What quantity is measurq9*bllmzlbs 4.u6r/ jed by a battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrondg 9i 1l(6ucxqs flow away from the negative terminal in the circuit. But within thec1x9( q6 udgli cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is beueruem/9ult; t(j ;h-ing used up: battery current, battery voltage, battery energy, battery power, or battery resistauu;he9l(/ rju-tmt ; ence? Explain.

One terminal of a car battery is said to be connected to “ground.”x)p:1yld+nj (obldsq2zcgvy)4y /,d Since it is not really connected to4v )qd +lscyd)y1 bzx on yd(/,2ljpg: the ground, what is meant by this expression?

When you turn on a water faucet, the i-k chjg* /7 w;aex1qqwater usually flows immediately. You don’t have to wait for water to flow from the faucet valve a q hwgx/e-*i1q7k;j cto the spout. Why not? Is the same thing true when you connect a wire to the terminals of a battery?

Can a copper wire and an aluminum wire of tkidow31*t g tkft,)*t he same length have the same resistance? Explaigt o 1w*tttk*,k)if d3n.

If the resistance of a small99bxe(-olqzqu l- am : immersion heater (to heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow down t9(lzqoaqxbe m :l9--uhe heating process? Explain.

If a rectangular solid made of carbon has sda kfs n g*m+.g5ne-zhj71bd7ides of lengths a, 2a, and 3a, how would you connect the wires from a battery * ka.g dnemsjfd7n1b+gh-z 75so as to obtain (a) the least resistance, (b) the greatest resistance?

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.

What happens when a lightbulb bur,ozgktr d z)f y-lr08/3o)w czns out?

Explain why lightbulby( 6 m:v .7h;mhuxopq7b ssde7s almost always burn out just as they are turned on and not after they have been on for sod h7 u.:mqvsy ;(xmbs77p eoh6me time.

Which draws more current, a 100-W lightbulb or a 7gu1pc(f bf8 pf562ung 5-W bulb? Which has the higher ref6upp 5fug 21gc8nfb( sistance?

Electric power is transferred over large distahfqg f ywk))/mw qjmr0bd3r -q( s77z(nces at very high voltages. Explain how the high vk7 q(swh -r gqzqw7ffd/jb)y0r 3m)(moltage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Ws24zl 2z5gq7 0csa 0rncng2 bshy is it dangerous to replace this fuse with a 2524css0 2nrn5 sa2z ggzcl7 b0q-A fuse?

When electric lights are operated on low-frequency acklax5cx9+nz 3ud :(vq (say, 5 Hz), they flicker noticeably. (v9kzx: a+xl 5udcnq3Why?

Driven by ac power, the same electrons pass back and for+w+om4,ch)e +x gd kdy*2qt mrth through your reading lamp over and over again. Explain why the light stays lit instead of going out after the first pass of qm w +dxrh24*)+ eym,kto+gc delectrons.

The heating element in a toaster is made of Nichrome wire.sqon1 qv)fi52k0p8cw Immediately after the toaster is turned on, is the c 2kp)v5onwis18 qqf0 current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? tenrrqh b,,lkto/ ;: )Explain.

Different lamps might have batteries connected in either of the two arrangemev/gs ri3e.svb;3zjm .nts j.bsiz grm;3s/.evv3 shown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flol+t 4ng(lek 2cws in a wire. How many electrons are flowing past any point in the wirln( 4eklt+gc2e per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a bkx gz(6x,p6 u()dvchuf 1qyf:attery using a current of 6.7 A for 5.0 h. How much char6fgz,)xx fv6pyu( cu( dhkq1 :ge passes through the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes+w5bh /ly- ufgek a3o8 *hbup, 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$

  What is the resistance of a toaster if 120 gx2vvoie1xg-18;eeui 94 go- ugbz )yV produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current through am7amv0roi)qr8i *o: p $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into: 4(swzw0m /y0rmpymw(kt /a a 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$

  An electric clothes dryer has a heating element wiju o 3t4c0nny0th 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$

  A 9.0-V battery is connected to a bulb whose resi*ubjce6 jzomq yu574p9e./o t 5s(jgastance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric 9a60lwsqblw8 zyv. )t transmission line carrying 2800 A (Fig. 18–34). The line hasy9bq)wasw680 vtz ll. $2.5\times10^{ -5}\;\Omega$ 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$

