What is the evidence that sound travels as ao3y y:j x6bks8.bj xhb,0on(x+z wah. wave?

What is the evidence that sound is a form9u9xcteim-oj5a4 0j t of energy?

Children sometimes play with a homema frfg:cn0a 3ao7c t9o3de “telephone” by attaching a string to the bottomf:ar33a07o c9ontfgcs 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 pashg.t8y3 nm, vs8kk:qghr:/y bses from air into water, do you expect the frequency or wav :/ :gmv qn.s3r y8,tkyhbhkg8elength to change?

What evidence can you give tha6q68ns 7 grdlo j+0abn) o(sutt the speed of sound in air does not depend significantly on frequencysjrau 6d(t80n7n)glo + sbo6q?

The voice of a person who has inhaled helium sounds veryzmvbnhb7 pi934tzv acwy,930 high-pitched. Why?

How will the air temperature in a room affeciq,l-:tq:nknh +-f un ols u-j8kp)6kt the pitch of organ pipes?

Explain how a tube might be used as a filters9 p1f1( xkr029ptqq ia+xlhh to reduce the amplitude of sounds in various frequency range 0xil (fq1pths9a rk9p+2qx1hs. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30)q p3ljrvva* 8y 6nyk.. spaced closer together as you move up the fingerboard jvn.r8vql3.y * p yka6toward the bridge?

A noisy truck approaches you from l mybr)s1j/xl j p4g,.)zrej, behind a building. Initially 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 hi jgls4br.y )/z m, p1,ejxj)rlgh-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due vz9 (bt q28ispto “interference in space,” whereas beats can be said z(tsivp29q 8b to be due to “interference in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered, would t62oy u:q y(belhe points D and C (where destructive and constructive interference occur) move fart2b6e:qo ly(uy her apart or closer together?

Traditional methods of protecting the hearing ofx5yjuz0mw:jo 5 -e le8 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 addil:w5zm 0e-ujyjo 85 xetion 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 wat-he- :r8f jltwb2ygb/ uua y)/m1kdk : p2o,sve can be thought of as a superposition of two sound waves with slightly d o -kklwu,:8)m d/-f1yj hs:g2rabt eb/yu2p tifferent 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 obser7 -jy)p kc2bqiver move in the same direction, with the same vel bc -k)jy7i2qpocity? Explain.

If a wind is blowing, will this alter t.(wai;lck) nihe frequency of the sound heard by a person at rest wit)cwi l(;k. ainh respect to the source? Is the wavelength or velocity changed?

Figure 12–32 shows various 1( 1tgwxmv0b8/rcb vwlqcer zt .,( *dpositions 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 vcztwc(1bt *wvq 08r ex,b/1 .dlr(mghighest frequency for the sound of the whistle? Explain your reasoning.

  A hiker determines the length of a lake by listening for t66w , ljhdt*0 u:fgdsehe 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 the ld,dg :fhjl06 ue*wts 6ake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of (p v2h*7gri imhis ship 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 v *pi7m(gihr2 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 air at 20 ube 8fkd4 cf 9 hbc4+9eeqlg*3$^{\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 boam 3kd brf x**q+ +d79aoj,raxvt is drifting just above a school of tuna on a foggy day. Wixfvr a dmo, 3dkx*jb++q*79arthout warning, an engine backfire occurs 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 the tomiqed9 1mx9w666inmf w p8 :yrp of a cliff. The splash it makes when striking the water below is heard 3.5 s later. How qnp wr6 y:m 9emw6xfi89m di61high is the cliff?    m

