What is the evidence that sound travels as a wav(*:lle-*dg vbyhk*i)nujdp z6 q,f5g e?

What is the evidence a4b/w)tl z7 h74znfcq ,k/j gj/2rykvthat sound is a form of energy?

Children sometimes play with a homemade “telephone” by attachic7j 1eckf9 3wbng a string to the bottoms of two paper cups. When the string is stretched and a child scjk9fcw13b 7epeaks 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, 3epykqx, 3 0(+1h; uox5 kd9hnxmvf vido you expect the frequency or wavelength to changeixp+dk9 m35hvnk (v xf 3y01xo;q ,hue?

What evidence can you give that the spew5c(cu+ az wy-ed of sound in air does not depend significant(-w5+cya uzc wly on frequency?

The voice of a person who has inhcid/.o89 g a(omdo ,ptg(eu,e aled helium sounds very high-pitched. Why?

How will the air temperature in a room affect the pitch of organ pipe:m(g02z3dpe wo hq*s v ;jg+wqs?

Explain how a tube might be used as a filter to reduce th5p o ooe12hhg v;rrf.:e amplitude of sounds in varif2 v. g:ho5rro1epho; ous frequency ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer tog chx 1v8lu4ruca6unga 2;yy7w2 : rtb0ether as you move up the fingerboa0xcutv 24a 16nblu28uya rr7ch g:yw;rd toward the bridge?

A noisy truck approaches you from behind a building. Initia7(x hs; q,ltqplly you hear it but cxh7lt qp,q( ;sannot 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 diffraction.]

Standing waves can be said to be due to “interference in sp2e63,.lsd hdskb 1zmaace,” whereas beats can be sai,6bl32e.zssdk d1 ma hd to be due to “interference in time.” Explain.

In Fig. 12–16, if the freqbmz;77 my j07yuk t1njuency of the speakers were lowered, would the points D and C (where destructive and constructyjbu y7 7 jmm1;70kntzive interference occur) move farther apart or closer together?

Traditional methods of protectinv1v*wmo9bia -6qo wv-g the hearing 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 electronicv1*aow--9ivoqbw6 vm ally, 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 wave can be thought of as1* vwomyg-gb+1v9e u h a superposition of two sound waves with slightly different frequencies, as in Fig. 12–18. In which of y wmhg9v1*g vu+e1bo-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 d2u m6enezb)pwvs1 9y;h( rb(: w ljk;zirection, with9 sy(vzpelw( e)h;b:2w;6mjbn z1k ur the same velocity? Explain.

If a wind is blowing, will this alter the frequency of the sound heard b 1z,e:q;qx9 uu:0nim6ax/cv l kv (yfiy a person at rest with respec1,ximk i uvz ::qlcxv6;yen/a 0(u9fqt to the source? Is the wavelength or velocity changed?

Figure 12–32 shows various position yhyu9u th);5as 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 the sound of the whistle? Explain your reasoning.u a9 utyhyh5);

  A hiker determines the length of a lake by listeni;eb24 8elnero ng 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 shouting. Estimate the length le2o e n;8b4reof the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below the waterlvxv y1 r-,el4 fgmx/1uine. 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 (Table 12–1) and does no-1x m e/4,yv1v uxlgfrt vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavep:apv.* zy zw1lengths 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 jus3n1g:y rr lc /o:toyo9t above a school 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 elapses before the backfire is c grntl1y::ro9oo /y 3heard (a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a cliff.9vrs2eqsxqy oxdt3/l 3+h- 4m The splash it makes when striking the water below is heard 3.5 s later. How hig -y/xomq39dtq+l rv43ss 2exhh is the cliff?    m

  A person, with his eaf* j)kz,hk3vl r to the ground, sees a huge stone strike the concrete pavement. A moment later two sounds are heard from tvlkj), h3 *fzkhe 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 ovm ak 7k9bo(h2her one mile of distance by the “5-second rule” fo72(kbho ak9hmr 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 aa .j)*t.k 3lrr() n*smjr y1dwq4 aerhh9xk1 c 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 a souqnugu.9 j( bj(nd whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers producexae)20mjs1p 3xg)k/ be ue(e p a sound level of 95 dB when fired simultaneously at a certain place, what will be the sound level if only one is exploded? [Hint: Add intensiup)0e2p/ a1 gk )m( 3sejxxebeties, not dB’s.]    dB

