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习题练习:gc textbook chapter 18 Electric Currents



 作者: admin   总分: 103分  得分: _____________

答题人: 匿名未登录  开始时间: 05月06日 13:02  切换到: 整卷模式

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1#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
What quantity is measurm1lk lux +:3c9p+ywf ved by a battery rating given in ampere-hours $(A\cdot H)$ ?
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2#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
When an electric cell is connected to a circuit, hj pg.g yf11r3electrons flow away from the negative terminal in the circuit. But within th1.ypgf hj1 r3ge cell, electrons flow to the negative terminal. Explain.
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3#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
When a flashlight is operated, whatmv/ah3w2 cwib 1w.f v;d.v ( fe6y-qzy is being used up: battery current, battery voltage, battery energy, battery power, or battery resistance? Ew/ w a-wc(e.zf.dfq3 yhbvm v;21 vyi6xplain.
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4#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
One terminal of a car battery is said to be connected to “gr qk08nfum:q tm, (pz*cound.” Since it is not really conne f:0,n*ckqm t8zq p(umcted to the ground, what is meant by this expression?
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5#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
When you turn on a water faucet, the water usually flows immediately. Yoi h4m9u5rxrkq(jd9 5ou don’t have to wau9x 45ko mi(5dr rhjq9it for water to flow from the faucet valve to the spout. Why not? Is the same thing true when you connect a wire to the terminals of a battery?
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6#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
Can a copper wire and an aluminum wire of the sagqvce nzvrp.3;i9oskye2 8/2 me length have the same resistance? vy2vion38p czq9.e 2k;gs/erExplain.
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7#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
If the resistance of a small pmmm87t9yfbe6u v 4x/ immersion heater (to heat water for tea or soup, Fig. 18–32) was increm8x94bym pt/ 7 6fuemvased, would it speed up or slow down the heating process? Explain.
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8#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
If a rectangular solid m)aw pho,0 t8ftade of carbon has sides of lengths a, 2a, and 3a, how would you connect the wires from a battery so as t0,pao tfw8t h)o obtain (a) the least resistance, (b) the greatest resistance?
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9#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
The equation $P\,=\,V^2/R$ indicates that the power dissipated in a resistor decreases if the resistance is increased, whereas the equation $P\,=\,I^2/R$ implies the opposite. Is there a contradiction here? Explain.
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10#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
What happens when a lmp(jg4/n6od mv d75mt b0 (undightbulb burns out?
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11#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
Explain why lightbulbs almost always burn nz-fbjt v (/rs s5l-7x4 w/cghout just as they are turned on and not aftjv s-g r-tzn7/l(h/ w5s4cbxf er they have been on for some time.
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12#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
Which draws more current, a 100-W lightbulb or a 75-W 67( gmw n (hwsrcp-fwjs f19)ibulb? Which has the higher resistance?sw1(nj( p)w6fs7c - mi9rgf wh
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13#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
Electric power is tr8*i:ml xs. (jaj0e.bp jhu,yuansferred over large distances at very high voltages. Explain how the high voltage reduces power losses in the transmiss.. yjmuh0b(lu jje 8pi:xas* ,ion lines.
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14#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
A 15-A fuse blows repea/+/t o/1nyiszgrd:1 xes43 hj3gsaa ktedly. Why is it dangerous to replace this fuse with a 25-A f a+3gg/a t/ y idz13sss4jxkhne/1:rouse?
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15#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
When electric lights are operated on low-frequency ac (9 d40m0ol j-*gff gtthsay, 5 Hz), they flicker t0t-jo9df * 4gm0hgl fnoticeably. Why?
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16#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
Driven by ac power, the same electrons pass back and forth through(;xpjc-1kf oq your reading lamp over and over again. Explain why the light stays lit instead of going ouj (;c- 1qopkxft after the first pass of electrons.
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17#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
The heating element in a toaster is made of Nichrome wire. Immediately ; - evts1pphpt8 1o2mivn)wu(p iq2b6after the toaster is turned on, is the cubo6tpswqm;ie )vpvp1tn- 28 p(12i hurrent $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.
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18#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
Is current used up in a rbewwe6 *ek4gn5d 1vn, yl*yp- esistor? Explain.
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19#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
Different lamps might have batteries connected in either of the two ar:9zv r/gr ,:ap iozs7xrangements shown in v r p/:9zigzs,aor:x7
Fig. 18–33. What would be the advantages of each scheme?

