What is the evidence that sound travel.aqb9qshv-d4s,9; j) xni9 jesn)a bss as a wave?

What is the evidence that sound ih/6jysx9u3c xs a form of energy?

Children sometimes play with a homemade “telephone” by abr y6cugep, - s ewo(w(wm -dble(7-,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 sou 6yo- e(gm7aepe (wdcs b,-,wlr-(wb und wave travels from one cup to the other.

When a sound wave passes from air into wa.qp08 vk6a-hr5 b9f(u jmr1gtvpjy.r ter, do you expect the frequency or wavelength to chanp8. .u jj1r fba9yt(pk mrhgq60- vv5rge?

What evidence can you give that the speed of sound in air does not depend signifj( *g3c6ltr;0 sb 9lwywzo7cy kioat/to/b( 59z lc lk3ract0oj/sgy(;to/w( ybtiw7 o6*5 bicantly on frequency?

The voice of a person who has inhaled helgxh rm2-9dm oalv,m ,:ium sounds very high-pitched. Why?

How will the air temperatur+)ctmbb 36qt -kz+ lmle in a room affect the pitch of organ pipes?

Explain how a tube might be used as a filts kixrdln5 9n **agm58er to reduce the amplitude of sounds in various nginxlm85*d sr5 a* 9kfrequency ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced cl 5cs/6h cq*brjoser together as you move up the fingerboard towarjc qr/cb*h6s5 d the bridge?

A noisy truck approaches you from ga g ka;*((dl(p;a 7d sk6jeyubehind a building. Initially you hear it but cannot see it. When it emerges and you do see it, its sound is suddenly “brighter” — you hea* y;gljagde((ua67k k (pds; ar 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 spa9w (g*v6+vi4finc vdj ce,” whereas beats can be said to be due to “interferencfi9wd 4*iv+v(6vgn jce in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered, would the point eqez7 es-ypb la9ho8p( k*v+nx+(:wgk7*cg ps D and C (where destructive and constructive interference occur) move fartherp9sl cgn+-wkopbpy+kgee 8z 7qhe xv*( *(a7: apart or closer together?

Traditional methods of protecting the hearing of people who work in area4;mlkhvkqh8 id18ai6s with very high noise levels have consisted mainly of efforts to block or reduce noise levels. With a relatively new technology, headphones are wor 16 lidhkm8i4h;qka8 vn 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 of as a sup aeom31ehy)s4u+ mg;lerposition 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 frequencies farther apart h3 1+ lmmue)4syg;oae? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and observe1 / myrdz8/lc,zq,u u( yw,evfr move in the same direction, with the ,y( uz/,cr/qz,d1v8ue lfm wysame velocity? Explain.

If a wind is blowing, will this alter the frequency of the sound hearui 1u-n z0 vc qov-p(3/zvaou3d by a person at rest with respect to the s0 uoi3zc/1v p3z(-uuvovn-aqource? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a c yv.n2 :x 5mqp9xpaim8hild 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 child hear the highest frequency for the sound of the whistle? Explaim25qmi9axy8pxv . pn :n your reasoning.

  A hiker determines the length of a lake by listening for the ec*)v 9e yltp/vkho 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 lakp)y v ve/kt*9le. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below v,47t hdbc3f ;te q/zp ar:hih.r,p+athe waterline. He hears the echo of the sound reflected from the ocean floor directly below 2.5 s later. How deep is the ,/p+ie q; 3t b4 ra7dzvrh.htfcahp:, 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 waveleng 4xenyjwe ho;))x dyj* :eo(q+9 t0mgfths 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 tuna on l vxu an /lwnyd9/qiq*u07,1k4pni0r a foggy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 120 quw1l *vpn /qiur4k,dl9yxn7/0ia n –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 theeb3r /p7wt4zz top of a cliff. The splash it makes when striking the water below is heard 3.5 s later. How high is the cl/rb 3tz e47pzwiff?    m