  A person standing a certain distance f u 2qac3zam( leg:1k/srom an airplane with four equally noisy jet engl aa q gm23z(1:kecu/sines 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, not dB’s.]    dB

  A cassette player is said to have a signal-to-noise ratio of 58 dB, 7sp ;- fzb*z92iui y-,ykly q g-mk9iwwhereas for a CD player i-kfsizypb;gy kum wi2, -zy i-7l *99qt is 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 frogxa.9.kidgt. 2 0g2lph k0vprm a person speaking in normal conversation. Use Table 12–2. Assume the sound spreads 2g9glxk.phg 0vpa .i 2k.d0 trroughly 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 strikesr;w,h:mc*ncj w 6ptpx9ja3 /q 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 br:o.fg+,e bbg2vjc ( is rated 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 fro(roe2jc gbv f,:b gb.+m 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 pl02* o w8ummhblaced 2.8 m in front of a loudspe2 l m0m8hw*oubaker 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 (9 l0sqxvu4tv.bd6d l difference in sound level of 2.0 dB. What is the ratio of the amplitudes of two sounds whose levels differ by this amount? [Hit4d9 subl(lvv.6 x0 dqnt: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is ahmgb,yq v7h /01ol/f+bfg jktr:9;htripled, (a) by what factor will the intensity increase? Inchkgojbl q7 fvyt0hrg;b/,m +9a/ 1hf:rease by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but on 0 /q9:cs3wqwf73l9owys qpywe has twice the frequency of the oty9 sqw3 0wc yw9fqo3q7lws/p:her. What is the ratio of their intensities?   

  What would be the sound level (in dB) of a soubsg6au az7-i) nd wave in air that corresponds to a displacement amplitude of vibrating air molzi-7a gs)au6becules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as louofr8 i wnnx5o6 e(c0p +.dw7srd as a 100-Hz tone that has a 50-dB sound level? (See Fro8p0 5inn eo r.sw(dfx 7cw6+ig. 12–6.)    dB

What are the lowest and highest frequenciesbw19wghvh;*1 df( cze that an ear can detect when the sound lvw 1 bc; e1w*f9hgh(zdevel is 30 dB? (See Fig. 12–6.)

  Your auditory system can accom a1::ojow,u eqmodate a huge range of sound levels. What is the rat:ujq: ea,oo1 wio of highest 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 hazb gt,7re;-up 1. alfq1 0dcxe0evw0ws a fundamental frequency of 440 Hz. The length of the vibrating portion is 32 cm, and it hev0a;. , wwpxle0 bq1 0 1ret7guz-dfcas 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 first thre+x nbklma+t3 ;e audible overtones if th+bx nam ;t3k+le 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 y4)l (evulws: . cmorf7u0t rn/ou expect from blowing across the top of an empty soda bottle tham0ro4. nswt)lcle:fr u( /v7 ut 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 witwwg 1lv7 4s4(iuhn3skh open-tube pipes spanning the range of human hearing (20 Hz to 20 kHz), i4swgns34hlw k7 1u(vwhat 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 harmcdy0ndd.a r+- onic. What will be its fundamental frequency if it is fingered atc.dr+ad dy0-n a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to play k0b(2ougp5iv 4 ze9,basps q8E above middle C (330 Hz5g zv84s ae p(kqb iub0,p9o2s).
(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 pipzx /1zj3yrhs;e that emits middle C (262 Hz) when the temperaz z 1;jx/shy3rture 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 ag p ,;pwcb5ys4t 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 h.-6qq brvgzo2 ole be that must be uncovered62o rvz- qg.bq 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 res (;r qstt fsz0j,av:q3onate at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (a) Show why(tf v;,at0:qsrjq 3sz 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 atn-0t uwe; h s7c8b)gog both ends. It resonates at two successive harmonics of frequencies 275)ghs n;et bug c-0o87w 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 0;zw/0pslhn ce2 ,tls$^{\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.ud:mm7:w xk8 u14-m-long organ pipe atw x8ku:du7mm : 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm long. It i02ywqeh: (q 2mzvpk ;uwyc4a)4dk ow)s open to the outside and is closed at the other end by 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 ) e ;204 yhk(cuwpyo)2dwz vwamq :kq4of 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, oneoet3 51)q8haqcku amd1w8tm9+pls0 j of which is sounding 440 Hz. u aetpcalwohq1)8+890d1 t 5mj3 m qksHow far off in frequency is the other string? ±    Hz

