What is the evidence that sound travels as a wave?n en;umu1x 6,u

What is the evidence that sound is a form of energy?d f o*im 5vdep/g/yqh)cs4)z8

Children sometimes play with a homemade “telephone” by a+-y s5ggzxc :7:s xworttaching 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 he:y :7zs-scr+5g oxxw gard at the 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 wgl1/v6y r)c8ahp k:qw ater, do you expect the frequency or wavelength to ch /kr acq 8):6y1vglwphange?

What evidence can you give that the speed of s)1wv tn4ynq o8+/s;qcwg8ccbound in air does not depend signif+18 8ow csc)bgwnq yn/q4;ctvicantly on frequency?

The voice of a person who has i ft5z/:gqy 0stnhaled helium sounds very high-pitched. Why?

How will the air temperature in a room affect the ke 2i u5c+jz-ipitch of organ pipes?

Explain how a tube might be used as a filter to reduce the amp.qcoke *8 hf,1 qlhb+olitude of sounds inf.ohbeqk oq8 1hc*,+l various frequency ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer together as you o slg7dhj. m juq9fafv8f5*+5move up the fin*+57lsm j .hfj5uvdf qaf 9o8ggerboard toward the bridge?

A noisy truck approa 8ml ;ulsl8kp,pv ra8i 2x9mx7(ccg-zches 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-frequency noise. Explain. [s87lz 98rc2(pxxpvul i lg-c;km8ma,Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due to “interference in space,” whereanb cw)49.v cexs beats can be said to be due to “interference in time.” Explain.ce) .n cx9wvb4

In Fig. 12–16, if the frequency of the speakers were lowered, would :r o*e;5jqef )lv9cew the points D and C (where destructive and constructive interference occur) move farther apart ovrfe ; q)9:5 cjee*wlor closer together?

Traditional methods of protecting the hearing o+mq;udj* o2a wlh (hu+f 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 ambio ;mlua hh 2wju*(+dq+ent 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 c660.7wd qorrjbq n4,lpnz i-thought of as a superposition of two o z7nnc,.0ij qwpr6-4ldr q6b sound waves with slightly different frequencies, 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 observemkg+u-r9e 2(-b:r h-iixte cjr move in the same direction, with the same velocity? Explai mitr -2ceij:+ 9-ubehx -(rkgn.

If a wind is blowing, wi:(bljkt 0kx o (7,wuqhll this alter the frequency of the sound heard by a person at rest with respect to the source? Is the wavelength or velocixo(j(wqk lkb0: t7,h uty changed?

Figure 12–32 shows various positions of a child in mot pzm8 x-yuy9hdg( .ye72 -qkk:5 u wzjx4wm3twion 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 thz wemdtk87y 25wu-jh( m-x9 y gkqpuzx4w3.y:e highest frequency for the sound of the whistle? Explain your reasoning.

  A hiker determines thex+ oih y0nd*e;;wydf3 length of a lake by listening for the echo of her shout reflected by a cliff at the far endy*;e 3;hfodxnd0y +iw of 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 th6)dse+b:x d nxe 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 exd+:x bnd) s6seawater is 1560 m/s (Table 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in air at qc2xzs;o3 smiv;u) j120 $^{\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 abq16t5x jqzs-jove a school of tuna on a foggy day. Without warning, an engine backfire occurs on another boat 1.0 km a jq-5 6jt1sxzqway (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.v:98 ls daxlhrge* h*04zdj0o The splash it makes when striking the water a rzded:*h*sl8 lh4gvx0oj 9 0below is heard 3.5 s later. How high is the cliff?    m

  A person, with his eata0k09282h+7uuq5 r7t owab bkcxaa tr 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 are9a r2 k7 abqh8cx+tu o57kauwtba020t 1.1 s apart. How far away did the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error madp j*g94t uvy3he over one mile of distance by the “5-second rule” for estimating the distance from a lightning strike if the tempera*v 9ugyt34j phture is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pain q+:zc.c1d8 h(rgkw*4bsglca 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 intensity isthh27ooz2 wb8t3;nrp/ove- i $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fml)abyj7us(sks- 0pg(8: r0 aqibqr-ired simultaneously at a certain jpmqbi)7 (:yr l (g--qrbss0k8aus0a place, what will be the sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain disf5*70za2v jp 3pja8u ;sfer ojtance from an airplane with four equally noisy jet engines is experiencing 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, az s2rfp3pjv;e0j57 *o8 aujf not dB’s.]    dB

