What is the evidence that irvn9 -(dj-/ci z-h4pgypkq /sound travels as a wave?

What is the evidence that sounp4tzry)) okr*d is a form of energy?

Children sometimes play with a homemade “tx8+;k( dzvaq 1ayuwn) elephone” 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. 12–2n)yvq8 a; 1kaz+xwdu (9). 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 4i27h so4xlt vthe frequency or wavelength ht o2ls4vxi 74to change?

What evidence can yo*b;*zu(9eqll a wnp) ou give that the speed of sound in air does not depend significantly oq(;9u b nezal*ol) *wpn frequency?

The voice of a person who has inhaled helium sounds very high-pitched. Whlbz-v3xhtj py6il31*a l - b/sy?

How will the air temperature in a room affect the pitch of k 4yb zs0 bz+zj+msslh621di4organ pipes?

Explain how a tube might be used asf )qjtnrj s:d5j1qe/k.h +c5q a filter to reduce the amplitude of sounds in various frequency ranges. (An exampl55c:/njhrqsjdj.e )+tf qqk1 e is a car muffler.)

Why are the frets on a guitar (rdck (tigx ))9gb(s2yFig. 12–30) spaced closer together as you move up the fingerboard toward the bridge? )isgxgk(yb )rdt ( 92c

A noisy truck approaches you from behind a) gwis0s8q j7l building. 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. [Hint: See Section 11–15 on diffractiqj0 issg8 )lw7on.]

Standing waves can be said to be due to “isa)+pknbxz +(zuzq h , ;lhq26nterference in space,” whereas beats can be said to be due to “interference in time.” Explainbhq hnx6 +s +2z(,)ka;zqz plu.

In Fig. 12–16, if the frequency of the speakers weruvnjyu o:6,errm omwk79(a h82g+,.n hldop3 e lowered, would the points D and C (where dem2ejo h.o ghnu7an v96 oy8:(,ul,wmdp +3rkrstructive and constructive interference occur) move farther apart or closer together?

Traditional methods of protecting the hfb:aj/17x jr /eld3 lfearing of people who 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 rea3:lf 1/7lxjr dbe /fjduce the sound levels reaching the ears?

Consider the two waves shown in Fig. 12–31. Each wave can bew8qyu (4q ih6a )mi:yr thought of as a superposition of two soun4yiyqu:( 6qi wh)8 amrd waves with slightly different 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 source and observer move in the same directios*qlv enfc/ o 35ki6.i (i7ievn, withkiqvvf/n7 (5 lei ei.6c*i os3 the same velocity? Explain.

If a wind is blowing, will this alter the frequency of the sound hed n7yxmew2 l+(ard by a person at rest with respect to the source? Is the wx2+7medny (lwavelength or velocity changed?

Figure 12–32 shows various positions of ndr3f3pm gdchm)gf/guemr nj60:* 9+ 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 throm*+n3gdpmrr3 )hjfegmdu/6 9:gcf 0nugh E, will the child hear the highest frequency for the sound of the whistle? Explain your reasoning.

  A hiker determines the length of a v;j6mn c+k/ha2ixflef fx-9. lake by listening for the echo of her shout reflected by a cliff at the far end of the lake. She hears the echo 2.0 s after fh+xav/mflnkc e6-;f2xi9. jshouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below the water sgz,l(km (yuhv6*7r nline. He hears the echo of the sound reflected from the ocean floor directly below 2.5 s lat7r*n( ,l (yukz h6vgmser. 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 wavele3+q 8 h e 7 79nesvlm5ffwqlo0w6bx5cengths 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; 1e;enn8)u.jxmwu o bg*m6nq is drifting just above a school of tuna on a foggy day. Without warning, ae w1 *xnje 86m.;g;obnun)qmun 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 3p rlq3:b c-*ej9eae6qqq/xtcliff. The splash it makes when striking the water below is heard 3./xjeaeqqc: 9 q3eb pl-6t*r3 q5 s later. How high is the cliff?    m

  A person, with his ear to z9dae28gd( k/apca1o s)-l oeb ;vrw5the 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 the concrete, and they are 1.1 s apart. How far away did the impact occur? See Table )-9o leakozwvda arb(s5p21d ceg/;8 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error mad 1*f oeaar 3sqei: ek1sn2v(qi/uk 69ce over one mile of distance by the “5-second rule” for est a s/ nk(*9oru1i6qq3vei1fes ak:e2cimating 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 level5 ecjx lf(vn*:etk ,a hd3u69g 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 whose intensity ii+ 3h np*yz t1o5;warqs $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sod t9u,m,fjkvc2jk-3 y tou3m: und level of 95 dB when fired simultaneously at a certain place, what will be the sound level if only one is exploded? [Hint: Add intensities 9mc2u fyjjtkt:v,km3u3do - ,, not dB’s.]    dB

