What is the evidence that sound travels as a m7+adux /- jn*q( 6kyy)nwmskwave?

What is the evidence that soc6vd 0ek cv9:mund is a form of energy?

Children sometimes play with a homemade “telephone” by attaching adm gh1,7p )sqv 9b.t9h9 mpdas string to the bottoms of two paper cups. When the 9dphtsm1 ,s. h9p)ab mvdg79 qstring is stretched and a child 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 passesc58akpegqe,y;kq2;7arhw h( t 2 ge5 d from air into water, do you expect the frequency or wavelength tt a;2ar k 8e(;k25pchye5edqh 7,qgw go change?

What evidence can you give that the speed of sound in air f6b0n 8kn1 gb75amsnkdoes not depend significa8 k51n0ab s6knf7mgbnntly on frequency?

The voice of a person who has inhaled helium sounds very high-pit rg *assu rkc) ab(,j-e*e+.tnched. Why?

How will the air temperature inzy 1bs5m8 hxgwth-d5c g 0zwy8;dc28o a room affect the pitch of organ pipes?

Explain how a tube might be used as ajp5q a)*a ok7x filter to reduce the amplitude of sounds in various frequency ranges. (An example is a kpx*a 5ajo )q7car muffler.)

Why are the frets onz*)xqqg2r v/hxj 6u w/ a guitar (Fig. 12–30) spaced closer together as you move up the fingerboardgqh2 *6 /uv rwz/xjxq) toward the bridge?

A noisy truck approaches you from behind a building. Initially lvz kbi94udyw8w75 t vrb8a(wfl, 7r8you hear it but cannot see it. When it emerges and you do vr98 i7td , 87r5(ylkwwl4bfu b vz8awsee 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,”3cmx ,v k-t-yt whereas beats can be said to be due tovmk 3- txty,c- “interference in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered, would the pointsgo:.kc+pew6; b zfbp6bk9/oz D and C (where destruc.6pbb wp/9k ezozb:o c+6f;gktive and constructive interference occur) move farther apart or closer together?

Traditional methods of pm77x+j ja l(ctrotecting 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 ma ( tjl77+xjcthe 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 wav997 + ucjkv1tm1wot dne 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 apart? Expla cnk7d9u9 wo1+1 tjtvmin.
(12-31)
(12-18)

Is there a Doppler shift if the source and observeqr:-cq 3ovov k2qf6 )jaxn;jp 6 :.lhxr move in the same direction, with the same 3 jqjprq;x: ox qoh6v .n:-c6 vk2f)alvelocity? Explain.

If a wind is blowing,+(dxnz z*pj6b will this alter the frequency of the sound heard by a person at rest with respect to the souxd*z(p6jnz + brce? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a child in motioemt;m - i av;2jpt h*6wm0psl9n on a swing. A monitor is blowing a whistle in front of the child on the ground. At which positionvpm -0tiep sw62l m*hat;9;jm , 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 h )ghh;l i3b8tder shout reflected by a cliff at the far end ofiblh3t ;8h )dg 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 n obyl hn+yam74 5c/6 itay.a;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 seawabyan+l4n oty;ah/ yi67.5mc ater is 1560 m/s (Table 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in 5u/3uqz;wj5. w8uka *kmwdq s 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 (shss2)s mmq/(nzd * () geurejust above a school of tuna on a foggy day. Without warning, an engine backfire occurs on another boat 1.0 *dn(s egsms2m/q)(u )re hsz( 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 clcg/d6r q+ gus(ezlp59iff. The splash it makes when striking the water g/ es+upgd (9lrc6q 5zbelow is heard 3.5 s later. How high is the cliff?    m

