What is the evidence that sound travels as a wave4/u-xmeby2m2 n60;fp bkw uar?

What is the evidence that sound is a form o 6a,1 8u0f 6 m8svxpkgga*5fc+bhx( rgggid w;f energy?

Children sometimes play with a homemade “telephone” by attachiivewlrrz,-+ 9,dpzr-rzi/ q ) ng 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 hearl z/i,r9-dzr iq-v)rwrzp+e,d 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 air into water, do you expect pieep( +6f vz/w ho4-athe frequency or wavelength +f6ea4 -opw i(/zev phto change?

What evidence can you give that the speed of sound in air does not depet:d. 2ihus n*6f x3alsnd significldnsa.xh* fs2:ut 3i6antly on frequency?

The voice of a person who has inhaled helium u r2zugu d32.jit37lksounds very high-pitched. Why?

How will the air temperature in a roo p-o * ,omkaazsecq+69m affect the pitch of organ pipes?

Explain how a tube might be used as a fil wlgc tf )+op2) esv06*rs3xrlter to reduce the amplitude of sounds in various frequency ranges. (An example)sw02r+ p)tefs*v loc lg6x3 r is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced c4d ,aeq1 1a4ps +kimjrloser together as you move up the fingerboardqm a4jd i4r es1+k1,pa toward the bridge?

A noisy truck approaches you from behind a bux 9q x-s0/jrtsilding. Initially you hear it but cannot see it. When it emerg 0 qrxxjss-9/tes 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 becumx 2h d:i9x5 said to be due to “interference in space,” whereas beats cimuh29 xc5d:xan be said to be due to “interference in time.” Explain.

In Fig. 12–16, if the frequency yh -yjj0 br+bl,2eek* of the speakers were lowered, would the points D and C (where destructive and construcjj0 b e2y-+ *,bheylkrtive interference occur) move farther apart or closer together?

Traditional methods of protecting the hearing of peo )14ad6sprfm xple who work in areas with very high noise levels have consisted mainly of efforts to block or sm6 x4r) a1fpdreduce 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 shown in Fig. 12–31. Each o4u*aacx 0 6rzm (:yifwave 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 c*uax:ofr0ia6z ym4( component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source andn1*axju xs*nrfneo4gt(t244yq+ 2sr observer move in the same direction, with the same uas qf2*stjy4nn 2n t41 4re(+gr x*oxvelocity? Explain.

If a wind is blowing, will difwaug/si q*3s01 /wthis alter the frequency of the sound heard by a person at rest with respect to the source? Is the wavelength or veloci q f*i1/giw0w3ssud a/ty changed?

Figure 12–32 shows various positions of a child in motion on a swi0y f0*zcd.+gh 5 sp7 prkzz(mvhd.-kqng. 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 sh *- 0zr.khz5qs0vyk (fzd+mdc.g7 ppound of the whistle? Explain your reasoning.

  A hiker determines the length of a lake by listening for the echo of he2rox k4b x ejy489bfn3r shout reflected by a cliff at the far end of the lake. She hears the echo 2.0 s after sebfxjy8o423 kx rb94nhouting. Estimate the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship yit y ndsj89)1erw; n1just below 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 j s 89)1yn1dyrew tni;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 wavelenrugai/38,7;xifj :md eab2hq gths in air 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 on a foggy dayd9i/u1se y -v l,p*qhw. Without vle-91/syhu dqi,*pw warning, 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 frjtxooi0 9mah7sq kr;r8k),) bt 5c+r )uv7ygoom the top of a cliff. The splash it makes when striking the water below is heard 3.5 s o s ty)m5b8o7 +)vg 9o,kc tu0h;ijxr7akqr)rlater. How high is the cliff?    m

