What is the evidence that sound travels as as )n kj.gbc71f/ /dgobr 9*pu;xc dco2 wave?

What is the evidence that sound is a fmhdmgz 8n v.+5orm of energy?

Children sometimes play with a homemade “telephone” by attaching a stric:h0k9su ns(*ud b83zsdgd-:ri se1q ng to the bottoms of two paper cups. When the string is stretched and a child 9b g13uh-ieskn dszd0srcs( 8:q:ud *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 wasx/d6i347i hy2kr ma*vu )g cnter, do you expect the frequency or wavel 7y4k) imd/v *hnug6a2x s3cirength to change?

What evidence can you give that the speed of sound in airci y,30qc k4ps does not depend significantly on frequency?4sc0kp ci,3q y

The voice of a person who z,qya+3fir5 pqz t z,55hfe8bec.u 9m has inhaled helium sounds very high-pitched. Why?

How will the air temperature in a room d;zl9 p)dk/ucm. 8r oraffect the pitch of organ pipes?

Explain how a tube might be used as a filter to red()r4xa-a 2s pggc lejq-* oa3ouce the amplitude of sounds in variouse24qsg-(*oopl c)ara 3jg- ax frequency ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer together as you56+ 5f-rfpd8 dp-i2zmp z w8xzo gy7qj move up the fingerboard toward the7fi5rd 8-y2o6 qz-fp+8zpzjwx 5pd g m bridge?

A noisy truck approaches you:zerp )r tl l(;tt4n4 xsqa7t hv wwuo3*/7:wb from behind a 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 higt;3er 7 (n 7z *:a/lt4tux4 blwpr)hv woqswt:h-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due tomcf;p:o3x s4d “interference in space,” whereas beats can bd3;4: smoc xpfe said to be due to “interference in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were loelb aa,g4gn n0:-(vevdi 7 v+cwered, would the points D and agavd-bv+i(7g vn ncl0 e,:e4C (where destructive and constructive interference occur) move farther apart or closer together?

Traditional methods of protecting the hearing of people who work in areac6n35nf/hm qzpz sn62s with very high noise levels have consist 6q6f5nzmc/h s23np zned 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 Figj 6 i6-vlopgm2. 12–31. Each wave can be thought of as a superposition of two sound waves with slightly differentp-6l2gmjo 6vi 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*r jz:q gf km+-- t0 agtcpy4o+a;squ1 move in the same direction, with the same velocity? Explaq-ufjm; +:tap1-trgyck0oz s4g+q* ain.

If a wind is blowing, will this a5k4rd5 mb pe+6 lsbzt9r;(w uklter the frequency of the sound heard by a person at rest with respect to the sour5r;6bp9r5b(tlu dzw4mks+e kce? Is the wavelength or velocity changed?

Figure 12–32 shows varioulqfm+skwj e ;/ cfa6ig1f*m2,s positions of 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 through E, will the child hear the highest frequency for th* wa+ 2 c1/mfefqf6,jmkisg ;le sound of the whistle? Explain your reasoning.

  A hiker determines the length of a laqm;+(jam8siv 5t : ihtke by listening for the echo of her shout reflected by a cliff at the :im vt+ 5h;(ajtsqmi8far 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 ofwsao*y)rg1 8 cb*owy 6,)qesu his ship just 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 seawater is 1560 m/s (c 1 ,o*q6yesuw)o *)wsbgyra8 Table 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelength7j9pqc-0 z ppx -6 w9oucgvc 5m9eghd.s 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 of tuna on a foggy day. Wix v)/f l3*wciqmhba( o ;*mt)bthout warning, an engine backfire occurs on another boam i*)t hx )mb/qbf(;3vwo*clat 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 p t2m: ekik+g)qo)-hl. The splash it makes when striking the water below is heard 3.5 s later. How highme2 kotpk:hg +)lqi)- is the cliff?    m

  A person, with his ear to the ground, sees a huge s sa 5alo1m2mx/ 1zao)mtone 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 impac/mo)amo 521lmaz1s axt occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one mile of distance by the “5-secajpge 5l(2t)9*xq ry1x neat -ond rule” for estimating the distance from a lightning strike if the temperature is (a) 30 ne(2 r p a9eyq*l x)atjtxg51-$^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound ati+cs y2o: azl0, i *huwh94hykvxj2m, 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 a somw28 w.bb tz+ z8qu7b-n38nuyqf2dhs und whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired simult4lw b-nz+bh+a aneously at a certain place, what will be the sound level if only one is exploded? [Hint: Add intensities, not dB’s.] 4w+bh -lb+zn a   dB

