What is the evidence 7g*pw(xcyd ep1gs z(. that sound travels as a wave?

What is the evidence that so(awwquc28 7n /2mcxo bund is a form of energy?

Children sometimes play with a homemade “tele:ky qhv3+m fn9phone” 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 cup (Fig. 12–29). Explain clearly how the sound wave traf+9:k 3vyqhm nvels from one cup to the other.

When a sound wave passes from /yovhew)9y g 9air into water, do you expect the frequency or wavelength to ch9)ywo y9v/ eghange?

What evidence can you give that the speed of sound in air does hw2gc/ +z 4txsnot depend significantly onwc24zsx tg/h+ frequency?

The voice of a person who has inhaled helium sounds very high-pitched.f::rsxw/rg0 r5qb xawvc +7/f6 ,pcds Why?

How will the air temperature in a room affect thtvuuhs80 ,nh.*m k fe/j2 na2xe pitch of organ pipes?

Explain how a tube might be used as a f0q qu;iw fq yy,fc/+h7ilter to reduce the amplitude of sounds inf;h f/yq+ iuq7,yq0wc various frequency ranges. (An example is a car muffler.)

Why are the frets on a guitar yh sffk*5g5awb .ww w+r x*:t*(Fig. 12–30) spaced closer together as you move up the fingerboard toward the f*a:5yw*wkw*gr hs +fb 5x .twbridge?

A noisy truck approaches you from behind a buildti e lnpe ,c18f2r)1al ey/,nuing. 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. Explai, lp/ 21lfee8ncn),y1urtiae n. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due to “interference in space,” whereas beatskbjim)6,74n1he mi2hpy i3g j can be said to be duk)niiph4yhe61 mjbjmgi 37 ,2e to “interference in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowu+20(g 1a ekoph7v9)yg ewyswered, would the points D aksah(w )go7e p19ge0+ u2vywynd C (where destructive and constructive interference occur) move farther apart or closer together?

Traditional methods wb +3gu ufms:t:ng+w6 j f tk0i)olm+-of protecting 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 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 t+ g:b+nti0 j sf63m okf-)guwuwml+ :noise reduce the sound levels reaching the ears?

Consider the two waves shown in Fig. 12–31. Each wave vz4qlcxg; g/8u3 mkd8can be thought of as a superposition of two sound waves with slightly different frequencies, as in Fig. 12–18. In wdg m 8 lz4vk8q/uc3;gxhich 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 move in the sm;5 7v oa1/glwy (wi/hw4mna jame direction, with the saww ov4aamhy7; /1igw /ml nj5(me velocity? Explain.

If a wind is blowingf1kyl 9 b9o97he ybp 4-u;tuze, will this alter the frequency of the sound heard by a person at rest with respoyz7 49b -ehkfpu;9t1lyb9eu ect to the source? Is the wavelength or velocity changed?

Figure 12–32 shows various positivwsu +tli c+.5ons 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 t it svu.++l5wchrough 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 for (5;hy29jvc de efyh-rthe echo of her shout reflected by a cliff at the far end of the lake. She hears the echo 2.0 s after shoee 9-f jh2yvy5 c(hd;ruting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the sid ,zjibzo, u;4ee of his ship just below 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 (Table 12–1) and does not vary significantly with dez;4i ,oj,uezbpth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in air advy -+p0j;5k wfaq ka7sf5(-xkma *td t 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 :/ kdxeaimg29 a school of tuna on a foggy day. Without warning, an engine backfireg: akm9/d i2xe occurs on another 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 splash it make*yv7s -8kpnl es when striking the water below is heard 3.5 s later. How high is the lvsky*8n7pe- cliff?    m

