What is the evidence that sound travelln6pd4 tz 6 l o-;rtd.dj72c9tq5s ehls as a wave?

What is the evidence that sound 9azp4* sub0ydis a form of energy?

Children sometimes play with a homem hvw0 mh-6 md+xetz8(rade “telephone” by attaching a string to the bottoms of two paper cups. When the string is stretched and a child speaks into one cupexhm6h0v( mtz - dw8+r, 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.

When a sound wave passes from air into water, do you expect the frequency or 1g* fxlv0hs7v+dz lj( wavelengt1dx + vs(*v70jlz lhgfh to change?

What evidence can you give that the speed of sound in air doe;rjsajx0*t 4c )3 3u;rc thqhjs not depend significantly on frequencyjcu ;hat jhx s)*043jr3r qtc;?

The voice of a person who has inhaled helium sf2-76d h:r to av;mnsdounds very high-pitched. Why?

How will the air temperature in a rvym1hkv1 m gpah )kc5x:wvn0:q :.w4koom affect the pitch of organ pipes?

Explain how a tube might be used as a filter to reduce the amplitude ofl;g (+w2i kfle sounds in various fr;fi 2ll+ e(wkgequency ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced cum,pvg:dtd-+/ t *qhj4xhsly z-l m90loser together as you move up the fingerboard toward d:mhgzs-j t t/ lqu+ 9hx0-ldm,*4yvpthe bridge?

A noisy truck approaches you from behindx .kg3: 1zmh cxsxpq5) 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 :qxg.zm3hckxxp s5)1 more of the high-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be5;uigim.4v n j due to “interference in space,” whereas beats can be said to be due to “interference in jiv 4u.in5gm ;time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered, would the poinz7 xg;oo2 /fvrts D and C (where destructive and constructive interferencgov 7zo ;r/f2xe occur) move farther apart or closer together?

Traditional methods of protecting the heari svekw( dz/l4/r +t* b6eqh1 nwvm5ei+ng 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 nois*(n4di ee+tkze/blq h1 /srvvw+m56 we. 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 F ,edkxnjt rvc28fux,qe,0nfgb17 3 ,f ig. 12–31. Each wave can be thought of as a superposition of two sound waves with slightly different frequencies, as in Fig. 122gff 7ne,n,eb,cq0f v ,3dkxx1rut8 j–18. In which of the waves, (a) or (b), are the two component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the somiezo xwm36);(3hndm urce and observer move in the same direction, wiz x w ;(3d6ihmne)3ommth the same velocity? Explain.

If a wind is blowing, will this alter thyvn,-ks mz/ h.e frequency of the sound heard by a person at rest with respect to the source? Is the wavelength o v/h.n msz-yk,r velocity changed?

Figure 12–32 shows various positiodg ibc:nn 5 u*a+hnfoi3d*)j9ns 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 iabiu*5g9h+jfn )d nn*c3:do E, 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 mrcw)3k ,qwbpcg3:w0for the echo of her shout reflecbg0cwkc w 3:qm,r p3)wted by a cliff at the far end of the 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 sh8p fggs(pin/i9v)3 (g1gy rzi ip just below the waterline. 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 9(gpis 1g/r viig )(z 8ng3yfpseawater is 1560 m/s (Table 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in aij;etfcotp . 6,r 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 foggy day. Wi6i un6+pu0 4wgttxr t6thout warning, an enginutx 66np r60gu4i+tw te backfire 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 s 2ib4ruk1dyej ja44m 5plash it makes when striking the water below is heard 3.5 s later. How high is i4jebd2 15yua4k4 mr jthe cliff?    m

  A person, with his ear t;vcwklp14k e cq, k83yo the ground, sees a huge stone strike the concrete pavement. A moment later two sounds are heard from the impact: one,k kcv3w 1;pcqyk84 el 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 distance by the “5-second( 62z0os qyxpom x8mb/ rule” for estimating the distance from a lightning strike if the t/osbo82xmq y 0zpxm(6emperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity old0-e r1yzaiv e0f :l. 28jgczf a sound at the pain 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 intensity is b 0t(iw;kbfy+du dw.yacqiwn *,a8 .($2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB whenjd; uv 8o uwxc9p3o7i; fired simultaneously at a certain place, what will be the sound level if only one is exploded? [Hint:38 ocxudvu; 7wi;o 9pj Add intensities, not dB’s.]    dB

