What is the evidence that sound tra+gy/tgrmcb di 6sa * t:x +h*9.on:yuyvels as a wave?

What is the evidence) fxw5/qh txaluzwk h,7 /yr r26ng(v9 that sound is a form of energy?

Children sometimes play with a homemade “telephone” by attaching a st2bkp+4rd e+ elring 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 ld+ kber4p +2eother 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 watejfuuin 1:y7kv-p5zj au 8x -;ir, do you expect the frequency or wavelength to 5-uunp;7k vjy:j8z1x -aufii change?

What evidence can you give that the jt43uf2kd538mmga,ifggjr 4 speed of sound in air does not depend significantly on frequej33ad,g gur2gtjm4 4 8ff m5kincy?

The voice of a person who has inhaled helium sounds very high-pitched. Whyp ;l2jn;x0h:cqv 9vdx( q; vrq?

How will the air temperature in a room affect z rd3 f4dr:(x9ca h2osthe pitch of organ pipes?

Explain how a tube might be used as a filtexge. lli*f0eygbt : 6:r to reduce the amplitude of sounds in va. l:e*lbe0:fi 6yt gxgrious frequency ranges. (An example is a car muffler.)

Why are the frets on a guiiw y- .nab33q(qd:lphg m; 4idtar (Fig. 12–30) spaced closer together as you move up the fingerboard-l d3 :hmnby3.p (gqi ;qa4iwd toward the bridge?

A noisy truck approaches you from behind a building. Initially you hear it ht6 42y:cjqdr5 :uglebut cannot see it. When it emerges and you do see it, its sound is suddenly “brighter” — you hearj5 4ydre 6:tg uqhlc2: more of the high-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said s 3nhdme7dc56 to be due to “interference in space,” whereas beats can be said to be due to “interfer36dh sc5m7ne dence in time.” Explain.

In Fig. 12–16, if the frequency of the speakers were lowe9f07tuzsu:w2v*+i ihez pc 0bred, would the points D and C (where destructive and constructive interference occur) move farther apart or close 2zc+zi*pi :u0ft u 9h0bvw7ser together?

Traditional methods of protecting the hearing of people who work in areas witnrxh*b3o (y,j h very high noise levels have consisted mainly ofjr *(xnh,3ob y 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 ears?

Consider the two waves shown in Fig. 12–31. Each wave cav 6j s1pwu4eh;4x5 tzrn 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), 6swtvx4uj;5ezp 4h r1 are the two component frequencies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and obseilpa- xu o d,s0nt959erver move in the same direction, with the same veloc,u 9s9-oxl 5nedi pta0ity? Explain.

If a wind is blowing, will this alter the frequency of the sd ;qh;syosc ;;)9ac1fzsv x7 : wrdo7aound heard by a person at fx;o9ac; v d )as7y;dwor7s sh:qz1c;rest with respect to the source? Is the wavelength or velocity changed?

Figure 12–32 shows varioh6 o 9ji-pmc5xctujgj/3jy( j;v:t-r us positions of a child in motion on a swing. A monitor is blowing a whistle in front of the child on the ground. A-5t: 6upgh9i; ct(oyxj c/vjj3-jrm jt which position, A through E, will the child hear the highest frequency for the sound of the whistle? Explain your reasoning.

  A hiker determines the length of a lake by listu yo ky:spazn(2+k; g4ening for the echo of her shout ry:k( zy 4;o 2ugkpsna+eflected by a cliff at 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 his ship just below the waterline. He hears the ech(2:q)x2aznr 6(shqd+px9p .xfz qeago of the soundp.a2x)(+r6 :zgdapxxz2(eqnfqs9h q reflected from the ocean floor directly below 2.5 s later. 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 wad5l m -ng2 dylgwy*3n5velengths 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 zuo a +5r9gqi6foggy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How much time elapses before the backfireg+ u9q rz5o6ia is heard (a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a cliff. The s tvev,r ff(ay0)f/5z6uq g ;nrxv51uqplash it makes when striking the water below is heard 3.t(z,rrfvvve5 qfquu1 f5xn)a6/0 ;yg 5 s later. How high is the cliff?    m

