What is the evidence that sound tjm/vpk *dp5 e7ravels as a wave?

What is the evidence t5x (3khz: awp2g c7ez+y r)fvvhat sound is a form of energy?

Children sometimes play with a homemadeiajo(n1u9l;smu0ufae t y+,0 “telephone” by attaching a string to the bottoms of two paper cups. Whitnu; m+asy o1 au0ej9, (l0fuen 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 wa j5q)arml,l 9xlw,o ;pll+9.thxeh j)ter, do you expect the frequency or wavelength ta j;9)) lqmlr+hw. xtop l,,lxle5h j9o change?

What evidence can you give that the speed of sound in air does not d1 qwhwtje3rm2g/3 l l3epend significantly on freqe lr1lq g/h3jw2w3 mt3uency?

The voice of a person who has inhaled o) h6kzu c8k-iigor; 8w-/bg fhelium sounds very high-pitched. Why?

How will the air temperature in a r 6o x/)pk(tgcqoom affect the pitch of organ pipes?

Explain how a tube might be used as a filter to reduce the amplitudc (u56cqpo ,3uc / z3usvq)znse of sounds in various frequency ranges. (An example)u/s ucnu3cszo5 cv(3p6q, zq is a car muffler.)

Why are the frets on a gu8ua-sj mgw 3h)itar (Fig. 12–30) spaced closer together as you move up the finger3sh8m -) gwjauboard toward the bridge?

A noisy truck approaches you from behind a building. icichcco- f*3v+pv8 6 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. -i3+ vp *cihofccvc86[Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due to “in. va;ge4i3h :z./sjmi7yciwx terference in space,” whereas beats can be said to be due to “interference in tii. c3 g:asxz.ihi /meyj; 7wv4me.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered, wou5 4vh hd6xvh 7ci9es :xquj.y8ld the points D and C (where destructive and constructive interference occur) move farther apart or closer togethd.jsqhx uhcx:ve 4 v59ih7 6y8er?

Traditional methods of protecting the hearing of people who work in - ea mfw;1ast2humnd296 +r pgareas with very high noise levels have consisted mainly of efforts to block or reduce nodma16gpnwm t+a 2u-2;9 hfserise 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 waves shown in Fig. 12–31. Each wave can be thought of as a sup60mvnw 1 nj-twci 4j.berposition 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 far1ibnvw- t6w 0m4j.n jcther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and observer move 14spl1i-9s fod zt /rh:t cz:sin the same direction, with the same velocity? Explainzc hrf/i ss1tl s:do19pt-4 :z.

If a wind is blowing, will this alter the frequency of the sound heard by abaw*rl w ft0a/*4lm0y person y f lm4twr aal*/w*0b0at rest with respect to the source? Is the wavelength or velocity changed?

Figure 12–32 shows various positisz4;9h5p8so kz-ipb.r kba m)ons 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 thek-. spa84kbs);9mhzro5b zpi 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 the echo of her shou x ,9nn* h:i)erspsrwu5:p 5lct reflected by a cliff at the f,5epu5::w slr hsprn9 nixc )*ar 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 bezprxle38 , bb.low 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 1.bez x 8l,rp3b2–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in aio 4;cava nsa) * 2i+ea:ake0z8ai(x rur 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 foggbw.kf )uzxw i e ,y;diz96:c)jy day. Without warndy wi je))9;,uzx:wk 6bfiz.cing, an engine 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 splash it makes when striking th 3gji;s**1o.akd m ftze water below is heard 3.5 s later. How high is the cliff?g31oz* asj;fd mi.*kt    m

  A person, with his ear to the ground, sees a hugevccd3-kss6 wr7yb+g 6ggjb *6 stone strike the concrete pavement. A moment later two sounds are heard from thygb *+73rbdg-c jg66scv ks6 we 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 mile ofa e+(b4.orcyg( 9vk wq distance by the “5-second rule” for estimating the distance from a lightning strike if the temp(vwargeq +k.ybc( o49erature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound ata )hhzb/cj9b*nvecp+ 2i b6 4i 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 9omeh 3t9t,of of a sound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired simultt ok((;,zxfjg.-xn f caneously at a certain place, what will be the sound level if only one is exploded? [Hint: Add intensities, not dB’j,x(f;xn(k.o zc gft- s.]    dB

