What is the evidence that sound travels as a wave,v*1mzmh na;ut b;xae6yf q+/ ?

What is the evidence that sound is a form dm qy84)47dzn 3hen wdof energy?

Children sometimes play with afjoh 3 y.ty3/w9*9hyptub3 8fi ebsq/pu;0 aw 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 othera tp./bjhhf/yu3 b*0 uiqp3 y;s w983wytefo9 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 water, daa g90 0dphvt ey6or0zb*;3r ts,eiyjj 8)n7 mo you expect the frequency or wavelength tjryie ea;b) 3o g7m t6vz 0d8,n*y0sthpj90rao change?

What evidence can you give that the speed od3:vr px x *;p 57uor9yaup3imf sound in air does not depend significantly on frequ yov pip3;umx*urdrp97x5 3a:ency?

The voice of a person who has inhaled helium sounds very high-5imyb(q-2n* k.jkf yrpitched. Why?

How will the air temperature iofwx ,to ;id,k-c84zd 5k.mj lt4rcl* n a room affect the pitch of organ pipes?

Explain how a tube might x ,f7 lauv+;pebe used as a filter to reduce the amplitude of sounds in various frequency rangesue;fav +7xl p,. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer toed1fw,3imy w/ b(yef( we06 kvgether as you move up the m0w (e (b6ye1/fdy,w3we fkivfingerboard toward the bridge?

A noisy truck approaches you from behind a d9rex8m.f fxegd.f ud,g4v+9 building. Initially you hear it but cannot see it. When it emerges and you d9g8e.m eugx ff4+ ddfvr9 x.,do see it, 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 ddzfd)zo 5d1s h7 i-71;hxerrbe due to “interference in space,” whereas beats c hfd 71-xe)5rddho;z17 riz sdan be said to be due to “interference in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered, woumy.y52 j0ms fx0z*jijld the points D and C (where destructive and constructive interference occur) move farther apart or cl2 y j.zmfxy0m*5s 0ijjoser together?

Traditional methods of protecting the hearing of people who work in areas wiilc cxe+xi+- ke 2i/ 4ucg6dt)th 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 electrc t-6/4 xildx+ ckui+ eg)cie2onically, 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 a b0x;4.iqrslea(7 ujvs a superposition of two sound waves with slightly different frequenci7aqj ervxi u.sb 40;l(es, 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 shift9 vg 9unf+2wb zvu18n p5spw.u if the source and observer move in the same direction, with the same vpp8u1w 95gf+2s vzvb9u uwn.nelocity? Explain.

If a wind is blowing, will this alter the frequency of the sound hedaq 89z1eq bz*-7qjfi ard by a person at rest with respect to the source? Is the wave qdbqq*j az7f819ze-i length or velocity changed?

Figure 12–32 shows various positions of a child in motion on a swing. A bdwwl.yy*3k j, bowj:4rq.1 z 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? Explain your reasoni l,wo: yb. r3d4wjy qzk*w1j.bng.

  A hiker determines the length of a lake by listening for the echo of her shouas) g5dk lr08m*jppo 7t reflected by a cliff at sp* 8amjgl o7kpd)r5 0the far end 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 the waterline. He hepb5wrvz:z7 fgu *m 7 gb+-is5dars the echo of rp*zz5sv7g m:-u7 gi f+bbw5 dthe 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 depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in a ifp 8pbw )k 42q(uy6h,bvhom5ir 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 a foggs3dfg jt*7+;+m-eps fc ylqu, y day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 1css +up+j7;qdffm3*y g t,l-e 2–33). 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.muts q ytfq ae)nk7)x3u t,o.hwp9c:l 3 4h*(c The splash it makes when striking the water below is heard 3.5 s later. How high is thehef )pt*4t q3 mkuwhc u( 3 :c,t)lyo9q.7nasx cliff?    m

