What is the evidence that sound travels as a wave?/ 3.hfusdh sh+uuh 1g+

What is the evidence that sound is a form ofg pli-z36e) jtz -*vuz energy?

Children sometimes play with a homemade “telephone” by attaching a stricv;p crdu1k p*wl)u43zdn+ 9ze)yr8ong 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 to the *u) 1u ocr+npldy8dzwe4pzr)v kc;3 9other.

When a sound wave passes from air into water, do you expect the frequencyl4di70hupv us, 6kq) q or wave6kpqhq40,)vl7 u id uslength to change?

What evidence can you give that the speed of sound in air does tf dd5y:e7ng2not depend significd :7eyf5tg dn2antly on frequency?

The voice of a person who has inhx2dj9 piqpq1( aled helium sounds very high-pitched. Why?

How will the air temperatui b h/i-gb-sy(re in a room affect the pitch of organ pipes?

Explain how a tube might be used as a filter to reduce the amplitude z jm27lda8df 2of sounds in various freque2dfjl m2d8a 7zncy ranges. (An example is a car muffler.)

Why are the frets on azw lfll :n2495rj7kpb guitar (Fig. 12–30) spaced closer together as you move up the fingerboard tp7 2k:z jb 4flnrl95wloward the bridge?

A noisy truck approaches you from behind a building. Initially you hear it but0 v-k2t,kum l 9lalv0c cannot see it. When it emerges and you do see it, its sound is suddenly “brightera0u,kk lctm-v l9 0l2v” — you hear more of the high-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be s(*3 qpmbx(v z3v l3)lhxu-/ew: gpqwlaid to be due to “interference in space,” whereas beats can bevxzvm3w:lph l ()l3 gu w*3/bp- x(eqq said to be due to “interference in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered, wo d.oxdq*e)h 3 vnwv1 z5za6sa0uld the points D and C (where destructive a0ezs 5d . 31)n*av aozhvqxd6wnd constructive interference occur) move farther apart or closer together?

Traditional methods of protecting the hearing of people who work in areas with vtq;qgvp1). 9la/g l(pz0hfbjery high noise levels have consl ; vqp0a. jlgqhp1t/z)gb (9fisted 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 reduce the sound levels reaching the ears?

Consider the two waves shown in Fig. 12–31. Each wutc5z y0ktn3 2ggo/ ,dave can be thought of as a superposition of two sound waves with slightly differeo,2u dz5 gcg3 0ktny/tnt 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 sou +t7p1r7bxx)j dd- 1myit:mmpc .(ubb rce and observer move in the same direction, with the sam- )mb: mbcdd.ubr7xtx(pmty1 ip7+1j e velocity? Explain.

If a wind is blowing, will this alter the frequency of the sound heard by a oparhsi)izx82 (:k et.q, 4esperson at rest with respect to the q ,(est oikp4s8e x.:)2rhza isource? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a child in motion on a ghk+v0mh 3hxvzc,2n6 swing. A monitor is blvm c h+kg6z ,v3n0hx2howing 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 reasoning.

  A hiker determines the length of a lake by listening for the ec6q 7f unhba9a9ho of her shout reflected by a cliff at the far end of the lake. She hears the echo 279nuqa6 9 afhb.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 hearh2-c cy(. xg)+gt(iomtzggg31pf b q3s the echo of the sound reflected frogg(i gq (c+ghxm3 3-g2t .ctbof1zy p)m 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 air oldx3 468u yxkl(ov, fat 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 +p k: 43kl 4uk*mmo- bsbwi4xlschool of tuna on a foggy day. Without warnin l4bmbop4u-ixwl4kkk :m3s*+g, 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 wemcab) ac(:n1 hen striking the water below is hea : bc)eam(anc1rd 3.5 s later. How high is the cliff?    m