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20#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A current of 1.30 A flows8gltk2fq 3mo7c,d b; f in a wire. How many electrons are flowing past any point in the wire 3q,fb dt2g fk;cm7ol8 per second?    $ \times10^{18 }\;electrons/s$

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21#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A service station charges a battery using a current of 6.7 A for 4z ajpb19u i.f5 v0,jqcil:lnou- .mhs+8wfa 5.0 h. How much chi8jq js hfbluwip0foc l.m u-91a z4,.v5+:an arge passes through the battery?    $ \times10^{ 5}\;C$

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22#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  What is the current in axdb7;02r : n k0 q;wchb1oteoqercr 3+mperes if $1200\,Na^+$ ions flow across a cell membrane in $3.5\mu s$? The charge on the sodium is the same as on an electron, but positive.    $ \times10^{-11 }\;A$

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23#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  What is the resistance of a toaster nanc* q wvt3r3)kp(cvul+)y8 if 120 V produces a current of 4.2 A?    $\Omega$

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24#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  What voltage will produce 0.25 A of current throug5+k gjp-:corn h a $3800-\Omega$ resistor?    V

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25#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A hair dryer draws 7.5ga 0qpi vm; 3maoy1/ ke(nsm/8 A when plugged into a 120-V line.
(a) What is its resistance?    $\Omega$
(b) How much charge passes through it in 15 min? (Assume direct current.)    $ \times10^{ 3}\;C$

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26#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  An electric clothes dryer has a heating element with a resislkoza5wx0d 73172fe7u nvtn vtance of $9.6-\Omega$.
(a) What is the current in the element when it is connected to 240 V?    A
(b) How much charge passes through the element in 50 min?    $ \times10^{ 4}\;C$

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27#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A 9.0-V battery is connected to a buju (x,vs1gt14 ciiq 2llb whose resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

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28#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A bird stands on a dc electric transmission line carrying 2800 A (Fig. 19npdt hfd5+;nn0 rw5a8–34). The line haf9apd n0+h nrw 5t5d;ns $2.5\times10^{ -5}\;\Omega$ resistance per meter, and the bird’s feet are 4.0 cm apart. What is the potential difference between the bird’s feet?    $ \times10^{-3 }\;V$

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29#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  An electric device draws 6.50 A at 240,lew 5, 4bxaoxuvg94r V.
(a) If the voltage drops by 15%, what will be the current, assuming nothing else changes? $\approx$    A (retain one decimal places)
(b) If the resistance of the device were reduced by 15%, what current would be drawn at 240 V? $\approx$    A (retain one decimal places)

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30#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A 12-V battery causes a current of 0.60 A through a resistoxbbg58-zi -cl yex*.u r.
(a) What is its resistance, $\approx$    $\Omega$
(b) how many joules of energy does the battery lose in a minute?    J

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31#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  What is the diameter of a 1.00-z 0dq12ww-r66vae nd t(5eyk.. jidcm m length of tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

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32#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  What is the resistanc kvrtq/m,f. /i uzn;w4e of a 3.5-m length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

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33#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  Calculate the ratio of the resi 0(a ily+vjg hge-uu0q ;3l/kestance of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mmu ly q03lg(a e-0iuk +j;vge/h in diameter.   

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34#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  Can a 2.5-mm-diameter copper wire have the s3xsm)b; : fmbname resistance as a tungsten wire of the same length? Give numerical denbbx :f3ms) m;tails.    mm

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35#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A certain copper wire has a resim.b7s re) ru:djp j lr jsl;7il*,v4e0stance of $10.0\Omega$ At what point along its length must the wire be cut so that the resistance of one piece is 4.0 times the resistance of the other? What is the resistance of each piece?
$R_{short }$   $\Omega$
$R_{long }$    $\Omega$

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36#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  How much would you have to bft( j1vc+s7zg :gt uq(e +z;lraise the temperature of a copper wire (originally at e vtjg; g z+u:l(cfz1+qb7 t(s$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

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37#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  Estimate at what temperature coppeyahc4 a/i qo01rutp;4r will have the same resistivity as tungsten does ata io;u /h1rpyaq0 44ct $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

