What is the evidence that sound travels as y* 1tq3qv:5tx) sfohos .ecs9 a wave?

What is the evidence that sound is a form of enfo+r d9160w9uzks 43 imerqnk ergy?

Children sometimes play with a homemade “telephone” by attaching a string 1bp e4r2:+2 mc97jydqwy ,g iuu7nbndto the bottoms of two paper cups. When the string is stretchedn9ybi qwepd g du+,27b4 :mn7u 1ryjc2 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 ir a s+ svg+g2y31cdsxfsi x)1,nto water, do you expect the frequency or wavelength to changd xrsg1+sgcyi v fa)3 2x1,s+se?

What evidence can you give that the speed ofz(p)oc g0keo1t9w 9c :f/q5jb 9sjxch sound in air does not depend significantly cof5p /9c: 9gtx 9bjeqwjzh) c1s( k0oon frequency?

The voice of a person who has inhaled helium sounds very high-pqxr23zpt :8wp7py9ek9z. ohsitched. Why?

How will the air temperature in a room affect the pitch of organ pipef4 o:bfki 2 np2b+uz3 5cz+xeo/iy+m os?

Explain how a tube might be used as a filter to red7k0 7 m-ohzt-joqxfn9 uce the amplitude of sounds in various freq - xn7qmkho to0f7jz9-uency ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer together as you mongg e e4r j4 yh9*8lo22ghqe oz4wrm90ve up the finger eeog w mh4r80o2*yj n49qlez9grg4h2board toward the bridge?

A noisy truck approaches you from behind a building. Initiallc4:6 7ab u yoc9q4ihfuzbt0k:y you hear 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 7k:90 i6ucozaqb: u t 4b4fyhcSection 11–15 on diffraction.]

Standing waves can be said to be due to “interference cjy(hkg rtoxy97 4 n;*in space,” whereas beats can be said y(jtgo7 ;ncy 9k*x4r hto be due to “interference in time.” Explain.

In Fig. 12–16, if the frequency l,aqlm bb*0;j 5as8fz of the speakers were lowered, would the points D and C (where destructive and conmla;zl8,b s5qa*f jb 0structive interference occur) move farther apart or closer together?

Traditional methods of protecting the hearing of u. * unib)ohru5v;+jw( qrt1wpeople 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 i)qbwur w1;o h.+v( junr5uit *t 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 wave can bewo +cmqo 2tabx8/ :nb2 :*8xaojmm s*g thought of as a superpoa2/t88sxobqaxw:*o cb+2mnmg* om:j sition 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? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and observe5qc5cxlyn sxu d:;3 l 9.2(byz4ru ugsr move in the same direction, with the same veloci245l nu.xsls 5d3uxrcgy;uqz :bc y9( ty? Explain.

If a wind is blowing, will this alter thdqx:39u7 fpmne frequency of the sound heard by a person at rest with 9 7pdmx3qnu: frespect to the source? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a child in mn, bwzg-.cut:otion 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? Explainu- cn bw:t,z.g your reasoning.

  A hiker determines the length of a lake by listening forvdx(*;l o3 k 6jwduaf597 bskj 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 of k( 6kod5ajv jb*x;du l7w39sfthe lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his shipwkdn 1 k :+(sphxn +v; 5awv*ywhge;zhjp8a1 8 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 12–1) and does not vary sigak:wh1 8(n81;p g;hv ajv+5e y +shw*dwkpnxznificantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in au)v9i).epmc; hq rcx 9ir 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 drifto :8 ,ljxd4kkting just above a school of tuna on a foggy day. Without warning, an engine backfire occurs on another :,jdlo48kt xk 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 the top of a cliff. Thezr b yy*mczk.6s)sp43zax7.g splash it makes when striking the water below is heard 3.5 s later*k)g6z x3pysm zz..4ay 7cbsr. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge stone strikno 4 mr((,htvne 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 Table 1(mh n,rv n4ot(2–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one mile of distance by the “5r63rgjt xu s9 +gox0p2-second rule” for estirxug3ro+0 j9t2xs pg6 mating 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 a so8ast6 ullu*tsoc0*e udl6,: i0w9nl vund 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 (e h8ugu3u-ts+all5cxz 9 :fb a sound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a soun;upv,zx+8h hkryf7xw 6b 8 jb.d level of 95 dB when fired simultaneously at a certain place, what will be the sound level if only one is exploded? [Hint: Add intensi8hju f rkbx.hxp;b+z, w y786vties, not dB’s.]    dB

