What is the evidence that sound travels as a waamt8 ozi(2ab kw8l t;4ve?

What is the evidence that sound is a fosp;4 ,wab)k)lzq: wwurm of energy?

Children sometimes play with a homemade “telephone” by attaching a string to t v/o/ 6yheoubr)e*e/mhe 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 (Fig. 12–29). Explain clearly how the sound wave *b)e e/muh6rye/oov/ travels from one cup to the other.

When a sound wave passes from air into water, do you expeoo ya9uij8l1p ,nt,m 5ct the frequency or waveleyj581m u ,na ,9piotlongth to change?

What evidence can you give that the speed jnsje72a /zd yaj;l83 of sound in air does not depend signifs jl;a2/7eyja38d nz jicantly on frequency?

The voice of a persoq*. hog6*bceun who has inhaled helium sounds very high-pitched. Why?

How will the air temperature in a room affect thenv:(wu qz2z z8/3jpd8 9j yuo (aw(odm pitch of organ pipes?

Explain how a tube might be use+juny- ureue7e+f,p3 d as a filter to reduce the amplitude of sounds in various frequency ranges. (An example is a car ye+ nupe7u3r+e ,fu-j muffler.)

Why are the frets on a guitar ( h.sgl9+)x*v u fbl: p5v,kdogFig. 12–30) spaced closer together as you move up the fingerboard tphx5.g,vk:duv9 +l l o)g *fbsoward the bridge?

A noisy truck approaches you from behind a buildiaw+gs1y*h*u fp,tz )f9n*lvl ng. Initially you hear it but cannot see it. a**l wsuhn p*,gfflvzyt19)+ When it emerges and you do see it, its sound 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 be due to “interference in sj.ze 6. bspjh1pace,” whereas beats can be said to be due to “interference in time.” Expl6h .bpz 1sj.jeain.

In Fig. 12–16, if the frequency of the speakers were lowered, would the points u2o2xa1cxoyezw7z7e:)z j m. D and C (where destructive and constructive interference occur) move farther apart or closer together? 7x. m ce2aexow:zzy217)ojzu

Traditional methods of protecting the hearing of people who work in ff1 la,y,h(zeq8rt(t8ddcy) 5y r9mgareas 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. How could adding more noise reduce the sound levels reaching trz9 q)8etycg,d 8md f fat5r1,l(yy(hhe ears?

Consider the two waves shown in Fig. 12–31. Each wave can be thouo6:+ g )paicsaght of as a superposition of two sound waves with slightly different p sao)a +:icg6frequencies, as in Fig. 12–18. 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 source and observer molld;0s fhe bfz wkw27j82ly 1 p;c:8ks+dz. lwve in the same direction, with the same velocity? 8ywfw:0 b;ll l;wkzsed kp 7fc22.h18zslj+dExplain.

If a wind is blowing, will this alter the frequency vlw.tju0wc 8,x 0j.*fbyv)kiof the sound heard by a person at rest with respect to the source? Is the wavelength or ve vt bj0w jvylc),0 k.f*i8u.xwlocity changed?

Figure 12–32 shows various positions of a child in motion on a swing. A:7;3)x 7ypfav f3a9vn dz qdum monitor is blowing a whistle in front of the child on the grom3):d dnf7 zvxuf y9p7vaq3a ;und. 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 oz:7w3 gc l1ujnz*:ycg+o8zs dbj8r: af a lake by listening 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. Estimate the length of the lake.ds7bo18cg g rz ca::8ul nyj+*3 jzzw: $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side o 7xqb0b*sw1.mxf*3dno d)ywlf his ship just below the waterline. He hears the echo of the sound reflected from the ocean floor direm of*7s d30wqdl) xbyw1*.n xbctly 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 wavelen: f. :txk-6ucd bjjo6sgths 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 f.zq:0 bti .zituna on a foggy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How much time elapses before the backfire is heard (a) by..ii :tqzzfb0 the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a cliff. The splash it makes d:zzl)yw2g/jvl,w-wf g 5 2k dwhen striking thed:f/zg dw-wg)kl,y5jv2 2z lw water below is heard 3.5 s later. How high is the cliff?    m

