What is the evidence that sound traveoo0ce: ii rlz(n 4.(cnls as a wave?

What is the evidence that nesick ql*u(9 5+(-trpnxodn 0 m+2zqsound is a form of energy?

Children sometimes play with a homemade “telephone” by attaching a string to7 9td 3 mq7qkwoy1x80h)ilzbx 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. 12–29). Explain clearly how the sound wave travels from one cup to the ot7khil zt 0oqxb13dyw98qm 7x)her.

When a sound wave passes from air into h g/stlz5+(rpugqd00water, do you expect the frequency or wavelenr0gsg+5uqz/dth ( lp0gth to change?

What evidence can you give that. 4y(nb:nmoou the speed of sound in air does not depend signifm ny4(on.bu:o icantly on frequency?

The voice of a person who has inhaled helium sounds very hight1f1x9ilt* iuid (r+d d;9ivb-pitched. Why?

How will the air temperature in a room affect the pitch of bkw :f7+r7afwy+4onn organ pipes?

Explain how a tube might be used as a filter to reduce theuu 6dse( 5ci6b amplitude of sounds in various frequency ranges. (An example is a car mu u656 (sbcediuffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closeocu my(zfj tyc+z87, 3r together as you move up the fingerboardyz8fo+zt cucm,7( 3jy toward the bridge?

A noisy truck approaches you from behind a building. Initially you hear it buzj ;e2*x amu( vw 0ii-azgh9-kt cannot see it. When it emerges and you do see it, its sound is suddenly “brighter” — you hear more of the high-freqju;0i zgm*9k-z( a-v xieh2wa uency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due to “interference in s-ak 8zrxd0hytg8)z3 qpace,” whereas beats can be said to be due to “interferekdz8 3x)qzt rh -g8ya0nce in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered,bn,q-ue ;arz4t rgql m857c )9kh1 7egwap bn; would the points D and C (where destructive and constructive interference on-zwa9lk; 5 e1gqc8) r tgr4uh;epnb 7,7 mqbaccur) move farther apart or closer together?

Traditional methods of protecfzuc0 (m (3wu, e;vzc, pah 7h:fbqk)lting 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 the noise, inverts it electronically, then feeds it to the headphones in addition to the ambient noi,cqpkfh e au7 b:chzz;wl3,f0(m(vu ) se. How could adding more noise reduce the sound levels reaching the ears?

Consider the two waves shown in Fig. 12–31. Each wave can br fs/oq2ap-3ze 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), arefpao/-2s q3rz the two component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and observer move in thw dcn(jpxt5a je wx,n-n 4738we same direction, with j wjp5dxc t7aw8,w4nnn3(ex- the same velocity? Explain.

If a wind is blowing, will this alter the frequency of the sound heard byt gw82;.8lae )ydeesr a person at rest with respect to the source? Is the wavelength or velocityre.lw say28deg;8e t) changed?

Figure 12–32 shows various positions of a child in motion on a swing. A mxs *(;)b3 buc dc00bzwflw- pbonitor is blowing a whistle in front of th xww(;0 s bfcbbd3- u0lpzb*c)e 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 length of a lake by listening for the es 2q6(y4 .zrk :ladycqcho of her shout reflected by a cliff at the far end of the lake. She hears the echo 2.0 s after shouting. Es4( r6.lq2 z:cydayq kstimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of hi/w 1w-z a:fzm7d7ve3cy zupt*s ship just below the waterline. He hears the echo of the sound reflected z:37*c1apyd w7wfu-v/tzm ez 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 significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the wavelengths in atzcl0 c.v59h fwx/v5 kir 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 jusaye,u 9/k fy:ct 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). How much time elapses before the backfire is heardyyf9,a :k/e cu (a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of3)sl,frbaga a+s 9si ) a cliff. The splash it makes when striking the water belowbsgs9raia sfa,+ ))3l is heard 3.5 s later. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge stone strike the concrett3turn 1irtgs/b zuq6,07*k be 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/t76birt*0 u1 ztqus3 b rn,kg the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one mile of dis5t*c 9ou x tlc4ks7t6- 2d)zrbyj ,svgtance by the “5-second rule” for estimating the distance from a lightning strike if 7ostbtccs,v 64rlj* xdku )5 tzgy9-2the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity n/w-dn drpc1 p/(oni)i (r1a a /w0iunof a sound 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 a sound whose inte5w(gtv h6l wuva39em:yd2; jn i9kzu.nsity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of4xuh/bg k,re : 95 dB when fired simultaneously at a certain place, what will be the sound level if only one is exploded? [Hint: Add intensities, not dB’s,x u/h4b :ekgr.]    dB

