What is the evidence that sound travels as a wws 3wqb67z y-fwl 8 5se7i5lttave?

What is the evidence that r-mr k ziy90hhu8k))g sound is a form of energy?

Children sometimes play with a homemade “telephone” by attaching a string to tk)- g-,cmcbp/cs i3 mcg8k y1uhe 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 wavcb1ig/-pk 8sc-c) y m3,cmkgue travels from one cup to the other.

When a sound wave passes from air into water, do you expect z/5wdb7bly zhy,f9 :mbt 0wi.the frequency or wavelength to ch:wb/5z f0dy z79. ti wbybh,lmange?

What evidence can you-(3y7nzwkil*o9 b i xx give that the speed of sound in air does not depend significantly on fn xi7l*ik9y zow-3bx(requency?

The voice of a person who1p) rgk j bquhfum65:ey7.zf3 has inhaled helium sounds very high-pitched. Why?

How will the air tempelgn9) xy8dq(c m-hy *xrature in a room affect the pitch of organ pipes?

Explain how a tube might be used as a filter to ree/o:7a(ov q sbfu w-6nduce the amplitude of sounds in various frequency ranges. (An exaf:qo w6b-/es(a o 7nuvmple is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer together awx-d n,1/jm hks you move up the fingerboard xn/jhk d, w-m1toward the bridge?

A noisy truck approaches you from behind a building. Initb;co6v9 wtbg ;ially 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 noi6 gt;bb9o; wvcse. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due to “interference in space,” whereas)g axtt;z6c5 v beats can be said to be due to “interfe5azgc t6t)vx;rence in time.” Explain.

In Fig. 12–16, if the frequency o, ,2h h/kokhpb4 -s20rl3obfoffr m i3*eax/y f the speakers were lowered, would the points D and C ,s,0b -rbh iafe2hk4oorh /3yf ox*2l/ 3pfkm (where destructive and constructive interference occur) move farther apart or closer together?

Traditional methods of protecting the hearing of q+ e5w 0rs+ x8az.heojpeople 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 adz5ae0 jx hs r+o8.we+qdition 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 x9w 8yj2cne1c thought of as a superposition o81 nje2wc9c yxf 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 ifno0(3 6 npkrvth0uwf9 o. t-nx the source and observer move in the same direction, with the same vel(uk0hvt9 -ro06 w xon.p3tnnfocity? Explain.

If a wind is blowing, wilg khrmttlz 1;ru88-*il this alter the frequency of the sound heard by a person at rest with respect to the source? Is the wavelength or velocity changu;rgrkm1 t -thl *i8z8ed?

Figure 12–32 shows various positions of a childbo-i;hn ;/wxpsz wl1yk qv- .4hi*-bub.9i nd 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 highest frequency for the sound of the whistle? s --bio9h; lv wk;*pd y iiz bhn-/1wqnx..b4uExplain your reasoning.

  A hiker determines the length of a lake by liste+43x8 f+t c1a hb.. o9 zahruw9hjryqtning for the echo of her shout reflected by a cliff at the far end of the lake. She hears the echo 2.0 s aft+yft+ o8h9b rhj.xt.u9a3z4wa1 c qh rer shouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his sq3zg 8l:yb x+ob,5 dlyhip 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 soundolyq,l+d:x z8 35 ygbb in seawater is 1560 m/s (Table 12–1) and does not vary significantly with depth.    $ \times10^{ 3}$m

  (a) Calculate the waveleng lw4 szl1enib 3px0)l5ths 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 foggy day. rq -3uebxp7t 8Witht 3eb7-x rp8uqout 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 top of a cliff. The splash it makes when striking thxj46acqc kq(1 88mkjze water below is heard 3.5 s later. How h4( jqc1qc 88xm kkza6jigh is the cliff?    m

