What is the evidence that sound trye87 wsg/i 5xtavels as a wave?

What is the evidence that sound is a form of vr 6 6i41jkcerm)lr; kenergy?

Children sometimes play with a hoe ;u sok4yzdl++pw(w7mjn1)s memade “telephone” by attaching a string to the bottoms of two paper cups. When the string is stretched and a child sp7 (epmn )+uwlsjzd1 w y4sk+;oeaks 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 ecs/b- j.b/ +-n-p wpiaplq2v if)joi)xpect the frequency or wavelength to a)jb) qb - ip/spn 2cpf+j-wl.v/-ioichange?

What evidence can you give th-::0e/ chk p3an/kckbzamjg 3 at the speed of sound in air does not depend significantly on frequ -k3p0a b/hzm:gk n:kc acj/e3ency?

The voice of a person whoz1);ic /xp/1kzg0 r azt9:wodmkmpj 9 has inhaled helium sounds very high-pitched. Why?

How will the air temperature in a room affect the pitch of organ pipe sh3 - 2ekzia)+vq3l.u ) pwewqu1ds-j;zi3b js?

Explain how a tube might be used as a filter to r oodb9w+o;sgw d7+u( ueduce the amplitude of sounds in various frequency ranges. (An example is a car muffler. ud(wu7o;b 9sod++ow g)

Why are the frets on a guitar (Fig. 12–30) spaced closer together as you move u tvpdzqq8*7sezsr l5 ge, 0l25p the fingerb l qrp7 zsqe80d,vl5 2*s5zetgoard toward the bridge?

A noisy truck approacans+; o5c0h* pitdy)fvd)d6 uhes you from behind a building. Initially you hear it but cannot see it. When i yv6iop5f )d+ts)d;u c* 0nhadt 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 diffraction.]

Standing waves can be said to be due to “interference in space,” wherea.02javz r;+ 8sye tzuyvw9gg4 s beats can be sa9r+jy4 sge2v.ugw8tv0ay z z; id to be due to “interference in time.” Explain.

In Fig. 12–16, if the frequency of the speakers weri8 ra69iozxk:e lowered, would the points D and C (where destructive and constructive interference occur) move farther apart or closer 8o 6xkza9iir:together?

Traditional methods of protecting the hearing of people who work in arer9gt 9v(*ck ozas 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 ro(9c*z g kt9vthe ambient noise. How could adding more noise reduce the sound levels reaching the ears?

Consider the two waves shown in Fig. 1tuht2e4rr ,ok ip:+ a2b1y+:wn qihq)2–31. Each wave can be thought of as a superposition)qq1, iybe kao:2phwu+ :+tirn4rth 2 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 apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source gk+;cfr+w -mcand observer move in the same direction, with the +gwr k+; f-cmcsame velocity? Explain.

If a wind is blowing, will this alter the frequency of the sound he:k)u zis*rm,zctd6: d ard by a person at rest with respect to the source? Is the wavelength cik* u ,tms)d:6zdr:zor velocity changed?

Figure 12–32 shows various positions of a child in motion on a swing. A mo. rlu/wtmb0n,d 3dyi )nitor 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 the sound of the whis,wl0.ndury)b/ itm 3d tle? Explain your reasoning.

  A hiker determines the length of a lake by listening for the ea 6vnyx;ys*3kcho of her shout reflected by a cliff at the far end of the lake. She hears the echo 2.0 s after shouting. Estimate the length of ;ya6kx* ys3vnthe lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship jus c-m9aipo r z 3d4oogy7* g.wz/5aw,xnt 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 sp*xw3p4. 57y9iad zoroc,g-n mgoa/zweed 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 ac tqcmx +1vxv 43 v3r-pz8oar4pnw j05ir 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 schoa o :g.aeqek1b1hgx 27ol of tuna on a foggy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How much time elapsesk g 7eeq ohaa21xg1.b: 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 why x*iz 4b5u7pren striking the water below is heard 3.5 s later. How high is the clix5*p4b7yuzi r ff?    m

  A person, with his ear to the ground, sees a huge stone stwae-r f5-njj/1mqy :x6:fqm8 gjw: larike 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 1 rn6qmq:alj:j / efw5m8y- gf a:jw1-x2–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made ove9 qv:-) m+lqazj 5qvs+6o vwear one mile of distance by the “5-second rule” for estimating the distance from a lightning strike if the temperj se+ v:lwqov5q- v+a)qmz a69ature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pain level of 120 f:1)lt c2fp hw mz9al(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(dif g8ipid* - is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired simultaneouslyku2 pye v8w;0snsb7t6tf:;ub at a certain place, what will be the sound level if only one is exploded? [Hint: Add intensities, not dB’ nw:putf8sb 2e07btkv;s6 ;yu s.]    dB

