What quantity is measu.trzd3b;7 lub3 q kb/ 0llnm5ured by a battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow away from +fik-g 0 qg pu/(ki1cdthe negative terminal in the c1qid-uc kgk/pf0(g i+ircuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operat)b a snvz4n-unxzwu645/s ; zqed, what is being used up: battery current, battery voltage, battery energy, battery power, onwsx q zuz/nnsa; 6) -z5buv44r battery resistance? Explain.

One terminal of a car battery is said to be c r +m.ner;j3 jx(dmdq4onnected to “ground.” Since it is not really connected ndj;+ jm3r.ed q4m(rx to the ground, what is meant by this expression?

When you turn on a water faucet, the water usually flows immediately. Yor41fngr 8 ep7mu don’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 terminalnrf p47g 8mr1es of a battery?

Can a copper wire an:ik9 ,j*ig rxsd an aluminum wire of the same length have the same resistance? ikgr :*sj9,xiExplain.

If the resistance of a small immersion headtoj2f.t ,bi2bsc-c19 t+mz o ter (to heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow down tcdbz1jo imt,22t+-c t.b9os f he heating process? Explain.

If a rectangular solid made of carbon has sidez ;xozn-fd )+jsw ,5cms of lengths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resistance, (b) the greatest resistance?d-;f5zjoxn)m, s+z cw

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 d o wbi1w/r*4zburns out?

Explain why lightbulbs almost always burn out just as they are turne2*1v lvrayrmx6w*r*yk d8t:m e +t8t70asghud on and not after they have been on for so12suxtm+e6ra8vavr 8yy*t0mtr*g *l7hw : d kme time.

Which draws more current, a 100-W lightbulb or a 7j dvc focl i2p;trod3u q521865-W bulb? Which has the higher resist26oc 8 idl;v5foujpr3t2 cq d1ance?

Electric power is transferred over large distances at very higpl r2;8 -enshrrzm*6o h voltages. Explain how the high voltage reduces power losses in the transmissr2 8-m z6sreh;o*rlnpion lines.

A 15-A fuse blows repeatedly. Why 6bxw0fulh a,qp p+g);/pf c9n is it dangerous to replace this fuse with a 25pab p ;x0ff,+9w/)cgh6lqn up-A fuse?

When electric lights are operated on low-frequency ac (say, 5 Hfaci3(wp o1(aymnm6 9z), they flicker noticeably. Why6 9a(in wf(aocmp31m y?

Driven by ac power, the same electrons pass back and forth through y x9g u(uj.+tmel+ew +:a7ds cqour reading lamp over and over again. Explain why the light stays lit instead of going out after the first passm.7jwcud +t ( e:esqxa+u9+gl of electrons.

The heating element in a toaster is made of Nic;idgk m7*n-*oqssav /daaa*2 hrome wire. Immediately after the toast/ai27v-a d*s**dam kqa;ogns er is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? E- m)jy..qk wmwm;k 8inxplain.

Different lamps might have batteries connected in either of the two arrangeme qe6;3s y(um2abzaph/nts shown ybph6; z/( uqsa3a2me in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in h ssdf0c:cio;l8ymk*h)6rw6 a wire. How many electrons are flowing past any point in the wirecs;ifwsc 6rky 8l)dh*h: 6 0om per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.h34s -zy rzq7gf ,bis07 A for 5.0 h. How much charge passez q ygsbf-, rzs07hi43s through the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes i*0ljb v.eyk9y 87.v3 d 7zbwgwf,dtilf $1200\,Na^+$ 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 toasteij)9ly*k 4pau r if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 Ae*fd8pc/6kmd5tt2 o d of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A wyc6*rb4ive )l hen 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 elemen4ekzxy3 3tu:9 ue1 :pexsx 0kgt 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 is x*ldp*o 5 7 o ;zzmzbizr;oc(2$1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electraxt 0tnr6oar86:1bb jig / o2nic transmission line carrying 2800 A (Fig. 18–34). The line h2j 8 bg xtrot6b 1in6o/a0nr:aas $2.5\times10^{ -5}\;\Omega$ 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 atui 1r*zyjh; 9n. c*r:/c h;ejnbrl2gj 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 fh k) soshj6o,cr:g38.60 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 of tungsten wi0 5 fsnpxwxfsa-a02a7 )uz 8qvre 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 in cmsb3i 2si 1 (kbqk ::epm/s)xdiameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminbhdj d)smqvv6 /-15o5 bdq6mxum wire 2.0 mm in diameter, to 20. vmb/s6od-b 6 dxh1q)djm 55vq0 m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire haveja /( v30xiegrz/qmh2 the same resistance as a tungsten wire of the same lenga0mx3j( zgrvehq /i /2th? Give numerical details.    mm

