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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: 25年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 measured by a battery a)oz;g4 vw,lgrating 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 celo 8p7g;0i2plt)k)5 bjml sjtxl is connected to a circuit, electrons flow away from the negative terminal in the circuit. But within the cell, electrons flow to the negative terminal. Explak ltpl2 jp;s)i75xb0mtj) go8 in.
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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, what is being used up h5jzwale*2a*jw c0 -i: battery current, battery voltag-0ic a5jwa l*2j*whzee, battery energy, battery power, or battery resistance? Explain.
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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 + h88yixkx7kgnls7 9q battery is said to be connected to “ground.” Since it is not really connected to the ground, what is meant by this expresg8x79qk8xlnks7 ihy+sion?
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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 immei(zaqyvsu26p i+fx(phkq.hd1kn9 : 3diately. You don’t have to wait for water to flow from the faucet valve to the spout. Why not? Is the same thyviasi+((kn: 3 h zh2 dpk.91ufqp6qxing 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 same lengx.ke xl.-jf ol4vz8u 7/0kzqh th have the same resistance? Explaukz xoq fl h/.j0.l- ez487vxkin.
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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 immersion heater (to aqfsw2 ok4mbh2 q0;,pheat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the heatin,4bf2k o 0;2qqmswphag 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 solmm5un+8zbl0oia ed 04id made of carbon has sides of lengths a, 2a, and 3a, how would you connect the wires from a battery so as to obb d5 0mo8anl4iem+0 uztain (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 lightbulb burn-ec kg /gt(pfr/(i)i js 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 out 7;pqt*( ocqh v8n)e o7ug-.ckj elc3ljust as they are turned on and not aft7*l v-cocutq 37ecpnol.j egh (k;8 q)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 bulb? Which has therk ha (ise:z+wh4nei i6,*-yo higher resist-zkn,iio*+ w6eh:hr4yiea( sance?
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13#
 
问答题 ( 1.0 分) 切至整卷模式 搜藏此题  
Electric power is transferred over2,n 14jhxj(cenf0s2g d /ehf s large distances at very high voltages. Explain how t4h /x2egf cs102(ndsfe,jnh jhe high voltage reduces power losses in the transmission 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 repeatedly. Wht apfc /7.dy,4w )xxzmy is it dangerous to replace this fuse with a 25-,7y)at4p.zxm/fxwd c A fuse?
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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 op zxj96 acvuvw 66+re )qa+tf+perated on low-frequency ac (say, 5 Hz), they flicker noticeablye pzr aqt) x+jwv+6 +9v6af6uc. 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 bag4qfold2 ;tz7ck and forth through your reading lamp over and over again. Explain why the light stays lit instead of goin7lo4dz2ftq;g g out 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. Imj/xletdw .*+ ) l:vlhtmediately after the toaster i )lwht.:lxtljedv/ *+ s turned on, is the current $(I_{rms})$ 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 l0 yclrr05vy,,rasuw x2 3 7anresistor? 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 arrangecj)g0q an;y/(uhpw-fments s0hw);pqf g (/-cujyna hown in
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 fl/ k5jc tmk;2b x v-s1d,hqyjd5ows in a wire. How many electrons are flowing past any point in the wir ykksvhj;xmddb, 1 q52 jt/c-5e 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 batter9d7 txsl ffs;gbi sfd 9+y3jz2+ 5m2;hfqn1cry using a current of 6.7 A for 5.0 h. How much charge passes through the batf2sltjmf79 d29g1; hscn+fs; 5f3dxbz+ qriy tery?    $ \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 amperesm5s3fbyry*n9y6hg1 r 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 toasteg86hd qo3pupg c f*z;hc un-7-r 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 througzxi iy;+idcu1 (au0yuo1d;.lh h4l* dh 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 7.5 A when plugged into a 120+ao a4ob 0a2oe-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 elazp2r)n9tdg8 )js3 scement with a resistance 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 b6 h9w0yigkgi2 ulb 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 transmisb6ts8 j7 ut/7yda/q kdsion line carrying 2800 A (Fig. 18–34). The l/ sq8b dy77ajk6u ttd/ine has $2.5\times10^{ -5}\;\Omega$ 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 t0v 0tjoyfc7i43x nh. 240 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:gtbtv6rkx6d c5 a :4byq/ v9t through a resistor.