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38#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A 100-W lightbulb has a resismf3cl hz8tj99 cak 0r1tance of about $12\Omega$ when cold ($20^{\circ}\,C$) and $140\Omega$ when on (hot). Estimate the temperature of the filament when hot assuming an average temperature coefficient of resistivity $\alpha\,=\,0.0060(C?)^{-1}$ .    $^{\circ}\,C$

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39#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  Compute the voltage drop along a 26-m l cm0kvv36 cij+ength of household no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm and carries a 12-A current. jm6vic v3c0k+   V

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40#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A rectangular solid made of carbon has sides of lengths g6gzgs0.gb fw da4qnf5 ( sr8/1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y6g w.0 bgdfrn(8zg f aq45gs/s, and z axes, respectively (Fig. 18–35). Determine the resistance for current that passes through the solid in
(a) the x direction,    $ \times10^{ -4}\;\Omega$
(b) the y direction,    $ \times10^{ -3}\;\Omega$
(c) the z direction. Assume the resistivity is $\rho\,=\,3.0\times10^{ -5}\;\Omega\cdot m$.
   $ \times10^{ -3}\;\Omega$



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41#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  Two aluminum wires have the same resistance. If one + p:ybc1cg-t ka4at 29fw0 vxlhas twice the length of the other, what is the ratio of the diameter of the longer -0+: b gvp x2ta14ca9lf kwcytwire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

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42#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A length of aluminum wire is connected to a precision 10.00-V power supply, anddh0z:q s;;henx kxq6. a current of 0.4212 A is precisely measured a k; ezdhn:x;06xs hq.qt 20.0$^{\circ}\,C$. The wire is placed in a new environment of unknown temperature where the measured current is 0.3618 A. What is the unknown temperature?    $^{\circ}\,C$

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43#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A 10.0-m length of wire consisujp- e.y/;q usts of 5.0 m of copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltagueq-jp; u /ys.e difference of 85 mV is placed across the composite wire.
(a) What is the total resistance (sum) of the two wires? $\approx$    $\Omega$(retain two decimal places)
(b) What is the current through the wire?    A(retain two decimal places)
(c) What are the voltages across the aluminum part and across the copper part?
$V_{Cu}$    V(retain three decimal places)
$V_{Al}$    V(retain three decimal places)

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44#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  For some applications, it is important that the value of a resistance not cx-i cm v5px1*n0lb-p k)d 7g cv.kwe+uhange with temperature. For example, suppose y7x*-kwi+v1 0 5l dmgcnpxk p ).vub-ecou made a $4.70-k\Omega$ resistor from a carbon resistor and a Nichrome wire-wound resistor connected together so the total resistance is the sum of their separate resistances. What value should each of these resistors have (at 0$^{\circ}\,C$) so that the combination is temperature independent?
$R_{0C}$   $\Omega$
$R_{0N}$   $\Omega$

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45#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  The heating element of an electric oven is designed to produce 3l t1(zm6 b1xry7jxj(r .3 kW of heat when connected to a 240-(x 1r1mtyx(76rbj lz jV source. What must be the resistance of the element?    $\Omega$

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46#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  What is the maximum z1p/ phk 8ylw8o6 zpytl*ci(.dx8cl*power consumption of a 3.0-V portable CD player that draws a maximum of 6w . z8*p/lclkxyh 8 t*1doczlip8p (y320 mA of current?    W

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47#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  What is the maximum voltage that can be applied acr,yh i:dwvw jk0a+64g* m:jumioss a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

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48#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  (a) Determine the ressdrpaat+z3 a2n52 fh5d++ cty istance of, and current through, a 75-W lightbulb connected to its prodnata+z+2d35r2ypc t+s5hf aper source voltage of 120 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

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49#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A 115-V fish-tank heater is rated at 110 W. Czyurns /w;n*r /n*u)m alculate
(a) the current through the heater when it is operating,    A
(b) its resistance?    $\Omega$(Round to the nearest integer)

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50#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A 120-V hair dryer has two vy,j2 ht./s+p96 45k+ht pwtdshaysc settings: 850 W and 1250 W.
(a) At which setting do you expect the resistance to be higher? After making a guess, determine the resistance at
(b) the lower setting;    $\Omega$
(c) the higher setting.    $\Omega$

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51#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  You buy a 75-W lightbulb in Europe, where electricity is deliveiydd 47ki/-qr- - nchyred to homes at 240 V. If you use the lightbulb in the United States at 120 V (assume its resistance does not change), how bright will it be relative to 75-W 120-V bulbs? [Hint: assume roughly thati4q--7c/dydk-yi h rn brightness is proportional to power consumed.]    as bright

