What is the evidence g vx9x: q2mut8that sound travels as a wave?

What is the evidence that semkmj.4, sr* 1 0/1uaafmpulsound is a form of energy?

Children sometimes play with a homemade “telephone” by attaching a st91 nh a5gm:-d(dy -iml *nmamcring to the bottoms of two paper cups. When the string is stretched and a child speaks into one cup, the sound (5g1mn -*iynmhd-ldaa cmm9: can be heard at the other 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 expe(q.lmixy .:r ,;c6l xlg ggn3l5:qx,u h8ryvzct the frequency or wavelength to change 5lmx, g.;qnzy hl8xr:3xr .icq g(u,6:lyvg l?

What evidence can you give that t qkyrc 1o)4)roqk) he5he speed of sound in air does not depend significantly on freq k45oh)k)qq1rro y )ecuency?

The voice of a person who has inhaled helium sounds very high-pitched. Why,7 ; g39xdotn vfs nn5sqlvm90?

How will the air temperature in a room9 /zy2vfhs2,k6 mmnnp affect the pitch of organ pipes?

Explain how a tube might be used as a filter to reduce no4zuid0 b8p 8the amplitude of sounds in various frequency ranges. (An example is a car 8ondp48u 0zi bmuffler.)

Why are the frets on a guit-4wslgys h uk1x. 8.dtar (Fig. 12–30) spaced closer together as you move up the fingerboard toward the bridges- wgktud.s8.h 1 yx4l?

A noisy truck approaches you fro.n q wni-vkw280/dn oxm behind a building. Initially you hear it but cannot see it. When it emerges and you do see it, its sound is suddenly “brighter” — you hear more of the high-frequency noise. Explain. [Hint: See Section i2x d/ nnn vkq0ww-8o.11–15 on diffraction.]

Standing waves can be said to be due to “interference in f:kcz p9g4m+* cfp sd v:ep5z+space,” whereas beats c ek*mz: g4sfp f+z+9p dcpvc5:an be said to be due to “interference in time.” Explain.

In Fig. 12–16, if the frequency of the speaker3it7y 8o4xussc +8 tvvhasg3v;f1j m(s were lowered, would the points D and C (where destructive and constructive interference occur) move farther apart or closer togeth4s81fv3 u( ;cism aysgv 7tjt83o+hvxer?

Traditional methods of protecting the hearing of people who work in areas e4p7c 8to9a ocwith 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 electronite o9co7cap48 cally, 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. 12–32fh)gowp1 v 6e1. Each 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 twowef)v26pg1 o h component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and observep)pd d+mda, i/t6nhpqx.ry32 r move in the same direction, with 2dpp +yr6.hxd3 qdmipa) ,nt/the same velocity? Explain.

If a wind is blowing, wil2zbzs+ggjixyf78k :2 l this alter the frequency of the sound heard by a person at rest with respect to theziz8 k2s g:2 b7fjg+yx source? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a childm k0g+)twl f;v in motion on a swing. A monitor is blowing a whistle in front of the child on thg m f+v0k;wl)te 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 t)hlj)c kzjved.745e ihe length 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 echolv4zch5)ekj)d7 .j ei 2.0 s after shouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below the waterline.7/ h(we5kvz3 qymdnb9z t fh/- He hears the echo of the 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 doesk h/-n 9yzb3( w/h7vedztf5qm not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengt)ym0 t*blsk hgud)2 mmv*/fk;hs 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 o obg2h:qt t)15nr fw1y6iglj1f tuna on a foggy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How much gghwfn orb 1jy )1tl :1qt56i2time 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 whq;r xsy dw95z1en striking the91wq5dy;r z sx water below is heard 3.5 s later. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge stone strike thee895 yk .tchz nb*ia5 pc5nn3f concrete pavement. A moment later two sounds are heard frepnyka55*fn 8.zccit h9n53b om 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 one mile of disa-0x/:x b/5 b7w kh)qpfhnujatance by the “5-second rule” for estimating the distance from a lightning strike if the temperatureju)n hfbw xp7/a 0x:ka/hb-q5 is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pai i3sbm7gj34 +tdhwe7b4lzkj 5n 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 .3rpwgti nrmvvhy ;:9,+ j wd(whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired simultaneously//ns jzaw4nut- (had: 0pc;uw at a certain place, what will be the sound level if only one is exploded? [Hint: Add intensities, not dw azsj-uu(n0; /wd/h:nat pc4 B’s.]    dB