  A person, with his ear to ttw* f j ro.-3xv-y)yyue)g, bdhe 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 wbj,- ux*rv)-f.y)g tye3d oy 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 p,qs 3r.8ldfny ) v,ndone mile of distance by the “5-second rule” for estimating the distance from a lightningpy,)3n lsvd8,q.nfr d strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a soundm.cy as;6voiefe+t (h8 17hte 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 **,h4napioo+t f (dlqw9jbb 3 a sound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound levelup0o k+62 vzwajlt*l/ of 95 dB when fired simultaneously at wt/z p+ 20 l6*lokauvja certain place, what will be the sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distan1;xjqfpuv -fp5iw ro (jl94o3ce 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 experience if th 3oo;w9(1jffjqiprl4 -vu5 p xe 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, 5n yhkmg) qt;*qvfu12 whereas for a CD player it is 95 n yu1t2qmh gqfv*k;)5 dB. What 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 fe*rkw-yv*4em0,q es vrom a person speaking in normal conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphere centerqevws*v0e* 4y,rkme-ed 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 strivxfc39 gqv0mmz(:7qz kes 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, wp 2cgngf-- -pqrs (y*rhile 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 fcs r(q- 2*ryn-g-ppgturn 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 /i*jof+:ucf xf8zn 5pdB meter registered 130 dB when placed 2.8 m in front of a lo8xz/ :+ 5u*foifpjfcnudspeaker 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 of 2. ((xhxxlh,pu92 o 1)hc9bb oii0 dB. What is the ratio of thex1x2hul )(b,ioo(cb ihpx 9h9 amplitudes of two sounds whose levels differ by this amount? [Hint: See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by whajmy8 j.g r0brr*lss*.z4fl2s /y yrs7t factor will the intensity increase? Increase by a flj.s0*4sygbrz fy.*jslr 2s7 / mr8ry actor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but one has twicv,:8p ajv nf,oe the frequency of the othav8,:ofj,nv p er. What is the ratio of their intensities?   

  What would be the sound level (in dB) of a soundm :eh m ,9*vjpfda/ii9jq 7fw2 rc-9ve wave in air that corresponds to a displacement amplitude of vibrating air molecules of 0.13 mm at 300 f pvv2/ r79qde*- ihcjefwmj,i:9m a9Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud as ai . cgsyx)nv84 100-Hz tone that has a 50-dB sound level? (See x)4. gic nvy8sFig. 12–6.)    dB

What are the lowest and highest frequencies that an ear can detect when thf7l/rc4 (mqay e sound level is 30 dB?m(y4f rl7/q ac (See Fig. 12–6.)

  Your auditory system can accommodate a huge rang3azxsmob; h s5 9(-2jvbjvh4ce of sound levels. What is the ratio of highe-2jaho5h sb sj4xb9;vmz3cv( st 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 440 Hz. Tnak 1h s.k 9eqh7vsy,r1,:k*mnty ja2he length of the vibr9ykay 1 k n ,2:qhm7n.1,shskr*ajtve ating portion is 32 cm, and it has a mass of 0.35 g. Under what tension must the string be placed?    N

  An organ pipe is 112 cm long. What areyh n: uq8n1 y(ifty :hl;dx1y; the fundamental and first three audible overtones if the pipe qdy :uy1:n h1x(lif; t8;nhyyis
(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 frequen yytfnz/0abjtp*1br)c 3 n9;a cy would you expect from blowing across the top of an empty soda bottle that is 18 cm deep, if you assu/j; apy)bbnf9t 30rzy n1c*atmed 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 cc5za*sc *ztkanrv 0 um3din0)5 8 -i *nyivo5pipes spanning the range of human hearing (20 Hz5 imu-5 v z0i*cnn0o3c** askcv a)8nrzity5d 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 as its third(p mj pj6:xjqh8e3t93i eg j:t harmonic. What will be its fundamental frequency if it is fingered jg et9em(:3 jhi8pq3 x:jp6tj at a length of only 60% of its original length?   Hz

  An unfingered guitar string is 0.7 y1t bcnz ft67k/x/ygs2 no(1g3 m long and is tuned to play E above middle C (330tz y16oykfbg1ns xnt(c/g7/2 Hz).
(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) .pumbt1sfqrbyqsmkq.--suu8 u */3 m77/spw when the temperab /ws-87ssfyump1pq qkrbut7msm u3*- /..u qture 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 a3k9i /odjt93hcou8szi 2lgs8lox .9$^{\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 should t4+r9fzd dd wr4l0uz( d3 bq9jihe hole be that must be uncovered to play D abovlzu d(w+jr3 4db0i 9qfd9 dzr4e 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, b8r;g p sr ;0cel5u6vwkut not at any other frev5l6;kw;u 8cr ps0grequencies 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 g1(ft-i;koh1m )fjyf at both ends. It resonates at two successiv11;ikg(h y f)-ofm tfje harmonics of frequencies 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 qwxka5 2(o 3sdk7a d,b$^{\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 2zxe,,xb iy5b7hl r/borgan pipe i2 eb,hz ,rylxbb57/x at 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,g/osb cqa l,3 the 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 is the relationship of your answer to the information in the o3,gqbs/ a,cl 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, o-t11 xt i6azuwne of which is sounding 440 Hz. How far off in fruawzx1i 1-t 6tequency is the other string? ±    Hz

