What is the evidence that souo. q.mbk 724u spms:esnd travels as a wave?

What is the evidence that soun7 oaa(bg *eyqec1d29k e v7)yvd is a form of energy?

Children sometimes play with a homemade “telephone” by atta(4dv h+ djrn7aching 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 otv4ddah+rn(j7 her cup (Fig. 12–29). Explain clearly how the sound wave travels from one cup to the other.

When a sound wave passes from c*4 hqfn(1joepo+fh 0c dt2m;air into water, do you expect the frequency or wavelength to chan tm; dhqc20oj 4hf(fe+ *c1pnoge?

What evidence can you give thatj-7rswv0 4)vhqkyanm 90s8d v the speed of sound in air does not depend significantly onyhv0vdw-rsa k7j 4qs 8v)9m0n frequency?

The voice of a person who has inhaled helium sounds very high-i9)a5m,2 d+wy og xmccu 0v-pwpitched. Why?

How will the air temperature in a room affect the pitch of organ p 53n j -zwwiz,5kmvt8ripes?

Explain how a tube might be used as a filter to reducep. tcert41 m+a the amplitude of sounds in various ct.+r p4t1emafrequency ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer 7)wxra)lm zb :together as you move up the fingerboar7bmawr:)) z xld toward the bridge?

A noisy truck approaches you from behind a building. Inw97b92 /figw o1dmarc itially you hear it but cannot see i wco2gm9a 91bfi7dr/w t. When it emerges and you do see 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 to2/ t3 dpxfz o sm.8jvq;t*;mxd “interference in space,” whereas beats cas 3mt/8t zx vd.f oxj2d;*qp;mn be said to be due to “interference in time.” Explain.

In Fig. 12–16, if the frequency of the s4g1v al 9bb.sfj+ozdkz:p p +-oz *0ejpeakers were lowered, would the points D and C (where destructive and*e0 pjdlbzbv- gk4.:so +9zjo+1fpza constructive interference occur) move farther apart or closer together?

Traditional methods of protecting the hearing of people who work in areas with qm7lx23cvhbdx 3 ) g3cl+c2 cgvery 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 detec7+hdgc2llv 33cbxq 3ccm2g )xts 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 be thought fyn c.4daq 8+y+)kmbfq)ac 6sof as a superposition of two sound waves with slightly different frequencies, as in Fig. 12–18. In which of the waves, (a) or (s)4 f8k++m .y)6ybq ccanqdf ab), are the two component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and ob6cc9vu3ng ;z zs1d g;ij0 oo(y lh7(xpserver move in the same direction, with the same velocity? Exo 7j i(zpyun13hx 6;c 9g(vs;gzlocd0plain.

If a wind is blowing, will this alter the frequency of the sound heard by ss b+ca-0xw:., c4 7 tlreywbra person at rest with respect to the sour t .cs,+:y-sb0wbxwr47c el arce? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a child in motion on a pf8h;)i 3cyg no2ym*l swing. A monitor is blowing a whistle in front of the child on the ground. At which position, A through E, will t3 pyghncf o2i);mly* 8he child hear the highest frequency for the sound of the whistle? Explain your reasoning.