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52#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  How many kWh of energy does a 550-W toaster use in the morning if it isd 0*daixr5n3gjt pz)x ja265e in operation for a total of 15 min? At a c6jda2tnz5xer gj5 a i*0d)p3xost of $9.0\,cents/kWh$, estimate how much this would add to your monthly electric energy bill if you made toast four mornings per week.
energy $\approx$    kWh
cost $\approx$    cents/mouth

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53#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  At 0.095 dollars per kWh, what does it cost to leave a sxdnp u64 e;vfy 6)zv46cnc(n25-W porch light on day annp;z4vc)n e 6cux 4s6dv n(yf6d night for a year? $\approx$    dollars

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54#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  An ordinary flashlight uses two D-cell 1.5-V batteries conn/wx/eylg /r8;s nklf.ected in series as in Fig. 18–4b (Fig.wsey x f//k8.g ll;/rn 18–36). The bulb draws 450 mA when turned on.
(a) Calculate the resistance of the bulb and the power dissipated.
$\approx$    $\Omega$(retain one decimal places)
   W
(b) By what factor would the power increase if four D-cells in series were used with the same bulb? (Neglect heating effects of the filament.) Why shouldn’t you try this?   

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55#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  What is the total amount of energy stored in a 12-tae/ y e(;o28keyjwomnm w20.V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

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56#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  How many 100-W lightbulbs, connected to 120 V as in Fig. 18–20, can be usedo;hfo 2 ;s9ey iqtdm)/b(xs0 m without blowing afht( eyo9d)xiqsb0 2 mm/s;o; 15-A fuse?    bulbs


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57#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  An extension cord made of two wires of,a2d-*t ql dnw diameter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric heater which draws 15.0 A on a 120-V line. How muc d td2n*w-lqa,h power is dissipated in the cord?    W

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58#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A power station delivers 62 yi1; 8+knsuz-wn .tfh0 kW of power at 12,000 V to a factory through wires with tt.-f;wy8u1ns ki +hnzotal resistance $3.0\Omega$ How much less power is wasted if the electricity is delivered at 50,000 V rather than 12,000 V?    $ \times10^{ 3}\;W$

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59#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  The current in an electromagnet connected to a 240;*rm vau6 zv4*he d+lgl pp2k1-V line is 17.5 A. At what rate must coolpdr mla ;u6 v+4gv*1p2z*kheling water pass over the coils if the water temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

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60#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A small immersion heater can be used in a ca+*ve (d zduqi-ife5 p3nzf.*jr to heat a cup of water for coffee or tea. If the heater can i.idj(nq + pfez f- zd5e*v*u3heat 120 mL of water from 25$^{\circ}\,C$ to 95$^{\circ}\,C$ in 8.0 min,
(a) approximately how much current does it draw from the car’s 12-V battery, $\approx$    A(Round to the nearest integer)
(b) what is its resistance? Assume the manufacturer’s claim of 60% efficiency.    $\Omega$

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61#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  Calculate the peak cym1 c v;r)jww0urrent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

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62#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  An ac voltage, whose peak valabn*(i6ce b *fue is 180 V, is across a $330-\Omega$ resistor. What are the rms and peak currents in the resistor?
$I_{peak}$$\approx$    A(retain two decimal places)
$I_{rms}$ =    A

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63#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  Estimate the resistance of the o6(nbdp4 :k i)asjq,l $120-V_{rms}$ circuits in your house as seen by the power company, when
(a) everything electrical is unplugged,
(b) there is a lone 75-W lightbulb burning.    $\Omega$

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64#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  The peak value of an alternating current in a 1500-W device *b yf)t5+ ifo)nkiizyj +t 96tis 5.4 A. What is the rms voltage across it nob9ffi+ k6ijz +y5) y*tti)t?    V (Round to the nearest integer)

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65#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  An 1800-W arc welder j lc) t(8p l1fvpxv:/ kdk+wt:;j:cjv is connected to a $660-V_{rms}$ ac line. Calculate
(a) the peak voltage$\approx$    V(retain one decimal places)
(b) the peak current.    A

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66#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  (a) What is the maximum instantanera *d4hw nil:4ous power dissipated by a 3.0-hp pump connected to a *nl4ihdw:r4 a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

