What is the evidence that sound tr;jeg)s4ka. r x8pg i*pavels as a wave?

What is the evidence that sound is a fom5k cug:ow x6( z4cv*orm of energy?

Children sometimes play with a homemadek)4b)vdnsq(8t do shma/ w56h “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 heh t4 k5a8hnod d/w)bqvm(s) s6ard at the other cup (Fig. 12–29). Explain clearly how the sound wave travels from one cup to the other.

When a sound wave passeseb0 upx *fk/6 z(kla;bej5o2m from air into water, do you expect the frequency or wavzu;l p( *afk5j k2oe6mx0/ bbeelength to change?

What evidence can you give that the speed of sound in air does not depend signifpw d9 o: evsm*h/q+-vxicantly on freque* dswme+/vh-xo:pq9 vncy?

The voice of a person who h *z/por2c vtrzh)r 7yyo::i*gas inhaled helium sounds very high-pitched. Why?

How will the air temperature in a room affect the pi /j.-szx n94fyotbio(tch of organ pipes?

Explain how a tube might be used as a filter to reduce the amplitude 65uo,j 9f a* bl)dlhceof sounds in various frequency ranges. (An example is a car muffleo)j6*ebd9h5 lul fca, r.)

Why are the frets on a guitar (Fh)cu91za86nc v tj;w uig. 12–30) spaced closer together as you move up the fiuw; 1vt)hza9j6c u8 cnngerboard toward the bridge?

A noisy truck approaches you from behind a building. I0:,k8jlrrpo;l +ejh 87u 9r9tgp vicanitially you hear it but cannot see it. When it emerges and you do see it, its so,k8gvl cti;l7uej0j o9ppar 8:9 rhr+und 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 rj04r3(eawdfuftd ,9d 0zr,fbe due to “interference in space,” whereas beats canf94tfur j0rr d(ez wa0 ,d,fd3 be said to be due to “interference in time.” Explain.

In Fig. 12–16, if the frequo(f,r)b gp,df gj4-iqency of the speakers were lowered, would the points D and C (where f,jg 4q) giofdr,(p-bdestructive and constructive interference occur) move farther apart or closer together?

Traditional methods of protecting the hearing oqxv2 a*qo 5tr771t bagf 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 g7br o5a*qtx7tq21v a 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 a sups zi askaipq:- rr f48g2*k5oml3;u (lerposition of two sound waves with slightly different frequencies, as in Fig. 12–18. In which of the waves, (a) or (b), are the two cgqsz:2rp 8fak( kom sr* u4li 5-i;a3lomponent frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and observer move in;*uvf*o4liw aigz* o: the same direction, with the same veloif;:* go wu*z *i4ovlacity? Explain.

If a wind is blowing, will this alter the frequency of the sounck0zl:1xku u ,nda -p5d heard by a person at rest with respect to the source? Is the wavelength or veloxukc10z-,5kpun:a ldcity changed?

Figure 12–32 shows variouswig+c7v7eo +rmo d j; sjl)1c,cd g79t 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, will the child hear the highest frequency for the sound of the whistle? Explain )+ ; c7mgw9jjot gsl+,dvo1cr7 ide7cyour reasoning.

  A hiker determines the length of a lake by :aqcxe5 iyw46o(6 h rgv:eq5 nlistening for the echo of her shout reflected by a cliff at the far end o4ac5nq6q xew: g6(:eoi hyrv5f 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 ship just below the waterline. He hears thxo+30t owg(wpv3gfs az e9b ;;p2/koke echo of the sound reflected from the ocean floor dxe3kwo9k t +oa3p ( sfp;;gb /v0zw2ogirectly 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 wavelength; 2(,.tp.j eahuq sqvos 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 dr7ltrz eh 4i,3kifting just above a school of tuna on a foggy day. Without warning, an engine backfire occurs on 3ri 4eht,k lz7another 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 mipesve51w;v; 4f r(usplash it makes when striking the water below is heard 3.5 s later. How high is the ;r54 ;p1(s emu feiwvvcliff?    m

