What quantity is measured by a battery rating xvd217 me1y5z)pmrynw , u0na given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connecg+u62fya/g. cpb:hejjjs x: 7ted to a circuit, electrons flow away from the negative terminal in the circuit. But within the cell, electrafhe gs uy/:j:j+c2gxb 6.7 jpons flow to the negative terminal. Explain.

When a flashlight is opera, kfztwpnbz117vi)9d ted, what is being used up: battery current, battery voltage, bf1,dz) wzn9k7 v1bipt attery energy, battery power, or battery resistance? Explain.

One terminal of a car battery is said to be connec)pwsl lnh l4cz92t-w*ted to “ground.” Since it is not really connected tollp shn2-9l4* zwcw t) the ground, what is meant by this expression?

When you turn on a water faucet, the water usually flows immediately. You donp ux9m*;leji3 oy re1tin9r)b)srm ,0’t have to wait for water to flow from the faucet valve to the spout. Why not? Is the same thing true when you connect a wire to the terminals of a battery? e j)p)sr y;*bi1om,me9r9 l ut30xnir

Can a copper wire and an aluminum wire of the same length have the 9k ofvi0iv t tge-q26-same resistance? Explain.kt2oi9ev-f6i gv -tq0

If the resistance of a small immersion heaqz(b.2 orcln :ter (to heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the .:(onz q crb2lheating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, ho :zdahbp41n ut1)t22a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resistance, (:htz h)bdta1 4nupo1 2b) 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 lightlow5qkny cw734 q2tu-bulb burns out?

Explain why lightbulzaij bw*z6 b4+bs almost always burn out just as they are turned on and not after they havb za z4bw6*i+je been on for some time.

Which draws more current, a 100-W li( e ,(g;ya.srqkdyp-*xxdtgrb . r :s/ghtbulb or a 75-W bulb? Which has the higher resistanc e/y-s(trb g,pary:d xr dq;sxg.k.(*e?

Electric power is transferred or3han 3meqi(: ver large distances at very high voltages. Explain how the high voltage reduces power losm :(3qhner 3iases in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fuse with aufa*6j tajrg m 4(+uz +0smrc) 25-A fuse?+ f4sctz6au+mjag ) (r*rm0uj

When electric lights are opz ch/f1h z i-hmof91-merated on low-frequency ac (say, 5 Hz), they flicker noticeab-1f/91h -chi zhm zfmoly. Why?

Driven by ac power, the same electrons pass back and forth through your re3fv -j,ybnw4tau- z e4ading lamp over and over again. Explain why the light stays lit instead of 4-yva,n t4ejw-fzb3u going out after the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. Imy2c( 4zerbo6/bksh8 wh f d-+bnx. i6fmediately after the toaster is turnenodx.(b6krw-zf +i4yhcb hs82 efb /6d on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a r;tdy* eggje:6esistor? Explain.

Different lamps might have batteries connected 1mrm ry p:xom201qez7 mt/0yu2e3lzb in either of the two arrangements sho0uml m ot7y 32e2pxb0z1mz1re/qry: mwn in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How 9 -x:z fr, gg8u waa1hwo3qhd1many electrons are flowing past any point in the wid3h,u-g1hwo zf1xaa:g9wrq 8re per second?    $ \times10^{18 }\;electrons/s$

  A service station ch* mqj);iud40 pf/b zucarges a battery using a current of 6.7 A for 5.0 h. How much cqjb)0* zm;di4f p/cuu harge passes through the battery?    $ \times10^{ 5}\;C$

  What is the current in amdrns77kudpm j *509hg peres 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 amcp m (ru,/+cf toaster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current9fegsw;uw(4h a f82tedd)z 3s through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-V line.rko +iqbga y(+j34fy 7
(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 dryerr x)tvm mi z.k(oyj y0/9hd0v x0ug.m, has a heating element 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 connec 8peu +aib twr8nd*yp d :(nd9d2mo;:hted to a bulb whose 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 car7nq4 ex jm11sarying 2800 A (Fig. 18–34). Thxjsam4 71 nqe1e line 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$

  An electric device draws 6.5asj uy60(). vcg*rgbe :xit u50 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 current of 0.60 spdcv8(xt1 / zi1b x ciqq2;ukkzy6:1A 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 of tu7vuz.utm f6r1k+sdj 0 ngsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copp(;9fw gy o9c-knz,,jw vn8ocwer wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire 2enx6*fi)*8sh x pt5*i7wt mlk .0 mm in diameter, to 20.0 m of copper wire 2.*) wk *mfxinis p58 xtthel*765 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tungmbh sc. 6ytm6 qr4t4whum926y sten wire of the same length? Give numerical details.6tc s q46 t9r2.w mmm6ybyhhu4    mm

