What is the evidence that sound tra3kucea qs3xd4/ s8nlz;/:q3 kej a.okvels as a wave?

What is the evidence that souns-o3/ g4)3gvv0 c x ekmhwkw)yd is a form of energy?

Children sometimes play with a homemadebivgx* ( p 2cv(bae.+g “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 atc g(2b*ea v x.pbg(v+i 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 frequency ioe,93fgofnqu fw 7 1fn a/634zcqo*x or wavelengthqun9f o goa7f1cze o/ ,346iffnqwx *3 to change?

What evidence can you give that the speed of sound in air b0r ywddfaw p*) x,w(+does not depend significfxb) rydwd(* w,w0ap +antly on frequency?

The voice of a person who has inhaled helium uh )yrh*bk64wsounds very high-pitched. Why?

How will the air temperature in a room affect the pitch z 97 qjvyu6ci4v8;6wjt6egjzof organ pipes?

Explain how a tube might be,( /bf2 bj2 r*lnmw4nsgc qbt/ used as a filter to reduce the amplitude of sounds in vari nfb(,c// gb2tsrjqwnm*b4 2lous frequency ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer together as you m-hl.13a spuuzove up the fin-3shz au.lu1p gerboard toward the bridge?

A noisy truck approaches you from behind a bu y;x j4+ jk61gytvfmi,ilding. Initially you hear it but cannot see it. When it emerges and you do see it, vjy;yk4t,6+jm1 igx f 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 hgm6ig9d 8k5gzv ;k3)ykol*n t3/upmsaid to be due to “interference in space,” whereas beats can be said to be due tio*z y3hmtkp5; kgndg6)9 vgl 3m8u k/o “interference in time.” Explain.

In Fig. 12–16, if the frequ xmha+2cdac62nc wz:,ency of the speakers were lowered, would the points D and C (where destructive and constructive interferenamaw2+:cz6dnxc2c h, ce occur) move farther apart or closer together?

Traditional methods of protecting the hearing of people ne u,.1o fq a+o-7ibmpwho 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 devob,aeom-.+qf 7pu ni 1ice 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 the ears?

Consider the two waves shown in Fig. 12–31. Each wave can be thought of as a sc em3i,-r7;tot l4ab6.hf pg ouperposition of two sound waves, 6ba4 mftoc7p-. igotre; l3h 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 obs + otfh5ylwfjo(k/rd (2 e59dvxqq20jerver move in the same direction, with thxeq5jvqd(/2f25( o+kh9wty frd 0j ol e same velocity? Explain.

If a wind is blowing, will tu92pp flr h ;g) sfce356(nvgshis alter the frequency of the sound heard by a person at rest with respect to the source? Is the wavelength or velocu6fpf5scg 2g spn(3ev9r);hlity changed?

Figure 12–32 shows various positions of a child in motion on a swing. A monitfnx6jjmm5u)fi ps*w4y (o/8 dor is blowing a whistle in front of the child on the ground. At which position, A through E, will the child hear the highf4/jm* x8m()f65oysnid uwp jest frequency for the sound of the whistle? Explain your reasoning.

  A hiker determines the length of a lake by listening for the echo o7 (9-jnztot rh9 g6qfsf her shout reflected by a cliff at the far end of the lake. She hears the echo 2.0 s after shou 6 (josqfrtg 7tnz-9h9ting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just beloz s8;5cgrpdl gul*eae8m,a78 w the waterline. He hears the echo of the sound reflected from the ocean floor directly below 2.5 s later. How deep is the g,rud z8 8lc a*e7m5sp8elg; aocean 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 insoh*vw+ s/*+rzd:mf n 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 * i1m*m 1p vsie,*vzoxtq0r p/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 much1,p1**0mir qvpsxez/ mo* v it 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 ma2ngcv6e +qe 1pkes when striking the water below is heard 3.5 s later. How high is tvneqg 2p 1c6+ehe cliff?    m

  A person, with his ear to the ground, sees a huge nddobu r8* p+/stone strike the concrete pavement. A mor+onu/ *pdb d8ment 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 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one mile of distance by the “5-secg7qnu *q64 vk:g)za xcond rule” for estimating the distance)q:ckx *7gu gqn a46vz 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 level ooq g 7uec px:hwl-/pqi ,p/e-9f 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 in 6i3nvl/1ex x) doima9tensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 9b/q09( ltr.8.sy3dgt: out pib2fnt+ dn lp9j5 dB when fired simultaneously at a certain place, what will be the sound level if only one is exploded? [Hint: Add intensi .0jn rf( ttqg:u.8oy9p9bb d2pts/+ld ti3nlties, not dB’s.]    dB