  A cassette player is said to have165x dja6twrdd9jk-pd6br k/ a signal-to-noise ratio of 58 dB, whereas for a CD player it is 95 dB. What pkj6bt56d/rd9d r-61kjdxwa 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 sounovz84 pmv+bmx)eu n6wc p6u 5)d from a person speaking in normal conversation. Use Table 12–2. Assu x 4e6pm65)bzmc)vpo8 wuv un+me 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 strdqc5k+t8: ftg ikes 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 ra qu2p ;4rzn1vp7 s)nzdted at 250 W, while the more modest amplifier B is rated at 40 W. (a) Estimate the sound level in decibels you wouldp4n;z1q7 vns upz )r2d 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 whenshgcj.2 qa3y- placed 2.8 m in front of a loudspeaker on 2yh jc- sq3ga.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. What isdou j;4 wk,s:ld:e-b x the ratio of the amplitudes of two sounds whose levels differ by this amount? [Hint: See Section u d: 4:;jds w-klbeo,x11–9.]$\approx$   

  If the amplitude of a sound wave is triple6s3q gyu e/ dga/eurwfgce6(1ie3,3 vd, (a) by what factor will the intensity increase? Increase bqvsce uygr 3(3/3wgue 661i,ef deg/a y a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but*1( 5uxg20ifvfxy; fefugt z7 one has twice the frequency of the other. What is the ratio of their i1 ug*v7xz(ye fx;tf5gfu2f0 intensities?   

  What would be the sound level (in dB) of a sound wave in air that co m9j1fmikh*3a rresponds to a displacemen3kafh * jm9m1it amplitude of vibrating air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must haq5b.;9(c i iog0gt )l)n-uz krni :a+i mk*hofve what sound level to seem as loud as a 100-Hz tone that has a 50-dB soun i 9k iot0n 5c-gzri(il) k+mqf gu*hb;o.:)and level? (See Fig. 12–6.)    dB

What are the lowest and highest fqpx3 p8hasbhc,j 7o+1 w)ucj9c 4;vd-b 0oip irequencies that an ear can detect when the sound level is 30 dB?jsdcib ;)4, 7hxqwhpj 3pca b-o op+u189 iv0c (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of sound9h.g)a;w qrux levels. What is the ratio of highest;.xh)guw q9 ar 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 fundambiw-9 run7l6untv3 e-ental frequency of 440 Hz. The length of the vibrating portion is 32 cm, and it has a mass of 0.35 g. Under what tensi3nw7nu - uer6vl9i bt-on must the string be placed?    N

  An organ pipe is 112 cm long) 4mmps,cc6il. What are the fundamental and first three audible overtones if thepc4mm6l)c, is 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 woulsog:64/b*6h,ephrk, qr s unud you expect from blowing across the top of an empty soda bottle that is 18 cm deep, if you assumed it was a closed tube? gok6urp,4n u/s*se qhb,: hr 6   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 :-u7 a:mqce1l qar*yg the range of human hearing (20 Hz to 20 kHz), what would be gmaeq*: : l-y71rqua cthe 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 third harmonic. Whatr7i u3 twdtq* l/p.-n-tt*hz1fe bw u3 will be its fundamentarpu .e31zntd*tqw/ tt-f*3 -hui lb7wl frequency if it is fingered at a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to play E a7;c;ag/ul5qivrn/vi6, bbg yp w8ye; bove middle C (330 Hzeyar;87lb5iyg6wqc/pb g /u ;,v;ni v).
(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 le(gab2*lh;-upmw h1uu ngth of an open organ pipe that emits middle C (262 Hz) when the -;2wul*pm1uhh(a u bgtemperature 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 rhfp*c rgjj(.)5xsff.h5iw ; $^{\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 nq:c 7lt0)3 wf gqa 7: rb k7(jt+nujb/c,zhaxthe hole be that must be uncovered to pl+ q0kqfn3c7ab(h jj,z )/r7t7cng:u t xwb:alay 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, anh5noiu,17/ocd3sloia2gl o-d 616 Hz, but not at any o o lodl3s7gic,-u 2noah5/i1other 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 ephc) h,)itb5 tnds. It resonates at two successive harmonics of frequencies 275 Hz and 330 Hz. What )cbtp ih5 h,t)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 bc b66:twa,(hw3v ez h$^{\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 audxjb-o+o2 +:dn( bkzzr ible range for a 2.14-m-long organ pipe atzb2rjx +zoon-d:k( b+ 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm longt: hf 4)rsrjf7-v5 vop*h4 mf7pa pm;x. 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. -5h ; xa* fvs:m47htmp4vf)p7 jfprroWhat 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 h ++ n7fd 2bzcmfwdp3z c.ef0-when trying to adjust two strings, one of which is sounding 440 Hz. How far off in frequency is the othere df7mdf -phw+zb c+2.n3fc 0z string? ±    Hz

