What is the evidence that sound(d ;q,(iqf1g1 i0qaq, zhn:du.bmjm v travels as a wave?

What is the evidence that sokw/brig*;t)tlr - bs/u4x h7hund is a form of energy?

Children sometimes play with a homemade “telephone” by attaching ap g v qah6ynv3a4vtr)x2e;0*z 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 cn4a02evrx)3 qgha v zy6*pv t;up to the other.

When a sound wave passes from air into water, do you expect the freqmnc5)a+hdhr0:9cjm,*o 4 y ajtih/zpuency or wavelength t:+yh 5/rc04i)daa z,hjhcpn mtjo*9 m o change?

What evidence can you give that the speed of sound c rc.cf*+vkhn0 )t*c5f;1 en4 snodtsin air does not depend significantly on frequencksc csoc;*n*10 n+r4c5dfvft)ehnt . y?

The voice of a person who has inhale)r7 orts;9ox pd helium sounds very high-pitched. Why?

How will the air temperature ,2+h9 8hiipk iv5 why*ujg3bf in a room affect the pitch of organ pipes?

Explain how a tube might be used as a filterdtd, zp2kwbz/)4 xsm 9 to reduce the amplitude of sounds in various frequency ranges. (An example is a car mzzbdm9)x p2sdw 4,t/ kuffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer together as you movegs s3r-e;3t8tft/d vsvg6 t nd:g+rq-8o7ljf up the fingerboard towar:f7tv8ogjt s-8 gt grn6l/ 3edsdq -fs+rt;3v d the bridge?

A noisy truck approaches you from behi yjs:4j:s uvm:)y(onfdk0ioxud 07* end a building. Initially you hear it but cannot see it. When it emerges and you do see it, its sou:j u 0ynu)sf:7 (:xji0*eksm4yvddoond is suddenly “brighter” — you hear more of the high-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due to “interference in space,” wh3k llr 1oes:0af1g4 egereas beats can be said to be due to “int04lar lgg113 kseeof: erference in time.” Explain.

In Fig. 12–16, if the freq/bftud 6 *q0sq j-usz8uency of the speakers were lowered, would the points D and C (where destructive and constructive interference occur) move farther apart or clo-qs0tb8zu/* fqju ds6ser together?

Traditional methods of protecting 3fxh -( 5-cshx:ic jpxthe hearing of people who work in areas with very high noise levels hhpx3 fcs5-c-( j:xixhave 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 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 be2mcutb az (58+nz3ejulfy;5 g:u xo1w thought of as a superposition of two sound waves with slightly differeb zgxan+3t;jy efulo5z(m:812uuc5w nt 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 observer move in the eqx vbdu8ejiy.x4 v,:ws8cc*d 40z .gsame direction, with the same 8veex4gsvix :0jz w8. ud qb, cyc.*d4velocity? Explain.

If a wind is blowing, will this alter the frequency h-n65 m fwl-ypof the sound heard by a person at rest with respect to thpy ln-wf m56-he source? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a child in motion on a swing.3.fv o3 cy3gv4o- snug 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 gnsyo.-3 cvvo3 gf43u whistle? Explain your reasoning.

  A hiker determines the length 6fxu4p v-5, oic+jqqa of a lake by listening for the echo of her shout reflected by a cliff at the far end of the lake. She hears tq5 6 ,j avu+iq4cpfx-ohe echo 2.0 s after shouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship b.rp,b+3a:d4gft9em+s ukai 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 th3t9idf bkb+ mr4p:a, .asue+ge 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 7.mj(uu mnnkq 1 m*h8sin 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 dayor pide*p+ 26n. Without warning, an engine backfire+ * pr2eip6don 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 striki*s6 04 eiotjrw /0*a7 o(v ko8hjhglsvng the watv0jksro o4gh*t/jio(*vw8he7 0ls a6er below is heard 3.5 s later. How high is the cliff?    m

  A person, with his ear to the ground, sees a ha 1,nda-bo ep,uge stone strike the concrete pavement. A moment later two soundsa pd-,eoa,1b n 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 macl h ;c5,jp; nyww-yo)de over one mile of distance by the “5-second rule” for estimating the distance from a lightning strike if the temperature is (a) 3h,5yponc yl) -jww;; c0 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pnt zt 3sfm)ec.9d-7 vwqwv2c7ain 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 k-ttybm91c r/c dm+ o/sound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB wk wmby-od k0k 6ae43k6hen fired simultaneously at a certain place, what will be the sound level if only one is exploded? [Hint: Add intensities, m36 o0akwdekby k6-4k not dB’s.]    dB