  A person, with his ear to tht ng ykxt ;vt*/voe)cebu*89 1e ground, sees a huge stone strike the concrete pavement. A motgocy )n **/tvv9ex1tkbeu8 ;ment 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+s f80rh g.grx the “5-second rule” for estimating the distancrg+sh80f.g r xe 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 the 1o s 1l4m*4k xcddmw+mpain 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 intensi:;j4(ue yej ez09kxkhty is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sou2n.+e2:jh bhqf v9z zu :cvvh2nd level of 95 dB when fired simultaneously at a certain place, whz u vcz 2:.v qveh22njb:9hh+fat will be the sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distakj9+ xhk.e of5nce 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 the captain shut down allh9koxf .je k5+ but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to have a signal-to-n)5d enz9udw a6oise ratio of 58 dB, whereas for a CD player it is 95 dB. What is the ratz)d6 den5u a9wio of intensities of the signal and the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power *,9 snf:4 vekjj1b97mo qpsu3o bu4zxoutput of sound from a person speaking in normal conversation. Use Table 12–2. Assuqevj,4s:smopub 7 uoxkjzf9 b*1 49n3me 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 q l9tbc-c: 56exh4bcr 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, qg jyt i4c w,82ce7jm3while the more modest amplifier B is rated at 40 W. (a) Estimate the sound level in decibels you would expect 3e7ytj,8 4jw2 cqimc gat 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 ry,3o / wdvh/ix,v5ae degistered 130 dB when placed 2.8 m in front of a loudspeaker on the stage. 5xw3 d e/davio,,h/v y
(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 typicalbgj(k4: i xq7-wip3q wly detect a difference in sound level of 2.0 dB. What is the ratio of tqw-g qp(:7k ij3xi4bw he 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 what factor will nr(wkf,4m st0gc7de / the intensity incrn e7(/k 0fc 4dgwmrst,ease? Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal dijbn3m8v:khhyipo: 08aq 69nvsplacement amplitudes, but one has twice the frequency of the other. jiah9:q3hvobm8n6 8k0np : yvWhat is the ratio of their intensities?   

  What would be the sound level (in dB)6udqje60 r/aa of a sound wave in air that corresponds to a displacement amplitude of vibrating aireajaq du6/6r0 molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem as loud as a 100-Hz tone tha1 b55x(6 0qmtkvqviq et( +lvgt has a 50-dB sound level? (Seeeb50q(tm vqvxv15ql6 kg+i (t Fig. 12–6.)    dB

What are the lowest and highest frequencies that an ea 4:1t a8of3gkga j4th5j*xx igr can detect when the sounok:x 1xa4i3hgag4t g58tjfj * d level is 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range o*+x xq/iyol q30se ic*igw1c+p8(z-mb etvk 7f sound levels. What is the ra*- q(e3 o8xqmi v 7gcwc tx /zl0+*b1pyi+kesitio 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 freque ue+,dk cuy8 48jfxcz(ncy of 440 Hz. The length of the vibrating portion is 32 cm, and it has a masu dxc48jyuf+kzc ,e 8(s of 0.35 g. Under what tension must the string be placed?    N

  An organ pipe is 112 cm long. What are the fundamental and first three amu( d zhf,5cev(, 3rzym00oowudible overtones if the pimy3d ,vz5efm ,oh00 u(orwc(zpe 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 frt)up-9b ut )hgequency would you expect from blowing across the top of an empty soda bottle that is 18 cm deep, if you assumed it wu thbgupt)9 )-as 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 spannitak088wjg9iig m 5/jo4eo 4zkng the range of human hearing (20 Hz to 20 kHz), what would be the range of the len8 g9g/oe ja5wz0ok4i t4 mi8kjgths 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 th(epqkz nu; g36ird harmonic. What will be its fundamental u;egzkp6( q3nfrequency 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 E abovo9wihe-y65gzl6pnz1 * ic.ki e middle C (330 Hzw*6ilp o.e6z nic59 yh1 -gzki).
(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 pio5p4f.+1uz m qgdwn,ppe that emits middle C (262 Hz) when the temperature iu n,qgm wop.fp45 d1+zs 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 23e/pnijv-3a 6g m5au4eid g8b 0 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpieceb3b*xaylg+on, twrvuy3 78ed(flvxx3q(g58 of the flute in Example 12–10 should the hole be that must3gy8*y857v lx,fnx qublt 3v r(x+dgwa bo(3e 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 wvm; 3r- bon9y616 Hz, but not at any other frequencies in between. (a) Show why this is an open o;y9mbowv- n3r r 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 sucob 3qbqt1 iqu-m)22 twcessive harmonics of frequencies 275 Hz bqqu2t1i32q)w b t-omand 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 o/8f,izrr-vu $^{\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 p n; zl:ftu c0(gbph- tips/v9 0jr-cn(resent within the audible range for a 2.14-m-long organ pip0b cis lrntnhjzc:90f(-p-p;ug(/v te at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approxjhv6 5kdvr-yy- 2/m81)b-htu mxrionimately 2.5 cm long. It is open to the outside and is closed at the other end b2nv--hy6jury dtm o-8xkv h )r1m5/ iby 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 graph of Fig. 12–6? $f_1$ =    Hz $f_3$ =    Hz $f_5$ =    Hz