  A person standing a certain distance from an airplane with four eky(y9 e/ +coek1e 7g 0elx-ddhqually 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 y0lg c/e-h+(o ey1xed7ke9kdone engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to h (-zk0p0si9uf ju +uruave a signal-to-noise ratio of 58 dB, whereas for a CD player it is 95 dB. What is the ratio of intens +uz(9 f-pju0uku0sirities 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 in normal con7asi(klr ww ) gr8lbix lg*v.1(4 eol8versa.k()(is wa8ll veir17rg*lxwo lb 48gtion. Use Table 12–2. Assume the sound spreads roughly uniformly over a 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 an eardrum*u4ec j2 9qaql 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 t1ojyh ocv4-fqml)y /0he 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 loudspy14oy0lq ) mch/j-vf oeaker 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 registermf f:rrvvk(ws(7 *y7ned 130 dB when placed 2.8 m in front of a loudspeaker on the rfk7(7 mrvs(fvw:ny * 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. vncx)45x ,rew5qy/bnWhat is the ratio of the amplitudes of two sounds whose levels differ by thi/, b)qrxv55 yxe c4nwns amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by v3;q2lrmuweq;tr 8 )gdh;ne 9what factor will the intensity increase? Ire8 nwmugr3 eq;l;tq2;v h) 9dncrease by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudessfc js9t(k;i 0j jn80p, but one has twice the frequency of the other. What is the ratisj9 8;(icfnskj 00p jto of their intensities?   

  What would be the sound level (losp f;)uvzi;tx0qx4. if v(uve( t 80in dB) of a sound wave in air that corresponds to a displacement amplitude of vibrating a0o;) u. t( u pvv0tzex(x;lvifs q8fi4ir molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what soul/ztr(p.i x r2 rjys,/k2yar.nd level to seem as loud as a 100-Hz tone that ha .2rk/(i. xats yprl2ryjr/,zs a 50-dB sound level? (See Fig. 12–6.)    dB

What are the lowest and highest frequencies that slxuvo:6xt qfxer 1t;8y9 -37b o2bxyan ear can detect when the sound level is so ql:x8oy;761tf32tyxb -reuvxxb9 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of soundli bid it5nz+ 00ph)4(qzcu 89ol3evi levels. What is the ratio of highestui0b 9pl v40ze( 35ilcho n8i +qdzit) 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. The length of 2fb o5znlu3d,w (t/t n+(wyn zthe vibrating portion is 32 cm, and it has a mass of 0.35 g. Under what tension nl/ 3w2 zo(f+y,n(duwtnztb5 must the string be placed?    N

  An organ pipe is 112 cm long. What are the fundamental and first thrf;g ab 3 ek6x1a)t5dcoee audible overtones if5b;tckfgao13d 6a ex) 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 you expect from blowing across the topc-f)q/xmf- 4te x0olz of an empty soda bottle that is 18 cm deep, if you assumed it was a closedf4z- xf/q)t e-x0lcm o 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-tubej 6dkzl3n60nj 9ydj, v pipes spanning the range of human hearing (20 Hz to 20 kHz), what would be the rajz, v6k30nydn 6j9djlnge of the lengths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has rdmlrmu5q3w:;k0k )b a frequency of 540 Hz as its third harmonic. What will be its fundamental frequency if it is fingered at a length of only 60% )mb5 ;urq3w0rl md k:kof its original length?   Hz