  An electric device draws 6.50 A at 240 V. r /fypx :)n,1 pgpkx0q
(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)

  A 12-V battery causes a current of 0.60 A through a r(zb1a2)gz o55jovtf hesistor.
(a) What is its resistance, $\approx$    $\Omega$
(b) how many joules of energy does the battery lose in a minute?    J

  What is the diameter of a 1.00-m length o hi (eqo8ta,o nor,*w9f tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m /yv .kd 3jjkifijv*b00twj32length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire 2.0 mm in diamj; 8 zngflepk64q6yj :eter, to 20.0 m of coppe:6klgey6;j j4qfp8n z r wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as aeyrx 6*s ;f3nt zg(a4i: eqyz: tungsten wire of thez( fyt yqse6ne :raz:3;4ig *x same length? Give numerical details.    mm

  A certain copper wire has a resistani3kw+k6g)o d33u)wd nhsy +; jjrlnq 9ce 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?
$R_{short }$   $\Omega$
$R_{long }$    $\Omega$

  How much would you have to raise the tw,1ih qv :henu-)ay2e emperature of a copper wire (originally ath ),eyvw-nh2eui1 q :a $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature co95 eg2w8wnmu ypper will have the same resistivity as tungsten d2w5 nu9ge ywm8oes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of abog6k y r+/z ehx0gfasmtw /f7cehj3 -lo :80lz1ut $12\Omega$ 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 $\alpha\,=\,0.0060(C?)^{-1}$ .    $^{\circ}\,C$

  Compute the voltage drop along a 26-m length of householdj*-d79kh )u ikf: uu/estreq .ct9e c- no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm an:*/-eik9c.e) teukhcs tfrjd uu 9 q7-d carries a 12-A current.    V

  A rectangular solid made of c*8 fj.cquaile2 /,o pcbt:1wmarbon has sides of lengths 1.0 cm, 2.0 cm, and 4.0 cm, ly pu:o/qaw2*8 ci.m f1lt,jbce ing along the x, y, 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$

  Two aluminum wires have the same resistance. If one ha 9x* cn2o/)ftghn hze-s twice the length of the other, what is the ratio of the diameter of the longer wire - tzxne)n /o2 *hhcgf9to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V poww:i*tddfjb32 2* z 8 xj(xhjbuer supply, and a currej(* uwibb* 2xj 3:dzfdx8hjt 2nt of 0.4212 A is 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?    $^{\circ}\,C$

  A 10.0-m length of wire consists of 5.0 m of copper c(4ldwfh s4 et;c+3nsfollowed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltagl nef w;s(+s4h cdt34ce 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)

  For some applications, it is importantjtm 5;qrh9 gw7 mp2a)z that the value of a resistance not change with tmhwgjm5tq7 ;29r a)pz emperature. For example, suppose you 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?
$R_{0C}$   $\Omega$
$R_{0N}$   $\Omega$

  The heating element of an electric oven is designed to prodtcu, z,hqff8* uce 3.3 kW of heat when connected to a 240-V sour c 8uzf,q,fh*tce. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption ofli 884 +ilib;qk lkmm+ a 3.0-V portable CD player that draws a maximum of 320 mA of culi+ qmk +bi8 m4kil;8lrrent?    W

  What is the maximum voltage that can bepx c8a.v67;)m4qp7rai yhmpq applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and curcb/lcj/c: q s0rent through, a 75-W lightbulb connected to its proper source voltage olc cc/0b/ q:sjf 120 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heater is rated at yk/(n1n3wafcsv7 cw.110 W. Calculate
(a) the current through the heater when it is operating,    A
(b) its resistance?    $\Omega$(Round to the nearest integer)

  A 120-V hair dryer has two srmrh44o7q poc0kkv29 ettings: 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.    $\Omega$

  You buy a 75-W lightbulb in Europe, wux6b/lwhwu1bfqn /)st r0.w6 here 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-V6h 6f0sbu)/ln 1qu rtx/wb.ww bulbs? [Hint: assume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use i9mza;qr1sno3, dmgu1cxk 9a3 n the morning if it is in operation for a total of 15 ,d3qsack9mn 9zu a3ro1; g1xmmin? 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

  At 0.095 dollars per kWh, x3 c r;,j4dsot7bse;e what does it cost to leave a 25-W porch light on day and night for a ye,sebsdtx; ej ;4or3 7car? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected in series as in21aahvkpp r,g-jmanffv/+0zts g3 +3 F-+3r/mj1as ngpzvaff h+ t2pav,0g k3ig. 18–4b (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?   

