What is the evidence that sound trah*qbdi7v;x d: j 93gz fne-x.xvels as a wave?

What is the evidence that sound is a fo* uza,xm 9ni(gvus()u rm of energy?

Children sometimes playcs e vcvj3e;)mag;(bdi0d6 y2 with a homemade “telephone” 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 souje b;a 0g i3v;s cyv62mce)dd(nd wave travels from one cup to the other.

When a sound wave passes m4(p tn-qyi/ wyed +jaez+a1)from air into water, do you expect the frequency or wav-+yp at+(/ dni eeqzway1m)4jelength to change?

What evidence can youw84vo:u2stzco ng65/w p 4 aoo give that the speed of sound in air does not depend significantly on frequepg o/w45vzn2aso u4:o68 c twoncy?

The voice of a person who has inhaled heli(x4oh)b0dma45x c fx tum sounds very high-pitched. Why?

How will the air temperatu)b 4fzh5qyzy (skpi.)ouj z x26e c8+fre in a room affect the pitch of organ pipes?

Explain how a tube might be usedsckx6,n(hq fv1 o2+hn as a filter to reduce the amplitude of sounds in various frequency ranges. (An example is a ca6x+1hs(,2 k hnq ncvfor muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer tooblb:oz*x)ikayi txbw )1c +a (; olbd;n 481ogether as you move up the fingerboai z11b;yx w+*xobb;d( :a)4canik lboto8 l)ord toward the bridge?

A noisy truck approaches you from behind a building. Initially you hear it but csbg*jjt 0 xkz2efj/kx 9a idg/2)h;f) annot see it. When it emerges and you do see ies *j//fxa x920)kkzfdgh2g ;j ibjt)t, its sound is suddenly “brighter” — you hear more of the high-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to rfp xfnws89)0be due to “interference in space,” whereas beats can be said to be due to “interfffnp )xr089swerence in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were;n2jza76kb.v h a ;,1dhi, *es:vxmzbjujx*l lowered, would the points D and C (where destructive and constructive interfnaz jzeb:uxm7 ;2kjxh 1d *l;6* .j,vabh, ivserence occur) move farther apart or closer together?

Traditional methods of protecting the hearing of pe: e0pi6x xpl-uople who work in areas with very high noise levels have consisted mainpul6 p-x:0eix ly 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 the sound levels reaching the ears?

Consider the two wav in(f k; 40zkidclzyszx c1g m83sdlb 2d389u6es shown in Fig. 12–31. Each wave can be thought of as a superposition oyi ml 1cxg3df0;8ks(bzl46udn2di zz 8k9sc3f 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 observer move in the sama ey4pkur ndpx8vz58q2. g6u ,e direction, with the 4uxprdna6,e 2kv8y u p.zq85g same velocity? Explain.

If a wind is blowing, will thikg mk-6cf;u (ast5- ves alter the frequency of the sound heard by a person at rest with respect to the source? s-aef (kuv tk65g-;cmIs the wavelength or velocity changed?

Figure 12–32 shows vari4)g6 r5o/orfergig 1hous positions 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 through E, will the child hear the highest frequency for the sh4g516rg/) oirgef o round of the whistle? Explain your reasoning.