  A hiker determines the length of a lake by listening for the +1pdbixttj*j5z0 e l :echo of her shout reflected by a cliff at the far end of the lake. She hears the echo 2.0 s aft :e i5tzx*jt1bl jd0+per shouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just beg:;rlccxd7oi3 i7tx/ low the waterline. He hears the echo of the sound reflected from the ocean floor directly below 2.5 s later. How deep is the ocean at this point? Assume th7gxl3cdxo7it/r : ic ;e 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 20 fvsw4w1/bnxgejr:y d. (x t, )$^{\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 mmmch8f 2m9r).:c wx *x-yupx foggy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 28hmr cmymxfuc9x)p *mwx- .: 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 mak0 7 ad2/lxzi*rzv qf4ees when striking the water below z f*dla er/ x4i02q7zvis heard 3.5 s later. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge vv;:aip v/dmzwvqt *,88 ons, 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 away did the impact occur?8 i ;za*8:dtvpvmq,w/vsov, n See Table 12–1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one maguk0b-.f / w6nsu 8twile of distance by the “5-second rule” for estimating the distance from a lightning strike if the s0un b8wwfa- k6u ./gttemperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity ofbytd 2 . at96pc.w8hpcd/4n9ukv;smg 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 whosx1ej.tt s /gsbi,g75ye intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound 67 xw6gub2 tzolevel of 95 dB when fired simultaneously at a certain place, what will be tt 6z2x7bgwou6 he sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distanf+vo 7es)0r3/nghepi ce 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 experi)h i+7g f0e3/nrosepvence 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 58 dB,5p.pij (fp20m o bo)hg whereas for a CD player it is 95 dB. What is the ratio of intensities of the signal and the background noise for each device? 58 fi bojp(0gp )mpoh5.2dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from a eoz*i7q mc(f (k8hfm* person speaking in normal conversation. Use Table 12–2. Assume the soun qk8f(*m*o ez (fich7md 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 s wig16c)n-; pkvm 8rrqb0(bbstrikes 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, oh*2oajcy nn:-pk ;) xwhile the more modest amplifier B is rated at 40 Wko; nx:ay-op hjc)* 2n. (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 dB w76v iiz;4j+cyvf+ ah t6t) bwjq eiq-bpy7(1 shen placed 2.8 m in front of a loudspeaker thvi7ie67ft(qby4 wpj+ys1; q)j b6c+a vi-zon 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 differenk aqdcgjsf-uclzj0*)40pi8y/ ky u26ce in sound level of 2.0 dB. What is the ratio of the amplitudes u84/kjzc ) jaiugdlcy -q6y s0fk0*2pof two sounds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (lcp vdo8fx c,fi0 7c90a) by what factor will the intensity increase?8fvd7,oc0cx c 0lfpi9 Increase 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 f j3p*sx.wn-ri8ili ;twice the frequency of the other. What is the ratio of their inlpjf8. xnsi3 ri-;w*itensities?   

  What would be the sound level (in dB) of a sound wave as w53l)a/73 ra *) xdytyquiyin air that corresponds to a displacement amplitude of vibrating air moleyi*l/7 5x tyy)qsuwr3aa d3a)cules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud;zo j cn c*fa4:o-kmu*3wr fei f;8d-g as a 100-Hz tone that has a 50-dB sounuo c -f;z:a3kri- o* gdfjwf ;mne84c*d level? (See Fig. 12–6.)    dB

What are the lowest and highest frequencies that an ear can detec+gkh m8:n .f9n kf/nmzt when the sound ln /mhnn:zm gk8+fk.f9evel is 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a p kwn7w r-6ge4k3 2cixhuge range of sound levels. What is the ratio of highest t g-6pik3 wk2rc we4nx7o 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 fqifh. 5yt 96i g(rtoc6undamental frequency of 440 Hz. The length of the vibrating portion is 32 cm, a6o6i.9ycrt (fthi5 g qnd it has a mass of 0.35 g. Under what tension must the string be placed?    N

  An organ pipe is 112 cmi/e2vt8c04o)pccl*wcy f s 7q long. What are the fundamental and first three audible o)q/ f*7lpi82wocyccs e0 v c4tvertones if 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 exmrkb y mdtnw.a76; n39pect from blowing across the top of an empty soda bottle that is 18 cm6t7n;mad kny 3rbw9 m. 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-tube pipes spanning the range pmqe4 uminhj98xkq,, +d)b7q of human hearing (20 Hz to 20 kHz), what would be the range of the lengths of pipes 4qpx+9mde 8,h 7knujm ,)qqbi 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. What,srw:x , ;jg ktah8dk/ will be its fundamental freque wr, atg: /xkhkjd,8s;ncy if it is 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 cr *kpdw-tr3 7kn5l1x E above middle C (330 Hz3n rc7k 1xdtplw5r-k*).
(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 opcl:.m (3 edild7p;l3 w ;1i dofufc8vren organ pipe that emits middle C (262 Hz) when thil1u dfle:cvpd ld8 wf;io3r3cm.7(; e temperature 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 ativ(wtr-. 39tqkps d9a 20 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece of the fluteyao0dqat zm:.266 tzx in Example 12–10 should the hole be that mm. aoz0tayd:q z62x t6ust be uncovered 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 c6gj;-l, vofcnot at any other frequencies in between. (a) Sho o-6;l,fgjcv cw 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 resonat )y/qg7) r3zypj)qh ygj+ c3oqes at two successive harmonics of frequencies 275 Hz and 3ro3q3) g 7/yz cy jjgq+)q)yph30 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 :iemk1u* j.jy$^{\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 range for a 2.14-m-long oibs0 (uqss4mq,zo8) 4 ayjn4e rgan pipe at(4oqb4uj8a0qsns 4 )myeszi , 20 $^{\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 thedeny0qsb,l/r*:bc .a outside and is closed at the other end by the eardrum. Estimate the frequencies (in the audible rang e,r.ns*d qybb/0:a cle) 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 to adjust two stry3zcm pf+jh-w2o 6p 5oings, one of which is sounding 440 Hz. How far off in frequency is the otherwfm2-y opz6oh3+cj p 5 string? ±    Hz