  A person standing a certain distance from an airplane with four equa3 *sl:kfjj-.dkhm / ic p,2sdclly 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 all but one engine? [Hint: Add intensities, notfs/2k,cks.:dc3jp-l*d mhj i dB’s.]    dB

  A cassette player is said to have a signal-to-noise ratio of 58 dB, whereas for nl( ewr/o lw67a CD player it is 95 dB. What is the ratio of intensities of the signal and the background noise for each 7lwn(6oe/w rldevice? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from a person speaking in omx7k3ul+:dh -*x aiwnormal conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphere centered on:+3 7*xkdaw lu-mhio x 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 anrr9fdbzm 0fxp5 2m0i* 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 mom9e 7 0pmb3:*u1 zpp lqccoj ;c13bfzare 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 turn to each amp.o13 fm0 1mlz*j c :;qbapzp p7uce93bc$I_{250}$ =    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)i4q9pz8 ny8rj h v+gs front of a loudspn98hjr8)spzi +gyq v4 eaker 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.,b kr-rwzh0txi+ w7uj /l*b 2f What is the ratio+- bkxw,irlu2 rf0 /tjh*z7bw of the amplitudes of two sounds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factor will8wu,d b 0tdbi* the intensity t0* 8buwdibd, increase? Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudb lg+b xnr13.les, but one has twice the frequency of the other. What is the ratio of then l xr3.l1+bgbir intensities?   

  What would be the sound level (in dB) of a sound ,q)q q:3yl urp31j xtywave in air that corresponds to a displacement amplitude of vibrating air molecules of 0.13 mmxyr,3 3qtqyj: pl) qu1 at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud)75w pa. uhibi as a 100-Hz tone that has a 50-dB soh.a5 )pubi7iw und level? (See Fig. 12–6.)    dB

What are the lowest and highest freque .90lbq2kh7(rq125yz k h xnon4qua dmncies that an ear can detect when the sound level is 30 dB? (See Fig. 12 2(m 2rh1qqk5 .az4byln09uokhd7 n xq–6.)

  Your auditory system can acco;7 i 9ki4hyvzpmmodate a huge range of sound levels. What is the ratio of hykhz4 ;7pii9 vighest 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 fundakzn7d59 m8,/ y+x rcimoti1 gfmental frequency of 440 Hz. The length of the vibrating portion is 32 cm, and it has a mass of 0.35 g. Under wmdo98i i/ r7n,c +zky1gf tm5xhat tension must the string be placed?    N

  An organ pipe is 112 cm long. What are t* w)nzs i,c8.aje*ee68 hgznyhe fundamental and first three audible overtones if ,ej)w.n8c* gn hz 8s6*iyeezathe 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 blowing acros pvg1x-1hen nrvnx;oh7 3nd84)i 1iax s the top of an empty soda bottle that is 18 cm deep, if you assumed it was a closed tuber x71;-nxio 4x)ni dnaehvhg8n p13v1?    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 0avo6xuie dw4u;fwu 5.n5 v+j spanning the range of human hearing (20 Hz to 20 kHz), what wo0vevui4x 5un dwu .; wja6of+5uld 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 iri17j* e1ijprts third harmonic. What will be its fundamental frequency if it is fingered at a length of only 60% of its original lei j*rr11 eip7jngth?   Hz

  An unfingered guitar stringuck8:+vsjs jmjb21 m6 r7ji1 j is 0.73 m long and is tuned to play E above middle C (330 jk jmcm86jjrbv 211s:js+i7 u 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 e4p0zah;n g3upi5vue yh8 +q/zmits middle C (262 Hz) when the te584i ;gn3z0pvy+h hqeuzua/ pmperature 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 ynlva y f3d54 t4qf2u620 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flute itg5t/84q oc)6tw ,mm zcn rn1in Example 12–10 should the hole be that must be unco/, mtrgz6 io1qtn4c8 5 wm)tncvered 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, and 616 Hz- b,5vdgz-g ie, but not at any other frequencies in between. (a) Show why this is an open or a closed pi5d- gbev,i -zgpe. ----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 boty-aj(m/he t o;h ends. It resonates at two successive harmonics of frequenciy - o/jh;e(mates 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 n 0wt.z d5tfstf78)h w$^{\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 wi2(kg3 xi7yvx bthin the audible range for a 2.14-m-long organ py 2(ki vx3g7xbipe 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 is open to tf2 8 jc4a 0dxnh gm5;gf3ycxf9he outside and is closed at the other end by 2gx g3;h jy dcxfan mf4f805c9the 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 wheetj :;(fc(/i9ycrjm vcvfo /-n trying to adjust two strings, one of which is sounding 440 Hz. How far off in : ry /eof-fct/vjcvjc; im9 ((frequency is the other string? ±    Hz

