What is the evidence that sound travels as a lqh*y8r hd-1:8yrpiv wave?

What is the evidence that sovs1 dt-(/c va1tmsf7rlnyr/7 und is a form of energy?

Children sometimes play with a homemade “telephone” by attaching arr1q8l6 hjb8o 6f;+5rhlcsb i string to the bottoms of two paper c 8 hbfr8sol b+h1jilr6;56q rcups. 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 froo a6+ ey4o)r cev:q;qfm air into water, do you expect the frequency or wavelength to change?4qroyc ;oqa+:ee)f6v

What evidence can you give that the speed of sound in air does not dep) izgidf6 rd/)end significantly on frequencf6ig))r/d dz iy?

The voice of a person f(,gc/8gc1b5 gsr bsc who has inhaled helium sounds very high-pitched. Why?

How will the air temperature in a room affect the pitch of organ pipe1*uoof 2;i 0qmlmf8cgjq// v hs?

Explain how a tube might be used as a filter to reduce the amplitude of : s ul:q hc,gwca5sjq8.bv0h .sounds in various frequency ranges. (An example is a 0 . gcubwsj s8,chv.:lq hqa5:car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced z3 h*pfso. bx;closer together as you move up thhs p*.3zxb o;fe fingerboard toward the bridge?

A noisy truck approaches you from behind a building. Initially you hea-wp l;fqk c (s;x+9jb4 d phqr1h3w.pkr it 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 11–15 on diffractiokc rd( w4 q+hjlp. q;3-p9 s;xkwhbfp1n.]

Standing waves can be said +))ktj lr: atpto be due to “interference in space,” whereas beats can be said to be due to “interference in tim): kjrtlp )ta+e.” Explain.

In Fig. 12–16, if the frequency of the sp-tzp2jw1vo *feakers were lowered, would the points D and C (where destructive and constructive interference occur) movej1-* owp vf2tz farther apart or closer together?

Traditional methods of protecting the hearing of people who e8 atjwm00 k7twork 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 wkt j0at 07m8ewhich 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 can b5 giu) obei 2-2fwecvf ,l6g9ye 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 frequenc6ei5u o y2f2)ggfv -ec ,9wlibies farther apart? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source and observer move*e fz6u)isk p8t*d3 cf in the same direction, with the same veki ft)8 3dse*pz*6ufc locity? Explain.

If a wind is blowing, will this alter the frequencf pv7vj*2c.j ly of the sound heard by a person at rest with respect to the source? Is the wavelength or velocitf7lcj.jv2pv *y changed?

Figure 12–32 shows various positions of a child in v,ae,4 /j ola/8 okugfrjp (c rxi9366dnv/pdmotion on a swing. A monitor ie6/af(, vx3u6ia/orj g/crl,4dkn po8pvj 9 ds 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 reasoning.

  A hiker determines the le+g*b7towva1ddx 6*t c ;uef pe h86gk*ngth of a lake by listening for the echo of her shout reflected by a cliff at the far end of the lake. She hears the echo 2.0 s after shouting. Estima 8xp*e;w*b+h 7 vt6aceoufgk tdg6d* 1te the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship just below the waterline.kasau d ,4l4-r He hears the echo of the sound reflected from the ocean floor directly below 2.5 s later. How deep is the ocean at t,l4d-auar4 k shis 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 wavelengthsgvf(hk9c0k/ x 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 day. Wiizr:lzu9 j--v3 zzuf -thout warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How much time elapses before the backfire is huz-3: -vujzz-l rizf9eard (a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a cliff. The splash it makes wh/n9n s4wom uv:en striking the watn9w4om unvs :/er below is heard 3.5 s later. How high is the cliff?    m

  A person, with his ear to the ground, seest9 d-u+ k n.o wlj/54q7extdj va1ane. 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 away did the impact occur? See Table 12–+txk957t ejdu.ej a1 wql-/.nndoa4v 1.$\approx$    $ \times10^{2 }$m

  Calculate the percent error made over one mile of distance by the “5-seco g o.rp:l-w xo8ile-)and rule” for estimating th-gwx. )ia-olp : rel8oe 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 the pain lh,sfk /fz()f(4b i v+0tzounievel 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 w,cr iz).)4io9vthebznv 3 y7sound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers rm t82uu,:emiproduce a sound level of 95 dB when fired simultaneously at a certain place, what will be the sound level if on2meut 8r:ui m,ly one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance frxo5 8(;p l1* epuk4xgm6j2 bxh7ungv com 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 all but one engine? [Hint: Add intensities, not dB’7;uncgj( p x85*bvx4khug1 plm2xeo6 s.]    dB