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67#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A heater coil connecte0f gqon +pu88xj, jeu/d to a $240-V_{rms}$ ac line has a resistance of $34\Omega$.
(a) What is the average power used?    W
(b) What are the maximum and minimum values of the instantaneous power?
$P_{max}$    W
$P_{min}$    W

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68#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A 0.65-mm-diameter copper wumr sc( +s*h9eire carries a tiny current of $2.3\mu A$. What is the electron drift speed in the wire?    $ \times10^{-10 }\;m/s$

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69#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A 5.80-m length of 2.0-mm-diameter wire carries a 750-mA curgzf v19xr -hqou9*oo9rent when 22.0 mV is applied to its ends. If the drif qo99*go-zhu rov 9x1ft speed is $ 1.7\times10^{-5 }\;m/s$, determine
(a) the resistance R of the wire, $\approx$    $\Omega$(retain three decimal places)
(b) the resistivity $\rho$.    $ \times10^{-8 }\;\Omega\cdot m$
(c) the number n of free electrons per unit volume.    $ \times10^{28 }\;e^-/m^3$

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70#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  At a point high in the Earth’sodxc 3:oni nu1t3yz893 p fr-m atmosphere, $He^{2+}$ ions in a concentration of $ 2.8\times10^{12 }\;/m^3$ are moving due north at a speed of $ 2.0\times10^{6 }\;m/s$. Also, a $ 7.0\times10^{11 }\;/m^3$ concentration of ${O_2}^-$ ions is moving due south at a speed of $ 7.2\times10^{6 }\;m/s$. Determine the magnitude and direction of the net current passing through unit area $(A/m^2)$.    $A/m^2$  

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71#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  At a point high in t2px8u9l k 9b 8axx ysm/qaco)(he Earth’s atmosphere, $He^{2+}$ ions in a concentration of $ 2.8\times10^{12 }\;/m^3$ are moving due north at a speed of $ 2.0\times10^{6 }\;m/s$. Also, a $ 7.0\times10^{11 }\;/m^3$ concentration of ${O_2}^-$ ions is moving due south at a speed of $ 7.2\times10^{6 }\;m/s$. Determine the magnitude and direction of the net current passing through unit area $(A/m^2)$.    $A/m^2$  

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72#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  What is the magnitude of the e5af -hy3b7 uiolectric field across an axon membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

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73#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A neuron is stimulated with an electric pulse. The action potential wv) n4 )nu3ocedx51cp is detected at a point 3.40 cm down the axon 0.0052 s later. When the action potential is detec15) u4)ncpo3xn dvcewted 7.20 cm from the point of stimulation, the time required is 0.0063 s. What is the speed of the electric pulse along the axon? (Why are two measurements needed instead of only one?)    m/s

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74#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  Estimate how much energy is required to transmit one action em*;/kn60tssul nw4t mw /)gspotential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored b0en* ku)sn; 4mtwmstsw6/g/ ly charging the axon capacitance; see Section 17–9]. What minimum average power is required for $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

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75#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  During an action potee:hgv(:4a azy d2f 2qsntial, $Na^+$ ions move into the cell at a rate of about $3 \times10^{-7 }\;mol/m^2\cdot s$. How much power must be produced by the “active $Na^+$ pumping” system to produce this flow against a $+30-Mv$ potential difference? Assume that the axon is 10 cm long and $20\mu m$ in diameter.    $ \times10^{-9 }\;W$

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76#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  How many coulombs are there in 1.00 amiinhgu o-ml9ze0a68 3c a4gd .pere-hour?    C

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77#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  What is the average current drawn by a 1.0-hp 120i* nb acy-5ju4-V motor? $(1 hp\,=\,746\,W.)$    A

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78#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A person accidentally leo3ez/t(uzryjwtj *2vibe 8m5 st 0;9maves a car with the lights on. If each of the two headlights uses 40 W and each of the two taillights 6 W, for a total of 92 W, how long will a fresh 12- js9tu/ 82bvr3z5j;wm e(imy0o * ztteV battery last if it is rated at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

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79#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  The heating element of a 110-V, 1500-W heater is 5.4 m f5gc.vl zr( 3-r81trjw0 oshmlong. If it is made of iron, what must irztovfs(. r ghmrl53j 18 0w-cts diameter be?    $ \times10^{ -4}\;m$

