What is the evidence that sound trkk ie;n+i48v cavels as a wave?

What is the evidence kt.:/nbcxha1 b+imz* that sound is a form of energy?

Children sometimes play with a homemade “telephone” by attaching a str2 dz55p9d0czq2o ly98zrdsc h ing 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 otherd0zrc dyp5 2zlhd929oqz85 sc 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 the frequen, pv9xqrwmbved g5.;h5o/pq:cy or wavelength to ch v.wxq:voqrpheb/, dpg5 5m9; ange?

What evidence can you give that the speed+s3 mm* kwv.5,yki5 pyhcj/fi of sound in air does not depend significantly on frequenc y5+k.w5,hmm/* c3ifiyv jkpsy?

The voice of a person who has inhaled helium sounds vyyi *a +x26mgony.ek/ery high-pitched. Why?

How will the air temperature in a room affect the pitch of organ xl4/jm bs 4b(tvhg-r/pipes?

Explain how a tube might beed0.l9q fqs) h used as a filter to reduce the amplitude of sounds in variou0f.lq9s eh) dqs frequency ranges. (An example is a car muffler.)

Why are the frets on a guitar (Fig. 12–30) spaced closer together asjqu,k r4suyz 9 sqz381 you move up the fingerboard toward the brs,14z z yjkqu s9qu38ridge?

A noisy truck approaches you from behind a building. Initia( 6duj84x yrzt-ne4 unlly you hear it but cannot see it. When it emerges and you do see it, its sound is 6 (u4jxr4ue zdnny-8t suddenly “brighter” — you hear more of the high-frequency noise. Explain. [Hint: See Section 11–15 on diffraction.]

Standing waves can be said to be due to “interference in space,” whercrc w52j*hdw,olo x3 3-zfr3ieas beats can be said to be due to “interference in time.” Explal ,ji*r w3oxc-w33rzhcf25od in.

In Fig. 12–16, if the frequency of the speakers were 5k/e470sdm /n+cu s tr xw n)m(s3bzamlowered, would the points D and C (whn (b5x0+ /7a4dkmscsu/rt s nemmz3)were destructive and constructive interference occur) move farther apart or closer together?

Traditional methods of protecting the hearin 1dnf+tck:h g7g of people who work 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 which detects th+t1 kfhnc:g7d e 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 b yvwhz8f .1lp+d ,:nyse thought of as a superposition of two sound waves with slightly different frequencies, as in Figwyls8vpf. yd ,:1hz +n. 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 s.we.rrq u, 8mahift if the source and observer move in the same direction, witq wm .,.urra8eh the same velocity? Explain.

If a wind is blowing, wi1 y5 76rv9e/pazshoysll this alter the frequency of the sound heard by a person at rest with respect to the source? Is thezsrs/ h75a9o6 1vy pye wavelength or velocity changed?

Figure 12–32 shows various positions of a child in motion on a swing. A monitors ys+fk wmyjzb7e7)( / 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 fjszmf7kw (7 ysb)+y/eor the sound of the whistle? Explain your reasoning.

  A hiker determines the length of jn j8(d .fadmw7a3j(va 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. Estimate the length of the lakeda( .njf8 vjmj d37(aw. $\approx$    $ \times10^{ 2}$m

  A sailor strikes themoz2lo 1b8h6w4b97a4w jwnf d side of his ship just below the waterline. He hears the echo of the sound reflected from the ocean floor directly below 2.5 s later. How 1w7b zl8dm a wbo4962wnjoh4f 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 wavelengthsq u1g hd+* kxi5emm;-o;p2opwq8r b;p 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 abovehqa -/ceh2vu g5pfrz 8gp76) g a school of tuna on a foggy day. Without warning, an engine backfire occurs on another boat 1.0 km away (Fig. 12–33). How much time 6 u/758p-g f hzpqhg )c2egvarelapses before the backfire is heard (a) by the fish,    s (b) by the fishermen?    s

  A stone is dropped from the top of a cliff. The splash it makesc;ti; vf67ael.g 2bu e when striking the water bel a2;c gv7el.;feui t6bow is heard 3.5 s later. How high is the cliff?    m

  A person, with his ear to the ground, sees(tt.js7 j z.ey a huge stone strike the concrete pavement. A moment later two sounds are heard from the impact: one travels in the a7 tsz.jyt(j.e ir 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 “d03mn r yojx1z-kx0n(0kyez.6.hm4 vve u o,e5-second rule” for estimating the distance from a lightning strikemm 0nvevkx x431 y0u.hz.nooy ,zk e06 dr(j-e if the temperature is (a) 30 $^{\circ} $ C, $\approx$    % (b) 10 $^{\circ} $ C$\approx$    %.