  A certain copper wire has a recs+qgdf:eh)3r ss ap1m)cvt/ k94j.fsistance 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 (originally at.pg2mrb7aw+sfl1n 9 xbe hf 83 3pr9 hafe72gml+ 1wb xnsb.f 8$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivity as tb.-g6ewsmvhh8s y* r87 ;obd tungsten does at h7rdo; b-g*bevw. hysm6 8t8s$20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a res(4g 0 cykm4oiwo32 vo q/sk:dhistance 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 0fn zg3,y f+kyvs+(9z mq7c uadrop along a 26-m length of household no. 14 copper wire (used in 15-A circuits). The wi3+ag 7szyy fmvn9q zu+(k ,cf0re has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has side,-qy m8qxnvp8s 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 through th,mn8qx -8 vqype 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/+f di.mjb4lj . If one has twice the length of the other, what is the ratio of the diameter of the longer wire to the diameter of th+. bf jj/dim4le shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.0xvgf( myea gann)+pb*cs(05n6 3a -.dgwj8lu0-V power supply, and a current of 0.4p(l(au m -dj86g e3xcagyfnnn) *+sa5vg w0b.212 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 followed by 5.0 m)z ij rba 2sfmn(trr;2hz)t.2 of aluminum, both of diameter 1.a2z rttj2; s))n(m .h rf2bzir0 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 resist 8)yiceo:x en7p(rq2 aance not changepa2cyx:8eo) (r e iqn7 with 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 electric oven is designed to gt4 3tu6e,8 avinl it+produce 3.3 kW of heat when 64avg3i8ul tt+ n,iet connected to a 240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption *a s5(hhln tl:of a 3.0-V portable CD player that draws a maximumht :n5s*l(hl a of 320 mA of current?    W

  What is the maximum voltage that can be applied across w i* ac1h-*/h i+pcigga $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and curreul*9mz 4cgvi+gz*b 6fd;o8r tnt through, a 75-W lightbulb connected to its proper source voltage of8guzd6f* itgl ;*rmocz+ 9b4v 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. Cala2l:q3 labgq;*.0 -j*drmxpdhh z,sz culate
(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: 850xh9*qj 0f +2p-ve cbdhr+5 .*dxde hqh 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, where electricitd6r; ng wxo*gxp,5pz- y 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 *gxo pg6 - wd5x;p,rnzit 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 550-W toaster use in the morning if it isuv62ptgh; 9 u)xgmti8 in operation for a total of 15 min?x 2m8hvg9)ip ugt;6 tu 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 leave +fc/ syo7qar1a 25-W porch light on day and night for a 1yoq cfr7+/s ayear? $\approx$    dollars

  An ordinary flashligiq oxn h n+0x;u2q 1/pyk-lc:nht uses two D-cell 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when turned -qxy/h1kq nop x n+:0n;2ucilon.
(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 energa umrs un.ud+ivvy,9pr/y/pc.p p8:2 y 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 1naomo 2j* 6ldj26xr;s4ci0lg 1 *hfpe20 V as in Fig. 18–20, can be used without blowing a 15-e0o 2 6; j*p6la*rjhn1c g2mxod4 islfA fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. )gbfhdl sxl 4;w 1z4 9ucwe:9p16 copper wire) and of length 2.7 m (9 ft) is connected to an electric h p:gc19lh 4 sl9wwu;xdfbe4) zeater 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 through pmpr7:yazsz/ 8:j1z s fmkh5py) r8 :ewires :ymjpszm 8: 51rk8sp7/ ):zyezpr f ahwith total resistance $3.0\Omega$ How much less power is wasted if the electricity is delivered at 50,000 V rather than 12,000 V?    $ \times10^{ 3}\;W$

  The current in an electromagnet connected to a 240-V line isf *zp /ubmw:(x z. +chd3s;dru 17.5 A. At what rate must cooling water pass over the coils if thedcm /.3sbzur+( *uw hdxzf;p : water temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater fwvl2d8cw egc59/+hbhnn (1l can be used in a car to heat a cup of water for coffee or tea. If the hn lhghb8/l1wwv cc9d 5f2+n(eeater can 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.    $\Omega$

  Calculate the peak current in aar 9laz *8gq+m $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, is across a dbm ;s1uhau 0,cy2ho-+bhs 8t $330-\Omega$ resistor. What are the rms and peak currents in the resistor?
$I_{peak}$$\approx$    A(retain two decimal places)
$I_{rms}$ =    A

  Estimate the resistanbzy0z x1n 22,rbyyd3 7wgm:lnce of 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 alternating current in a 1500)namw:. +dv f7y/shxx -W device is 5.4 A. What is the rms vs d. f/xv+wx7hm)n:ayoltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder isi*v:p ol2hst;9vb p( qkd9s8un;k qr9 connected 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 2 qyfj(oyko/m78cl( s power dissipated by a 3.0-hp pump connected t( (ol/fy8s27 ymjock qo a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to a;au)bz:mjqr8 $240-V_{rms}$ 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 curr 9.x+ r(xjmxement 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 currenytkh uk nw3-32ad4o(5f v+uxnt when 22.0 mV is applied tou5 +2vo3ufk-d xt nanh4w(ky3 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 Earto8pb tv7sr(ep 0z wwa9 1m8v5 lzm7z)th’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 Earth’s atmosphere, 1js fp-2c2wcf)fiqcgg ++u3svt4 :wk $He^{2+}$ 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 i 73 d,vjzng(p+dzb(qaxon membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with an elect9k, itjj g*px1s a*5zqric pulse. The action potential is detected at a point 3.40 cm down the axon 0.0052 s,gzxtjq1**i 59j kpas 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 instead of only one?)    m/s

