What is the evidence that sound travels-eu*,nbydsacoa 9fe :98rsy 6 as a wave?

What is the evidence thatlbpklo5- 4g84zf x2 s*j ofnu5 sound is a form of energy?

Children sometimes play with a homem3 0wm- m1kanrmade “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 heard at the other cup3mmr-n1 m0 wka (Fig. 12–29). Explain clearly how the sound wave travels from one cup to the other.

When a sound wave passea: 1(wctq1.*ad)0gl8 ine t ms(lwmhs s from air into water, do you expect the frequency or wavelength to cha(e:tlwmid8g )ml 0s sqh.ct*11a wn( ange?

What evidence can you give that the speed of sound in air does not depend sm;i m8)ufn 1qyeq4*b3js5f zvignificantly on frequency?e48m fb3 5 syqni) *u1fqvjmz;

The voice of a person who has inhaled helium sounds very-):5 o/ggk(r cx neyyw high-pitched. Why?

How will the air temperature in a rhgo;iu:r*)xm a2m2x 0cm+nw c1ue m) zoom affect the pitch of organ pipes?

Explain how a tube might 7 w(7tnv/hlw .ndud(xbe used as a filter to reduce the amplitude of sounds in vari .dw7wtxhd l7nun/(v(ous frequency ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced yb h:- i-p4ab2t usus*6y(yte closer together as you move up the fingerboard toward thee yty 24 -u ass:ypt(i-bh*bu6 bridge?

A noisy truck approaches you from behind a building. Initially you hear it bu8r1i :0 ,p kq ejw,9d:tbxn p0abnkie5t cannot see it. When it emerges and you do see it, its sound is suddenly “brighter” — you hear more of the high-frqbj t5i d,:0bk pe1e9pn,: xk8wani0r equency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to .z69*j6 at v(ekk ymhhbe due to “interference in space,” whereas beats c *zm69kj.ah v6 h(tykean be said to be due to “interference in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered, wouldeegj,dj ; vq-zh/e)5jb o00 bo0hmgn3 the points D and C (where destructive and constructive interfeeoe),-jjq /o0 0gzh;he d03ng5 mbbvjrence occur) move farther apart or closer together?

Traditional methods of protecting the hear0 o4 mat)wcyu8ing of people who work in areas with very high noise levelsu08 wotmcy4)a 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. How could adding more noise reduce the sound levels reaching the ears?

Consider the two waves shown indsl,qam):w 4f6 k ti8oxrak:) Fig. 12–31. Each wave can be thought of as a superposition of two sound waves with slightly different frequencies, as in Fig. 12–18. In m): k)x: slq,o46fad8 rtakiwwhich 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 obse6g47 ldg :gdxix., owuuuc2k *)th: xxrver move in the same direction, with the ,kd )*u: wgcixl.6h4u7: gd ugxo2txx same velocity? Explain.

If a wind is blowing, will this alter the frequency of the sound heard th ;bb6sw8nz8ty9j /ya- lu3b by a person8sw nt;bu hj3bl 6 tay-b8z/9y at rest with respect to the source? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a child in motion on a sc/trf nj yr-1 h*lam7)wing. A monitor is blowing a whistle in front of the child on the gfljc) /-nh * 17rarmytround. 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 the length of a lake by listening cxr*cu;9rb*k for the echo of her shout reflected by a cliff at the far end of the lake. She hears the echo 2.0 s after shouting. Estr c9*;u cbkx*rimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below the waterline. He hears i pajqr5jgo : vw78j:4the 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 does not vary r:i7j8:o45q vpgjj wa significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths mzh;bwjg 1fn5l4a.z/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 foggy dae ys.8lcf z6x8wep k,7y. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How mefpk 78lys.8 ,xz e6cwuch time elapses before the backfire is heard (a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped fb e)g1qp n doury833k zu7t5o7rom the top of a cliff. The splash it makes when striking the water below is heard 3.5 s later. Hqg)7d3zk5tu or7nbo8p3e y1 uow high is the cliff?    m

  A person, with his ear to the ground, sees a huge stonv6qs gn-3p x/he strike the concrete pavement. A moment later two sounds are heard from the impact: one travels in the air and the other in the conchq 36sn/gpv-x rete, 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 errx0fbe eqlz-04 - mo/kior made over one mile of distance by the “5-second rule” for estimating the distance from a lightoxe-zi0-mlb e /f4 0qkning strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the i5iyl z te(+ly +2,cuo x3w)jrd-gl-: 2udrylpain 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 leve.qyb7aa ;y 20j+p zsyhl of a sound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 4 kmrtrbpal5; 8pg 4dp 7 i0f8u2ojop3dB when fired simultaneously at a certain place, what will be the sound level if only one is exploded? [Hint: Add intensities, not dam;73 t pupk8 r0 opd2i4p84ofbr5jglB’s.]    dB