  What is the beat frequenc .ig3we5shdh lr d4d*7y 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 operates at 23.5 kHz, whydzap48n- kj1 ile another (brand X) operates at an unknown frequency. If neither whistle can be heard by humans when played separately, but a shrill wh418ydk-nj zap ine 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 tuni2b7i nsejl7rdi, g2.k ng fork and 9 beats/s when sounded with a 355-Hz tuning fork. What isd,br2 ie7. kj2nl sig7 the vibrational frequency of the string? Explain your reasoning.    Hz

  Two violin strings are z*d ;2xknp2vftuned to the same frequency, 294 Hz. The tension in one string is then decreased by 2.0dfnxvpk z22*;%. What will be the beat frequency 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 midd//rabl 4j)tp5 xewt) g4pkkn2 le C (262 Hz), but one is at 5.0°C and the other at 25.04wk /pet p)4k5 b/ra2lgx)t nj $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, u/thc+o fi,u15fjbtoo-m0u; 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, tho/+f- ,ufjm b; cu1o5tth i0uoe 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 one s5rfw mkoxxat,i1 m) 46xw ud)-peaker and 3.50 m from the oth)-x r u)5d xwo,twixm4f6ak1m er.
(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 at 132 Hz, but a piano t+i1c y zj-gwi1uner hears three beats 1+1gwz cijy-ievery 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. Hor*8vdp)1rp g dw many beats per second will be heard? (Assume 1d*8vgr d )prpT = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s siren is 1550 Hz when at (rkxz4d3 oi )qrest. What frequency do you detect if you move wi kd)z4q(3xrio th 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 a fgp 9rmb 0c4q+p c9x*)pda.kn vire engine whose siren emits at 1550 Hz moves at a speed of 32 m/k 9x .bnp4rq*dm0 c+)vapp cg9s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz source is moving towazqnz-v h y3e46rd you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exactly the same? Are they cl- 34ehvznzy q6ose? $f'_{source\,movine}$    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 freqo1 w) c04foefruency horn. When one is at rest and the other is m4 we 0fcrof)1ooving toward the first at 15 m/s the driver 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 at 50.0 kHz and receives them ret8q*7v sl.wzgnurned from an object moving dn 7.*z vwgq8slirectly away from it at 25 m/s What is the received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speedt/q3p a4z6kt/5uaj7m.zw bee5j8hk g l(ir: f of 5 m/s As it flies, the bat emits an ultrasonic sound wave with frequency 30.0 kHz. What fre/5/ g8piuw ba t(zzk3q5e6 4ht :jje7.marklfquency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler expoy08v+f4 a8q.4ztz0 hps fds yb r0d3zeriments, a tuba was played on a moving flat train car at a frequency of 75 Hz, and adyp4 30dab ot+h48zf0vys 08sz rzfq. 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 ultrasoundw,e:9y /qp ftvg+36pj,ocdzt waves to measure blood-flow speeds. Suppose the device emits sound at 3.5 MHz, and the speed of sound in+t,co6:3f9zgdvqjwtpp, /ye 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 using3fqi jelkm :-8 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 wiu*: 39b6fdu 2ltilw 8n wljt6wnd velocity is 12 m/s from the north, what frequency will observers hear who 362d l896n wl:jt *uutwlbwifare 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 land i)/uge,8dro(,t tcoxh a(m gb 3f 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 wttkh1qe 31w p2here the speed of sound is 310 m/s (a) What is the angle the shock wave makes with the direction of the airplane’s mo 1 3h12tkteqwption?    $^{\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 pla66uz61qaglrj*l. qp9p/8 d ztgerm )b+u:vs fnet where the speed of sound is omv z8: a l*b6zt+jerls)u/gpfg 6 q69dqu1.rpnly 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} $