What is the evidence that sound1f(l yy6 qei 6kpb.76gmtky m5d1po(a travels as a wave?

What is the evidence that shvd,txmxhofu9wm y 0 /9hxua d.+-,y8ound is a form of energy?

Children sometimes play with a homemade0pbsm2+nx rqq i0-r h a6h6td/ “telephone” by attaching a string to the bottoms of two paper cups. When r-+hh0pdt6 s620i rn mq/qxb athe 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 water, do you expect the frequezoo( /nq58su3n g;y klncy or wavelength to;y3nn 85uz/kgl so o(q change?

What evidence can you give that the speed of sound in air does notfb(8x7wefk h 29dmf(6epf gg- depend significantly on frequenc e 9fmgg(6wf hp(bd87fxe2-kf y?

The voice of a persoqfsg qg5v1.iz* 6a :+csqw.ain who has inhaled helium sounds very high-pitched. Why?

How will the air temperature in a room -+ dgooe: br9taffect the pitch of organ pipes?

Explain how a tube might be used as a filter to reduzs 0q2w lkz2qcxe/5; jrh (i)ace the amplitude of sounds in various frequeh2a0q2 zjk/xsi;5zl( w)ceqr ncy ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer together as you movejc8uwln5 - gd1wqj +elzh/ ;;s up the fingerboard toward thzd;lg/ lusj+-;e8nc5wh qjw1e bridge?

A noisy truck approaches you from behind a building. Initially yo 25ulqgh)pr5 k*lqvi :;k dgwcutk4( 9u hear it but cannot see it. When it emerges and you do see it, its sound is suddenly “brighter” — you hear more of)9u(rv42h: ggdkptlq *5 klw;5kuicq the high-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due to “interference in space,” 4-kva eu fwzle9u(7c4 whereas beats can be said to be due to “interference 4vlawz7u9 - kcu4( efein time.” Explain.

In Fig. 12–16, if the8cwe .;68dzsfj-hv ;2lo8xyt1n xuxi frequency of the speakers were lowered, would the points D and C (where destructive and constructive interference occur) move farlwd2 e 8x6;scj8xt uf no.h8z1; vi-yxther apart or closer together?

Traditional methods of protecting the hearing of people who work in areawt it- xlpnzn17vra;+ 9 6ly1as with very high noise levels have consisted mainly of efforts to block or reduce noise levels. Wl1t;1 vrwyi+ anz9x- ptn76alith 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–(t w- rb8 oi7dkh4 w4,jf1jmvu31. 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) or (b), are the two component frequencies farther aovb-7 4fhuj4rd,kt18 mi w(jw part? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and observer move in t 4 p+1a5:4mvys dwdlcfhe same direction, with the same+f 5wmsv1 y4dca4dp:l velocity? Explain.

If a wind is blowing, will this alter the frequency of z8tq .ux57w(ce nn -nhi8ru7ythe sound heard by a person at rest with respect to the source? Is the wave zwnt-.n iey7n5qxu8ch 7 (ru8length or velocity changed?

Figure 12–32 shows various positions of a child bp:7bguzqw3gi 6 m9k,in motion on a swing. A monitor is blowing a whistle ibgwg3 ,m 67 uqkbzp:9in 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 tvk; :5f2 b9cp(spycpzhe length of a lake by listening for the echo of her shout reflectedzspv:c9pp ; fc5 2(kby by a cliff at the 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 safsno1n b:m. hxlr v 3m9;z6845q hdowhip just below the waterline. He hears the echo of the sound reflected from the ocean floor directly below 2.5 s ox4mh;l3znm61f .w5a o8 nshr : bq9vdlater. 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 waveeav664 a7i bzz8an d;clengths 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 above a school of3a kk 0p7n irtfh5nv (xqea5++ tuna on a foggy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). Hk5tn7( hfi+vn3 +kq 0arx5peaow 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 op imd-:gxe( p4f a cliff. The splash it makes when striking the water below is heard 3.5 s later. How high is:d-p i gx(epm4 the cliff?    m