  A cassette player is said to have a signal-to-noise ratio of 58 djeiv14,gu v 0cB, whereas for a CD player it is 95 dB. What is the ratio cgveu i41 vj0,of intensities of the signal and the background noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output v9 :m ,),htf(adyjegfof sound from a person speaking in normal conversation. Use Ta t,hvafdj:y )gfm(9,e ble 12–2. Assume 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 eardrum whosex5 xh gtp43ar: 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(3cv3ole19 mlz; 2xmk 3 a7kfz f kc0ka*/drks amplifier B is rated at 40 W. (a) Estimate the sound level in decibels you would elzlkm3x3v ; drs a (*kfa2zkm9ckk/e73o 1c 0fxpect 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 130k utojn:19rn/9l/bw z8np3gxsc ok3 d*y-bv 5 dB when placed 2.8 m in front of a loudspeaker on t gt5zkx*9sko/ n13-:cuo3ly8v / nj bpnb d9wrhe 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 typica ,uzwl/a7:o bclly detect a difference in sound level of 2.0 dB. What is the ratio of the amplitaz l7/bwuc:,o udes 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 b ye8r9q ii,*uwill the intensity increase? brq, 89eiui*yIncrease by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacementk62w0xiiy: :uwo0j uj amplitudes, but one has twice the frequency of the other. What is the ratio of thiui yk2 0jow0::w uxj6eir intensities?   

  What would be the sound level (in dB) of a sound w+k9k-r 6yxxhth f1dy2 e0u ov5w un1-pave in air that corresponds to a displacement amplitude of vibrating p0wx r1x dvf2 +nykt-1- hhu69o5ykeuair molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem dvw znl4(k m,8as loud as a 100-Hz tone that has a 50-dB sound level? (See Fig wzd, 8lmv(4kn. 12–6.)    dB

What are the lowest and highest frequencies that an ear can detect when therq7p 4td; jy-i,nya(a ee.d2k sound level is 30 dB? (See Fig. i(-dyd etr.ke;2 nyj,7 p4aqa12–6.)

  Your auditory system can accommodate a huge range of sound levelsq)+ pii 8m6f-*vaj7v1 fmbrzfn)q zp1. What is the ratio of highest to lowest intens zqmvvb816 a)p*niji1mp7)fr -z+f qfity 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. The len;6nsgpf0vz0 t gth of the vibrating p;vgtfpsz 0n 60ortion 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 ary.tthohe t4-f wb*3y7e the fundamental and first three audible overtonewhthf 7t yto4*y.e-3bs 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 expect from blowing acrossf . t mf5bc.56p/zx:ra+mpzjf the top of an empty soda bottle that is 18 cm deep, if you assumed it p5m x.c+ rzf6./bfmjta: pz5fwas 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 spannin s9) xo: phzgt)rtu;k8g the range of human hearing (20 Hz to 20 kHz), w)tx89:) ;gopzu stkhrhat would be the range of the lengths of pipes required? $L_{20 Hz}$ =    m $L_{20 kHz}$ =    $ \times10^{ -3}$m

  A tight guitar string hasscmg u+ 8789iupkno. n a frequency of 540 Hz as its third harmonic. What will be its fundamental frequency if it is fingered at a length of only 60%8ni7g nk+c9.umospu 8 of its original length?   Hz

  An unfingered guitar string is 0.73 m long and is tuned to6 py 8lcvlzgo( 8qze.* play E above middle C (330 Hz).zy6zolqvlp g. (88c e*
(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 (24m 35mkkdw7 / wlz0max62 Hz) when the m/4mwl azk5x mk73w0dtemperature 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 j:;s40qrlsv,e t2vozzb k 7dp c1d,4kat 20 $^{\circ} $ C. By what percent will the frequency be off at 5.0 $^{\circ} $ C?    %