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80#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  The conductance G of an object is defined as the reciprocal of the resisq79liz e(hg1 jtance R; tha(7 jz1g9iql het is, $G\,=\,1/R$. The unit of conductance is a mho $(=ohm^{-1})$, which is also called the siemens (S). What is the conductance (in siemens) of an object that draws 730 mA of current at 3.0 V?    S

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81#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A small city requires about 10 Md5(6up* qy b pw*h/xznwec--jW of power. Suppose that instead of using high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a two-wire line of 0.50-cm-diameter copper wire, estimate the cost of the energy lost to heat per hour per meter. Assume the cost of ec/ h-dw 6z 5w*pj*nxpqbu-ye (lectricity is about 10 cents per kWh.    dollars per hour per meter

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82#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  (a) A particular household uses a 1.8-kv5dpfuhge;*7s 4:2y y l-roi fW heater $3.0 h/day$ (“on” time), four 100-W lightbulbs $6.0 h/day$, a 3.0-kW electric stove element for a total of $1.4 h/day$ and miscellaneous power amounting to $2.0 kWh/day$. If electricity costs $0.105 per kWh, what will be their monthly bill (30 d)?    dollars per month
(b) How much coal (which produces $7000 kcal/kg$) must be burned by a 35%-efficient power plant to provide the yearly needs of this household?    kg of coal

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83#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
A length of wire is cut in half and the two lyn)wl:- cmxt:engths are wrapped together side by side to make a thicker wire. How does the resistance of thi): c ynm-xltw:s new combination compare to the resistance of the original wire?
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84#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A 1200-W hair dryer is designed f2 x-un4c qgi;gor 117 V.
(a) What will be the percentage change in power output if the voltage drops to 105 V? Assume no change in resistance.    % decrease
(b) How would the actual change in resistivity with temperature affect your answer?

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85#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  The wiring in a house must be thick enough so it does not become skc2gr5 kvr,-aoq3 +p jo hot as to start a fire. What diameter must a copper wire be if it r garq2kv,5+ 3-op cjkis to carry a maximum current of 35 A and produce no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

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86#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  Suppose a current is given by c+lj he +w8g96,jm snathe equation $I\,=\,1.80sin210t$, where I is in amperes and t in seconds.
(a) What is the frequency?    Hz
(b) What is the rms value of the current?    A
(c) If this is the current through a $42-\Omega$ resistor, write the equation that describes the voltage as a function of time. (  sin 210 t)V

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87#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A microwave oven running at 65% efficiency delivers 950 W:6qso8x8y jyl of energy per second to the interior. Fin8joyly:qx s 68d
(a) the power drawn from the source,    W
(b) the current drawn. Assume a source voltage of 120 V.    A

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88#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A $1.00-\Omega$ wire is stretched uniformly to 3.00 times its original length. What is its resistance now?    $\Omega$

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89#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  220 V is applied to two different conductors made of the same material. One cv pv 9om 2(on1-obeg3eonductor is twice as long and twice the diameter of the second. What is the ratio of the power transformed in the first rvm2 geo-1nbov9o p e3(elative to the second? $P_1$ : $P_2$ =    : 1

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90#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  An electric heater is used to heat a ex .p;o./w j nhsq9t4w.mc h97eo*ezkroom of volume $62\,m^3$ Air is brought into the room at 5$^{\circ}\,C$ and is completely replaced twice per hour. Heat loss through the walls amounts to approximately $850 kcal/h$. If the air is to be maintained at 20$^{\circ}\,C$, what minimum wattage must the heater have? (The specific heat of air is about $0.17 kcal/kg\cdot C?$)    W

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91#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A 2200-W oven is hooked to a 240-V so5yb, ;wdfc lhki:ic; 4urce.
(a) What is the resistance of the oven?    $\Omega$
(b) How long will it take to bring 120 mL of 15$^{\circ}\,C$ water to 100$^{\circ}\,C$ assuming 75% efficiency?    s
(c) How much will this cost at $11 cents/kWh?$    cents

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92#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A projected electric vehicle makes use of storage batteri4wkkg e60wde6*f wd*xj9m jg*es as its source of energy. Its mass is 1560 kg and it is powered by 24 batteries, each j*4kw** wdj kxd6gfm 9we0e 6g12 V, $95A\cdot h$. Assume that the car is driven on level roads at an average speed of $45 km/h$ and the average friction force is 240 N. Assume 100% efficiency and neglect energy used for acceleration. No energy is consumed when the vehicle is stopped, since the engine doesn’t need to idle.
(a) Determine the horsepower required.    hp
(b) After approximately how many kilometers must the batteries be recharged?    km