  A person, with his ear to the groutp ouz;bezf85 e1(i/ tnd, sees a huge stone strike the concrete pavement. A mom;zb(eu 5optf/ezi 1 t8ent 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 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one mile of distance by the “5-second rd b47sv7bm c5fule” for estimating the distance from c vbs75b 47dmfa 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 iizga8+1xcd - 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 sonfqz(c5x 2 8r;o he n;o,1hpeyund whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a s1d6: 72/acwh nhhsii pound level of 95 dB when fired simultaneously at a certain place, what will be the sound leveliwp7 12hciah :6sh /dn if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a kk8kv*lncklu ok/ ,1vn+/*qucertain distance from an airplane with four equally noisy jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would this person experq*vvlk /u+1k ku8l, *kon/nkc ience 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, el tg+s g)b7.l85z dgcwhereas for a CD player it is 95 dB. What is the ratio of lg g75dg.ztcl )s +be8intensities 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 f, gg vz i*ixk+hd sn;/wmj49g) jeoq3/+;iwea person speaking in normal conversation. Use Table 12–2. Assume the sound spreads f,9g*gi+ kijw/ )j g;sw4mdi o+vzqxh /3;e neroughly 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 whose area x7 p(nll*w8qwis $5 \times10^{ -5} m^2$ (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 mmm9ujga*ld( + 9kc* 4bwgyt l3odest 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 loud d+gk*m4(3btjwy l*9mgc9a luspeaker 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 90a5it8l1aeyu : rmnqregistered 130 dB when placed 2.8 m in front of a loudspeaker on the stageu8t5m1 0riq aaey9ln: .
(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 dete(b/tr 9m)rw/ga 30a(p;k3uc ghqg hq6caidw1ct a difference in sound level of 2.0 dB. What is the ratio of the amplitudes of two sounds whose lev tgbuq(ackd (3rh g;1h/9a6wp0gwr m)caq3 /iels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factor will the intensij2,l w:03bnd27y,lujx oc/ q+mu lfaw:)wa rtty incrb:2w r: ,qmuxn/jj0wa ylalw ) tfcl3do7 u,+2ease? Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitud a*fd 2,op;tk.st a3jyes, but one has twice the frequency of the other. What is 3 day,o.fst2t kp;a*jthe ratio of their intensities?   

  What would be the sound level (in dB) of absg3,hlr. r8m (t)jcp sound wave in air that corresponds to a displacementchp,t8)bs 3rlj.g(rm amplitude of vibrating air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud as ax y2oe/ikaf3 5n;g+uk 100-Hz tone that has a 50-dB sound level? (Sea;yfikn2gx+o 3 ue k/5e Fig. 12–6.)    dB

What are the lowest and highest frequencies that3(of :s yy7 fi++iocuesyu 8o86r az6k an ear can detect when the sound levs ou+8z: yisr6 uayf(f76+3eokiy8o c el is 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of sound leveva 29 wxc0tu g uyup3:6yi:q9els. What is the ratio of highest9 w3v:yq9g :tuue y2u6pi xca0 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 4;l/crxku i0y :40 Hz. The length of the vibrating portion is 32 cm, and it rc0: y/l; ikuxhas 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 three aud,;cna0w;sb m bible overtones if the pib, 0cnw;ams; bpe 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 acro- bl a ilq7l4kl7por/a.b5;aoss the top of an empty soda bottle that is 18 cm-;oollkla /ipl a4 5b7.braq7 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 p w7wvb/j*uld:0oqu5r ipe organ with open-tube pipes spanning the range of human hearing (20 Hz to 20 kHz), what would be the range of the lengths of p jv */dbou5w70u r:qlwipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a frequency of 540 Hz as its thiy /:46:stvmj ; livtmzrd harmonic. What will be its fundamental frequency if it is fingered at a length of only 60% of its o6i:v;mvt ymlsz tj/4:riginal length?   Hz