  A person, with his ear to the ground, sees a huge stone strike the cod pa t;;div0f8ncrete pavement. A momeaf08dtiv;p ; dnt 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 impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over opk(p; evytl 33ne mile of distance by the “5-second rule” fork3p;yt pe(l 3v estimating the distance from a lightning strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pain lev 4ihirqs,s23 uou; 4wmel 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 w ,*1xkhts. 9riz +tkd3cyon n*hose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired simultaneously eypgw50pm cf3i0c0 jp/c/o/hat a certain place, what will5/mwo 0c pjp he 0ipfc0/yc/g3 be the sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane with four equally no9b)4;obe , yzlmwc-m na+m7oxisy jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would this person experience ixb9;+za7 om y),4 no-ebm cwmlf 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-noig+7 fztngm,b5se ratio of 58 dB, whereas for a CD player it iztg7m5 ,fgbn+ s 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 a person spg5 /c-sfwb sw/x6 3 +cw;kxxqoeaking in normal conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over aw w6;bg f/ -/+wx3 xqoccxs5sk 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 anr9l j/cx/j7 4ww ;aarm 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 250 W, while the more modest amplifil4no-yllo -dni7q 03p7ulz 6per B is rated at 40 W. (a) Estimate the sound level in decibels you would expect at a point nzppyuoo67di-3 ll q4 -l7nl03.5 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 myq qt2o +zl., bbb0q-placed 2.8 m in front of a loudspeaker on the stag.tzb q+,y2m0qblb q-oe.
(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 sounb(a k:1km xun)/eiu8 p+- vhumd level of 2.0 dB. What is the ratio of the amplitudes of two sounds whose level (ua) -/mm1kubxhk8e :pn+uvis differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) byc t42v lv qu9p;hwlfsk5) t0p2 what factor will the intensity incrq5lp)t9vkt 02clvs4w;h u p2fease? Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacl:fv2ms rf*)eement amplitudes, but one has twice the frequevl sffem2)r* :ncy of the other. What is the ratio of their intensities?   

  What would be the sound level (in dB) of a7 s/p0e tdr1yq sound wave in air that corresponds to a displacement amplitude of vibrating air molecules of 0.1r70yq t1d/p es3 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as logo08-s g4oh xvc,ub0ay2 7bsv ud as a 100-Hz tone that has a 50-dB soundugv, v4b-oah2xoscb0s 78 0g y level? (See Fig. 12–6.)    dB

What are the lowest and highest frequencies that an ear can detect when h.)z7wr w5hlrthe sound level is 30 dB? (See Fig. 12–6.z 5.hw7 lrw)hr)

  Your auditory system can accommodate a huge r:hunf q* 7y+()uzm f eg:0lwrxange of sound levels. What is the ratio of highest to lowest n0x+:: (zhqumyu e*r)flg7fw intensity at
(a) 100 Hz,$ \times10^{ a }$ a =   
(b) 5000 Hz? $ \times10^{ a }$ a =   
(See Fig. 12–6.)

  The A string on a violinkxaaxk v3,q8;m3 yp4v has a fundamental frequency of 440 Hz. The length of the vibrating portion isv3yaxq ,k 8mp4kva3 x; 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 are the fundamental and fi -5+d*1ffv:mf ec*a3ige btd t/e -hxgrst three audible ofi/ecf :3- 5vm agt x1*e*gtbdhed f+-vertones 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 yourd01yca5ywp.6 l 2jd08w b rxp expect from blowing across the top of an empty soda bottle th 0j 8 wywdxl ba6drr1pyp5c.02at 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 xz0kepmc, 7 bq ,se/n 4g-wh1erange of human hearing (20 Hz to 20 kHz), w74hpg,zmnq1b/ewk c-se,xe0 hat 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 a10br,47qi 7 n / kmv za7(lkukdhu:hah frequency of 540 Hz as its third harmonic. What will be its fundamental frequency if it is fina(u4h1i07 bkmahl / vzqkhur:7 ,dk 7ngered at a length of only 60% of its original length?   Hz

  An unfingered guitar string icshv/ 6xropg7q 90:kas 0.73 m long and is tuned to play E above middle C cko/gaxp7sr vh 6:90q(330 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 organ pipe that emits middle C (26z 5 *b oay,8puqin5+cyu24 +zed qca:t2 Hz) when th:uopt5q+n4u+aeycb8zqa 5c2 *id, zye 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 a tnanx:*pz *5it 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 shoul:lvy3; o0ctl 3.3,8zqlfyfopwr fcd1d the hole be that must be uncovered to play D above middle C.zlc qfv83l olf:3,yd0c r o31y wfpt; 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, 440rtq9zduu5 a g8g136e p Hz, and 616 Hz, but not at any other frequencies in betwea1tu5zu6ergg d98qp3en. (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 ends. It resona dzx:k d:oa1sc;erb; *tes at two successive harmonics of frequencies 275 Hz and ed 1ox ;d:c;zb*k:asr330 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 3+. ta+n. +yqqco kzzv$^{\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 t,ntpj2 w3zt b;rr2 ep.he audible range for a 2.14-m-long organ pipe rtb,;n22pp z er .tjw3at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximat f /top)l5lfl,ely 2.5 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) f)pltl f/o,5l 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 onoqigdz1l)).jg61 gdgc ei-w o);le;re beat every 2.0 s when trying to adjust two strings, one of which is sounding 440 Hc g;d.o1izl1gqrl));g6 -w oid jege)z. How far off in frequency is the other string? ±    Hz

