What is the evidence that sound trn1usnwsh2 l8 6m(mux67blg x)avels as a wave?

What is the evidence that sound is a fo7xekb 8v+m8uarm of energy?

Children sometimes play with a homemade “telephone” by atn/f:ka d(j:h upot v9:taching 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 (Fio9f/ a:uhp::jdv nkt(g. 12–29). Explain clearly how the sound wave travels from one cup to the other.

When a sound wave passes from air ictbw; l1zk.swnv9z1o 1)uf )hl y5jr+nto water, do you expect the frequency or wavel nkj1+cluyvrsf))wbz1l9z w o.1t5 ;hength to change?

What evidence can you give that the speed of sound in air does nvlhx.d4vg1s xb-*;kl),+*j yfykuz cot depend significantly on frequ gxjzk*, -.lxsh byy4+fv)c1lkd;v* uency?

The voice of a person who has inhal;lhkr*n77kp 1yb,acl y4k;geed helium sounds very high-pitched. Why?

How will the air temperaturecpy/hdq)fku- 6di m ,3 in a room affect the pitch of organ pipes?

Explain how a tube might be used t24 wl1d s*jwras a filter to reduce the amplitude of sounds in various frequenctj 4lw2s 1*wrdy ranges. (An example is a car muffler.)

Why are the frets on a guitar 1ed n*m0p j0zj,/iz s8v qxvv)(Fig. 12–30) spaced closer together as you move up the finnmev zsj8xpz010q)/vv,id j * gerboard toward the bridge?

A noisy truck approaches you from behin f36. 3y9p evwz3ep.wrjn,ivpd a building. Initially you hear it but cannot see it. When it emerges and you do s ,e ve.nz33f y. wvw6r9p3ppjiee it, its sound 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 beaazt;3zti3v;bg3 z 8sj0umuw9ts can be said to be due to “interference in time.” wu3b0i9asz t ;umv3 jg3;8tz zExplain.

In Fig. 12–16, if the frequency of the speakers were lv8,3kmdb0s o8) fikt lowered, would the points Dtl)svi88ko0 ,dk f3bm and C (where destructive and constructive interference occur) move farther apart or closer together?

Traditional methods of protecting the hearing of people who w wckq69x13cjxork 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.qw3c16x9 xkc j 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 y*m93 nkw,qbvin Fig. 12–31. Each wave can be thought of as a superposition of 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 farther3 b*,n9qmywk v apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and observer mo:pm6u s:fhf-n;y:mj2n jpu5x ve in the same direction, with the same vely6uj:fu fn xspjnh :m;-p5:m2ocity? Explain.

If a wind is blowing, will this alter the frequencg8xxg . n2j-wry of the sound heard by a person at rest with respect to the source? Ig x jrg.n-2w8xs the wavelength or velocity changed?

Figure 12–32 shows various positions of a child in motion on a swin xo 2fybr;ns0 voc5e20g. 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? Explain your r02 5cnfvx2b s;e yoor0easoning.

  A hiker determines the length ofu7vuprys*/ 2s a lake by listening for the echo of her shout reflected by a cliff at the far end of the lake. She hears the ec/*s2urpuv 7 ysho 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 ecrcc to/ nw3fkd0+6ll .ho of the sound reflected from the ocean floor directly below 2.5 s later. How deep is the ocean at thi/+6ndlk3.rctw0lco f s 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 -c)ufrr,5 snzxh(vb+ 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 q m )d3e2 e;clr3xddn-on a foggy day. Without warning, an engine backfire occurs on another 2rd; x3qemc dlnd)-e3boat 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 ht 5 0(8jk0v7pghldum0v5vrtntf 7l; when striking the water below is heard 3.5 s la8 ; h0t70tn0 fgru5(v lvh7jd pkmtl5vter. How high is the cliff?    m

  A person, with his ear to the groundd.ir4 ; glm16 gzbh.jujxy44 b)cmdn*, 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 are 1.1 s apart. How far *.j4;4md )4b6gdilhygjx1. m ucz rnb away did the impact occur? See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one mile of d8u-i 8b*fcoa*avip4* 7 sqts xmc+q)bistance by the “5-second rule” for estimating the distance from a lightning strike if the temperature is (a) 30ai*is 8suc+f vc8amq* *p74bx)o q-tb $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at l9w gjuqzp*:/ k ;8lzbthe 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 so5uzmq 3 ma2-;t,ybafyund whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level bo ro. b3i2-ksw3e-voof 95 dB when fired simultaneously at a certain place, what will be the sound level if only one is exploded? [Hint: Add intenseo-koi- 2br b w3s.vo3ities, not dB’s.]    dB

