What is the evidence that :cz(kzgr y(h5sound travels as a wave?

What is the evidence that sound is a formad3 blv u -yu/;y9d,ao of energy?

Children sometimes play with a h 6j6fd/sf:z qdt 0: x prv7x.,v1btvrnomemade “telephone” by attaching a string to the bottoms of two papeqfttrxvns xvz6./d: f1,7r vpj:b06dr 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 other.

When a sound wave passes from a tp3dwo:ba( huly6e*(z/. - li if8dnqir into water, do you expect the frequency or wavelength to b(yli(uwfp8n-6aq.tl *d ei :/o zh 3dchange?

What evidence can you/q8(xa b 9akt;ehj c1u give that the speed of sound in air does not depend significantly on frek e1baq ; (txj9ua8ch/quency?

The voice of a person who has inhaled helium sounds very high-pit.9we u g 7pij/o:pr(iyched. Why?

How will the air temperature in a room affect the gw(0mk gjm7x0 pitch of organ pipes?

Explain how a tube might be used as a filter to reduce the j84s1;ujby p hamplitude of sounds in various frequeh1 8pbyujj;s 4ncy ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer together as you mo9+h(arnc dp/r)ycuz , ve up the fingerboard toward the /rz dcc,9)+p uanryh(bridge?

A noisy truck approaches you frmkm9ch. 2ccae..nz * lom behind a building. Initially you hear it but cannot see it. When it emerges and you do see it, its sound is suddenc.h.knc a.m 29ezm c*lly “brighter” — you hear more of the high-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said*di:( o38itum e/c2whl;lquth kb5n+ to be due to “interference in space,” whereas beats can be said to be due to “interference in time.” Ehm ik/ lqt;nu*w+ u8l3 t:5 ed(coibh2xplain.

In Fig. 12–16, if the frequency of the speakers were lo.vk)zfg 6ylio 0xll+ 6wered, would the points D and C (where destructive and constructive interference ol l 0+ yz6kvif.6lx)goccur) move farther apart or closer together?

Traditional methods of protecting the hearing of peop;k): p)y0 y-wcauzaiele who work in areas with very high noise levels have consisted mainly of efforts to block or redwca)0-y u; ea: )zkyipuce 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-vd,rmbzm 80o shown in Fig. 12–31. Each wave can be thought of as a superposition m -m,0rbo8vd zof 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 if the source and obseg mzq1 qjgg:5v/a/ c8drver move in the same direction, with the same velocity? Explain.a5jmcg/1q z/vg8:q g d

If a wind is blowing, will this alter the frequenc n82.hsnyd2db-vc, j ee 78fsay of the sound heard by a person at rest with respect to the source? Is the wavelength or veloci2,8jesb2deacdf-h.v nsny78 ty changed?

Figure 12–32 shows various positions of a child in motion on -h/or6 zh5mlma swing. A monitor is blowing a whistle in front of the child on the ground. At which position, A through E, will the child h5mrlm/z -h oh6ear the highest frequency for the sound of the whistle? Explain your reasoning.

  A hiker determines the length of a lake by 7 olctnt/rcoq 5 ,3:d2dxvqp8listening for the echo of her shout reflected by a cliff aoc ldo/v ,53prtq7:n82dcxqtt 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 hii 2qira5*yd7;jp-j gls ship just below the waterline. He hears the echo of the sound reflected from the ocean floor directly below 2.5 s later. How deepdlj -* r5;2qgia7 piyj 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 in air .h4dtml-kl3 b 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 yk, vjce0* /*pxebt oxwtv50fu9 k(; ktuna on a foggy day. Without warning, efckt,x/kypt;k*5 vj(bv *ow 09e u0x 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 tanjgtxwj;*9m0 g(3khcr*hm) he top of a cliff. The splash it makes when striking the water be;9j)cg0g**hhn tm3(xk mj w arlow is heard 3.5 s later. How high is the cliff?    m

  A person, with his ear ti* o 4mz/9d dhmqh9z 4fpb)i0eo the ground, sees a huge stone strike the concrete pavement.) hdziieqhb o04pf /99z4md*m A moment 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-secon gsdq t:/+3(46qtn g 0ciajkcxd rule” for estimating the distance from a lightning strike if the temperature is (a +jc/(0gc36t qx:kdi nsgtaq 4) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity e wbf9 k0)ztiz.bvk6i 7*ehf;of a 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 intensity is90x, m:idc z 0b(r m4m chb+csloj(dp: $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB whbn7lf pqz0frcd + 1-+nen fired simultaneously at a certain place, what will be the sound level if only one is exploded? [Hint: Add intensiti c fzq0pnfdrbn7 l+1-+es, not dB’s.]    dB

