What is the evidencepynb ) ghmiqv3,g)7l yxt0j o9:5bk4m that sound travels as a wave?

What is the evidence that sound is a form of pt.ly ) z/26: l 5, dnkymj(b-mrcweypenergy?

Children sometimes play with a homemadezg0g*h 4wrk frr:4af( “telephone” by attaching a string to the bottoms of two paper cups. When the string is stretched and a child speaks into one cup, the sound can be heard at the other cup (Fig. ahg(:rkfrf*4g4z w0r 12–29). Explain clearly how the sound wave travels from one cup to the other.

When a sound wave passes from air into water;(ot zv-si9l o, do you expect the frequency or waveleng(iz9o lo;-vt sth to change?

What evidence can you give that the speed of sound in air does m:6hy,b s:maoxt 9h 3kp,x0scn9 7yr ynot depend significantly on frepm79,c ry 9ts, 3ykoy:x0 x:6bhnmsah quency?

The voice of a person who has inhaled helium sounds very high-pitoa*g)jg 9gcl+ched. Why?

How will the air temperature in a room afa7 ;v/wkkbn 0jfect the pitch of organ pipes?

Explain how a tube might be used as a filter to reduce the amplituh.m/uv )4hjf03vp bo 8*j soaude of sounds in various frequency ranges. (Anuvhosj j/p4bh0)mfoa *u 8 v.3 example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer together as you move upp6:loc01ol /ht5a( 37mlbhr/vi z zhw the fingerbob3h0zlr i/h(:5wlapot 6h/ 7lvzm1 ocard toward the bridge?

A noisy truck approaches you from behind a building. tg0w9))tbekq4+rtewInitially you hear it but cannotebrq+k9teww)gtt 4 )0 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 sriws.s q:s pvbf(8n+9 pace,” whereas beats can be said to be due to “interferenc psb 8vsi:q.(snf+r9we in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered, would the poin*ub4 *t i(skdrts D and C (where destructive and constructive interference tdb* 4r*s( uikoccur) move farther apart or closer together?

Traditional methods of protecting the hearing of people who work in area6xn3p,b pi o/js 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 reaching, /pxpbn3 6oij the ears?

Consider the two waves shown in Fig. 12–31. Each wave can be thought of axqwch ru (1jl0ay3eh n6y2,a9s a superposition of two sound waves with slightly different frequyhq,lxu hawyaj0( c2n9re361encies, 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 ifv(:zfrymvit *6 gy(o+ the source and observer move in the same direction, with the same velocityvroivtz+m( gy6y( f*:? Explain.

If a wind is blowing, will this alter the frequency of the sound heard.0/rpgsjkn yi: .it /j by a person at rest with respect to the source? Is the wavelen0gri t jjni/y sk.:p./gth or velocity changed?

Figure 12–32 shows various ymg.u 4fytx5/a3l0 c,3 gw+ sdl9nmsd 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 heawg.lyydm3l sd /n f430s,a9+xtmuc 5gr the highest frequency for the sound of the whistle? Explain your reasoning.

  A hiker determines theix8d;c(f g:7tme mj 4j length of a lake by listening 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 ofg:de ;7(mxij jt8 fm4c the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below the waterline. He h, 3qfsuw ;m3clears the echo of the sound reflected from the ocean floor directly below 2.5 s later. How deep is the ocean at th3; fqw,3u lmscis point? Assume the speed 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 air0cl(wfgu5 1 qe;mudo8 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 drifting0kmo:t- z,-zqg40z6s u aqbg slxdbcnt ;4:*p just 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):0z qpga dqbg z 0:,zk*t;xs-6t4osun 4 -blcm. 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. The splash it makese,.tt. zm v .f4q.1okq,ckt cs when striking the ,qtvse1..fkc o4.mt c. q,tzk water below is heard 3.5 s later. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge strei qnf;)zs**7fhz4 9 oji(vvone strike the concrete pavement. A moment later two sounds are heard from the impact: one travels in the air and the other in the e*r;h f9 io4snz*i vjqzv)( f7concrete, 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 distancetd *c jts(qg2uu n:b)1r9 xh4a by the “5-second rule” for estimating the dis)rctat*u9 xd 41: gqn2h js(ubtance from a 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 lezf.rpb1d 5+k2.j rmxj vel 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 souhstu6r z,;7zum1r sanh8 63ghlee k)(nd whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level fd1i- 29bqzswof 95 dB when fired simultaneously at a certain place, what will be the sound level if only one is exploded? [Hint: Add intensities,9s b f-21iqwzd not dB’s.]    dB