  A person, with his ear to the ground r z)b3h0mimgr3 bent,;z1.hgqn)7 pd, sees a huge stone strike the concrete pavement. A moment later two sounds are heard from the impact: on;gh3,bindh7 zmbeqpt))10z.rnr g m3e travels in the air and the other in the concrete, 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 errosrl ug- g:t s4u4)q* z4n0vpzxr made over one mile of distance by the “5-second rule” for estimating vn*pq)z -0lu44z:uggsrt 4 sxthe distance from a lightning strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity or8xs *f)dk.y nrssz8, f 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 intensity is i4/ il jp a3jx:kc09h,.yjbt0la7 wk p$2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound y/ f lv5d*us-t7fc,vqlevel of 95 dB when fired simultaneously at a certain place, what will be the sound level if onlc7l5ff dy/qs vt*,uv -y one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane with four equally nytrlkz2 s .f8-oisy jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would this person experience if the captain shut dows yzfl.-82 ktrn all but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to have a signal-gg wt(2o6 z2evbtlt 0:k5io6fto-noise ratio of 58 dB, whereas for a CD player it is 95 dB. What is ( t0o z5k i6ob6lef:tv2 2gwgtthe 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 fr/f4j6 llaftp, om a person speaking in normal conversation. Use Table 12–2. Assume the sound sprea6j4p ftll/a,fds 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 strikes2h z)z-*x ho zbtsb.i/ 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, while the more modest amplifier B ia;n ap2 rotb 7fl/r70fs rated at 40 W. (a) Estimate the sound level in decibels you would expect at a point 3.5 m frof7nla at fr;0rp27/bom 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 when placed 2.8 ssv;a4t/6xp m m in front of a loudspeaker on/;6 4smvpxsat 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 differer(-e z6 6 fsrlj0z;wrpnce 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 Section f6(lez jrw-z 60s;rrp 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factor will the intensd :f8d7 ;ev7h oqe6hsrity increase? Increase by a factor ohs7 f;6d78eh odeqr v:f    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitude9f*(c zp/e mtk/:ekqcx -m ;lfs, but one has twice the frequency of the*/cm9ef/ ctkpx-k zl:mfq;e ( other. What is the ratio of their intensities?   

  What would be the sound level (in dB) of a soufo*(-epqj; aq nd wave in air that corresponds to a djf;q (p*-aqo eisplacement 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 100-lut/e35kj wt9 Hz tone that has a 50-dB sound lu/l t j5k9we3tevel? (See Fig. 12–6.)    dB

What are the lowest and highest frequencies that an ear caycq.a:+xuzcubt: / a9nosb) 2n detect when the sound level baunzb y92c )tc s.:+/qoa :xuis 30 dB? (See Fig. 12–6.)

  Your auditory system can accommo40js ,uz,)7w vw-k mz fccsn0 wmurv(,date a huge range of sound levels. What is the ratio of highest t juk-fvcnwmvzrmw)w 04, ,7z,u(ssc 0o 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 fundamentxq:3/ xeoay 8iezrf8g vz+x5a 79xa+tal frequency of 440 Hz. The length of the vibrating portion is 32 cm, and it a7tx5z gx/ryefo+8z9a xe8+va:3x qi has a mass of 0.35 g. Under what tension must the string be placed?    N

  An organ pipe is 112 8k+u9ugiwe-+pnc ( twcm long. What are the fundamental and first three audible overtones if the -cwe( +k +un9wi 8tpgupipe 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 yocln b/*hysp sv ;e/0i)y, wcx)ko f(bh.s1bi.u expect from blowing across the top of an empty soda bottle that is 18 c0 ph yil;k.syb)v* n.ewixs//cb 1f)hb( s,ocm deep, 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 with open-tube pipes spanning the range of h+ig9ijuz7teb w.,c * 8)xly bvuman hearing (20 Hz to 20 kHz), what would be x i wj*b.cbe)t89z ,g +7vuylithe 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 asfqt w48 w 2pui8b:6dcx j6wbe8 its third harmonic. What will beepjq4 w:dw68c2x8 t fbwu8ib6 its fundamental frequency if it is fingered at a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0bxul37 ig9y q).73 m long and is tuned to play E above middle C (330 H) 7glb3q9uiyxz).
(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 t4rv+kp 7/ tdm1n:t3jm liif7b hat emits middle C (262 Hz) whenm+b4i :tli3m7pn 17rvk jftd/ 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 p+vio,wr 1v+ -rn:,dyrn:yftat 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 Exampds(7p pe 2 4msfv7;ewtm23z wjle 12–10 should the hole be that must be uncovered to play D above mwej 34tm 72m vd7( pwz2sep;fsiddle 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 js0fu9:k ky;7ivdq j4can resonate at 264 Hz, 440 Hz, and 616 Hz, but not at any othe;q9idv7js :04 yu jkfkr 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 ati7sg 5k0 ndk0a;nj. gf two successive harmonics of ;n dnf75k.g0isgja0kfrequencies 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 jugjp;d/0b8f:m )g0,cw wa nd$^{\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 aie; /2i)9drs,rj su wnn3li x.re present within the audible range for a 2.14-m-long organ pipri u9si/e rni ,djl)w2.ns; x3e at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal isvsj94 ha5 en8j approximately 2.5 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 the ear canal. What is the relationship of your answer to the information in the graph of Fig. 58hjns4 j e9va12–6? $f_1$ =    Hz $f_3$ =    Hz $f_5$ =    Hz