  What is the intensity of a sound at the pa sfdg2ngln/ 8oo71 x.oin 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 sle1a.1/t r 24vy j sczs:r9whpound whose intensity is $2 \times10^{ -6}W/m^2$?    dB

  If two firecrackers produce a sound level of 95 dB when fired simultaneousjn1*)m0) vv 1o6 odosvbnnfo,w y3m .nly at a cerf nwsv36vnn o) dy0.bo11oj)mvomn *,tain place, 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 equall6f2ysxakh5s b 11fy5ms (v- zdy noisy jet engines is experiencing a sound level bordering on pain, 120 dB. What sound level would this person experience if the capt1f 26vkz(sy5 1y 5hmfs-dxb asain shut down all but one engine? [Hint: Add intensities, not dB’s.]    dB

  A cassette player is said to havto1nby28;h , mg+hgwwcom q 2/e a signal-to-noise ratio of 58 dB, whereas for a CD player it is 95 dB. Wha;h1m o ,mwq82t/n ybg+hcg2wot 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 speaking in normaz6qo7 ,dn tx :(kw9vttl conversation. Use Table 12–2. Assume the soundn( 9twv76x :z,oq tdkt 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 whoseauvj ma0:t5p7 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 mor+wgt p nnbz.;y de5rfam,5)u2e 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 n5fpbu.y;r mzneg5+w , a)td2connected 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 me:5n/oci 8qz (fuw lnv)ter registered 130 dB when placed 2.8 m in front of a loudspeaker on the sn/) c u8nvlwo(q fi5z: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 2zg)g rgy1tolm8g(;tx0*oe5u .0 dB. What is the ratio of the amplitudes of two sounds whose levels differ by this amount? [Hint:ug1gzx )l(g 5tyor;0m* 8etog See Section 11–9.]$\approx$   

  If the amplitude of a sound wave is tripled, (a) by what factor will (-4;1/li(cuyn /agdcvv qqx uthe intensity increase // acv glcuyqxuqnd1v(i4- ;(? Increase by a factor of    (b) By how many dB will the sound level increase?    dB

  Two sound waves have equal displacement amplitudes, but onqfcnn96i r.q5i 8co/v e has twice the frequency of the othe 8fqi56c./n ni v9ocrqr. What is the ratio of their intensities?   

  What would be the so, )mg1:lujvygepnlm ku71a 43und level (in dB) of a sound wave in air that corresponds to a umguj)l 1lp7mnkg1ev a4:,y 3displacement amplitude of vibrating air molecules of 0.13 mm at 300 Hz?    dB

  A 6000-Hz tone must have what td; tc;rjr-h xzhk8+*sound level to seem as loud as a 100-Hz tone that has a 50-dB sound level? (See Fi*x tdh;z;8k rthjr+-cg. 12–6.)    dB

What are the lowest and highest frequencies that an eylv1q(gpn+ a qvh kr0;8l*1ko ar can detect when the sound level is 3k8(go1hq p+a;1l*vlvq0 yknr 0 dB? (See Fig. 12–6.)

  Your auditory systemu6s ghw9hbh9(t9; * 8nwmcr js can accommodate a huge range of sound levels. What is the ratio of highest to lowests9thhm8 9j;bw *sn gwru6(9 ch 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. The length o 8gr kdmdi 1e0-k of-e.(a 2uxu*/wcljf the vibrating portion is 32 cm, and itmj(cl d- /0*gauekdue -x2 oi8w1r .fk has a mass of 0.35 g. Under what tension must the string be placed?    N

  An organ pipe is 112 cm long. Wh1z+ , a )dkkvsrv*l1t 4wxv(ftat are the fundamental and first three audible overtones i d1lx v +*a zt1tkk,rvf(4)swvf 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 across the top of asdao7 ip e6ai3pmo())n empty soda bott m pods iea7(p36))aiole that is 18 cm deep, if you assumed 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 orga xxz. ,u0wy 6z)ro)rdics5ux1n with open-tube pipes spanning the range of human hearing (20 Hz to 20 kHz), what would r.s)duiw0 6 u1, xr5zz)oxy cxbe 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 harmonic. What l0xd/49alyy-j m/ epfwill be its fundamental frequency if it is 0p-9 xjy d/layef/4lmfingered 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 above q2 9;mgbdvsq7qv) xs 0middle C (330q)q 9gsv x7 d20mq;bsv 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 emi4/uscf gm rhvmgq5wl.ch1 siy 0m374; ts middle C (262 Hz) whenu1y vgmw /circl m5h4;sqf73.s m0h4g the 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 athcpar s86z9y qxq*+-zs e6rn) 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 be ;iumd3-n) r-k okceg+56eaun that must be unc3 o)-d;e+uekam nu5k -ir6cgnovered 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 616 Hz,i3xr y.y jb.;r but not at any other frequencies iir.yx 3; .rjybn 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 at (6 azb +p4;bbw0py;zs eb,upf both ends. It resonates at two successi pp;f wb6s +,az4b(ub0zpb;yeve 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 mbuhh94 6xkvx6y2*wr ;jcl1 a$^{\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 pr2b dml 6yx* ygter qk:g3r,22nesent within the audible range for a 2.14-m-long organ pipe at :m * ,t22qbrg2lye xy6rd3 ngk20 $^{\circ} $ C
(a) if it is open,   
(b) if it is closed?   