  A person standing a certain distance from an airplaoygczt-2qm 9 00 /:lbqdq aru6ne with four equally noisy jet engines is experiencing a sound level bordering on pain, 120 dB. What sound levrdaouqt26g 0m-qq b 9z: /0yclel 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 signal-to-noise ratio of 544tos9ynh-hcm; +): p to bm)pcbud)j8 dB, whereas for a CD player it is 95 dB. d 9o:)+;ccn)ptyu-hob4)btm 4hmp js 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 con9k i+yl0* umq:lbzrhcw 8cu5 *versation. Use uyl5 wrcl9:+8i0q z*kbm h u*cTable 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 strikennn-1,3js ,j tx dexv.jd k/n,s 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 W, while the more modest ampli;*opvwi: ej c; c5k34fpt,sq afier B is rated at 40 W. (a) Estimate the sound level in ,ck4a*ptfwq5; :ce3 oijs ; pvdecibels 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 plact94xqjadzib (lz50s w,wt1,ted 2.8 m in front of a loudspeaker on the stagettdzi s wzj,409wa5l1q( bt,x.
(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 dh.y fthr /vf 1p8m*6ttB. What is the ratio of the amplitudes of two sounds whose lefr.*t hp mvh1 fty8t6/vels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled wbbosv4nacr,:w.(a8, (a) by what factor will the intensity increase? Increase by a factobv:a(wws c nb,4. ro8ar of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal disbvnz/6jo o+ w6placement amplitudes, but one has twice the frequency of the other. What is the ratio of their intensitiesw66 j/bv+ znoo?   

  What would be the sound level (in dB) of a sound wave in air that corroopfnui0 1 re3(sjm* 7esponds to a displacement amplioe(7 0jsfprno u1*i3mtude of vibrating air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what soundb8zlftj4fh yc/ sn+/9 level to seem as loud as a 100-Hz tone that has a 50-dB sound 49lsz8cf /tj yfbhn+ /level? (See Fig. 12–6.)    dB

What are the lowest and;n,k c/xtne-fj+zb:k4nh yk( highest frequencies that an ear can detect when the sound le tnh (c kz:,;/fxkn-n+e4kjybvel is 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of sound level6sz*grhri)am( eku4ssy c-+8lr p61c s. What is the ratio of highest to lowec8ls-a ysiz+r6 *)mr4p(h g1kc u6rsest 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 fundam8zny v9 nlp5r2zy:7pjental 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 styppyv l5n:rz8 nz927 jring be placed?    N

  An organ pipe is 112 cm long. What are the fundamental and first three anma*4gpob+ 7 audible overtones if7 +*apa4gonmb the 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 from blowinga+ jilly9 xjjnr 8y2*p9o9mc* across the top of an empty soda bottle that is 18 cm de p iacnr98+ jxl9 yly9jomj*2*ep, 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 , egfgno.h*g*z4yti:open-tube pipes spanning the range of human hearing (20 .hige4z:,g*yo* tg n fHz 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 frhq*t v98sx /qa3ov3 cbequency 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 orit* cboav9xqv/3q8sh3ginal length?   Hz

  An unfingered guitar striy /5ksir8 op4y;q9fpbng is 0.73 m long and is tuned to play E above middle C (330 Hoy ypbi 8fq9k 54r;p/sz).
(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 byx5/uq3 d4qg7 ahsis70qv s* pipe that emits middle C (262 Hz) when the 7qi0xs3h 5as7g* /qsqd4uy bvtemperature 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 1wmnue 6g pf*c-umf( /$^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpieceqego:pv i(dfro7 i w/q:+23ii of the flute in Example 12–10 should the hole be that must be uqe 2o irvgw qfp:7o+ii3(d/i:ncovered 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, 440 Hz, and 616 Hz, bm,gkv(d59 r djq:hu7rut not at any other frequencies in between. (a) Show why :k r(7mjdqrgd hv u9,5this 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 resonate nu.(uttihl nia 86kt575 d:hps at two successive harmonhi5ut:t8. an5 pkidn( u7l6thics 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 /mn,mq3xnvz/ $^{\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 withi6scx ; /+ys*pk3jmpw in the audible range for a 2.14-m-long organ pipe at 20x+ cs36pps /w;jkmyi* $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is appro87x43gx,v nmio yak;hg-y ef5ximately 2.5 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) ofx, x3 mg;kg7vhi-y8 e5yon4fa 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 one beat every f,/,9oon f ard1sf5)uyugeuxb +3i: o 2.0 s when trying to adjust two strings, one of which is sounding 440 o1)oe9,5+g: xfyr, fouf/nus3uaib d Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency if middle C (262h 7fmz bzr6d (e(q(6a3;ewnkg 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, whil, gvr) +yzyw 7lhd18jue another (brand X) operates at anyu)rwdj,v + 1yzl7 hg8 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 frequency of brand X.    kHz