(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-m length of tungstenc iplbldoa4a-(2 : b3/nuw k-edodtl/92 vb8k 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 resistance of a 3.5-m lengtp6tki5iml4 c;6iz0n7yd:- 7wdgnxdeh 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 resistance of 10.0 m of aluminum wire 2.0 mm in diamvmmal ahx 4gq1/e xa p/o*s9+u.e ;p6eg i*ry(eter, to 20.0 m of copperg/mxep a4ra9/sg av 1pu 6qxm ele;hi(+o.**y wire 2.5 mm 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 same resis46vh q:) tx .irob,yzttance as a tungsten wire of the sqo.tv)yx tr6i bz,h: 4ame length? Give numerical details.    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 ac:mk p*r.;s*5s(h+ v qk u*qn-wb ovrhas a resistance 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 raise the temperature of a coppidl, *ku;xzk w m2t(i*0yw it,er wire (originally at ,(ixd w0 km t,*itkizuy2w*;l $20^{\circ}\,C$) 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 copper will have the same resisti5g rvf661.0m2vn xhulwc7vxh vity as tungsten do1 vxvfl xgmh67uv02.w 56 nrhces at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (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 rs g2 ei0s-aitqli : p-2*eqjs6esistance 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 length of househt)j,(hk gdef7rt*s2 9osq xxdato0*err8d20 old no. 14 copper wire (used in 15-A circuits).,t*rt8 go0jsxo7tk eqd2a* hrsf0(d2 x9der ) The wire has diameter 1.628 mm and carries a 12-A current.    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 os d .3iybk1z +()cacyjf carbon has sides of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for current that passes throc1sj(i +y y .cad)3kzbugh 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 samfy// 0ug(8 mdfhidol-e resistance. If one has twice the length of the other, what is the ratio of the diameter of the longer wire to the diameter of the short i fm/y(fdo /0uglh8-der 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 wir*wa0df s c- 0njn )y9qiq./cz v2f7dsxe is connected to a precision 10.00-V power supply, and a current of 0.4212 A isfdvf9q0znin ./ds7q 0s x)wy*c2 cja- precisely measured at 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 noq9 5di,gu5z consists of 5.0 m of copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85u9d,zinoq5 5g 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 chan +vl*nw 5c:zzege with temperature. For example, suppose youen5l*vz z+ wc: 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 producajn/gto 7cluz3w. xwn348+ wz e 3.3 kW of heat when connected to a 240-V source. What must be the rgalw 3cnut.w w/87 3zx+ 4ozjnesistance 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 power consumption of a 3.0-V portable CD player that dr 6sac* qq9on1raws a maximum o9ar o*qsn1 c6qf 320 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 s ab,s(regt 15be applied across 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 resistance of, and rlft,)d /jn -kcurrent through, a 75-W lightbulb connected to i- /dklnfjr )t,ts proper 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 110g4 qydh+ hff1bcr* it5wq-9 :g W. Calculate
(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 settings: 850 c:ib+ :hq cpz4-ru-mo cype85W 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 Euro6jggnfx8 j,dlg *ahv(fr 46. zpe, where electricity is delivered 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 roughz48(jlafvx.,n6*rjg h fdg g6ly that 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 mjck 0e.6-idb toaster use in the morning if it is in operation for a total of 15 mb0ek j i.dmc-6in? At a cost 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 25-W porch light on day a+rej j qwe1t)1nd niwee1+jq )r t1jght 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 ch ywi)ij(67 nzs:q t(xonnected in series as in Fig. 18–4bjx()t7qyhz ( 6swn:ii (Fig. 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 ec8b,km * 4dplinergy stored in a 12-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. 18g,ln vz yl8g)c7vu9b8–20, can be used without blowing a 15-A fusez8yv bcv 7u8l,lg n)g9?    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 diamebi5syw)3wh prc+8x 4eter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric heateewh4b rx8)p+s 5wcyi3 r which draws 15.0 A on a 120-V line. How much 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 620 kW of power at +( ;j; xbd hgyqul0u)c12,000 V to a factory through wires with total resi yxuhuq;g lb+dc(; j0)stance $3.0\Omega$ 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 connecte x5ouu( l1yfapup05 f3ly6sa(d to a 240-V line is 17.5 A. At what rate must cooling water pass over the coils if the wateusppu1o(ax a(lfy lyf 56 305ur 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 nr/6j pt ,p1n5 .(m ryd,eaayybe used in a car to heat a cup of water for coffee or tea. If the heater can t/y, p(m .,rdayay5j1nerp n6 heat 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 cur8h39hm,gbhd *o) c vzirent 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 value is 180 V, is acro37j-ugj zm8 bpss 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 wzfae2q q3psfwvoc0 .x1*g pf 6s+u44$120-V_{rms}$ 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 is 5.4 A. What i mw6pu-8 d.shqs the.m d8uwq6p h-s rms voltage across it?    