What quantity is measured by a bati*vhr+zl ,: qptery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow awapfos4/ u d;4y56gbf2xc5r mzmy from the negative terminal in t2o /g4ys6u z;x4dmm bf 5cr5fphe circuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what iab,dv 7r.ndx6 ( da.czs being used up: battery current, battery voltage, battery energy, battery power, or battery ,c a. . (dxb6vdr7azndresistance? Explain.

One terminal of a car battery is said to be connected to “ground.” S2;mvx84ipg)ae* bc w kince it is not really connected to the ground, what is mea;pkw*vm2)a cei x4g8bnt by this expression?

When you turn on a water fauc-cdx:em7l rgc 8 xolri.l-7g6et, the water usually flows immediately. You 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 terminals o- 8g c7dlx6x-r7.gcl:ioel mrf a battery?

Can a copper wire and an al bk92majwi 3y(uminum wire of the same length have the same resistance? Expbiw3yamk2 9 j(lain.

If the resistance of a sm 48bhj(l9k scaall immersion heater (to heat water for tea or soup, Fig. 18–32) j ak4sc 8h(l9bwas increased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, and 3an s*t.tirb lf+prby3 .n598 mv, how would you connect the wires from a battery so as to obtain (a) the least resistance, (b) the greatest r.+ l 8vtbnim.3s9ty*fr nbp5 resistance?

The equation $P\,=\,V^2/R$ indicates that the power dissipated in a resistor decreases if the resistance is increased, whereas the equation $P\,=\,I^2/R$ implies the opposite. Is there a contradiction here? Explain.

What happens when a lightbulb burns oyal7h 0 rzqh8up)9njb 8e+1kcx s;sj3ut?

Explain why lightbulbs almost al8 ttgr 1oow)6ew2qc9q 6dfg5++l opixq2g0dzways burn out just as they are turned on and not after they hlpigt g0do69 c+q 2trqe12) z5qwfo8w+xg6odave been on for some time.

Which draws more current, a iok/8e32spg8dk*gs z, i o a1hpb3 h7u100-W lightbulb or a 75-W bulb? Which has the higher resistancebp1h3 e8pasg o8kg ,zh7d/i3iuso* k2 ?

Electric power is tranb6m++kbxu :ap sferred over large distances at very high voltages. Explain how the high voltage reduces power losses in6a p :mbxu++kb the transmission lines.

A 15-A fuse blows repeatedly. Wh0r8mt/,u dvpuy is it dangerous to replace this fuse with a 25-0p/d,uvur8mt A fuse?

When electric lights are operated on low-frequency ac (say, 5 Hz),odxar3tg y/ t.38b-h e they flicker noticeablyyo-3r htxd8ea.3b/t g. Why?

Driven by ac power, the same electrons pass back and forth through your e5 -hu 1hm7dtw (la u1eb4ps3xreading lamp over and over again. Explain why the light stays lit instead of going out after the first pass of els5te wmuhd1p3h7 a1 (b4e-uxlectrons.

The heating element in a toaster is madevemit6o75g*k,iy:4 s e ggqm xi)0wb3 of Nichrome wire. Immediately after the toaster isbgv7s3)xy 40keweo gmq i *,itm:65g i turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resis-5xvcd82- b m zqvyl(stor? Explain.

Different lamps might havaf:l3ji9 5g8prg a.xw pqh:g,rr0ws 1e batteries connected in either of the two arrangements sho5fxq wlspa .ir0rw 31:g9:ap8 g,hgjrwn in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many electx9p*ee / xr(a9dpcb 7lrons are flowing past any point in the wire per second? eabp9c(9d7 xp*x/elr   $ \times10^{18 }\;electrons/s$

