What is the evidence that sound travels as a way e.*irx+ tc5:-rd8k vzc mt6ave?

What is the evidence that sound i.ck6 ktdm )nm4s a form of energy?

Children sometimes play with a homemade “telephone” by attaching a string to thw5 h9ukwdq1+ se 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 c w+dw59shuk q1learly how the sound wave travels from one cup to the other.

When a sound wave passes from airz**hhbycwot t8m pt fk-w 4 cq)y:2t9+x;1 zok into water, do you expect the frequency or wavelength tkh9h towy*)4cfw-y2 c mqx18kt b;:zt*zt+poo change?

What evidence can you givehunj8) 9nlj *e that the speed of sound in air does not depend significantly on frequencyjl )n u8*e9jhn?

The voice of a person who has inhaled helium sounds very high-pitched. W z.w,pu ego8e1 bb:vy)hy?

How will the air temperature in a room affect the pitch of organ ;as1fls9bhj;xs3t *y/o ga: v zah1j8pipes?

Explain how a tube might be uogjs i9/1mm36 e9): r)e) se bukmzhacsed as a filter to reduce the amplitude of sounds in various frequency ranges. (An example is a car mufflerb ):m ezmo 9cs6a1imk3shje9 )/eug)r.)

Why are the frets on a guitar (Fig. 12–30) spaced closer together as yo)4z:u8cb q;lcv hu t/qu move up the fingerboard tow/4 qt:cczbu ;lh8 vqu)ard the bridge?

A noisy truck approaches youdh 5mmp t1hjm5o4,y; deuw7+ja9u;/v hd a4d q from behind a building. Initially you hear it but cannot see it. When it emerges and you do see it, its j/1e;jud9h7mmdwd5p5tm yd 4 ;qaoh a4,h vu+sound is suddenly “brighter” — 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 “inte;hqgd ;(8+uc:telx c4jx(li grference in space,” whereas beats can be ex8;i uxc +g ;g(dl:qht4( jclsaid to be due to “interference in time.” Explain.

In Fig. 12–16, if th c*pbzi.:;esr e frequency of the speakers were lowered, would the points D and C (where destructive and constructive interference orz;ci.: sb* epccur) move farther apart or closer together?

Traditional methods of protecting the hearing of people m.5 6li;kr)00nwhu xjs d jvl*who work in areas with very high noise levels havs i0 jrulv 6h)k;xnm*ldw50 .je 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 reduce the sound levels reaching the ears?

Consider the two waves shown in Fig. 12–31. Each wavnd/m7,9qnsx /2mbm kzdl ng5 8e 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 apa 98 ,ddkn /bngxs/n m5m2lqz7mrt? Explain.
(12-31)
(12-18)

Is there a Doppler shift if l9j*qu;t0(kk z fi (kgthe source and observer move in the same direction, with the same velocityk;fz( i*0g9j kkq lu(t? Explain.

