What quantity is measured by a battery rating5yd7q,)/s.vxs eiyb f 4jgi, u given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow away eg56ejzk k/j(1m/.:azk hqv yfrom the negative terminal in tq1m.(ghkeye/6v5kza /zj :j khe circuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battery current, 2lcigvso j76qt4 .z(hbattery voltage, battery energy, battery power, or battery resistance? Explal4t6g q7zsoi.vcjh2( in.

One terminal of a car battery is said to 8jiu ;jtqr+ zvvg :t)4 l3 do0zi8)wfybe connected to “ground.” Since it is not really connecte)8 tvo gviif z 0:;3qld)rjz 8t+4ujywd to the ground, what is meant by this expression?

When you turn on a water faucet, the water usually flows immediately. You do*6s 1ou8yjukf n’t have to wait for water to flow from the faucet valve to the spout. Why not? Is the same thing true whenku8o u6*js1y f you connect a wire to the terminals of a battery?

Can a copper wire and a9-vt/0 ouq f3ju-gyw gn aluminum wire of the same length have the same resistance? 0jgt-9/3- gfuuy owqvExplain.

If the resistance of a small immersion heater (to heat water for tea 2(h z obb1u1emcx.4 vwor soup, Fig. 18–32) was increased, would it speed up or slow down the heatixhbz 4c1wmouv1b2.e( ng process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, and 3a, hops1znf+20s jm4 xl z+hqpy: q-w would you connect the wires from a battery so as to obtain (a) the least resistance, (b) the greatest resistapph4q-+jm1q 2n s:z z+ fysxl0nce?

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 burns outyi7cuhqi c m/6((jz0zjf+7 fy?

Explain why lightbulbs almost always burn out just as they are turned onc1*mq: in w*rk;z7fur and not after they have been on for some:kunq*7*;r1im rzf wc time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Whl0t* 5.+*k9 lg x ewqpew*xiqdich has the higher resistanci lqege*d + *5qtk 0p9xwlwx.*e?

Electric power is transferred over l(gse/z / fg2bk+kw:szarge distances at very high voltages. Explain how the high voltagekw(essf +/kz/ zb:2gg reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fuse with+ c a9luy38qww a 25-Aal u8 3+yqcww9 fuse?

When electric lights are operatedkz1 w2 o/zyyf3 on low-frequency ac (say, 5 Hz), they flicker not /f2ywkoz13 yziceably. Why?

Driven by ac power, the same electrons pass back and forth through your o4y.*n)kk*cg a1 wyho -)kkxgreading lamp over and over again. Explain why the lightkn) - 4wo.x c*a oh1kkg)yk*gy stays lit instead of going out after the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. Imm ka4per-xr7w-ediately after the toaster is turned on, is the currek4- w xerpa-r7nt $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? /t2w vu*h/tvs ) p)omyExplain.

Different lamps might have batteries conneg94 ttzudg7 k -whq2v8cted in either of the two arrangements shown in v4z-w28dtkqu ggh 97t
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wir.r+odk **qw 7 xtzd; bjnqd/-ne. How many electrons are flowing past any point in the xrt7*nn.+;qddk *- /jbqdozw wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A for 5.0 h qre+6*dswy i8. How much charge passes through t qiwdey6+8 *srhe battery?    $ \times10^{ 5}\;C$

  What is the current in amperes if * z6rwyf .9m -q.cf5ran1qng w$1200\,Na^+$ 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; civ ,i:meijip43 4uh V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current thx6co9 ucc fzk,0zp50grough a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into aue.e4o+z kc)ye0 ot0 9lk.ieq 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 elementm v rg/xm34*syugp v,wn7c85d 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$

  A 9.0-V battery is connected to a bulb whose resistance isq 6ogax1t+j*lf u1;drncg 64s $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transmission line carrying 2800 A (csjh v8ip)u(7 Fig. 18–34). The line has iu 7(v)8jschp$2.5\times10^{ -5}\;\Omega$ 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 qij1:y ri6; up6.50 A at 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)

  A 12-V battery causes a currep16iiih pj+; m uhh1as j+0qu-nt of 0.60 A through a resistor.
(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 j9vaz-uke lb4g:(zl.qh pd. +of tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m lengthb-m;u7o7 opqi,ase68vrbia0rgr w404mbr/p of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wirpd b 2-v+vehs k:* a:x-pznj)wad;xq (e 2.0 mm in diameter, to 20.0 m of copper wire 2.v:jqs k-x(xd+a *h-n);d ab v:2p wezp5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as7n2y1gqqg :kx a tungsten wire of the same length? 72nkg qq1x:gyGive numerical details.    mm

  A certain copper wire has ayd ikgn: .mg, 5d rtx1nn-z(/y 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?
$R_{short }$   $\Omega$
$R_{long }$    $\Omega$

