What is the evidence thak, v1sl //vgkst sound travels as a wave?

What is the evidence that sound is )md jc -+bxw91/ 8aqr mefrxp;a form of energy?

Children sometimes play with a homemade “telephone” by att:*lord lg.s(6hy 8gl daching a string to the bottoms of two paper cups. When the string is stretched and a childl gd .ds:lgyl(8oh r*6 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 water, do you exf7 m)quo2n,yibs , +ispect the frequency or wavelength to cha+7inyf 2bu)s,ism o ,qnge?

What evidence can you give that the speed off 95 +sfootxd75x.arx sound in air does not depend signif7ofaxsxrdxo9t .+ 5 5ficantly on frequency?

The voice of a person who has inhaled helium sounds very hig2ro55kj m t:zm0nac: i( fik4ch-pitched. Why?

How will the air temperature in a room affect the pitch of *t 3pf3cb0s+h xk.ebz organ pipes?

Explain how a tube might be used as a filter to reduce the amplitude of sounfn1ppxst+ e y.dc5 i51ds in various frequency ranges. (An example is a car mufflerc.d tfp1+ 5x1ysi5ne p.)

Why are the frets on a g-pdnh 7 4m2fgcuitar (Fig. 12–30) spaced closer together as you move up the fingerb27- hn4 pgdcmfoard toward the bridge?

A noisy truck approaches you from behind a building. Initially you hea .e ,.x-axazear it but cannot see it. When it emerges and you do see it, its sound is suddenly “brighter” — you hear more ofaze.aa .xx-e , the high-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due to “int6d*lwf/ts*z gerference in space,” whereas beats can be said to be due to “interference in time.” /t* swd* lfzg6Explain.

In Fig. 12–16, if the frequency of the so qo(pzh o1gc;+kp(a-peakers were lowered, would the points D and C (where destructive and constructive interference occur) move farther apart or closer together? ac h1(zoqo +pg-ok(p;

Traditional methods of protecting the hearing of people sl3d)d)n oobg-8d j g5t8.ttnwho 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 electronically, then feeds it to the headphones in addition to the ambient noise. How could adding more noise reduce the sound levels reach8lo5t).8g n-)ddnojt3st dg bing the ears?

Consider the two waves shown in Fig. 12–31. Each wave can be thought /9ssg y 3gb12+d1n t/kaqmcrbof as a superposition of two sound waves with slightly different frequencies, as in Fig. 12–18. In which cyd+ bmb91t nrsg1gqsa2/3/k 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 move in the,n wfc 2)y6mbhpvy +d84tu5pm same direction, with the svbu,)n5 t8pymc 4ypw +mf6d2hame velocity? Explain.

If a wind is blowing, will this alter thee8 (4x y ifpjcj; ;.onoc+xt8c frequency of the sound heard by a person at rest w+;f j c in pxc.exty(88o4cj;oith respect to the source? Is the wavelength or velocity changed?

Figure 12–32 shows varioul o;w6j d/okt7yky/w )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 the sound of the whistle? Explain your reasoo;l yj/ky w/tdw 6k)o7ning.

  A hiker determines the length of a lake by listening for the echjoers, 0 0rsyj)vga*4o 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 the 0v ) rsos,jegja*r04ylake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his shi/nm/.k3p*r,xzoq2y xsn)r3et+m p 4 sawy(efp 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 (Table 12–mq(yr2)*s xtmexep43s zw ,nyr.fkap/+o/ 3n 1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths v fy/:f9 v9gy1.m*ma3r bl x0yx yq0yh.d7bk din 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 u *e1)yjk jcsm4thu6z1);gr:tv z 1 tdjust above a school of tuna on a foggy day. Without warning, an engine backfire occurs on anod jkzzm)je* 1gvust1r6uy c)th 1t;:4ther boat 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 thns5gbb*e6w -f e top of a cliff. The splash it makes when striking the watergswn f be5b*6- below is heard 3.5 s later. How high is the cliff?    m

  A person, with his ear to the ground, sees a huga+ 5 ius w3a4ux3bcrfemzy.,oe5sw 9 )e stone 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 impact occur? See Tableyue +r9u,ze )ba f4w.53xascw 5oism3 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent errorr 4() f6(5qug,l(r;le.o 6jxgq-pppfhavirn made over one mile of distance by the “5-second rule” for estimating the distance from a .gerl,ru (q4(r6plhp foq -ingfa( xj;) pv56lightning 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 level of 120 f0h:yiyw +cj7 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 inte o)rk pytl)ku (*;8gw0zuot 2gnsity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired simuxt x2f b.jdv*.ltaneously at a certain place, what will be the sound level if only one is exploded? [Hint: Add intensitjb xdv f*x..2ties, not dB’s.]    dB