  What is the beat frequency if middle g8 yw,;wshst-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 at 23.5 kHz, while another (brand X) opf uj4mx9cm4/ terates at anumm9 /xt4 4fjc 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 frequency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded with a j1 p-98vn 6kayqk/ dhz350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency-kykzq/ 9aj6phnv d 18 of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz. The tension in q3qc2 zb+a q/e97wv j* i6f*ycuasvw4one string is then decreased by 2.0%. What will be the beat frequency heard when the two strings are played together? [Hint: Recall Eq. 1 ui9e *jyaswq 3acqvq6w/+zvfb7*24 c 1–13.]    Hz

  How many beats will be heard if two id.m allr/i1b ;jj0bjr4entical flutes each try to play middle C (262 Hz), but one is at 5.0°C ab rjab1/ri 0;jl.jml4 nd the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuninv :,temn6 whz2g 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, :2,t w6zvmhe nthe 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 speaker ant*:m pkq*rze1 d 3.50 m*erkzt* :1 pqm from 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 aregh +,o5v8.qwy 9zmj 3alzu92kdnmw*c supposed to be vibrating at 132 Hz, 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 zuw9mz jld+ov.ch*y5gq k2amn8, 3w 9must 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 wavelengths3eii: xe 1,ukz4(jg iqf.rj:r 2.64 m and 2.76 m in air. How many beats per secon.z rqxu ,j 1grj43:iiek(:feid will be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequenw8 x jjm6mv6k(cy of a certain fire engine’s siren is 1550 Hz when at rest. What frequency do you detect if you m6m6jxj8kw v (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 figb uf(biacuu93 27jo(re engine whose siren emits at 1550 Hz moves at a speed o9uibo7gc f(u3au2bj (f 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequngmaclkdele6l t s: 6: /.6s5iency if a 2000-Hz source is moving toward you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencislesgt:5 6: m /l6n6.cldeikaes 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 esk nlpdzyhiv +w93kni43t 659 quipped with the same single frequency horn. When one is at rest and the othershywk 4kil+t n395ni6d v3 9pz 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 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves a34h h mci3 (spphf* 0( e/hudlzxrl:l7t 50.0 kHz and receives them returned from an object moving directly away from (epm hs 4 l/flzh*up0(:lrc 3 h3hid7xit at 25 m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at lbcbww+dx5 **7vki .x2 p7kmwums ) 9na speed of 5 m/s As it flies, the bat emits an ultralx*+wmukbisx5kp*7 )db2mv 7wc .9nwsonic sound wave with frequency 30.0 kHz. What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler e+ovc 3()sikspf3z (wpxperiments, a tuba was played on a moving flat train car at a frequency of 75 Hz, and a second identical tuba played the (cv(3 zsk 3ifspo+w)p 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 l7kqv hca+(bv1 zg:y/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 if blood is flla( g yh/b+ q1zv7ckv:owing in large leg arteries at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using ultrasoni7diy+j6/j -u xm;2 k qlmne9el i0-lnsc 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 vc32.r5wez)o ds dbf+v ,l ;x.e g:shvkelocity is 12 m/s from the north, what frequency will obserkex.w5e)bv s32ho.r :zdg;svcd , l+fvers 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 onh6 in6*oaj6 aq8p hj bar6u*f ro3-fv+ 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 speed of sou4gqg6cz/m:mu*o y 6yt0wlm 0qnd is 310 m/s (a) What is the angle u /tg:oqqz*w6gmm 04 0l6m yycthe shock 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 atmoige1w42c r6+jyl qp4 dz1ae+ n5mik6 asphere of a planet where the speed of sound is o41 ymn4r51 qi dp zel+w6e+ag kcj62ainly about 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} $