  A person, with his earq.7x)1s eaaos 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 apart. How far away did the impact occexo1.s aaqs7 )ur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one mile of distance by the “5-second rv/q3/j ydnxlbt;t9)nb, 40q oq7 xhoeule” for estimating the distance from a lightning strike if the temperature it/7/jx3 4edb; y ov9qo0nnqbx q,)lhts (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at n k zj- l9)d4: ntava:c7ccq0qthe 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 wh3 cy2tco5g fhya6lh zi )u77f*ose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound ) oygn1 lug r *klx;m*exul;:.level of 95 dB when fired simultaneously at a certain place, what will be the sound level if only one is exploded? ;xo ;e* .yg rl)mlg:x uln1uk*[Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane with four e,pzxas5 w (gl4ht+ hc5qually noisy jet engines is experiencing a sound level borderin zawlp5hgt+x cs( 4h,5g 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 swz v38e48(inryjbb vbtvx8uha,9(6 cignal-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 noise for each device? 58 dua y rezjb6n v8(9iwvhvc4 t,xbb(838B =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from a person speaking in normal r 8ldg3: r38s f3y ufqc*z;nv0i cbj7cconversation. Use Table 12–2. Assume the sound sprea;7fgznfsryr: 3id qv0*3b88cu j c3 clds 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 strikespxi-,anqhd3 w8-q1( nr t 7p8vwt plm+ 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 rated at 250 W, whi1di vz u,b3g35pr-p)bi7bya ble the more modest amplifier B is rated at 40 W. (a) Estimate the sound level in decibels you would expect at ag)p7 bb33ubbp i5,ri v1z- ady 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 registere3y*zzcc5 om; it al p7-.xblomgi5 x86d 130 dB when placed 2.8 m in front of a louy75xx.m;impg-cloi5z a*cb zolt 368dspeaker 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..8 .q l)djl fphdbn5c*0 dB. What is the ratio oj*bc5q .fhnd)8dll. pf the amplitudes of two sounds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sounp e t:xa k9syz*xqer1.n7sw74xy b*h+d wave is tripled, (a) by what factor will the intensity increase? Increase by a fe ry*hpk s yq x:xx1es7+9*tn7w a.bz4actor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but ; +4*ixu-jnhx t 9onokone has twice the frequency of the other. What is the ratio of their intensi+4 x itnn xj;uk-ho*o9ties?   

  What would be the sound level (in dB) of a sound wav+ ns:cmdu) o8 fxi,gj0s etq,2e in air that corresponds to a disp8dq02),fsnxo: mj, cti eus+glacement amplitude of vibrating air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud as a 100h50:ru es)g(fc tc-z u-Hz tone that has a 50h)su5g(:-cf uc0te zr -dB sound level? (See Fig. 12–6.)    dB