  A person, with his ear to the ground, sees a huge stone strike the conc x7bi:6ktsf dkk)i7 1)oc(rrcrete pavement. A moment later two sounds are heard from the impact: one travels in the air and the other in the concrete, and theyc7rxt1b6 rckkd(fsi) ):7o ki 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-s-q /eq;5h5g feufd l e3hbi:m t:2bhr2econd rule” for estimating the distance from a lightningh 55ehbe:r-ig:;fmut / bfqld2h32q e strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a souguoc 9bgu8unnytk1hf( i51-6 nd 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 whoseba3vivf0 i)t-pv/ 4t2pi xwv - intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce gr vx/ob3ls7+*n1e u fa sound level of 95 dB when fired simultaneously at a certain place, what wilnvo3ru/xl+s1g7* fe bl 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 fourn jzsha4jg((.vjb2sd c gh/ 5, equally noisy jet engines is exp2hvjb.a5d( jc,zhsj( sg/4 g neriencing a sound level 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 ha.zioyka1(oa 8p2 (9 em 1e5x0xmalsv lve a signal-to-noise ratio of 58 dB, whereas for a CD player it is 95 dB. What is the ratio of intensiamo i2lpmz8 x9sa vx05(. e1k(l1yoaeties of the signal and the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power og1-6 bp;)e9 e be yr0xss:(fkx6f+j; lkovesputput of sound from a person speaking in normal conversation. Use Table 12–2. Assume ;+ybejke:f)6f0g;sp16 r- osksx(e leb vxp 9the 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 strikes an eardrqeg70v rv 39xrum 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 rated at 250 W, while the more modest amplifier B is foyoat : gfs;83ivh-ac4u 5l;rated at 40 W. (a) Estimate the sound level in decibels you would expect at a point 3.5 m from a loudf8gi5-3o vasa cftu4oy; :h;lspeaker 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 pvc 41:mwc ;fxolaced 2.8 m in front of a loudspeakeo xfvc4m:1wc;r 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 in sound level of 2.0 dB. Whaty7g*b/ znm 3fj is the ratio of the amplitudes of two sounds whose levels differ 3*y/b7 gnjmfz by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of afh1/1 8 ybqdnq sound wave is tripled, (a) by what factor will the intensitfdqn1bq/ yh1 8y increase? 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 h3gz- b*py uerm8,r. loas twice the frequency of the * ,8r3bgzl-m.y rueopother. What is the ratio of their intensities?   

  What would be the sound level (in dB) of a sound wave in air that correspond0m nlcws. 2c: np6o+ugs to a displacement amplitude of vibrating air molepmc 0+6os. u2w:nnclgcules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem asp4ae wd2 6g1t sg q61 h1jo,yz,kyqse( loud as a 100-Hz tone that has a 50-dB sound level? (See Fig. 12d h o(6wgs ,g4q pzyyk111e2 aejt,6sq–6.)    dB

What are the lowest and hi)m -i9k 5;z pknmz) z/0lfof 9zgin nqz:m5*gkghest frequencies that an ear can detect when the sound l-9fklm:0k m)g5;nkq*ogn5z mpi n/zi fz) 9zzevel is 30 dB? (See Fig. 12–6.)

  Your auditory system can azllbmogl;- 79d z..coccommodate a huge range of sound levels. What is the ratio of highest t-l.bdczzl7.; o ol 9gmo 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 l2ctwxxh jvki6rzw/ 7 r3)/s6of 440 Hz. The length of the vibrating portion is 32 cm, and it has a massk3 xlcwtwr) 7i/x/hv srz62j6 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 aus0jawku(;,stb6kl.r0l; qe mdible overtones if the pipe issejwbq;(uk06.0 s;mklal, t r
(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 wor,yks8/ dryop4 76wda2bn:e-v) kpgduld you expect from blowing across the top of an empty soda bottle that is 18 cm deep, if you assumedp rkwddos ny,:2av6-7rey4bk8 /p g )d 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+hgkv(f) 72y 4 :sudu:djztus a pipe organ with open-tube pipes spanning the range of human hearindj k)f:( d:usgzus 7h4+yv 2utg (20 Hz to 20 kHz), 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 540ev(u fw sim;,2 pvh9-4/ gfbay4ss*lz Hz as its third harmonic. What will be its fundamental 4if-s;2legv v4hfyma zp9(b,sw/ *sufrequency if it is fingered at a length of only 60% of its original length?   Hz

  An unfingered guitar strls,jhkm8kacud bbhm92r/ 8:* ing is 0.73 m long and is tuned to play E above middle C (33cdjkushl2b: /,8kb*h8m9 ar m0 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 emitex(z k(.:2j vb:ly+qra t5wsqs middle C (262 Hz) when the temperatleq+xv(5.: yrst wkazqj2( b:ure 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 2-4:qs9q oxkz1vz 0wd b k 0h*kebii+e:0 $^{\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 hge l9-n lcw+o4ole be that must be uncovered to play D above middle +nl4wec9o l -gC 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 Hz, and 61fgx()pski) : y6 Hz, but not at any other frequencies in between. (a) Show why this is an open okgy) xs:()ifpr a closed pipe. ----待选择----closedopen  (b) What is the fundamental frequency of this pipe?   Hz