  A guitar string produces7) 4awjsx/rcf 4 beats/s when sounded with a 350-Hz tuning fork and 9 beats/s when sounded with a 35x7fr)ac/jsw4 5-Hz tuning fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same freque l-18rxo og pk3s1yx8ency, 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? [Hint: Recall Eqeg-8pxyxok8s 1o rl1 3. 11–13.]    Hz

  How many beats will be he tdoa uti+*k 9(n/w:ndard if two identical flutes each try to play middle C (262 Hz), but one is at 5.0°C and the other at 25udo*aid+wn 9k: t/(tn.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a frequency of 441 Hz; h wcmp3 wlj.1/4ca,ku4los/ ewhen 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 Hz. What are the possible frequencies of A and C? Wha c4co/mp ,waej hlk /.luw3s41t 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 apawh pywm01. w( h4lkyob49tc1qrt. A person stands 3.00 m from one speaker and 3.50 m from the ho(tqylk 9 mw10byh4pwc1 w4.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 vibrati gr;o3,pk; sjong at 132 Hz, but a piano tuner hears three beats ego ,;rksjop;3very 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 anco8 n 8d2ayq: a)-j(fdo,cz sgr .f9pbd 2.76 m in air. How many beats per second will be heard? (Assume T pc f8doaso:q) j9.afydczg 8n-(2 rb,= 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire teoe::+3 mgzg engine’s siren is 1550 Hz when at rest. What frequency do you detect if you move with a speed of ogemt+ :e 3gz:30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequency dotbbdx:pa)l-nz ( kf; /8 qyxf)po*c5y you detect if a fire engine whose siren emits at 1550n8o(bk- p )/;pyx xblf):aztyq5*f dc 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 moving to0chr )1l 3uxmt9t ppq5ward you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exactly the sa3t1 m05)u lqhtrx9 pcpme? 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 th/fx;kkh89;sv i7 w zlte same single frequency horn. When one is at rest and the other is moving toward the first at 15 m/s t; /;7lxkhzis f9tvkw8he 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 ultrasonic sound waves at 50.078 oqzoybb(/ ssee+:yh 2 t6fx kHz and receives them returned from an object moving directly away from iyy x+ ethbqosfb 6z7:e2s8(/ot at 25 m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wa,d3qrzhpr qfrj)czp8 w0 j-)b lia752ll at a speed of 5 m/s As it flies, the bat emits an ultrasonic sound wave with frequency , 2 p5w3clif7)rhz0da q8rbjjr -q)pz30.0 kHz. What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was playeak t wru-zb1fey rj -+l+p5q,4d on a moving flat trai -ekzulf1qr4rp-a+w+jt y 5,bn 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 a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to mea) v5+w-a e/.hjv xlx9mreq .dbwj o,p+sure 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 flowing in large leg arteries at 2 cm/s directly away from the soundb qm-.5lvav,/exew +jdj pw)+.o 9rhx source?   Hz

  The Doppler effect using ultrasork/67qcq d e9unic 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 w3,g dm67htezaz(, y8mt,kkf frequency 570 Hz. When the wind velocity is 12 m/s from the north, what frequency will observersezgk mt3 ydk( whftm,8,7,za6 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 on lwa*:ctx3ljb*o +zf0k and 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 offt enr :.z96my3lk/ u9+(ztlz dk6my o sound is 310 m/s (a) What is the /ytoulr9 kke6 my +df6:n z3 zmtz9(l.angle the shock wave makes with 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 the speed of8z7 fe-owx7h j sound ishfxeo7j7 zw8- 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} $