  What is the beat freg l,y 8fyeuh5oa4+ g)hiosc +cp y9;b2quency 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 operates at 23.5 kHz, while another (brand X) operates aw loif:61ulm/ c(hz2wlc b:s) t an unknown frequency. If neither whistle can be heard by humans when played separately, but a shrill whine of frequency 5000 Hz occurs when2licfu:sl /lw c wzm(:16)boh they are played simultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded with a 350-Hz tuning fork anqwo s u; x9ej.f itc4(,1ti9fjd 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of the sq(9o ;t,w j.1ciux9je4fft sitring? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz. The tensio+lp1bdl. oo:c s,ink 84h kd2nn in one string is then decreased by 2.0%. What willdb 1khnd2pl,4:.ko cn8+lois be the beat frequency heard when the two strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard ifacat0ux y74f,cvf j7nt)v 5d8 two identical flutes each try to play middle C (262 Hz), but one is at 5.0°C ,5 antfv80 a4cfy7vu x)jcdt 7and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a frequency of 4(,e,:mtgn +g xw+e9 kffyiv ;c41 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 frequencies of A and C? What beat frequencies are possible when A and C arf+gg,ie:cvf9 e; xmkntw ,y+(e 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 apa fzt7s2um;aj zhh a a/9z5+xj4rt. A person stands 3.00 m from one speaker and 3.50 m from the zha asx2ma 7;z4h uf9+t/5jjzother.
(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 su qgodo)/ jzt:5arwn6k2/y 4ku pposed to be vibrating at 132 Hz, but a piano tuner hears three beats every 2.0 s when they are played to54orw2a kj)u/: 6/z goqk dyntgether. (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. How many bea ks9-oy 2pq5rmts per second will be heard? (A rykmos9p-52 qssume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant freque u0xnhlv m ifbv15nzoo3,g*; *ncy of a certain fire engine’s siren is 1550 Hz when at rest. What frequency do you detect if you mobil5f gozo;xvn, v ** 13um0nhve 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 e -blt i-9awj5)7v eoifngine whose siren emits at 1550 Hz moves att)7voifl5 iab 9--jew 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 3satah5 gd1j r vumxul2ni6q b):+be4q56 3tftoward you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exactly the same? Ar3 ) 1nah t3b+4t5fa6 6ueblqv:2g u 5mrsjdqixe 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 cd.stg/czfl6oh.2p ; 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 Hz. What is the frequency the horns emit? Assp.fd2;clt6/h zs .cgo ume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound walpm 5fv70ht08lx, e7ddgf3qlr j ;s+wwr -b j6ves at 50.0 kHz and receives them returned from an object moving directly away from it at 25 m/s What is the rbf-,hew l d3m7+5psvd8x rfqgl07jj ;0wtr 6leceived sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As ci*wguqt65k(ma mg 59 it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency does the ba6aug5 5kcq*it(m9 wmgt hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler expe2f, )/xwlbx i6v(kawpy0 6 addriments, a tuba was played 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 s/yddvw26axp f0(b,lkia6 w x) tation at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measure blood-flow speeds.oam7d z*z -xzxea:+9 s k,wqk0 Suppose the device emits sound at 3.5 MHz, and the speed of sound in human tissue is taken to be 1540 m/s Wh zq+a- :0 ,s7dx9ek *akxmzzwoat 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 ultrasonic waves of frequencyyp :-6s+o6x jbp :1upeheu e1v $2.25 \times10^{ 6}$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.( g/n)nb9cx w:cpey. p When the wind velocity is 12 m/s from thg b )nc/(:pe9p wcxn.ye 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 its speed atff6at7 7+,cx asqiof; 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 sound is 310 v *p- x (1jc7kpbq+ofqm/s (a) What is the 7kx q 1p*(povbfc+jq- angle the 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 atmosphere of a planet where the speed of sound is-fug2i r )3yfe o-2u 3frgi fy)enly 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} $