  A person, with his ear togtx03qxzq .n2 the ground, sees a huge stone strike the concrete pavement. A moment later two sounds are heard from the impact: one travels in the air q3q g 0xtn.x2zand 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 mile of distance by the 3p u5tv6.1eyri2tc pu “5-second rule” for estimating the distancep v6ptu 31tcue5iyr.2 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 lej6b:jrxb +v)k 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 sound whose intgu l8l e9rk/t/;ka7nx ensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired simultaneously jsu.h- g yvf;+ugma l/ca;3r4l do5h9at a certain place, what will be the sound level if only one is explyd/ 5f4;9u+3sh .alhjrlc;u- o m ggavoded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance fcq ( rqk.3j)+r2ti vbqrom an airplane with four equally noisy jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level tbij2qqr.3( v)cr+ kq would this 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 signaltlo0m w9gm 2)i yl2gl6-to-noise ratio of 58 dB, whereas for a CD player it is 95 dB. What is the ratio of intensities of tmoylg 06lt 9i2lm)g2whe signal and the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound .ilap4t1/ m5mpd trw*from a person speaking in normal conversation. Use4p1t ltdi*pwa/r5.mm Table 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 .4tg09 p ywze meupb,4g -,u1pc6lkfqeardrum 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 modest amplifier xph t1xe/i9l/ B is rated at 40 W. (a) Estil/ px9 /tex1himate the sound level 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 met6s01yc+:ho* fpzg gq(n ssu :t s;do(ler registered 130 dB when placed 2.8 m in front of a loudspeaker ongf:us +nohqzsoysd*:6 l1g0(ts p(;c 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 detectohe;gxzl;q: +ijz 5pk41b x8s a difference in sound level of 2.0 dB. What is eqk4xzp15;i s hg: xob8l;z+jthe ratio of the 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 what factor will the intensbdz )hml -9.doity incrd)9 hdozbml.-ease? Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal3nyc:5k1pbr3z)qyl *tb v -d j displacement amplitudes, but one has twice the frequency of the other. What is the ratio of their intdt3 1y-r:)v5bzj*lycq n kp 3bensities?   

  What would be the sound level (in dB) ofrm p2:j-xmiz 8 a sound wave in air that corresponds to a displacement amplitude of vibrating aiji8p-m r2mz x:r molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must havh 2kao 9;;jrzce what sound level to seem as loud as a 100-Hz tone that has a 50-dB sound level? (See Fig. ;kj 2r9zao;ch 12–6.)    dB

What are the lowest and highest frequencies that an ear can detect when thekyqq6st-2ty y 3hjmy iy xo2t75/ jvsd8a i:-5 sounsi o qa5- 5-:7k sj xqytyty2vt3 dh2/ymj8y6id level is 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range +9etg 3 3tfipjof sound levels. What is the ratio of highest to lowestt 3i93ej fp+gt intensity at
(a) 100 Hz,$ \times10^{ a }$ a =   
(b) 5000 Hz? $ \times10^{ a }$ a =   
(See Fig. 12–6.)

  The A string on a violin -qm+ 9;3uwa j,ojrl eihas a fundamental frequency of 440 Hz. The length of theeu9m;j -r +lqwio,a3j vibrating 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 g( x*8qppkou 7and first three audible overtones if the pipe is pq( xku *pg8o7
(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 blowing across the0x cv* 1:ixtsb top of an empty soda bottle that is 18 cm deep, if you assumed it wa tb :xcxv0s1i*s 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 pi autquvvbh 8wr,l7j3587u m4 h:p.qdnpes spanning the range of humaqu:npvbv4au8qw r78h 35tuhdj., 7 m ln hearing (20 Hz 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 freqx;mtswm7( wx(uency of 540 Hz as its third harmonic. What will be its fundamental frequency if it is finger 7w(mm; xsxwt(ed at a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to play g./ofr ,wwst c9.cd c4E above middle C ccwd4c r. 9gws./f,ot(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 emit/ :k)1kyado nj1:hg-9bnxojss middle C (262 Hz) when tgys1/:knox1n9d)o j jak b:h- he temperature 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 20 eiw9a5)fr - to0i* mjt$^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flute 8 yj5k3 wkrrb)in Example 12–10 should the hole be that must brk5ky 3rb )j8we 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 can resonate at 264 Hz, w+ /hgmlu;-z8o6jurf 440 Hz, and 616 Hz, but not at any other frequencies in between. (a) Sho +zorum/ ujf86-lghw;w 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 end0h5lut gg.pf 1s. It resonates at two successive hargghlf pt u5.01monics 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 azu.veoc eq5 97q/jb o6w+,kl$^{\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 tax 2b:2gnvs:present within the audible range for a 2.14-m-long organ pipe at 2:x 2t:2g bsvan0 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.c; pi4u23 asrx9ye y5o5 cm long. 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. Wypoux39 ye i;r4c2a5s hat 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 beat3.sig572 tm(jcac iay every 2.0 s when trying to adjust two strings, one 5ayms7i 3 gacjict. (2of which is sounding 440 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency if psj)d xitg39*y,bd50 8tnj rkmiddle 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, while another (brand X) operates ckkg)r (7dm:l at an unknown frkk(l dm7g:c) requency. 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 of brand X.    kHz