  A person standing a certain distance from an airpr*r0 gsfym5u5u +1 ywnzo)7x wlane with four equally noisy jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would this persu m5 7rxfn) +0z5wgwru1y y*oson 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 sibxe jxpsi 0(/jhqjo*c8m2fh)- 4k t/q gnal-to-noise ratio of 58 dB, whereas for a CD player it is 95 dB. What is the ratio of intensities of the signal and the background noise for each kj/ix 8e4 q-q0fhxb)j jmo/p2t(* h scdevice? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from a person s uw- tcqas(/l2peaking in normal conversattu/ ascl-2(w qion. Use Table 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 wxbbfo2ica:s /h* r)1 vhose 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 thev(wh*- acb8( 8;ezzfpzvd(cy more modest amplifier B is rated at 40 W. (a) Estimate the sound level in decibels you would expect at a poivefc (vbzdaczhy* w; z 8(8(-pnt 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 regis 6 7iejoo(jjurgli8y 3oe)) i9tered 130 dB when placed 2.8 m in front of a louds6(gjiejlr ju e8i7 3ooy)9o)i 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 typically detect a differe vkwaj;1;a 4zbnce in sound level of 2.0 dB. What is the ratio of the amplitudes of two sounds whose levels differ by this amount? [Hint:b azvwk41 a;;j See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factor will the intensi 2 vjbw qnaw/nr*k1jt)qd(9 j.ty increase? Increase by * aq 9rw.d2(j/wqkj1bnt)vj na factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, butnz.9hvi4tij88 8i+hrmbdoly f 4. k j7 one has twice the frequency of the other. What is the ratio of their intensitie.i om h+8tzy7vhdk 8i.j li4f49n8bjrs?   

  What would be the sound lecxnyd),.2u 5fz xtonko 9d. 7gvel (in dB) of a sound wave in air that corresponds to a displacement am.y 5g)o. 72udn o9,fcnz kxxtdplitude 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-Hz toneye(v6bgez+ gj7.1 cgr2ahs 2m that has a 50-d 72js v g1z a(+.6cehbm2geygrB sound level? (See Fig. 12–6.)    dB

What are the lowest and highest frequencies that an ear can detect when the sgd0;kd - w1zzqby+ju0ound level is 30 dB? (;z -zu+djk0gd0b1ywqSee Fig. 12–6.)

  Your auditory systemk6op7r wdh1eii)0klt6on) i0u z of ,( can accommodate a huge range of sound levels. What is the r) odo0 7 ii rn6(p1i,e0hwlk o6uftz)katio 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 2kpi5zu ii4uuj b8-ps139cr g has a fundamental frequency of 440 Hz. The length of the vibrating portion is 32 cm, and it has a mass of ruug4iu-s1i zj2p bi9 8k3c5p 0.35 g. Under what tension must the string be placed?    N

  An organ pipe is 112 cm long. What ar+xa)svhr(yj/r-4x u b bs6c m9e the fundamental and first three audible overtones if t-amj6csyrb +b rsuxh()v49 x/he 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 blowi uce :f68rn6xbduf3g 1ng across the top of an empty soda bottle g61bc fd u8n6e uxf3:rthat is 18 cm 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 hum 4 :libgy4quv(f ec)t+an hearing (20 Hz to 20 kHz), what would b4uyq i(c gt4v:flb)+ee the range of the lengths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar strinyx*yly7 4;x7 gq ne5:4urfwk gg has a frequency of 540 Hz as its third harmonic. What will be its fundamental frequency if it is fingered at a length of only 60% of its original lenglr x7g kwn:yf 4;5yu4qx7yeg*th?   Hz

