What is the evidence tfc ds)g-r1)bhhat sound travels as a wave?

What is the evidence lwrx b1rkq:12that sound is a form of energy?

Children sometimes play with a homemade “telepo7 :l;/ ihrglghone” by attaching a string to the bottoms of two paper cuho r;ll7/: gigps. 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 frxw8m/dj g9 -t*z-*n0q erhcfw om air into water, do you expect the frequency or wavelength to changeh08r 9gjm *xd*c/-qn wt wfz-e?

What evidence can you give that the*7o y-xx smw :xw2gs,k speed of sound in air does not depend significantlys ,kxsx*7- wxom:w2gy on frequency?

The voice of a person who has inhaled helium ,ewhy k4 lp/p 70d b3fpy1f8hpsounds very high-pitched. Why?

How will the air temperature in a room affect the pitch of organ pi/hdk.z ao 95fnvyv6jq;9g ba 2pes?

Explain how a tube might be used as a fil,. 0h v(diljw7ulsggw3 - k+kwys)6 rmter to reduce the amplitude of sounds in various frequency ranges. ws3k+l 6)k-yvw0jdr(gsuhg7m. i w,l (An example is a car muffler.)

Why are the frets on a guitar (Figeqd6jx4q3* g 8/vwgcrt9 wm(i. 12–30) spaced closer together as you move up the fingerboar * dctxw/38qgm9 6 (jr4ivegqwd toward the bridge?

A noisy truck approaches you from behind a building. Initially you hear .t1q3j8iun zqb:l-arit but cannot see it. 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–-.q t318n b:rja uizlq15 on diffraction.]

Standing waves can be s -8 av4xkl)m1w pzcl)maid to be due to “interference in space,” whereas beats c c 4az)m1pkllwv8-)mx an be said to be due to “interference in time.” Explain.

In Fig. 12–16, if the frequency of the speay hzkcn72 v/ ka0,ga kdo9-t;akers were lowered, would the points D and C (where destructive - za okkd9h,2t7 ;vn/acagyk0and constructive interference occur) move farther apart or closer together?

Traditional methods ofqe:6-pftxg1 p protecting the 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 levels reaching the ea: f g6-q1txppers?

Consider the two waves shown in F6*w e.ky6ac dyig. 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 fr.cwy6aykd 6 *eequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if tht1 6d; aspn/ duk6o a073vryoke source and observer move in the same direction, with thednta r6ovd0 ;o63pk u/71asyk same velocity? Explain.

If a wind is blowing, will this alter the frequency beip34y6cb)myta q pd.*5 yc5(1dcy nof the sound heard by a person at rest with respect to the source? Is the wavelength or velocity cpcin(5.)ycedtyym5 1b3a6 * 4 qpd bcyhanged?

Figure 12–32 shows various positions of a child in motion on a swid cpj b29sv24kw)kfh z9nw(1ang. A monitor is blowing a whistle in front of the child on the ground. At which position, A through E, will thnvj)1kw9sc24 p d afwhz29(bk e 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 ech5ea 05pbj 7inh9n:niwo of her shout reflected by a cliff at the far end of the lake. She :5pn09eni5hn7b ijawhears the echo 2.0 s after shouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the so5i:cnviv g6/cq n:.bide of his ship just below the waterline. He hears the echo of the sound reflected from the ocean floor directly below 2.5 s bc n:.i5vgi:v/6q n colater. How deep 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 1)*i two ()6cuyu tq yjbkno1/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 boay)s: dbx7ss;. mqr6gwt is drifting just above a school of tuna on a foggy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How much time elapses before thmsy:;sg.x 7)6b rdsw qe backfire is heard (a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top f g 7usuka9f*(at- 3uvof a cliff. The splash it makes when striking the water below is heardkuuu-f9tf aa gv(* 3s7 3.5 s later. How high is the cliff?    m

  A person, with his ear to the ground, sees ,a iumretx 99r1nh5p1a 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 1mptir5a9 ,h9rnxu1 e 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 milrkprg*ty03xz 7pr.yiwub 2v0 3yy - my.i(n7le of distance by the “5-second ruleluiryr y .2b0v (g3 *yryxtn 77yimz0.-kp 3wp” for estimating the distance from a lightning strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at thdg y;0br i,o2we 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 intenx di3)*mqhguo9z3qps xx7:1 m sity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired l/a* 5jcpasd9 simultaneously at a certain place, what will be the sound level if only one is exploded? [Hint: Add intensities, not dBa*pdlac/s5 9j ’s.]    dB