  A person standing a cert jz -gix0y 7sjm)/w hjav*;19(waenct ain distance 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 engine? [H0-tayv ch gm71*a je/zxw;(w njs9)jiint: Add intensities, not dB’s.]    dB

  A cassette player is said to have g 4343e 4xq( zussqpwna signal-to-noise ratio of 58 dB, whereas for a CD player it is 95 dB. What is the ratio of intensities of the signal and the background noi44zx3sqn 3uq4w egp (sse for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output ua;mt+5j ;5 s dpvcya-dgl 6qsj883 45sjtgozof sound from a person speaking in normal conversation. Use Table 12–2. Assume the sound spre-po ;3szd 64j jj85lqsggsu ;a+vtmta5y cd 58ads 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 strikes an eardrum r0yrhi/k9uw xk z mcc9 d*e-(6whose 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 6f ;iwi9)eby b3uv:r(i)v mfqA 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 point 3.5 m from a loudspeaker connectediiybr)e(9w3:6i )u fmv; fvqb 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 wh8 2orub.*vtjwen placed 2.8 m in front of a loudspeaker on the stag 2jo*t.rv8wbue.
(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 differnrvux88gpxn oa3cg p6281 sb 5ence in sound level of 2.0 dB. What is the ratio of the amplitudes of two sounds whose levels differ by this amount? [x p 2n6v5n ou3capbs8g8rg 8x1Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what 1t 5vm)phwws8ikuoldh. ,r9i a r/22yfactor will the intensity inc owuahy hi)t9wd8m ls/2.rr p2k5vi1,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 the fr p yvt(v +:22aolfj-akequency of the other. What is j (k+-l:vo2a2 patyfvthe ratio of their intensities?   

  What would be the sou;h)x;ucc/if; ) fi jd92 gnrjvnd level (in dB) of a sound wave in air that corresponds to a displacement amplitude ofu;d9/ ijcnri;ch2)v;gj f f)x vibrating air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem abhg+-4/ mr7am :f ewhks loud as a 100-Hz tone that has a 50-dB s+b: grafm4h-mk/7 hewound level? (See Fig. 12–6.)    dB

What are the lowest and highest frequencies that an ear can detect when the sougdjl3mi),t:ub) 4)bx gkvjt 9nd level is 30 dB? (See Fig. 12–dbim j g)),tuk9tlvgjb x) :346.)

  Your auditory system can accohi nh n.n4yoex,l)(*bmmodate a huge range of sound levels. What is the ratio of high )hlxn(bne4n.y oi,*h est 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 440 Hz. Thhm q*eb py:ikz. .))ebe length of the vibrating portion is 32 cm, and it )ekz*e:)i bp.mb.yh q 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 thredx0dqz:w8;sj73 - uy q8swayt 28yves e audible overto-vywe 8sa2quxd z yq30wts7yd 8j;:8snes 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 tztz3fj 1tt1 d-op of an empty soda bottle that is 18 cm deep, if you assumed it was a closed tu11f-t3 tzj tzdbe?    Hz (b) How would that change if it was one-third full of soda?   Hz

  If you were to build a pipe organ with 31 nm 5mhvsj8 dsra-+uopen-tube pipes spanning the range of human hearing (20 Hz to 20 kHz),hj8n1+ds- vum3 samr 5 what would be the 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 harmonic. What will ztvs.y1 lt/pagy-*e/ d(gi j4 be its fundamental frequency if it is fingered at a lengtz 4tgy-*a y i1/l.pjsvdge t/(h of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to playo2qa g*;31d+7ltlr vp fn 2a-e/s amrb E above middle C pa mr1n 2+2t*gqsbea;7vr3d f al-/lo(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 that emits middle C (262 Hz) v mg us.9ypo9uyhhh 4inac8 -(2n2dl9when the tempe2 gy9n4y.l9 hi va98(2ucsmdo-nuhhp rature 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 4 v6ytjy 1qrhwzx*nt:6o3 *u qat 20 $^{\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 should the hole bn7 q(xw d2j h,*ylj.nae that must nl( 27*d x.yhwq jj,nabe uncovered to 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 can resonate at gxkuep m(9:z(x -q3s-lkh.v.3 2 5kcuh qjwmm 264 Hz, 440 Hz, and 616 Hz, but not at any other freq 3mm 9hqkcj- z(l(u5q.hgkkxxmve3:s.- p2 w uuencies 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 ends. It la5 )7 x5l hy,u,u0 -bubmywvpresonates at two successive harmonics of frequencies 275 Hz and 33ub)h,b0mw -ul,uv7yx5ya5 p l0 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 f m9ys,5ub)jl t0hrv*$^{\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*efsn8 v: *pok-long organ pipe at 20 *f8s :npov *ek$^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximate/mi:-61ao;nog0 3oh qehl c fsly 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 caf/l 0i31eon-qamoh:6; cos hgnal. 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 rm6 (xm +-)-+t rclunkbg dcf;trying to adjust two strings, one of which is sounding 440 Hz. How far off in frequency is the other strincu)rmrdg ;flk-+- t xn b6cm+(g? ±    Hz

