What is the evidence that sound trakvfry c v9-3d0vels as a wave?

What is the evidence that sound is a form of ener+og 5sxwzsu*1gy?

Children sometimes play with a homemade “telephone” by attaching a strine.;xf caqdhf;8; 4gj jg to the bo.jxcfdg4e;; afh8j ;qttoms 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. 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 expect the frequenct3 5ni chcswl)d+*ox04c z cs6y or wavelength to change?i h)5dsctlcw coc 6zxn34s* 0+

What evidence can you give that the speed of sound in air does not dqlp 5,i.o2vrcq,mm 4 repend significantly on freque q5mrqm,vrl2p4 oci,. ncy?

The voice of a person t gniz4o:e1 t; *mpuf-who has inhaled helium sounds very high-pitched. Why?

How will the air temperature in aacxvyn h4,8 b gvh(uc:6,3fvi room affect the pitch of organ pipes?

Explain how a tube might be used as a filter to reduce the amplitude of sork2mf u)2d i,kunds in various frequ ,)md22ukik frency ranges. (An example is a car muffler.)

Why are the frets on a gui*k:o , (zyzg fn9 l/9rcua0wtutar (Fig. 12–30) spaced closer together as you move up, twn *o9l:u uca09zz/ grk(yf the fingerboard toward the bridge?

A noisy truck approaches you from behind a building. Initially you hear av,gj 6; g2qx ky*0rk;jb/uct it but cannot 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 Sec; trcuk; jg*2/jbqaxkg,v6y 0 tion 11–15 on diffraction.]

Standing waves can be said to be due to “t(z0i)al gkl ,interference in space,” whereas beats can be sa zkgtl,(ail )0id to be due to “interference in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered, would the points q5zh0 .8 djg(8mjrskn7t )nc rD and C (where destructive and constructive interference occur) move farther apart or closer together05kn8dj h8qgntrjz. 7()r msc?

Traditional methods of protecting the hearing of m )h(,7dc mvappeople 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 electronically, then fe cdv,am )pm(h7eds 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 canr.a3n5p0in g: z-wlxv be thought of as a superposition of two sound waves with slightly different frequenzxw0.vp:-3i nglna5 rcies, 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 and wg3ytz db. p0vp t/3n)7jaq3tobserver move in the same direction, with the same velocity? jb3p3tn/dg)tq tawy0 3.7vz p Explain.

If a wind is blowing, will this alter tc2i0uo,zf o rp:i *-zihe frequency of the sound heard by a person at rest with respect to the source? Is the wavelength or velocitz:,i*2picf o z-0iuroy changed?

Figure 12–32 shows various positions of a child in motion on a swing. A 1yakfa+6 v3mlmonitor is blowing a whistle in fa vmy1f+3ka6l ront 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.

  A hiker determines the ltsx,u 3ns)1 dnl:vi:gength 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 ov:dl1,txiunn:sg) 3 sf the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below the waterline. He heay0 mp(dwf:;ec rs the echo of the sound reflected from the ocean flmc(0 yew fdp:;oor 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 not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wa:+lt/lhp4vqf4f u g)o velengths 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 just above a school of tuna on a foggycopr6( 3d lzt0 ;-wo1xnlvaw+ day. Without warning, an engine backfire ocw ;alo-w (pxtn6zod30c lvr1+curs on another 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 t.j f vyhd*yh2u ng;5v 1bh03swhe top of a cliff. The splash it makes when striking the water below is heard 3.5 s late w2gy .*v1vbn5y hs0jd3u hfh;r. How high is the cliff?    m

