What quantity is measured by a battery rating given in ampere-hoursc *y ivgk jgh):v;8;jp $(A\cdot H)$ ?

When an electric cell is connected kka+7jlk xfi ,4)rc,pto a circuit, electrons flow away from the negative terminal in the circuit. But within the cell, electrons flow to the nega7+,xkkc,f) lj kip ra4tive terminal. Explain.

When a flashlight is operated, what is be z7fm1nkro(a acbc(s9+4 f 6zzing used up: battery current, battery voltage, batt7c4 (a fz6cb9 ksofz1a+mrz(nery energy, battery power, or battery resistance? Explain.

One terminal of a car battery is said to be connected to “ground.” Since it is nbe)h*z3rm0wa ot really connected tozae 3)*wm0bhr the ground, what is meant by this expression?

When you turn on a water faucet 2i uo,m1g0feqf1 bbm4, the water usually flows immediately. You don’t have to wait for water to flow from the faucet valve to the spout. Why no1b1 imo gm0ue2b4ff q,t? Is the same thing true when you connect a wire to the terminals of a battery?

Can a copper wire and an am-xi;o8sa ;rjdgvs 4 f): s,whluminum wire of the same length have the same resistance? Eogjhwdvm)sx i;ass-8,: fr ; 4xplain.

If the resistance of a small immej1vjv3i1yn5 ;hwwg x npatz r/,, zq64rsion heater (to heat water for tea or soup, Fig. 18–32) was increased, wou 1hz4 aptv ,y 6wing/;q1vrjnj ,5x3wzld it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a,j fghj-fzui,.v6yp - 0 and 3a, how would you connect the wires ffu fv-. j,g y-6ji0hzprom 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 lighhk6x) /u6 t1bwvv e0 .;zmviqetbulb burns out?

Explain why lightbulbs( 5- xbluajkt8 almost always burn out just as they are turned on and not after they have j(5 - 8alkxtubbeen on for some time.

Which draws more current, a 1bm n6e0;8ukpj00-W lightbulb or a 75-W bulb? Which has the higher resi b6m80u p;jnkestance?

Electric power is transferred se ubc;*y--sr;cyy q6u9x9/ (otw z kvover large distances at very high voltages. Explain how the high voltage reduces power losses in the troyv c/tyrx *s uyqz;cws -(b;ku6e -99ansmission lines.

A 15-A fuse blows repeatedly. Whyqxkb)nz lt7,7 is it dangerous to replace this fuse with a 25-A fusen )zb7lk,tqx7?

When electric lights are operated on low-frn2 ix9 sk,f* oj50 uotpwh)oz4nrqkdj;1-d2v equency ac (say, 5 Hz), they flicker noticeabl h;-*k2x ijwop1 tqd v5 )9u,n0jr 24nkzsdoofy. Why?

Driven by ac power, the same electrons pass back and forpds/:ihr s7h ,qo90hn mm8e.uth through your reading lamp over and over again. Explain why the light stays lit instead of going out after the first pass of electhh7rde 0iqu. hs :ps o/m9,8nmrons.

The heating element in a toaster is madcudgivz(o -ft (z7w0( 2)8u jwnk4gfne of Nichrome wire. Immediately after the toaster is k w fvuzu -(o(w74tjnizgn)2d80c fg( turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor?qqk 8o8rorq+b40ks : o Explain.

Different lamps might have batteries connected in either of the two arrangz e-hyqek zp jtjd .(4r2kh*/47xud3 gements show-dzde/44 k7j3tr(yq*j k z guh.exhp 2n in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many eleuf4 fzug.:1kj ctrons are flowing past any point in the w4 jkfz f:ug.1uire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a curre65 ih,ff c,h ldqzxzr56 k9qrbsh7j:0nt of 6.7 A for 5.0 h. How much chargr6kz0jf fh5q,h,xr9cbl q6z5d h:si7e passes through the battery?    $ \times10^{ 5}\;C$

  What is the current il1pcx7 f) l jfsx5p/b,08 qpr4vr(mndn amperes if $1200\,Na^+$ ions flow across a cell membrane in $3.5\mu s$? The charge on the sodium is the same as on an electron, but positive.    $ \times10^{-11 }\;A$

  What is the resistance of a toaster if 120 V produces a current of 4.(:j htwxo h)w2y43cey 2 A?    $\Omega$