  A certain copper wire has a resis5nde.s4 xmx86zjw7ls tance 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 i(ugu5k7br *:nbfo b)the temperature of a copper wire (originally at *br g7f)u : b5ukbn(io$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same reo6l/efk ij m36sistivity as tungsten d kflom3i66e/ joes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistann e:pyu6x1xr m*hd; p1ce 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 n,; 2pn j,vxsx7j rzlx.o. 14 copper wire (used in 15-A circuits). The wire has djxrxz;jv ,ns7 , xpl.2iameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of bc(ok); riv1 kcarbon has sides of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resis1kco)i (v;rk btance 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 san6l2 68 5hvvkdvnzz: ome resistance. If one has twice the length of the other, what isznk2o zv:l 6vvn68d5h the ratio of the diameter 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 powhahd .*mdg mm7 jc+l. d0m:5drer supply, and a current of 0.4212 A is precisel gm:c0d r djah*md.7m5.+mdh ly 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 follos 7to io6q4wt .k)4megk*i-pdwed by 5.0 m of aluminum, both of diameter 1.0 mm. A it).q 4d-omokekp4t*i 6g7sw 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 is3icf. blmcm y*4dxv ,8 important that the value of a resistance not change with temperature. For example, suf.i x m,4d8c*vmby3clppose 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 designedwv p(g7zaua s+). 5tp1:mkj u(wrt.tz to produce 3.3 kW of heat when connected to a 240-V source. What must be the resistance of the element?p)t. a:wra z+ w ugtu1mp7kv tj.((5sz    $\Omega$

  What is the maximum power consumption of a 3.0-V portableq:s yurl-14sg*lh)8z9 n ybbs CD player that draws a m:8ubl s9zqn b4shgl 1-)sry* yaximum of 320 mA of current?    W

  What is the maximum voltage that can be 4hwik3v rf90 9bg* ttdapplied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, a 75-W lightbulb wfsn1d942 vja connected to its proper source voltadjsv129 4w afnge 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. Calculal -tdyk10l2q v(wc vx-te
(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 setto tn9bzrv7q)2 ings: 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, w kg;7bv)vwgz +h/ cv7rhere 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 7kg;gvh bv+zv )r7cw /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 550-W toaster use in taq5ko .p wpqp4, -s67ht1c fwphe morning if it is in operationpt1swp phck p-q4f wq7.65 oa, 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 leave a 25-W porch ligh:bkiva d*ub;(iuq uax-e .(;wt on day and night for a x.qu(v :iub;a(d iek-;uwb*ayear? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteriesq fv8fi .bflqzl1 i (f*d*0,kb connected in series as in Fig. 18–4b (Fig. 18–36). The bulb drawzlb.* fi0 f(8fflk1bd,v q*q is 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 of energy st;l k+ bn6dgw7;uao t-yored 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 i4*p b67jh,8hdqpr.fy 4bhw47tewgx used without b tb7pw pb84 *64 dqh4 xwhihgfe,.7jrylowing a 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no.pdxl63+ct *f v 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric heater which draws 1l+c6xt 3 *pvfd5.0 A on a 120-V line. How much power is dissipated in the cord?    W

  A power station delivers 620 kW of power atc 26o: .bnfm zsqz(gr: 12,000 V to a factory through wires with total resistanccro62(z:fq.mngz bs :e $3.0\Omega$ 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 is 177k,b7x -d mnwdu zs+1xq4ekr *:/ue4nea syj(.5 A. At what rate must cooling water pass over the coils if the water temperature is to rise by no moburm7w x4suke+/,4xena7(* : dnjyk1edzq s-re than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to heat a cup of p v+; eaoa ubtu*/s:n/water for coffee or tea. If the heater can heat 120 mL of water fro o +; *ut:ue/apavn/bsm 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 c7+q .tfb 6cnccurrent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, is a) 1 wl/o 3j6lx b7k,oqhr(jrpxcross 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 resistanccnwl94k6 v.d* ob;o jqu5ac9s e 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 aqnc* w h6wtbt:32lqf 3 1500-W device is 5.4 A. What is the rms vo :qhl*nf3 cbw 3t6qt2wltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected i *r20s w9tv2i -i5;r)hb t*myinewmw 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 instantanez( c+oszkkqy07obb53 ous power dissipated by a 3.0-hp pump connected to a b o+o35k7kzs cyqb0z( $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connectf7t 81 emkam*tx( :omged to 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 2od(**urtp:f c ia 9c3vpn :gfcurrent 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 22.0 mV i2iiqobmfibu1 (c 7f61s applied to 1iicf(2f 1ou6bb 7i mqits 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 atmosphere,cp0s) pm+mt /kgyj+-f $He^{2+}$ 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 Earthbxre( t(p7o mlp,h,ep.mng ugn* *s9*’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 electricdaj ne5 4f0bky a-v-j1 field 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 actio0k5l,5b)z vp+, u7k r hwnw mws8e1hbmn 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 ohshr8w n+,, m p5we51zb)vukl 0kmwb7f 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 requirfq4few// 1 txred 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 capacitance;1rtf//e x fq4w 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 poten7xsi;wc::n fytial, $Na^+$ 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-m 41lk(h.tue dhour?    C