  Estimate how much energy is required to transmit one action potential al+-f)zmg/fz yh:) *mgb/jycv l ong the axon of Example 18–15. [Hint: the energy to tra f:jf*vy+-mmz/bg) c zg/h)ylnsmit 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 poten dc;2 p vvnw(wh3i-snz*)6xzp.ej:uktial, $Na^+$ 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 ampere-hourh) 9a m*3vrrszc 8q)kx?    C

  What is the average csjjh /)pkex ,)urrent drawn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of the oa3 (*svodp v* tcd*( uem/*nrtwo headlights uses 40 W and each of the two taillights 6 W, for a total of 92 W, how long will a svp muva** do n*r(co3t(*de/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 heater is 5.4 m long. If it is made of im 1rjpp0;kz9ovpx;)v ron, what must its diamet;;kvx)pr1ojp9m vpz 0er be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal o( *jjt5q((daqo 9 y9uyrfu hi2f the resistance R; that is (r q yidhujoyq(tju*95(f9a2 , $G\,=\,1/R$. 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 powedz gc,-x+q)gvr. Suppose that instead of using high-voltage lines to supply the power, the power is delivered at 120 V. Assum g gz)d,qcvx+-ing 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 househonxti,7y q0zp3g2ana 9 qj1 v1r8vfzi.ld 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 andf,o 0mb1ifra ( the two lengths are wrapped together side by side to make a thicker wire. How does the rebaf moifr0, 1(sistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 117 V. .bthuqd +ri/5c y2c a:
(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 doen :mqy80 a5szys not become so hot as to start a fire. What diameter must a copper wire be if it is to cayy8q5: 0amnzs rry 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 tpxs hgm) riex5(/oo; 0he 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 delivers 950 W of eohdo cv) hofi)ta)c.q*.o 8f .nergy per second to the intercoao .)*8.h ooc h)vqif )ft.dior. 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 material. One congx/6us+lr ck xw b/3 *l7zew/sductor is twice as long and twice the diameter of the second. What is the ratio of the power transformed in the first relatlg z3cb/x6s7/*xsl/u rw e k+wive to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is usqb y s29-k ow5b8ha7nted to heat 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 sourcekkz*oa8x (xe9 .mxv v4.
(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 vehiclezib6nd g ;px -d+pgsw6b596nlxcl 5u 1 makes use of storage batteries as its source of energy.cwun +5 gp1zls g bx;66d-xbld5i9pn6 Its 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 resista/das * tw+3owfnce 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 accelerato;vi*zh p2z,nzy diu oldl1 j9-q fm-3*wh;hh3r at Fermilab (Illinois) is designed to carry an 11-mA beam of protons travhh *idfy;i2hl-31*wn o;zh9z md p3qu,jzl -veling 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 ewwq+zy6jkh0q1cq-q f.:+-zg ijr;x is copper wire with k cqiq+xw:1+6y j;zqh- jqr 0 -ew.gzfa 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 ra+wi0zc /yz( +*h1npi fil1r njaz+6je ted at 95 W when connected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wirzezi++ lj1y *p1j/wn f cn6(0iaz r+ihe has a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system vol+ynh5+tsa ,(* duk cogg kuf;9tage varies from about 12 V when the car is off to about 13.8 V when the car is on and the charging system is in operation, a difference of 15%. By what percentage does the power delivered to the headlights vary as the voltage changes from 12 V tofo t(du h5ak; snc k+*9,ug+yg 13.8 V? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V ande5u v1k6ke q)h 40 W for household applications. Lightbulb B is rated at 12 V and 40 W for automotive applicakvhu6e 1kq5)etions.
(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 et8a ) az;5sympi3bn(0whv d :120 V, which draw 2250 W of powi5s);e: (th8md n0 zpwbyav3aer 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 5.00czvn; 7*g/hoj cm (Fig. 18–37). What is the resistance of 10.0 m of thisv*/jogc h7 ;nz pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistan ll90 n2sxzeu k0 xpej)8oyp(8ce R is stretched uniformly so that its length doubles, by what factor does the power dissipated in the wire change, assumine u0xjzx88op(02ps)l e ylnk9g it remains hooked up to the same voltage source?

  A tungsten filament used in a flashzijf2 m; ,pu(vlight bulb operates at 0.20 A and 3.2 V. If its resistance at uvm j,;izp2(f 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$