  A person standing a ch/f, vv.idq0 certain 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 c/,qi. dvfh0v person experience if the captain shut down all but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to have a f d:39q/5ojlgkzm 68 kl.uulp signal-to-noise ratio of 58 dB, whereas for a CD player it is 95 dB. What is the ratio of inte6kol3dl:.kuzf85g uq9p /m jlnsities 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 kwh9 e.zld3zr9-q +gc person speaking in normal conversation. Use Ta-d+e3krwch9lzg q z9 .ble 12–2. Assume the sound spreads 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 eardr.v tmf)+qz6saum 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 ajb,br6:( kyb( 3tf+fjehh /jg,7 gqp rated at 250 W, while the more modest amplifier B is rated at 40 W. (a) Estimate the sound level in decibels ya73:trfh 6yhkb/e+ b j,gb (q,f(jgjp ou 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 ah0imnp0 ++n lduwl75zn2e p1130 dB when placed 2.8 m in front of a loudspeaker on the s0 +1p u7 nln nepw2li05+hmadztage.
(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 levesu ry(e6 dc 21*qah6udl of 2.0 dB. What is the ratio of the amplitudes of two sounds whose levels difcd1u6ur*(sa 62dy ehqfer by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sfof-0a h13 dbsound wave is tripled, (a) by what factor will the intensity increase? Incd10afb3f- h sorease by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacopi +,vl gee+8ement amplitudes, but one has twice the frequency of the other. What is the ratioe8 l,ev+og pi+ of their intensities?   

  What would be the sound level (h/gg(ie+kad h3hg-- xin dB) of a sound wave in air that corresponds to a displadi( ggkxe3-- /hg+h ahcement 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 louy*;odn 0i +nkud as a 100-Hz tone that has a 50-dB sound leve0kdnnyi+ou * ;l? (See Fig. 12–6.)    dB

What are the lowest and higi4vojjq.5r 8a hest frequencies that an ear can detect when the sound level is 30 dB? (See Fig. 1vrj5 qj4ao i.82–6.)

  Your auditory system can accommodate a huge range of sound levk80h5c7+r5 ihb +i khagwv- )9w rgbfeels. What is the ratio ofb cihe8kg9aw rf 5rw0vh kg-i+5h7+) b highest 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 hasxnxkf2c(4 *od a fundamental frequency of 440 Hz. The length of the vibrating portion is 32 cm, and it has a mass of 0.35 g. Unfc4d2 (nxko*xder what tension must the string be placed?    N

  An organ pipe is 112 cm long. What are the fundamental and feu0lii fi,* t)irst three audible overtones if thel) i0t,*uf iei 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 frequency would you expect 7/n0q xhtjgyiya:cu,i ; ikt6a x0gw1n)8h0efrom blowing across the top of an empty soda bottle that is 18 cm deep, if you assumed ii0 i;chi 7aw)aq0xnthg1u8 0gk ,nt jex: 6/yyt 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 pip52p9k osw k*goes spanning the range of human hearing (20 Hz9so pwog25 *kk 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 y94 -c- j 3fmt3tqs p.tycdn, 8h7qvjia frequency of 540 Hz as its third harmonic. What will be its fundamental frequency if it is fingered at a length of on in.cqv ttfsjd-hy3qc tm87y93 4p -,jly 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to pl,o x v7qipl85ray E above middle C (330 H,v 7x8 p5lioqrz).
(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 oft(+qp7dvz.a1w g jya* an open organ pipe that emits middle C (262 Hz) when the tempey(vq7p *jz 1+ w.dtgaarature 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 syaw)cd6)e w* (p4i oqat 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 hole be timkdwrrh71b+ xj 4) ifp.v9v 5hat must be uncovered to play D above dx+pf759v4vh)kibr. j wi1 m rmiddle 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 4lfxw-5eg /cn6(j yunat 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (a) Show why thisny46- /glu j(n5wcefx 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 resonates at two sucvpi -f;*mf +iycessive hp +iffy; *im-varmonics 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 *w/ ix- +,pzbsjb i.xd$^{\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 rh1iq+ql ep.(n+ q3us w m(8bptange for a 2.14-m-long organ pi +(qlb (.ni+ ptqhmq3 uwe8s1ppe at 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 outside andml tfpjt) ;t )hn0.m,m is closed at the other end by the eardrum. Estimate the frequencies (in the audible range) of the standing waves in the etftmm t,j0h).lnm p);ar 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 every 2.0 s when trying to adjust two strings, ona),yrmhu 1 fi6)pb:zf e of which is sounding 440 Hz. How far off in frequency is the other sf) :raz)h,b u1ym6 fiptring? ±    Hz