  A person standing a certain distance fq c3xb(*x-( b 6*ttshk,dg6vce;cqoj7 ci-g xrom an airplane with four equally noisy jetxc(e6b;ogt-k ( xcv -qjx6s7t 3*,gcdbic* q h 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’s.]    dB

  A cassette player is said ci8op 3c/2kd pto have a signal-to-noise ratio of 58 dB, whereas for a CD player it is 95 dB. What is the ratio of intensities of the signal and the backgro/pdk8c 32i cpound noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power outpan( : kqp3 qp7vbe,;wout of sound from a person speaking in normal conversation. ;ao:nve (pp q3 kq7bw,Use Table 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 strikes an eardrum whoset1w0-0 fckk hg8xq1nadr)h y8 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, wh igfp1omd 23aykq+ 3u3m 9g+szile the more modest amplifier 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 connected in turng z 3s+k2+aq33fogymdpimu 19 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 placedpso7 ai3/)scz 12j0 (ea/zmw og; wabb 2.8 m in front of a loudspeaker on the sta2a 1/s zwmacp ij3;a7swbo0z o/g)b(e ge.
(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. (4r, -.lg)q y*2ykxw qqmgppp.av 5 v;bvtiy0What is the ratio of the amplitudes of two sounds whose levels differ by this amount? [Hint: See Section 1g bv-i. mkyvg,pya.qr 4vx0(tqp q5yl*2p;)w 1–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factor will the intensi5gip w-qpf q6xz+*z-sty increase? Increas-gsw5i+ p-6pzzfq* xqe by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but one has twice the freq/f e8uridf*l/uency of the other. What is the rli/ud/f *e fr8atio of their intensities?   

  What would be the sound level (in dB) of a sound wave in air that corresn1d)i) : en,eclngpd0ponds to a displacement amplitude of vibratingc pnn),l0)idde :g 1en air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud lux 8(l,smp shypq8, m3cb -3las a 100-Hz tone that has a 50-dB sound level? (Sexl,mmpy8lq-u ( lhbc8,3p3ss e Fig. 12–6.)    dB

What are the lowest and highest frequencies that an ear can detect when:-2x 2g;a+imufhcam b the soundf xaua;:g c+bmm- 22ih level is 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of soubs7 s) vn3 z2 jog(etv485hfu(zlnkw5 nd levels. What is the rat4glfo) e(s8 nh37uz(5nj25v s wkvt zbio of highest 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 fundamental frequency of 4h 5xzvhi w(f8/co;4ns 40 Hz. The length of the vibrating portion is 32 cm, and it has a mass of 0.35 g. Under wwnc/xfo85 v4s(h ;zihhat tension must the string be placed?    N

  An organ pipe is 112 cm long. What are the fundamental and fiv mx*25 p ;3j5kyuiwahrst three audible overtones if t*x;jawy 5k m2i3vuh 5phe 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 fromd66rf3hk q 6hf9kf. 9s;rqi op blowing across the top of an empty soda bottle that is 18 cm deep, if you opr; 39q 6diqf9fh s6k rfkh.6assumed 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 or/mwg i)2b+uosnq+p8s vq5(ad a.md(tgan with open-tube pipes spanning the range of human hearing (20 + s/aqi vwtb5(aoq)gpm2d .n(du+ms8 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 ad(qr qki(v2h55+mcm mc+h +qcs its third harmonic. What will be its fundamental frequency (h(q+v5d m5+ c qkmicm+qcrh2 if it is fingered at a length of only 60% of its original length?   Hz

  An unfingered guitar/y qatb f9m6( 2.) von6kxmjvd string is 0.73 m long and is tuned to play E above middle C (330 6vd o 9 ( j.)kf6ay/nqbtxm2mvHz).
(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 that emits middle C (262 Hz) when+hh .iw7du jm4xa/p- d the temperature i4j-7/a xhi .hwudp m+ds 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 el,x* b vm 5brykxnt /2.f7w/rat 20 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the sqq q hie wu/aj;)*ef69sf5+c flute in Example 12–10 should the hole be that must be uncovered to play D above middle C +wf)e qq5ja/q9u 6f*i;shse cat 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 a r;1eqxux .l86sxji* vny otheri*q8 u1elxxxjv6 .;sr 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 two suczzo0h/+e. mxiuc 7 yq9cessive harmonics of frequencies 275 Hz and 330 Hz. Wha 9meyhq7z zic.xu/0o+t 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 ;culo.la nxkmu(6 q7 wx-,r/u $^{\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 pres k2*5 bc2n:4 nsniisl 9hqpzc6ent within the audible range for a 2.14-m-long organ pipe at 2i 4s s9 kpil2*5nbhccznq6: n20 $^{\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 ze ebaa 3hd1.b1i3* d.md 3wzxthe 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 .3wdda3.b z* di31 amxb 1ehezis 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 2p/j cf9)k z5ujkqe9*lg7n m6y.0 s when trying to adjust two strings, one of 56g y) 9zckl7fp9mu*jkj en/qwhich is sounding 440 Hz. How far off in frequency is the other string? ±    Hz