  What voltage will prodbl0 vx22v n1f/a 7rqiluce 0.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-V line. p 5 4y3jkywko85j55vflzkfs )
(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 dryf:*h;qcsyojf. o wev. w2,l93wb3y lser 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 connected to a bulb whos 8zi)+v-rrij1w:c ag +kb siz)e 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. 18–34nv g(0)0xtk at). The line hakav x(gtn0 0)ts $2.5\times10^{ -5}\;\Omega$ 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. ;o, cwkrt59o rhne -b.6s+byc
(a) If the voltage drops by 15%, what will be the current, assuming nothing else changes? $\approx$    A (retain one decimal places)
(b) If the resistance of the device were reduced by 15%, what current would be drawn at 240 V? $\approx$    A (retain one decimal places)

  A 12-V battery causes a current of 0.60 A c(qmaekj2m s m16gcnb:*1fi7through 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 aar .6nlc)1 5l455 viv obtnvwx 1.00-m length of tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance oo eot(cz6i 11jf a 3.5-m length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire 2.0 mmd g0w-o5z7 8vzw;dpac in diameter, to 20.0 m of copper wire 2.5 mm in diametz85pd; zdaw-c 07v owger.   

  Can a 2.5-mm-diameter copper wire have 6+bh5e7mjpgugi*8kw the same resistance as a tungsten wire of the sam8 j7i *+5h gbw6eukmpge length? Give numerical details.    mm

  A certain copper wire has a resistansl1 u,+s)* .6u9bt zgeqhfnb c;nv) shce 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 fy5kjng,b95i lx:nn: of a copper wire (originally atkfnybn x:,9n5 ljg:5 i $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the s5npm89myj mx a,n5-bjame resistivity as tungsten does at 59mm -y,bn j8p5amjxn$20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a red wn2cq)n5: d s,r-anrsistance 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 houxlx zq)+b6 ln:*a l*:mm3e yefsehold no. 14 copper wire (used in 15-A circuifelm) qa e6 blyn3lm+* z:*x:xts). The wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon haswgv+ :r :jof0f 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 resistance for current ::fj g+wr0 ovfthat 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 o47encpmn kia2k3v4 ;. If one has twice the length of the otn7e23ockm n ip4k; a4vher, what 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 wire is connected to a precision 10.00-V power supply, andnv d(:x;ke.e9fu (ymxh)+b11itoq vx a current of 0hx uqvkfitbx xe): m1y ;1nv+od (9(e..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 wireoa6zx8 un1q c :,2aexe consists 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 placed across the composite wircxq :nx eoue1za, a268e.
(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 x.s ,moit x+(hrx5qb; the value of a resistance not change with temperature. For example, suppose you madm5; s ir,oxhb(xtq+.x e 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 heat w6k 4lx; gb*lp87ztm sshen connected to a 240-V source. What must be the resistance of the e4p8 zsxg l l*s6kbm;7tlement?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player that draws a txh*u56. zvcb maxim6bx.z*c u5tv hum of 320 mA of current?    W

  What is the maximum voltage that can be applied acrosstim;zh0 s7g;k a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and my yperf* s r6xr1g6yw v,+j36current through, a 75-W lightbulb connected to fv3yy66mxrp srj *16y,+ergw its proper source voltage of 120 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heater is rated at 110 W. C xdy h5,b7bff9e9fh6walculate
(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 an 48a85x8ig s/0zh (boem kak1qq qmdf9d 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 delivebbg6geqami e2z t1;*0 red 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 relative to 75-W 120-V bulbs? [Hint: assume roughly that brightness is proportionq gi 6mtb*ee2gz01;baal to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use in the morning i.fnfsw/wr: k6f it is in operation for a total of 15 min? At a ckswn/: wrf6.f ost 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 kW5;ye/wavu 63h b q-3zpg.zpiah, what does it cost to leave a 25-W porch light on day and nigaw56 h;pz/p3uzv3bi-ygqae . ht for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cej7l l:z9 p(nqbreou(nm82v c8ll 1.5-V batteries connected in series as in Fig. 18–4b ( r q pov(bulc82ez: 7nnml9(8jFig. 18–36). The 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 amohlc9m ;:cx7k 1ez9p dgunt of energy 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 t8mdk9bvjal i*p *jg;/o 120 V as in Fig. 18–20, can be used without blowing a 15-Ai g*lajkm*jdp 9;vb8/ fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 c,clz,:k k uaq0opper wire) and,k :ckzal 0,qu 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 dissipated in the cord?    W