  A person standing a certain di/g/y;80 qd5xpv9 -tpfd3zav awmz*hustance from an airplane with four equally noisy jet engines is experiencing a sound level bordering on pain, 120 dB. What8 vz9;d/05zty ppav3mx g/wh -*qaufd 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 ratio of 58 dB, w :/z-:/:jbvdf h fkncwcb b,m8hereas for a CD player it is 95 dB. What is the ratio of intensities of the signal and the background noise for each device? 58 dB hmd:cbw :fk-v8z:/j fncb/ b, =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from a person speaking in normal ; 8p4x.veeg9e22y rwfq elmjd9 8cfm:conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphere centered on the moup .28r9ecl4e2eey jfmgm:f8 d9wqvx ;th. $\approx$    $ \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 area i t):yeddk- (-ij g4x jdk;y)jhs $5 \times10^{ -5} m^2$ (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,ioxj-zo o.sj+-9 .qk+fr6dj z 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 loudspeaker connected in tur.oj osd+j ik6zorz.xq9f+j--n 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 invr/tflvdth9js b:.i t4,0t j5 front of a loudspeaker on the st.ft5s j /t,0vth4il9 :jtdrbvage.
(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 levfy9.1rh icnm3el of 2.0 dB. What is the ratio of the amplitudes of two sounds whose levels differ by this hy.9m1rni3 fcamount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is trrtt z1c+t p;mnm o680eipled, (a) by what factor will the intensity increase? Increase by a facor0cp zt+nt; t8emm61 tor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal dis9 o2 kt;ewmta8placement amplitudes, but one has twice the frequency of the other. What is the ra;w8 2 9tmkteoatio of their intensities?   

  What would be the sound level (in dB) of a sound wave in air that cowg0nps0:/be a)q hwx *rresponds to a displacement am habn :gxs0p)w0 w/eq*plitude of vibrating air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud as a 100-Hz tone tmygte23 p+l x/hat has a 50-dB sound level? (See Fig. 12–6.)+2ygtm3p / xle    dB

What are the lowest and highest frequencies that an ear can detect when zdeek8zlm/l3w* m n5 ;the sound level is 30 dB? (See Fig. 12–6.) 3/8l;l edwzem*k5z nm

  Your auditory system can accommodate.fl((c:nxa os a huge range of sound levels. What is the ratio of highes(l.( afonx:c st 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 44 cevuwe k/1bp x:dx-/: v,dq1k0 Hz. The length of the vibrating portion is 32 cme1d,vk:pexdx:- /uk1/wvc qb, 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. What are the fundamental and first three e 7m25il)qy2n vcce*w/yng zw54srp* audible overtones if the pipe izg 5 w22v5i*ny47n yelqrmc*w e)/c pss
(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 vc/:kwc*d s)r would you expect from blowing across the top of an empty soda bottle that is 18 cm :cr c/*)vds wkdeep, 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 pipe organ with open-tube pipes spanning )r :2nr(pp8jdi 93avkfhc4kuthe range of human hearing (20 Hz to 20 kHz), what would be t v(ph29k : r)8iap cfu3r4djknhe 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 its third harmo fj3.w9 qcmbv6*wnsaexm6, tk5:v5pm nic. What will be its fundamental frequency if it is fingered at a length of only 60% of its wjwxs:t6 v6fm m.am,3b9 c *k5p5vneqoriginal length?   Hz