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 is connect9xlhdjlk go t;*g )u0 .e59a)poohuz98n9l zaed 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 instantaneous power dissipated by a 3.0-hp pu6juvlatcv/u uuo 5* w7uq8.4cnn 9tw)mp connecte c v)uvuo t46u j 8/qcw7tn*u5wun9l.ad to 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 connected tohc sgdj): ,02 b;ly:1bwg vecq 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 wirx(30 jjw pkn)fmwo:-fk+m6c +fv(sdwe 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 cur;z yq5ysi/ 5,dg*tjsxrent when 22.0 mV is appliq,yxisj55;t yg s/zd*ed to its ends. If the drift 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’m )1z43wzuavoch; dj7mx4: hts 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 the Earth’s atmosphere, hrs0f5: hd76lfsy1i + d2hbup$He^{2+}$ 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 electric field *uze;2n -r wzk8u2s wfa(-dyz 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 is detectlv)(xdou3m f wg1 /;+d6koyxbed at a point 3.40 cm down the axon 0.0052 s later. When the action potential is detected 7.20 cm from the poingxbw;6v(od 3)uol/md f ykx1+t 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 tt1 5m(fyh wo 3. k)ch c+ew,(q:jqyaffeo9ei /o transmit one action potential along the iqf/k1t(o3yfj+w( fm,)eo whhac5qecye9: .axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored by 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 potentwu9i rp.c /zbb pu00ar;.ayw2 ial, $Na^+$ 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 ampere-houivy *ck ath8)xb;9q aqk he8:h0s.5w hr?    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 currentq93bbfo se:pq tv /3j( 2)patr drawn by a 1.0-hp 120-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 leaves a car with the lights on. If each of the two heado,m(3h6 e4gm7jte,x oijcx np0 7abh.lights uses 40 W and each of the two taillights 6 W, for a total of 92 W, how long will a fresh 12-V battery last if it is rated at hj6o g m 3i7ea0xxc,4(.p b,hem7ojnt$95A\cdot h$? 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 long. If it is mad koje0bt 8d4am:,q -yke of iron, what must its diameter bo,0am8dt 4jk b- key:qe?    $ \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 recipr8p qxufppaxpp ,*c:*9 ocal of the resistance R; tha *p 8xpfx,*p:qapc9u pt 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 MW of power. Suppow1asn derzdbj +-( ;q2se that instead of using high-voltage lines to supply the power, the power is de1ws+bn;z q(ed ar-d2jlivered 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 electricity 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 househdankhi) am +5r3qo.y +mfs(w;old uses a 1.8-kW 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 lengths aulvo /k s7sm:8re wrapped together side by side to make uok7 s :8vm/lsa thicker wire. How does the resistance of this 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 for 117 x 8ea cngp u /8e ifn:am0uc,d9*d48fjV.
(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 becom *; yxh jqvn9rnkos (zj.7:kl/e so hot as to start a fire. What diameter must a copper wire be if it is to carry a maximrvxz7nyho :(k js*. 9jq; /nlkum 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 the equaq+ ;klpg+ifj 0tion $I\,=\,1.80sin210t$, 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 atp3tb ycts. br)3k :.x+i- ,m 2jzkqsmz 65% efficiency delivers 950 W of energy per second to the interior.zzbq+m.2s)k-c:sy x pmit rjtb,3.3 k Find
(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 mad9q63mbeek + lee of the same material. One conductor is twice as long and twice the diameter of the second. What is the ratio of the power transformed in thee9+ mkq bl6e3e first relative 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 heat3dodufa,cjs8bahk q81)j 1m* a room 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 s5j hhd*ala4*m kczht/a d,jtps8g 634 ource.
(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 makd,tvsruhum w +/(i)kzda-69 c es use of storage batteries as its source of energy. Its mass is 1560 kg and it is powh si+t r cu-d9wz(uv)k,6/damered by 24 batteries, each 12 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 hi/ zchx7w ph 3xiukom6gjdsh3,/g8.7 as a resistance 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 ano*m9 o5duw-zu 11-mA beam of protons traveling at5 -oz*uomu dw9 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 isn*;j-0)melo f 8mszqx ak2(w b copper wire with a diaw2(axj n0;k)mof 8z-m*le q sbmeter 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 at 93pju,sq pcdx+mp70b0 5 W when connected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What is the diameu x7s+bpcq 0j0 pd3p,mter 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 system voltage varies from abovgsc 63 8hsg1u,br/r bk 96igjut 12 V when the car is off to about 13.8 V when the car is on and the charging system is in operatiov396b g rbji ggsuh/s816r,c kn, 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 headlight 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 at 120 V and 40 W for household applications. Lightbul/onun3- f6 yqcklmy1(b B is rated at 12 V and 4n y-n6y3 m 1(ol/kcquf0 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 cm is used to connect a +d:y tn7s;1 rulx51ii u fs:oyset of appliances at 120 V, which draw 2+rut 75iysyoin :uls;d1 1fx:250 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 insi4b0m.)1refoa lv 5qy; od3c qfde diameter of 3.00 cm and an outside diameter of 5.00 cm oyfq51c0.f3 ler db)am4;q ov(Fig. 18–37). What is the resistance of 10.0 m of this pipe?    $ \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 uniformly so tha siox:4xcy8*zmdg*gyr 8gdb kj7 8(i. t its length doubles, by what factor does the power dissipated in the wire change, assuming it remains hooked y88.brs*4jmx *kd: gz cy7(8gxio idg 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 a flashlight bul,v 3vtivy-6 mltv5klk r22,npb operates at 0.20 A and 3.2 V. If its resistance at r nvvim,lkyt3 ,6kvlv p2-t 2520$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$

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