If a wind is blowing, will this alter the frequency of the sound heard by a persfv5 zq6p )(ihfon at rest with respectfi h)z65 f(qpv to the source? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a child in motion on a swing. A monitorvrqi2 tx(2b p1qoay ersb*19f* 1jrh. is blowing a whistle in front of the child on the gr*.r fi ba1r(hty oqvjsp*9er1q21 b2xound. 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 echo of hezodh+hbdh5gvj j k 23:9 )4z+(xk- )pkywyf ctr shout reflectdb 3o9 hz ktzyjh)hc+jk4v5 2d-xf)+yp :gk(w ed 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 ship jus d5+y06grnhx8yv3 iwvq6- f xemfi2+wt below 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 seawatvmy5- f6rq23dw+ 8ng0 w6yxxev+ii fher is 1560 m/s (Table 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in ae(sya i.e5m lwcu( 6w+ir 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 drifting90 pbd0u vq 5e 1awivvx1:et w7)ggw*g just above a school of tuna on a foggy day. Without warning, an engine backfire occurs on another boat 11x:v 7*0g wiwb)pvedg1 q v0wutgea95.0 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 clif .kqylk x crel98 w1f)/m 3l;)-xfuabvf. The splash it makes when striking the wate)9xqb /m8 lk ;lr)vklf 3c-x ewufa1y.r below is heard 3.5 s later. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge stone strike the concrete pk/f9vr.;6 y;z/ulzg fvi;zhiavement. A moment later two sounds are heard frr6 zyg/v uf/kz;i9;z;li fvh.om 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 one mile of distar8q 5k dm7r4tb8zus -rnce by the “5-second rule” for estimating the distance from a lightning strike if the tem8 rzb udst8q54 rk-7rmperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of 0 qy3xr. :q7dzmtvd(s a sound at 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 of a4 huac,jg9 w+zx)mz-o sound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when firoa;/dex ;..wpjjya6;7 s0shrp2hll yed simultaneously at a certain place, what will be the sound level i;2jj ae7l.o;0py sl6.shh;/py r dwa xf only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplxebevc t1ml9i b5xe2;r l n5-:ane with four equally noisy jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would this person experiencb l:; elmncivb9ex51xt5 re2-e 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 ratio of 58 dB, wh1zlk*h2(7)e- p kyghrvrzn 3 ndug8)kereas for a CD player it is 95 dB. Wrelzz -2g 1n8dp unhr)*)y3vk (7gh kkhat 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 speaking ignbazedq ps)m 99-(;qn normal conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphere c-ae9ds q)p nzm9 (bq;gentered 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 whosm gm4* ic3*qra miqbwd:,u+*ie 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 amplifilfn(paw kk (a;njyei1p ( *13ver B is rated at 40 W. (a) Estimate;p3* lnaa( yvj nkk1(f1ei(wp the sound level in decibels you would expect at a point 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*+ab; lagpwh a;y6d(q/+eqw g meter registered 130 dB when placed 2.8 m in front of a loudspeakgw a+g ;a;ey+ab l6dh/ (qw*pqer 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 .(y6b09h* 7wnf r9 tct pic8v wxir(xla difference in sound level of 2.0 dB. What is the ratio of the amplitudes of two sp 6rvnwxlc7i0(*bt( 8x y r. wcth9if9ounds 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 will ty5cyal( drpa n2:w73k he intensity increasea3pyk75r adnw 2 ylc:(? 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 fr.cq z8c0aswd1 -sx v6uequency of the other. What is the ratz wscsvcd u0a6.x1-q 8io of their intensities?   

  What would be the sound level (in dB) of a k l)y *qt8v92 g-twra,ijjwm(8 gyi; esound wave in air that corresponds to a displacement amplitude of vibrating air molecum8ki(g,ri;t e y atww jqy 9v)2*lg8-jles of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound giugr*va;1d/trytj; 26u e t6level to seem as loud as a 100-Hz tone that has a 501/2g*rj6 tdri u;y v 6au;tgte-dB sound level? (See Fig. 12–6.)    dB

What are the lowest and highest frequenciehs hm65+6( .toeylxdf s that an ear can detect when the sound level is 30 dB? (See Fihyf(h66 l5 eto.x+sm dg. 12–6.)

  Your auditory system can accommodate a huge range of sound le gce.8n l39e7p el9sa,bs-rcsvels. What is the ratio of highest to lowesrg,s9s 78e-3.9ale pl nbc sect 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 (m 9ctrlk 2p,yfrequency of 440 Hz. The length of the vibrating portion is 32 cm, and it has a mass of 0.35 g. ltk 9c2m,(rypUnder what tension must the string be placed?    N

  An organ pipe is 112 cm long. What are thelltm1roa 018v ,m9ozd fundamental and first three audible overtones if the pi,r1a dv9o llz8m tm01ope 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 wo) z v4-usyxdw+ x):hvould you expect from blowing across the top of an empty soda bottle that is 18 cm deep, if you ass4yz : )sv)+wxhuxovd-umed 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-tub6mf(pl.9wmzd9 bj*pfh zu* )ye pipes spanning the range of human hearing (20 Hz to 20 kHz), what would be the rangmu9h.f yp*jb *md(lf96)wz pze of the lengths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a oxzs-duv/k)e ru6c- 3ue- rg.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 oko/gu-x-u)edr r cs.-zv 3u6e riginal length?   Hz