  A hiker determines the length of a lake by listening for the echo of her shoutu. e ;:yxvt(rg ib5zl*-r:jav reflected by a cliff at the far end of the lake. She hea ieru5-vjbr:(z * avty:x .l;grs 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 the wate5r kdzt5rc1mk1u n2l*3nmh-s rline. He hears the echo of the sound reflected from the ocean floor directkn5l3nr ku d1c t1h5szr2 -*mmly 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 waveles2x nnm/+fq 5;xik4rwa1mx0 engths 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 abovmqtn./.a.el m es,4eje a school of tuna on a foggy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How much time elapses before the backfire is heard (a) j.l /nm.tee se, 4.qamby the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a cliff. The splash it makes ;b+04yvzaxs + qs ofk.when striking the water below is heard 3.5 s latbkx;q sz0v4+. +oa syfer. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge stone strike the ceu+l rck*s/7( kd5wrb oncrete pavement. A moment later two sounds are heardek(b/r c5+wkrdl* 7u s 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? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one g6a apa (z)tt;mile of distance by the “5-second rule” for estimating the distance from a lightning strptt)a(az ; ga6ike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity z0g akbnm) 2(gof 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 ge+r,(owd+jo intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB whenpka/ p,kx;vh850zekh fired simultaneously at a cer k5aph8 ;xp vz0,hekk/tain place, what will be the sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain5 *0,4d. xmdydn:5.chfeupik dbh z 1gpe0tq4 distance from an airplane with four equally noisy jet en*zud nd e5tc phf0gp.041d m4.h:yb5dx ke ,qigines 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 said to have a signa1 elvd: 4m jtia 4,d681.gdrcytade *tl-to-noise ratio of 58 dB, whereas for a CD player it is 95 dB. What cet16j8,*t d glryd 4t4daiad:1me .v 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.(z5cg*: ccjag-06px odu p zp from a person speaking in normal conversation. Use Table 12–2. Assume the :x(zcgupc56* z0c.p pdagjo - 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 al yr5o72 1/uh 2+or8wbs.jhfl ;yrghhrea 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 is ra/,+f5 -wmxt jxpqr;m qted at 40 W. (a) Estimate the sound level in decibels you would expect at a point 3.5 t-rpqjwmmq+ xx,f /;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 i9bac*)n rg/ otn front of a loudspeaker on9arc* bg n/o)t 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 s-epuadpx z(5yc23fy-l fm+)hound level of 2.0 dB. What is the ratio of thexuc)p-y lhd-e2mpff5zy(+ a3 amplitudes of two sounds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tr5s4cqxsf 9c* tipled, (a) by what factor will the intensity increxqf 9s5 4t*sccase? Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but one ha7jxm zr w9a. bwdhs(j 4td:d7;s twice the frequency of the other. What is the ratio of their intensitijrt h4z w wds9:mabd(j xd;7.7es?   

  What would be the sound level (in dB) of qgvz 9ieuqn0ioz. mz- t7es er5:8 a+3a sound wave in air that corresponds to a displacement amplitude 0qm z87.q u3sez+:ae -voiziegrt5n9of 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-Hzr -crp 4k nm:b4x39d(by;gxx p tone that has a 50-dB sound leve k x4xx4r;bynprdb m39:g-(pcl? (See Fig. 12–6.)    dB

What are the lowest and highest frequencies that an ear can dey9te,fu iaew m3(l.c/tect when the sound level is 30 /i(,e.fwm ey u l3ca9tdB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of 7 +20 lh;fmllqgwq(gp sound levels. What is the ra(pq2;lwfhm70+q lg lgtio 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 fu-/-7tr ok +r.jf i4kh bufv.lrndamental frequency of 440 Hz. The length of the vibrating portion is 32 cm, and .4lifr r+-f kojv7kt/-ur.hb 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-/sbx b2xx.u x fundamental and first three audible ox b s/xx-b.xu2vertones 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 expect from blowing acro :i4 +hi*mh,vsm dke6)to.sgxss the top of an empty soda bottle that is 18 cm deep, if youmi4, kms .t *v: esdh)+xoi6gh 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 tjqs i20y3u;;quq8h uxhe range of human hearing (20 Hz to 20 kHz), what would be the range of the lengths of pqsu02;h j u8;xi3q quyipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a frequency of 540 Hz p 9oh:; n /gzmmackbh jf4.v2 l7yy/kxlfv/60as its third harmonic. What will be its fundamental frequency if it is fingered at a length of only 60xfoj/lavh yh;vbm7 f/m ylg c0 ./kk4n z962:p% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is fv.5cq3 /ox svbnhl;4o,p s p/tuned to play E above middle C (330,csvp; h ob/v p5xnolqf/s.34 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 orgv :e)mv9jvst, an pipe that emits middle C (262 Hz) when the temperature is 21 v)jtvv: ,ems9 $^{\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 atg ,6y7f z1hsbm 20 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the fluz j8uq(3.wgtv4 wja c8te in Example 12–10 should the hole be that must be uncove jtuc 8jvw8(4qz. ga3wred to play 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 pip8tpf: w0hyb 6ie can resonate at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (a) Show why this is hi0t:py6 8bwfan 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 7meuoq/ nf jxr6/yg0)yrre ,0is open at both ends. It resonates at two successive harmonics of frequencies 275 Hz andx/rrnje uy,y6e/0)70fq mgor 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 z.xo: e,c, jw6o 5t(x-oi m+gjmig( oo$^{\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 audible range fo wium2d3s9207jgny nb r a 2.14-m-long organ pigud0m7n2nis9ybw32 j pe at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm long. It is open to the out)lj k9nnsi8z 0side 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.08z nsln9ji k) 12–6? $f_1$ =    Hz $f_3$ =    Hz $f_5$ =    Hz

