What is the evidence that sound tranqh*+ xo- .:1bg phx,in2npm xyy(3nbvels as a wave?

What is the evidence that sound is a form of energy?82fpkx35 rsol

Children sometimes play with a homemadeuwo m2+qm; 6pw “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 sound wave travels from one cup tomupw + ;w26omq the other.

When a sound wave passes from air into water, do you expect thep2ryx7/y u3;iowm7 u v; ox b8dvxj1k) frequency or wavelength to chan3;ryyoxji8wom7 xv/ dk)2x ;p7 uvb1uge?

What evidence can you give that the speed ofbh5 r cn8wf3,mq4lr9u sound in air does not depend significantly on fr38b h9mq,rl u5f 4cnwrequency?

The voice of a person wh kz drf74ts (r4yc 0.m:t4uplto has inhaled helium sounds very high-pitched. Why?

How will the air temperature in a room affect the pitch of organ pipbcy1c 0 1 tn*w4bypl;qes?

Explain how a tube might be used as a filter to u)kov3 xbk1r zkhb4 (8reduce the amplitude of sounds inuv8xk k4 h 1bkro(3)bz various frequency ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) stvo2ga(6/ku 8af (cnl paced closer together as you move up the fingerboard toward the u2(t aak86v/(og cfnlbridge?

A noisy truck approaches you from behind a vn;u te co2 *n*k.tw7jbuilding. Initially you hear it but cannot see it. When it emerges and you do see it, its sound is suddenly “brigvt;tnjo* 7.ukw2c n*ehter” — you hear more of the high-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due to “interfereq vcnc3(;s zp,nce in space,” whereas beats can be said to be due to “interfeq( scvz, c;np3rence in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered, wj /n owlg pnm*j u/)i:t)l(ac)ould the points D and C (where destructive and constructive interference occurun* ): gwiaj/ml/ct)nl p(jo)) move farther apart or closer together?

Traditional methods of protecting the hearing of people 4r:0 ou8dcds, *v8stwqv wu34 hf(t t7nvi.gmwho 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 rev.t4t0 w wgvu sh:d7vsd t(f*on,c 8i8mu34 qrduce the sound levels reaching the ears?

Consider the two waves tqqi9(*6x-b-xc bmey /nje.g shown in Fig. 12–31. Each wave can be thought of as a superposition of two sound waves with slightly different frequencies, as in Fig. 12–18. In which of the waves, (a) oqx -m-y(e i9* cn6b. gqj/ebtxr (b), are the two component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source an- *sx-pq5evg ud observer move in the same direction, wit -e5 psqx*-gvuh the same velocity? Explain.

If a wind is blowing, will this alter the frequencyt 9br6u0m b*v5nwscc. of the sound heard by a person at rest with respect to the source? Is the wavelength or velsb0cbw v5cn.mtur 9*6ocity changed?

Figure 12–32 shows various positions of a ch8i)h( yg: buc1qggyx5 ild in motion on a swing. A monitor is blowing a whistle in front of the child on the ground. At which position, bchuy1g :gq( xy5i)g8A 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 listening for the echo of her shout u+4p4c rz7 oowreflected by a cliff at the far end of the lake. She hears the echo 2.c 4rwpz+47oo u0 s after shouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below the waterp*yd;bza *)4 2npmavlline. 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 12–1) and does not var; ab zv4 apnd)*ym2lp*y significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths i nbn gilrf,exj) (8k -3yg33cbn 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 offcz p8rp(;zph9wri * 6 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 thp8w6 r *z fp(pi9zh;cre 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 )bj9jeq jvx/4 striking the water below)jq4b/ej9x vj is heard 3.5 s later. How high is the cliff?    m