  A piano tuner hears one bew+ xo.t*5i;( o1.w-ug1otl luqfdsp vat every 2.0 s when trying to adjust two strings, one of which is sounding 440 Hz. How far off in frequency is the other string? i; xqpo1v+( ll*wdg sut.fu t-owo1.5 ±    Hz

  What is the beat frequency if middle C (262 5p;9ml fg(ypzHz) 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 kv 4vt cwjy7v,q.o 3-aat 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 frequency 5000 Hz occurs when they are 3wcvvtkjo,- .7q 4yv aplayed simultaneously, estimate the operating frequency of brand X.    kHz

  A guitar string produce8lo (bxt6uwghe48qia 2ohrr /vb0) c;s 4 beats/s when sounded with a 350-Hz tuning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequencx o8b(uqcweo2v)a /gitbh846 lrr h0; y of the string? Explain your reasoning.    Hz

  Two violin strings are tuned to the same frequency, 294 Hz. The tension ifcsq vwf z/m40d -:y*w:3ol htn one string is then decreased by 2.0%. What will be the beat frequency heard when the two y : qmf3 sd 4ht:cf0wlo*vzw-/strings are played together? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be hedcrwvec6jsb;0 y.de ml ,783kard if two identical flutes each try to play middle C (262 Hz), but one is at 5s78w0dyjme rb6ce, ckv;3. ld.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 freqtpcge 1k5(ypn1wjh/,p +;gsz uency of 441 Hz; when A and B are sounded together, hgt(1 c5/y z;p,np +we1psjgk 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 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 persq*rh-**2 mkm )ccdhjapt3a81jte8 hl on stands 3.00 m from one speaker and 3.50 m from the other.c2r d8mh8-j)* lhhk t*a 1pctmjaq*e3
(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 b-.dkoqaj6hr-3m)q g uner hears three beats every 2.0 s when they are -qm j3rbdh6 a.-gq)ok 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. Hom kch564r rl;7 yf1lhjw many beats per second will be heardk6jllrmc1fy4h 7 ;5h r? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant freqf oi0w3on87 fuuency of a certain fire engine’s siren is 1550 Hz when at rest. What frequency do you detect if you move with a speed of 30 muf783oowif0 n/s
(a) toward the fire engine,    Hz
(b) away from it?   Hz

  You are standing still. What frequency do you detect if a fire engine whose 9 8ix0xjum)utsiren emits at 1550 Hz moves at a speed o txuixuj98)0 mf 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz source is movino :qw4-k- qrpbg toward you at 15 m/s versus you moving toward it at ok:r -bwpq4q- 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 with thdax3 mnbsa, x); 6us3*izl ;ise 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 hear sx;z3mialb x)6a3;*nd , ssius 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 )d *d u)gkq cab ,u,7ojz5y3 c+dzf8ldkHz and receives them returned from an object moving directly away from it at 25 m/s What is the received so,y z3 gdujd+))ouqbdz k7c*d5l, c fa8und frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As it flies, the bat emits an ultalp) fce y.3:2 3wfezarasonic sound wave with frequency 30.0 kHz. What frequency does the bat hear in the c3p fya2f:w .)a3e lezreflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was pl -5dbojpa9;;:4kkf ozl*p e ccayed on a moving flat train car at a frequency of 75 Hz, and 4dlpp;o;j 59kafccbok ez:-* 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 waves to measure blood-flom*uoo htn4:5m w 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 ih4ut o *onm:m5s 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 o,g1ej3vc 3k;dc2 zywm /gd : j(ut,vlff 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. p,ot ue83+(5lqtfgga When the wind velocity is 12 m/s from the north, what frequency will observers hear who are located, at r( ,t+et 5 uolpafggq38est,
(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 if 7jz8fu h-fh-)0+xxr( vjj fqu 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 y3ypvzc/y e*i; sq2d 0speed of sound is 310 m/s (a) What is the angle the shock wave makes with the direction of the airplane’sdv 2;c0s z*yqeiyp3 /y 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 planetldr:rlwb+. 1 d where the speed of sound is ob ld:+.lrwdr 1nly 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} $