What is the evidence that soundpkvc7 o 9wpn o 7/jcqe8z9i71v travels as a wave?

What is the evidence-bb+ke 2e znmryb w3)2/g* idk o.tp4r that sound is a form of energy?

Children sometimes play with a 4, +zfzkv0ammrjx 0* shomemade “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 a0msj z+4mva*k,rx0zf t 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-pq vey9; )sdpx 8v:dw or wavel vewxd:qp9; 8 )dsypv-ength to change?

What evidence can you give that the speed of sound in air does not depeewfd/f *4h7uvnd significantlvuf 7 fwdhe/*4y on frequency?

The voice of a person who has uclu 5w;q1/el :lfe ip ldh/-8inhaled helium sounds very high-pitched. Why?

How will the air temperature ,pyl2sdvmxys4qn:1 : in a room affect the pitch of organ pipes?

Explain how a tube might be used as a filterh9hu lsh*d8y: to reduce the amplitude of sounds in various frequency ranges. (An ex*:d8yl 9shhu hample is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spa k9uw(/, kwq fx 03 r7n69utsudfe9dzgced closer together as you move up the fingerboard toward the bridg0 uk (f6ztfdk9,gn uers37u/x w9wq9de?

A noisy truck approaches you from behind a building. Initially you hear it b-j wmk/l+0gehlq:i t8 ut cannot see it. When it emerges and you do see it, its sound /m jwigqh8 e0kl:t- l+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,” whereas beats c4bbg5uuk0d .6wk dqd8an be said to be due to “int db .q6dkbuu0wk4d5g 8erference in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowered, woul e81+frtxa q68 8 h*8wcdbu*z6 frzngzn0: lbmd the points Dunmh88 dclq gt06*r zbxa*:w1zf zf+886nrb e and C (where destructive and constructive interference occur) move farther apart or closer together?

Traditional methods of protecting the xa*2cp:5e7ht xsw3ja hearing of 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 addition to the ambient noise. How could adding more noise reduce the sound level:73ah xx*pc5ws2ej a ts reaching the ears?

Consider the two waves shown in Fmq9 :5 agaqcxtt;v/b 4ig. 12–31. Each wave can be thought of as a superposition of two sound waqat9 5:;a /ctgb4x mqvves 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 then 0pkhy ;-8ldv source and observer move in the same direction, with the savlk-;np0d y 8hme velocity? Explain.

If a wind is blowing, will this alter the frequency of the so4faj0yy y74-j9lhs vdund heard by a person at rest with respect to the source? Is the wavelengthf y0 ydh -j79vljasy44 or velocity changed?

Figure 12–32 shows various positions of a child in motion on a swing.0 zm reo) ( ./f+)mbfpahmvw)q 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 hwfvq )fb/(m)) 0apozm+.mreh ighest frequency for the sound of the whistle? Explain your reasoning.

  A hiker determines the l,d95 f;u dwppcf :s9lfength of a lake by listening for the echo of her shout reflected by a ;:9cfwlsffd pd5up9, cliff at the far end of the 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 below the waterline. He hears the ecae884jd kp)y4vc o.7kb,sd fqmj 25 bfho of the sound reflected from the ocean floor directly below 2.5 s later. How deep is the ocean at this point? Ass v75jfbq p fyk2dj,48ocm8sed4 k.)ba ume 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 2v7dyl ((zu u81sef 7z* -/gxl8 wyecrg0 $^{\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 e.7fmg3 4 l zlfyfya*8b.ty,3ow dne4day. Without warning, azy7y,m3of4tg.*8 elbl.ed yfn43wf 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 frt+5z 4 2si)itdliju;eom the top of a cliff. The splash it makes when striking the water below is heard 3.5 s later. How high is the cliff? ji s t2li;d4)t+iu5ze    m

