What is the evidence that s-phmr 7cy gedm:sbjms-o19(3ound travels as a wave?

What is the evidence that sound ist/g5k z k:ev5sa v9no9 a form of energy?

Children sometimes play with a homemade “telephone” by attaching a strizm xby/j)i9h6 ; uqj6oxu 21tyng 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 thy t/)u2xy6h jxi jbzq 1o9um;6e 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 wav8l 9jzeohkcaa23:s7 x s :5hqd bj-iq(ele58 72esbz:o:3h- s jaaqc9xj dikhlq(ngth to change?

What evidence can you give that the speed of sound in air does na6 yrwpu65rmqbt9-5-9qeyqa ot depend significantly ou-b9 5eyq9a-q5a 6 rqm w6ptryn frequency?

The voice of a person who has inhaled helium sounds very hig r5 is -wes +f)q54-zrcnk*yngh-pitched. Why?

How will the air temperature in a room affect the pitch of orgfyg;f)v/ brsc dw*2:0u .sgc qzfak; 9an pipes?

Explain how a tube might be used as a filter to res)8m8 5zgkiw pduce the amplitude of sounds in various frm)spzwgk5i 88equency ranges. (An example is a car muffler.)

Why are the frets on ahid*7yu*k ,(pr3 a ktt guitar (Fig. 12–30) spaced closer together as you move up the fingerboard toward the k3a(ti t yu*7*kdr p,hbridge?

A noisy truck approaches you from behind a building. Ini7y7 (5yve*k-3k4w4mjjjz qy sb(aocqtially you hear it but cannot see it. When it emerges and you do see it, its q*m 4yv7z7kskwej q(y4c jj-a(5 o3ybsound is suddenly “brighter” — you hear more of the high-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be saidb 1 1r y9l1avmia.exd+ to be due to “interference in space,” whereas beats can be said to be due to “in 1iv+rm1 aya.e 1dx9lbterference in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowereo 143kvay1cy 1f.pg ,tbf*tja d, would the points D and C (where destructive and constructive interference occur) move farther apart or closer.4y1113 g kjo,b vc aapfyf*tt together?

Traditional methods of protecting the hearing of peo+y:nmrcy. pnbzey: b z8l;3 6vple who work in areas with very high noise levels have consisted mainly of efforts to block or reduce noi nbyzm.: r:;8vc lb6y+py3zense 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 ears?

Consider the two waves shown in Fig. 12–31. Each wave can be thought of as:p ,qh fh/f5gk y i0wwxdq18vc(a/c g/ a superposition of two sound waves with slightly different frequencies, as in Fig. 12–18. 1 /h8yc khw/(gwaqdcqvp g 5:0f/xf,iIn 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 source and observer move in the same c )7nvd4k;dx ya4 u*sluch nm6d+m4 -qdirection, with the samuv4) n4*n6xuh cl;dds mak7+dq - 4cyme velocity? Explain.

If a wind is blowing, will this aow/x+zn++ 7ha f1h uahnai )m(lter the frequency of the sound heard by a person at rest with respect to the somwxh hz(io7fhu1 +aan +/n a)+urce? Is the wavelength or velocity changed?

Figure 12–32 shows variousykv t238 3e vo+rjd /s;qg+qal positions 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, jy8 s+aql/gqed;v2+ 3tov3kr 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 for the echo of her shoutwiq gv7ezebbmp2f p6ei4 i5l53l2,(a reflected by a cliff at the far end of the lake. She hears the echo 2.0 s after shouting. Estimate the length of the 7lvambepipi q 2(ef,4g3 we6b255z illake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship jus5iupfzw)1gh bdqey+ ehz/ )),v : g 3,qnnhdv-t 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? A3yh/,,:znu5p q hib) dhz)) -egw+gf n vqde1vssume 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 wab3nd.b.ayl( ) fw ug5gvelengths 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 driftingf-v5xl9/ *s.;zw ihexad,w do just above a school of tuna on a foggy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How mx l e,w;diad x .-*w/5fzos9hvuch 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 1,6hg+z q9lfe x)lkfdstriking the water below is heard 3.5 s later. Hleqhgf,) 1 ld+6fxk 9zow high is the cliff?    m