  A person standing a certain distance from an airplane with four er /rvdas k +)g(ty6,jpqually 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?(td a)y s6kgv/,pjr+r [Hint: Add intensities, not dB’s.]    dB

  A cassette player is saidjt1w 0tinw5c1 to have a signal-to-noise ratio of 58 dB, whereas for a CD player it is 95 dB. Whw1 t1j5ciw0nt at 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 so *bvyr )be5du 4jd9*wgund from a person speaking in normal conversation. Use Table 12–2. Assume the sound spreads roughly uniforml5 * bb*y4w gv)jddeu9ry 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 strikv9k9rclss 8kn4a a1 .pes 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 ratedm)d/e..bcg6 kjlm 87lc7 j xjp at 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 point 3.5 m from a loudspeaker connected in turn to each )j7blmcpxd 67kmec .8g /jjl. 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 pla + ps3b6zhoyq 6y0mf6kced 2.8 m in front of a loudyzp30m66 6qskb y+hofspeaker 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 di1p;)biuf- i16 odfgrzfference in sound level of 2.0 dB. What is the ratio of the amplitudes of two sounds whose levels difr ; z1)g-i61pf ofduibfer by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave iywg)se6 zb( w9s tripled, (a) by what factor will the intensity increase? Increase by a factor we(sbg )yzw96 of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but one has twiceqs .4oq5lfhj0 d7qm nf 86 vfacbfhn780g4x 5d the frequency of the other. What is the ratio offd8 lf7f0hq d f4gnnm0 8b4c7 5v.5ojqha6xsq their intensities?   

  What would be the sond/wvbanv5 * 4* (oafqund level (in dB) of a sound wave in air that corresponds to a disoqd5vn nwb *(4/a* favplacement amplitude of vibrating air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound aoew -99b9j xclevel to seem as loud as a 100-Hz tone that has a 50-dB sound level? (See Fig. jcb-9a x9ewo9 12–6.)    dB

What are the lowest and highest frequencies that an ear can detc0mrr86b+fh n 97xel d flb3j+ c./kjlect when the sound level is 30 dB? (See Fig. 12– /drncle lkrhf c6b+ 80 j+f3b9mj7x.l6.)

  Your auditory system can a kjk va2u- m1 0f5:kv r/ga).c9reyx +iraf9vhccommodate a huge range of sound levels. What is the ratio of highest to lowest intenkr 9/ f m- :arvu )f1eavhj 05.vc2y9r+kgxkaisity 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 (cnegh;dt 7v dg8rk5 (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?(gv 5kcde hn78;gtdr(    N

  An organ pipe is 112 cm long. Wh qf.4bux(2zlji; 9vuo at are the fundamental and first three audible overtones if the p 4l9;2x zb.iqvjou(f uipe 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 frp bwe v4 4ltvglws/g75 1hhq1, k0 etb4z(s:gdequency would you expect from blowing across the top of an empty soda bottle that is 18 cm deep, if you assumed it was a clo t pgl,s4:(w/e 4lhq1zdg07 b4hvv 5ktbgse w1sed 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 spanni l,dp rxnqf+81ng the range of human hearing (20 Hz to 20 kHz), what would be the range of the l+,f dl pr18nxqengths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string has a frequency of bu2/oty* p+lv540 Hz as its third harmonic. What will be its fundamental frequency if it itbplv 2yu*o +/s fingered at a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to play E above middle q4j *3*v4sbfi *agdzm7 bd( 6ruadzm1C (330 Hz). z(bd*da7du v*q3fmibaz6 m j1s*44 rg
(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 pii-((ub*y z,x fjnk1o vpe that emits middle C (262 Hz) when the tempfi x-*b (,(1kvujo yznerature 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 atow,62 ck0ts cujj n(prm m/b-8 20 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the flute ch guhf z(l7-f w(s1q7in Example 12–10 should the hole be that must be uncovered to play D above middh7 -7lwhffs (uqcz(g1 le 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 26jqa3wwp: . tz3y4 3gbr4 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in betwe43wzy3w. rb3g: jqp aten. (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 1.80fr3/q 3l4 cxckaje 3v)ba9lu) m long is open at both ends. It resonates at two successive harmonics of freqr )x3al49/fkal)uebcv 3 c3q juencies 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 ,iuk- idms/aqz/.,v c$^{\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 within the audible ra8 exxbxmcy3 ) 2wcg51rnge for a 2.14-m-long organ pipe at 20 mw cgex 51b3xc)yxr 82$^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm lonp*u-nvg 8(81/vwbu2mw gnrg kg. It 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*pw2(ggkuuv8 b-mr18v nwg/ n 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 to adjust two strings, onx3fk5/ /x gwn2* iscpqe of which is sounding 440 Hz. How far off in frequency is the other str i5nw p*3sxcx/kgq2f /ing? ±    Hz