  A service station charges a jibhq 3):hc zsu:8u a*battery using a current of 6.7 A for 5.0 h. How much charge passes through a:)uqh cu* iz8jbs:h3 the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes iflh4 ecrri9busg (0( pn9n v300w+v:s ly ,zcpd $1200\,Na^+$ 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 ia2nfv88d+n;gf bsen-o8 jc c0 ze6j(120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current rdfj 7vad. tfi7vt,*8 (e0 g/o1tped 0zlqj,bthrough a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-V line. p2kopx uvqjefk8;8w.8e),m q
(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 ha 8 ltslc;uxbt* uw7.5 p(igj ugn,1/als 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 connectev)bzeozv:n94( g3baa d 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;ac j 2c:.xlw.k/m spw carrying 2800 A (Fig. 18–34). The lwa/. wmjs2xkl:c .c;pine 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 6.50 A at 240 V. 2/x y1sraql )lut9:uc
(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 s4fcb 4:z-bm9sym/ie 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 /+gd 3 ska7id *ltcx:sa 1.00-m length of tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m *v;(vi+ 8hwtkbwz4 qm9ads- z length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0-e+c -m nl.utm m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in din.cmm-+ tl u-eameter.   

  Can a 2.5-mm-diameter copper wire have the samer *m6vak8rae 0fbog64 resistance as a tungsten wire of the same lengte8g4o6rk6a*b a fvmr0h? Give numerical details.    mm

  A certain copper wire has a resistance et ,h6puqjs+ ;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 (ori2x* brysu t jeh8*/x1fginally at f*ux jtb*he / 18sy2xr$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will ha6p/ko0ogbfz*5 r s j2esv7 ghk )-sub;ve the same resistivity as tungsten dbf )kg u eos g/062poh7sjb5s*; kzrv-oes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of pbsnzvlm*m 6 8-9z 3jdabout $12\Omega$ 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 alongl6bx:559wa( tnxtjxe a 26-m length of household no. 14 copper wire (used in 15-A circuits). Thetw5 anel(5:9bxtj 6xx 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, a j4i v6;ehqtx*nd 4.0 cm, lying along the x, y, and z axes, respectivelyh v*;ejq6 4ixt (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 so p;) xd2dev:yame resistance. If one has twice the length of the other, wx d:2evy;po )dhat is 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 wi+1j) avl j).co a/t5rybzd mc(8hvhu7re is connected to a precision 10.00-V power supply, and a current of 0.4212 A8l)mvoh j(15d +.czuc/t vrby7)jaa h 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 coi1lg z)ze.ke dapw66rs a6mgz.o6i29nsists of 5.0 m of copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is pka2o6wzz 1 g6dp.9m) 66gi e.raeis lzlaced 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 resiy5h(:t:pycf8tt b1p hdq(-a estance not change with temperature. For examcypeh5dpq t: (y:ft8b-h t (1aple, 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 produce 3.3 kW of hem4+iqux g i*vldr+0 2gat when connected to a 240-V source. What must be the 4+ vu2gg+ drim lix*0qresistance of the element?    $\Omega$

  What is the maximum power consumption of a9 8th- xjai(cw 3.0-V portable CD player that draws a maxta 9hx 8c(wj-iimum of 320 mA of current?    W

  What is the maximum voltage that can be applied across dwd, wd5 5m7:(+ojnv xrtr 9bea $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the re t e(z, ruwyf.qb968m-rqg; x4uxs1ur sistance of, and current through, a 75-W lightbulb connected to its proper source voltage ofz-1bwmxrgu,4y q8sx9 ;rr(. etf6uu q 120 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heat 6zi 6;vqvjjgn5fxk1: er is rated at 110 W. Calculate
(a) the current through the heater when it is operating,    A
(b) its resistance?    $\Omega$(Round to the nearest integer)

  A 120-V hair dryer has two sev* uwds,m2 * mhq3.:*lpy;kus5f mp olttings: 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, where electricity is delivered to homej4tnd4 vlm. gip5/jzp01gu+is at 240 V. If you use the lightbulb in the United Sjnpi4t/g5 m0lj+ .pd1i vgzu4tates at 120 V (assume its resistance 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 550-W toaster q.q6y8sihk1f use in the morning if it is in operation for a total of 15 mi1h.k68qf q ysin? 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 light6q+mwgzvt 9zwi9t9 fqq.cp3x,+y.pj on day anwg ztmq q9py6 ijtpf qc+zwx v.993+,.d night for a year? $\approx$    dollars

  An ordinary flashlight 6r u2a0 qhu2;gwrr8kosh rd67uses two D-cell 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). Thrrh7khrr0so822 ;66w gqadu ue bulb draws 450 mA when turned on.
(a) Calculate the resistance of the bulb and the power dissipated.
$\approx$    $\Omega$(retain one decimal places)
   W
(b) By what factor would the power increase if four D-cells in series were used with the same bulb? (Neglect heating effects of the filament.) Why shouldn’t you try this?   