  A person standing a certain distance from an airplane with four equally nois1.m qhwdhg8u b0bx13vb6xk l3 y jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would this person ex 6qbhw0hxbul 18 v 1d.3gbk3xmperience if the 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 ratio of 58 dB, wherea7wh 7c;al1ca zs for a CD player it is 95 dB. Wh7al awz7 c;1hcat 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 persoc qmt-mf/a4ubx 1m0b*1nrtyz 8q8) as n speaking in normal conversation. Use Table 12–2. Assume the sou8axqct r -fnu/0bt4zm 8*a y)m 1qsbm1nd 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 str8 j4r qosd- 5a1d1l ehhsasp03f np:e/x2z*krikes 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 at 250 Wdv ;8i4 us9z9 hkfuz9l, while the more modest amplifier B is rated at ihu9kl4v9d s; u8zfz940 W. (a) Estimate 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 meter registered 130 dB when plapha74xkn q;u f+c *qi)ced 2.8 m in front of a loudspeake k*hqixf 47p;c+anq)ur 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 difference in sound level of 2.0 dB eu -zyhet *fmtg1+4qrk-4d9 d. What is the ratio of the amplitudes of two sounds whose levels differ by this amount? [Hint: See Sez*-9 mrye 4dg+ fu 4h-1tkdetqction 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) bc z*mt.rf*8 d(/gb vwn;n;zhzy what factor will the intensity increase? Increase by a zz8dbm (;n; n.wrz /fght*vc*factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but ons.ksul w3h(82(n lfqde has twice the frequency of the other. What is the ratio of their intenukhsfql(8ld3ws2n .( sities?   

  What would be the sound level (in dB) of a sound wav* wnx8 atqlxj9f; 5vn/e in air that corresponds to a displacement amplitude of vibrating air molecules of 0.13 mm at 300 Hztv l8faq9n 5wx;/njx*?    dB

  A 6000-Hz tone must have what sound level to;+ufo6hord69 e5 jqvo seem as loud as a 100-Hz tone that has a 50-df6qo o udvor5e +j6h;9B sound level? (See Fig. 12–6.)    dB

What are the lowest and hig jn snsx+r/*ec rzhcp ..033zohest frequencies that an ear can detect when the sound level is 30 dz 0p/c*o.ne+rz3sc x3.jhnr sB? (See Fig. 12–6.)

  Your auditory system can accommodat4qb8,vt 5 b8qpjq7 dmte a huge range of sound levels. What is the ratio of highest to lowest intensity atm,574j8bbqvqt 8qp dt
(a) 100 Hz,$ \times10^{ a }$ a =   
(b) 5000 Hz? $ \times10^{ a }$ a =   
(See Fig. 12–6.)

  The A string on a violin has a fun.1vt*aj,y,c8fvvolq:n r pr8 damental frequency of 440 Hz. The length of the vibrating portion is 32 cm, and it has a ,n1trpl*.aq yj c,8 fvrvo8:vmass of 0.35 g. Under what tension must the string be placed?    N

  An organ pipe is 112 cm long. What are the fundamental andb+ q e.1(ffesh first three audible overtones if the pipe i+febq (1feh.s s
(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 acc:3j +wxr *xfmross the top of an empty soda bottle that is 18 cm deep, if you assumed it wac3m+xjfwrx : *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 openf cwsb6-zzzg* * msl,:h scg34-tube pipes spanning the range of human hearing (20 Hz to 20 kHz), what would be the range of the lengths ofzb4* 6scf-l,zw cg * :s3shzgm pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a frequena ho1 x0ec5yl7 /t0vyscy of 540 Hz as its third harmonic. What will be its fundamental frequency if it is fingered at a length of only 60% of its original lenx 0t 0ls1y 75acevo/yhgth?   Hz