  A person standing a certain distance from an 7 krv l ndx1vwng/*.e2airplane with four equally noisy jet engines isk2g . rv7*x 1/dnlwnve 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 to have a signal-to-noise ratio of 58 dB, w7fckzfei6 x: 2;zt c(n+6zm 9/ita ixahereas for a CD player it is 95 dB. What is the ratio of iz/7ka czt :2x +;(6 ize6fifanxcmt9i ntensities 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 norma68/e3 eq cg wtdqoj1s0l conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphere cente/eo 1s 8qjc6g3d0qwtered 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 aaqi*/* ,5h gi8zx eeuen 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 amplifier B is r-9e hp;ox( wywdq.ki waq.79aated at 40 W. (a) Estimate the sound level in decibels you would xa i 9(;edo p awy9qw..hqwk-7expect 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 placed 2.:*bq r e,x( h7zab5itg8 m in front of a loudspearq5*htz:xb ,baeg i7( ker 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 difference in sound level sej,rwbez* q8f9;g w.p vds8( of 2.0 dB. What is the ratio of the amplitudes of two sounds whose levels differ by this amount? [*bvs.;, f (wr9zg8pqe jed8swHint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what fact5 6sl;89k fgw x3ryfdoor will the intensity increass wfog;65dr3xl y9f 8ke? Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displaceacywr1n*y m8 t12(l(wfcv cq8ment amplitudes, but one has twice the frequency of the other. What is the rawynw(q y1 2(*1rfv tal 8cccm8tio of their intensities?   

  What would be the sound le++ qplyk/m )4s:vshd poej 93evel (in dB) of a sound wave in air that corresponds to a displacement amqp9vse3ol)++k 4yh/pm de j:splitude of vibrating air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have wn5 ,hvd d; b25pvhusjz09ddv.hat sound level to seem as loud as a 100-Hz tone that has a 50-dB soudj.z0n5h5b ud,p hvsv29;dv dnd level? (See Fig. 12–6.)    dB

What are the lowest and highest frequencies thh6xsmm:1) b exdi *g)e/pq:ooat an ear can detect when the soundqo ) *memop:61x / xgieh):bsd level is 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodw tch qtqf-m 58 pz1 ).k*,qqepl+1-n7sjwdpbate a huge range of sound levels. What is the ratio ofp1f+- w jc qhz)lqp-d q. ,*w7m1npe q8sktt5b 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 h* pfnez7f3cv 9as a fundamental frequency of 440 Hz. The length of the vibrating portion is 32 cm,zv7 f3f *pcn9e and it has a mass of 0.35 g. Under what tension must the string be placed?    N

  An organ pipe is 112 cm l(,.y gefc7jln k s6+vjong. What are the fundamental and first three audible overtones if the n jv.+(se,l7 kgc f6yjpipe 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 a.s96n)j ifmdgcross the top of an empty soda bottle that is 18 cm deep, if yo9sg6 )m.f nijdu 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 organ5wlruzr-u *o( with open-tube pipes spanning the range of human hearing (20 Hz to 20lu*r(rouz- 5w 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 a2q,im* 5bwgwns its third harmonic. What will be its fundamental frequency if it is fingered at a len *qmw2nbgi,5 wgth of only 60% of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to play E above l oq, r3l; b2qr 2e;qomc14yvamiddle C (330 Hz).;l;em1yr32qbv4 2cq rl q, ooa
(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 embw:xwr )l/ sz .3:wqflits middle C (262 Hz) when the tempef.l:)q/wb w w:rx3lzs rature 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 zxpb.)g 2 sl(h$^{\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 1c12 t - wgwql2n5;sk;hs+dkla2–10 should the hole be that must be uncovered to play D above middle C at 294 H-2qnsl+5k hcda; l 2w1tkg ;swz?    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 r; b7:n/yzyojk esonate at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in bet;7ok/yj: zbn yween. (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 w9ymvf r2v ccdz ,b/,*successive harmonics of frequencies 275 vz,b,9ymr vcf/*dcw2Hz 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 15 gm/ce d xeqb-oajh/48gq/e $^{\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-lonk g(67 az;ef.da i.mw max8lf8g organ pipe at 20 8 . a( fxawm7akmgdl.fz;6i8e $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm l( 2gg kvcu1vj0ong. It is open to the outside and is closed at the other end by the eardrum. Estimate theg(j2 1u0ckv vg 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 to adjust two strings,hvgyh j/zh3p+edbc e*vd+2i) 9xr3l , one of which is sounding 440 Hz. How far off in frequency is th3* 3veb ,ljpe)2vhy9cxir/ dgh+dhz+e other string? ±    Hz