What are the lowest and highest frequencies that an ear can det9*4x1-f q,i6an wfkbugdjtn .xyq 3: bect when the sound level is 30 dB?j-d,x*ynbq .nf9xik634waf 1gu bq: t (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of sound levs1 5 7o pm2iyfh)je1yaels. What is the ratio of hief1h)a2 joy 17ysim5pghest 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 freqgg f,smc+:/ac)v6vsp/elu- c uency of 440 Hz. The length of the vibrating portion isc,:cvpsc 6 +f)-lagu //evgms 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 fundamentaoolt5h 91z1cj rtm-p4 l and first three audible overtones zmtrj91lph4 ot-5 o1cif 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 an e,w e 0sxk0ue9bmpty soda bottle that is 18 cm deep, if you assumed it was a clos9kx ew0us0eb ,ed 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 pipes8 1-yk lnwjej4 spanning the range of human hearing (20 Hz to 20 kHz), what would be the range of the lengths of p4y81jkwej- ln ipes 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. ,e2t gb5 lrc wjvr+7p0n-v j7gWhat will be its fundamental frequency if it is fingered at a length of only 6077tlr n-p2b0r5 v+e vjj, gcwg% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to play E above middw .we1 jxpvdmri:m5 -/7t 7sqmle C (330 Hz).7xq5:j twir7-m m/ewdmv. ps1
(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 lcdgmfg irujtj4l90v )+f6lh75r c()) when the temperatu5lv)ir7l)lu jg f frh9+4 dgjcc (0m6tre 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 20 uj o5qocqaq:a28vf . 5$^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiei6yma3za o/m5ce of the flute in Example 12–10 should the hole be that must be uncoveizoa / m56am3yred 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 264 Hz, 440 Hz, and 616 Hz, but not o-k r70 aoz6fwn :5mcaat any other frequencies in between. (a) Show why this is an open or a closeawm-caoozk67f 5 0 nr:d 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 t,b1vixupbqa.:e4ue8;md 8z s wo successive harmonics of frequenud:8zspma e; 8 xvbu bi4q.1e,cies 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 oc b; xuoq0)hn2fh6f+jh1 g-u$^{\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 t89d.ueyvd 3wri9ryj5l mo8 ; mhe audible range for a 2.14-m-long organ p9vow5rmd;delu ym.ry8j 3 i89 ipe 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 is open5kmb b+zxd2t ) 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 t 25)dmtkx+bz bhe 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 e,3d6n hlo*uuj*c m8arvery 2.0 s when trying to adjust two strings, one of which is sounding 4*cj3hmnr 8oa l du6*,u40 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequenuas 9f:b95;yywa ys 1qcy 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 anothw02 oj i6 )ua;p*sltiter (brand X) operates at an unknown frequency. If neither whistle can be heard by humans when played separately, but a shrilti0;*jiawutl6)p 2 o sl 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 wh k43 3zw.bakusen sounded with a 350-Hz tuning fork and 9 beats/s when sounded with a a4.wk3zbku s3 355-Hz tuning fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned toee ml fn-7n1x3 the same frequency, 294 Hz. The tension in one string is then decreased by 2.7 n1 lmfx-3ene0%. What will be the beat frequency heard when the two strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identical flutes each try to playga/jo :1y qybjm rfpwif -w .eh78lu p/3.5iv) middle C (26if wphw. mr g75 3.fjejva:u) b/ p/li-y18qyo2 Hz), but one is at 5.0°C and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, an,g bu9uzi mt::kgr3v5 w -8jqfd 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 are sounded together, the beat frequency is 4 Hz. What are the possible frequencies m wu,vqrg j-zigu9b3t 5:f:k8of 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 wkxs pi;yt589one speaker and 3.50 m8y s9pw ktx5;i from the 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 areo p8r ,4j7eofi supposed 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 of the ip 4foorje, 87other ?   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 wavelc 7a/+g/qzbq5 ady vq7k)qi)ekr/wq;engths 2.64 m and 2.76 m in air. How many beats per second will be heard? (Assumei q7/k );g z5 vwbq)rqk7 cqeaa/yq+d/ T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s siren is 1550 Hzw7zh4n 5r6 :4baof4z ecj;t tz when at rest. What frequency do you d4cte47bown fhr:j z46;a zt z5etect 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 detect if a fire engin+/wgj( s62/dd40jq-lls 8g xcarfe rde whose siren emits at 1550 Hz moves at al dl(-0df/s68r/d gcsqa42 x+e wgj rj speed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz sourcemv+ oi g;sv q3ljx/587fj4xsguw co91 is moving toward you at 15 m/s versus yo v1j8953u4sl ovqxg cj+7sw g;/imoxfu moving toward it at 15 m/s Are the two 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 on4 mn86yb uc6eyqc1u, isz4bs*e 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 t41*b sq bc6e86i ysm4,unzyuc he frequency the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at 50.0 kHz and reca ;m*ahi jod 0.t,6yjzeives them returned from an object moving directly away fromh.m yajazo dt,i;6 *j0 it at 25 m/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 emits an ultrlrw,m m1)mp(34cvv lsasonic sound wave w lv(pcl3rmv,w ) sm41mith 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 movinamn.l1ok5 .n vg 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 thenno1. km a5.lv train car approached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound9 z0n)(npi 9tbrcz8 oq 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 arteriizn bptzr 8n90(q)oc9es at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using ultrasonic waves o5 eoo /7i6 -5k4fu7xyemh vakxf 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 velocityrk,ir 2gog3e+ en7gi h; c8xk7:g3zgw is 12 m/s from the north, whatg rh+27i7 rg kg c,wg3e8 n:zogki;ex3 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 movi2caqx4db k n6;3 dm5)ktoaq,qng 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 z (yfi s (p8iyps*mz(ofq.(o8 2.3 where the speed of sound is 310 m/s (a) What is the angle the q8m(ips zp (f(ooy8 (yzf*s.ishock 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 atmo,acao w3dfu+ gl3 s9;a d3/uohsphere of a planet where the speed of sound is ona3au g3ac3of solw/,;dd 9+uhly 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} $