+dgd from an object moving directly away from it at 25 m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wallzf3drl),7 qq a at a speed of 5 m/s As it flies, the bat emits an ultrasonic sound wave with f73, zad lqrf)qrequency 30.0 kHz. What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a3 jt9ubzi* 4kb 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 frequency was heard if the train car approached the station at a speed of 10 k*bz3j ibtu49 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measurf vwvdr-:, b.oe blood-flow speeds. Suppose the device emits sound at 3.5 MHz, and the speed of sound in human tissue is taken to be b:ovwfdv ,r. -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 nv fcm)0fk2 i; zy,;x 1-zyagatwz0:uwaves 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 velocitydu5t/1*c4pbj eo 7 ;ie 9v0dkm ike8ea is 12 m/s from the north, what frequency will observers hear who are ej4/k t7d58 d*ceeau p1imek;o9bv0 ilocated, 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 objecte n4zo-k(u pk *+jqe5 xy2e ,wmj0)3xckhm3s l 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 wh5 e-gexh7ci j)f kdn(r) 8xge2ere the speed of sound is 310 m/s (a) What is the angle the shock wave makes with the dh) e-7e eing)dkxr(cx jf2g58 irection 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 atmospher4ikyl4vh3w 1 f, ekd*q 59dnsse of a planet where the speed of sound isnvdq5,wfks 4 y93ei1 hd*k 4sl only 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} $