  A person, with his ear to the ground, sees a huge stone strike thkc1 em:/ b tgg1ye(1cxe concrete pavement. A moment later two sounds are heard from the ie:kt1ym1ce g /g( cb1xmpact: 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 disn vah+/ym-3n mq yv39ftance by the “5-second rule” for estimating the distance from a lightning strike if the temperature is (a) 30 vyn9+vh3/ym qfanm 3-$^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a lnsc (bz-agpg4: wb/a;,gj 1h 37damq 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 i5yx4u a605z-cah j0znhlv s)dntensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a soua /dh19:ppeky0; vxmh nd level of 95 dB when fired simultaneously at ; 0md1akv :y 9xhp/hpea certain place, what will be the sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain dpe+3x( 9 pu/iyj2d 2ztix2f pnistance 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 shu 2(/pdue+yjifi n 9 xxpz223ptt down all but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to have a sq8 u gq j gih7.h0ld12n8ajp-mignal-to-noise ratio of 58 dB, whereas for a CD player ip.-iq dhgg lu81mj07 qaj8n 2ht 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 speaking in normal cbgh44tb no 66n,oxgeo x.:vy2onversation. Use Table 12–2. Assume the sound spreads roughly uniformly oven2gnxh.6 ovoy e b6g,x 44:btor 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 eardrum whose area isnudw0w*l m. c/tfln:7 $5 \times10^{ -5} m^2$ (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 exf-3tpma-37px5(yuc a wo .rat 250 W, while the more modest amplifier B is rated at 40 W. (a) Estimate the sound level in decibels you would expect at a pxyctw57m ef( o.3uap 3r-a p-xoint 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 w6d05paw :wydtyi (g*meter registered 130 dB when placed 2.8 m in front of a loudspeaker on the stage dww*ty 6 i:apwg0y5(d.
(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 differe pompgsa04x 3nbynvu);0gx(7 nce in sound level of 2.0 dB. What is the ratio of 0 gax )ys3bovg 47m0np(pxnu; 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 ijm x716rflcb3 ntensity increase? Increasmlrxj bf1763 ce by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displace50 lq +*xhwz /n65lbbyjm3kjlment amplitudes, but one has twice the frequency of the other. What is the ratio of their intensitmz5+wlqlbnb* jk3j/xh50 y 6 lies?   

  What would be the sound level (in dB) of a sn1ykq2zz h2;8mju2e jound wave in air that corresponds to a displacement ampljz2; 2mq81 ukej yh2znitude of vibrating air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seemybyevu1 z1q j ,f/d+z; as loud as a 100-Hz tone that has a 50-dB sou1qebz zv uj1+,;/fyy dnd level? (See Fig. 12–6.)    dB

What are the lowest and hinq:2nsln;fv c8kf .l 7ghest frequencies that an ear can detect when the sound level is 3n8 v ;fl7.nknclf2 s:q0 dB? (See Fig. 12–6.)

  Your auditory system can accomma6 + yr5 ,hju bozmhkrzv:(5 kfdu,66bodate a huge range of sound levels. What is the ratio of highest6kbha hyd,: u omj6(z,rk zrfu65vb+5 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 has a fundumc 77px+3/dpx -i; vb :fotldamental frequency 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 string be placed? dpx cp: fio/xbuv77mlt+-3 d;   N

  An organ pipe is 112 cm pj b;rh s/2/py4i wayrb8dafo u7 p*,-long. What are the fundamental and first three audible overtones if the pip u2ah /-oy*4yaiwbr ;pp8frb7s/j ,dpe 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 wouldf3muy/qsf n -1 you expect from blowing across the top of an empty soda bottle that isf u3m-/fys1n q 18 cm deep, if you assumed 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-* sz)lty 4qbz*tube pipes spanning the range of human hearing (20 Hz to 20 kHz), what would be the range of the lengths of pipes require bz ts4*qz)l*yd? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has z kxg2z/h)j j xl6k-d:a frequency of 540 Hz as its third harmonic. What will be its fundamental frequen:xk/z zd-glh kx )j6j2cy if it is fingered at a length of only 60% of its original length?   Hz

  An unfingered guitar strin keqin)5 7ec9jzia b-b*m)d m-g is 0.73 m long and is tuned to play E above middle C (330 Hze--)ibez9qid 7b*ak 5mj n)mc).
(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 h0h9 nj;zh.ax4r0n vopipe that emits middle C (262 Hz) whenz rn4 j0ohxh.v0nh9a ; the 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 atxsdv8p :,jr*k 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 h9 zxi1s3cp7,d u0oxrjb.g )l that must be uncovered to ph9lopix u1 )b3js,rx0dg.c7 zlay 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, 440 Hz, and 616 Hz, but not at zto po* 5ol430w4zixx any other frequencies in between. (a) Show why this is an open or a cloxt*x w3zo0z5o 4io4 lpsed pipe. ----待选择----closedopen  (b) What is the fundamental frequency of this pipe?   Hz