  A person, with his ear to the ground, sees a huge stone strike the concrete pavec rv-v9g n d*.v trmcu-/d2cf.ment. 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 im.dv g9/ *2r v cdv-c-nrt.ucmfpact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one mile of distance by thez+t2se-pm k*bx,)mw b “5-second rule” for estimating the distance from a lightning strike if the*p+t)e-k2 bzsm wmbx, temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a soundq1ac 3 7ge(zsh 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 wzy8k 6,3jjtzf hose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level 7 p0-jkfsrke)of 95 dB when fired simultaneously at a certain place, what will be the sjp0re ks )-f7kound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a c8rym9ogh+(2 x ts v( 8ya/smfkertain distance 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 avmy89 t y s/gma8(+kof2(hrxs ll but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to have a signal-to-noise ratio of 58 dB, whereas316uw6r- )e owmtfluc for a CD player it is 95 dB. What is the ratio of intensities of the signal and the background noise for each13wfcro )w-mut6 le6u device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from a person speaking in normoq+ nl-wm x:)nal conversation. Use Table 12–2. Assume the sound sxm)n:ownl-q+ preads 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 wo89 (ee 9 03igdg5jfwbql 3ewbhose 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 i zpn2,mik1 +fzh 8tlz-s rated at 40 W. (a) Estimate the sound level in decibels you would expect at a point 3.5 m from a lou18kfph t+z,2m zz inl-dspeaker 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 placedy7w bmllobr-,1;9f w et :b6vd 2.8 m in front of a l fbe l,-lr;9 :mty6d o1bvw7bwoudspeaker 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 typicallyjdt1 k5+wr 1c se.v4dl detect a difference in sound level of 2.0 dB. What is the ratio of the amplitudes of two sounds whose lev1tv5d.+rj wek 1dc4lsels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factorvfpng4 m7qahu54t42u will the intensity increasq4v5am u7hu2tpg4 n4 fe? Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have ezmb.o ,l0 7r xc)g-j/ pe3pva5tz.wuuqual displacement amplitudes, but one has twice the frequency of the other.l m /xt eu b05,go7zu.w3). -jpcavrpz What is the ratio of their intensities?   

  What would be the sound level (in dB) ob m8r c/hg.ecco(k3l+f a sound wave in air that corresponds to a disk3e 8+m/ob(l.r chcg cplacement amplitude of vibrating air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have)co ,eefqf.8eqa.a0 a what sound level to seem as loud as a 100-Hz tone that aa, e8qe 0).of.afe qchas a 50-dB sound level? (See Fig. 12–6.)    dB

What are the lowest and highest *(qd1 l.2vzlimru d,mfrequencies that an ear can detect when the sound level is 30 dB? (See Fig. 12–6ld i1(mq zrd*lm, .v2u.)

  Your auditory system cansk vno /d 8r4wo8zh di1ju19y3x-bm/y accommodate a huge range of sound levels. What is the ratx91nvk3//ow dz4i -jm dyyo8h s1r8ubio 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 fundamental frequency of 440 Hz. The lengthfby1oyd /f t87 of the vibrating portion is 32 cm, abyo7ytf18f /d nd 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 thxn, au4fth, *cb6 xs1oe fundamental and first three audible overtoo,fun1h4 xb,c x ts6*anes 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 fromv jls) -q(sibya2 bx0b9 d(n88ko1qox blowing across the top of an empty soda bottle that is 18 cm deep, if you assumed it was a closed t(2xx80k()s1 slin- bvao8jy9 d oqbqbube?    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 hum *h. 1il njxkk28ik23f +fneskan hearing ( 2ikkx+8fhlnisf*jknke3 . 2120 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)6hgahyzya5rh qo +q(;tis 85 will be its fundamental frequency if it is fingered at a length of only 60% of its original length ahh)s56 rqa+qtgy yh;i8z(o 5?   Hz

  An unfingered guitar string is 0.773 i3cj; i a7fuftsi0i3 m long and is tuned to play E above middle C (330 Hz337fci i 0ft;iisaju 7).
(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 m0/r ,opt.tdkC (262 Hz) when tptomt/d .r k0,he 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 nlkp.aydn/s ci7a s qm 660r8: an;l(tat 20 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiedwqfo;4w iie24)/fmkce of the flute in Example 12–10 should the hole be that must be uncovq4wf 4 /i;fk oemiw2)dered 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 pipe can resonate at 264 Hz, 440 Hz, ani(0tjvme t6; nd 616 Hz, but not at any othjnm0;( t6vteier 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 bonv sixfz) 8*2tth ends. It resonates at two succesvf8 x)s nz2*itsive harmonics 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 o, iwav-jy95z 7p*ble$^{\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 for a 2.14-m-long /5; yo(k0ptosz 4ser corgan pipe at 2s/(4k5s0t z eorc;pyo 0 $^{\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 toy8 x56o1 krka2hcqc w+ the outside and is closed at the ot yarw +2q8kc ox15kh6cher 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. 12–6? $f_1$ =    Hz $f_3$ =    Hz $f_5$ =    Hz