  What is the average current drawn by a p(l g8 g-iq(a nrz6ej*/cr 0qr1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each-k gxjn 2y2w/i smg1a9 of the two headlights uses 40 W and each of the two tailli/n a1i2kgmg 2 9sj-xywghts 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 heat:)k87ocjl;6jhk8; i mb qrgzmer is 5.4 m long. If it is made of iron, whjm:iz8m q8 kb;gloh6j7k ; c)rat must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal oz. zinwr6/ c2*nmzcy5 f the resistance R; thaiyzc/z 2nzwn6* cr .5mt 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 6t-x,wmqyn (kglq/tz 1kd98m of power. 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 per metlwmqz/qy,9(1t6k k dxnmt8- g er. 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 heatxk3j.i c n2tzg /sr2fj4e77zw f/5wby er $3.0 h/day$ (“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 a1zox8,ca z,fk jymc1, s 60hgere wrapped together side by side to make a th jkme6h,so0,81 yzcfx,za1 cgicker wire. How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is deh 7hp 9yxa:(x u .prtasq.0s;psigned 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 be thick enough so ar8)8fu jrkjqdey(.ur bt/ w-ar6k+5 it does not become so hot as to start a fire. What diameter must af-(dua jt5 rw)r.e/8 +ryjkuqk bra86 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 gn 5bice*n,efz.3v - ej2 xwbg(iven 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 runnr6 r x2l7ib/thjqse*)ing at 65% efficiency delivers 950 W of energy per second to the interior*qs72brie 6 hjxtl/r ). 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. Oneb t+xos :s x:(0q1h.a34hokikeih pg 4 conductor is twice as long and twice the diameter of the second. What is the ratio ofkkx 4it is bo:p ago0xe:h sh1.4(3h+q the power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is ubos/9p,31tmghj2m- 1 it 2xdu 5yoljxsed 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 sour/9g yv7c vqrnfl6)/d 21d e zd/hbhq3ace.
(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 5v794yny7fobnn, l o1d,)c ynm7 dokrvehicle makes use of storage batteries as its source of energy. Its mass is 1560 kg od97)y ynbc7l,rm y,no47nfd v1 k5onand 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 offq/r+womb,luo /e /6.rqpf e+ $12\Omega$ 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 .zz+lh wfq 22v(Illinois) is designed to carry an 11-mA beam of protons traveling at very nearly the s lf2.vq+w hzz2peed 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 con( q(lrt bq8ibu45c1 o;lab+ ard is copper wire with a diameter of 1.628 mm. 5b48ra(+clb ion ;1lqabtqu(
(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 rat3 b9znx1,31psaw bkee ed at 95 W when connected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What is the diameter1s,bzk 3e ab93xp1we n of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from about 12 V when the tc 0ugo 331/8ttoy8vo3wal zt 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 headlight resistance remains constant. t8v3 8z1tc0a/3 tytow ou3gol   % increase

  Lightbulb A is rated 8 7w2 dgjka8m.auvz9sat 120 V and 40 W for household applications. Lightbulb B iss2z kam7 jd9agv8uw 8. rated 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 v.72+r-dc9l6f y7v josnjtdv connect a set of appliances at 120 V, which draw 2250 W of powernj7y-vcfdr 6d2lv+ 9os7j v.t 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 ins54v: z 5ei 62vxfhbkfpide diameter of 3.00 cm and an outside diameter of 5.00 cm (6 4 h5z fvkvbx2epi:f5Fig. 18–37). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uni4pelfjl( qj:3k 6 c2jsformly so that its length doubles, by what factor does the power dissipated in the wire change, assuming it remains hooc3e jjk 6(lpqjl:f4s2 ked up to the same voltage source?

  A tungsten filament used in jdttc42lgohe :o 6j6o2vh05ca flashlight bulb operates at 0.20 A and 3.2 V. If its resistance at 2d 6hecjhctoo0og :52vjtl 4620$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$