What is the evidence o 4fkx3/i7;dgw jj- 0qv+ewuhthat sound travels as a wave?

What is the evidence that sound is a 7;uc qjaqbn ( 4neyk9yz m+s)-form of energy?

Children sometimes play with a homemade “telephone” by attacj +ns)*si hd ysc.ye;+hing a string to the bottoms of two pa+.sn chjd;*ei+ sys)y per 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 the other.

When a sound wave passes from air into cvb1b3 qtso8pel2: ,htl1h9awater, do you expect the frequency or wavelength oc 1e bllha83v:sqh2tb,p19tto change?

What evidence can you 5hp f0767qh jqyeva y)0n)g9tfxvjk5 give that the speed of sound in air does not depend significantlyyvyfnfa 9tjp 0q 0)75)h 65egxkvqj7h on frequency?

The voice of a person who has inhaled helium sounds very high-pitched. Why? h12 7w.hc,a 6qnvmjgu

How will the air temperature in a room affect gyxh ggzoq97p: 8w)p9the pitch of organ pipes?

Explain how a tube might be used as a filter to reduce the amp 40 fy ohm;s;r qmfzu+ij)8v w1eq5ok0litude of sounds in various frequency ranges. (An example is a car muffler)rowe 0fh; mf+s05o4ymz u;qqk 18ivj.)

Why are the frets on a guitar (Fig. 12–30) sp.0wkgingket8 y ,*..vooocz9ptoy nv);fb9(aced closer together as you move up the fingerboaroykign9,9c ewp08 vz) .( t;ntfko*ov y..gobd toward the bridge?

A noisy truck approaches you from behind a8 z ve)xe0g*dw building. Initially you hear 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 noisd vzgx 0we8)e*e. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due to “interference in space,” whereas 9vfte p,*o 4 c4no)b+y )gipgrbeats can be p )+4t )gp *n,bof94evcoir gysaid to be due to “interference in time.” Explain.

In Fig. 12–16, if the frequenpsrle* 34ml1fcy of the speakers were lowered, would the points D and C (where destructive and constfp1sr *3me l4lructive interference occur) move farther apart or closer together?

Traditional methods of protectinlf)y+ plj xw.h)-gp(:,vh w0 eqepi;sg the hearing of people who work in areas with very h.si)jqy wp e,eg f pp-0:w;vl l+)xh(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 ears?

Consider the two waves shown in Fig. 12–31. Each wave can be thought of as a s8q+,csg8 gpc7. sguv ;c8wanduperposigggn7 wp ccd;s, q8cusv8a+.8tion 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? Explain.
(12-31)
(12-18)

Is there a Doppler shift if the source andnd+o0 /8xbw jz observer move in the same direction, with the sameb o/8 xnz+0jwd velocity? Explain.

If a wind is blowing, bi (jeiej upblhb:. ,4eh;(u.will this alter the frequency of the sound heard by a person at rest with respect to the source? Is the wavelenbe( b: ju,ehjh;4 pl.be (i.uigth or velocity changed?

Figure 12–32 shows various positions of a child in motion on a swing. A monito,utnq(e5 w:z fr is blo tw: u5z,(nfqewing 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 length of a lake by listeni (q)4; zavj8x :qfazivng for the echo of her shout reflected a4;qx (jzqi:)8 fzvav 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 o qx73aj *br3crf his ship just below the waterline. He hears the echo of the sound refjqc rb3 x7r*3alected 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 wavelength a(i1vqgtimmp7b:a s9z w-0s4s 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 o1hbh32icaayx, po p-,n a foggy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How much time elapses before the backfire is heard ,,ab23h1pixo -ch ya p(a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a cliff. The splash it makes when stridw.4tc b 6csb4king the water below is heard 3.5 s late6.ccw4sb bd4tr. How high is the cliff?    m

  A person, with his ear to the ground, sees a huge stone strike the concre9 fmwioh4 mc3)x ytch7v :hp4*te pavement. A moment later two sounds are heard from the impact: one travehvct7yx ho)94:mmf chi*w 4p 3ls 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 the “5-secooh5ut 1j vt8(3qj1fx5so1ib s nd rule” for estimating the distance frob ht q(1osj1tvxu 5 513si8ojfm a lightning strike if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound /jl ;vuxa uak037m6qd 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 a sound a .ho 3-3rasc twzg,b4t9sbo:whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired simultan:6q3 stpu uxo/eously at a certain plao3/pu:t x 6uqsce, what will be the sound level if only one is exploded? [Hint: Add intensities, not dB’s.]    dB

  A person standing a certain distance from an airplane with four eqe2o *cxj9rexf.k ;o uql7j6g,z8 2gehually noisy jet engiul 9 2exo;f2chjr ,ekgej*zx oq768 .gnes 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’s.]    dB