  A piano tuner hears one beat every 2.0 s when trying to adjust two strings, one xdg,l u*(nw1uowxd3.ue(j5n of whicun g(w ul*dxu,x ndj31ow5e.(h is sounding 440 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency if middle C / :tb6koju 7wz(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 operate fnnk)dq.:y6eod6ih. s at 23.5 kHz, while another (brand 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 simultaneously, estimate the operating freque fyo. )kn66hdd:qnie.ncy of brand X.    kHz

  A guitar string produces 4 beats/s when sounded with a (j,q -68qz6.amkxh5zhbui e g350-Hz tuning fork and 9 beats/s whe,g6( ehzijk5.um6z-h x ab q8qn 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 t5*9ja/xk*7+lu;ptf14d(fkt kwoj ys;wp sfe he same frequency, 294 Hz. The tension in one string is then decreased by 2.0%. What will be the beat frequency heard when the two strings are pla+wokp5; /p k9y7f1*sf a4ts ;ljtjx*d(eu f wkyed together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if tw9r/ep cmoqm1/s ;ztb. o identical flutes each try to play middle C (262 Hz), but one is at mm/r.e; b9tzc/pq1o s 5.0°C and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fo(s1x+3jdc.yevlx/ xu/dv(w qo gb : .krk 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 sound:+ly.wu /xockq/x dev(d v( xgb.j1s3ed 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-u x yca5f su+(lnw41,fay8gm 1.80 m apart. A person stands 3.00 m from one speaker and 3.50 m from the osf-x nawua,15ym g (f 4yl+uc8ther.
(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, 0u5t(y1 kehzk(qog z)but a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibrating at 132 Heuq (oz t 1hg)(50kkyzz, 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 beats oy c+k lt 0tm1,pdw6b)per ,1+ cm dkt)lypb 6o0twsecond 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 w0b +,:mp hfixzj4kfu p5gv68shen at rest. What frequency do you detect if you move with a speed of pfiv +,k:jfp06s 8m5xgbz4 hu30 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 engine whwp ew1nw- m0c9 gzq(/vose siren emits at 1550 Hz moves n1v gwwm/-p0(qewc 9zat 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 moving toward y2 j lr.s5arqm0au+0eg ou at 15 m/s versus you+ 25gjur s.la0eamq0r moving toward it at 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 equipped withwv m h67r b1mf8a,mhanw2 f*uf )+uzh, 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 the horns emit? Assume T = 20 * f6u72w ),+b amfruna,hhz18mvhwfm$^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at 50.0v5w; 8 ks4ntss kHz and receives them returned from an object moving directly awaks;w54tss n v8y 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 a60szsxpa8 hjn l15ve 7n ultrasonic sound wave with frequency 30.0 kHz. What frequency does the bat hear in the reflected wz5v1aslj 76 x nes8hp0ave?    $ \times10^{4}$ Hz

  In one of the original Doppler experim l ;g mp2;wlko48ys/hyents, 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 o4lhk;2ylpm;/ syw8gin 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 bloj x.i(2f ui ojy z0gl/ /hohkum7c)3o*od-flow speeds. Suppose the device emits sound at 3.5 MHz, and thm3 /uu.0(ol/xoi2j j h) o*fy kicgz7he 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 n y m; f;t7fcs9zjrjez:f ob9a,2+ z.hof 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 s q6yvh* j4o22kxd2aer6+ nladxpx t(7 ound of frequency 570 Hz. When the wind velocity is 12 m/s from the north, what frequency will obse+ r 2dn24pytkaax2ojxq7l evh6 *6(xdrvers 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 o/j ):z*ib ogzon land 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 speed5ua0f: tm +fxh of sound is 310 m/s (a) What is the angle the shock wave makes with the direction of the airplane’s motion?m:tuah5 f0 +fx    $^{\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 sop- )5( gjz0h .k0*dojxm 4da:isvzlsuund is only ajilpmk dh).j z :ogs (adsv-50x0u*4zbout 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} $