What is the evidence that sound travels as a wavecbe9h,tz;3u*j vpfb ;t3p2ct?

What is the evidence that sound is a f,w +whjrth4q+ vzt:r+ orm of energy?

Children sometimes playp 8vz/w;u8hq 22vkctj with a homemade “telephone” by attaching a string to the bottoms of/8qc2vhku wv z8tp2j; 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 travels from one cup to the other.

When a sound wave passes from air into x 43 e-yquk7vnv.*lbnwater, do you expect the frequency or wavelength to ku q7v*vn3y4nle bx-.change?

What evidence can you give that the speed of sound in air doe:bwqcxjo8p )8: -j q7wkg w5xrs not depend significantly on frequencyo qq7r:c w8-)58xj gwxwkj: pb?

The voice of a person who has inhaled helium sounds very high-pitched. Why? :x2r2g8 yicb+ ic:hjl

How will the air tempery+ he;9.j78fiqr m b+iins9muature in a room affect the pitch of organ pipes?

Explain how a tube might be used as a filter to reduce the amplitude owgwv .n tgp)v8*u*.aof sounds in various frequency ranges. (An exa)*n uag t*wwvvp 8.og.mple is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced clh *ym9.nl y2mm/*yykpa,9rm coser together as you move up the fingerbr92 c*h ,my /yanmkpl 9*mymy.oard toward the bridge?

A noisy truck approac3fh/epsyjnl o ,2/z2ahes 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. [Hint: See Section 11–15 on diffraction,o/p3fza2jhy s/ e2 ln.]

Standing waves can be said to be due to “interfery8 rfah; us61sence in space,” whereas beats can be said to be due to “interference in t6 18y ssr;auhfime.” Explain.

In Fig. 12–16, if the frequency of the speakers were lxor bl2 qc6-r1owered, would the points D and C (where destructive and cono 16r-2 bcrxqlstructive interference occur) move farther apart or closer together?

Traditional methods of proteca/.xb)rvq* 7 bgzs:peting 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 noise reduce thegqr b.7s:/pzvxae*b ) sound levels reaching the ears?

Consider the two waves shown in Fig. 12–31. Each wave can be thought of arolg:)hs j1(ds a superposition of gorhs):j(dl1 two 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 obser* e6fj e5vn 3h+q1wohml8ztbi /g.g4t ver move in the same direction, with 54e.*bv8jfl en 1q ght/zgit+o6hw 3m the same velocity? Explain.

If a wind is blowing, will this xe p xtnh)7bp13 l,6btalter the frequency of the sound heard by a person at rest withx1xpt,h 7l b3n)ep6bt respect to the source? Is the wavelength or velocity changed?

Figure 12–32 shows various position )i+kgtu)bvs tc*w25t) i3pk(ac ny 5hc-zi u9s of a child in motion on a swing. A monitor is blowing a whistle inh()9u)-)*5g bcy3i i25s +tvw ckkt auncpt zi front of the child on the ground. 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+)tekt /mqg* rreg9/nw vj z)tx28bq 3 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 shgt2z/ b +x t jwre)mkn9vqtq3e rg)*/8outing. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below the waterlines3(x.6 thiu hx aw.q.x. He hears the echo of the sound reflected is.hut(w q xh.6. xax3from 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 depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in air at 20j vh pih112x:q $^{\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 ju: pgi-r:joyj -st above a school of tuna on a foggy day. Without warning, an e-irojg:j -y p:ngine backfire 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 s 26 orqn+q;)tyyzvl eyi,0*doplash it makes when striking the water below is heard 3.5 s lqv;olrd y ) 2nyzqoy*+6i 0e,tater. How high is the cliff?    m

  A person, with his earrd6o bw j(pgsq83b0 r) 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 occur? p(rr w6ogbd 0jqb8)s3See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one 3a5tb3em gqj;mile of distance by the “5-second rule” for 35q3ejbgm;at estimating the distance from a lightning strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the xvezc-z8bs*8;do .qacejbpi-ss /; 0 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 intensityum q2,e jl89 bjsf;d :*tzxuxr6,q2nn is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired s qrfm5t- 7m/y 1ll,gpiimultaneously at a certain place, what will be the sound l i /p tf1r,qg75mm-llyevel if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance k+x m rm5khnf e)6y+b1from an airplane with four equally noisy jet engineek5mkfy1)r bnx+m6+ hs 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, not dB’s.]    dB