  A guitar string produ)zrw u-*a3wtcces 4 beats/s when sounded with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrat -wc*twzuar )3ional frequency of the string? Explain your reasoning.    Hz

  Two violin strings areluqp /d7.y om -v1).6pkhkrjn tuned to the same frequency, 294 Hz. The tension in one string is then decreased by 2.0%. What will be the beat frequency heard when the two strings are played together? [j.h7pq. /1 knu6olrv)pm - kdyHint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identigc,ww yoz(:jzi +)dm3 cal flutes each try to play middle C (262 Hz), but one is at 5.0°C and the other at 25.0 +)ww o(z gj:d3zc, iym$^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, anfb1px*t l+6i)u* ogle/a-xz( d nss8md 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/tielm s1*ud8 l-o6s(zx * g)af+ xpnb 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; d 3w5nmdm2ta stands 3.00 m from one speaker and 3.m wa253;tn mdd50 m from 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 suppo+n te/w(w5 bl;cguks)sed 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(kuwln;)g 5b/t ewc+ s 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. Hix hl8mko:5 4evpft0z ++tuy,ow many beats per second will be heard? (Assume T = 5f0m4,xz:vyphe8t+ti+ ulo k 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency offg-e+4l fh cq5 a certain fire engine’s siren is 1550 Hz when at rest. What frequency do you detect-hf4 fqcl5g +e if you move with a speed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequen8b2ulyka ;:aeaem a rx4 1g1o7yj5 )t9kosd9 pcy do you detect if a fire engine whose siren emd 1294rl5:9k gyoaxkbse87um1; tyaojap a)eits 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-Hzth2+*unomv1o3 991zd+zc6r 3v tr8rrwi oabn source is moving toward you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exactly the same? Are they o3*u 1 rdma9ontr3tr b2ic +1+zvz9 nhr8o6wvclose? $f'_{source\,movine}$    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 frequencbu+l1p zjnnl0,(17 mdr99jdmo d y rt2y horn. When one is at rest and the other is moving toward the fi2p bjnurd71mlo9rn ,d9tzldj 0 + y1(mrst 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 ultrasoy( j6sieh oethzqa alx19:)* :nic sound waves at 50.0 kHz and receives them returned from an object movie:th9 ) asl :zo(1*hxj iae6yqng 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 s.xg( nr6kphw; aa abv(i4c4 x7peed of 5 m/s As it flies, the bat emits an ultrasonic sound x.n;crax(b4k4ih gw7aa ( 6vpwave with frequency 30.0 kHz. What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experimejug :ue3(eatre)shm: : 3 ho9pijw:/znts, a tuba was played on a moving flat train car at a frequency of 75 Hz, and a second identical tuba phij) u/gt :pu: 9s o(eemrhwje3z a:3:layed 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 m6mkny s2- 8:ni1iov cjn zge;.easure blood-flow speeds. Suppose the device emits sound at 3.5 MHz, and the speed of sound in human tissue is taken to be c-:nmv ;ze y81nnigkis. 6 oj21540 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 8 m; /1t bfa/28 jckmyemyoz9iof 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 57090yzc 8l22vrg v(d usx Hz. When the wind velocity is 12 m/s frvvu8y rd x slg2z90c(2om the 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 mof3hx)2d;nq 8mpk6 -eeg( ikc.r kq r+sving 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 (m5rjcqqn ();jfr :/aga) What is the angle the shock wave makes with the direction of the airplane’s mot;)(cjrqam 5/: jgfnq rion?    $^{\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 atmosphbgvk*+0kghh1,0 dw .u( dlxgpere of a planet where the speed of sound is only aboutw kg1x d+,b0hp *g0v(uhg.ldk 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} $