What quantity is measured by a battery j gz2k*o6t/elrating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow a6 nrujbu7e0 zw5d d sd*7m 2g1fgdm+8qway from the negative terminal in the cirgq7 n5r+d 18fu7gusdwe zm6m0 *2jddb cuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is opera;6ignrwdmc oi.pr. 8 .5:azrlted, what is being used up: battery current, battery voltage, battery energy, battery power, or battery resi5lr8mz6i.r;ow r:ig na..pcd stance? Explain.

One terminal of a car battery is said to be connected t)t(s-zy6z9plz uepg3 o “ground.” Since it is not really connected to the ground, what is meant by this exst69u3zpp- le( zyz)g pression?

When you turn on a water faucet).ar cdmxo*e r 49vn*oe.r8ub, 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 thi9o).er8o *rd r .neum* xabcv4ng true when you connect a wire to the terminals of a battery?

Can a copper wire and an aluminum wire of the same length have the same resistp,wxa0y :n 8cleyy .:+gd6m) lmjrp0v ance? Expa+0cp ::6 m x)yrv8,llwjg.0dpym yenlain.

If the resistance of a small immersion heater (to heat water for tea al +d xs w3l7s9, 1kcea+,ibooor soup, Fig. 18–32) was increased, would it speed up or slow down the heating pro,e39,sbca+ l laiosd kx1w o7+cess? Explain.

If a rectangular solid made of carbon has mzw+08x1e gzbm, -a tjsides of lengths a, 2a, and 3a, how would you connect thea1+ej gwz,m bm 8tz-x0 wires from a battery so 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 z) vh+tcnwlj * q-9x.r.0k.;y r alrq: 6gofnplightbulb burns out?

Explain why lightbulbs almost always burn out just as they are turned on and w7c,d un as-6y go 4l4aup/4eqcjp (t.not aftjau,n q(aeu ccops ty g w-44l4/.dp76er they have been on for some time.

Which draws more current, a 100-W lightbulb or a 75-Wwv ky)-lqoe;cz:2lg ; bulb? Which has the higher resis):ce l; -vwz; yolk2qgtance?

Electric power is transferred over large distances at very high vjvmhtj9j2 p1+oltages. Explain how the high voltage reduces power losses in the transmission vthj92+mj1j p lines.

A 15-A fuse blows repeatedly. Why is it dangerous to repy deskhw w: 0cae-wh)u00vwa5,q:p*jlace this fuse with a 25-A fuse5wy *0whh:jvae0e- :dp aqw0 sk)c,wu?

When electric lights are operated on low-frequency ac (say, 5 Hz), they flbjd-sy 34pao 2fxcbi,(* b8 mdicker n (b*b 4,2xdof-8 msbyc3ijdap oticeably. Why?

Driven by ac power, the same electr-v mpemald -(9ons pass back and forth through your reading lamp over9e- mpva(d-l m and over again. Explain why the light stays lit instead of going out after the first pass of electrons.

The heating element in a toaster is madx.4yu*yw4lca;cj5 xm4 vbcb 9e of Nichrome wire. Immediately after the to9u4bbcca4x vywlj*cx .5 4my; aster is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resisthmmsyvwq;+ az k*5) m7or? Explain.

Different lamps might have batteries fpk,29rst 6v6e lzo0kh(lh1mv0 :yl mconnected in either of the two arrangements shown 1m2y0k,:o v rlz6k0pl(v6lfehtms9h in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many electrons are flowiv+18e dpbjfa .ng past any point in the wi.+1dp8b eavf jre per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery ujhsj-3q lf d*6sing a current of 6.7 A for 5.0 h. How much charge passes throjs *6fd3-hq ljugh the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes is..73amxhh c+tjf2 oxf $1200\,Na^+$ 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 produm4k2)tvwe ,pf60 c) xv (bflofces a current of 4.2 A?    $\Omega$

  What voltage will pr(te 1e7jh ;vl(w*bf ploduce 0.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 378 xc*c kksld120-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 with a rp,hu ,k7vm e8vesistance 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 whosefi 3yorc ()5 -e) gtokem(nzj0 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 (Fig. 189usby8: drk+ j–34). The line has8b+suy 9r k:dj $2.5\times10^{ -5}\;\Omega$ 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 (nj:oexrzd9ol bo*n9/7)u rgat 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 z 8x6tg6ogulz d3c; o70.60 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-(855n7ye 3cqa)e2tsxoq cubmm length of tungsten 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 k5gvqdj6;sr6o)nk c *ce ;w 3din diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistancww3 d 7t(.i.:otambulr, z vh7..dv qde of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in di z.w dmolrb.tv7. 7d3h,dai.wv:utq( ameter.   