  A person, with his eardj(0cwsfe. ,q 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,f dw se(0qj.c 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 : zok((svy q,yerror made over one mile of distance by the “5-second rule” for estimating the distance from a lightning strike if syk,zq((yv: o the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pain )ktnj+qp v +33;gbb0mhzwu)i 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 u97lo cb,feb13yt5cb intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers prod 4eq ( f(qzfkn):usnu,uce a sound level of 95 dB when fired simultaneously at a certain pz: nfuqn u)sqek,f((4lace, what will be the sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane with four equallr;,uz,rfo+dk* c u: x:c0pgh )pul9pmy noisy jet engines is experiencing a sound level bordering *),oz:kp:ug pr upulfr;m+ c,d 9h0xcon 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-nc6yh.u jatce+,p,tc*oise ratio of 58 dB, whereas for a CD player it is 95 dB. What is the ratio of intensities of the signal and the bacc6+t ,p u *ht.,yccjaekground noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the powex:w3jwfynrg, x8u e*1,q /jm 7fmm tp+r output of sound from a person speaking in normal conversation. Use Table w,m8pmjgqwxrxmy t/,ju nf+*:fe173 12–2. Assume the sound spreads 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 strhcu*f 0yw 1fh3s w+et*f 0ig4nikes an eardrum whose 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 A is rat r0g8h;q9snoqwi s*x,ed at 250 W, while the more modest amplifier B is rated at 40 W. (a) Estimwx g8i,nrs*0sho9q ;qate 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 mvr6 e6e- dnem. in front of a loudsed6v-6e. enrmpeaker 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 in8ojthvs. +7m9wnag 6t sound level of 2.0 dB. What is the ratio of the amplitudes of two sounds whose levels differsnagwjmv87o 9t t.h+6 by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is triplesp56 fwvh,ro;twb 1b) d, (a) by what factor will the intensity ;6rs tobw5p fw,)1v bhincrease? Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but o7y0ui-t4xn om(+br v ine has twice the frequency of the othenx(+ 0bom7r4t-yiviur. What is the ratio of their intensities?   

  What would be the sound levgwy*ji *5mf4 wel (in dB) of a sound wave in air that corresponds to a displacement amplitude of mj g**45wyfi wvibrating air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must havcrw 5dtwm )nhx5zz vl.58n+-pe what sound level to seem as loud as a 100-Hz tone that has a 50-dB sound level? 5pzzn+dr5h5m.cl8- wtwvn) x (See Fig. 12–6.)    dB

What are the lowest and highest frequesrqt5h -2qk 7r;/ gwawncies that an ear can detect when the soun-srtrg/ awq57 khq2w;d level is 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of sound lev1 mg /at :5cy0nqqd5byels. What is the ratio of highb5:qm 50yya g/qctnd 1est 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 violw.:nuraq ks09 hru6s1in has a fundamental 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 mu r sw.6hs0u:qrakn91ust the string be placed?    N

  An organ pipe is 112 cm long. What are the fundamental and fi0+w gt3ahg ov5rst three audible overton3 0to+vhggaw5 es 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 blowingur1( yl qrw y/),c.rfi across the top of an empty soda bottle that is 18 cm deep, if you assumed it was a closed (yry if/r1. )lq,cwurtube?    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-tubfgb ty/- is+qs23lqt5e pipes spanning the range of human hearing (20 Hz to 20 kHz), what would be the range of the lengths of pipestt2qys+fg/ ls35 qb-i required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a frequency of 540 Hz as its thit4b /dzrgmd1 rm 5(8wnrd harmonic. What will be its fundamental frequency if it is fingered at a length of5w dr 41/ngtbrzmd8(m only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to play E abovxfzuaaj s *e1j5 8w8krullyvf /7 3z*8e middle C (330 Hz*ez8l 58/u*jk rfx8lwjvazfs 1ay3 u7).
(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 lengagm* n c7f/f-ox+5i okth of an open organ pipe that emits middle C (262 Hz) when the temperature ion+x7o f*/if5ac-km g s 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 20r2c og sxx-t r9n:j0m) $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flute in Exam;ihov aw1 5.n/ x4-rdp y(uvpdple 12–10 should the hole be that must be uncovered to play.p oy (aw-nvu/d4 ix51vdph;r 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 264 Hz, 440;-myttt .5-kjtkz4- ;wyhqr 1,pa big Hz, and 616 Hz, but not at any other frequenciek tty4-,ym;-qak.t zh g-5;wrbjpi t1s 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 qt:kez um+28m open at both ends. It resonates at two successive2km :u+zmq 8et harmonics 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 n t ulq/ditoz g s 0par2cm*(q15u0c+6$^{\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 ap2 k9srs));pd3 qbd;:vyja o rre present within the audible range for a 2.14-m-long organ pipesp yq;a9v d) b)k2ro pj3rsd;: at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approxima a6e vai7dy6 u uo yb9g33z0ysp:zgr0+tely 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 rela:b36yya zau +vog ur90de g 0zi376ysptionship 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++d l:t/ifn(df421 meujzgoy s when trying to adjust two strings, one of which is sounding 440 Hz. How far off in frequency is the other s1+ 2mfy(i lodn4gzut je/: fd+tring? ±    Hz

