What is the evidence that1w /wnzmw)4sw sound travels as a wave?

What is the evidence tgygy pzi6ft3: w99g*)xp ut d-hat sound is a form of energy?

Children sometimes play with a homemade “telephone” by 76t.n8ut s zijattaching 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 cup (Fig. 12–29). Explain clearlz 8j7ni t6tus.y how the sound wave travels from one cup to the other.

When a sound wave passes from air into water, do you expect the frn zg32kjue2vv ,y+h*sequency or wavelength to ch 2jesk 23vgzv,*ynh+uange?

What evidence can you give that the speed of sound in cl4jg7 j. *dyzair does not depend significantlyy 4jg7.dlj* cz on frequency?

The voice of a person who has inhaled hel(.w-bya 4qd8k/ jrdf(:ha abdel 3e7y ium sounds very high-pitched. Why?

How will the air temperature in a room affect thhuur7 ) yiul;f(3pae6 e pitch of organ pipes?

Explain how a tube might be used as a filter to reduce the aj1; md)lhnge8 mplitude of sounds in various frequency ranges. (An example is ag8dj1e )hnml ; car muffler.)

Why are the frets on a guitar (Fig.:ot pvm9gi, zf+9 visqn/:2lo 12–30) spaced closer together as you move up the fingerboard towzv2 ,:ml soti9:vo+fp/9g qni ard the bridge?

A noisy truck approak1m;+g9 /w t arqthh8oches you from behind 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 more of the high/ohg98 ;tqmrh twk1a+ -frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said rw *wy9;)z gsyrin h0/to be due to “interference in space,” whereas beats can be said to be due to “interference in time /yisn rw)zgwy9;hr0 *.” Explain.

In Fig. 12–16, if the frequency of the speakers were lo6q bj y5.z,bz5cr;q:ma o.jmp1p9yq 6qy ud4s wered, would the points D and Co,c5m 6.1 m.zp6 9qqd;4byzuaq5 jq: rs pjyyb (where destructive and constructive interference occur) move farther apart or closer together?

Traditional methods of protect 7pgmxdfu1 ,4ging the hearing 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 uxpgm7f14g ,d 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 orxgsr3sz3g* 3 s+svf +f as a superposition of two sound waves with slightly different frequencies, as in Fig. 12–18. In which of the waves, (a) or (b), are the two component frequ*+ szsx3frsvg3 r+g3 sencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the sdpzy xn.;(um nhzgu.1:,g.io j.ox6mource and observer move in the same direction, with the same velocity? Expl6xu; n gunox1 miogmjz z .dh.:..(,pyain.

If a wind is blowing, will this altlzz fr9,ndd 6bir)+)w er the frequency of the sound heard by a person at rest with respect to the source? Is thz r9,+bd6zn))f wdrile wavelength or velocity changed?

Figure 12–32 shows various positions of a cm byreld21dj :bh/ j 8ig2/jd58z0nwphild 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 chyjizn8 bm8ddpgw2b5j:r/ hl/e1 d j02ild 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 :-otcj27ju8jc4l at(si 8v ca of her shout reflected by a cliff at the far end oj 7(cos2: ivual 84 aj-8tjctcf 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 belu*nay o/xh o0p( / 1e0(oygcxgow 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 seawater is 1560 m/s (Tabx0 xo/chnp(u* eoy(gyoa g10/le 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in air3np0hr rw )djdsdo f,a36(r6 o 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. 9hvaj.qh8 wgx1e.g u; Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How much time elapses beforea . xugw vg;9j1h.8hqe the backfire is heard (a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a cliff.:k6b: xy.r*hxb:bn 0 tuuth5x The splash it makes when striking the water below is heard 3.5 s*6ubb:t::yh rkh xxt 05x. nbu later. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge stone strike the8j4wgm7 *qr*zuvmc- c 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 ivm4w ru7z8gcm*jq c-*mpact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error madeha;9lwf.n5b q-gjai, over one mile of distance by the “5-second rule” for estimating the distance from a lightnb ,gi;q ahw.-a 95jnlfing strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensita7gp:) ;oppa 4,tbffiy of 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( (nx7-(t0vbz hj jmoo intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound e t25v l8jcryuds31w2level of 95 dB when fired simultaneously at a certain place, what will be the sound level if only one is exploded? [Hint: Add intensities, not dB s2w8e31c2l5d rvutjy’s.]    dB