  How much would you have to raise the temperature of a c1(5ba2smlzov pp9; wq opper wire (originally at s5a mlopzw91 q(2p b;v$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature coppdmbj mp8 .h* c4a:ua0uer will have the same resistivity as tungsten do8pbauh .d j:4c *mu0ames at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a ;xy :+27 fw ld:ltg;zx:yxgodresistance 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 $\alpha\,=\,0.0060(C?)^{-1}$ .    $^{\circ}\,C$

  Compute the voltage drop along a 26-m liwxomo/2 5*,;yriek zength of household no. 14 copper wire (used in 15-A circuits). The wire has diameter 1orm*/ezy io5;2xiwk, .628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm, 2.0 cm, and 0:iq*kvp*,x-q8 fkml:iynyc 2 l 1mg. j dw0kx4.0 cm, lying along mycj:d q*w vlmnx: x1*,- qipkg8lyi20kfk 0.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 has twice the lee0qhzympme * s;2,63l )w bzlength of the other, what is the ratio of the diameter of3mzwe,b6lm 0;l*yqs2 zep)e h the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V power supply,,;ys,vfa7v,r x g2dyl and a current of 0.4212 A is precisely measured atrav xf,y2s y;v7,l dg, 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 copphp +3v +csadybog0 w:h6n 29,nt;eytg g-lnp6er followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is placed across the composite wire.bhc: n n0 3 gtgde-2+vpnp+h 9a6g6 y;ywl,tso
(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 important thaogwv hiv. )al3,an;q(69 p1*qbhpgin t the value of a resistance not change with temperaturen) i*1alvgw9(6 qhp3p hbag .;qio ,nv. 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 h0t-ty 4uj(( 50c1gtrqx iilgis designed to produce 3.3 kW of heat when connected to a 240-V sourcelr40tg- iyg t5(cq(01 jihu tx. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a2 qy3r)8xa0pz krkv . ve+,ljy 3.0-V portable CD player that draws a maximum of .e +v8kax0vyy jrkp, rl 2)z3q320 mA of current?    W

  What is the maximum voltage that can be applied q.ax1a 9 l)yk7+ue j3:xnc hepacross a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, a 75-W lightbu -li3+ tgahpa4xw* )fxlb connected to its proper source voltai4 xl)at-3p+ fxg*hwage of 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 110 W. Cal mzkuxr3br2/ j6(i t+,+rz6q n;bmj r .w;nnplculate
(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 se/f v0+ +txegfegkm-:mbv0/ jt oz+ sg;ttings: 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 lightbul 2u 0rqfxcb8v1b in Europe, where electricity is delivered to homes at 240 V. If you use the lightbulb in the United States at 120 V (assume its res qfu82r 0vc1xbistance does not change), how bright will it be relative to 75-W 120-V bulbs? [Hint: assume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy does a 9gg 1w3tvs8vy550-W toaster use in the morning if it is in operatiowyv t9gg 183vsn for a total of 15 min? 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, what does it cost to *-n re7 wrwo(cleave a 25-W porch light on day and night forn w-ro(7*rwec a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1+l-mlk;an)0gydc8qc 1ez3 w: e tb,gs.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 4c 3lgmyen cl10 s)kq-z+g8:e ,a;bdtw50 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 of elfg0r;.a dy/i nergy 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 used wim*0tk)bsyg - pthout kp)t-y b*sg0 mblowing a 15-A fuse?    bulbs

  An extension cord made of two wires ojwyf0j ,a )0njh8t h3df diameter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric heater which draws 15a)0hn h jt0 j8d,yfwj3.0 A on a 120-V line. How much power is dissipated in the cord?    W

  A power station delivers 620 kW of power at 12,00+ mbo.2 hqsyz.0 V to a factory through wires with total resistam+s. oqz.h2 bynce $3.0\Omega$ 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 electromanga9zzkb ,yj ka0-zr8a,,p 5ggnet connected to a 240-V line is 17.5 A. At what rate must cooling water pass over the coils if the wajgz rg5ya,pna8 ,9a0zk ,kz-bter temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a cr(l: 02eb jyyh3 n 1glx a91mus6n, ofz4ti8liar to heat a cup of water for coffee or tea. If the heater can heat 120 mL of way 8ez1f6lu m4j ylb :lnnio2a3,ri 0x tg(19hster 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 j qut5w89xk, 44ty atzin a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 1804d:.34nk)bfigp. qwx db fl.w 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 theo /7*v2aeqil3.frhur $120-V_{rms}$ 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 alternbh+5d qi ojbu88j /kp9ating current in a 1500-W device is 5.4 A. What is the rms voltage acros hq8bjd9ou/kjb ip5+8s it?    V (Round to the nearest integer)

  An 1800-W arc welder is conne d6vmbql**::pw: u nlxh -rz4hcted to 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 maximum instantaneous power dissip:q ewf9t+jm t:ated by a 3.0-hp pump connecte9ef w qtmj+:t:d to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to r;8xufbgk ghwez 6:h 51: *bnma $240-V_{rms}$ 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 coppf:z1(qs * f4p8 ravvjher wire carries a tiny 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 carr+zq6i2il 3yhxnu5+ qd3j3 bhaies a 750-mA current when 22.0 mV is applied to its endi zq3u3a2hi x+5 by3qldh6j+ns. 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 tk nsh okd5368 htnuh(5he 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 $(A/m^2)$.    $A/m^2$  ----待选择----NorthSouth 