  How far from the mouthpiece ofg/b;wil r+:rt x*4)y egwlvt( the flute in Example 12–10 should the hole be that must be uncovered to play D above middw4: +itl/l)(gr* xbwev try;gle 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 resonaewl -r)z8 ,xccxlms+4 w+k9aq te at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (a) Show why this erm ) ac,w -4+x9lxzs8 c+lkqwis 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 atw+qsnew hi) +qrw.t* 9 two successive harmonics of frequencies 275 Hz and 330 Hz. What is tiwq)s .wn+ e9hq*r+ w
(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 w + 1bs2irh30h k9zusq$^{\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 wk).+mi8dr lfywo/c1h2 cixs55yfs , uithin the audible range for a 2.14-m-long organ sy+1shwm iyu 5c )fi2o,58lc f/x.k drpipe at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5nz msw:td12,dsg 3g. o cm long. 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 in the ear canal. What is the relationo.g zm 12dd3:,sgstwnship 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 onj)2:cikz-nacy/fe 8 x92gu ql e beat every 2.0 s when trying to adjust two strings, one of which is sounding 440 Hz. How far off in frequency is the othez2 2 cnu qg )8ycl-f:/k9ajxier string? ±    Hz

  What is the beat frequ2exwp)crm4eikt1c mw89v w l 2j jr/6.ency 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, while another (brand Xc;(peebw * b0d(mm+l/qtb pz-) 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 played simultaneously, estimate the operating frem-(bd0p b et/ e +pmbl(c*;wzqquency of brand X.    kHz

  A guitar string produces 4 bea(h5bvl)1 qgejts/s when sounded with a 350-Hz tuning fork and 9 beatsl) qeg5j(1hvb /s when sounded 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 yk-)o,qdxtl9qx 8:rz. The tension in one string is then decreased by 2.0%. What will be the beat frequency heard when the two strings are played togethe8:)zxoxk q,-9 lydrtq r? [Hint: Recall Eq. 11–13.]    Hz

  How many beats will be her4 m:e8wf/l 2zt tjhp6f8 kc6k (eo8rdard if two identical flutes each try to play middle C (262 8p 8rm26zor elkw f/et (kd6t4h :f8cjHz), but one is at 5.0°C and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fo 8kxfsbhgfm:+7 3u b.krk 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, the beat frequency is 4 Hz. What are the possible frequencies of A and C? What beatsk.m3xh:fbu +7 fgk8b 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 speaker and g*ks 7qgd9 ueid7 u+g53.50 m from theuq9d7se gg+udgi* 7k 5 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 at 132 H, o .6exh,ipm47huum iz, but a piano tuner hears three beats every 2.0 s when they are played together. (a) If one is vibrating at 6mi m 4 ,he,o7iphuux.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. How many beatsgtle8vu 57 +1 iwu;9devt3ghn per second +e8 3lniwt1d97v5the;ugvu g will be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequenc w1mlhi *xr6a6y of a certain fire engine’s siren is 1550 Hz when at rest. What frequency do you det6hrxlmi *61awect 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 iew5s6kf4x:pk vafo8 n -g)-rjy/i4u e f a fire engine whose siren emits at 1550 Hz moves at a spee8:rw5-f /k4 s aounkvf6-yei4) gx jped of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz s0 a+c9m *erthzource is moving toward you at 15 m/s versus you moving toward it at 15 m/s Are the twoa 9m rz+ct*0eh 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 equi6 ) n66ix;r8rmwo7ijihp9h xipped with 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)ro 679w8xn6h;ii jpmhiir x6 is the frequency the horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends h v-7vg sx,: toke1w-tout ultrasonic sound waves at 50.0 kHz and receives them returned from an object moving directly away from it at 25 m-v,xwt :vsh1e7-tk go /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 emitsgyv)c9d q5h b q0o22 kj6g fk wdqq1i(5tt1bo- an ultrasonic sound wave with freqdqb-bf qjd)g 6059wt ovkqho5 1icq2tk2(1 yg uency 30.0 kHz. What frequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was played o0e 1sy k rnfv)ve8vd-9n a moving flat train car at a frequency of 75 Hz, and a second identical tuba played the same tone w)eyds nv8v- e fvr0k19hile 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 wave21yx fsg flg.2s 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 expectesx1ylf2.2fgg d 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 wy48y cbn/o ;oultrasonic 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 573x( p5ivckydjl5) 1 jj0 Hz. When the wind velocity is 12 m/s from the north, what frequency will observers hear who are lo1jjyikx5()v c5p ldj3cated, 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 if its speed avm90anhho 6/ glf5ez; t 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 anp7kn-ny0ymyt0 o4 tsbu36/ qv 1od 3ot Mach 2.3 where the speed of sound is 310 m/s (a) What is the angle the shock wave make s3byu071-dntqyom0y43ovtkp n6 no/s 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 where the speedtxdeq5si:jn63 6u3yah(i o1d of sound is only abouy6jeun3di:dqa 6i oh3x1t 5s(t 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} $