  An unfingered guitar string is 0.73 m long and bo+w co: .+ktcis tuned to play E above middle C (330 Hz). :bwk+ooct+ c.
(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 thatimn5g15pj ,ht+7 gul e emits middle C (262 Hz) when the temperajh5m1 ligu,+ gnte75pture 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 ;t 0kxpzt6 fw7f9hv9nl8m)r9lujl3 b $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpir l xf9 9x8jez5tx7qkos 4f,52th+x tjece of the flute in Example 12–10 should the hole be that must be un9 5zo4 lxx2hq897 tjffs,xt5e tj+rkxcovered 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 y,j6 ;dkycc/ 90l+ c3snevcn yHz, 440 Hz, and 616 Hz, but not at any otc63l ,sc9dn+yccn ;yev0/ykj her frequencies in between. (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 resonates at two2osctyw3bu 8oj7+ i+ gbj 7fg pe-78xf successive harmonics of frequencies 275 Hz and 330 H fi72 x bjcgfbj7uwts +p+37-o8 e8yogz. 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 c d)b- vdlm3f3joy25 dgbt 0z9$^{\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 pr0r08eng2 muh5nq re0n eg 4:wqb. z/sqesent within the audible range for a 2.14-m-long organ pipe q mgur40e8 :segnw5nq2rq e bh 0n./0zat 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 anvbrk;zt pt5vbi xnn, 9,m/itp*r+ ;n4d is + ;b94nt/tmtpikr,in,xrv; z*b 5 vpn 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 answer to the information in the graph of Fig. 12–6? $f_1$ =    Hz $f_3$ =    Hz $f_5$ =    Hz

  A piano tuner hears ona21ukb6 o m27zq;fzui ):swr xe beat every 2.0 s when trying to adjust two strings, one of which is sounding 440 Hz. xkaz)1w6;b zs i 7:moru fq2u2How far off in frequency is the other string? ±    Hz

  What is the beat frequency i1w f hrr((+i wywfn haq4w0(/kf 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, while another (brandxv 5p,okgq+*o up0jn( X) operates at an unknown frequency. If neither whistle can be heard by humans when played separately, but a shrill whinepvo5, u+* 0pkogqx(nj 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 when sounded *j j ))+nqfoo g-br7tbwith a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is j- +bgforqnjb )to) *7the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz. Theeuyx7 /q/l 1uo tension in one string is then decreased by 2.0%. What will be the beat frequency heard when the two7 l//youqeu1 x strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identicam tz phj;z+h+/,6 tmjol flutes each try to play middle C (262 Hz), but one is at 5.0°C andzj h;/p +mojt+, 6htzm the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a frequency of 441 Hz;s- d5wge vri/ d )7bjlvd*7 mfaz)-gb. when A and B are soune/dm vg r dbb5sz*.7) )lajif7-gwv-dded together, 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 1.8d 38 7sqczfb xwgze0:*0 m apart. A person stands 3.00 m from one speaker and 3.50 m from 0 d*:qs3b87egzczxwf 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 vibrating qio8c,:lu-ev at 132 Hz, but a piano tuner hears three beats every 2.0 s when they are played together. (a) If oneci:, lqoe -8vu 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.bes wt*vf48 o464 m and 2.76 m in air. How many beats per second will be heard? (f4eto* wvb4s 8Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s si ni4b ;.qer/kjren is 1550 Hz when at rest. What frequency do you detect if you move with a s.rq;k/ ni4e bjpeed 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 fi xrvo/:t7 r+/n 6jabegre engine whose siren emits at 15b6r:oe+nvg/7 jxatr/50 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-Hz source is muqq +aoqh: z4 p0(o9bnoving toward you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exactly the same? Are they:zh apq94uo0 oqnq+(b 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 ittkzua 7o: 19 apg9b7qs at rest and the other is moving toward the first at 15 m/s the driver at rest h7batk1:z ut9qa9 gp7o ears 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 sqshf r. a t/*ya,idvyam d*;35ound waves at 50.0 kHz and receives them returned from an object moving dirr.at*3ya v fd*h5ia;, qds /myectly away from it at 25 m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall h mvz;g d ol+ onp+dbvz 1,50ap:,b0nvat a speed of 5 m/s As it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency does the ,d;1 + l vzah5p pg,0 0znvnbdo:om+vbbat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the originjskwat:4;)t 2qrovwx)n /vs / al Doppler experiments, 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 statiw2 vat4s: /ovx qs ;)rwjk/tn)on. 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 sfi. jngn/i 44to 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 beat frequency if blood is 4/gfnnis4j i. flowing in large leg arteries at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using ultrasonic waves of freq t.yx3oqlxb(:uency $2.25 \times10^{ 6}$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. When the wind velocity is p/k wyd, ybduil,djtm9q - -,912 m/s from the north, what frequency will obser y-i,,q,9 lbwmd9jt-ud d/pky vers 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 moving onxgz6ugdp, )d-k*ny. n 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 Macn 9;*n g9:lhnex5jhtsh 2.3 where the speed of sound is 310 m/s (a) What is the angle the shock wave makes with the :x sl9j;nhgen9h*t 5ndirection 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 th..l.p z do3ohme speed of sound is only abod o. mzl.hp.o3ut 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} $