  An unfingered guitar string is pqo*.5h rryu; 0.73 m long and is tuned to play E above middle C (330 Hz5 hrqo*up.y; r).
(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 o3kyfyqkqg* 5w+s9 ak. f an open organ pipe that emits middle C (262 Hz) when the temperafk*qyq9kks a gyw+ .53ture 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 a2het u35v(* y .bi4zvgu9lctpt 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 i nf.x4 bs.l+co8s*c ybe that +bfni c 4.cssol8*yx.must be 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 atnpm2 ,ghqz: n+tk;w;h 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (a) Shw qp;:z2tk;ghm,+ nnhow 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 opeckr k i(hr)48mn at both ends. It resonates at two succes hmc(rik4) 8rksive harmonics of frequencies 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 nxk88x. .dor fm xr7c/$^{\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 for a 2.14-mg7hc(y yo *c;9f8,f(:zjmkd(u tbxoa -long organ pipe (tc;k:auyg oom f*j79 b fyx8zd(h (,cat 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm long. It im;qfdwsg ;3de q.4itmr /ls+8s open to the outside and is closed at the other end bl; wrsq+mds3e;dqi t.4m 8 f/gy 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 graph of Fig. 12–6? $f_1$ =    Hz $f_3$ =    Hz $f_5$ =    Hz

  A piano tuner hears one beat ev5 ,awzoqtpu7.) miw0a ery 2.0 s when trying to adjust two strings, one of which is sounding 440 Hz. How far off in frequew mq5zpai) .7o,tuaw0ncy is the other string? ±    Hz

  What is the beat freque ddd35z ++t ,3 ,arhvaz.q2p8hcib-kd.nmqs lncy 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 (brandmg7.1lk di q8c 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.m1qd lig8k7c 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 and pa9 7 nt;d r28 xi.cs9xxx5zxa9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of the string?i7 xap;c. x5x snxt92 8zxar9d Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, f7n.gw(f(oy;flndy,rle m 6/ 294 Hz. The tension in one string is then decrease,e6 n(l/r 7 ld.yfny f(ofgw;md by 2.0%. What will be the beat frequency heard when the two strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identical flute at5ugsvo9c)3c) e ,7(6o t.wafuasiu s each try to play middle C (262 Hz), but one is at 5.0°C and the other aw uuiac)cve5a) a,t s3st9 6f(7u .goot 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forkxpb2wa/o: qn 1s, 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 heb 2wn xq1p:/oaard. 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 pers9f4xn5y4otu pon stands 3.00 m from one speaker and 3.50 m from xt4fpo954uny 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, but a piano tundo70t zj1 )fluer hears three beats every 2.0 s when they are played together. (a) If one is vibrating at 1327 ofduj0t lz)1 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 wavelengtej9ft(; ifw tz+xdk 89hs 2.64 m and 2.76 m in air. How many beats per second wilt t9kx 8f;ijf+9(dz wel be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certdulx 74;2irjcain fire engine’s siren is 1550 Hz when at rest. What frequency do you detect if you 4;xujr2ldic7 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 mh zh tf(d; yvzr;3)+ifire engine whose siren emits at 1550 Hz movf i )dzvy; ;3(rth+zmhes 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 toatygp*m ;g*v 8ward you at 15 m/s versus you moving toward *gg*m8t; py vait 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 wvu37j/u 6 g znq82pgbwith 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 qjuu 7 /2 6pgwg38bnzvfrequency the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultras:; a;a 6p9fdesh zhg9qonic sound waves at 50.0 kHz and receives them returnaz; dh6;es:q 9g9pa hfed from an object moving 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 of 5 m/s As it flies, the bat emits an ul 2c0gm6ce(o1 ge*pn8c ,dgguo trasonic sound,2c pg c*ge numdgego co860(1 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 experiments, a tuba was played on a movinfay wxu);3 m2ug flat train car fa)uw xmy2 3u;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 ?   Hz

  A Doppler flow meter uses ultrasound waves to meas 0 oxpc/+dzk9wy3 +c ns;4fb 7fsm*izn 1d0qqzure 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 flowing in large leg arteries at 2 cm/s directly away from the sound s+n30 foss*z 1xc / dbz kizwdfyp94c0m7 qqn+;ource?   Hz

  The Doppler effect using ultra5 s, 6ziiddffopvu 5;2z2+) 3.tlql xnl t.xocsonic 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 5:to;ss 7os70tnpal ;l b lo)tjvxf81 ma*2tc Hz. When the wind velocity is 12 m/s from th;a* otsot0p8 77 lj 2)tf ms:l1vstc 5nb;oalxe 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 movi)sk9:78jqgz0do hjj8j02f-oozu xm eng 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 2.3 where th jxa o8 eqxvz21q41p(ge speed of sound is 310 m/s (a) What is the angle the shock wave makes with th4q qeg 18 vx12z(oxjape 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 thzb;h)dh3i ; obe thin atmosphere of a planet where the speed of sound is only doh 3i)hb;;zb 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} $