What is the evidence that sound ax;r2 g w pqux-0)h)hjtravels as a wave?

What is the evidence that sound is a form of energy?zpda ++nkg1x2mr0g 7k

Children sometimes play -f4bfr tj0w b-with a homemade “telephone” by attaching 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 other cup (Fig. 12–29). Explain clearly how the sound wave travels from one cup to tj-t4 brfbw-f0he other.

When a sound wave pas, ati nr.t)0mfses from air into water, do you expect the frequency or wavelength0,ttrain.) fm to change?

What evidence can you give that the speed om6c0u xg9 2 rop9bl7lnf sound in air does not depend significlm u92p7cgrl b0x9no6 antly on frequency?

The voice of a person who has inhaled helium sounds very highy7xo .3w7uuhdwmu.cxi70 c 9h-pitched. Why?

How will the air temperature in a room affect ho: 8f2sfjy -iypt0a 2 i/t4cwthe pitch of organ pipes?

Explain how a tube might be used as a filter to reduce tm )adba/wnjvt-s5z 20he amplitude of sounds in various frequency ranges. (An example imjv 2ab-s dz tnw)/50as a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer together a2jk9jybtv kr8z- jt-3 +i/ vuvs you move up the fingerboard toward the brid 3jtziyjturv-2jk-v kb8 /9v+ge?

A noisy truck approaches you from behind a building. Initially you he 6ysjdf53h xa+ar 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 a xj 6y+sh3d5fdiffraction.]

Standing waves can be said to be due to gzkz gxl 1s.t0:5y2 m uf1ee;zlf)2le“interference in space,” whereas beats can be said to be d1 u0f ezf:mzgz k.5t2el 21ge)l xl;syue to “interference in time.” Explain.

In Fig. 12–16, if the frequency of th i,kpm6 ij f54lo.pgj,e speakers were lowered, would the points D and C (where destructive and constructive interferenj,pm6o f4i5pil ., jkgce occur) move farther apart or closer together?

Traditional methods of pfy,x6n62 .dqv4bt a acrotecting the hearing of people who work in areas with very high noise levels have consisted mainly of efforts to block or reducev,x4 c2badt.6q6aynf 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 ici:4 6ue6bwot1u xe5fn Fig. 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 frequencies farther apart? Et465b6 cxwueo1feu:i xplain.
(12-31)
(12-18)

Is there a Doppler shift if the source and observer move in the same5c7c jbv8 z fo:i3,xzx direction, wicx,cz:57vf83x zi ojb th the same velocity? Explain.

If a wind is blowing, will this alter the frequency of the sound heard by a pept/kw q2ss9 /hrson at rest with respect to th9sq swh/ 2tpk/e source? Is the wavelength or velocity changed?

Figure 12–32 shows various positions of a child ivem1kya20fr86i s9;c axubs 9n motion on a swing. A monitor is blowing a whistle in front of the chiiy;rce 1f ma kbsu x9869va0s2ld 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 length of a lake by listening for the echo oinu/ x(g1;eyr f her shout reflected by a cliff at the far end of the lake. She hears the echo 2.0 s after shouting. Estimatex ;rgiy1( n/ue the length of the lake. $\approx$    $ \times10^{ 2}$m

  A sailor strikes the side of his ship ju6v :+c6rqo bm(dnggf / j1wu9sst 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 ocecqsr(m:g j1 /nf o6ubd vgw69+an 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 wavelengt2 w+7wg8hy2rsv6vq mo hs 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 abc+naf+5 rso9hove a school of tuna on a foggy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). Howcfha9 n +sr5o+ 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 clifwl rsd)v ye;j2 /jkl*;f. The splash it makes when striking the water b) v;jk/sl;j2 r*l wedyelow is heard 3.5 s later. How high is the cliff?    m