  A piano tuner hears one beat every 2.0 s when trying to adjust+h5fp)ze5 ay,z mr3cg two strings, one of which is sounding 440 Hz. How far off in frequency is the other sr5p ,)a gzcy e+hfmz53tring? ±    Hz

  What is the beat frequency if middle C ( uk o1hw2)xs uvp4;(qj262 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 operax6*v1 xrz2 livii .ik(tes at 23.5 kHz, while another (brand X) operates at an unknown frequenv*i26 kivii(1x .lz xrcy. 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 frequency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded with a 350-Hz tuning fork an /il 7 dmj kms5u)ob.-2me.hell qo/3yd 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of the string? Explain your reaso/3-/d eljy75 m m .bi.lomos2elhu)kqning.    Hz

  Two violin strings are tuned to the same frequency, 290nkw;hke +r 8y4 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. 80hrenk k+;yw 11–13.]    Hz

  How many beats will be heard if two identical flutes each try to pla cyfi5f1rv4i/94 mweyj + v4a,pj;wxry middle C (262 Hz), but one is at 5.0°C and the other at 25mr+9/i v 4a1w5pje4c yyjfrw4xi;vf,.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a frequency of 441 Hz; whh u8ivg)luy-n/td+it.un* g,7. am.rps; kzqen A and B are sounded together, a beat frequency of 3 Hz n* dkui ah)l.+;8rt i .-nvu.t7/ysg,pmuqzgis 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- 6wi;gc.gb m0wy7hzg person stands 3.00 m from one speaker and 3.50 m whmgb6-c 07gwyz.i;g 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 are suppoa wg8 wne uz bkw-+b14-k/4mifsed to be vibrating at 132 Hz, but a piano tuner hearskg-n4a kb fw eu/wizmb8 41w+- 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 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. H *0 22pd6vl 9 v cv0u/ksd,:wuvekjafqow many beats per seconw ,92 vu*fejsvv/uql0ck2k pda6:0 dvd will 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 Hz when at.6 yt ).nq q71p yxiy2pfpw0vn7r -qeu rest. What frequency do you detect ifxw-ypt0 qn)ipq 7y6vr.un .7ey p21qf 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 engie9/w )p tb5jqp+vbj71sn7hxd 5mjtszhr9* *tne whose siren emitsj*e1r*s5mzp5b9 n 7) + dsthjtpb7 vqtwh9/x j at 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-Hz source is mo0u v,r.5 vcrkqving toward you at 15 m/s versus you moving toward it 0q. ucv5,rkrvat 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 eqvzvmc+b5 )6 7pdq sa7rwu9t9u uipped with the same single frequency horn. When one 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 the frequency zrw mv)scut9qu 975pv7ab +d6the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at 50.0 kHz and receiw astj u4cu7;3l rs. la5tv24dves them retw2u av4;rl tc4sldj 3ua.t 57surned 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 wall at a speed of 5 ms0g, 1 dkowk(o/s As it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency does the bat hear in the refk dwg 10so,o(klected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler*t y* uhsk p(.vml9i)i 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 rest in the railway station. What beat frequency was heard if the train car appro k y9i.ihl()p*tmuvs*ached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measure blood-flow speeds. Slts8. d5nv(xkrll3 7q ;o vus3uppose 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(trduo337n5ssv kl .x; v l8ql cm/s directly away from the sound source?   Hz

  The Doppler effect using ulqne5k e(f-3c6 qcjir3trasonic 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 fren,(z5v . ngsggquency 570 Hz. When the wind velocity is 12 m/g,ng.znvsg (5s from 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 id e*5sk1veqey) 3t- rmf 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 gs-trl;kq: + g(a) What is the angle the shock wave makes with the direction of the airplanekst g l+g:-r;q’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 soundtin;i r7(al;4y-w dox is only about 35 ;x7-ito ;d(awn4 irlym/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} $