  A person, with his ea wsflt7h r*9k n189 m4xlhr3por to the ground, 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 thexf 8lntw3 lr9m47o sp1r *9hkh 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 e uuyskaf 84 (*rugf(1jbu w*8one mile of distance by the “5-second rule” for estimating the distance from a lightning strike if the temperature is (((f*f* s8b4u 8u u wa1uyegkjra) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pain level of 120 d2uwecr0a (c3w2dat- r B?    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 i g96 eadj(9t4 lpie7lwntensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired sg(o 6tpn/k9uqimultaneously at a certain place, what will be the sound leve6qtgn9opu( /kl if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an ai f38g(;slqn:f7 *jlur i evgh4rplane with four equally noisy jet engines is experiencing a sound leven3;j4ifq g :lsg7rul(h*fev8 l 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 po-62zit cr tt8z5y4lh ph0c-qz,*za said to have a signal-to-noise ratio of 58 dB, whereas for a CD player it is 95 dB. What is the ratio of intensities of the signal at6zp 0y84zz q-tp ai2-5 l,ct*z ohrchnd the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from a person speaking if-(vf 7bu e0ep9baui 6n normal conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a a7v fueei 6u(p90b-fbsphere 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 an5-r6sdozh1f;*1vjt 7 kk tfo rwk3e;z eardrum whose 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 250ca/ihg :(e 6 ng3q.xxefc.7vm 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 conne(. mgevcnic 6:.gf37xheax/ qcted 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 renzllk/ jl5x(ajcga )/z .n6ryv 253tq gistered 130 dB when placed 2.8 m in front of a loudspeakj)lza 3 ctjk6.5q5l/(l /z rny ganxv2er 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 in sound level of 2.0 dB. Whzs 5; unv8gyzvb5 t oh-bu.x7*at is the ratio of the amplitudes of t8.;5buy*h z5 v-7tvonzsgbu xwo sounds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) br pe+rs4cat-44n nz-ay what factor will the intensiers +-n 4zr- ta4p4ncaty increase? 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 has twice the freque9dtxcqh4 )r)dkc,f2dt0o pt(ncy of the other. What is the ratio td2 h(qc,)ox09 t4 ckt)fpddrof their intensities?   

  What would be the sound level (in dB) of a sei*rruhx:8o7ciso4 e jg4s /5ound wave in air that corresponds to a displacement amplitude of vibrating air moleculesi c8eo4 7x* ro/uirh:jeg5s 4s of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud as a 100-H*6e:m uwoh7s 1qxd9 zzek;rg,4d .o upz tone that has a 50h6 z,peuuo9 r:7e.qm1 ;o4z gwk*sdxd-dB sound level? (See Fig. 12–6.)    dB

What are the lowest and highest q0sl976rhdf/xync i y -h+xkwef54v2 frequencies that an ear can detect when the sound level is 30 hs2h y5e4dklfxq6cr 9f70wn ivx /+- ydB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of sound levem;7f(4n2pye9uufrs b ls. What is the ratio of f yrm(sf;2bu p4u97en 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 fundament pjvl8/ds /9zlal frequency of 440 Hz. The length of the vibratin /dvjl9 /pszl8g portion 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. Wha 1q:h;qifa)g +req.zjt are the fundamental and first three audible overtones if the pipe is 1+qq;fgh ezj) ri. :aq
(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 across the top of 6*gi4j yd9bkh:quhb dcg/4 t 7an empty soda bottle that is 18 cm deep, dh:gb9 7 ubq*gj4kihdyc6 /t4if 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-t5k.xkvap4wm0 e 8 /*qwshk* qjube pipes spanning the range of human hearing (20 Hz to 20 kHz), what would bej 4v/pq8wk05hkqwm .kas ** ex 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 wills 1 l 8t:lf(rblfgn,:w be its fundamental frequenc(1:sg nbrlf8wf:tll , y if it is fingered at a length of only 60% of its original length?   Hz

  An unfingered guitar strinmf c4mzz. :fq:3nu 6x. dafo2kg is 0.73 m long and is tuned to play E above middle C (330 Hzmc4.f2auq:3fd.m onz x 6:kzf).
(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 Hz);yzz36; k+xof ij+elo when the tempez6x; k+oio ;+3jlyezfrature 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 +br/u (:-z1h .ad8vbie ugexw at 20 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece ofcfzq )s,a9u2bviv.)p0(qx au the flute in Example 12–10 should the hole be that must bpv0az9uu(b)xf aqci.sv2) q,e uncovered 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 2hdt5ra z5,pt:o2( o itg t3qs464 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (a) Show why this is an open tg 4 i 3:(dtzt5sa52hrq opot,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 bo bi d29 q8*fbatx3cbu;th ends. It resonates at two successive harmonics of ftbic; 8bfd*a9u xq3b2requencies 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 tq8 (rtqf*es( 08nggq ;kocc7$^{\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 pr1xi z-s4ft+ xtesent within the audible range for a 2.14-m-long organ pipe af x+-zi4 st1txt 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.50gcswq*wo r h3 mxeikd4i2*.2kv4d x7 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 answer to the information in the gras k h c3x*2id4m7geqr0 d24x*ikow.vwph of Fig. 12–6? $f_1$ =    Hz $f_3$ =    Hz $f_5$ =    Hz