  A person standing a cer pyi-;:cliv7z6w /nuq tain 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 experience if the captain shut down all but one engine? [Hint: Add intensities, no vyiqwn6cu; z ilp/:-7t dB’s.]    dB

  A cassette player is said to have a signal-to-noise ratio of 58 dB, where4kk2lsop 8ra1c, 2isaas for a CD player it is 95 dB. What is the ratio of intensities of the signal and the background noise for each device? 58 i4sr2cka aplo21k,s 8dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound;w; ol-7gkqpt from a person speaking in normal conversation. Use Table 12–2. Assume the sound spreads roughly uniformg;k-q7t po; lwly 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 pbsd3 6e b:ii8n9j,uoan 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 h0c8o: 4d1xkf vcjvj3more modest amplifier B is rated at 40 W. (a) Estimate the sound level in decibels you would expect at a poind jv4ox 1c: hcv3fjk08t 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 e d+ 91d2vmcn l t-k1m/4icb;fnqip1xdB meter registered 130 dB when placed 2.8 m in front of a loudspeaker cn 4 f9xnc2mi1vp+q1 bi/lt;d-k1dme 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 detecl+:ig /a2a etzki)ef0 t a difference in sound level of 2.0 dB. What is the ratio of the amplitudes of two sounds whose levels diff/i l)ite+gk: a2z efa0er by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what*gzt hosv( aln4-3:su factor will the intensity increase? Io n 3sls (-4huag:tvz*ncrease by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement6a1i et6ar6x;u vi4qg amplitudes, but one has twice the frequency of the g x61tv4uqi66aear; iother. What is the ratio of their intensities?   

  What would be the sound level (in dB) of a jcoxk6de.;uw t(6 vm51w+- , trwvfzrsound wave in air that corresponds to a dispw dcwzrt5t(oev61u- k.;, vjxwm+6rflacement 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 9jdhokw4smu22o: j26 b rdmg 4as a 100-Hz tone that has a 50-dB sound level? (See Fig. 12–6.mhm4kd jdw222 r6s4o j 9ugbo:)    dB

What are the lowest and highest frequencies that anvp /+/tj3rwif ear can detect when the sound level is3if vtj// wr+p 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of soun,h4n49blmnua-ynp *hau m:ej gf -y1 ,d levels. What is the ratio of highest to lowest intensity at4bmf,,n numya 1hp4-*lyan 9-egh:uj
(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 frequenz/g8ovls vx tfvm6-3. cy of 440 Hz. The length of the vibrating portion is 32 cm, and it has a mass of 0.35 g. Under what tension must the / vv xv8-6. 3fmgstlzostring be placed?    N

  An organ pipe is 112 cm long. What are the fundamental and firsta kf:/k/0n4n hnwh6nhtp38f t three audible overtones ik 64hh3nht8 0/pw:fnkt nafn/f 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 frt xmw9g8 gpc.9 rz.c 3j(chrx/equency would you expect from blowing across the top of an empty soda bottle that is 18 cm deep, if you asghcj.w/ccz8rxx 9.p93(rg tmsumed 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 open-tube pipes spanning the rangc/vofd ,bbj 40+2lv32slrow t e of human hearing (20 Hz to 20 kHz), what would be the range of the lengths02,lbof vcbt /ws3lr +2 dvjo4 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. What wille6tjnj59+u7yxq vdw j 3,3hum be its fundamental frequency if it is fingered at a length of only 60% of its original leng7v w+yue6td j 3hqx9m5jj u,n3th?   Hz