  A piano tuner hears one beat every 2.0 s when trying to ;)t dmz/q 3qpao8qor/gr1mv-adjust two strings, one of which is sounding 440 Hz. How far mvar ;3pmd r-g/) zoq/to8qq 1off in frequency is the other string? ±    Hz

  What is the beat fredkd13 rl)8 gt jk(v;;i.vnb aoquency if middle 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 whistlk2 5zad3(qof se operates 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 oper3a s(dkf2z5o qating frequency of brand X.    kHz

  A guitar string produces 4 beats/s w9sl d)i)zn x(wr5s7 ko.mf2e 3 wtbj0xhen sounded with a 350-Hz tuning fork and 9 beats/s when sounded wrwjbk s9.w2lf5 7eiod )s 3t0n()xm zxith a 355-Hz tuning fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to n ezn0y/-tvvf 0z8;ag+ atw2ethe same frequency, 294 Hz. The tension in one string is then decreased eza0nv2fwa tt -8g/eyn0z+v; 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 heahd02:6oe a7ab o glmn0rd if two identical flutes each try to play middle C (262 Hz), but one is at 5.0°C and the other a7bmaloo0a2g h6d0 en:t 25.0 $^{\circ} $ C?    beats/sec

  You have three tuningn4 pozvhcar/ b(ir91/ forks, A, B, and 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 beac1p bh9 (i4n/raor /vzt 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.dye d/ds yh6ig5;0xo m from one speaker and 3.50 m from the other. ihde;0 .dx odyg6y 5s/
(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 are5p c3e lr t)0l(gev(ajuobzc )ir:02e supposed to be vibrating at 132 Hz, but a piano tuner hears three beats every 2.0 s when they are p(r(l:e)zg 5c02oa evc3je)biurlt0played 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 airy()tp/v d uf0ge p+5g/av4 bbmah, -pbyt,q4r. How many beats per second will be hp,pg) mytv-p/e bu4+ry,/dhba4(vq tbgf 0a5eard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s siren dt ewz uch5-.x+fbvy(9o) uf.is 1550 Hz when at rest. What frequency do yu vhxb.)df5u.w+z o(-9ft yceou 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. Whaiy6q (r u6+xnt3kgzs(t frequency do you detect if a fire engine whose siren emits at 1550 Hz moves at a speed of 32+ kqz(gs( 6n6tixryu3 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz source is moving towari iais4h3j3gld*43jqlu5 dalnn) g() d you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exactly the samuhsnn) q5i 4ll(j gi*g3ia3j3 ald4 )de? 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 singlezf bbbjl(4sd/fl7 50v 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 isz fd50flv7bbb (j/ l4s the frequency the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at 50.0 ll t 2fz8y3pb+kHz and receives them returned from an object moving directly away from it at 25 m/s What is the receivzyf tp+b ll328ed sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As it flies, the b1wxc7wq;bbd:un7 -w e c woba,r1jq70at emits an ultrasonic sound wave with frequency 30.0 kHz. Wwcq7b01 w7n w r x7aju1ebb-wd c;:,oqhat frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was rfz.zj7:lk/t .i; y yeplayed 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 approached the st ziftk 7yj/z :.r;l.eyation at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultraso ai+vi(e.p g;kund waves to measure blood-flow speeds. Suppose the device emits sound at 3.5 MHz, and the speed of sound in human ti;kge pi v.a(+issue 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 usi2pka pe8hem xn +9zq9e7o ,u5ung ultrasonic 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 frequency 570 Hz. When the wind velocity is 14g5wecd+vb* u qif t182 m/s fromq 8uv1 fd *wciet54+gb 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 if itju 5r201y hen 6cc7nnxs 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 spe1 uw)q , oz)tttd6noae3 23pgded of sound is 310 m/s (a) What is the angle the shock wave makes with the)2wotddt16pqg)teoun,a33 z direction 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 j;- dknbp++l dplanet where the speed of sound is only about 35 m/s +-d+jldbkp ;n
(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} $