  What is the total amount o/mjz k-1ndkl 0q9mv *yf energy stored in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connected to 120 V as in Fig. 18–20, can be uqdap e57r2tl;/bj .o vsed without blowing a 15 .ap /ob;lq7rve5jd2 t-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm () (dsk utof o8v:wi/9hno. 16 copper wire) and of length 2.7 m (9 ft) is connected to anwh8fs/o ui:dovkt )9( electric heater which draws 15.0 A on a 120-V line. How much power is dissipated in the cord?    W

  A power station delivers 620 kW of power at 12,000 Vt*.;drci zj+8b s,k u wkwf:q8 to a factory through wires with total resistan q d8kbir;,utc.*fjw 8z+:kswce $3.0\Omega$ How much less power is wasted if the electricity is delivered at 50,000 V rather than 12,000 V?    $ \times10^{ 3}\;W$

  The current in an electromagnet connected to 8tm8 fm6aie/d hn 7t-mcu8sm1a ) .wvra 240-V line is 17.5 A. At what rate must cooling water pass over the coils if the water tem6m18fnt8c7mud ./htm-ea) m 8asiv rwperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used is0cs9 7y( xtsa,i w zh4x(ywo9k)ji3wn a car to heat a cup of water for coffee or tea. If the heater can heat 120 mL ofihs7,w)0 (xyt34za9 oy j wx9cw(si sk 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.    $\Omega$

  Calculate the peak current injkypk8v..q - )*x w;j0 lqeldz a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value isxf+ y/mhkrpe7x/;wvml,- x tm f )va13 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

  Estimate the resistance of the ccrs gt) +0vsf9tcprr4 v;t 26$120-V_{rms}$ 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.    $\Omega$

  The peak value of an /9w 1 cdktu1lksgj,,nalternating current in a 1500-W device is 5.4 A. What is the rms voltage acro tjk,w 1u1/l9c, knsgdss it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected fqidl9sdhyl , )blo 6-v oka 0m;.a, -c*id,fpto a $660-V_{rms}$ ac line. Calculate
(a) the peak voltage$\approx$    V(retain one decimal places)
(b) the peak current.    A

  (a) What is the maximum7* ts1n2ibj5jyop:mdz*il7,hjg bk / instantaneous power dissipated by a 3.0-hp pump connected to n oz*k,sljg 571*2y7tbjb p:ii /dmjha $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected tjc53ci0aovo r.)qeg;o 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

  A 0.65-mm-diameter copper wire carries a tiny x 8bmlmd*w5 v*current of $2.3\mu A$. What is the electron drift speed in the wire?    $ \times10^{-10 }\;m/s$

  A 5.80-m length of 2.0-mm-diameter wire carries a 750-mA current when 3fsk4 s2i-)x : lyuz.1zo al ytsb6e6u22.0 mV is appb3se zz.1:)ustuo afyk-il624 ly6s xlied 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$

  At a point high in the Earth’s atmospq(h4;p8tv 4;ej1phd xo 8l epthere, $He^{2+}$ 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 $(A/m^2)$.    $A/m^2$  ----待选择----NorthSouth 

  At a point high in the Ea8s0d gz7p y)4 4e(cia(g2e w9rt grfadrth’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 $(A/m^2)$.    $A/m^2$  ----待选择----NorthSouth 

  What is the magnitude of the electric field across an axon membrane0oue*n v lra o:my0 :qef0x//e $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with an electh+a fl;i x,ltq/zz//5az arc: ;xmsy ,ric pulse. The action potential is detected at a point 3.40 cm down the axon 0.0052 s later. When the action potential is detected 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 instecar/yx /zta l:islqm,a;xfz;+, hz/ 5ad of only one?)    m/s

  Estimate how much energy is required.-qxhddbo r v sw0*/k9 to transmit one action potential along the axon of Example 18–15. [Hint: the energy to tranx kb0 sd9 qwv/-rho*.dsmit 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$

  During an action pote.jpm nx pn.+qq-4 lw*srvz b82ntial, $Na^+$ 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$