  What is the beat frequency ift y:kb(,dxr w; middle 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, whi ofk81sqm0xl vz ,dw5-le 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 occu-1 xf8vk5s mzwol, d0qrs when they are played simultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded witxlnbfjyi / 1*uld 9s8,h a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational freb9ln*,il sjdu8 /yx1fquency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the 43ba3e/z l 0r vg9lfkz;yzj* xfhtk(-same frequency, 294 Hz. The tension in one string is kayh fz * b4 vg ltj/3lex9zfrk;(-0z3then decreased by 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 eachxk4nstj(g l 5 y 7vfrs-13s2pzb0 ,lki try to play middle C (262 Hz), but one is at 5.0°C and t1-srt fl,n5vi(j2kgs07sk3 lpb4xyz he other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. F. sler0vfh:sqzd9oh;mk77p zc j / ar w45-yd/ork B has a frequency of 441 Hz; when A and B are sounded together, a beat frequency orm /h-rjd /ed7v:zw . 7cqpl49zss0ofy5; ahkf 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 (e xa 28chpof/p f-ano;p-:vh stands 3.00 m from one speaker and 3.50 m from the o fp- o2 avpfanpo/h 8xc;e(-:hther.
(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 p;zfccj1 w ymbc /3c 68zfez2 1kss/8epiano tuner hears three beats every 2.0 s when they are played together. (a) If one/c 1zkjsz ep 2 y1f8e cc6zs3;8wcbm/f 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 in air. How many beats)kwk 0wkod y9 ;c6z n5c4:jdrz per second will be heard? (Assume T = 20;yj9 kzk5r dn:c4 6 owwcdzk)0 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s siren is 1550 n9 jn 5csde4c)yg5c;l Hz when at rest. What frequency do you detect if ycyje 49n ng;c)55ld csou move with a speed 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 engine whose sirqfor167+4ivopn/l x g en emq6 7r+gvfxo 4o/nl p1iits at 1550 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 2000+az8x m-.;1c0ou v 5vjgmarc j-Hz source is moving toward you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exactly the szm-c5jx; c av mu0+gjarv81o.ame? 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 ise,vq+,zg3 p/:n) -jweb m qe *rcvss9k at rest 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 e m9v/pg* -erz),v cb,js+q e: nkwsq3emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at 50.0 kHz and receives them retfc,;hif * z1dturned from an object moving directly away from it at 25 m/s What is the receid z1h;* ,cftfived sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As it flies, the bat emipybgzbmpo rx+2 *t my.4v6d*:ts an ultrasonic sound wave with frequency 30.0 kHz. Whatzprt*vp*y m.d: 4 byo2mbx+ g6 frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was played on a)4rx(xnu5ad pxg*1g l moving flat train car at a frequency of 75 Hz, and a second identical tuba playxlx* d15ng (4uparxg)ed 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 ultrasoun;6 6o6sjewq1z deq: qu4b7epb d waves to measure blood-flow speeds. 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 pe; eujz7qs1b do646 q:eq w6bbeat frequency if blood is flowing in large leg arteries at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using ultr02 )qju+le46x bg dbwwl.ux 2xasonic 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 )et t/nzew08r/sjvqe kl2k r- da+2 8gHz. When the wind velocity is 12 m/s from th rverqawg +8n/z)dstt82l-kej02k/ee 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 mhs2 ee 6ip:a0*hf8jm eoving 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)0 ic)it x5ttg+ What is the angle the shock wave makes witctii5 +g 0xt)th 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 tms+mt5e i,n2 hpg:m1z he speed of sound is only,:+sg5i empnm zm1t2h 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} $