  A uniform narrow tube 1.80 m long yh/l7st)7 99nf0 + shgrunu sjis open at both ends. It resonates at two successive harmonics hlu 99/tgn7 shns)y7fu0jsr+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 i n/32pgm o)sq -mhki+$^{\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 withiw f* pm9-nq:a-d;fdtmn the audible range for a 2.14-m-long organ pipe at 2 wf9;m:aqd- d*-t nfpm0 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm long. It is ope /*4 k8xb5-ut tittdoen to the outside and is closed at /euitt 5tb4k- odt*8 xthe 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 tpu,(3;z ar hq-h;aeg)s8 hkrone beat every 2.0 s when trying to adjust two strings, one of which is sounding 440 Hz. How far off in frequency is,3r qre8-ht ) h(spk hgaau;;z the other string? ±    Hz

  What is the beat frequency if middle C (262 Hz) an2jx zkabb5x i +7a4k0cd $C^＃$ (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) opera4lnun6- e 1l6fcuyah8onq: w3 q0r i(utes at an unknown frequency. If nei ui4u0 r:lolanhu(ye q n16cf6q-w8 3nther 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 produces 4 beats/s when sqx(ykn yd,ime f6;,f8ounded with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of the string? Explami ,yn6 k( df;,8yeqxfin your reasoning.    Hz

  Two violin strings are m8n 5; yhp-rj(dnfp, pn8cgc1 tuned to the same frequency, 294 Hz. The tension in one string is then decreased by 2.0%. What will be the beat frequenc(,cdhg588 rynp- np1c;m p nfjy heard when the two strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heagm(aum ;g hn36rd if two identical flutes each try to play middle C (262 Hz), but one is at 5.0°C and the 3h am6un(g; mgother at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a frequency of 441 Hz; whenjkpll//8w9ogc0 dtze ewe 6x j+m00)n A and B are sounded together, a beat frequency of 3 Hz is heard. When B and C are sounded together,0+jj9e)kwo0 6p0w/8tlze/lc e dgmxn 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 1.8, -,/ io) fzphcmm (wz-z+gfkb0 m apart. A person stands 3.00 m from one speaker and 3.50 m from the ogo i(zz/ kf)zw,pf ,-m-+cmhb ther.
(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,.w8w b -zwu8sf but a piano tuner hears three beb8www-z8u fs.ats every 2.0 s when they are played together. (a) If one 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 2.76zqp1*u29 trwfq48z dc m in air. How many beats per second will be heard? (Assume T = 204tcz *1zpfu 2w8dr9q q $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s si;: uce1z3nw2z t8rhwqaheb +yd n4. 5jren is 1550 Hz when at rest. What frequency do you detect if you move with a speed of 3c :nn y5bh uj+2zw3wzdh 8era;1t4eq .0 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 sir/5/ pc( qruyzren emits ayqz/( rpr/5 uct 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-Hz source is moq;m,jti 4c82.yqbk jzving toward you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exactly the same? Are they,4 j ytm;.kicqz2jb8q 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 v-c1 olc9)ecjvd ;3oh 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 oj)cvl;d cho- 93ecv1frequency 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 ouoq qf l*1m4xhz(b/1 returned from an object m *q(ol14hq1/uof zmxboving 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 speed of 5 m/s As it flies, the bat emits aimu.o7gb6 g1t wraahm 676b 4i k+sq.ln ultrasonic sound wave with frequency 30.0 kHz. What frequency does im+ahs4ug6 7lg 66tbmk.w aqr1bi. 7 othe bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba c /l433 2v/qsysjtjggff9z3k 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 approached the station at a3sl9gz ft2 vkgs3 jy//cf4jq3 speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measure blood-flow speeds. 4lhx+d,b+k e b ni68lwSuppose 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 hi6 llk,8 +ebbn4+dwxfrequency if blood is flowing in large leg arteries at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using ultrasonic wkurf rlu 8oxfi1x )01:aves 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 Hz. When the wind velocity is 12ah4 dh; 26-5mtmluesp m/s from t-p 4d65teh sm;amuhl 2he 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 moving ( 4jbel/sr,b6k:r 7 )gl/gr.kswli)2suctpo 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 3106+ y0 m5lg25gm kf qvydh-*iqx m/s (a) What is the angle the shock wave makes with the direction of the airplane’s motion? *0y2 xdlqkgf5 yg+-5i vhmm6q   $^{\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 ats. xg i;d 2am4zcm* zyh(dbf0e)9mo6fmosphere of a planet where the speed of sound is only about 35 m/ zd(ay) gs*.hio9m; dfzc x0e24b6mm fs
(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} $