What is the evidence that sound travels as a wa08i dm8yp 2jo8x.zh6grvs 08 hoi qh1hve?

What is the evidence tha l9lf 69o0njq:g6 faiet sound is a form of energy?

Children sometimes play with a homemade “telephone” by attachi0ry lcgtg(h;-ug4v r3 ng 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 (Figrh;l(ugcg4t- 3 yg r0v. 12–29). Explain clearly how the sound wave travels from one cup to the other.

When a sound wave passes from air int1be qeqo,7iqw/km*d7lw+0v dt)3j lo o water, do you expect the frequency or wavelength to e /ei7wjlq0d kt*)lv mbwdq oo1q3+,7change?

What evidence can you give that thet.ma6)cugx1 9i u2q/( jtpiik speed of sound in air does not depend significaxpgt9qk1uuja/2ti6 c( im.i) ntly on frequency?

The voice of a person who has inhaled helium sounds very high-pitchemkgc9i3-oq e; ) com4oed5.im d. Why?

How will the air temperature in a room affect the pitch tq. u-m; 7ijgq arqx./of organ pipes?

Explain how a tube miyac sb5me qeoog;z5oa f*;7;.ght be used as a filter to reduce the amplitude of sounds in various frequency ranges. (An ebaosyczgo5;5e *mo7; f; q.ea xample is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced c;ru6c. g -hydoloser together as you move up the fingerboard toward the bridgo;.yru-g dc 6he?

A noisy truck approaches you from behind a building. Initially yi(vmom56vd f3w ysm6ey q s8 qke)5;*rou 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-frequen(sqem 6)im86;mok3dqrv* v wyy 5 5efscy noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due to “interference in sp zb wu;p9nj+slo-/:wmace,” whereas beats can be said to be due to “interference in time.” Expla-/9 pbz ns om;u+wj:lwin.

In Fig. 12–16, if the frequency of the speakers were lowered, would the poi)-u fkho2te (lnts D and C (where destructive and constructet (k)f-2h louive interference occur) move farther apart or closer together?

Traditional methods of protecting the hearing of peouc71jm 0im8p sple 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. Houcmsmi1 p780jw could adding more noise reduce the sound levels reaching the ears?

Consider the two waves shown in Fig. 12–31. Each wave can be tgx*xrobl i*+2u pu8u ;hought 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 ur o2;8i*plxxg +bu*u farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and observer move in th.mb1rs* )l(wknzkjf ; e same direction, with the same velocity? Explaiksbmr1.j*(w) kzl f;nn.

If a wind is blowing, will this alter the frequency of the sound hez z/y .hi6f,xoard by a person at rest with respect to the source? Is the wavelength or veloczh o,6/f i.yzxity changed?

Figure 12–32 shows various positions oft3l v;4op- *cklg*ier: whji9 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 t4pow h;t:r *lil3*cge- v i9jkhe whistle? Explain your reasoning.

  A hiker determines the length of8/n2batzpn ba am)4 w hu(s6,m a lake by listening for the echo of her shout reflected by a cliff at the far end of tht)mp84z h u/snb6bna2,wam( ae lake. She hears the echo 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 t kewggf ,5/+7rr byw8nhe waterline. He hears the echo of the sound reflected from the ocean floor directly below 2.wr 5ggeyf7bk w8n,+r/ 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 wavelengthsbw ls bf.ts.m4 voj p,l+*-h*g 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 on a fsc91 r;+w xe-v(f/nt7vw sfiepf e.3aoggy day. Without warning, an engine backfire occurs on another boat 1.f(p7;cw-nw 3+ vr.xs1 fafe eiv 9/ets0 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 strikingtqcd :i 3x*mr9 the water below is heard 3.5 s later. How hitx 9 qmd3cr*i:gh is the cliff?    m

  A person, with his eargufqv:.*z yi1/f m ;wm to the ground, 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 1.1 s gzmfm ;/1wu qf .iv:*yapart. How far away did the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one mile of distancsiox;q44dx /y e by the “5-second rule” for estimating the distanceyi;sqx4 x /d4o 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 pain leve++ywvn-+bgk0yj 0 9ddd j3vbz,gvq4 rl 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 *3j5gb- v8wt- c4xkefis rc/f a sound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound le,ur,qe b*j d1bvel of 95 dB when fired simultaneously at a certain place, what will be the sound level if only one is exploded? [Hint: Add inten,jd 1,eq bru*bsities, not dB’s.]    dB