  What is the beat frequency if milejm e;i-j1 8ccof* /7xcl4lkddle 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 3 f -xgsbh;2; hm;/ixiizh0fxoperates at 23.5 kHz, while another (brand X) operates at an unknown frequency. If neither whistle can be heard by humans when played separatfx igi;3f /sx-; hh2bm;izxh 0ely, 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 beats/s when sounded with a 350-Hz tuniwdvc0/s-qq u9 0.ur2vfr)k )rlnv 8xzng fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequenc8 -wkqfdvvc09 l zu rr0.uq)v/xn2sr)y of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz. The tension cejdt2ojud*/k9;ygj x : j)ahq, *4shin one string is then decreased by 2.0%. What will be the beat frequency heard when the two strings are played together? [Hinjj;4* :co,uthqx2)dj e/gj hdk*y 9as t: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identical flutes each tr pm-orm3rsv1fe ,*iy7vw 6 /ely to play middle C (262 Hz), but oee3-w6 v,riv mo*lp7fr1m s y/ne is at 5.0°C and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a frequency of 441 H 6;0cmtbd l +b1l0z wgjko(7fjz; 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 freqdw7;kt6mj0 ocbg+l lb j0f( 1zuencies 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 3.00 m from hqh9vm 2y8iq 7gwy46cy pj;x4 one speaker and 3.50 m from t4qmyw; i86g7 y 9 xhjpqvcyh24he 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 supposem.gk* jb bx(list5:h( ;mf)mgd to 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 the frequency *5ifs.b t(ghk ;mg:xjb (m )mlof 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 manya7ztq3 m rh+8gwxyb7j.z 4) wo) hox9c beats per second will bozw7 +bh x toqyc)w374h 9.8r xm)zgaje heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s si+txl gi-,gy+ vvs xj*.ren is 1550 Hz when at rest. Whg+xyg+i ,x ltv*sv.j -at 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-g0d jfq6,g3rr-+nc t7dy epi detect if a fire engine whose siren emit,ced-r6j 3n- yt7gfpd0gr+i qs 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 moving towardl5599tmbp ido you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exactly the saml9i pm5o td95be? 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 frequek1zg* l,4n edk6v)wz hncy 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 ezw6hn, )d 4lkkev g*z1mit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at 50.0 kHz and receives them:(k0 blc;*x iam.wknjp19 im0qykp; i returned from an object moving directly away from it at 25 mj .xclpk ma;b:miikpi*qn y01;k0w( 9/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 emitsk /r hzm.4:dhc an ultra:/ zcdkhhm4 .rsonic 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 oq zvah 3ihc4xh7/5r8experiments, a 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 at5a87qhchvi4/3 xz rho 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 yzkfn*e a+a: ,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 Whanz*k+ :e ,yafat 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 wa(wcbntxro+y4x*:d 7 aves 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 velo; ,l okc(0x9 moku*mv set;nu0cx6a;r city is 12 m/s from the north, what frequency will o 0mlx;costeu* 9m; v xrcakon,6k (;0ubservers 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 s v et*el+mus9-peed 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) Whq 78sd+uzg6 ik7l p,;v )jvzlhat is the angle the shock wave makes with the direction of the au,pdqg ksl6 )z z;vhvj8 l7i7+irplane’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 soundss(.;eucb rgd3i(rpr/9c s0quvq f 92abzb9( is on9q.urv aprfu 9is;cq92bb((g 0/bds s3c(re z ly 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} $