  What is the beat frequency iw0a/(dv, tlgx f 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 kHzj eq .-szsx+2xi ;3nqfn6d2tj, while another (brand X) operates at an unknown frequency. If neither whistle can be heard by humans whi ensj s qxd3;jz.tx6n+-2fq2 en 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 sounded with a 350-Hz tuning foiwohd;63t -a mrk and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of the string? Explain you3 m;6 ohiwatd-r reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz:izt +5ahv-ut ps08w p. The tension in one string is then decreased by 2.0%. What will be the beat frequency heard when the two strings are played toa8is 0w v5 zpttpu-h+:gether? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be heard if two identical flutes each try to pla r +h/ocuof3-wy middle C (262 Hz), but one is at 5.0°C and the other at 25.0f/-+ 3wouco rh $^{\circ} $ C?    beats/sec

  You have three tunin 3cruy-utfl)4g forks, 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 Hz. What are the possible frequencies of A and C? What beat frequencies are possible when A and3l)c -tu4yruf C are sounded together?$f_A$ =    Hz or    Hz
$f_C$ =    Hz or    Hz
|$f_A$-$f_C$|    Hz or    Hz

  Two loudspeakers are 12u(// tu4dcw 8sfca df.80 m apart. A person stands 3.00 m from one speaker and 3.50 m from the other.s/28 ctd /u(wf4c dauf
(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 33iusgk8rr:a vibrating at 132 Hz, but a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibratin r 8aig:3r3kusg 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 autoh*2mbgnebmyt.mk wmf:4s)/f-, /nd 2.76 m in air. How many beats per second will be heard? (m fk2mw, *u-b/ m:yg .bstm)otn4/ehfAssume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certaivyl ae6 lnc 93vm9j1h0n fire engine’s siren is 1550 Hz when at rest. What frequency do you detect if you move with cn993j 0ea6v lhlvmy1 a speed of 30 m/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequency do you detect i+xlob7oehf1f w6b (0 yf a fire engine whose siren emits at 1550 Hz moves at a speed of 32 mbf7o b+f(hwoy16xl e0 /s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz source is moving toward you jeq 8sbx7b/gh- osam+7 i r3,pat 15 m/s versus you moving toward it at 15 m/s Are the-8aox hm7 7+ sqeisgbbrj/,3 p 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 wi;f /mpk kqv)l6th the same single frequency horn. When one is at rest and the other is moving toward the first at 15 m/s the 6 qk/lm) k;fpvdriver 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 atn j;24 lshpf*h 50.0 kHz and receives them returned from an object moving directly away from it at 25 m/s What is the received sound freqhjnp* hf ;sl42uency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As it hh 2ywkd+uw ,7flies, the bat emits an ultrasonic sound wave with fru2y,dwwhh7 +kequency 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 olf83ypjd 8c z,n a moving flat trl f pzyd,38j8cain 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 waveqmf, ,;vi6xe s+0;q)pohh obbs to measure blood-flow speeds. Suppose the device emits sound at 3.5 MHz, and the speed of sou bioh, heqfbmpx+q;;6)v0,os nd 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 ultrasonic waves of freqp8-coi -ahq,xzl ch: .mt* gmd-hf4j4uency $2.25 \times10^{ 6}$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 sounxygyq c; 7h9yzq4 -9wrmdo5v+d of frequency 570 Hz. When the wind velocity is 12 m/s from the north, what frequency will observers hear who are loc d5gz-cqv;q9h+w rxm9o4yy7 yated, 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 lan+p;07nf3qw-ovzivfuna wamvh) 7t 3.d 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 at4qzwv:+gn5ixc9 h1 fa Mach 2.3 where the speed of sound is 310 m/s (a) What is the angle thc 5i9gn1wh+fa vq4z :xe 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 of sounf . w3fbsb q3k5*u) ie+4gkvjqd is only kf4b uf5 wbqkgje.s+q3 *)vi3 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} $