  A cassette player is said to have a signal-to-noise ra m l:zam4mjl:z, 4qhu0tio of 58 dB, whereas for a CD player it is 95:lah qz4 4 jmm,l0:zmu 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 from a person speakbhz x iph1,:y 52j5wovif23no ing in normal conversation. Use Table 12–2. Assume the sound spreads roughly uniformly over a sphere centered on the mouth.,5ii13pjn 25oyf2hxv bhoz:w $\approx$    $ \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 t ym3l0mu.2)wc le+ gw -ones4whose 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 isb-o q )3joca4.2wsjhs rated at 40 W. (a) Estimate the sound level in decibels you would expect at a point 3.5 m from a loudspeaker connecte bcsja.)-jsh q2owo4 3d 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 pl)4wccwh 5jegtbyaym +u/(*t9 aced 2.8 m in front of a loudspeaker on the sj cu ca9(bt4e h ty/)5ww+myg*tage.
(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 2.0 dB. What vks;j 3 cnx2z7is the ratio of the amplitudes of two sounds whose levels differ by this amount? [Hint: S;7c nsj k3vzx2ee Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factor will t(o)btc jyh(p5 f,*bsthe intensity increase? Increase by a factor*5 tf ths(pboy bj)(,c of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal ;uoc87v tdj(+ ba)6pffcsz. b displacement amplitudes, but one has twice the frequency ofa( ;ju 7cz.f sdc+)b ovtb86fp the other. What is the ratio of their intensities?   

  What would be the sound level (in dB) of a sound wave p)s/wpyr 0 ej4in air that corresponds to a displacement amplitude of vibrating air molecules ofes yppj/ 04rw) 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what sound level to seem yvx k7 uu-;h8qas loud as a 100-Hz tone that has a 50-dB sounxh 7k- qvu8;uyd level? (See Fig. 12–6.)    dB

What are the lowest and hy ys*fe w7zn6/ighest frequencies that an ear can detect when the sound level is 30 dB? (See Fig. 127y ewf*/s6ynz –6.)

  Your auditory system can accommowr2jmf/6:fj rdate a huge range of sound levels. What is the ratio of hf2 jmj/ wr:rf6ighest 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 violinin4dr fp+vol 5: (cwn(935khz tfkn7(ic(v xp has a fundamental frequency of 440 Hz. The length of the vibrating portion is 32 cm, and it has a mhnc(lc3x7z(:(vk5+t9 dfrn5oi4w ( ppkni vfass of 0.35 g. Under what tension must the string be placed?    N

  An organ pipe is 112 cm longn r i3mortmn+2sojw-5 15q7fqgc9p 4j. What are the fundamental and first three audible ovitrc4qronq 7 sm5-g 15wfomj2np+39jertones 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 woul(ch mz*yrl/p (54lhafd you expect from blowing across the top of an empty soda bottle that is 18 cm deep, if you assumed rm( (za4l*l5hcy/fhpit 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-tubeu ep5 +n-6jvme pipes spanning the range of human hearing (20 Hz to 20 kHz), what would be the range omjp6 eu5 e-v+nf 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 thirk0p7np0xfx e0-fh q6 td harmonic. What will be its fundamental frequency if it is fingered at a length of only 60% of its original 0k0f76ex -f 0ppxtnhqlength?   Hz

  An unfingered guitar string is 0.73 m long akj+8 w0d8)) g6xbz,xfd es arond is tuned to play E above middle C (330 Hz)w,ab8 s8f6gozdx r+ ed0 x)k)j.
(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 middnpzqr(l; (0 /fcwee* jle C (262 Hz) when the temperature r (nw ;ecqez*p 0(jl/fis 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 a s-wlja,3l elg+lu+8r gm.l2it 20 $^{\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 the hole b6gt3q5x r q8:ex9xrxyss+/-rb cs 4ebe that must be uncovered to play D ab 9r+x5/sxt4 3re8x -:exbssycr bqqg6ove 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 vq tbvj wzbni)*(d /m qu882-acan resonate at 264 Hz, 440 Hz, and 616 Hz, but not at any other frequencies in between. (a) Show why this is an open or a(8- *vuzdjtm)wiqb8 aqv/2bn closed pipe. ----待选择----closedopen  (b) What is the fundamental frequency of this pipe?   Hz