  A person standing a certain distance from an airplane with four equal zt3bvd6 uir/ e-9d3qlly noisy jet engines is experiencing a sound leveldqive39tzr- bu6 l3/d 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 for glwrwq4/jh2 ,h::ic ym- 6jdia CD player it is 95 dB. What is the4: /wym hiq6j:r-g2jlh, w dci ratio of intensities of the signal and the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power out(d frbcacsu, 0i by-22put of sound from a person speaking in normal conversation. Use Table 12–2. Assume the sound spreads roughldiy cb u2ar20cb-( f,sy 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 area isqlhrg y)x6zc:vzrrk81 3 ,8ii $5 \times10^{ -5} m^2$ (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 amplifieiwlm. c:78 tdfaik8+* o6f tker B is rated at 40 W. (a) Estimate the sound level in decibels you wolekkoim d*.:78 t+6awift8 cfuld 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 mt)nsltz ;)4e2en:1ow l6fg f deter registered 130 dB when placed 2.8 m in front of a loudspew)f4 tn)zl2os ftndg;e:l1e 6aker 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 typt 8j)rak-p8h,j lhkr/4 lvm9dically detect a difference in sound level of 2.0 dB. What is the ratio of the amplitudes of two sounds whose levels differ by this amount? [Hint: See h4 - am9h8k)l,8l krtjjv pd/rSection 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factor will the intenh,f8 smedm** esity increase? Increasem *msfed* h,e8 by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but n+)s,tce+c pg2c, zpza+7y edone has twice the frequency of the other. What is the ratio of their intensitiezc+st +2dp p)7zacg ,nee+ yc,s?   

  What would be the sound level (in dB) of a sound wauegvt()4+pc(*kzmo pz ckc2e s:o37fve in air that corresponds to a displacemest7(fzpk2o * ku)cm4gv +3(:ze ccpoent amplitude of vibrating air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound levelmc+u5 b:0smel(z r-yr3 t d3kw to seem as loud as a 100-Hz tone that has a 50-dB sound level? (See 0rm3k b3(l5+ y-zwmcuts:dre Fig. 12–6.)    dB

What are the lowest and highest frequencies 9.goi5sj9bv 6csa w7f that an ear can detect when the sound level is 30 dB? (See Fig. 12–6.owabs9vs6i g5f97 .cj)

  Your auditory system can accommodate i kf8s7u3)c dbt,g*cka huge range of sound levels. What is the ratio of highest to lowest intensity at*kk7 fctbsdi )u gc3,8
(a) 100 Hz,$ \times10^{ a }$ a =   
(b) 5000 Hz? $ \times10^{ a }$ a =   
(See Fig. 12–6.)

  The A string on a violjpj ;h 8t5o/*kr.4tb:w e-8dioxm t kqin has a fundamental frequency of 440 Hz. The length of the vibrating port8qxj4 w.er/ pk jdtm 5*t:o;hi-kb 8otion 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. Whaaqp11hs : 6x5+nh(z8)o+x,ti hise mt b/obkot are the fundamental and first three audible overtone8e5ox, x):1phbo +/(a kisnhb zt6itqo m1h+ss 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,ir 1ds01s 1jgzzf.tz blowing across the top of an empty soda bottle that is 18 cm deep, if you assumed it was a closed tz 0i.1g z,td1r zf1jssube?    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 4k* e d4j5jwevzeq;h9the range of human hearing (20 Hz to 20 kHz), what would be the range of 4k4hz q jv5wj; ee9ed*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. Wbxf:vkzz4 hx:l t :1(uhat will be its fundamental frequu:h1(xtlv bz:kz: 4xfency if it is fingered at a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long ab o5dxo3di 33x 1bgr k9k)j0/5gdht*rps ijd0nd is tuned to play E above middle C (330 Hz). dp)5xtkdrk d j51x3rsgd033 oi90ig/bh*oj b
(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) whpn) h)mmu*ktw9 je+) ren)k jre 9+pnu mw)ht*)m the temperature 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 no0t f8f80clhat 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 7 lav)k)9 1xb,ervzsrdbkc61h19 oin the hole be thatd )nsi,r6lo e7vk1zr v91xchb )a9 bk1 must be 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 resonatmiq3,jthr,t/k n.th uv pxww2( d3 i,u-lq 11ze at 264 Hz, 440 Hz, and 616 Hz, but not at a q2i jt/k-3,twdu muxr3,h 1ihq ,lv1 wt.(pznny other frequencies 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 resonates at two su0m/ mko/ )pjcl) qva c3qdd)*gccessive harmonics of frequencies 275 Hz g) /kaop) )dm mcldv*qq3j0c/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 ho3fabv pa( 6 k41uws)$^{\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 ther ;a0curif2u2m o6h6 d audible range for a 2.14-m-long organ pipe h 62io mru;a udf620crat 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm long. It is open to the outside a/j dvqls3o4u * am)j8jg,fxb/ nd 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 relabm *jv/4,3 d/l8g)qjsxof aujtionship 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 rew6/ sl8l b/es when trying to adjust two strings, one of which is sounding 440 Hz. How far off in frequency is the other string? ±e/8/ l6sebrlw    Hz