  An unfingered guitar strin(pr sp lp 84:kj;8bdtm+5igwrd o56u hg is 0.73 m long and is tuned to play E above middle C (j;dr4rt86p8 k5 udgsmpi( 5hb: op+wl330 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 m5rncxlxud d.1c7; 8 jn0 cfc3bz28lxorgan pipe that emits middle C (262 Hz) when the tedlb81. cx x75n82lzcfdc u nxjcr;m 30mperature 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 2cxv2fvm7n:z0:zi c a50 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flute in 7o/50poqlqe o Example 12–10 should the hole be that must be uncovered to play D above middle C at 294 H7qpo5 el 0/oqoz?    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 26 nmam 9mb6,xqw*zb3 9m4 Hz, 440 Hz, and 616 Hz, but not at any other frequenc6mnxm*9bbzm ,3 q wa9mies in between. (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 endobo z/nyjlyg2,5 ek */:trh)es. It resonates at two successive harmonics of frequencies 275 Hz and 330 Hz. What is/ytnlz) r/eky be :hgoj,25 o*
(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 f, cdqen0zp-u9 p+m2g$^{\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 ar xg,sq56u g05ln:ssfkool d:- e present within the audible range for a 2.14-m-long organ pipe at:50ngkls5sg u: ,dqlf os -6ox 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 the outside a 99jsngf (ccx1nd is closed at the other end by thj1fg 9n9xc (sce 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 e61y(wad : cps2voitm .very 2.0 s when trying to adjust two strings, one of whict(d2aw is.v 1 mo6:cyph is sounding 440 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency if middle Cabm+(k 8lxf6j (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) operateu2ofzis0 ag q*j)-knj)v,0ob s at an unknown frequency. If neither whistle can be heard by humans when pjzo *vbo0ng ua qfs,k) )j2-i0layed 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 napes0z y;8byoq 0, h78edu)ybeats/s when sounded with a 350-Hz tuning fork and 9 beats/s when sounded wity)bp7sean0;zq y8,y8ho0 eduh a 355-Hz tuning fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings a o;l2l8up tj m:sfk9e:re tuned to the same frequency, 294 Hz. The tension in one string is then decreased by 2.0%. What will be the beat frequency:ll ;j9m2e8skfu:pot heard when the two strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identical flutes5g ,w iuf94ktl each try to play middle C (262 Hz), but one is at 5.0t,5wklf4i 9gu°C and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a frequency of 441 Hz; wa fqzt,q :r+a/hen 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 are,ta:/qz qaf +r 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.hzlqk8as7 ) crt. A person stands 3.00 m from one speaker and 3.50 ml)c.as k7 qhz8 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 are supposed to be vibrating at 132 Hz, but pn 53cet(nxk (a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibratinctn(k 3e x5np(g 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 2.8 jk:jvwc;xf -64 m and 2.76 m in air. How many beats per second will be hex wjfj kc:;-v8ard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s siren is 1550 Hz when jc-b r)f 6wbyv51qfvu- i2hd2at rest. What frequency do you detect if you movec1)-b25wf vv6-ru yj2idfqbh 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 engine rb-;ri 6s)x 5rejmho* whose siren emits at 1550 Hz moves at e)xiohr;rb j- 6sr5m* 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 toward youfna8clp)se37l9 rh9a at 15 m/s versus you moving tows3r9lp 78ce)haf9a nlard 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 equippedhpaiw6 h 4lye43)g*u fsg px2w50is(s 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 bea6sgspg0)s4wexhpi h l3*i ( 2w4fyua5t frequency of 5.5 Hz. What is the frequency the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultraso * ud-8xb aeef(/g7hdxnic sound waves at 50.0 kHz and receives them returned from an object moving directly away from it at 25 m/s What is the receh/ed u7e(agxx -bd* f8ived sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at ay y4n 6mq85jx 3igk2rn speed of 5 m/s As it flies, the bat emits an ultrasonic sound wave with freqxr86 iy q3g4j5k2ny nmuency 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 moving flat b5.nenwjj lw lavaco+.v d/7(l,d v+ (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 ev w+,5/l7a+jova(d. bjnvdnc lw(l. ?   Hz

  A Doppler flow meter uses ultrasoun *uq i5hniq1dlhjit;(aj:y7+gd om(1f+kh3n d waves to 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 if blood is flowing in large leg a + ;(qm iht f5nod+i*11d3h:nau7gqhj(ylkijrteries at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using ultrrq.*zyzg71vv 7d vm 7hasonic 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 Hai u *e5j0gkgm.xud1 hc0 7l7pz. When the wind velocity is 12 m/s from phc ug1 x0laugijk5 7m* e7.0dthe 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 mot/7x afb(lgbd shl13q , t/q;dving 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 the speed of sound is 310 m/s (apt+jh+s z 8rwpdxgx (o(. l,a.) What is the angle the shock wave makes with the direction of tzpx ,.s+8(tp (xgroa jh+dlw.he 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 wr) kni,0lh/x ek;c2tu(z i4splj 8-sohere the speed of sound is only about 35 mskkr;t4s2-,loinil 8zp xuj )e(/h0c/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} $