  A person, with his ear to the ground, sees a m icd346tm8sul ie 2z1huge 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, andm3li1t 2m4e6szudi c8 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 9gwe8 xost)c) tj*m+tone mile of distance by the “5-second rule” for estimating* x c9e+ms)tt)jowt8g 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 the pa:b2q)jevttwd+ *sf z9in 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 s b(gqw,n;ot/ a sound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired simultan6zy9:r zh7,ms kxd r;y..crujj; 1vhdeously at a certain place, what will be the sound level9szjyc6 ;rhr z,d . um7h1 :r.;ykdxvj if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane with four equally noisyv:)ejbzgzo i egq t2pe. t;khsr /s20j*r6h9, jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would this person experience if the captaioh*6heetrgs0 p, g b2it/ ; j:9ezz2jk)rqv s.n 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, whereas forh9gpf m8q9eb* a CD player it is 95 dB. What is the ratio of intensities of the signal and the bamq *gp hf9b9e8ckground noise for each device? 58 dB =    $ \times10^{ 5}$ dB =    $ \times10^{9 }$

  (a) Estimate the power output of sound from a person speaking in normal converst91w q i wte 4wm8cy)n.jcc12eation. Use Table 12–2. Assume the so j 49 tm2t8ww1.eyecqw)1c nicund 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 whg flc5o:xp ajk 5p1m76ose 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,lpe 6n4ib8o r) while the more modest amplifier B is rated a)peni4b r l8o6t 40 W. (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 meterwm9wtlz :ty .2 registered 130 dB when placed 2.8 m in front of a loudspeaker on thelm :y9tz2wt w. 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 sounbj2z8l5 ( -r+qe5stz1jk laksd level of 2.0 dB. What is the ratio of the amplitudes of two sounds whose levels differ by this amount? [Hint: See Section 11j5tq2(1sl-k5z k z le+saj 8br–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factor will the intji pwv4m1 q1:eensity increase? Increase by w qvi4pje1m1:a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal diwao90*p:( sczvd 4xkosplacement amplitudes, but one has twice the frequency of the other. What is the ratio of their intensities? do0wx(vz4 9* kc:pa os  

  What would be the sound level (in dB) of a sound wave zcj*mg:q zt68in air that corresponds to a displacement amplitude of vibrating air molecules of 0.13 mm at 30086cz* jmq zgt: Hz?    dB

  A 6000-Hz tone must have what sound level to3(6jo ejq esm( seem as loud as a 100-Hz tone that h mj 6s(joe(eq3as a 50-dB sound level? (See Fig. 12–6.)    dB

What are the lowest and highest frequencies that an ear po2ef(j .9xw,cf/ j lbcan detect when the sound .fbjc9 j(wp/ol,xe2 f level is 30 dB? (See Fig. 12–6.)

  Your auditory system can accommodate a huge range of sound levels. What s/e)9ff9m0 wk5epzs w is the ratio of higfszs 5mfwe/9 0p 9e)wkhest 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 exi fmw2i 2)2vpn2s9dve/:e hfundamental frequency of 440 Hz. The length of the vibrating portion is 32 cm, and it has a mass of 0.35 g. Under what tension must the stv2ws2fn h2 ivp2i9)ee/:x dmering be placed?    N

  An organ pipe is 112 cm long. What are the fundamental and first*: fl :7 uquipd3r/ezy*j(sua three audible overtones if thj ua:upfd7zs* ryi(3q: l*/uee 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 yd4*aq,,hf4v qju q u+you expect from blowing across the top of an empty soda bottle that is 18 cm deep, if you assq+v d4y*qfua qj4,u,humed 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 ah s qc,7/e5clopen-tube pipes spanning the range of human hearing (20 Hq5a c7 lsec,/hz 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 )a) 65;d:y ywnsmkbba;.lfyr 540 Hz as its third harmonic. What will be its fundamenbfr6a)w)y y.;s;ad ml5 k:nbytal frequency 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 vc0uj11k v.ru tuned to play E above middle C cu1ur0.jkvv1 (330 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 (262qw5tiq( jq:nw b sae-e0) q(s/ Hz) when tq nwtewa(qqs b :j/0qie(5-s)he 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 at tr-vzwxd2 07 t j/ui0cupwf):na:d j120 $^{\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 12–10t;xin3c 72b ol should the hole be that must be un2nct; oxbl3i7covered 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 pw5im.qx*cdf -aw 0))bvqw 8 reipe can resonate at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (a) Show why this is i vwq)wdfc0r .*- waqe xb85m)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 succp q3bvs3.f* -cbh: fzqessive harm:vb.zb 3q sqhcpf-*3f onics 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 1g,ocd9 :txfz$^{\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 aud k7rnc 27ev78og ldxe(9 unxi+ible range for a 2.14-m-long organ p7c+oxnvu8r kx9n7edli 7 ( 2egipe 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 the outsidiof54 v om 8zv ace4u,a6qao67e 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 8c7ooe45oamzq6 4uvafiva, 6. 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 tr*, mbvb 4*cmrw ,df-kcying to adjust two strings, one of which is sounding 440 Hz. How far off in frequency is the o4bwrcc bk*v,f- ,mmd*ther string? ±    Hz