  A person, with his ear to the g9mfo8 5u.x t7 ,pf 8oym)pvoksround, 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 ykox)f vup7.os5f,o 89 8mmtpapart. How far away did the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error mad/it2s3w8z3 c1eya8 x kgx/t lme over one mile of distance by the “5-second rule” for estimatil 31ct8/8 iez2gtky3mxasxw/ ng 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 sounlidqf7/;gjqzrf *q1 ptw1r/ ) d 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 5whq88: -b f)be mjdvvis $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired simultaneo0,xp/wc-jma c usly at a certain place, what will be the sound level ijc/ amcx,p0-w f only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance fklc7 zi-f+m: 21 jaen ov+r+xzrom an airplane with four equally noisy jet engines is experiencing a sound level bordering on pain, 120 dB. Who+ jv n+7:-kzla i+cmfxr 2ez1at 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 awf93lyq4ssq7, /ypq x signal-to-noise ratio of 58 dB, whereas for a CD player it is 95 dB. What is the ratio of intensities 7q,sf3 /y4yp9slxwqqof the signal and the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output :m ;giu g wsarxrd3/:nw4w), zof sound from a person speaking in normal conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphere centered w/:3 ;:rgr wa4n)z,u gmsdxiwon 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 whostby1dz+ , gfy0e 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 amfkz/)-i f r3a )6mhjm nbuz.4rplifier B is rated at 40 W. (a) Estimate the sound level in decibels you would expect at a point 3.5 m from a lz f 3a. b)mz64hu-/k nrrmjfi)oudspeaker 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 fryi:d 41j*acbf ont of a loudspf1c*bi4a :djyeaker 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 inafwsdm3*4 +s;jb y m(m*t .fpt sound level of 2.0 dB. What is the ratio of the bm *3 wtj fs+yam(m4d ;*ts.fpamplitudes of two sounds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave np*zus; ;2 ;nvi 2daxais tripled, (a) by what factor will the intensity increase? Increase b2 ;2;zdun;vpnaia* xs y a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but one has wah8pm.xh yl wn,4xb e7nyx9(e f9p;/twice the frequency of the other. ex 8p9x. 9nnhahw b ,(4py/mwefxy 7;lWhat is the ratio of their intensities?   

  What would be the sound level (in dB) of a sound wave in air46 li;ngrzysh 0xzu3) that corresponds to a displacement amplitude of vibrating air molecules of 0.13u)glzy6i4n xr;s h3z0 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud avrbqab(d :igwl)q :8 c)uar 0:s a 100-Hz tone that has a 50-dB sound level? (See Fig. :rw:icvau 0lqbagb)r8 (q) d :12–6.)    dB

What are the lowest and highest frequencies /4 .xg-arb/xin6) f6tqr cf hlthat an ear can detect when the sound level is 30 dB? (See Fig. 12–6.) 4-cb6lrqrffh i/)t.x xa/6ng

  Your auditory system can accommodate a huge range of soun6yyon9tz u8) m1jym7uv5 d z1ad levels. What is the ratio of highest to lowest intensity atmjyyz9vunyzt5o116d um a) 87
(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 frequency of 440 Hz* ,jxuxcu2r;fs., o o r8zvk/q2j: dwy. The length of the vibrating pu.zuw v*28r ,rdx2jo/sqy ;fjkc:xo , ortion is 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 fundamental and first thre tw+yv+0q 0wyd+t non4e audible overtones if the pipe is qw+woyd t yv++n n400t
(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 a2dx i028 kaktscross the top of an empty soda bottle that is 18 cm deep, if you 8k022 dktisaxassumed 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 piws *wt9k7 iwph.1nv(b pes spanning the range of human hearing (20 Hz tow 7nwwk.t*si(19h p bv 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 xcb 8/2u0 .owfsesom4of 540 Hz as its third harmonic. What will be its fundamental frequency if it is fingered at a length of only 60% of itmcw o fss2ub4.8x /o0es original length?   Hz