  A person standing a certain disk* 7 gh yz (sg;3i q2l2p y*zsfmge:jd2(wd;jwtance from an airplane with four equally noisy jet engines is experiencing agykj;*:dzygm3qs2 i ps wje2* (2 hl( dwg;f7z 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 have awnk-1p:ra 3 a7m89ix(xg jmo a signal-to-noise ratio of 58 dB, whereas for a CD player ixka98r-x(1wna:3m ima7j p got is 95 dB. What is the ratio of intensities of the signal and the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound frc xoc-a(5mm w2om a person speaking in normal conversatio(c amxo2cm -w5n. Use Table 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 strikes an ear -vkbo;2 aykc/qvs p6rsp6k47 drum 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 2503zalm/t1n0jhef ++8 +i ggfdb 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 connected in t+ 0i 8b/jlgd1fm +h3ezf a+ntgurn 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 metabv 0jk;s:c)x-6 lrqzg t c9t3er registered 130 dB when placed 2.8 m in front of a loudsp6jtszk0b;3 tlxv - )cca gqr:9eaker 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 da6t4b *dop vyv+/cg0c6ptgyy v)x k/ .B. What is the ratio of the amplitudes of two sounds whose levels differ by tpd/ kx ta*v oc4 6ybt06) /vgvg.cyp+yhis amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factor cih6aj xf*i)5 will the intensity increase? Increase byjc) 5i*6if axh a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, hn 3 xay eo 4tk++,+4wj:eqhibbut one has twice the frequency of the other. What is the rat+ ,oetqn +jey4w h3xkb4hi:a +io of their intensities?   

  What would be the sound level (in dB) of a so, b ex-ydkkp*+und wave in air that corresponds to a displacement amplitude of vibrating air molecules of 0.13 mm k+b*yd,pe -kx at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud as aj,ayql; . kg m1(bwmbq+0d*wl 100-Hz tone that has aw,ml 0y ;l1.jgwaq+d* qbk bm( 50-dB sound level? (See Fig. 12–6.)    dB

What are the lowest and highest frequencies that an ear can detect whe0 uonq/ee5v: p bup82jd7pcd 5n the sound level is 30 dB 2eqdu:oc np0jev pd87 /5pub5? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of sound levels. What is the rf y nx3/hhi 6h)z/3i*whx,mev axie*yfzw)m/6hi/v3h , hx nh3 tio of highest 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*4f9bbxy2vforb zhq7 h lp9 0:gvr5/-qy 6hnz 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 must the string be ozbvpr5hq*l z 027-946hb ny /vh:gyfrbfxq9 placed?    N

  An organ pipe is 112 cm long. What are the fundamental and first three qj::kf phc ib1*c/tcj 8*txy)audible overtonejy)jc :h cct:xtk bpi8f*q/1*s 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 expecxhr+ :c.im1n ft from blowing across the top of an empty soda bottle that is 18 cm deepch1 i.xm+r: nf, if you assumed 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 a pipe organ wit, 3p6.hsgx wxoh open-tube pipes spanning the range of human hearing (23whx p6,xs.g o0 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 540 Hz as its thi z;,zr rhxe:h8rd harmonic. What will be its fundamental frequency if it is fingered at a le8z,hrr ;:hxz ength of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to pxogfy a.*mau8+01fu play E above middle C (330 Hp0ox g.a u*a+1ffuy8mz).
(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 pinpy(0f;qrz a/ pe that emits middle C (262 Hz) when thepfnr(/ya;0 z q 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 at 20psx x0vju 1(gx (2quq; $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flute in Ex 5qy2hxs7eg,c(ow9uujr+y6 d ample 12–10 should the hole be that must be uncovered to play D above middls5 edyuy,7j cowq62gx+9 r( hue 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,ag5+.kc7 + u0op0etyyzmv 9ja and 616 Hz, but not at any other frequencies in bet+0 7 5yuy mjc0pzvaoat +e.k9gween. (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 openzsvtx/u.n g 7cg(r9z* at both ends. It resonates at two successive harmo.rug*v(xszz/9 7ctg nnics 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 s x6ho :,h q/c2exb3ht$^{\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 preseeqkgg 0tkkrh*. 8;,hznt within the audible range for a 2.14-m-long organ pip8hegt q rz*0kk.;g hk,e at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm lz g.w- g ux(un2peq)snr,4u3gong. It is open to the outside and is closed at the other end by the eardrum. Estimate the frequencies (in the audible r-gnp3 2, 4un.e)guuzxqwr (gsange) of the standing waves in 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 evou6.gh 8osnnj4ne l8mo uj +)sjykys9)w*4 d9ery 2.0 s when trying to adjust two strings, one of which is sounding 440 Hz. How far off in freqonsuk6g84*o w j4.j9 syodue9h)m +snn)lj8 yuency is the other string? ±    Hz

