What is the evidence that sound travels as a wavak h --x6yxdq5e?

What is the evidence that sound is 1(c/*tr hmuq46edk ana form of energy?

Children sometimes play with a homemadxpc+2v,fz 4kr e “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 at the other cup (Fig. 12–29). Explain clearly how the sound wave travels from one cup to the o2vr+kp x ,z4fcther.

When a sound wave passes from air into water, -1o )k j/ odswy10+n a+ct+ ktq8naazcdo you expect the frequency or wavelength to chwa-0/a+++ysjk8ocoqt1 k) c1d nt anzange?

What evidence can you give that the speed of sound in air does not depend signifuu 2:,sv4q2wgc.qedg icantly ogwe,4.2s quq:dugc v2n frequency?

The voice of a person who has inhaled heliuvwt9k (7dbwhy9/-oe*l p1kxy xgt q1; m sounds very high-pitched. Why?

How will the air temperature in a room affect the pitch of orgwfuc3f;99ib hfj1d,55 iscv y6 wmo;gan pipes?

Explain how a tube might be used as a filtez 1b ,ngs(nk,- ;agdier to reduce the amplitude of sounds i-; 1,bde (z,ngi gsnkan various frequency ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer together a84x - zj1; agstyty1rcs you move up the 8t;1-rsx tg1azc4jyy fingerboard toward the bridge?

A noisy truck approaches you from b*db1w 35ps w.dvre. e5 gkdnqzre0/q01j tv6iehind 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 tz0kqd b1eqe/n jvr e 0.t5igrs w.dp3 wv*d651he high-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due to “interference in space,” whereasw2 fo)rflr..s beats can be said ..froswrf) 2l to be due to “interference in time.” Explain.

In Fig. 12–16, if the frequency of the speakers werrpe( 6hex z,w;x81zufe lowered, would the points D and C (where destructive and constructive interference occur) move farther apf xx;8z1( ee6z ,ruwphart or closer together?

Traditional methods of protecting the hearing of peopl 6iass1+oh/i*h w)ml : xskgkl6zk+9 ae 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 thatzo )i/smh s6kxg9*hl ia+aslkwk+:6 1 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 noise. How could adding more noise reduce the sound levels reaching the ears?

Consider the two waves shown inj+eb0j ys;0-sftd2qe-mz (r7d2rcws Fig. 12–31. Each wave can be thought of as a superposition of two sound waves with slightly different frequenci 7cz-srysbrj0ee w(2- +dfm j02sqt ;des, 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 thew*up7 nx ts9;f source and observer move in the same direction, win;7 *wust9pfxth the same velocity? Explain.

If a wind is blowing,3q)4wlz/ t udz will this alter the frequency of the sound heard by a person at rest with respect to the source? Is the wavelength or velocity43w /)udlzt zq changed?

Figure 12–32 shows various positions of a child in mo) z 9q ljp(lrg8-q,pxrtion 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 frequencx( 9l)-p jqzrlgr8q, py for the sound of the whistle? Explain your reasoning.

  A hiker determines the length of a lake by listening for the e b w53rxrgpicl9 ,fz);cho of her shout reflected by a cliff at the far end of t9g ,3bczrrfix;5)lwp he lake. She hears the echo 2.0 s after shouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just belzi2ro zl* 2m0row the waterline. He hears the echo of the sound reflected from the ocean floor directly below 2.5 s l* lrro0 izz22mater. 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 i ihmqxh585e;yg/fy ul ))kv9tn 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 sju )/7y n3gjnnkh6 .qfchool 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 befo.6nj3yqh7uf nnjk/ g) re 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 e9mpquty 2qg6+j.ut- the water below is heard 3.5 s later. How high is the cliff?9e2tq6 ujq.m +tguy- p    m

  A person, with his ear to the ground, sees a whyt-2 .errg :mc ;i*4z: yywbhuge stone strike the concrete pavement. A moment later two sounds are heard fromc:;tr . e:yz y*hbig2yw rw4-m 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 mag ;nsrvvvf*tr:n6 *g5. glc,a de over one mile of distance by the “5-second rule” for estimating the distance from a lightnr,l6 *srv*v;: g .gcnvfgtn5aing 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 of 120 dB?ulymdr)4 d(h a uytwg: li-,;;    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 intensity gd8u i9wo1 kq7is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95z5)d u31zff2e mtx+/dbv poj3 dB when fired simultaneously at a certain place, what will be the sound level iftfu5xo3em p) z32bfd1 j+vz d/ only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain di)2jb rblo8s ,e1e mzdw5+9hiostance 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, not dB’,bi)z 1ms ohl wo9 re+eb82d5js.]    dB