  A person standing a certain distance from an airplanefdiee0 9;r qm- syt-x2 with four equally noisy jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would this person expr- 20ee d;-xqis9 tfmyerience 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,b 6wxi:,yqas-)xdh 7iqqx7 d6 whereas for a CD player it is 95 dB. What is the ratio of intensities of the signal and the background noise for each devicexx-7)q6yd:q, aw dbhi s6xi7q? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from 89ep gk-v ,g z/uhl.pho b81jia person speaking in normal conversation. Use Table 12–2. Assume the sound spreads roughly uniforhl ogj.8pbz/p9gh e,1iu8v k- mly 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 st2 vt1az7xgi4 zg wf,k8rikes 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 rated at 250 W, while the more 1f:pe-2sis.m1r xipymodest 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 connected in turnfrsx m.s:2y ip1pe1 i- 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 placede3r 3lk7s2+cl 7pem uf 2.8 m in front of a loud77rp3u3fs lc 2el+mekspeaker 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 difference in sound level om(xmxqw 1ok6vi j5 12:obpw3jf 2.0 dB. What is the ratio of the amplitudes of two sounds whose levels differ by this amount? [Hint: See Section 11–9.]o 3 w6x(:m opkvxj2jwq11bmi5 $\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factcje.v3yfjx8r(hs 0v y4e)fj e/;b yn0or will the intensity increase? Increaj. r)3f v 8ecv0n(ej;f/hx y0ysy4b jese by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have e2g b b1ita52ezqual displacement amplitudes, but one has twice the frequency of the other. What is the ratio of their 22t1gia zbbe5intensities?   

  What would be the sound level (in dB) of a sound wave in a whfd.)x(uf7s o v 4ay--0jqevir that corresponds to a displacement amplitude of vibrating air mo0.du- eavf xfw4(-v q)7jsyholecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud as a 100-Hz tone thzbdo4ub*jxs p l:k:-i0( lv)o at has a 50-dB sound level? (See Fig. v(x d:)b-4l oobs*i jlpz u0:k12–6.)    dB

What are the lowest anud+xz /d5*f 6o nuz;q ugg5x0kd highest frequencies that an ear can detect when the sound level is 30 dB? (See Fig. 12– zdgdq5;ng5k x6xuo* 0/+ ufzu6.)

  Your auditory system can accommodate a huge range of sound levels. Wfdt9e6z d6n4z hat is the ratio of highest to lowest intensity at9zzf ed64 tnd6
(a) 100 Hz,$ \times10^{ a }$ a =   
(b) 5000 Hz? $ \times10^{ a }$ a =   
(See Fig. 12–6.)

  The A string on a violin has a fundame ;)uakdn51p xjn9smtww;9 4ufntal frequency of 440 Hz. The length of the vibrating portion is 1d nmw9;4u)k;ux p5jsw ta 9nf32 cm, and it has 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 audiblehxa2f9a re0)-z9 ;tyvad8e lmk5i x h;mt6uw3 overtones if the pipe is mxtlyua ;8e erad w03k ;vh mz2ti6)995fha-x
(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 blowin0w0;so sdubwrxns: *fv(1 ks*g across the top of an empty soda bottle tk*:0s ; s0(*dsvbnr1 foxwuswhat 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 abs/uo y.:( ff 1rhk4g0zk8auj pipe organ with open-tube pipes spanning the range of human hearing (20 Hz to 20 kHz), what would be the range of the lengf j:ohg4fyka/b1. uz8 (r ksu0ths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a frequenc zq)2xg k6flg dsrmfl 5rds,0+j3a2;ly of 540 Hz as its third harmonic. What will be its fundamental frequency if it is fingered at 3 q gr;rj2 lffg)mad, dxslsz5+6l2k0a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long andm.n7e+9qmj gskq3j- u is tuned to play E above middle C (330 m-m9e +7qkjj.q 3gusn 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 organ pipe that emitnn+k . aw dju(osz3*)rs middle C (262 Hz) when the temperature is 2ds.j+ua on)rw zk*n3(1 $^{\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 20 +fyl:9 2i z fkuwal7a66sf,: l qj(bqt$^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece 1:07glv evx,mdkic 3 kof the flute in Example 12–10 should the hole be that must be uncovered to play D above middle C av:me3k1,k7gxv c dl0it 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, and 616 Hz, buqkl s:o61 )yhct not at any other frequencies in between. (a) Show why this is yl h:)1q kos6can 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 openymlln ,zings(b. 0p- 446v myt at both ends. It resonates at two successive harmonics of frequencies 275 Hz a,-4my6n0 gn t z4pi mv(lsylb.nd 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 zq-n*zj7q( nx $^{\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 ra, o *jdriigygo ij),7;nge for a 2.14-m-long organ pipe at 20 rdo iy, o ij*i,7gj)g;$^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is apg fbvx2w0*r -gz;jc+lproximately 2.5 cm long. It is open to the outside and is closed at the other end by the eardrum. Estimate the frjcv ; lxr0 2w*+zbgf-gequencies (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 blpvf/xa ;m/d *eat every 2.0 s when trying to adjust two strings, one of which is sounding 440 Hz. How far off in frequency is the other strim xda;v* flp//ng? ±    Hz