  What is the beat frequency if middle C (262 Hz) eqhw f(tw be3o* bf6f,ig0)8uand $C^＃$ (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 anot.( 3wog(p ffqzher (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 simultaneously, estimate the operating frequencyfg.pq3fz (w (o of brand X.    kHz

  A guitar string produces 4 beats/s when so wln,a-)wkaq 2unded with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency ofa wkwq)l2, an- the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequenq.i e;bitqi u3*gta p;/0s.fh cy, 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. 11–i;*;.its b3tu/aq .i eqp0 gfh13.]    Hz

  How many beats will be heard if two identicns 4 (0apk bags2aokpri )4n2:al flutes each try to play middle C (262 Hz), but one is at 5.0°C and the other at 25.0 ani(2pg:o kp40bka24rsa )n s$^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a z m:9f nkcuxnjh;o 0,;frequency of 441 Hz; when A and B are sounded together, a beat frequency of 3 Hz is heard. When B and C are so;x;9homfn j 0,znuk:cunded 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 3.00 m frot6ybtuxc*u+ /m one speaker and 3.50 m from the otbu/x ctuy +*t6her.
(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 afi j),k g+t ,i,kg ojpd(/kq1pt 132 Hz, but a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibr, j(kig)jp/,fg 1tipkd+k , qoating 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 beats3.lws :gmj 2t ryn0o;bvsv*8 h per second wilgt0s hyw.m2nobsv*v8ljr :3 ; l be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s siren is 1550 sx22n r(3okwcHz when at rest. What frequency do you der22o(3kcwnx s tect 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 frequenv.;9i :mljj yyx/ u6kbd cwb9p ;(e9ffcy do you detect if a fire engine whose siren emits at 1550 Hz moves at a speed of 3/e ky9 :bxf9vydf6;(luc iwjj;m. 9bp2 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz source is movin0 ;-fwyyhxzej6m-0b,k eide 0g toward you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exactly thex0-6hz0 ey jd0 iefmb;-w,yek 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 s4dcx/ wkwzb 7*z xz88qi/4uzthe same single frequency horn. When one is at rest and the other is moving toward the first at 15 m/s zb w /s4dkuiq4xxzc8 w*z7/ z8the 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 receives t.xf5 n. /qi/tvrt* d wnh;bpqq8x:bq)hem returned from an object moving directly away from it at 25 m/s What is the rec. 8xt:*n;f)n/ 5rqtbi qqhx/bdw p qv.eived sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wal00te9ssb -l hnl at a speed of 5 m/s As it flies, the bat emits an ultrasonic sound wave with frequency 0hbss-e 09lnt 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 moving flat peb w-x .g8, 5ye3gj5rz 9yhuh5oqr/f train car at a frequency of 75 Hz, and a second idenwh eqgj5 8b-h,yr9e5p/y z.3uf5gx or tical tuba played the same tone while at 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 ultrasound waves to measure blood-flow speee doe.q1km1 h :46byizxk ;z9nds. Suppose the device emits sound at 3.5 MHz, and the:q b. h 1kzekedo6zn y94i;mx1 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 sound source?   Hz

  The Doppler effect using ultrasonic wa*etj4u(u oqb 5hhh(*z ves 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 a-pal;onb o ,996v.ww9g jdjgof frequency 570 Hz. When the wind velocity is 12 m/s frdv;b ogwa9 9ogjp nl 6.9-,awjom 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 iqldj- ./kr1o(+rteq z ts 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 Mac0:.+q8 olxrdorpz2 2x aad16x9c pfndh 2.3 where the speed of sound is 310 m/s (a) What is a90.ar 2oxp frx:cn1q+odlzp8d 2 6d xthe angle 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 souy qj(yb,81z.we u1uiwb1uey -nd is only about 35 m1,je.8z1ue 1wb y ywuub(iy -q/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} $