  A cassette player is saidiz +ae9p dlqz*,j3n;j to have a signal-to-noise ratio of 58 dB, whereas for a CD player it is 95 dB. What is the ratio of intensities of the signezi lnp jz+ ,j*3qa9d;al and the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from a xl;w5u ojx7z7j5uf-n person speaking in normal conversation. Use Tj-; uufwjz7 xxln 57o5able 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 eardrum whose arzekm,lssf n v /g;6;8ha2;jst ea 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 morlutfigdv88+-;2hed .jqpcx 2 e modest amplifier B is raedltv.j i -qd28ch2gfu+p8x; ted at 40 W. (a) Estimate the sound level in decibels you would 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 when placed 2.8 m in front oh/ k;ho6w, kbkf a loudskbk hw;/o6h k,peaker 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 typiceny*),niz(d ):i:qs j2qojq qally detect a difference in sound level of 2.0 dB. What is the ratio of the amplitudes of two so es:, j*)o:) diq(2nzqnyijqqunds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripledmer ij;-ryktn6 i7 41j, (a) by what factor will the intensity increase? Increase br;m1- ji4 y7 enkit6jry a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equ nap2ud+ ytq +9tir9x/w:.yfsal displacement amplitudes, but one has twice the frequency of ts9aqtnf2pi+y wry+9u :t/ x.dhe other. What is the ratio of their intensities?   

  What would be the sound level (in dB) of a sound wave in ah birmt,ed0 n/1o4i5w-tm/ krdf/xh:ir that corresponds to a displacement amplitude of vibrating air mole nibtkt w4o1m,-/ mh0dx/hr5i /fd :ercules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud as a 100-Hz toxk /u1 8bj5 aix;jyuw7ne that has a 50-dB sound level? (See Fig. 12–6;8k1j/yba5 u 7uwxxij.)    dB

What are the lowest and highest frequencies that an ear caw2*gtwr0 fgxgee+y5b3*uo8s.fn j u 2n detect when the sound level is 30g*n+ftw 22guu3e5gbysfj *ew xr80. o dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of sound yykgx h1o(xo0-e x,s3levels. What is the ratio of highest to lok0o1 y xxo3hy-(x g,sewest 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 fundamenq9)wpthu h)x 0r92 uipe l+w-wtal frequency of 440 Hz. The length of the vibrating portion is 32 cm, and it has a mass of 0.35 g. Under what tensiw9equitp-w )u)2h lwhxpr9+ 0on must the string be placed?    N

  An organ pipe is 112 cm lvqe*mv x +htrpnc9/ 17ong. What are the fundamental and first three audible overtones if th*tcxmp/ve+1nr 7 qvh9 e 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 0 zmb5yh j9z ctwia8o+/)hk-ywould you expect from blowing across the top of an empty soda bottle that is 18 cm deep, ifthaymw8-/+yh9kbzzco5)i j 0 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 s9jyk b)ta -do6panning the range of human hearing (20 jky9b-oa6t d)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 third harmonic. What wil*2*xq f sd7 -x mgfal9qp0c9oil be its fundamental frequency if it is fingered at a length of q m*fxsca l 0g9q79p-*f2dixo only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to peb c7z6axt) 1q,m 4bxwlay E above middle C (xc1tq, 6za b47be m)wx330 Hz).
(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 r7s4q da,qe a*-b;.l1i vyvx/ i5cz wwthat emits middle C (262 Hz) when the tempera-q d.lzw 7vqy1*bcs,vaewx;/ ra ii4 5ture 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 dwhhsb6 zc c69.gj +*tat 20 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece,un4g(g ae. mfnki(q7 dc-k3s of the flute in Example 12–10 should the hole be that must be uncovered to play D above mid4.3e(7n kgfd uc mka,sgq( -nidle 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 Hxrf*xws x5 7gmt 2fo;pg-i *y+z, 440 Hz, and 616 Hz, but not at any other frequencies in betwexy*worp-7f gf2+sgi x;x* t5men. (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 gu 8mkeio7 w6w br) 2o7nd1d3sboth ends. It resonates at two successive harmonics of frequencies 275 Hz and 330 Hz6ikwubdmg7o2n 8 )rs 3de 71wo. 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 -hiq, py*cux2uyu4 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 pre73pds. l tyo;ch:n-bh sent within the audible range for a 2.14-m-long organ pipe atn3l;h p sy- 7ot:cd.bh 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is appb4lh pv0rt:) kroximately 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 answer4 kvtp0r)bl :h 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 2yuben 04+k (v+ueb l6p.0 s when trying to adjust two strings, one of which is sounding 440 Hz. How far off in frequency is the other strink+bl u y+ev0nueb46(pg? ±    Hz