  An unfingered guitar string is 0.73snw4xl2q* 2v6qa/ qk w m long and is tuned to play E above middle C (330 Hz). nlv6w42axqkw/sq* 2q
(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 ol1m.i qy g:0;d(4h6srz typljl* u v*epen organ pipe that emits middle C (262 Hz) when emy *tyi l0:r. (; hv*upq6lj1lzs4dg 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 at 206h9ptp5arhbf9cn:/3wuck ; f( lfp1 m $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flute in Ei9/hf3r vu 0ad8 hop;qxample 12–10 should the hole be that must be uncovered to play D above middle C at 2/iaqp; vr u38fd h9h0o94 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 pip dxtm72m0a y2fe can resonate at 264 Hz, 440 Hz, and 616 Hz, but not at any otd2fyx 2tmm0 7aher 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 aty fei) x(+w(on both ends. It resonates at two successive harmonics of frequencies 275 x wy)+ne(oif( 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 g8oe /m5r - kzzkyo)8p$^{\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 fl/9g7vnay/w, qr;x ltor a 2.14-m-long organ p 7n/vw/t; gqr9ly,alxipe 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 b goqnoo0s-s:uo - )p:is open to the outside and is closed at the other end by the eardrum. Estimate the frequencies (in the audible range) of the stas-o ou)o g0bno:qsp: -nding 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 l */ 2jmbrsn9 mp4l8ns*ik*hqbeat every 2.0 s when trying to adjust two strings, one of which is sounding 440 Hz. How far off inlnr/ s**j8ks9 hmbq2 *m4in pl frequency is the other string? ±    Hz

  What is the beat frequency if middle C (2d ,qftlnd;3g962 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 (brz-sgd ll;)af0c+p+0 s8 jtxjm and 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 frej;0d8tzgc+l xpjs )al0sm-+ fquency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded with a 35* -mj7(jpbe lzx3lo9 uxj4ag90-Hz tuning fork and 9 beats/s when soundedjl(zb3a x *-jogm9u 74jx9elp with a 355-Hz tuning fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz. The sv cxxyj0; 89ztension in one string is then decreased by 2.0%. What will be the beat frequency heard when the two strings are played together? [Hint: Rxcz s;v j80x9yecall Eq. 11–13.]    Hz

  How many beats will be heard if two identical flutes each try tou:ev;0:apr em play middle C (262 Hz), but one is at 5.0°C an 0v;mep :e:urad the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a freq 6ipeixu/vlx50(nqv:uency 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 frequeiln(qxv i0ve5 xp/:6uncies 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 amo, cmcvf-vpq 1bmy*0a:zm/ pyz*44t6c mr+ spart. A person stands 3.00 m from one speaker and 3.50 m frvys6:b0mm+ptmr/zmza c*4-1q*f vc ypoc 4m, om 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/-ktjnx)s r0efd 6 5bw, but a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibrating at 132 Hz, what mxjrfst) -ned/0bw 56kust 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 and9dkzc 4ej8z,e ro4m3y 2.76 m in air. How many beats per second e ozke dm9,zr j8y434cwill 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 atyg2a5a- ;hrqc e(+ gvl5ubzz : rest. What frequency do yz+ab5z v-c :ge2y gah5l q(u;rou 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 fire engine whos-jkac k-fli 3v3 u l:8;dcfws6e siren emits at 1550 Hz moves at a speed of 32 m/wucld6vsj 3 i8-kff-a:lck;3s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz sourkb8 1 ea9gu/hbce is moving toward you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exactly the sae9k / b81guhabme? 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 freques mhx8o14 7iq o*-qmuency 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 freque me xhq74s1o8uoim*q-ncy the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at 50.at ya*p skm4l 52v x-bqt:z,vip1ywt)-74shh0 kHz and receives them returned from an object moving v4ph5z-ti4s tp hyms- 1atyq):xkb w7av*2l,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 oqpp/ aw*ij uxf+ sv*rn 9r(3ka6e9un/f 5 m/s As it flies, the bat emits an ultrasonic sound wave with frequency 30.0 f nnxa9aqe/wu+6r 3 up(9p*rj*/skiv kHz. What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was played on a movi 0r.u * 4dp*2euzivdoing flat train car at a frequency of 75 Hz, and a .4e* iu 2o*i zurvddp0second 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 3+69h yzvufko blood-flow speeds. Suppose the device emits sound at 3.5 MHz, an +9ouhk6y 3fzvd 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 +p85 m0y8bpgc- sjdx+ldz (9eq(quj q 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 emitsple. ghyq;kjqwb 7 8// sound of frequency 570 Hz. When the wind velocity is 12 m/s from the north, what frequency8b;7ky/ qhjwgl. qep/ 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 its speed at 2l*h -ot8 u7y1 k7j8ywvzvxpn-0 $^{\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 sounkv/q:*h+amnhx, 3 el zd is 310 m/s (a) What is the angle the shock wave makes with the direction of the airplane’ kal+,n:qh/mhvx3 e* zs 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 n :pb-(r nt+jxsound is only about 35 m/s b(tnxn :rj-+p
(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} $