  A person, with his ear tor;hwk9 +pyr1ua.g,gg 8i4ija43(mx kzb n pd : 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 and the other in the concrete, and they ar4 uarigyr( ;+ . gjanpkghw,8mibk1:p9 dz4 3xe 1.1 s apart. How far away did the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent 8upcd)e3ttghh* (b2k:mxtn;+k1 utp error made over one mile of distance by the “5-second rule” for estimating the distance from a lightning stp tkbg:ku 8*e12ud)(mh+;x 3 cn htpttrike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pmlg2 e*kv20 9xld6yg me5jyg 3ain 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 levewcq;gu7qdv b, h;6u ,jl of a sound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired ftu(xo92h +dcpa f ;4vsimultaneously at a certain place, wh4cof v+ (du2th9xf;apat will be the sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane with four equally noic(nye0qsiq4z* . mm le/.n)zusy jet engines is experiencing a sound level bordering on pain, 120 dB. What znc) eq4ms*u e/l(qz.mn i.y0sound level 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 ham4dw 2cf9)gzhve a signal-to-noise ratio of 58 dB, whereas for a CD player it is 95 dB. Whatf2)cdg 4wm zh9 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 conv .3c;bdu5dr 18z q1 fh35if buwgydat3ersation. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphere centered on the mouthqu 3db8ddz1 fi.1ht5b;ucgay53 3frw. $\approx$    $ \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 af n,zlsk4- c6r6q ,ewkn 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 amb x-8 h8skqepwbq2 8,3)h mxa9py4b ghplifier B is rated at 40 W. (a) Estimate the sound level in decibels you would expect at a point 3.5 m from a loudspeaker conne9b gekyhbp8q8x8w pxa2)4h sq3-hmb,cted 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 regist ag,20aklcb lb:ee w49ered 130 dB when placed 2.8 m in front of a loudsl4cl ,e:aewg2ab9 b0kpeaker 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 differe 3;q pus1i98ppryx 3tsnce in sound level of 2.0 dB. What is the ratio of the amplitudes of two sounds whop13u r;9s spxy3ti8qp se levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factor yca- j;sv)0ncv h.cb( will the intensity increase? Increase by vy)0 a.bc-jv(; cnshca factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have yu5 e t q5iu7w5;zpyn,equal displacement amplitudes, but one has twice the frequency of the other. What is the ratio of their int,p q wn;t5uiz57 5yueyensities?   

  What would be the sound level wl2n .bl17sdf (in dB) of a sound wave in air that corresponds to a displacemenw1.n27s dlblft amplitude of vibrating air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud as a 100-Hz tone ,ckeaewa9w* uq+/j hn37 r2o xthat has a 50-dB sound level? (See Fig. 12–6uj7wer 2 xe n3qcoa9,* +haw/k.)    dB

What are the lowest and highest frequencies that an ear;9a: ykli -. q)orsib21ijy tk can detect when the sound level is 3k:oiit- ikry;a1s9y2 q lj)b.0 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of sound levels. /ba ),,ybz:euvdfu3so9h)r tWhat is the ratio of highest tod b3rzv,fuba/ :s),9yout)he 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 fundamental frelb,;9k 3agjjvtrx(lgf.,s z0 7ui t9mquency of 440 Hz. The length of the vibrating portion is 32 cm, and it has a itvzgx s3glj;(maj t f7,.k99rl0b, umass of 0.35 g. Under what tension must the string be placed?    N

  An organ pipe is 112 cm long.e( l;4 qzg7 usgbef6c5ck6,sr,i- iya What are the fundamental and first three audible overtones if the pip ,5;zys( lf6iuk,g-bi6 sgcc 4 ere7aqe 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 blowing across the top ofcindrzk20 ;a(/8f isa3e x4oz an empty soda bottle that is 18 cm deep, if you assumed frosi4a i( xc2ae;d8z0/n3kz 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-tube pipes spanning the h -x-gczjy;0m3 i-byp range of human hearing (20 Hz to 20 kHz), what would be the range of the lengths of pipes require0hj-bc-y;y pzm3x -igd? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a frezpe7ca*, cp5 bquency of 540 Hz as its third harmonic. What will be its fundamental frequency if it is fingered at a length of only 60% of ib eca*p,c7zp5ts original length?   Hz