  A person, with his ear to the ground, sees a hugsgye-t,-ixk/ s o4omivp: jx:y u 7*)j1na. cye stone strike the concrete pavement. A moment lapv*j onuyc x-,)i1i.say- 4::/y7xme tgo sjkter 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? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made2 9p9qpb 9izf0.xzrokuc 88*n9gq cw k over one mile of distance by the “5-second rule” for estimating the distance from a lightning strike if the tempekpq cqnwzoc r9xbfu gi280999z kp8* .rature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at thev.s zix :m7jr3 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 w6qzr;w4j i. wxhose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 d d yo9 w79q2pj/0fxeuoB when fired simultaneously at a certain place, what will pd fyo0q w/7xouj29e9be the sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a n6 h9i+ da9 v14hdrvnjcertain distance from an airplane with four equally noisy jet ed6 vavn9ij91rn +dh4hngines 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 signal-to-noise rdwdb+)+vmp2 iz .(dat3q/p gdatio of 58 dB, whereas for a CD player itdadw/+btz+. vgpdqidm2(p)3 is 95 dB. What 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 from al).fckmn-m(ogmdp4 im 6o4 5lu )2xsw person speaking in normal conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphere centered on the m4 (6c)g5dmmn px-u)klfmo o4 s2liw.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 whom5v,wy9r 4 30blt3bya( bios lse 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 2 jh6-2c3 h o)/ttfnqgc50 W, while the more modest amplifier B is rated at 40 W. (a) Estimate the sound level in decibels you would expect at a point 3.5 m from a loudspeaker connected in hj c2)fh-tg/qotc6n3turn 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 of yu jt+ mq5*m3/yih ge6a loudspeakeyq+ /*3ji y 6mehtm5ugr 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 de bhp23:yq iqd0eyg:4 etect a difference in sound level of 2.0 dB. What is the ratio of the amplitudes of two sounds whose levels differ by qhpyb4:y3g e e2q0i:d this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factor will a2jun,8( d ; qlfpib.rqy3e9,k+dyqe the intensity increase? Increase by a faa3f(r .pb,qq; yi2e ej8dnqlu9 +,dk yctor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amme y47g vic i.eoe2/,klj 8v8splitudes, but one has twice the frequency of the other. What is the rajl2s km7ve,.g 4c ee8yiv8io/tio of their intensities?   

  What would be the sound level (in dB) of a soupu 7k25ipgvq we7lm 2(nd wave in air that corresponds to5w 7gupq kl2vi2em(p7 a displacement amplitude 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 tone that-72ysst6cqpb* jw mq8 has a qjcy mq8p6st2 *w -b7s50-dB sound level? (See Fig. 12–6.)    dB

What are the lowest and highest fr65lh fq8benw4n jk0+tqp/,n cequencies that an ear can detect when the sound level is 30 dB? (See Fig. 185/q 6jn+,tbnfq4kc0he lpnw2–6.)

  Your auditory system can a p k(;m*gcf6kn lpzx/7ccommodate a huge range of sound levels. What is the ratio of highest7( lx ppfznmg;c/6k *k 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. The4 o/wmspi4wr4( awag: /ujh2v length of the vibrating porti4:vhg 4wa/umjpws 4oa(/ri2won 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 ad018g )ch -scwy jqmci ,ipaa+e60 /pare the fundamental and first three audible overtones if the pip 6dcg+m/pcy1ah )eqi a0aw cj,ips-8 0e 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 bq8y,/pc9-g mj+apqx)ub 0fta lowing across the top of an empty soda bottle that is 1 b)qa my0+tug9p c,p 8xjaf/-q8 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 pip cjk7,7w 2pdhwx8u2zau3lw / oes spanning the range of human hearing (plw w,d2 uu 8w7/3zha2oxc7kj20 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 j+2pj,zb2c jra frequency of 540 Hz as its third harmonic. What will be its fundamental frequency if it is fingered at a length of onj,r zb 2jp2c+jly 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to play E abo tp 3l)e;2 rlje;fr9uvve middle C (330 H2 ept3r)ejlrf9v ;u l;z).
(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 emits407 b,0 x 4q;odwd4ste qasad,v/fj yn)y(z rv middle C (262 Hz) when the tem /4sty)ay4 q n(dzsqrxd vbe7v,d4 ,; af0o0wjperature 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 amq2s6nuqgtii h5r,c) w6luv stx064;t 20 $^{\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 should the hole be tha :yeodu*sg q :-((mwwnb3a6-svjr x p 6t*vg7at must be uncovered to play D above middle C at 2w:(wor*aaspyqvudg b 6mgnte s-* ( x 7j-v:3694 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 4z3kxj6h*y ftresonate at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between.j3xh kfy46 *tz (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 both enuslw/g0k0 +*vsi inqa0/nt :nds. It resonates at two successive harmonics of fre0ia nv+u0n/t0skqn iwsl/:g* quencies 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 -srjkic) az3+$^{\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 audibl5a aewvx,;f r8e range for a 2.14-m-long organ pipe at 2;w58vxraea, f 0 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm lonmun sugdkdx; 9-, zxqp9a+5.ng. It is open to the outside and is closed at the other end by the eardrum. Estimate the frequencies (in theds. dmk9 pux znq-un59g,;x+a 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 adjust t x4zxrkdn h)t0.,e*1 ft4 gdnewo strings, one of which is sounding 440 Hz. How far off in freqrht)knxx0z4 dd* f,etn .g41e uency is the other string? ±    Hz