  What is the beat frequen*le-fcj rk7 b,g5 0sv*hyt1ul cy 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 kHzqw ttd3-fu4i/- hzh.n, while another (brand X) operates at an unknown frequency. If neither whistle can be heard by humans when playezi-.3hdfwq tt4/hnu -d separately, 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 tugwc 71bwo1en3bow)9ha8l +oz ning fork and 9 beatlewg c1o3 8 b)z 7+nohw9bwa1os/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, m8 u5be wq spgs v*oa;-s cmja99,p.u8294 Hz. The tension in one string is then decreased by 2.0%. What will be the beat frequency heaeb8p- 5sqp8casu*u vjo,.g ws;9ma 9mrd 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 play middle 9:dcqd (6i g4 (j,p2nhxwe hzwC (262 Hz), but one is at 5.0°C and the oth(hn2d9w,(dwci g: jp4zxhe q 6er at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A:c w p1h4jscu mv-ihjq1c9: (u, B, and 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 toge9vwpu c1ijms 1(u- hhc::4qcjther, 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 sta frw0tg4d t 1d8i;dv)ends 3.00 m from one speaker and 3.50 m froe4fgt i )d10; d8drvtwm 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 are supposed to be vibratny :om--. oipxing at 132 Hz, but a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibrating-:opm ony-.xi 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 2.7 e wjl+ggs xv2ej-,eqnq0q:fk+b,0* m6 m in air. How many beats per second will be - qe2m x+jeglbf 0 v0+*,qkwg:,ejsq nheard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certainmo(6m q :g0( lx)ydvbsle vm;* fire engine’s siren is 1550 Hz when at rest. What frequency do you detect if you move m;q6y )(0o :ls*xdmbv(lgve mwith 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 6re9:msf*.* 6y xx4hv,mgorfycrm, jdetect if a fire engine whose siren emits at 1550 Hz moves at a speed of 32 m/ r f:hr ,m*oye 4gj6rm.f9xcv* ,6xsmys
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shiftxrizhi:qjs+ n0j, ciqz t6- (( in frequency if a 2000-Hz source is moving toward you at 15 m/s versus you moving toward it at 15 m/szr6(jqs,h :i+tn( 0ijz-c qix 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 samepd00u(s- fmwys k9zxu .b.sg9 single frequency horn. When one is at rest and the other is moving toward the first at 15 m/s the driversug-bx z90m(ysf upw.sk.d9 0 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 suv bz.q8 yf8o,ound waves at 50.0 kHz and receives them returned from an object moving directly away f,f z8v 8y.oqburom it at 25 m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a spe5)r yslxw ;oq1 d vog5 zrecj70n832+yv7zwxaed of 5 m/s As it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency does the bat heos w1 ren l5q357w78 j)0x+vvzyr;doygca2z xar in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was played on a moving flat0 ctn;n-u2 xhli +drv4c:-v cr train car at a lt+x rc:;4h-c ci0v2vr n-ndu 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 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 savhdnz0f 6/,xldjip;o)g.d* f+ dz t+ peeds. 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 larggdz+pz+.of)* 0xtadn v, djh f 6ild/;e leg arteries at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using ultr1. r,gmki .r,qn*mp kg.coc3dasonic 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 velzbzh;8 :yson6uy 27 vptj 2mp;ocity is 12 m/s from the north, what frequency will obstp;6j2z;:bz7ny 8mo2 sv p uyhervers 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 speed aw:5 udz1w ao6it 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+rory4ypu*2 kgh4h s (a) What is t 4+gyp*yrrhksh42o-u he 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 thinv14osez,u6;-bx f1 uvr; gv wl-tmu5c atmosphere of a planet where the speed of sound is only about 35 m/sxvbv;5 u-tuc1fsr4ze1 o,l6 vm ;gu-w
(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} $