  A person standing a certain distance from an airplane with four equally t5,wgy/55k ep 4yjg al1+dvafnoisy jet engines is experiencing a sound lev4fw y5j 5+ 1gy,a/ke5apl tvgdel 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’s.]    dB

  A cassette player is said to have a signal-to-noise ratio of 58 dB, whereas fo1hvh jqilp6)bnr9rr5 (7. qlc r a CD player it is 95 dB. What is the ratio of intensities of the signal and the backgrounl5r(q. 9hb7r6i nrcvh1p )lqjd noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output o:+ qbv z9e.v yqum kp/0pl5i0af sound from a person speaking in normal conversation. Use Table 12–2. Assume the sound spreads roughly pi5vlem 9b vq+y/:a.kqz u0p0 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 strikes an eardrum whose w f8-7h 6fssjys7g-hgarea 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 Wdlfhnlk+vw pz+7n jyvh,xvse 5pe 4)dp./89/, while the more modest amplifier B is rated a)d4 n7lnj. hxzf h +e9k//pv,8dve ls+ 5ppvywt 40 W. (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 metern n-bt 4,yh,xfbh5y ,i registered 130 dB when placed 2.8 m in front of a loudspeaker on the -t,ix,5bb, fhyn hyn4stage.
(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 d p-m(kap:j+a jo7iwd.e2fc/dB. What is the ratio of the amplitudes of two sounds whose levels differ by this amount? [Hint: See Sectiwcj+a - d2mapo ep:f7kdj ./i(on 11–9.]$\approx$   

  If the amplitude of a sousdeqci-, 9d5w nd wave is tripled, (a) by what factor will the intensity increase? Incri, dqed-s5wc 9ease 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 twi:ux)refu 8 8ance the frequency of the other. What is the ratio of ua8x):uf8en rtheir intensities?   

  What would be the sound level (in dB) of a sound wave in air that /6)ghphl zj9wls8 x y;corresponds to a displacement amplitude of vibh z86s9l)lj;gpwy/ xh rating air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound le0s 1 .h;zcylz 2k;6mqlga7amyvel to seem as loud as a 100-Hz tone that has a 50-dB sound m21s.gqy zhy; mc k6;z7lal0a level? (See Fig. 12–6.)    dB

What are the lowest and highestahio 42sdog5yq(0 vpsb1 v;,cz um 2(q frequencies that an ear can detect when the sound level is 30 dB? (See Fig.a2qqg ; zco4d(vs 0h5(pvy1i 2sub,om 12–6.)

  Your auditory system *:c27twpz;fb a (dj3nhoaw+ pcan accommodate a huge range of sound levels. What is the ratio of highest to lowest 3dfca7a*pptwnwh2+ (j z;o:b intensity at
(a) 100 Hz,$ \times10^{ a }$ a =   
(b) 5000 Hz? $ \times10^{ a }$ a =   
(See Fig. 12–6.)

  The A string on a violins :bqn0x9p1mp has a fundamental frequency of 440 Hz. The length of the vibrat pxmbps1n: 9q0ing 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. What are the fundamental and first three audible:y 8scdf;hd- p,ysw.s6t 7jla overtonh jst .7cd sa6 y:wfp-8,sdy;les if 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 top of ez7e.rmg h 5ox( 2lei-an empty soda bezh5i ge e7-(mxlo .2rottle that 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 pipe organ with open-tube pipes spanning the range of nc 4hxx6h 79pvhuman hearing (20 Hz to 20 kHz), what would be the range of the lengths of pipes rhxcpxh4v 79n6 equired? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a frequency of 540 Hz as its third harmonic. Wptx mbdn dyiou/*- o. z9ut.t29r8d(ohat will be its fundamental frequency 8ot dx2bzdriyn -u.odmt p. 9(9*uot/if it is fingered at a length of only 60% of its original length?   Hz