  What is the beat frequey/qihac;djna :9+s:o+)1nemusb-gp ncy 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 r0mes 4f 7jz0nary- i:onk7h2 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 played simultaneously, estimate the 0 e7a2o-fskj:4irny 0 nzhrm7operating frequency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded with a 350-Hz tunin5 +5gclwfby;e/wrfuu9x g r25g fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frec9 ue /gyfb55u x; grl+rww52fquency of the string? Explain your reasoning.    Hz

  Two violin strings are tundu 44r*wam .ofs3k+ rhed to the same 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 Eqkmda+r*4.s 43wh ufor. 11–13.]    Hz

  How many beats will be heard if two identical fl io a3;6qwafi5utes each try to play middle C (262 Hz), but one is at 5.0°C and thoiq56aaw 3i; fe other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and C. Fork B has a frer;0o9o nyxs80dy4*z (zp ma taquency 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 beat frequencies are possible when A0zx4*t mr9ns ;opo dy(ay0a8z 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 onez,uh x-/y5 n: ylszh+r speaker and 3.50 m from the/5lyzr +u -:zsx,y hnh 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 suppen0+na0 9 lneqosed to be vibrating at 132 Hz, but a piano tuner hears tnlaqn+ 0 0ene9hree beats every 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. How many b:nfwk;w8ae7 x eats per second will be heard? (Ax:wkwne a8f; 7ssume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain fire engine’s siren isq q yy+9etr.g 54(cj /yof08wdwez-qs 1550 Hz when at rest. What frequency do you detect if you move with a spq+.f qw-49qy8orz0( 5 wsd/cjty yegeeed 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 fire e *5*ghj:kkk qmodk08kngine whose siren emits at 18k jkg*km0 ko* k5:hdq550 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 towara;zqww6 4mp 3 hj,curhb;mc/:d you at 15 m/s versus you moving wj /rmb 3 :w;6,zcpm uqcha;4htoward 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 with the sa7(z 5,dd.qwp78m+xrvjhri lq me 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 the horns e dvpm ql78(w,+ i5jrd.q rxz7hmit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic sound waves atb mhk(55du49lmycp8 17w yjg h 50.0 kHz and receives them returned from an object moving directly away from it at 25 m/s What is 51my 4(d 75kwh 9l8cjubhmypgthe received sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wal .:qr mj7q2 :ncqciml3l at a speed of 5 m/s As it flies, the bat emits an ultrasonic sound wave with frequency 30qmmrjq n::qli7.2c3c .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 plaoeq f ),wois.o;b8m j7yed on a moving flat train car at a frequency of 75 Hz, and a second identio7f)w8m .qiooe s;j,b cal 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-flow spwdz 3 qk d15)ecwl3l3eeeds. 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 thlz1 wdqk3 )l cde353wee 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 ultrag -luaqw 1:lm3x- wmwf4wr98ddaa)6y/ qj bn-sonic 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 emitsl-;gdbfdv e )v0bxm ,6v:u t2eh9jrj5 sound of frequency 570 Hz. When the wind velocity is 12 m/jje2x)rdf: 9vv0t6, ;bb mg-el d5uvhs from the north, what frequency 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 movitq,l-tk6s iwl *7mv 2vng on 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 tpbw+b d8 7q7lMach 2.3 where the speed of sound is 310 m/s (a) What is the angle the shock wave makes 7bq7 d8bp tw+lwith 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 en4ah1uj0 g3l3.cef zspeed of sound is only aba34eh .lfg1zjnec0u 3out 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} $