  A piano tuner hears one beat every 23o;lrgo* almw --tw;qvsi* s1.0 s when trying to adjust two strings, one of which is sounding 4ot- wl l -i sqvo;srg3;aw*1m*40 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequeoz5tcwu2ctmnxdy8 s7ina) (a2+ zi8, ncy 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 whistle ope af wrzd0in,* xg3gl(,rates 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 simi3,lr g*xfa,w0g(zndultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded with a 350-Hz tuning fork and 9 .bx56ohb x v-ebeats/s when sounded with a 355-Hz tuning fork. What is the vibrational fre-x b oh5b.exv6quency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz. The tensi+gbkpo pv*d0 3a+ grs2on in one string is then decreased by 2.0%. What will be the beat frequency heard when the two strings are played rs a+kopgg3 dbv+0p2*together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identical flutes - ujzkk.5 ie:teach try to play middle C (262 Hz), but one is at 5.0°C and the other at uk.t:5ej- iz k25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B s8h: (ldxd; cnh0glu8has a frequency of 441 Hz; when A and B are sounded together, a8:lc d hn0s ld;(hg8xu 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 person stands 3.00 m from one speaj6/s3 ,h5 qj8i rw ubc umnao69oztv59ker and 3.50 m from the otb9ujvm c65ju,53oq awtor 8 z96s/hinher.
(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, but a piano tuner hea 03gyfb/tka47ld/nzirs three beats every 2.0 s when they are played togetk yft/zli7dabgn 340 /her. (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 wav1lv3px 1n 3eoji0+ e5ks3puxu elengths 2.64 m and 2.76 m in air. How many beats per second will be heard? (Assume T = 2+jnp0x up 1i e1uvko 3ex353ls0 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency ) d7j+ohg skwj- v17j/r ezn1zof a certain fire engine’s siren is 1550 Hz when at rest. What frequenv j+skz-w 1e7dh zn1goj/r)7jcy do you 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 fzkk d;og6j +a8z3eu 3engine whose siren emits ke+6 3ogujza; k3fz8d at 1550 Hz moves at 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 tow )p.v6yjxvydl/ 4yd9rard you at 15 m/s versu/)4 lr px 9vdjyv6.yyds 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 equipptq,1 .pbcet v0a 8-cloed with 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 H.0,1le -q 8c tobtpacvz. 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 recr 9*4 +fktaad4+pfzlneives them returned from an object moving directly r+fla n*4tzd94kf+ pa away from it at 25 m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall 6xj7okelr jt/n5 8 zz5at a speed of 5 m/s As it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency does the bat hear in the reflected wave?5jkr6/xjtle 75nz oz8    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was played on a moving +e 5ry(wwz:k fflat 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 station at a speed of 10 m/s ?5w( zrkwfe+y:    Hz

  A Doppler flow meter uses ultrasound waves tt7 ivq(jiot*h ,1f -qno measure blood-flow speeds. 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 expected beat frequency ioiqq1,-f(7ivt* h nj tf 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 frequeneu/z rl wa7hnx kix5cg762ndu m*9v))cy $2.25 \times10^{ 6}$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 kpvgi))rm hx e4etm393f0 )pois 12 m/s from the north, what frequency will observers h)mi 3f3e0k)r)vppe 9gt4 x omhear 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 2fkm n mm0szy74qtm ez(9()k: z0 $^{\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 whercn pyw/0xloz5dt0 +g-e the speed of sound is 310 m/s (a) What is the angle the shog y+0 -0/zntx wl5dcpock 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 the thin atmosphere of a planet where the speed gg)zxp;j0*he of sound is only abo*xgghe zj p)0;ut 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} $