  An unfingered guitar string is 0.73 m ls n6bmbsb 4qxeh (h*9/ong and is tuned to play E above middle C (330 H6b4qn(hshms b9* e/xb z).
(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 emi8)s.ye i-fsjy0zo v ,qts middle C (262 Hz) when the temperature is 21 ez) ,siy qo8f.-j0sy v$^{\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 as z ywoc91w23xt 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 h63ll r5*tyw)j soq 8gyn+sk9pole be that must be uncovered to play D above middl ps3* rwl89s5ky ) 6g+jltqynoe 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, 43h; ; uq5xmqux40 Hz, and 616 Hz, but not at any other frequencies in between. (a) Show why this is an x3qqxu5m h;u; 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 a1,.qko/o;g *jxghf vnt;zchm k16) zyt both ends. It resonates at two successiv1 y;f ohtm.zc /xzjg1 kqn;k*6v gh),oe 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 i- -jd*gpgh9gs3aevi f/g up8(px82x$^{\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 rangc0gj.j 43esvtmaal 9 ,e for a 2.14-m-long organ ,j 90 .em4acjtalgs3 vpipe at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximaten4bfbpx.14+ p vlt,l ily 2.5 cm long. It is 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 tpb+b. l x4tlvpi1nf4,o 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 strin/hf gnrvkx 1mqt/8+2op rf;k5 gs, one of which is sounding 440 Hz. H fg/x+frv kr5;pn2 t1m okq8/how far off in frequency is the other string? ±    Hz

  What is the beat frequency if middle C (2wgw3jw 7gv6dkqn-pelt- -*lmz bv 77/62 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 atnux3pf5xm(a(+ 0c l jx an unknown frequency. If neither whistle can be heard by humans when played separatelyx +(c u0jpfnl53 mxa(x, 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 be cz5zb g,;j+8zmxeco /ats/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 frequen/m z85ez, jzbc;c g+oxcy of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz.ru4 k jpln:6 sp4tue,( The tension in one string is then decreased byu6s pl4ju,:4(rknte p 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 flutes each try to play middle Cai/ elr)0zt eqbui*2( (262 Hz),iq(2buz/* ta eelr0 i) but one is at 5.0°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 b +;kvg g-n0,y4zufwc 441 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 freqyw0gf; +,4gnuzcb -v kuencies 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. i6vxjoyp7cv2d; ek 7/80 m apart. A person stands 3.00 m from one speaker and 3.50 m fixe27;po jdk/cvv7 6y rom 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 n*s )u2*;pton+kls p iHz, but a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibrating at 132 Hz, what must be the fli+)2;ks pn*st *o upnrequency 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 wavms +)kd6zad*9e mhzu+ elengths 2.64 m and 2.76 m in air. How many beats per +zh*+dzas9md 6uem) ksecond will be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s siren is 155q-wbh(w ct*/fg7cnwo7-j wj6 0 Hz when at rest. Whac nfojj7--cwg7 (hw 6qt*ww/bt frequency 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 frequwqzwsjkh1 ( ;scr/*lv wh3 ).mency do you detect if a fire engine whose siren emits at whvwk/sjc1( szwr;*q)l 3.m h1550 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 2/;wyz4,7le: hlcqxp tgj wt)( 000-Hz source is moving toward you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies /cl:7ywt;wq4zl, e) (jgp txh 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 equippsq q w419 wq.fx3l*joved 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 res.4*39l1wvoqqws jqfx t 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 r)j9d193 fmzr3d lgaxm-p7r fueceives them retuddp9rfzx fm 3a-1g9l)rj u37 mrned 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 wallbvc (y0l jm9k3 at a speed of 5 m/s As it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. Whjvbml30 y c9k(at frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was plfku x q+9ji*6m+ w; .cx-onypwayed 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 statiy 6fn9u+q+j;xc-*wm iw oxk p.on. 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-floqcbeqec 9,e+ :;rf-k4+fdsst r 0ril5w speeds. Suppose the device emits sound at 3.5 MHz, and the speed of sound in human tissue is taken to be 1540frcq:sq5 e eedfs-+tb ,cr04i9 ;+rlk 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 ultrasoniznge f. .5*fxic 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. When1 jo 5b2:mfru.)eejbtkno0i0 the wind velocity is 12 m/s frf 2)jieo k5b.b:uemjo1 t 00rnom the 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,ew cqt0zn)8s 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 of8xmsx)pjar.: 2kv d5u sound is 310 m/s (a) What is the angle xpras)u8k .xj d 2v5:mthe 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 s lqm h*-c83hzhkgt;w.ound is only about 35 m/s-8tkghh *;c.hm 3wlzq
(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} $