  Can a 2.5-mm-diameter copper wire 9vto* /n +smahdu*1rhhave the same resistance as a tungsten wire of the same /*tvanrs+*h 9hduo m 1length? Give numerical details.    mm

  A certain copper wire has nsg/qmv j 083,8s)iad9t:qdk-nx xoza resistance of $10.0\Omega$ At what point along its length must the wire be cut so that the resistance of one piece is 4.0 times the resistance of the other? What is the resistance of each piece?
$R_{short }$   $\Omega$
$R_{long }$    $\Omega$

  How much would you have to raise the temperature of a czs+ weqw2;pn0opper wire (originally at2 z0;e+sq npww $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper )xja qthsx.su 1mc4f*v53r 4hwill have the same resistivity as tungsten dc4 3hh.15ssjv4 xuq*rxf ma)toes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a res )azxqn )hl+rai2 ri;2istance 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 9fl k,mqz+l-u n3crk( of household no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm and carries a 12-A cur+9nfrmkz c(l, luq 3-krent.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm, 2.0 cm, and 4.k 7jqbj 9.u(1zc/ g:zldi7yamum(9 ne0 cm, lying along the x, y, andjzluu9.i (71 7zbj9qmcg ea:yd(mn/k z axes, respectively (Fig. 18–35). Determine the resistance for current that passes through the solid in
(a) the x direction,    $ \times10^{ -4}\;\Omega$
(b) the y direction,    $ \times10^{ -3}\;\Omega$
(c) the z direction. Assume the resistivity is $\rho\,=\,3.0\times10^{ -5}\;\Omega\cdot m$.
   $ \times10^{ -3}\;\Omega$

  Two aluminum wires have the same resistance. If one has twice the length o+io;s0fzn4) ,gekd6jmycp+e f the other, what is the ratigdj+fszc )e+ 6kyi0pnm eo4;,o 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 l,ee hvljh ++:to a precision 10.00-V power supply, and ajvee+,+h h:ll current of 0.4212 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 og gx/erpa1 3.pf aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is placed across the xgar e13pgp/. 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 importan tqqun;hhei2 y3+o05 pt that the value of a resistance not change with temperature. For example, suppouhhpe025o q+yn;ti q3se 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 tmk i,fj,9 akk mt:,p(zo produce 3.3 kW of heat when connected to a 240-V source. What must be the res9mmf,(i:t pkjzakk, ,istance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player t , -szk7;wdlbmhat draws a maximum of 320 s 7z d-lk,bm;wmA of current?    W

  What is the maximum voltage thajp5czq ).nnw/8iub 8j v*t(/xdb)h v wt can be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current thrx55kg cq:izg44sy4/nztv nh* ough, a 75-W lightbulb connected to its proper source voltage of 1:ks45ny54 *ih/gz qvc4 txgz n20 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. C0cik)wczlc*b ;w xb5s,8k g-d alculate
(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 and 1250y b39j,oe3il1qg4l iiv 0* cuf 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 el+ eq0.t5hg98hhl jesi ectricity 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 it be rela9e h+8 i0eh th5lqjg.stive to 75-W 120-V bulbs? [Hint: assume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy fea(/k 8r7z fuc*y ra5does a 550-W toaster use in the morning if it is in operation for a total of 15 min? At 8ye5k(uf/cra*z 7fr aa 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 light omfa-mvl6d 1rx3 jy: s.vgl8g ;cb2t9s d*be 3vn day and night for a yex 2;fld 1vvd8gb6 39jtyb- :.re mvmassl3g*car? $\approx$    dollars

  An ordinary flashlight uses t:(2xz j cmmd,nwo D-cell 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb dr,: cmmxzn2( djaws 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 energyrw.h;lpz3p mf5esgtfcm;1r9 h e2 o9) stored in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connected to 120 V as in Fig. 18–20, can be usedg2 /r,q7akc gb:q+kb +wbz:nm without bloc, +b +ka:g b 7qg:/nbwkr2mqzwing a 15-A fuse?    bulbs

  An extension cord made of two wires;a v ,tht4i0*rx)bk 7fbnz1ni of diameter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric heater which draws 15.0 A on a 120-V line. How much power is dissipatedhi4z1v;*f0 ant itx k,bnb)r 7 in the cord?    W

  A power station delivers 620 kW of power at 12,0cq: l68s wzf)rlv-*dy00 V to a factory through wires with total resiy 6zq)llf8*scwvd - r:stance $3.0\Omega$ 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 17.5 A. At whxy,ptb yd;k -ljy* a83at rate must cooling water pass over the coils if the waterk yta,j*- dxpb38yy;l temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car cl): aab4hre1y a3 h(gto heat a cup of water for coffee or tea. If the heater can heat 120)bhgclay1 : rah3ae(4 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 f8/b8w kcbym pn6 j.gte4u.;ba $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is0tf+aa.fyk a g8s y::xp/*t9dqba sx: 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 rflz/x; st3u.ok6 z;gthe $120-V_{rms}$ 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 1500j46 o6p;hwhxk0 kw- dd-W device is 5.4 A. What is the rms voltage acro;6 p jdwh-64dkox 0khwss it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected top;vrfn q6z3p (i f2zxiw0*-kw 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 dissipated01te6 8jzmh4 aj . q/kci+nlle by a 3.0-hp pump connecte q/t llkz4 .+8ijjme6e10ahncd to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected*j uq. tkcfbvxe wgtv2( i6su-134 ut9 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 currfz462nmlk)av6 3spe e ent 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 wirowyh4zrm j3e bns:36 ;e carries a 750-mA current when 22.0 mV is z;w4moh e3nsj r63y: bapplied to 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 Earth’s atmoft rq/d1*d;.j i(tmnv sphere, $He^{2+}$ 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,t::ftq3 (k uh+pw)r op $He^{2+}$ 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 eledjr/i 0 )mh,ivctric 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 action potentia3 8.afmwxcy )n-ssnap1 6wl7bl 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 needed instead of only one?8xswb 7mfl.-ny pn1 swa)a3c 6)    m/s