  A uniform narrow tube 1.80 m lt6*vz a g-t6/o sgfsw(ong is open at both ends. It resonates at two successive harmonics of frequencies 275 Hz and 330 Hz. What i(6/swf6gto at* zgs-vs
(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 h umv v,4k q+qf*,bqu0$^{\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 oa wo7hg70f vo+;11r)wy teolcrgan pi1h7c1og0 w ov)tl wera7;o +yfpe at 20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximn d( wxvo am/i;p yc,)a0vi/3hately 2.5 cm long. It is open to the outside and is closed at the other end by the eardrum. Estimatvxa/d i0ni y/(w3pm,oacvh ; )e 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 beat every 2.0 s when trying to adjus:tbh,pd+1fcrq*xz qkd 4/*d ht two strings, one of which is sounding 440 Hz. How far off in frequency is the other sxfd1q dr:q+ cdh,k* 4z*th pb/tring? ±    Hz

  What is the beat frequency if middled (+ b,+pdp s):gmy6ktnud,w zb3)hie 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 23.5f)5 ova mt hu76/l /6x9cdykfuyjl o2. 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, e2kyf .6 vh )65t7ymoful/a c/o ujxld9stimate the operating frequency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded with a 350-Hz tut3 j7njl. lgw)ning fork and 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of the string? Explain y3wg)t 7jnl.jlour reasoning.    Hz

  Two violin strings akn(062q:wrd40- qy8 8wcuek vdvhb3g tik5vure tuned to the same frequency, 294 Hz. The tension in one string is then decreased b wr6q8cgui (v5ev k3kdbqn:uht2k d- 004w y8vy 2.0%. 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 twd9x( j *e uq)5zg;mvtao identical flutes each try to play middle C (262 Hz), but one is at 5.0°C and the other at 259t*xqz dg(av) jum;5e .0 $^{\circ} $ C?    beats/sec

  You have three tuning( 2szy/ls0vqg forks, A, B, 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(qls/z 2vgsy0 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 person l a1+,qa lm5kostands 3.00 m from one speaker and 3.50 m from the1l5+ kqlaom a, 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 1cp* n*n c2 n7vr.fep7 7xzfzw732 Hz, but a piano tuner hears three beats every 2.0 s when they are played together. (a)rn7e2v* p7zz7nc* f xw7f .cnp 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 ma 5unk25 wnf) 6ka qjeae lfaa1,w*,h*hny beats per second wf u5 kaanhlfw6n*,k w*h, 1qe5ae2 a)jill be heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of azl u(* 1qesk,+lvi s-g certain fire engine’s siren is 1550 Hz when at rest. What freques, z li1vk egus*+-(qlncy 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 a fire engine whose sir2c f(b(ax3/.lokq bj ten emits at 1550 Hz moves at a speedj x((l3o.tb/bak cf 2q of 32 m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz source iyoxom;/; hd(xs moving toward you at 15 m/s versus you moving toward it at 15 m/s Are the two frequencies exactly the same? Are they xx(o /ymdh;o;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 5-.y vg8dgc7gl poylexem). 6 with the same single frequency horn. When one is at rest and the other is moving toward the first at 15 m/6lyelo). gm8e. 5p7 ygxcgdv-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 62w sdg-mwwg. t t-*blat 50.0 kHz and receives them returned from an object moving directly away from it at 25 m/s What is the recei-d.-g gb*w6 wmw l2sttved sound frequency?    $ \times10^{ 4}$ Hz

  A bat flies toward a wall at a speed of 5 m/s As it flies, t1 ,j iv5ba db.,u)+u menyta7-kue6ai he bat emits an ultrasonic sound wave with frequency 30.0 kHz. What frequency does th -bade56tam+) ub1j7uukva,yi, i. nee bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the originalma85ltq4q rcz :qn35mj 2g b y,ue9c9e Doppler experiments, a tuba was played on a moving flat trcc:9e5 94qr3, 58y mbqu lnq2jmegtazain car at a frequency of 75 Hz, and 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 osq kbepp:6:e di-o2 1+uu ab6ultrasound waves to measure blood-flow speeds. Suppose the device emits sound at 3.5 MHz, and the speed of sound in human tissue is takeuodsb6p6bq- oi+ e p:2k eu1a:n 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 using ultrasonic waves of frequb ew5(w jhmaqx q(,n55ency $2.25 \times10^{ 6}$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 velocity is 12s v9/3)s4sepazi9o bb m/s from the north, wh/b)piv3 e4 ss absoz99at 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 moving on land ie5i k/,e.+zsqwpneib9 )gh+ a f 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 speedm6 x54y4uf o 1/meafzutf 2r0o of sound is 310 m/s (a) What is the angle the shock wave makes with the direo4u1for zftf5xea2uy6 m04m/ ction 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 speed of souyj;eeth+ 1ok-8i tth:zn6d t; nd is only about 3ht k+1en;; :ztoyi6 hj8td-te5 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} $