What quantity is measured by a battery rat3gs/ h xm5),w,k2 pb qkzzz6wc4y udo;ing given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electron: yw)wy4o fkdcf k88u.dad .k8s flow away from the negative terminal in the circuit. But within the cel4daf8k8. uy:f.wwd 8) dcokkyl, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is beif+ )xsj-(;p qh a.rbnzha w(8bng used up: battery current, battery vof xp a +qhwz(hban(rb8;-s .j)ltage, battery energy, battery power, or battery resistance? Explain.

One terminal of a car battery is said to be connected)gb /f, kap)cy to “ground.” Since it is not really pk,abf /g )y)cconnected to the ground, what is meant by this expression?

When you turn on a water faucetn9 bzw2juj+x 4;w(yktv;na/ ,f k:px z, the water usually flows immediately. You don’t have to wait for water to flow from the faucet +vu ,x:/ f;4nn9 x2zb zjpyw(kakj;wt valve to 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 the same len )cp4,eahxac -gth have the same resistance? 4xa, ah-)e cpcExplain.

If the resistance of a small immersion heater 6q( sov,r.l zk(to heat water for tea or soup, Fig. 18–32) was increased, would s (o,vk.6z lrqit speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of dr6oi4qs,k3 hnq1 qm/lengths a, 2a, and 3a, how would you connect the wires from a battery soom6nq rh4kqd 13 qs/,i 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 light(tip ) 8i rghf7kvb9t7bulb burns out?

Explain why lightbulbs almost always burn out just as 4)r u 3h6u91n sqexxdethey are turned on and not afqu1 e3 )xn9e64ud hxrster they have been on for some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Whi4a): -k7h+izpcf0 rpfxob4gwf 2ojo1 ch has the higher resistance?4bf+ icaj4fg :1o zx o-o 7)p0whkpfr2

Electric power is transferred over large distances at very high voltages. Explq 31o -nnq8 gu)c0fje8 cg-sngain how the hig enoq-s 1cf0g8un qg)8cjng-3 h voltage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerou;wzp n-:dyg 2ks to replace this fuse with a 25-Az yd:- ;ngwkp2 fuse?

When electric lights are operated on low-frequency ac (say, 5 Hz), th -t; kbq5g0c ntsyj5x:hj,7 koey flicker noticeably.,5jk 0 ckb-5h 7o:t;nqtxgysj Why?

Driven by ac power, the same electrons pass back and forth throughl rp4 vmba)b* *ku0qb/ your reading lamp over and over again. Explain why the light stays lit i*u)lbb 4a*/kq0 vpbmrnstead of going out after the first pass of electrons.

The heating element in a tx aapp+:t)i9m4n6dt2 apb p*boaster is made of Nichrome wire. Immediately after the toaster is turned on, is the c2ixbp * p:a6am 4pnbat9 dp+)turrent $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a cte 0 ys9jq4j2resistor? Explain.

Different lamps might have batteries connected in either of the two )p z .wwwz.vh78b s7zearrangements zbh.7 w) pvsw7w8 zze.shown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How p7ix3s-2h wi w::kewh many electrons are flowing past any point in the wire per secep- w::7 hhs3wk w2iixond?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A for 5.0) x)lbv8 ) gq(:gtnh70g enrcb h. How much charge passes through the battery? (:n)h gqe gbx8)lbr7tcgv ) 0n   $ \times10^{ 5}\;C$

  What is the current in amp c5w z5p,hijl r8coaoz:*4fd uwj8 -v6eres 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 V produces a r3ds ar z 3jq;,5z7q5 7crwij1vcwnl8current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current through a 2sjzg,i,6lrk $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 hxt tof9u e g4ch:l-,70:h oqqA 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$

  An electric clothes dryer has a heating element witx ph50eng fetnxv.5 f;k496 mlh 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 p0m:;rv.y jufwhose resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transmission line carrying 2800 A mld3:k4 9w ,1 3thedqktrw:un(Fig. 18–34). The line h9qhmk1eu4 rnw d3:t :w3dk,tlas $2.5\times10^{ -5}\;\Omega$ 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 6/;x2oohz , 7i4 zrgrc;vyx yx240 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 current of 0.60 A thp/g, cixm 0j93kspe 7irough 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 of tungsten 0ks o*r8-kgl :nsemu: wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1.5 mm idg 3d7di t ps)mgyt;sl9qo+s-l9zv 7pr6- nf .n diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire 2.0 mm c, m7l*tmjj:yin diameter, to 20.0 m of copper wire 2.5 m m7t:lcjm,yj* m in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance dx 8l1t*uplg3 as a tungsten wire of the xlu1*g tp83d lsame length? Give numerical details.    mm