  What is the beat frequency if mvi +)m q8;**o kruzopt8ws4lj iddle 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 ae, p:k (t lqqkru5o:draq,; t,t 23.5 kHz, while another (brand X) operates at an unknown frequency. If neither whistle can be heard by humans when played separately, b5uqrlqp k ae, (:,ordtt ;,q:kut 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 wsjmm6z8 sif;2 p,r cm.hen 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? Expla m86j;imrz sm2sf, c.pin your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz. The teqg,d y.;fyt02 bfngg. nsion in one string is then decreased by 2.0%. What will be the beat frequency heard when the two g 20yq.g ,nb fty;fd.gstrings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if t.6 76viqjqd z7gg/,:jqt :es,z q ltxgwo identical flutes each try to play middle C (262 Hz), but onei,jlz qqt6vxgd .qs/e: 7q6,jtg:g z7 is at 5.0°C and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Forkw2j5ulhodznb)/ + hz. 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 4zlzhj/ )+ 2o.5h undwb 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.z34f j-t/uk biw7xl+k 95dhcs 80 m apart. A person stands 3.00 m from one speaker and 3.50 m from t-kxd+tj /cki3 s4fl7zwh bu5 9he 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 vibrating at c5y/3afz k j7b krw7.f132 Hz, but a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibrat5.j7bkw c7f /a3fzrkying 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)qhxi/yax0i.t.ig 9 e r second will be heard? (A9.i )qg/y ixtiah0 x.essume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’shx dn e oswjz--tk-c0 ;:02yht siren is 1550 Hz when at rest. What frequency donc-0otjht-zyh- ds;kwxe0 : 2 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 deoy2j q;u:)* q7aa xinio2fdv5tect if a fire engine whose siren emits at a2qvx7oo5 :)iua2*jfq;di yn 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 moving toward yf8m htmi697 goou at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exactly the same? A6 o9mtf8i7 mhgre 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 sm) ib df;*h2bjingle frequency horn. When one is at rest and the other is moving toward the first at 15 m/ h;*dfbb2mj i)s the driver at 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 ul 2n7djs;w;dz,gxdps bm :1( 6cdic3kntrasonic sound waves at 50.0 kHz and receives them returned from an object moving directly away from ijzs,;:n p3m2bcds7idxw gd1 dnc;(6k t at 25 m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a w7ajuphjeu/fu lf1yxn;*1bv x te1;6 +all at a speed of 5 m/s As it flies, the bat emits an ultrasonic sound wave witphfx+xj v;ulet 1 f;*y1a /ujeubn716h 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 tuba was played on a w-srq9 dqh4zp*fl4 y5moving flat train car at a frequency of 75 Hz, and a second identical tuba played the same tone while at *pyzdq 9f 4lq wh5r-4srest 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 wavkdk2kbk.8* cunfc17 wes 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 beat frequency if blood is flowing in large leg arteries at 2 cm/s directly away from the souw.nf c2 d1* 8cbkkk7kund source?   Hz

  The Doppler effect using ultrasonic waves of ftcf62g0e jp* urequency $2.25 \times10^{ 6}$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 .ma 8 z;axxkv,sound of frequency 570 Hz. When the wind velocity is 12 m/.8vmx; xka, zas from 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 on land if its spee6a jia;/h4dn bd 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 inz wymu;;vbi.-3 qk7 m/s (a) What is the a-7vuw. ; k biqyzi;n3mngle the 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 of a planet where the speed of soun7+td l1rt)u sd)tixk +6h7 tgud is only about 35 m/ lk1xsit+)tr g7tudh)du t 67+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} $