  Estimate how much energy is required to 2jwpfoe( ,8b)jz;juv3ab ib5transmit one action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored by ch fb5;pj(8) bba uj2e 3,ijvowzarging 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 poteij xt ym5s;/aor,s0 +gntial, $Na^+$ 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 ampj6(e - *ffrqmpere-hour?    C

  What is the average current drawn by a 1.0-hp 120-V m. 6kr2kbjw-9 0ewxukt otor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of tht 6 nq;2sl; mlj:auspfe/ .b/le two headlights uses 40 W and each of the two taillights 6 W, for a total of 92 W, how long will a fresh 12-V batterys jsqf6 t:/uape2 ;m.nbl/ ;ll 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 8l+fvrf p+jcl * l0q-qis 5.4 m long. If it is made of iron, what must its diamet j+*lf8q 0fcvq-p+rller be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the re+f h/ieh95hr )yfla3n df s/i4ciprocal of the resistance R; l4r/ 9h5 dei3hsf f f)n+a/yihthat 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. Suppose that instead o2u*/s2 tehwkmf using high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a two-wire li2mh2es kwu/t *ne 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 heater hhvv91r /-oh p$3.0 h/day$ (“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 thb*w(r,a/ etip e two lengths are wrapped together side by side to make a thicker wire. How does the resistap/tbire (, w*ance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed f+zc (qahr d 7 5nge/:u8n5icgc9h(hhyor 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 housej zg l9i/tar)um2.pc 4)h 8ywa must be thick enough so it does not become so hot as to start a fire. What diameter) au) a4/29il8gct.jhmzrp yw must a copper wire be if it is to carry a maximum current of 35 A and produce no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by the equa q7j imz7.0czr:qvjdj: o/j is+d/ *xotion $I\,=\,1.80sin210t$, 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 runni u r,c1;gz.onlng at 65% efficiency delivers 950 W of energy per second tnu o.g1zc r;,lo the interior. 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 v. 6a2h *a fq5cwft.zfthe same material. One conductor is twice as long and twice the diameter of the second. What is the ratio of the power transformed in the fiqhaa 2tffwf65*. c.zvrst relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room of volummg7 3rc4 bgvezc r*o,je*9gx4e $62\,m^3$ 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 hookev 784jy3s.0mla: 9 rttuxdijkd to a 240-V 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 so- kuagg m(8ha5u wdr(/h/ l(w 8l*iiplu9xqx(urce of energy. Its mass is 156u5ai( gg-phaulxw((h 9l(lrmw d x*qki 8// 8u0 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 resistaby 464ej-7k;wuik*i wu8r.ghqur b6once 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 (Illinogf5h:ytbq .; bis) is designed to carry an 11-mA beam of protons traveling at very nearly the speed o5y.;h:f b bqgtf 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 2fyj 6 *k,qizsA at 220-V ac. The connecting cord is copper wire with a diametersjy* q ,2k6zfi 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 connected to 120 V. The heating elxr3k 5/n; /unwuaev e .ezqw7+ement is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What is the diameter of v/;73a+n k qxnwuzwue ee/5.rthe wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage variesl/ cu0vdj6qs 8 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 per6vdj 8u q0/slccentage 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.    % increase

  Lightbulb A is rated at 120 V and 40 W for household applications. Ligh om+tdao0np+hlb , u ,e410o-a.cjnhv tbulb B is rated at 12 V and 40 W for automotive application a 0hnobo1c0+t.vje4dno+ al,,uh-m ps.
(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 atz 23xgg3kv-t set of appliances at 120 V, which draw 2250 W of power xg k2z3-gt 3vttotal.
(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 diame1lezt2:adg( eter of 3.00 cm and an outside diameter of 5.00 cmgl 2eezt(1ad : (Fig. 18–37). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R i3z xmskg0i/97-p;jrx5h z *nzrczbo0s stretched uniformly so that its length doubles, by what fabz oj 0m-7 cxzz g*sx0 r;3h5/kz9ripnctor does the power dissipated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operates at 0.20 A and 3.2 V. If ioe1+ sgxvag7mj+u9r/ ts resistance a a+m/v17o+jexgrgs 9ut 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$