  A certain copper wire has a rern snjd.a a+6 i oydk- ;*eb,qzssu-:4msa80 hsistance 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 copper wire (oris*v8qxs:hd g; ginally at*gv; d:qxssh8 $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivity as t+v br 8ukwd;( 1 ,b etkh::bzvg0wyg(zungsten dwhb krg,ky: +z018(u(zv tbeg dbw;:voes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb hasitv/sbc hr (6b p/sil40/vn6a a resistance 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 length of household no. 14 copper wi- abr8g-qd,kzume )0are (used in 15-A circuibr, m)8akdegaqzu -- 0ts). The wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm, 2.0 cm*l.n1qc kuh25ao q/ ri w*r(mq, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18– *.luqqq( w5i1mrahoc /n*r2k35). 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 h uup:y0o9-qx has twice the length of the other, what is the ratio of the :u 9yuqx0-ophdiameter of 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, anf c(o)+jmdjtk9*by r ;d a current of 0.4212 A is precisd)j j oryfbc9*tk+( m;ely 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 4wo4t2p:nm tpm of copper followed by 5.0 m of aluminum, both of diamen42wpm: optt4 ter 1.0 mm. A voltage 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 important that the value of a resistance not choo cw4-9izg4*pt8bo w ange ww*t cgpoz9o bow84i-4ith temperature. 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 electrqf prli 4 cjbpw.;d5+ 25fro/nic oven is designed to produce 3.3 kW of heat when connected to a 240-V source. What musrqj id ; 4n.p5 2l5f/bcpfwro+t be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V p:ny qp:tde xnza-l5.d4ed72eortable CD player that draws a maximum of 320 mA of ce 7:qd dz5-xt la2ypedn4en :.urrent?    W

  What is the maximum voltage that can be applie,ozkuc rlwh+ ej6x .d0202 jpjd across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, andsu0(iyr i.azl6h r/ x5 current through, a 75-W lightbulb connected to its proper sou.y0(u si rxi5z/ ah6lrrce voltage 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 z 0/4e7jpc uxw+e73 oqrgj3zz110 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 settings: 850 W q( (mwt)4n ekzand 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, where electricity is dtf 6j zp5qlo,sh :o1x0elivered to homes at 240 V. If you use the lightbulb in the United States at 120 V (assume its resistance does not change), how bh5st0 jql :o px61ofz,right 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+ iqc;vjzt: c9zzo ow-o 6(vx9 550-W toaster use in the morning if it is in operation forccvt vo9( o9-iozq+zw;x6: z j 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/fxyw1 z5ypv *q)w:5etzdw*v does it cost to leave a 25-W porch light on day andeywp ):5vw 5*z*t1vy wzfx/qd night for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-6bfw0e xk8:r zyi.xx1V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA whe0x ezyb6xf8r.:kw1x i n 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 energy stored in a 12-7b1 mju0le 7d 0iqwv,dV, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connected to 120 V as in Fig. 18–2xb8p w p 7+d.l-dzceq20, can be used without8 d lq2xpc7e- +zdpbw. blowing a 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.12iepcxw4+hz l+. /f/m a9 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric hfahezc. wm/lip+x+/ 4eater 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 V to a factory thror xix,ex9ha ap6 2 .:(ziz:pncugh wires with total re2p z cei:6axa: hzx.xi9(,rnpsistance $3.0\Omega$ 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 eleckkfilz01lmu .,rwui5bug5 -: tromagnet connected to a 240-V line is 17.5 A. At what rate must cooling water pass ove. ug5,1fu klb rwi l5-z:kumi0r the coils if the water temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to heat a culk8.t x7h:.u 52cq ilv- sjuqpp of water for coffee or tea. If the heater can heat 120 mL of water from 25ilc -u8l 5:..qtj7v usqpxh2k$^{\circ}\,C$ 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 currend t7kv3pqk 7zhjys; )/awz5: xgxb/ h7t in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 m7 n21 ffljf .+dih(sh96 ylfpV, 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 dpqn mm+9h m (0nrj/m6of the $120-V_{rms}$ 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 alternaza3npxk0. r; )bx mgq(v 8-munting current in a 1500-W device is 5.4 A. What is the rms voltage a0gq m uz ) k8nxrb(pxm;.-3nvacross it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected to a 8chu j83(lote $660-V_{rms}$ 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 dissipated by a 3.0-hp pump connecvxwmtjk- ++ai;x. .h /r-vmjm2;ccs rtecjh;+s tw. - kar;2-x+ ./micjmv mvxrd to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected mr/u. 7ag hc5pto 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 currk8 cjpc,m i 7l-br0rp.utt zgu,uv+ 92ent 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 du;) ig*bmog*m+u kd)-;v skA current when 22.0 mV is applied to its ends.gmmkgud;i*)ua- *) od+;vbks 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 Eart4h, ua6im xk*4ok ohtyc-*pw5h’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 the +s/zkv2r9wzst, xe- w 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 fiecl5v zd0c )yljqlup -g.4: qm0ld 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 el2u.ek o3nsevhov+2rli 9o cx, 79 le)wectric 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, thlr ooelx23cs 79uo ei2v,).+9n vekwhe 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