  A person, with his ear to tcl*a5o7htvma1xigg;g * j xc*: :y- mehe ground, sees a huge stone strike the concrete pavement. A moment later two sounds are heard from thmg*omc ;ci:vx ag :*1a xj75y*leh-tge 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 7h40i8p8mt(f g bdw bgmile of distance by the “5-second rule” for estimating the distance from a ligb87d g(bg mfhpiwt804htning 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 dB )nk b7komj;v8?    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 is +/)ml e 7zwd ojiz y8lv2bm5 -wuvsz*-$2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired simult8rnukf22rw1-g: z r iuaneously at a certain place-rrwunfi2g uz 12kr8:, what will be the sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane with four equally nois1h(/xzb9 -cgd wdx aj8y jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would this person experi-zdxa1bwg jxh/9 (c d8ence if the captain shut down all but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said t(/) tzz57u:h p fdehsuo have a signal-to-noise ratio of 58 dB, whereas for a hf d)/e ph:zu7u(st5z CD player it 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 from a person spea nb: muc+3se,yr4pujp)6q c0 eking in normal conversation. Use Table 12–2. Assume the sound spreads roughly uniformly o3 ps+)4qycebcjm0p:e ,uu6 nrver 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 ( 1u,o bd-d xr;ooddw(4nuzr+ 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 ae uf 6im5bjeh nn6h a.qat7ie-)6: ;aqt 250 W, while the more modest amplifier B is rated at 40 W. (a) Estimate the sound level e:n6;it.5-7qaebeaua6 ihjm f hq n)6 in 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 registeresu8d:7b8qxf(iazo9 a 0v gfw*/m o7c fd 130 dB when placed 2.8 m in front of a loud 9o* gis7vmzaq8(8b/u0fxdof:c7 w afspeaker 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 differq90-dq5nyy( vvww2tdzpyq g* i:* b5jence in sound level of 2.0 dB. What is the ratio of the amplitudes jg by*dn:vw 5itv(p 90wq-q* d5qyy z2of two sounds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a so q0 a2ami+0m/qit+gq qund wave is tripled, (a) by what factor will the intensity increase? Increase by a factor o2/gq +qq a0m0miq t+iaf    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but one has twice the frequfal-) 0j ck3 9l1brxz bdh48juency of the other. What is the ratajub9 j1cd4 0xfr b )3hl-k8lzio of their intensities?   

  What would be the sound level (in dB) of a soun3k 8rta p:gks:k9r2bl d wave in air that corresponds to a displacement amplitude of vibrating air molecu l29 kk:gprs ka38t:brles of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud am bdzmq(, l3w.f dm(/as a 100-Hz tone that has a 50-dB/bq (w.afm, 3dd(mmzl sound level? (See Fig. 12–6.)    dB

What are the lowest and highest frequencies that an ear can detect when the s8 bh.+gvi 9, nqx)fc09yzd 6zvovi qj+ound level is 30 dB? (See v9c9q0vq+ybjiix8vn 6 , oz.d +)fhgz Fig. 12–6.)

  Your auditory system can accommodatsf+kf/lo 3fu rz )84jozt0 9xhe a huge range of sound levels. What is the ratio of highest to zj)sr0 k9ztx8l34off /uh+ o flowest 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 of thu68 k.wcz(d0 nzr9hy fe vibratingfk9.wc08zd(n6rhy zu portion is 32 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 f9utreqx5cb;hthji( c m 33: 9rirst three audible overtones ie(b 39;i rt thqc:j3hu5rxm 9cf the 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 fr+v9b)ljq1s goequency would you expect from blowing across the top of an empty soda bottle that is 18 cm deep, if you assumed it was a closed t1+lg qsvo9j )bube?    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 pipes d(rlt4g rje j( , w lr :2fy*25vg3wszp0hnvk:spanning the range of human hearing (20 Hzsh 4jrr zn(g3vtd*el ywk,(:grv5w 2l2:p j 0f to 20 kHz), 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 harmonic. Wggngh yphgws,b/(4 :7hat will be its fundamental frequency y( gs/g,hg:w 4pgbh7nif it is fingered at a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and ;y5* xi rrckjwktb8 )1is tuned to play E above middle C (33r;*wk x k8j b51r)city0 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 orga,7m54;pxxifu njy1jvcv t* 8kn pipe that emits middle C (262 Hz) when the temperayuv4fj 8xmv71, *pckx5i jn;tture 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 2v 2jd/ut k/wuw.zic0uasi:).lo ;a f*0 $^{\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 hole be tdap)q va( vp)(hadv)a(p) p qav(t must be uncovered 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 cankn ft.eb+m t1,lby)am2ylr4 30r l8o n resonate at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (a) Show why this is an openo rbtnanf4e l3 2r.lkt)1,m bm8+y0 ly 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 resonates at two s7 u+x,vf *j p/ n jv90hf8jdxi;lbz-.2chkpdzuccessive harmonics of frequencies 275 Hz and 38b0xhi.-, v+cjfzdun7 ;lhvxjjk d/ 92* fzpp30 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 *e od7t rvu +rxziwxai3650s.$^{\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 2.145.v4drm7 jdid:nkj z gwd-1; d-m-long organ p1id kjrn4dw v5d:d7j-m d.g; zipe at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm long6lneng(7 5 iu7jmorr,l/ak h *. 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 ans*g ljre7( n /76h,rl mnau5kiower 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 2.0ljc+k/jqm:ll jg r68qq3g 3 l) s when trying to adjust two strings, one of which is sounding 440 Hz. How far off in frequency is the other string?q 6grjl+l:c )jk q q83j/3lgml ±    Hz