  An unfingered guitar zs (f2bd/uo ;qh; .xgxstring is 0.73 m long and is tuned to play E above middle C b;2 .dfzx(qoghx/u s;(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 pipe th;dhq jptgcgx+/u a1/i f46 1wzat emits middle C (262 Hz) when the tempera4zdfi1 u1+p/hwa;q/jg gx 6 tcture 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 j5ughz0*ykw2 $^{\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 shol(x;wo-46mnj ;gs78s1 vuxvqa sajy 9 uld the hole be that must be uncovered to play D above middle C at 29 mgo67;a1u4 (wq-nsvs;a xlsvyx 8jj94 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 at atb0q.k n.d d5iny other frequencies in between. (a) Show why this id0kt..bdq 5n 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. It resonates2 .0e7 ;kcsiypp3s1u hkffefh)1(x rg at two successive harmonics of frequencies 275 Hz and es70g.3pfh1cfx)21e;(furk i kysph 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 5cgij8 1 0oye oig:2tj$^{\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 rasx1y 2+mh2qnwd-6e renge for a 2.14-m-long organ pipenqhs6 e2mrw 2 y1x-d+e at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.0dyyn+km1y u/v wg0:f5 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 your answer to the info 1v0ykmunyg:0ywd/ +frmation 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 tr.tgf wllgdp 0,ulg;/) ying to adjust two strings, one of which is sounding 440 Hz. How fdpllw,gu;0) g/. tl fgar off in frequency is the other string? ±    Hz

  What is the beat frequency if middle C (262 Hz) a8 +v c7ep 3owc3a.)gwvqpsqb2 nd $C^＃$ (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 2 mxiqo u;7nz:ss p5186v: kajw3.5 kHz, 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 simultaneouam6:7sv z1;p58oniqu: jwksxsly, estimate the operating frequency of brand X.    kHz

  A guitar string produces q,zqo( 6sy/5n b(-lmapz- ajt4 beats/s when sounded with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequeqlzjays, o(b/-p-a 5mt6(q znncy of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 2kf90a5 zj*9f; 5wjz 6 ,jrivmydk0blk 94 Hz. The tension in one string is then decreased by 2.0%. What will be the beat frequency heard when thi59zwjj, 9kkf0f ;lbm*d j0 zkyar6v5e 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 mp9np.d q,;3sb/ i r2ybyo.llg iddle C (262 Hz), but one is at 5.0°drn9bopbi, 2ysqpl 3y .;g.l/C and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, c1 m 0fq) 6)cillsz2mmand 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 m fmc0l)c1ms6iz2 )q ltogether, 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 stadp,+xs7q ckx28m(s gh5h,r fdnds 3.00 m from one speaker and 3d5d2fh7(, rs+g,m pxq8sckx h.50 m from 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 vibr0vb4jr g9,mux ating at 132 Hz, but a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibrating atj m09b4,vg uxr 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 --qlbii:qih;. How many beats peri--hq ; il:qbi second will be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequenfh .yey q)nwnmvum 2.k;u n)*0cy of a certain fire engine’s siren is 1550 Hz when at rest. What frequency do you detect if you move with a speed of 30vhf ky2 0umnm..e)y)n qwun*; m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequency do you detect if a kwvli1 8fdm+ q.os je4o8,o(t fire engine whose sireni+d8q,. ltkowesvjof 841(mo emits 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 zv w*xd)yh1o4o:w-)bnqdn g : 2000-Hz source is moving toward you at 15 m/s versus you moving toward it at 15 )o :v hd*1y w odgzxb):w4-qnnm/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 frequency horn. When odzs -)h2f,hn3wsa; mkne 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 ewh sns kf da2,hm3-z);mit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out uzv,g -+t6ppu3z6bx taltrasonic sound waves at 50.0 kHz and receives them returned from an object moving directly away futpgzx6 63, v+p-bzat rom it at 25 m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a ac,)6 sdnqxp/c.x jf( wall at a speed of 5 m/s As it flies, the bat emits an ultrasonic .,6c/fpn qsx(jx)ad c sound wave with frequency 30.0 kHz. What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a c-elsvn 281i2g;5usis8uk 5ov.tjw o 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 is njkwv5usgoei2;8o .c- 8l21v5tus 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 aga y.)gf76zd 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 154af7dg) g.azy6 0 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 ux4w ;j;vq2qc*q:jsb04e in g jltrasonic 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 velocity:+dk;pvhafw +)mh x 0n(bay3p is 12 m/s from wfhxy3b d:+ p+0 mpahnak)v( ;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 ( oftr wj6.:s 00tgsmkon 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 3(rte.d it u4a43*kcn4 nvlo7w10 m/s (a) What is the angle the shock wave makes with the direction of (rtwunat *3 nvl4d 7c4e4o i.kthe 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 7 x(tf,rper; ta planet where the speed of sound is only about 35 m/;xfre 7t p,r(ts
(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} $