  An unfingered guitar +4 as/tcg s1cgstring is 0.73 m long and is tuned to play E above middle C (3s+ gst41a/ gcc30 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 tix kkj5ky,l5 +hat emits middle C (262 Hz) when the tempex+k,l55 ki kjyrature 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 xb9n61zcf 2rxat 20 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpa cc af40-f-nxiece of the flute in Example 12–10 should the hole be that must be uncovered to play D abovex-fc04n fa- ac 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 bh+d* i +q8u2qrgpv m(264 Hz, 440 Hz, and 616 Hz, but not at any other freque(vp8m d ri*++g bquhq2ncies 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 ei t4079.i8rjhx2n( d qltw jtn2+lrxnnds. It resonates at two successive harmonics of x9rt.n 2t2ilwh qntdx (r0+ i 784ljjnfrequencies 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 ax 29s9 hvu8ow$^{\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 organigtxns (/xe3:yesd.11c ato- pi(s:ge 13osydn tt/cx- ea1xi .pe at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm long. It istxu1c97 yr04rud;f j9/chngt open to the outside and is closed at the other end by the eardrum. Estimate the frequencies (in the audible range) of the s1;y9d9/utc4hc xtg ur7rnj0ftanding 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 whef9cp20h o*gojn9o 0xin trying to adjust two strings, one of which is sounding 440 Hz. How far off in frequency iscph0jxg o0o92f *on9i the other string? ±    Hz

  What is the beat frequency if rf k)c7dsnzk;gi8t++; 3j5rh enda ;ymiddle 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 21;tlmb n6 (,r- nvw xe*aohu wov(9o1e3.5 kHz, while another (brand X) operates at an unmeb h , ln-oex(ur;(to 1vwwnv*o a169known 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 beah+zmg mbmd dtzm; n*vr 7z..8(.dkli*ts/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 frequency of the string? Explzh.d.iv* 8z*(dgr 7t+z lm.;kdmmmnbain your reasoning.    Hz

  Two violin strings are tuned2ejf5 o lj i(i*2ding17h a*gj 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 are played together?iidfj5oh *a* e1ingl2 72jg (j [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identical flutes eaa,xwo), o.7;p zizn.f*hdy esch try to play middle C (262 Hz), but one is at 5.0°C and the other at,.p ;oe)h,wx faynodz .siz *7 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forh :r:txa0 k9sehai,h jwxl+9) ks, 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 aj ,x99skthe)lhi ah0 + r:axw:re 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,dnxlm/ xq-n f.8ni 5e 3.00 m from one speaker and 3.50 m from the ote/innfqxn.d8, lm5- x her.
(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 sun 2r5gex.0qlm .il xv:pposed to be vibrating at 132 Hz, but a piano tuner hears three beats eell5x x 0i.nr2 :v.mqgvery 2.0 s 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. How many beats pe g o8qcj+ 5qfkys9;nz9r second will be heard? (Assume T8jnq9so yzq+f;9g5c k = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency ofd 4wp8xev23 sni atn78 a certain fire engine’s siren is 1550 Hz when at rest. What frequency do you detect if you move w2ewn788i3tdxsv4n p a ith 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 detect if a fire enl 2;z wy7myg 2deqi( 0yk(c1jjgine whose siren emits at 1550 Hz moves at a speed of 2m1w z0yjyij( 2k gc(dye7;ql32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz source is moving toanl2d n+aui. (ward you at 15 m/s versus you moving toward it at 15 m/s Are the two frequenc.n ild+ (na2auies 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 7vd*sehmy q9/ horn. When one is at rest and the other is moving toward the first at 15 m/s the driver qevdh*s9 m 7/yat rest hears a beat frequency of 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 50.0 kHz and receives ,m+; / c+d bcolfci5jfldhcc uf :47g1them returned from an object moving directly away from it at 25 m/s What is the receivedblcg+h4,fu oc5d/1 +: cdcl mc7if;jf sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As it flies, the bat emits an ultri 972 wo6kxo4nx7 jeyzasonic sound wave with frequency 30.0 kHz. Whax26wooki9xn 7e4yj7z t frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was pl1a+2rhi nza 2,nggnj )ayed 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 traaij)h agr+22nzng1 n,in car approached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses lmwwa/:z 0y5h ultrasound waves to 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 expected ml0awzw /:hy5 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 wav7*pqb. +ubqsfes 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 velocityx6n 9:/rtpmp lnl q )htr,n8u3 is 12 m/s frohtxl,/n6): pqmnn 8lp3rtr9 u m 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 km0:iwo g6n+m 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) yd *//srjhtuk6s9bvw(o 6.yu) gif8 rWhat is the angle *)6si (h/ 9gvrwtfbdou 6ysr u.yk/j8the shock wave makes with the direction 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 8olcp+) fle o/zqtv i1rm 0.m9of a planet where the speed of sound is only1p lq.8v+ro9 ecommlzfi /0)t 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} $