  What is the total amount of energy stored in a 1ais4ngh. 5/0lc fd1 za2-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 ct2g ro+/pv,z Fig. 18–20, can be used without blowc2togv+/, zrp ing a 15-A fuse?    bulbs

  An extension cord made of two wires of+n(j0duo 07,qn bcvxj diameter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to a+j0q jondux0,c( bv7n n electric heater which draws 15.0 A on a 120-V line. How much power is dissipated in the cord?    W

  A power station delivers 620 kW of power at 12,0nsol to8mj 6) )ka/b8yx:nbr 100 V to a factory through wires with total resistance6o )1:am 8t/yl )kob 8jsbnnxr $3.0\Omega$ 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 aub c.kg29kk c;9 wvr0l 240-V line is 17.5 A. At what rate must cooling water pass ov.c9bkuv 0 gl29rwkkc; er 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 h pmdpk1*)p6fhrb/w -h eat a cup of water for coffee or tea. If the heater can heat 120 mL of water from 1pp/kbd6-mw)f*rphh 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 curren k;j f agumimp,068f4dt in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak) r7dxjnl./xnq s.c v; value is 180 V, is across a $330-\Omega$ resistor. What are the rms and peak currents in the resistor?
$I_{peak}$$\approx$    A(retain two decimal places)
$I_{rms}$ =    A

  Estimate the resistance of thg r-tk9k te5eblft(5e)s l:8we $120-V_{rms}$ 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-Wa vs*,8 ge:a.hxk.fvk device is 5.4 A. What is the rms voltgaf,a se :vv.kkx*.h8age across it?    V (Round to the nearest integer)

  An 1800-W arc welder5 zti7buu ,+ eh*loqr47sik4g is 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 power dissipah 5vfe8i.siiw- nan42kpa+m 5 3mjql(ted by a 3.0-hp pump connected fl(i5m jpes.qmi vaw5h- 8 kn4a23ni+to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connect1; niypt acxg(q9 zf-v.poq:9ed 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 s g trec4o. kn4(nyp,*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 carries a 750-mkm0t,9xom*;mc 7h6n fdy 0e efA current when 22.0 mV is applied to its ends. If th6m*nf9f0ek;om xmch7 y,d 0t ee 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 at tdk3c fkxl4/*mosphere, $He^{2+}$ 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 atmosph6pk.m alavex-i u)ndc(we:)v0az9; pere, $He^{2+}$ 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 8w bqb 5fg//b /wwlac,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 potenj2r :urgxs6ie.+jdp ynv + 5p5tial is detected at a point 3.40 cm down the axon 0.0052 s later. When the action potential is detected 7.20 cm from the point of stimulation, the time required is 0.0063 s. What is the speed of the electric pulse along the axon? (Why are two measurements n :6+nex d.yj pi52sgu jprv5+reeded instead of only one?)    m/s

  Estimate how much energy is required to transmit one action potenticvn-b(1 k/ 8ymltdv3i al 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; see Section (d-1ycm8/b v3nik tl v17–9]. 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-s68lynlq16wmi y,u m tial, $Na^+$ 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 t10szqvp7 w l2mhere in 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0-hp 120-V t x 3zvmx8ssc.9fa*jzr 1 0(jqmotor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. I7m ik,datwnwyf;1- j5f each of the two headlights uses 40 W 7m1atd kw, -j;y5wnifand 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 heater is 5.4 cw*u+l r6 (ll 8ahr8e4cdzi7tm long. If it is made of iron,c*z6rtc li+ul l(7848dhaewr what must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the re1 -cwj)q5u rk +rh(rslciprocal of the resistance R; trrr+1uk sh(lw j5 )-qchat is, $G\,=\,1/R$. The unit of conductance is a mho $(=ohm^{-1})$, which is also called the siemens (S). What is the conductance (in siemens) of an object that draws 730 mA of current at 3.0 V?    S