  A uniform narrow tube 1.80 m h* gkd6e6ij21q4 allslong is open at both ends. It resonates at two successive harmonics of fregd4l* 1k2j l6 hsaqe6iquencies 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 3;4ani a2jze- p rtfn1$^{\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 (zu*mcwh w8wp:, /ocg 2.14-m-long organ pipwm:cgpc, zu * oh(ww8/e at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5wdjsii)7s.:tg* yh 2y 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 iiyg2dys:sw7. htj)* 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 when trying to adjustxy q(t l/yutldu/)3h 0g+kr,c two strings, one of which is sound+q ghly/x(d/ 0uryc)ultt ,3king 440 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequenct)+en:t70 ma 5yki)iik /oc fly if middle 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 (brandxcwe (b,24daeeq 7j f, 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, esawj(7q x,e2b fc4dee,timate the operating frequency of brand X.    kHz

  A guitar string produces 4 beat ls(w r*z3otts8 ffos;(ffhn2z.5ss8s/s when sounded with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrh(wtssf .tnf(s;5*zfl sfo rs3o82z8ational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the -p. t a0iz,(20cmnz xvagh6qr 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? [Hint: Recall Eq..ch2az(v 0rtizn0q x6-g,p ma 11–13.]    Hz

  How many beats will be heard if two identical flutes each try to play middle tgoi:mh7 n 1r1yx(oy 51l)sveC (262 Hz), but one is at 5.0°C and the othiy1:t mvoyeo 1sgxhn (5l1 )7rer at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, 9o;+5fmycoct2oy0 u.x4ll emB, and C. Fork B has a frequency of 441 Hz; when A and B are sounded together, a beat frequency of 3 Hz is hearcemuom20;+x. f l oyo59 clty4d. 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 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+cy2oj r-u:g wbh* ci(.00 m from one speaker and 3.50 m from the other. *:cc uoi gj+r yw-2hb(
(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 132 Hz, but a w6sg5krqq te51vxt vj78 5 ug8piano 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 frequencg7t5sk856wxq8j rtvvue5g 1qy 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 bwpa9s hxd+f8 5eats per second will be heard? 9pd5xs +a f8wh(Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequqo* ,tslwlgzp( zb939 1,ymp zency 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 30 m/s l*o9z ( z3mbtg1 wspyl9qp,z,
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still.qvkki;*j qyi b 3q5e+op+n8)c What frequency do you detect if a fire engine whose siren emits at 1550 Hz moves at a speed of 32 m/s b;3cq8ej+pq nykivk5q +*oi)
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz source is movinfoi1 3e(48i7l.rb vuo tzj u m;oe35kwu0d1ctg toward you at 15 m/s versus you moving toward it at 15 m/s Are the tw8o1it4tej i bl7 uz1e.0w v k3c3r5omu;o (dufo 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 o v0gb.j4s ax/jc,n7mt ne is at rest and the other is moving tos0mj/c4 tan.jx7b v, gward the first at 15 m/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 ultrasonic sound waves at 50.0 kHz and jtnvm+ba3 6jk zd5 i4*receives them retv ji*n zb65 ja+mk4dt3urned 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 walzpr k b(kl;xei* :2;9rtbfh 6uguy)- .3kfekv l at a speed of 5 m/s As it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency does lkk *)kh;2; v:3br(f rux 9-f .p6tiguekezbythe bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Dos1 vo(e4 hfs5g1*eztp4zgxs3 ppler experiments, 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 at r*15hf4 1esgsx to zg pv3sz(4eest 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 u7/ ha nr1.drvmltrasound 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 beat frequency if blood is flowing in large leg arteries at 2 cm/s directly away fr ah7 .1dnm/vrrom the sound source?   Hz

  The Doppler effect using ultraiysopb vz0 .u/j4(n1wmh f59 gsonic 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 is 12c p3ne(q ; jiz 0xb/gxaads,55 m/s from the north, what frequency will observers hear who are located, at rest, i;cs0e5 g,bq5dp( 3jzna ax /x
(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 landvl ralk n/y2c/ 672tov 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) What iz ,uvykq8x8u* s the angle the shock wave makes with the diry8k * zvx,quu8ection 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 wt tpi8x*i8-pb hcs(9 where the speed of sound is only abi pt8 s p(8c-ih*bx9wtout 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} $