  What is the beat frequency if middle C (262 Hz) aqace 3d3r:cmi 4scr4( nd $C^＃$ (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 anothelo59ja,09m:yarxz h a r (brand X) operates at an unknown frequency. If neither whistle can be heard by humans when played separately, buz9 5o9m0ajya, lr:xh at 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 :r/(fn f7mx ziwith a 350-Hz tuning fork and 9 beats/s when sounde izf/f:7nx rm(d with a 355-Hz tuning fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to t*4eudh)q: )*8 xxhwnmid wy1x he same frequency, 294 Hz. The tension in one string is then decreased by 2.0%. What will be the beat frequxm8 wxw :idx41y)h)nheu *q*dency heard when 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 md 6ooyx)a0be+v h5gj4iddle C (262 Hz), but one is at 5.0°C and thjoveob0hy)4a +6d5gx e other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a frequx +c .pzjppg f3)bxhv,c-22t oency 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, .fp,2jzv-h+c32xbpxo p tcg) 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 1.80 m apart. A person stands 3.00 m from onew.9o2;a.n izdsu znf dmso(*vd5 5b+x speaker and 3.50 m from theo; if+w(n.v *5axsdn9zdodmz2b5.su 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 vibrating att.eunt v*d,t (e)jyrjo y30rbtv d.)6 132 Hz, but a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibrating at 132 Hz, what must be the djuryy06t.( e)torjv b3t* n)t,.devfrequency 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 8ip:8,xr5yqd6 1 nox kfd2rjvwavelengths 2.64 m and 2.76 m in air. How many beats per second wili,685vx1:ox8pn dy krj q2 rdfl be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’ s:a8o 8qge+ics siren is 1550 Hz when at rest. What frequency do you detect if you move with geo: qa8s+ ci8a 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 )o/3y:.kvb m xiyr0cp if a fire engine whose siren emits at 1550 Hz moves at a speed of 32 cprvi) 0/:m o 3.ybkyxm/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 at 1nfjltoo3;tq*9cc; -z 5 m/s versus you moving toward it at 15 m/s Are the ;cof *o3tnqc9;j-tz ltwo 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 frequency hogske,9pha*i )z*lyvjho evy /zb 1j.b-b:4t5 rn. 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 hjy*voahivet-*le9.s h,: p zkg y)jbz45/1bb orns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at 50.0 kHz and receit0xys2 wm7x a3ves them returned from an object moving directly awa 72saxtm3xy 0wy 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 zvn -aatri9iq8 3s:47/w cmxvm/s As it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. Whawri9axt/ m4n8 c-:ia7zvq 3svt 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 movisrxxnx9.uz9q8guwh9f45x j m-;r+ r v v8jm.jng 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 9xrhx .5 jxx;gzr9uu4vsmm v-8qj+w.8nrf 9jif the train car approached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter u.(+urko w5u)odxvdbkl 4.3j uses ultrasound waves to measure 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 r4v u l3.uo.) kjbw(x+kdu d5ocm/s directly away from the sound source?   Hz

  The Doppler effect using ultrasonic waves of frequency jq70- eoh 3kvm,ci pxv7v7 fg6$2.25 \times10^{ 6}$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. Whe; wetrjx27ch 3n the wind velocity is 12 m/s from the north, what freq ;cthw er73xj2uency 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 movbci*6 l0 wph1aing 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 ofr )ssom9t;wm8)sm zn- sound is 310 m/s (a) What is the angle the shock wave makes with the direction of the airplane’s mr9st w- ))m8m ms;znosotion?    $^{\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 ,hjq2y0axqr2 a planet where the speed of sound is o2rhqa 20y x,jqnly 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} $