  What is the beat frequency if mid9j l- t 1mc0+f ;i,u6qfraglckdle C (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, wh 51 pztn8j3ugsile another (brand X) operates at an unknown frequency. If neither whistle can 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 zt81jus 3gp 5nof brand X.    kHz

  A guitar string produces 4 beats/s when sou6 djuu5(f6i ecx- s)e4 ph97 emfl4olynded with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tunice7is9(5 6 fu)hxe4m yuol 4- e6djlpfng fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency 9tl,i2 -wewizg0z6(mam paq adj8+w; , 294 Hz. The tension in one string is then decreased by 2.0%. What will be the beat frequency heard when the two strings w9ilaaw wj;e a6 gz-,i2(0qtdmzm+ 8p are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two iden .) f:c)zlr rf8n3azasm*sle7tical flutes each try to play middle C (262 Hz), but one is azr*as7.ce 8:s3 lrm)nzf)fl 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 o6co) i:lgi 3h v8c2jfrf 441 Hz; when A and B are sounded together, a beat frequency of 3 Hz is heard.gvr 8c )f 2lhj6coii:3 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 1tyyo (hdpz **g:4gtt3.00 m from one speaker and 3.50 m from the other. tygg14: z ytho *tp(*d
(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,ubv7e 4 dni+x to be vibrating at 132 Hz, but a piano tuner hears three beats every 2.0 s when they are played together. (a) If dix7, n+4ubv eone 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 f d4kbk/ 1f;iodqrq*j1)3h uz92g bfkin air. How many beats per second g j2oz irb *1fh93dq dkf4k)1fq;ku/b will be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engtqe4hx89r g p my-:; wfdj 2cwpu9x1)yine’s siren is 1550 Hz when at rest. What frequency do you detect if you move with a )-uc19er ;8gpq4 ydh:w ytp9 mx fwx2jspeed 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 fire aqi*pb s k1g;h7h*3eeengine whose siren emits at 1550 Hz mohbeqge7ipks 3 1;h**aves at a speed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if r*kr:lvq: w g.9aymx ;a 2000-Hz source is moving toward you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exa gwm* 9la :qyr:.r;vkxctly 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 frequency horn. When one is;frubdehr m0ol twe vu2/o -+7k*, s-k at rest and the other vu-oe* 2rl f0uk,ms+brheod;7-wtk/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 receives them rlu85g u83p0d pxqagi 8fm)x;w:ra o)weturned from an object moving directly away from it at 25 m/s What is the received sound frequency?wlpfx8w3rdaai; mu5ugq0x )8): o8 pg    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As it flies, the baxof /tmze:zu 4 (n dfem75;;frt emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency does the bat heto;x7 mue5m4efn (fr/dz ;f z:ar in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experimnvtcq 0 z+k60 deeo1r-ents, 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 approae1cn6 kodrqze-0 t+v0ched the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measure blood-flow speezdqc gt.5gv6 j p16vc:ds. 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 a:16pcct.d gv gjz5v6qt 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using ultrasonic waves u5q+uwjhy7u.8d q 2imof 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 emitsgng8of mlt8q+dr89y, sound of frequency 570 Hz. When the wind velocity is 12 m/s from the north, what frequency will observers hear who are locatof,dn9 qg+my g8rlt 88ed, 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 at 20 q y7nf.ip.ihq z,ys29 $^{\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 Mt;ozu*be-j 7 i 819xqsyj/w zvach 2.3 where the speed of sound is 310 m/s (a) What is the ang89xw 7qe;*jb1/ozj- vts iyzule 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 where the speed ofs;()fz h9xhkrr,v b) k sound is only aboukvbf;(rkh)x9h z,) srt 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} $