  What is the beat frequency if middle C (262 99m d c1lyf8dl.b *tetHz) 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) op62ujg6 fkcbf1erates at an unknown frequency. If neither whistle can be heard by humans when played sj6 1kcfbf gu26eparately, 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 producesq exxn6 3c5*aj 6 akfrlx1xsh;-e)7xi 4 beats/s when sounded with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequenc k *q xn ;67x elcxh6-)e35srix1aajxfy of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294;bw u d9e g6z2k7dmap: Hz. The tension in one string is then decreased by 2.0%zgadum:dp; 972b e6 kw. 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 identij,): b0/bdto y oxv2fscal flutes each try to play middle C (262 Hz), but one is at 5.0°C and the os)b:vf xooy2tb ,/0djther at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a frequency of 441 Huaqfgfp/f 26 ,z; when A and B are sounded together, a beat frequency offugpf6a/ 2q, f 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 1ejda-s hv:0hm-9(q yj.80 m apart. A person stands 3.00 m from one speaker and 3.50 m from th ej:0 (hsmv9-dy-haj qe 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 /o 9 ymz.p9i0dfiiw59*xt+i l- keshu tuner hears three bep -h u9m5t0* lxk s9+o./w iiidifz9yeats 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 h.(a5 nf ys dv2m0ok/nof wavelengths 2.64 m and 2.76 m in air. How many beats per second w0k hnyao2nvfm/d .5 (sill be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s siren ixs1dk v, ;:zc m+xh*ges 1550 Hz when at rest. What frequency do you detect if you move withe:1scdm xvkx *;z,+ gh a speed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frqfc1g z8sd3 e/equency do you detect if a fire engine whose siren emits at 1/ sf13zcd qe8g550 Hz moves at a speed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 20jzkczmbq(-, e lk6y6:00-Hz source is moving toward you at 15 m/s versus yo:ezj6kzmbc(, ky-6q lu moving toward 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 equipped with the sdego3ciz 25 6same single frequency horn. When one is at rest and the other is moving towa oigdzs 62ce53rd 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 receives them reyesy.xmf ide0 i/r6 0 48(cydwturned from an object movin 6y8ye(is.xy0cir fd 4/mwe 0dg 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 ory(e+ ) 4peht uv )q;ur9d4ppgf 5 m/s As it flies, the bat emits an ultrasonic sound4q;tre9dep )( y gr)v upuh+4p 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 ofuyk1w)2z 4rq siw9 ;i6x9,e vg)wykmn a moving flat train car at a frequency of 75 Hz, and a second identical tuba playe)2 s)vqz6g1yxy9 wif,uw ir wk4e;k9md 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 measure blood-m34jxo01 iw omflow 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 om wim1j04o x32 cm/s directly away from the sound source?   Hz

  The Doppler effect usi 8 zjc9a59xeu :n0ckyong ultrasonic 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 veloc+;8 gkw8 4 qczgoqrr5mity is 12 m/s from the north, what frequency will observers hear who are located, at resgr;c8k 4zw+ qg8qorm5t,
(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 at 20j36jdbo.s.b gc v+4wh a4 7xbe $^{\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 thtt1y(c(xqtl1q36 vx*n d3 eeq e speed of sound is 310 m/s (a) What is the angle the shock wave makes with tdetq3xtt*ly n6v (1ecxq3(q1 he 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, 43meoxgr ea tnzr-*9cbnq63 a planet where the speed of sound is xacno6t r3,*bg er-qm enz943only 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} $