  A person standing a certain distance fry:6io c0yhff fu8nyc;0lcn9a 9v:iyx*)e ey/om an airplane with four equally noisy jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would this person experience if theyao yi :ycyci9 :;e9f8)hnyc6nfe v00fxul*/ 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 rat(fv0lk9dhr a i3u: 5uwksz5f8)-gi dqio of 58 dB, whereas for a CD player it is 95 dB. What is the ratio of intensitiezdfqk5a9(g)-dkfri: w8 v 0u sh i35lus of the signal and the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of s ;x8;zh,z 7d, fcunxvd1nfw/gq5cy0sound from a person speaking in normal conversation. Use Table 12–2. Assume the sound ,x7 f8h c;y dszu,/qcw ;0 xnz5fdgvn1spreads 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, +w6mipy3k80v h(jq7pbi 1tuj)la r u 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 w),q:/ yr m3 utu(j9 sxxj djm);uen;uthe more modest amplifier B is rated at 40 W. (a) Estimate the sound level in j)u n/:t9y3rwujdqm m u ,;x;s )xuej(decibels you would expect at a point 3.5 m from 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 placp6s xnnnn5s) vi2 h0p3ed 2.8 m in front of a loudspeaker on the stagexn s 03n6n2 5p)vspihn.
(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. 6j0t-sx asq+ c(m*syw0 dB. What is the ratio of j *syxm0tqc (-s 6w+asthe amplitudes of two sounds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by whatn5k2,o18 b2y gm*6j fa tnwwpp factor will the intensity inck2p*gw2 jwfyap no 586 ,ntm1brease? Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal l,jcmyu6w e39lgea(l :jl. h; displacement amplitudes, but one has twice the frequency of the other. What is the ratio of their intensities?.ej( l:hl;uma c6w9e jgl,yl 3   

  What would be the sound level (in uu m63h/la gq-dB) of a sound wave in air that corresponds to a dismu3hq/gl 6u-aplacement 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 loa3z6u0orbu ( utk2ysy2d8ol,ud as a 100-Hz tone that has a 50-dB sound level? (See Fig. 12–6.)uuukaoy2(, yl0d ozbs3t r628    dB

What are the lowest and highest frequencies that an ear can detect when thetsh9g s, g5w;l sound level is 30 dB? (See Fig. 12–6.) h5 tg;wsl, sg9

  Your auditory system can accommodate a huge range of sound (7td hclbz8 8jlevels. What is the ratio of highest to lod87jhb (8cztlwest 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 q:onv ur+di5k t. s.1bof the vibrating portion is 32 cm, and it has a mass of 0.35 g. Under what tension must tkin+qot.d 5 v.br1 u:she string be placed?    N

  An organ pipe is 112 cm long. What are the fundamental and first three audib/t- ,s;u*yiojl 2gp7 ojv ;qcale overtones if the pipe isu7pyvt *oi2- s /,l;acq;jj og
(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 d:hb: l b ;2kmli)ztqbzf;m)0 blowing across the top of an empty soda bo0mm; li2bdqt)zhlk;: f: bz)b ttle that 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 with opegsp; 1okqs90z(d hoye ,(s6umn-tube pipes spanning the range of human hearing (20 Hz to 20 kHz), what would be ty;9 0(us,k qdsoo( 1mzgsh6ephe range of the lengths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a freque +33a axto*dskncy of 540 Hz as its third harmonic. What will be its fundamental f+ o* ak3dx3atsrequency if it is fingered at a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m ldgus+k6d..m m /0li csii m9b-ong and is tuned to play E above middle C d6ui9i/. mm.is lbmcd0g+- ks(330 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 emits middg 1w9a:m hh/ni r92 dmtntxp5*le C (262 Hz) when the tempehidrt12*nm nxw gph9a9:5/mt rature 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 1,ah3oq*2eob,uujw l 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 shou :97vro-usojuld the hole be that must be uncovered to play D above middle C at 294 Ho u-oj:7u9srvz?    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 p9utv5+ll q9xr ipe can resonate at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (a) Sh9 xl rl5u9v+qtow 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 ends. It resonatebho mg*f42te;d9ky5qj4l au 7s at two successive harmonics of frequencies 275 Hz and 330 H* ehfobjtd ;49ugm274ky q a5lz. 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 q.;srleg cy5 -$^{\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 2.14-m-londk4g3turqs 2krb) s);tgc-)kg organ pipe at 2 rdggcr3;tt))k- 2su)4 kqkb s0 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm long. It iwe4fpg a jjo8( 1i;w,kphhz,0s open to the outside and is closed at the other end by the eardrum,ojfh kppwz;,w4h(jg a8ie1 0. 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 ejig*qq0 kela zf-y 8/1very 2.0 s when trying to adjust two strings, one of which is sounding 440 Hz. How far off in frequency is th8lzj 0q/i *fq1-aeykge other string? ±    Hz