  At a point high in tetaxj6 4-d erx 5r-m9bhe 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 $(A/m^2)$.    $A/m^2$  ----待选择----NorthSouth 

  What is the magnitude of the electric fmz)yxuu;nzb:* / qw*e ield across an axon membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with an electric pulse. The action potential is dew5*q 54e nqiextected 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 thxiqqe* w4en5 5e axon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much energy is rc x/ ( bephd6ir0n+a+hequired to transmit one action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored by charging the axon cbpcxa+ nhh6 (rd+ie/ 0apacitance; 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 potential, 6qp8 3oqtpsy5 $Na^+$ 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 f*p;li( 9(xmt wdzpfh3x:gd 8 4nx(quthere in 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0-hp 120-V moy,3;emhx yf8 2 +mh;qrx+t1n du; knojtor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a+ntgmpaq9fyvd c;96 )kh/ t.c car with the lights on. If each of the two headlights usesn/+kh9mac6fcp y d9;vqtt g) . 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, 1500-W heo);bb h3b )obw4 y1blrater is 5.4 m long. If it is made of iron, what must it or 3b)lbbow b;)4hyb1s diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocpuqb h .0it6t 6l+dbn( e,du+cal of the resistance R; tqct0+lh6b(d+iub u tdp .,6enhat 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 pow4rpu)1qxu(u v 7(9qxc cuju )wer. 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 perwvc(q uq 1)crp u(xux49uj)7u meter. Assume the cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular household uses a 1.8-kW heaterv0 t10 o(6otgtjaj7p*8ffvav $3.0 h/day$ (“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 lengths a(k8j7r o mwq9 zy/ieya) j1j/zre wrapped together side by side to make a thicker wire. How does the resistance of this new combination compare to the jo1)y/kz /yaw 9q8izje( j7mrresistance of the original wire?

  A 1200-W hair dryer is designedr6/ 8d+i1** wovn wtoboz*dme for 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?

  The wiring in a house must wg6c. jh wgucw+ /:*ofbe thick enough so it does not become so hot as to start a fire. What diameg/o+u c6:wj w *hfcw.gter 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 give.l ca/ jy7x.nkn by the 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

  A microwave oven running at 65% efficiency dele6 x .,xay x,ur6x/pym:5wjqiivers 950 W of energy per second to the in6p: ye/x,x.m ,xj5 yiwuxra6q terior. 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 conductors made of the same u; 1-;olg:z ded cv(fmmaterial. One conductor is twice as long and twice the diameter of tomd- 1: uedl zg;v;f(che second. What is the ratio of the power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a roome;9 pb w nx+ 5pw)4wfurf;8msa 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

  A 2200-W oven is hooked to a 240-V sourqz fz85y;6-1ufwegizce.
(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 storage batteries as its source27 op85 z (y4mtmecees of energy. Itp5 c7(zt8e smm y4e2eos mass is 1560 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 resistance /s mj hnoo+a18of $12\Omega$ 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 (Illino;:uk)mx nwx+b28qt5wobcuw p( 58onjis) is designed to carry an 11-mA beam of protons travelingun xxq8o8pwuo5j( bc t5 ;bwmkw n2+:) 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 hz +jvro8)0 qt4, ia ,aqjv+snat 220-V ac. The connecting cord is copper wire with a diameter of ,j,oava nsrqvqt8+h i 4j0z)+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 connected to 120 V. - hr53oxpjp:fy3 w-ds The heating element is a coil of Nichrome wire. When uncoiled, the wire has a totalop-3:x p5r y jwsdfh-3 length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from about 12 V w24 qbsy(vo;n rhen 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 heador24 bnqy(sv ;light resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for household applications. Lightbulb ;;: oqpfj,w8z e3+ qiu2/a7 sgqigbjgB is ra;:g28+ /;ibuqzjq3ogq7s i,j fwapg eted at 12 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?  ----待选择----Bulb BBulb A 

  Copper wire of diameter 0.259 cm is used to connect a set of a.9oh7 c0d3 +bozaofqnppliances at 120 V, which draw 2250 W of power totaoo90o zndaf+q7 .c3hb l.
(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 an inside diameter of 3.00 cm and an outside diameter of imjw27era g15 5.00 c17wrg2i a me5jm (Fig. 18–37). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uz 2.9 rh:tx; sinvi:mfniformly so that its length doubles, by what fax9 irhv ::.;z snitmf2ctor does the power dissipated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bu o9w ay(kmw1s-t-nd1y lb operates at 0.20 A and 3.2 V. If iywyd tm1a -k1wnso(-9ts resistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$