  What is the beat frequency if mni gq(..uv y/fw2 3nnaiddle 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 kHz, while another (brand X) operates at 8vx1 liu a2xslvil9:4an unknown frequency. If neither whistle can be heard by humans when played separately, but a shrill whine of frequency 5000 Hz o iv2:8 llx14x lsv9aiuccurs when they are played simultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/s wh/wd i2djb59/op xum8 k3w tlv7en sounded with a 350-Hz tuning fork and 9 beats/s when sounded5bwlk9j3 txd8m 2i /w p/vd7uo with a 355-Hz tuning fork. What is the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz. The tension n- fpq iu6z33lin one string is then decreased by 2.0%. What will be the beat frequen z36nuq3if p-lcy heard when the two strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be hea0nan1 b-(plrz69pt 2gc .nc8ka/mufjrd if two identical flutes each try to play middle C (262 Hz), but one isnn6mckt-1punaar b p2l 0/8(fj. gz9c at 5.0°C and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a frequency of 441 Hz; 6 /w vyvtenu5(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 ofvnw6vut5(/ ye 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 3ryrusy- l,g *3.00 m from one speaker and 3.*l ,gu3-rry ys50 m from 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 be vibratinbrgeru13o ql;;pvq2 ;g at 132 Hz, but a piano tuner hears three beats everrlo;q; 1uv pegqbr3 ;2y 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 27 (rck*.wnu qg.64 m and 2.76 m in air. How many beats per second will be heard? (Akgr. (u7w *ncqssume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’srfvv1 it7g zkv: 2o7)o siren is 1550 Hz when at rest. What frrik tvg):f7v 1 oz2vo7equency 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 detect if abk uj:6n.itt, fire engine whose siren emits at 1550iut :n 6,tjb.k 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 towa vtn4 w6znir/-rd you at 15 m/s versus you moving toward it at 15 m/s Are t6r z-nintv4w/ he 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 with the same single frequency horn. When one is aa j4xft3b /vl3t 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 isv4t3x/l f3j ba the frequency the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves at 50.0 kHz a3zula u5y(-vk nd receives them returned from an object moving yual-v(kz35u directly 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 emits ayu; aqlgo skc)1ix*u-:q: k: an ultrasonic sound wave with frequency 30.0 kHz. What frequency does the bat hear uqcl k g k1siqa::)axuy-o;:*in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler expeuyt3q9v9ozh7r.4wlitbhjo2 kp1 a8 :riments, a tuba was played on a moving flat train car at a frequency of 75 Hz, and a second identical tuba played the oz9a v9.t:4l qibkru8w2 7hop 3hty1j 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 ul;ac--+ hw25u xdq a1 +tpdfogvwvh g;5trasound waves to measure blood-flow speeds. Suppose the device emits sound at 3.5 MHz, andwt5w;-v; +aoacgvd- hqdx2 1fu h5g +p 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 sound source?   Hz

  The Doppler effect usin(c :my)5 xwg0 g zay8dv3yow5zg 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 frequency 570 Hz. When the wind 0+jr i3 hs4(rzdq0polvelocity is 12 m/s from the north, what freque0 rjzhli rpq0(3d4o+sncy 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 moving on jt0x ,),agy 4yyk3wd 1wowbm: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 speedv0p ,n ,)zxi9q.imp 1ak5kyri of sound is 310 m/s (a) What is the angle the shock wave makes with the direction ofirkva mp.9k0qyi,,n5z) i1 px 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 pla+ s6m zp:e3--p+czie rcs 3rijnet where the speed of sound isprmz+3z3s :cjisrecp+ 6-i -e 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} $