  Estimate how much energy is required 1:s 1k0mdqwc d;s+ hcsto transmit one action potential along the axon of Example 18– scqw ;1 sdhck1sd0+m: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$

  During an action potent. of+b.gi/lj uwag*/61vz xteial, $Na^+$ 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 theatdc8q x:oj(7re in 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0-hp 120+(jq*+n/l; a j257pwhnmymh/ ibbgrb -V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of the two headli3 3itsdnuqt5 g)-u 8uhji: k:aghts uses 40 W and each ofn3ik-)u:j8dthgqs5 a uiu3t : 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 ofud* 3xk q5d:izpm/+ cd(( aagqafjy3xj4 q2j8 a 110-V, 1500-W heater is 5.4 m long. If it is made of iron, what must its diamyxd235p+mkq(ciud/ 4(:3f ajq*j 8 azjg qadx eter be?    $ \times10^{ -4}\;m$

  The conductance G ofyu)p ( f0xccw(*-x3kosqhli: an object is defined as the reciprocal of the resistance R; tl-(*xkx ( h iop03u):qc sycwfhat 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 2d owgu/p-pf *power. Suppose that instead of using high-voltage lines to supply the power, the power is delivered at 120 V. Assuming puf/o*p-d2g w 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

  (a) A particular household uses a 1.8-kW he, j, eqfekli.96a*x5 6qyegnrater $3.0 h/day$ (“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 are wrapped together i .pkme+n)kch3x/swlhuj 898side by side to make a thicker wire. How does the resistance of this new combickl)./3h 8 pi9w mjs+ hx8ukennation compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 117 V.7ojf kn.cm/fzb 073ip
(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 env.2j:f5ermsm md*d7 eough so it does not become so hot as to start a fire. What diameter must a copper wire be if it is to carry a maximedm m5 fr* em2.s:vd7jum current of 35 A and produce no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is6.c .c3: tayrfe( syny given 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% efca kh6e* 30 :dculuzu.ficiency delivers 950 W of energy per second to the interior. 6h uc z:dukc3ua0.le*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 twt1x:)jjki d,cpr : wl8o different conductors made of the same material. One conductor is twice as long and twice the diametcj::i, lxt kw 8j)d1prer of the 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 heatra(uzoc6s8;n/l3*hi3bfkd w 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

  A 2200-W oven is hooked to a 240-V source.l2*yyvbyw)93 jh4 9eovw 8yh8q xu1v6c t kcb9
(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 gz qgy;-:8gr4e 4rovsuse of storage batteries as its source of energy. Its mass is 1560 kg and it is powqr4g8z g:gs4 -vroy;e ered 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 awrj) xj,v)oq w5l2+ r 1p+bnmc 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

  The Tevatron accelerator at Fermilab (Illinois) is e5,zdf)4, mt.l nydde oz(:dhdesigned to carry an 11-mA beam of prfyotn, )d5d:dmdhl ez.(,4 zeotons 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 connecting cord is (mxl;pp0q b*n: :jnvzcopper wire with a d;nmv*(:q xj pl :np0bziameter 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 conne .v8rid7lvc 4mcted 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 diameter o4i8 vm 7lrdvc.f the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from about 12 V when thys2 61pnea cnmt3zb10e 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 voy2t 1b6 03pcnme1n sazltage changes from 12 V to 13.8 V? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for fflt9(( 7 eedrhousehold applications. Lightbulb B is rated at 12 V and 40 W for autoef( 9lre7( tfdmotive 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 diameter3*-w lg (nlbac:p-*fdkz( m bg 0.259 cm is used to connect a set of appliances at 120 V, which draw 2250 W of3g- gm*p(lba:cfz nl -bk*(wd 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 an inside diameter of 3.00 cm and an outside diameter of 5.0kjcdnfx/ctl n;7,,x7 0 cm (Fig. 18–37). What is the resistance of 10.0 m of this pipe?nkt7nx7,,/;cfj d lxc    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its6;e iqu: 2y*tpwy5q+zshmircqh+ 3fez66 io/ length doubles, by what factor does the power dissipated in the wire change, assuming it rem6eh 3+zmz /frq266+5:hsc wt p;i oqiuyyq*ieains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operates nw ca1p0p/3iv at 0.20 A and 3.2 V. If it0ppcn 3wv1i/as resistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$