  What is the beat frequency if middle C (262 Hz) andkep:/ha-wvy + $C^＃$ (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 23.8ii u1mzr/0c2p ey 8yn5 kHz, while another (brand X) operates at an unknown frequency. If neither whistle can be heard by humans when played separately, but a shrill whine of cmy8i z1n p20ru /8yiefrequency 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 i r +ly3krtfn88(x)yc5r am7t350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of the string? Explain yln8mx+krf 3tya( rric )8t75your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz. The tension in oh3: 8krpd j;gv u-,lkcne string is then decreased by 2.0%. What will be the beat frequency heard when the two strings are played together? [Hint: ; cr:vkjuk8lg ,-d3h pRecall Eq. 11–13.]    Hz

  How many beats will be heard if two identical flutes each trn; d elpn;x(c0y to play middle C (262 Hz), but one ip( ;xdn 0lc;ens 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 48 o0 8potzyby* m9vxkme js02441 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 H2 kjbo8 yys0emz*t8v 904mxpo z. 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 mlc.c 9( cr-jx4r jg09nzjte j1 from one speaker and 3.50 m from 49cjcgr1jjzr-. c9t(xnjle0 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 vibratin avno0j7.uu quh,b4 .jg at 132 Hz, but a piano tuner hears three beats every 2.0 s when they are played4j.,.ua h 7jv 0uobnqu 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 (t -zfy0xa.nrm in air. How many beats per second will be heard? (Assume T = 20 -ar.tfn 0z(yx$^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency g2xgb.d 264ra eiw fjp5e+.duof a certain fire engine’s siren is 1550 Hz when at rest. What frequency do you detect if you move with a speed of 30 m/ w2 2+u.xdip5edb.g jr af46ges
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What f6hm kawnqas6e,6c 1,grequency do you detect if a fire engine whose siren,nw sa, ek6hmq1g a6c6 emits at 1550 Hz moves at a speed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shiftehxw)qj7ar8o iuv) e)d) ;wd 5 in frequency if a 2000-Hz source is moving toward you at 15 m/s versus you moving teo7)8) djaw h5)erwu)d;x viq oward 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 same sdgx(.e5r 9hr ez5il7;bk; flbingle 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 h;.5if57lgz9rdb ; lb (eerkx 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 rrdc8u m8kqr abl7/-c 6qs1q 3teturned from an object mrd/q73a8cqbc k8s 1-lt6rmuqoving 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 of 5 m/s As it flies, enm66ua 7jc6l the bat emits an ultrasonic sound wave wim76 eujacln6 6th 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 tzo7t66ocn 2fzuba was played on a moving flat train cao6fzc26 t7 zonr 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 ?   Hz

  A Doppler flow meter uses ultrasound waves to measure bloz2izfzl8 k:bd ;4m k*ood-flow speeds. Suppose the device emits sound at 3.5 MHz, and the speed of sound in human tissue is takzz8b zmo*;lif 4 k:d2ken 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 frequencnj.gg2k4i 2kq y $2.25 \times10^{ 6}$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 fy;:rveyiw4 o5requency 570 Hz. When the wind velocity is 12 m/s from the north, what frequency will orv5:wyi; 4e oybservers 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 movin2 g bq1ox5(17)b luekfr1bd2fydjzp (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 sound is 310 m/s (a) What is bzkabsy-t,rq;7-g) o1np8 i q the angle the shock wave makes with the direction of the airplanp-ikrayo b1-tg,8nzqs7q); be’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 speer awx-i 01 4g7kqis)u8mltw)zd of sound is qt7gwiir0 48m luxa1k zw)s-) only 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} $