  What is the beat fre5 ut dw9c3kpw8quency 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 opera0 ;myspd9;0 qlcmn9lltes at 23.5 kHz, while another (brand X) operates at an unknown frequency. If neither whistle can be heard by humans when played separately, but a shrill whine of; q99dl lcp0lsm0n;y m 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 soundu/ za4-aqb 7fmr zhn75dt jg,*ed with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of the string? Explain yoa nqm5zjza4b7 gf-uh*r,7 / tdur reasoning.    Hz

  Two violin strings are tuned to the a; apgilbm,n-*bma/0same frequency, 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 Eq. 11–13.l bg,p;am/bma*n 0i- a]    Hz

  How many beats will be heard if two identical flutes each try to plx qh1w/4fe5e lay middle C (262 Hz), but one is at 5.0°C /ew4qf5 lxhe1 and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a fre0,bf,+ igq dcpful c6-quency of 441 Hz; when A and B are sounded together, a beat frequency of 3 Hz is heard. When B and C are sounded to,c f qgi c06u,dplf+-bgether, 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 per a5y:4mye7 wrfson stands 3.00 m from one speaker and 3.50 m from the am7y 4rey5:fwother.
(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 t-* h f+fxlxzxx 6whp5yq6q7s3o 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 wxxqs-hhp65flf *qy3zx6+x7 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. 6bhlv:nn7j+h d *(gvxm;h xc8How many beats per second wg:x hv(;6ndc hnhbl7 v 8m+xj*ill be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain f 3fofc8t; ubv8m a:trh av-h,-ire engine’s siren is 1550 Hz when at rest. What frequa-h8ff8vo ar tb,-u; : tmv3hcency do you detect 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. What frequency do you duoi/qe5:+s ze0q-fb0u lmw: rx3f :seetect if a fire engine whose siren emitese0+qq:eu:53m -0x bs/fuz roi f:lws at 1550 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 t 5gnzj7ae. ,kqix-vg1oward you at 15 m/s versus you moving towardj x.zgegkva75nqi -1 , 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 wis,bz hu88x hv:th the 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 frequency ,h8xsu:b zvh8 the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonichcocp4qu bp *09 -+qka(a fv*v yib.7o sound waves at 50.0 kHz and receives them returned from an object moving directly awav(o*9oh-+u qb a0cif*p baqk4c. pv7yy 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 A gp:6 : s; rzvwuqpy4r91avpd/s it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency p;:/:w1dzqg pa ys9vv4r6rp u does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was x2u.z2 iy8r. ewcv8 ggplayed 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 railway station. What beat frequency was heard if the train car xzu82y.w c 2.eigg8rvapproached the station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measure blo2tp*b985 kvk;nry bumj nor;8 od-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 flo*knn9;8b rur5 kovmp8 2byjt ;wing in large leg arteries at 2 cm/s directly away from the sound source?   Hz

  The Doppler effect usbw5ldr+ 9 c i:e5je hewvtc2)6ing ultrasonic 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 fre; p(ity cml.m+t;wx 5mk+l6 ybquency 570 Hz. When the wind velocity is 12 m/s from the north, what frequency will observers hear who are located, t+(pw+. ikmmc ;mxb 5yt ly6l;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 land i3tz 8p6agcl(qpt/ gdl1xy.vzr 4w4a-f 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 wew :c5t90sv0b (jm(aww0 jm4 yhsqpe7here the speed of sound is 310 m/s (a) What is the anglm wj 0bc:ayj5m h9(qps ve4(t0w7se0we 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 whsh/,1l) fsn ibere the speed of sound is only ,/b i1sf)lns habout 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} $