  What is the beat frequency if middle C (262 w x +t nv,0x-fl7t7verHz) 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 opx k4qabn 3 2m35uym1c a97pfeierates at 23.5 kHz, while another (brand X) operates at an unknown frequency. If neither whistle c k q3cbneu 571iy9pf4mxma2a3an be heard by humans when played 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 beats/s when sounded with a + u wn3hwm))f5e bp*yb350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of the string? Ex)3wb h5u)fmwepn+*y bplain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz. The tension in one szy,e9wr7q (nw/ 6q ea1 x*dgvu06 biihtring is then decreased by 2.0%. What will be the beat frequency heard when the two strings ,xiw6q h/yngqa76w e0d 1iv9eb( *zurare played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identical flutes each tgmc g/wxp5;s -ry to play middle C (262 Hz), but one is at 5.0°C and the o;/-sxgg 5mp wcther at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A,ssovx. u9h-x:hexi :8 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 heard. When B and C are sounded togetherv 9 h8s. xox:xh:u-sie, 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 and cs pex5s19uka:76 3ojel voq;3.50 m from the other.a9le3;q p5oo6euc x s 7:v1jsk
(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 tun2vbq hg(7 q8seer hears three beats every 2.0 s when they are played together. (a) If one is vibrating at 132 Hz, what must be the 87qe2 bqv(ghsfrequency 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 bea -,q(sb2 wgv0dh+jr+v/tfd e mts per second will be b+/ 0ddjqmh g v t(ef,r2svw+-heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certa(eo.;8z bsc:ug ,rh lsin fire engine’s siren is 1550 Hz when at rest. What frequency do you detect if you move with a speed of b.sesuo h(:rgz ;8,lc 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 whose siht:qgq (yrp32ren emits at 1550 Hz move23gphrq(t:q ys 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 towakdf8kh8 qk:vvxd;9/e*mkbk. rd you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exactly the same? Are they*xv8fmve db98k;k.kqkk d h :/ 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 frequency horn. When one 2*jq+wc wvo l x*4f;7cc qo;zqis at rest and the other is moving toward the oj*2wx;lcq4ov7 q*qfc; c+z wfirst 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 ulte.n bt,g6jcbm aiy-fq/ +cn(b5k(qjfi* w93o rasonic 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 receiv.*q5eb nowkfijn(b qfj /96m cit yg(c,a+3b-ed sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall kv6llnu/8e.q at a speed of 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 rk6 qvlue/.ln 8eflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler expedegu;gau+2.c a /suu1 riments, 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 railway station. What beat frequency was heard if the train car approac. g1a;egduu as2u+c /uhed the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measure blood-flow pd2.6nrow4 smjvod ,o-d 7.ajspeeds. 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 source. orw6oa. 2-n dd,vo jdp4msj7?   Hz

  The Doppler effect um93c(ier4e8 jjkemx e 6d w4u7sing 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 Hx)uhv-so7 qk14qvyk+z. When the wind velocity is 12 m/s from the north, what frequency will observers hear who are locatv)hxoqu7 +ks -yqvk41ed, 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 io), f8knn)sjm f 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 oforhz 50c6i i;es33wx1ts*w p)alx7txbv /b. m sound is 310 m/s (a) What is the .w*tv p hit5b ;exmxw 03o3sb 1x6/cr7lia)szangle the 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 wt b49 6fdnho6 vgcwry)g4la4* here the speed of sound is only 4 4baf 9*vc 4nrdl )g6w6ohygtabout 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} $