  An unfingered guitar string is 0.73 m long anxw4k8lhm +0xseb.g(,b3 d5 jds sd;cnd is tuned to play E above middle C (330 Hzkswx5 .hsd,d;(ge84dn+ mxj b3 lbc0s).
(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 op64 d3qq)nu op* mbzhs,en organ pipe that emits middle C (262 Hz) when the temperh6 m)*d4u qbp,z3nsoqature 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 206.htvw)/hq epkm53 i l $^{\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 sho32 j i1bnxoyb+uld the hole be that must be uncyijbb1n3o +x2 overed 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, but not at;t xkjc+j+k9wz bg8z z sc9/e) any other frequencies in bk;j9ce+z k st/b x9)cz jw8z+getween. (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 db4 wm1oe+z ,*lv j:( kyam6emlong is open at both ends. It resonates at two successive harmonics of frequ w(d vzmke*6+lmb a ye:1m4,joencies 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 wt:ov juhlt - sux4*-;$^{\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 1iy 3brtf8myt4., eaxlb,t7a present within the audible range for a 2.14-m-long organ pi 8rxb7mt41y,b,ty e.a3afilt pe at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cf rd0)n (g1+odv qz-:-cykudmm long. It is open to the outside and is closed at the oun+ g(m1z :d0-drkycqdvf-)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 one beat every 2.0 s when trying toax,,v uw a,8/ i-pttft adjust two strings, one of which is sounding 440 Hz. How far off in frequency is the other string/ vt,au,p-twixat ,8f? ±    Hz

  What is the beat frequency if middxc4 v9 v,3esvele 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 ,h6(9rf .jgndv5r wty at 23.5 kHz, while another (brand X) operates at an unknown frequency. If neither whistle can be heard by humans when played sep rt6 .dnv(wr 9hf5ygj,arately, 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 sounded with a 350-Hz tuning fork ae,ok5g1gya8) u 9vovpnd 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of the string? Explain your reasoning 8)1ypvove a ou5k9gg,.    Hz

  Two violin strings are tuned to the same frequency, 2e+kpt) +l+dtk kc8h v2o)z4xb 94 Hz. The tension in one string is then decreased by 2.0%. What will be the beat frequency heard when ot)+lke+ hp k) bv2x+8ckdtz4 the two strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identical flutes each try to play m*3+.jyz ny (axe1dfb viddle C (262 Hz), but one is at 5.0°C and the other at 25yfv.nbz(e ax +* jdy13.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B,p:vjl(wry 62mwpm3 *x 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 Hz. What are the possible frequencies of A and C? What beat frequencies are possible when A and C ar3m2rlpwwym*j :xv(6 pe 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 stanz:+ bn znk;zq2do v/.yds 3.00 m from one speaker and 3.50 m fdb 2ny. z:qnko zv/z+;rom 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 be1qj5bdy 0.ooo vibrating at 132 Hz, but a piano tuner hears threeyq 1. d5oobjo0 beats 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 2.76 m in air. How many b5y-x o or 8dz/h h*r;h(+dfxcdeats per second *ox-zyd 8hhcofd/r hd 5+;rx( will be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency;9e1igjvg 3 by of a certain fire engine’s siren is 1550 Hz when at rest. What frequency do you detect if you move witv iy1ej gb3g;9h a speed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. Wm90cyc8yb y -yn; 2qzvhat frequency do you detect if a fire engine whose siren emits at 1550 Hz moves at a speed of c 9c2-0zyybyq8 ; mynv32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz source is e7pu 2k .m:zcdmoving toward you at 15 m/s versus you moving toward it at 15 m/s Are the tw.27dcem p kz:uo 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 thezt7w9h g hy.h6 same single frequency 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 frequenczh9wtg yh6 h.7y the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ull./cuub;*+a z bv+vunij1s +mtrasonic sound waves at 50.0 kHz and receives them returned from an object moving dn.j+v s +;/l z*mb+uuu bc1aivirectly 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 emi+pb1z ,zi )*ms fzwwf8ts an ultrasonic sound wave with frequency 30.0 kHz. What frequency 1b8 fz wfp+zi ms,w)*zdoes the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba whlj wr r h9u2,1*a1sqwas 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 railwa 2r uwrj1qlsh,1wha9*y 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 ultrasokwk8ph bwu/(9;yauoc ) fw53y und waves to measure blood-flow speeds. Suppose the device emits sound at 3.5 MHz, and thw(/8ybwfkuchu; w yo9a 53p )ke 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 ultrash3j .yugfcs*pm4.8s h onic 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 the b;wlb z) 0 6jy5q-tvdd2b f g7;2j1xepmsq7fpwind velocity is 12 m/s from the north, what fpyjlq2g;jt f d67-)2b7sb d 0b;we 5 pzfmxvq1requency 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 z2pc ts0ykrf)-zpy(n09eh 0k moving 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 3nfjori1 t.p6 510 m/s (a) What is the angle the sho poift.156 njrck 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 mn*s nzns6/t2 a planet where the speed of sound is only abnn2ms*tns6z / out 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} $