  The human ear canal is approximately 2.5 cm long. It isx)xzw.r/h7k tw 5 bylgl tj:o.i0 ps7p9,(b rf open to the outside and is closed at the other end by the eardrwyh7gl) ,k(b9x .pr.rpws/0tz 5 foilxbt:j7um. 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 onclnx hb; *6eh0b:uu3 oe beat every 2.0 s when trying to adjust two strings, one of which is sounding 440 Hz. How far off in frequency ;0:b6bhuuel n3 chx* ois the other string? ±    Hz

  What is the beat frequency if middle C (26n 1 nvl(3 ibyzf-t :l.(wpxsv-2 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 Xpwmb/viw 34,wi1e1 fio; g1ymq.)fwv ) operates at an unknf pi3o1;vi4.gwbiwm)q/1e v,y f1wmwown 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 frequency of brand X.    kHz

  A guitar string produces 4 beats/s when sounded with a 350-Hz tuning fork ad*jft( je9 6utzc *zy8nd 9 beats/s when sounded with a 355-Hz tuning fork. What is the vibrational frequency of the string? Explai fy69d* t8ejc(*ztujzn your reasoning.    Hz

  Two violin strings are tuned to the r r0gv; g:a+ ye9bu+ct.(o4 aayae1 fwsame 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: a+y gaa19cu +4:rgv0wae(r;ofb y t.eRecall Eq. 11–13.]    Hz

  How many beats will be heard if two identical flutsrfi*0q+o l5 zccl17e hy:,a ves each try to play middle C (262 Hz), but one is at 5.cz* qf: alol,cev 1y0 s7rhi5+0°C and the other at 25.0 $^{\circ} $ C?    beats/sec

  You have three tuning forks, A, B, and xx fd +0 fd p41fxjq97eulu 7i b8qme4y**a4zoC. 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, the beat frequency is 4 Hz. What are the possible frequencies of A and C? What beat frequimed* 41q4qx lz+bpyf7exaj fu 8f9u7x4*d0 oencies 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 akztcvbf o-fq(x+c 0+sp k0i*9 ;s/gmipart. A person stands 3.00 m from one speaker and 3.50 m frigzm-f+*pq ic 9tkx+0 f ;kc0(sbs v/oom the 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 Hz, burh.7l9 gxltmj7i /4 brt a piano tuner hears threih7x/rlb4 7trl9 gmj. e 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 wavelen .c(:l: oqrihrzs z.imy8l-n(gths 2.64 m and 2.76 m in air. How many beats per second will (snzirq-. lzci yh8:.m l(r: obe heard? (Assume T = 20 $^{\circ} $C)$\approx$    Hz(round to one decimal place)

  The predominant frequency of a certain,cxnd lo5;x, e8mwzsg9i.iz 9 fire engine’s siren is 1550 Hz when at reiczw;o zxg 5.sml 89 9einx,d,st. What frequency 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 sire5f .+9sjdbn ji3v4d pbztxf:1n emits at 1550 Hz moves at a speed of 32:i bj9tsvfd3b4pxjn15z.df + m/s
(a) toward you,    Hz
(b) away from you?   Hz

  (a) Compare the shift in frequency if a 2000-Hz source is mba0rvgj+e3o ,g*y ba15fgk9 uoving toward you at 15 m/s versus you moving toward it at 15 m/s Are *u13 yo,gbgjea ka95rf+ vg0 bthe 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 equo p .xl8o(r(rcipped 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 is the frequency .o8cx(( rro lpthe horns emit? Assume T = 20 $^{\circ} $C    Hz

  A bat at rest sends out ultrasonic soun5q4uhai y ffs*p8v 1u;d waves at 50.0 kHz and receives them returned from an obfsiyfp54a;q 8h1u *vu ject moving directly away from it at 25 m/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 eej b-zxc .1g77fa0pwa 1mo 6tcmits an ultrasonic sound wave with frequency 30.0 kHz. What fre0j z11mba7x7p.cwoa6f gc - tequency does the bat hear in the reflected wave?    $ \times10^{4}$ Hz

  In one of the original Doppler experiments, a tuba was playedahmc x:54f qq: on a moving flat train 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 thqfxh: :c qm4a5e station at a speed of 10 m/s ?   Hz

  A Doppler flow meter uses ultrasound waves to measure blood-flow speeds. Supposf)c */eu5 bu.id vhxrtyu2p7-e the device emits sound at 3.5 MHz, and the speed of sound in . feuxtpu)b/2c y5-v h7i*druhuman 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 using ultrasonic waves of freque/e, o agw)ka l1(4zb(jm aov8nncy $2.25 \times10^{ 6}$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.zwlmu8*5on 0cko4c zsb6 mw13 When the wind velocity is 12 m/s from the north, what frequency will observers hear who mzmuok3b4cww86szo cl5n 01* 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 movi+sbo oai )vqwg7e1*n8 ng 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 Mixdh35) 5+w rgd0 vsofach 2.3 where the speed of sound is 310 m/s (a) What is the angle the shock wave makes withis frdw53+0h x dgov)5 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 c(w (l/ le.u6qmsva(fthe speed of sound is only about 35 v(awlu lfmeq6.(/sc(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} $