  What is the beat frequency if middle C (262 Hz1 ibyhgwg0y:l .6b3sboyv x xs31tit y3-4a6z) 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, whileo)btmgsvi,l4f 4y 6r8 another (brand X) operates at an unknown frequency. b gv4oy)l 6ms4ti,r8fIf 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 frequency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded with a 350-Hz tuning fork, smjx0 c:,kue and 9 beats/s when sounded with a 355-Hz tunink 0,ec:jx,umsg fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings arupvnr+6dya 1y+ 0c 0of-( xtxze tuned to the same frequency, 294 Hz. The tension in one string is then decrea -nryxxy 0ozp16dc(0vuf a t++sed by 2.0%. 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 play midb/yui6y53y lt ar:q o*dle C (262 Hz), but one is at 5.0°C and th:6ay b3royi/lu5t* qy e other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a frequ 4fil*(-gl7crh bma4-b+nyzpency of 441 Hz; when A and B are sounded toget py7g+4b l z4b*ch(afm-nl ri-her, 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 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 one spe ck,rsse +cf b8.rq,g6aker and 3.50 m from thg,kq,6 fs8+rrc c. esbe 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 vibhhl+hqi+l+5qq xi * piz+v7 x8f5-za frating 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 freqi ++ pf-iqq5+zhvh7l *xah qxf+5z8liuency 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 guk - r5f1mt;0wgwc k/in air. How many beats per second will be heard?0/ 5ww;u-1 kgmfcgtkr (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency ooiba dgqxt1.5l(8* ;zpnlg:yf a certain fire engine’s siren is 1550 Hz when at rest. What frequency do you detect if you move with a*5ga 1gdz tlnx(oypl ;i8q:b. 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 fi0 iyvfv/rt d23re engine whose siren emits dt 0fri/ 2y3vvat 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-Hzfl yae*)t9 *w4d,h fwz source is moving toward you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exfywf*4dwe t*h) lza ,9actly 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. Wriaq3 91b6rl4 zu4m jbhen one is at rest and the otherar ubim6q j419 rlz3b4 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 emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at mtka 6)f* wrt; vv+ks250.0 kHz and receives them returned from an object moving directly away from it2 rvfw vm*tt; ka)6k+s at 25 m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a i *j4flpka 8o5wall at a speed of 5 m/s As it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. W koa*4j5i pl8fhat frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Dopplw q+3y r1hdva3er 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 resw 3yqrva+1d3h t 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 ul:h c; wrsu-shg:2.enotrasound waves to measure blood-flow speeds. Suppose the device emits sound at 3.5 MHz, and the speeho: -2hg;.nw s: uercsd 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 + )6c n:-njw*rmrapu9aa70tgt emm +jves 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 o/1gn h3/h ywcy25sdzzij31 caf frequency 570 Hz. When the wind velocity is 12 m/s from the north, what freqg z/3hwsyd 11h 5izy jn32cca/uency 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 lux)phgll3.9 gz .s-hzand 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)n t8 44hg5*ejny:,i qcd(iy(,sxyx gt What is the angle the shock wave makes with the direction of the airplane’s moti ,gycxgq4n8 i*:i(j(sy nytt d, h54exon?    $^{\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 pg*b3exz0ja -glanet where the speed of sound is bg - x0a*zejg3only 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} $