  A person standing a certain distance from an airplane with four eqc0end78m 1rbdually 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 engdmn80r cd7 eb1ine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to have a signal-to-noise ratio of 58 dB, whereasc7 1k+5 yxbos*fl,,rta+in co for a CD player it is 95 dB. What is the ratio of intensities of the signal and t+,lcfk*ocs ti xorn yb7+a ,51he background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from a person spea6l:v.uuvi)tek 0iqjq6 k c6i)79bon nking in normal conversation. Use Tablel)c v .v690qe:iq7niub 66 ktk)njo iu 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 strip/,lqwhi1o zg nd jd*:q1r/t (kes an 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 ra:m/4lt-tdigt w jgdi7rm.gckz )o7;(ted at 250 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 connectedim4/ tjk m7ro)dlg7;c -:g idg.wztt( 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 registeri7l*o;kem7sflh w70t3ov ; lred 130 dB when placed 2.8 m in front of a loudspeaker fm;vsli7 ll *e 03 k77oho;rwton 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 dB4x* tc:gi su8:wm 2vvh. What is the ratio of the amplitudes of two sounds whose lev*gh:u: mvsx28 tc4wviels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) bcwhg (pt;gv )0y what factor will the intensity increase? Increase by a factor o;tgwhc)0vg p (f    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displace;6pa gc2 u9f) m3duvldment amplitudes, but one has twice the frequency o)vlg ;fdcamd2 93puu6 f the other. What is the ratio of their intensities?   

  What would be the sound level (in dB) of a sound wave iv;0,7,gbc ; o haosjd fxc4 yu4,*y 1t;ppmnppn air that corresponds to a displacement amplitude of vibrating air molecules of 0.13 mm at 300 Hz*y o14xun;s,m,40bp ptpch; opg;f7j v ,dyca?    dB

  A 6000-Hz tone must hatl0bbmf *-ys+ qja9 mpi2q17 mve what sound level to seem as loud as a 100-Hz tone that has a 50-dB sound level? (See F tsm q2fmj1*lpa790qmy+ b-bi ig. 12–6.)    dB

What are the lowest and highest frequencies that an ear can det,rds 6 r *hp:nm8jahuj(7kj3 t,c,ujs ect when the sound level is 30 dB?up,s3art8jh:n u jr k,hd*, cms(76jj (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of sound levels. What is0 +uaa9ws,zv ,ia p y4d.z-rsh.oao3l the ratio of highest to , o.0,49 zsa d pal+ha.wvarisouyz-3lowest 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 Hzga+ ta;k +wj:f. The length of the vibrating portion is 32 cm, and it has a mass of 0.35 g. Under what tension must the strf:gkt ; jwa++aing be placed?    N

  An organ pipe is 112 cm long. What are the fundamental and first three audlhl 3ud) ,,o/bge )pevible overtones if the pip )/gl,lbou3)h dp ,evee 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 you2b tbnr;q) w-m expect from blowing across the top of an empty soda bottle that is 18 cm deep, if you assumed it was a closed tt) w;qrbbn2- mube?    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 pi ds(/zz:bjtukjyij +2f+ i 6z sa2lx5)pes spanning the range of human hearing (20 Hz to 20 kHzzd i(sz/)2 ij zf:s+ a jlty+k6bu2j5x), what 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 a frequency of 540 Hz as its third hje++mim/y. h jarmonic. What will be its fundamental frequency if it is fingered+yje/mhj.+m i at a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to play E -.wlwtb x.eyu39yu l9j t tos,(*sgz8above middle C (330 Hz)t-bt wx3,uetg l( 9y l*ysw8u..zojs9.
(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 leni3x-gd 2lu-rn gth of an open organ pipe that emits middle C (262 Hz) when the temperature is n- -d uxrig2l321 $^{\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 fu,ep:j(6;dh*p gcr h 4;atif 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 s(w h )diuywx7xo0-m7 ahould the hole be that must be uncovered to pm7x0h 7uwo dwx -ay()ilay 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, an-;s7s/.g8o ckt3pb w d yaubbh4p7+qpd 616 Hz, but not at any other frequencies in between. (a) Show why this is an open d4 p skwtg./ p 8bphu +oya-b7b;7qcs3or 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*xwt7xvo,v4k lxh y 9, ends. It resonates at two successive harmonics of frequencies 275 Hz and, vl*9yh7t4okw xxv, x 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 m*tx- o/mccgb 3 vu4(h$^{\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 r eyp:w/y*yr89*7ovhi(gec-wk vb+ h e present within the audible range for a 2.14-m-long organ pipe atv/cg* -yk: eyihhe ryv +8wr7w*(9 opb 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 opebpx 0p+ioa7 crm41vs/d8yp) o 1 lln,xn to the outside and is closed at the other end by the eardrum. Estimate the frequencies (in the audible range) of the standing waves ,r /psxm7ocyd bvl+a)np11o 4 px08li 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 when trying to adjust two strings )ryrg8 kw60cz, one of which is sounding 440 Hz. How far off inr0kw g68cyz )r frequency is the other string? ±    Hz