  How many coulombs are there in 1.00 ampryc 95oqp vl-5ere-hour?    C

  What is the average current drawn by a 1.0-hp 12 e/m7ti7b m15 naz-ehu71gkvh0-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a carg,kv* ytm m/r7 with the lights on. If each of the two headlight,m/t* kr 7ymvgs 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 $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of a 110-V, 104r9 kir)06o n ogf*cc7c dgya500-W heater is 5.4 m long. If it is made of ir) o ca*fc6g7 40 g9iyodcrnk0ron, what must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined asgonvzxd-c i v9a/pc,0p068sq the reciprocal of the resistance R; ci0v cx qza60g/,n-9sp 8dopvthat 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

  A small city requires about 10 MW of power. Suppose that instead of6w lj5dnv le3* dj3*ys using high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a two-wire line of 0.50-cm j36n*lvwyds*l5 de3 j-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

  (a) A particular hou8ugq2t0 osfkze9w0* asehold 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

A length of wire is cut in half and the two lengo6(ktw;cqs r b :49jn.kze nj6ths are wrapped together side by side to make a thicker wire. How does the resistance of this new combination compare to the o(wzkn6 9j tj6:nreq.c;s bk4 resistance of the original wire?

  A 1200-W hair dryer is designed for r:c28x v+cotw b6ye)v117 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?

  The wiring in a house must be thick enough so it does not become so hot bb/ b;s /*du vg2oturui4z3+cas to stg 2ur/ z +bo/*ibu;ubd3c4tvs art a fire. What diameter must a copper wire be if it is 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$

  Suppose a current is given by the equation.:dayo hdptaa(j40, a $I\,=\,1.80sin210t$, 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

  A microwave oven running at 65% efficiency delivers 950 W of ene jd*d5punj652a,gf tu-c9k5wfim7x krgy per second to th2maif6p-kjwd c 5d *,f5g unu97tk5j xe interior. Find
(a) the power drawn from the source,    W
(b) the current drawn. Assume a source voltage of 120 V.    A

  A $1.00-\Omega$ wire is stretched uniformly to 3.00 times its original length. What is its resistance now?    $\Omega$

  220 V is applied to two different conduc f nac386m9v9*y krvdctors made of the same material. One conductor is twice as long and twice the diameter of the second. What is the ratio of the power transfordvmy998na6vkcf3rc *med in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room of vav**kntr .giea7x3o ;th7e- : 7ajfvvolume $62\,m^3$ 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

  A 2200-W oven is hooked to a g:z9 z.fpgqsa76)1a yxqe ;kz240-V source.
(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

  A projected electric vehicle makes use of storagtaks ;oyh 2l+-e batteries as its source of energy. Its mass is 15tlo-k 2y;s ah+60 kg and it is powered 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

  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$

  A 100-W, 120-V lightbulb has a resistadv7x do6o*o-muo )r+knce 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

  The Tevatron accelerator at Fermilab (Illinois) is designed to carry an 11-mA beba/ 3w+pfh.xpam of prbfhw. a3pp+ x/otons 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$

  An air conditioner draws 12 A at 220-V ac. The connect , ;xfddzj86hh(vw3rping cord is copper wire withzhrjvfw ,d8 p;(6 xhd3 a diameter 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)

  A fish-tank heater is rated at 95 W when connec.rdzuqi6 -j/ yted to 120 V. The heating element 6qd /jyriz-u. is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from aboutj oll,tf e u, m ex925fotakv3vjh4isiz 644,0 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,e6t5 t90mv2l3jfaeszj4 v, k fx,h4o liuoi4? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for household applications. L ;b*f: gxsq0d , k0*kdewa xyi-r,q:zkightbulb B is rated at 12 V and,xdq wsgdk r0y:kze -:xa0*kb,*q ;if 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?  ----待选择----Bulb BBulb A 

  Copper wire of diameter 0.259 cm is used to connect a set of appliances at 120 V010 li89awfds l0 l*ay qcvs*vy 0c asl9v8fd0 s* aiw01vlql*, which 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

  A copper pipe has anei 59p1k+32: sdcpi hfo8xboa4s x us( inside diameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37)hss2f oio 451xex9(k d:3p8bu+cpsia . What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is strev x)zju/pn u mc7d79h;tched uniformly so that its length doubles, by what factor does the power dissipated in the wire h/;dzvuxc 7 pm9) 7unjchange, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operates at 0.20 nxigg9 2p 8se0A and 3.2 V. If its r psg9in0x8e g2esistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$