  What is the beat frequency if middle C (262 Hz) 7ku4xhm zj0 kz 6s-u4oand $C^＃$ (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 another (brand X) opernu:r8z;f+r ncf,mxl-ates 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 simultanez, cf n-rx8url m;+n:fously, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded with a 350-Hz tuning fork ayyx21fdp9n - ai) zsvk gk1vs17uk:e.nd 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrationp)dx g kkv2sk ay91if1.7uvyn:1s -zeal frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, rkbtbd 7 j2arw1 pl137294 Hz. The tension in one strin1wbpt 7rbr27 1ka dj3lg is then decreased 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 a-5 :nzc5foob identical flutes each try to play middle C (262 Hz)z-:of a 5nc5ob, but one is at 5.0°C and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has ya,t+*;p8+avgatmy2hw gg 4h 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 of A and C? What beat frequencies are possible when A and C are8agm+*hy t2 w phv,4yt;aag+g 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 speakewzwdowi 5:km- .5g5+us3lv py r and 3.s5o uky: vwlmi3gp-z5.+w 5dw50 m 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 supposed to be vibrating at 132 Hz, but a piano yw,xtxpwhew 2 5j8,3atuner hears three beats every 2.0 s when they are pjpx2x, , 8wet5wayhw 3layed 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 /tv nm-4:phix m and 2.76 m in air. How many beats per second will be heard? (Assumem/p-:ti4nv xh T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a ce.5 41r0w sujdmi+ pe h+,tquyqrtain fire engine’s siren is 1550 Hz when at rest. What frequency do j.1uw qmdh qtiy4,erps+ 5+u0you detect 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 fi-gog-km jg3c;) l9hn lre engine whose siren emits at 1550 Hz moves at a speed;gohgg3-) k n-lj9l mc of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency ihk/2aqb3kf l7 f a 2000-Hz source is moving toward you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exactly the same? Are tk2l3abkfq7 / hhey 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 o4va9 wvgm a04 1c9rpqwith the same single frequency horn. When one is at rest and the other is moving19w4 49com agvarqvp0 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 50.0 kHz and 6ft7e/y .nyp jggp6s h7-ngc)receives them retpe-.f7g6g t n/gj shn67y)cypurned 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 m/s As it flies, the bat emits any0f 7g0krbpv qz.c ;yz8*x5us ultrasonic sound wave with frequency 30.0 kHz. x f8y*.;gbzs 0qvpz7u rkyc05 What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tub2a w ehxthn*tx-k zp)y3k)* v7yh)ra3a was played on a moving flat train car at a frequency of 75 Hz, and a secon *h-p)a*ht2x hayy ) zkxw3n )evrt3k7d 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-flovmxv-4n6x8mv e*5v y8 mhjgb )w speeds. Suppose the device emits sound at 3.5 M)vey5*m mvxhj v4gb88v n-6xmHz, 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 cm/s directly away from the sound source?   Hz

  The Doppler effect using ultrasonic waves of frequency wd wz+:zipvhm (,+9on$2.25 \times10^{ 6}$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 f 4 hiom:)sa6wo7lh 39ml5 qm,dwb 1iyof frequency 570 Hz. When the wind velocity is 12 m/s from the north, what frequency will observers ,7h3)b qmloww5fy1s im96:midl4a h ohear 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 at 20*,xbc iu 24:wr/egmey $^{\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 alo9 b .-6oyrdcxf2k +is 310 m/s (a) What is the angle the shock wave makes with the directiobakd r.6 yfx-2 l+co9on 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 0dxw b0-i 1d* qbirr5uspeed of sound is only about 35 mb0 bu-i id50x*1qr wrd/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} $