  An unfingered guitar string is74logrzum(aj(3 de2voit4 6v 0.73 m long and is tuned to play E above middle Co d 3m4a7uol(grvvj(2i6 tez 4 (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 middle C (262 Hz) whe5t n9*5l dshqyn the te9hy d5l5*st nqmperature 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 atjm c9r* - bk4.vns5p9wu, jxes 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 6kgt. 5b-whbi 12–10 should the hole be that must be uncovered to play D abovewbg k6h.i -tb5 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 rebgu( o1+ e1r4r hekrb7sonate at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between.r1uerg1hke+b7 or4b( (a) Show 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 resonate sd9:ldc2jy/ qxnrfa8,c.mfiib4x6 5 s at two successive harmonics of frequencies 275 Hz and 330 Hz. Whadbdm4ff jxx.n:9ilc86/ 2ryia5s,cq t 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 .2ij6m fq(x lv7of,l ,pif 5ep$^{\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 preuky2) u(mxur8 sent within the audible range for a 2.14-m-long organ pipe at mxy uu(k)2ur8 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm long. It is open to the l07f ursx 8qh06czn:k o;mgw9 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.unf k ;6zmsl:x79o 8wr qg00ch 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 every 2.0 s when trying to adjust two strk(a 62u4xp h93g.pk3wzdf ,ypxsh bp. ings, one of which isyhd 3 w.4xkp9pphzpagx3,6 b .fk 2u(s sounding 440 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency if middtp/+rf/y tsz 1vfrw,;7 g rr;vle 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.i 4:a/0xq)bkb j 9n()g c8ze)5z0 bsmgzlanbf5 kHz, while another (brand X) operates at an unknown frequency. If neither whistle can be heard by humansjlbe ibaz g(zk 0qzb5fcn9sx8ba) n :g4/0m) ) 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 w77u 5/kdek phshen sounded with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-H5 p77uh kesd/kz tuning fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same freque 1svk j;d e8+fwima.lh:mjt4i)2yzs, ncy, 294 Hz. The tension in one string is then decreased by 2.0%. What will be the beat frequency heard when the two stri lvh mt:zk 1ds+f,.s4a)mwy82i ie;jjngs are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identical flutes each try to plaq+ak xg-e8t, 8+yciacy middle C (262 Hz), but one is at 5.0°C a8yx gkiqa,-tc 8cea++ nd the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning f2nz(69covyc corks, A, B, and C. Fork B has a frequency of 441 Hz; when A and B are sounded togetherz2cn6( 9c cvyo, 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 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 oneky0t9u rb vg77 speaker and 3.50 m from thtvgy7r907 ku be 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 supposedba8utzn lq;*-ql0x 5 b/p6orfuw * d)g to be vibrating at 132 Hz, but a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibrating at 132 ;0t fadlbu/u w lqn8)z6-bx rp*g5qo*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 in air. H7hx qyerdn-s hj*h2 * a-cj;i5-z obn6ow many beats per second will be hh;ni 2ba-hn- z7jj5e*qcrdo* ysx-6heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fir/3s uow+br/6zde. j0lxxtn5 tm h2-nge engine’s siren is 1550 Hz when at rest. What frequency do you detect if you move with/so0l 3tz/rx5g6n umjw2b-+ne.htx d a speed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequencky6( t6 vzv)wcy do you detect if a fire engine whose siren emits at 1550 Hz moves at a speed of t(w 6)c vyz6vk32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz source is movin o2+2wpr, ;q)k7 doexl sxyn9wg toward you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exactly the same? Are they close9q k) lxowdyr;on72s 2,xp+we? $f'_{source\,movine}$    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. Wh3nlk,qd) 53u9i ez2qzoknf; aen one is at resuid2f,ezlk n ;3oz5 qkn q)a93t and the other 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 sl):o7fys20r) p xb2ozw ,nfzs ound waves at 50.0 kHz and receives them returned from an object moving directly away fo lfn:wb0f,xp 7) sozr s)zy22rom 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, thea x12zqu m*ck1 1dh9gv bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency 91m1 cq2xg1zhu a vd*kdoes the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was played on a movin26n+i 3eitaqgou;fgcj k 93u.g 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 approached the stito ;3+g2.e6k9q j3a uucif gnation at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measure blood-flow speednz+s aeegde6cq8s4-;s: crpdl a,;9 b s. 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:6 ncqa8dd;pea sze4 ;s-,lcr9+gesb at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using ultrasonic waves ofi9csjz6jg;)e 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. npl:y q,6 l uwi5vbxoc xk23cn5x69d9When the wind velocity is 12 m/s from the north, what frequency will observers hear who are located, atcin,695pl bovuxc xq23 x:ky nd95l6w 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 d 9 - wfw,;;vsrlydm -ly)gkdkx,2t3o 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 iley4 7pmsdxw-20 1csthe angle the sh pd2mix01s4wecly s7 -ock 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 sp yp -xl)z8b25gyen3nbeed of sound is ob5) ne -2zpbn 38yyxglnly 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} $