  An unfingered guitar str s75 *zjjz/lhying is 0.73 m long and is tuned to play E above middle C (33sy5* j/hz7z jl0 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 that emits middle C (262 /pg2yyt9sp4dh)a7x1k/ vaek)za5 av Hz) when the temperature is 2ad py5 7 sk/ )vtx ha4ek)aga2pv/zy191 $^{\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 donh71m;awz qwkeu ):ud : 6s720 $^{\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 1 bqx*upyvrd 2vs0a:, should the hole be that must be uncovered to play D aqy2avv *dbp,ru1x : 0sbove 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 nu9f1lk ;r+ e:;we4 prcoedmt4 ot at any other frequencies in between. (a) Show why this is an ople c4fme;1;rwok+:t 4udpe r9en 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 at tw:a.;jerz 1bn gm,(y i4t 6flmmo successive harmon;rmlgtz 1jb .ai ,4n6e(:ymfmics 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 1fil*c;;xbj-lriegsujg4-t9 bt ;si7qo 1 2t$^{\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 withiv):/lgb* d;o chf*qr gn the audible range for a 2.14-m-long organ b** gvoclh g;d )f:qr/pipe at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is ap1lvj,w, j5 ph t76cgeeproximately 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 anspwe7thlc, ev6j5g1 j,wer 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 whsqy t v0k1yz+m9kv (4*2mbtu aen trying to adjust two strings, one of whkyb yt uvza*vq0+92m4 tk1 sm(ich is sounding 440 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency if middlt71 hwbnoi8 s5e 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 another (brand8 -n:f28fodf t;jgh qk X) operates 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 simu;8ffntjgqd:fk- 8o h 2ltaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4 beakma+ kk45 xoy(ts/s when sounded with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuni+( kmyo5k4a kxng fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the nf56b0a,lu a6l(yl hjsame frequency, 294 Hz. The tension in one string is then decreased b6 lbj, lla65 yhna0fu(y 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 if9 c(tw zmk-/xw two identical flutes each try to play middle C (262 Hz), but one is at 5.0°C and the othkmzw9( t/-xc wer at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, ab5 */tm:2ka p ealk4esnd 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 poss ate:sb 2k*5emak/4lp ible 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:fk wnp: cfxt t0w:1y0 1.80 m apart. A person stands 3.00 m from one speaker and 3.nw1fk0p:y :txc wf:t050 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 hf*02w xte4qt at 132 Hz, but a piano tuner hears thrwet 4q0* 2htxfee 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. How many beatsu2t8qp fe3:d fw q7t4 vxg)d:z per second will be heard? (Assum:v d:qftz8xp u24ewf3)tg q7de T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engjhscn /uv 8ahhrb6+ 34ine’s siren is 1550 Hz when at rest. What frequency do you detect if yrs nh86v/hbhc3 a4ju+ou move with a speed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What nc:q :9h0yk(,pzrz px frequency do you detect if a fire engine whose siren emits at 1550 Hz moves at a speed ofxpnz, : :rzhy09pc kq( 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz source is movin b0.r8m/d.( rvogq dc3qpix l6g toward you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exrxlcqi 0d vqrpg b3 68md(.o/.actly 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 one i jy*l8yn 5aa -if( )ajefxkt*r14ds)gs at rest and the other is moving towa ifxjyak*1 ft)4y8grs* nja)ed (-5al rd 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 dpetj+(m29xqw( gw ys;ka(q2receives them returned from an object moving directly away from it at 25 m/s What is the receia ((2spj qx9wy2t+qg; dekm w(ved sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wg 4)w21qbwpq(p;ktrjz.)t* klr uo , oall at a speed of 5 m/s As it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frzlq*jpg) u) wwp(;rbktt .o24qk o,r1 equency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was played on a moving flat t(bn7e1u:, b2 a 6voo9cuj poikrain car at a frequency of 75 Hz, ao,i7e jabc1un6 op9k v:b o2u(nd 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 ultrasp9p/5n ae) ac9c6myh found waves to measure blood-flow speeds. Suppose the device emits sound at 3.5 MHz, and the speed of sound in human tissue is ta9e cmf9 /ahn56c p)ypaken 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 frequencw3xqr+l-p7b .fuib,tsf p .p )y $2.25 \times10^{ 6}$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 emit9w +fvlkaqkh s* +,7oh8btdx9 s sound of frequency 570 Hz. When the wind velocity is 12 m/s from the north, what frequency will observers heh a ox7k +bfkv,*+ds8 q99htlwar 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 laqzt s;: dcso liop*5 q-f9(j7pnd 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 wh o* 2a8b ofovbe.fru)e0sst.; ere the speed of sound is 310 m/s (a) What is the angle the shock wave makes with the direction of the airplane’s motion? ob)8vfr.fs*u.;t0eo e s b2oa    $^{\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 atc4 x*vt w1yw ic-yx ncdn*/ ntp-/x).pmosphere of a planet where the speed of sound is only about 3i*pyxn/)c.x -w/yn tnvd4w 1t -*xccp 5 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} $