  What is the beat frequency if middle C (jzh8 )l7nmder1gx+g (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) operategfdht-u:e0ahxu 1 6xzd n q/5y;fmz**s at an unknown frequency. If neither whistle can be heard by humans when played separately, but a shrill whine of frequyz*x/x5- 6 e f d gdt1mh*:fq0zuhuan;ency 5000 Hz occurs when they are played simultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/s )perltr) (r:5(bvoszwhen sounded with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of the strierr ))p(:ovb5tr slz( ng? Explain your reasoning.    Hz

  Two violin strings are tuned to i/y l pg6k.v-nthe same frequency, 294 Hz. The tension in one string is then decreased by 2.0%. What will be the beat frequency hear.l-iypng 6vk/ d when the two strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identical fx6xky5k 7 xt)plutes each try to play middle C (262 Hz), but one is at 5.0°C and the othery 6xk 5tpk7)xx at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning yrb bc4qune .(a,6*u*sm(8gkly ; bc wforks, A, B, and C. Fork B has a frequency of 441 Hz; when A anu kl (6g,*y*m ec ;ncqu8b4rswybab(.d 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 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 ans6w 84al bcmlm 33yc0pw6+f omd 3.50 m from the other3pfw4 l mslb co06m8 6+aw3ymc.
(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 hear); t-gj;iap0s0aep aks three ba )tgja;asp k 0ep-0i;eats every 2.0 s when they are played together. (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 ;fh(0dux do 5ibeats per second will be heard? (Assumiu ohf0;(5ddxe T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s siren is 155k6x jhxw5sl)au:m5, t0 Hz when at rest. What frequ,5jxx5 mhtu waslk):6ency 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 firevgxfbs*wubo;2 2ktk / dx,*/ f engine whose siren emits at 1550 Hz moves at a spx *22t; k/ogkux,bbf*sv dwf/ eed 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)- hq8so98 ws vg;5ep5mgwmoc moving toward you at 15 m/s versus you moving toward it at 15 m/s e mg9qs5wvs)o8- ;cg mp5ow8hAre 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 with the same single ,3uf0s exvt8cfrequency horn. When one is at resuefv s,03x 8tct 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? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at 50.0 kHz and rec7pbm w8cy2xf)ncwb5 jx8 uk.0 eives them returned from an object mo7pxn y c 5 bbck.0uw)8mj8f2wxving 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 hc41c 1x,ghm pr7b0nd1sh 4qdof 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 1hgcsdd qhh,cm 1 b04r47x1 pnwave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiment,w xxzh.8,s 4un 5rb/qgos c1gs, 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 .ozw gxc 4sqnb h/518,,gr uxsrailway 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 blood-flow speeds. Su1gww 8qqn,- j8/dhj8 qwmx5 wrppose the device emits sound at 3.5 MHz, and the speed of m1j5 88 /dqwxw,hr8wgqnw-qj 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 source?   Hz

  The Doppler effect using ultrasonic waves of frequency x; rr,5e) gxla(j(2r6y x q8/rekvtku$2.25 \times10^{ 6}$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 theazrmcnsw9(ym 9 6) ;nt wind velocity is 12 m/s from the north6)ma( 9 ;swrm cyntnz9, 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 movin 2h butp+5lgacju526x g 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 sw jk,em5cm xm7-e 77huc+eal+ound is 310 m/s (a) What is the angle the shock wave makes with the direction of tecau+ m7e lm, mc7hxwekj+-5 7he 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 jdpmx. -j+er0jtw e,fxnvya /1b 1m2 4the thin atmosphere of a planet where the speed of sound is only about ,14t xwjmvj/ ed2bayx 01+pr-jenf m. 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} $