  What is the beat frequency if mv yjv0w+ s0xy/ywie1n1b5g -niddle 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 ak*)oqgws-t1j d)i vg0t 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 the0wi )dstgok)g*1v- j qy are played simultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/s wt)s( .+bo8kg huqy*ashen sounded with a 350-Hz tuning fork and 9 beats/s when sounded wi+ t.y sab8ohs(qug *)kth 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 tension in one s ojt *+d3+ u(ohceytvp md93t.tring is then decreased by 2.0%. What will be the beat frequency heard when the two strings are played togethtc.d 93*o+jyo+ (mthdutv3 pe er? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if tw0q*c e *u;(ci3zc nzhao identical flutes each try to play middle C (26zz(3neq* h;0c cai*uc2 Hz), but one is at 5.0°C and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, 8nu-vj6mkh .g 3is:byA, B, and C. Fork B has a frequency of 441 Hz; when A and B are sounde8m-:nhs 6vuibgj.y3 k d 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 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 pelu7kv3n6. p 6fvpcns 7rson stands 3.00 m from one speaker and 3.50 m fl76ufn3vksv p67c .p nrom 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 bxde+w k3rc g3.e vibrating at 132 Hz, but a piano tuner hears three beats eve r3 3gx+wd.eckry 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. *i u/slwccx,jd+7-k bHow many beats per second will be heard? (Assume T-+i lk,u/jwd7csc *bx = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s siren :jdx 9j10 bb9fmhcjxk1 ., pjris 1550 Hz when at rest. What frequency do you detect if you move wib:cjm xd9.1,hr jj01fb j kpx9th 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 dete zk2 zlt 6yfxxyg2x-*:ct if a fire engine whose siren emits at 1550 Hz moves at a speed of 32 m/s 2kx6z xxg*y ztf-:l 2y
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz sjhb 7g* o-0wolource is moving toward you at 15 m/s veo-07wb* jgolhrsus you 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 w93gcqa3, bu3e8bawh aith 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 freb83bw 3q3euhaaga,c 9quency the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at 50.0 kHz and rz4yls;s(n 5 bh7v:nz5izv yf-eceives them returned from an object moving directly away from it at 25 m/s What is the received sound fre l;izvzbn5 75-h (fyzssy:n4vquency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As it flies9najqup iz-xe76drx9. ix7w ., the bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency does the bat hear in the reflectx97pq79ii 6d.ez-xr a.u jnwxed wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was played o o mz*,ubmvfg;*ww; f:n 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 c,v:*; uwomg;*ffw m bzar approached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measure blood-flow speej3fkzt6/ pfc7l.b .qp ,g /yflds. Suppose the device emits sound at 3.5 MHz, and the speed of sound in human tissue is taken to be 1540 m/s What is the expectedy6fz,f7jq./ 3pfcpl tbg.k /l 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 wavfdj3/ y0 oe*ibes 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 velb:u:v mtfz) 05oczr c6ocity is 12 m/s from the north, what freq) fzo50z:vtb c rcmu:6uency 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 objec82pe; kup2qk/* k:;f-y8pvhu wnjffpt moving on 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.. )xa nnlf-cj4d 2xcs23 where the speed of sound is 310 m/s (a) What is the angle the sho.ac4nsfdx2j2- c)n xl ck wave makes with the 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:j/k kwyrr36s the thin atmosphere of a planet where the speed of sound is only about 35 m/s r6ky3 w s/j:rk
(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} $