  A cassette player is said to have a signal-to-nois(b xyo0 tplafvy b8+:5e ratio of 58 dB, whereas for a CD plao8yt0 ( bv: plxfb5y+ayer it 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 spea2x)kcced6ganyx: / 2ihi 0 i:uking in normal conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphere centered on the xn : 2xiy/2 0:eihckuadgi6)c 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)cid6,.. ,t6h f fflogrm e zg9dc6o-v 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 amplifw * o*wssn1dza4i- u;jier B is raws1- ji*zw4 oas *un;dted at 40 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 vc5vq s j(x/d)dB when placed 2.8 m in front of a loudspeaker on the / v c)jxsvq(5dstage.
(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 o mkaj7een+d n bex zj7/7v1v9)f 2.0 dB. What is the ratio of the amplitudes of two sounds whose levels differ by this amount? [Hint: vnj/z)7eak7ve71 dexbj m9+ nSee Section 11–9.]$\approx$   

  If the amplitude of a sound waves k8( 49co c.gy2 pe9q9:omh zr(cmebn is tripled, (a) by what factor will the intensity increase? Increase by c m9ko:rh cpze.4c ((2oeyb9sn mq9 8ga factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, baxk/c/3pc(elp 8g ibp v .x/6wut one has twice the frequency of the other. Wpc/3.b6/ gli epac8/v(wxkpxhat is the ratio of their intensities?   

  What would be the sound level (in dB) od):,uw 1gs kjvf a sound wave in air that corresponds to a displacement amplitude of vibrating air molecks,: vd gju1)wules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sou.8hlwr mr f y:9f-j)h;ppb5gtnd level to seem as loud as a 100-Hz tone that has a 50-dB sound levp;.wb) fh-g5 f jyrpm 8:rl9htel? (See Fig. 12–6.)    dB

What are the lowest and highest fr zhzxf cvu7/edh95bq c: *0(viequencies that an ear can detect when the sound level is 30 dB? (0d h:7v(5zxuf9/cbz v cieq*h See Fig. 12–6.)

  Your auditory system can accommodate a huge range of s b9ono27,lgu), mheka 7avy)cound levels. What is the ratio of highest to lo o7,,n2 ay e7lbku))m9ghocv awest 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 fund6xc6f-v ltb m2:h5-;pknr ti eamental 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 stringht2 xmnc;ikl t-vpe -6 r6f5b: be placed?    N

  An organ pipe is 112 cm long. What are thvw2 l8f o1fe-cqx9; uov: x5c azga-2me fundamental and first three audible overtones if :eqa9uoz ;wm2a1v2oxfg v 85c-- lxcfthe 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 woul gchy+7yd iv3*5rz 2dpd you expect from blowing across the top of an empty soda botc h7gri*yp5vd + ydz23tle that is 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-tubenvkf + +a:, xjia(n08mrfuvc ( pipes spanning the range of human hearing (c(fjaax0 fv v(mn8i k++ unr,: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 frequency of 540 Hz as its third harmonic. W +a mrnb7l7u+that will be its fundamental frequency if it is fingered at a length of only 60% of its original lengthburm+al n77+ t?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to play E above middlenz-cnh,5cky c*rm t 5) C (330 Hz)c kt* mcrh,y-z5cnn5) .
(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 pi/n5l9c9x9,pi v kcksfbd;*w 5trs)4oaoy hd1pe that emits middle C (262 Hz) when the temperature is 21 5s)a whxo9rs9*k tbpcv4y5ddnk ,ic ;9/1fol$^{\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 *r9/ 1d ga4i*h1k i;nr grwxza20 $^{\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 shouldcm+(h.a pshmo0q2 hp9 the hole be that must be uncovered to play D above middlp2qshcp.( h 09moahm+ e 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 H m.pfoz023e 2;kpsyj cz, but not at any other freqj2.y;f 23 kmpces0zopuencies 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 two y7*xwx)c,2i c 5re guzsuccessive harmonics of frequencies 275 Hz and 330 Hz. What is xz),wg7ecir*u5x2 y c
(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 jj50h-(jti sv$^{\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 d 7c. )25 trd6pnyt cwjav( o4rz34yevpresent within the audible range for a 2.14-m-long organ pipe at 2tc4.cvdt rw762 y ovy3j5dn)4ea(zrp0 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm long. 3 va;: qhurlc2It 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. What is the relationship of your answer to the information in the graph oq:ulcv2;ar3h f Fig. 12–6? $f_1$ =    Hz $f_3$ =    Hz $f_5$ =    Hz