  A small city requires about 10 MW of power. S5 ub fwp)j*oq/1qh(;q 4subqa uppose 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 meter. Assume the cost of electricity is about 10 centsu/o sf;b5aw qhbjpqq( uq4*1) per kWh.    dollars per hour per meter

  (a) A particular housetak1 rq(/vpp5hold 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 6xzbg91q9 c klhalf and the two lengths are wrapped together side by side to make a thicker wire. How doqk9x16gc bzl9 es the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 117 usi8* 1kqgn7rV.
(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 itq: :j7j ) 1ccx+od(n il/33 pbrroitnw does not become so hot as to start a fire. What diameter must a copper wire be if it is to carry a maximum current of 35 A and produce no moc 3/jqwij3+ b :( lt rx7:dnor1npoic)re than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by the elr cr;0eiv2it6ut ; fxvj qo6c(6y62j quation $I\,=\,1.80sin210t$, 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 delive77n q0hgyolr 7*cpo5 crs 950 W of energy per second to the interior. h*p o7q057oc7ycnrgl 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 t +3q 1j;cu pv-jp;j+ mttpr1s0n8eluehe same material. One conductor is twice as long and twice the diameter t u;8p lq; +n1pp+ tjcve30jmurj1-seof 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 heat a room om(,be i8x zk+ 28zuoijf 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 240-6 d:lgaezhd6at gr ,o 23m5p/oV source.
(a) What is the resistance of the oven?    $\Omega$
(b) How long will it take to bring 120 mL of 15$^{\circ}\,C$ water to 100$^{\circ}\,C$ assuming 75% efficiency?    s
(c) How much will this cost at $11 cents/kWh?$    cents

  A projected electric vehicle makes use of storage batteries as its source o -ik4cx0kx4 x*+ r /ad2zbjozzo+m9taf energy. Its mass is 1560 kg and it is powered by 24 batteries, each4zt- jo2kb*moxz icx0a9d+4x k z+/ra 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 )-y4bks xq;-fx3e oyf 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 .pqu6enbgk7;i8gv gq7k,6j m )-dl padesigned to carry an 11-mA beam of protons traveling at verq j, 7qkg gmpa8bn 6e pkil.)-gu6;v7dy 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 )f 91jzio9kvr ac. The connecting cord is copper wire with a diameter of 1.628 mvki9 1foj9z) rm.
(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 954qenzw,k 4 cw7 W when connected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, 4 wz47,kcnqwe the wire has a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system volta7x,v*jqx 0yg;t)j:bcf, miw bge 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 powexm:,; 7w )*tijbb0ygxqcf vj, r delivered to the headlights vary as the voltage 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 household applications. Lightbulb uvt 4-c:om38eoeu :7s1tiiq mftw n(9B is rat uete3m9o1mt-nowsi(uciq : v7tf8:4 ed 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 applirb y)5/ l(o;u/qsraeb: tx:su6gkh 8aances at 120 V, which draw 2250 W ofltsu/r: q 6bs yrae(8/x b)okau;5g :h 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 insidc(m -sruomso pp:86d1 e diameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the resistance of 10.0 m of(ous6 md-:pscmr8 o1p this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched unir7ng 7oo58acox)o)kd 7c0j kbf+xxjv;xe4d+formly so that its length doubles, by what factor does the power dissipated in the wire change, assuming it remains hooked up tx;n agdx)4o8x+b fk ro7kcj oj0x5oe7) v+7cdo the same voltage source?

  A tungsten filament use3iz9e ;uvdlr:: ki1ixhr hy7,v 6a1b td in a flashlight bulb operates at 0.20 A and 3.2 V. If its resistanry a3u:l6i9 khvbti; hvz71r,1 x:idece at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$