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93#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A $12.5-\Omega$ resistor is made from a coil of copper wire whose total mass is 18.0 g. What is the diameter of the wire, and how long is it?
L =    m
A =    $ \times10^{-4 }\;m$

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94#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A 100-W, 120-V lightbulb has a m0m+ 3t:qsonuresistance of $12\Omega$ when cold (20$^{\circ}\,C$) and $140\Omega$ when on (hot). Calculate its power consumption at
(a) the instant it is turned on,    W
(b) after a few moments when it is hot.    W

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95#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  The Tevatron accelerator at Fermilab (Illinois) is designed to carry an 11-mA bh2z5 pijr(8l6v 0oit ieam of pi8 t(l rp25jzvh0io6i rotons traveling at very nearly the speed of light ($ 3.0\times10^{8 }\;m/s$) around a ring 6300 m in circumference. How many protons are stored in the beam?    $ \times10^{12 }\;protons$

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96#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  An air conditioner draws 12 A at 220-V ac. The connecting cord is copper wire wo.m ez9-*wpe sith a diameteee. 9wzpo-m *sr of 1.628 mm.
(a) How much power does the air conditioner draw?    W
(b) If the total length of wire is 15 m, how much power is dissipated in the wiring? $\approx$   W(Round to the nearest integer)
(c) If no. 12 wire, with a diameter of 2.053 mm, was used instead, how much power would be dissipated? $\approx$   W(Round to the nearest integer)
(d) Assuming that the air conditioner is run 12 h per day, how much money per month (30 days) would be saved by using no. 12 wire? Assume that the cost of electricity is 12 cents per kWh. $\approx$   cents per month (Round to the nearest integer)

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97#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A fish-tank heater is rated atu;; m +kzi52nubbx :ik 95 W when connected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total lengthb:iixmk zb2;+5nk ;u u of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

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98#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  In an automobile, the sikee tz-:y, /qystem voltage varies from about 12 V when the car is off to about 13.8 V when the car is on and the charging system is in operation, a difference of 15%. By what percentage does the power delivered to the headlights vary as the voltage changes from 12 V to 13.8 V? Assume the hz-kt:yi/ e, eqeadlight resistance remains constant.    % increase

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99#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  Lightbulb A is rated atbg +. :dl:oa bobz8f9u 120 V and 40 W for household applications. Lightbulb B is rated at 1 bag fo:+:obzlu8 .9bd2 V and 40 W for automotive applications.
(a) What is the current through each bulb? $I_A$ =    A $I_B$ =    A
(b) What is the resistance of each bulb? $R_A$ =  $\Omega$ $R_B$ =  $\Omega$
(c) In one hour, how much charge passes through each bulb? $Q_A$ =    C$Q_B$ =    C
(d) In one hour, how much energy does each bulb use?    $ \times10^{5 }\;J$
(e) Which bulb requires larger diameter wires to connect its power source and the bulb?  

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100#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  Copper wire of diameter 0.259 -i;z- wquiyukop cy + /uvhd2k( e+76kcm is used to connect a set of appliances at 120 V, wh6cidy;zyiuh kpq2(k-v e uwo+k7 +u- /ich draw 2250 W of power total.
(a) What power is wasted in 25.0 m of this wire?    W
(b) What is your answer if wire of diameter 0.412 cm is used?    W

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101#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A copper pipe has an inside diameter of 3.0 2uc9kyjj6ozk+** vju0 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the resistance of 10.0 m of this pipe? z**j ckj6u9jov y+2uk   $ \times10^{-4 }\;\Omega$


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102#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
If a wire of resistance R is stretched uniformy rm15p9lvbmv/. f+vyly so that its length doubles, by what factor doesrb+fvvvy1 l/.mpmy 59 the power dissipated in the wire change, assuming it remains hooked up to the same voltage source?
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103#
 
填空题 ( 1.0 分) 切至整卷模式 搜藏此题  
  A tungsten filament used in tx2:nqsf .r0 - o3 pgrivxdv/2a flashlight bulb operates at 0.20 A and 3.2 V. If its resistance at 0q nvo ix2-3s pt:rvx2rgd./f20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$

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