  A piano tuner hears one beat every 2.0 s uu1z)g (s21cr2vnawejx 9bc: when trying to adjust two strings, one of which wuaj 1):2gbsze2(cuc n1 vx9r is sounding 440 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequs4l/0 qude19pdv 2rgp ency if 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, wv4k th5o(s(-yq -bv 6wwsn8nahile 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 occurs when they are played simultaneously, estimate the operating frequew(k48 t(b-6sv w5 noysvahn- qncy of brand X.    kHz

  A guitar string produces 4 beats/s when sounded with a 350-5mjb2q: f: ,krgcmd)yapg 1g6Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency 6 :yg)bgjc5adm mrfq,:k 1 gp2of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 oyw9t/ cgu-1ktqkh -1-xng2uHz. The tension in one string is then decreased by 2.0%. What will be the beat frequency heard when the two strings ak--1uhn1txqg9 c 2oy- u/ wgtkre played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if b*7uroha6f3 d-xfbxtr2 u) :xtwo identical flutes each try to play middle C (262 Hz), but one is a*:xba uo-urx2 d b3fxtf76)hrt 5.0°C and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning fortt mo;k;(l;l hks, A, B, and 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 together, the beat frequency is 4 o; hlktl;(mt; 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 apalkb-/6dfvw 8 xrhy34; l8y )zplw6qftrt. A person stands 3.00 m from one speaker and 3.50 m from the othllh-kwvqpl6 4bzrd fy6x8/ 3fwt 8y);er.
(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 9dz;cut-z*fh 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 vibratingd;f-u*zz c9ht 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 ma2afite( ; v lfey:x31xny beats per second will be h:fe3vl 1xfxyati2( ;eeard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certa :x(iyrnoy,1m +i/b6tx *x(yfvlf 2j qin fire engine’s siren is 1550 Hz when at rest. What frequency do you deteci j(nq1ofl(+ir:x x/btm yf62yvx,* y t 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. Whattn*m-g ,e2 h,ni 3zqez frequency do you detect if a fire engine whose siren emits at 15503t,engizq zn*2 - e,mh Hz moves at a speed of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frla.r n6 ew)p4k,.i-xrp nw) zgequency if a 2000-Hz source is moving toward you at 15 m/s versus you moving tre rlp k4-nw. n6.)i)gzwx,ap oward it at 15 m/s Are the two frequencies exactly the same? 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 fre5iu x)luc2)a:eqmk8vd) h t3t4-v,ndy 7uknbquency horn. When one is 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 emit? Assume8l dbu3qvv5knue)n uahxy )ci2,tmk7t-d) 4: T = 20 $^{\circ} $C    Hz

  A bat at rest sends out h 9npgv8tj: 7+hbsmc)ultrasonic sound waves at 50.0 kHz and receives them returned from an object moving directly away from it at 25 m/s What is the received sound frequenc+h7tnsc m8p:g )hv j9by?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s At; ira .say8g;,nuy;2ryaa 9js it flies, the bat emits an ultrasonic souny; say9,tr ya;j i;an28garu. d wave with frequency 30.0 kHz. What 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 moving flat mr,*glt/dej5 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 apjmgl 5et /,r*dproached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound wav ily0a j 6.(0g5rzuwnvxi4 j*ues to measure blood-flow speeds. Suppose the de.5* unijr4vl( xwi0ajz6uy 0 gvice 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 at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect using ulv5i gdw f10bs1trasonic 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 Hz. When).8*ga 5 bdggdg kk6ny the wind velocity is 12 m/s from the north, what frequency will observers hear who are located, ag.dgbkdna )k 65g8* ygt 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 ivk -e4o) qc0usf 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 sound6egljn g8k.;8 jd3u x9rq dovc6.wf,d is 310 m/s (a) What is the angle the shock wave makes with thw. dl8u gojerfgd .vn9xjdc6k;6,3 8 qe 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 atmosph9ucd k gtu-f45ere of a planet where the speed of sound isg fkd9-uct4 u5 only 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} $