  A power station delivers 620 kW of power at 12,000 V to 4t2az f*+ys:ofyozl , a factory through wires with total resiszoa,2yf zslty+f4:o * tance $3.0\Omega$ 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-, :+- qt)nxex1h:5q ynhvc(sjhbznv q qy83n/V line is 17.5 A. At what rate must coolc /xqhqb-n,:8 v zen1ys3(+jxqn tv5:hy)hq ning water pass over 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 ca5)fb exseo* v+r to heat a cup of water for coffee or tea. If the heater can heat 120 mL of water from e +bos)5v exf*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 ct (gfm6hg - 59x6hy4fn oz sqv+z8vvi+w1b:uburrent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value 9 qv bh90ik* 4qjrv.jwis 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 resistanom kc aj,vgoy2r4kw3 b ibtxh:h(93j+yh7 .*yce 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- )v wjs +kxdqbw+5h:b-W device is 5.4 A. What is the rms voltage acs :wqx +d )kvwbh5b-+jross it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected to j 2g; rpflr k-fh6/8damc-fa;i) ogo*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 dissipated by a 3.0-hp pumn-gnv p)7yt6jp connected to a7pyg)tn 6jv- n $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected vs7w 9 rks3hr wqf;0+qejx-l5h /rn6zto 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 copp4t3en/ k (czkker 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.pk+yv j2h6jyr q 37 ohwx+g1ug6a: h7o0-mm-diameter wire carries a 750-mA current when 22.0 mV is 2w3gouh1vjyhp+ x6aq7 kho7r gy j:+6 applied 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 atmosphere,x c3sce7p,b m/;qj/x g $He^{2+}$ 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 tr: ;z;yt8lbi-pnb(hEarth’s atmosphere, $He^{2+}$ ions in a concentration of $ 2.8\times10^{12 }\;/m^3$ are moving due north at a speed of $ 2.0\times10^{6 }\;m/s$. Also, a $ 7.0\times10^{11 }\;/m^3$ concentration of ${O_2}^-$ ions is moving due south at a speed of $ 7.2\times10^{6 }\;m/s$. Determine the magnitude and direction of the net current passing through unit area $(A/m^2)$.    $A/m^2$  ----待选择----NorthSouth 

  What is the magnitude of the electric field ag f,wp9 48jot6l9kevdumzy; 8cross an axon membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with anc7e ;vnk q-8*zvvje,u electric pulse. The action potential is detected at a point 3.40 cm down the axon 0.0052 s later. When the action potential is detected 7.20 cm from the point of stimulation, the time required is 0.006e;vqe*v7j czk,v un8- 3 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 potentialipj6)vl :3m gw along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to )pm:vwg i6j l3the 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 potential, z/etozza,.4g$Na^+$ 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-hour u8vlhwldv9 bpf3l5 *5?    C

  What is the average current drawn by a 1.0-hp 120-V mot5cars 4kz b(lz2;8c 0n3yzw pzor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. Ifkpx(:a-x2b*j q fn,x8shrdzf +vnp38 each of the two headlights uses 40 W and each of the two taillights 6 W, for a total 2x83, jrp+avnphx-nffqb* zk(x:8ds 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 m)lzh5 t9rz1 yc0b4egqom v 70n long. If it is made of iron, what qe9 mh4 7 y lt)5zbcrv1go0zn0must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of the resistancgj-fyxhmpundxd(fo2 0 :;z5 .i thk +6e R; tny25j-;pxtgod( dk.f+uhh i:6z x 0fmhat 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. Supposb ky5vg lb7/ vvl730j*qjezr;e 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 rqegvb;/kvv30jy*5 blj 77zlof 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 usj hi1k6d.l/vzh -nz6 ues 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 and the two lenw+pl7*pzea fpo u-mtt *4h a50gths are wrapped together side by side to make a+p*oml5t07 *huae zwf pt a-p4 thicker wire. How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is deei) z- 2hf +wyvi/3spbsigned 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 it do0 6p*1 -qr otoipc.pzmes not become so hot as to start a fire. What diameter must a copper wire be if it is to carry a maximum current z*0toq1 ipc op6 -rmp.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 byzfx.fv 4*gi5 t 9s9l* iuzon6a the equation $I\,=\,1.80sin210t$, where I is in amperes and t in seconds.
(a) What is the frequency?    Hz
(b) What is the rms value of the current?    A
(c) If this is the current through a $42-\Omega$ resistor, write the equation that describes the voltage as a function of time. (  sin 210 t)V

  A microwave oven running at 65% ealehes at sc/-c:x:)c ej 308ufficiency delivers 950 W of energy per second to the interior. Finda3: s8eet:)ec0 x/jh-ua clcs
(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 sa)2t4gh)0c( fn hty8 d+vrqi we;pg)vjme material. One conductor is twice as long and twice the diameter of the second. What is the ratio of the powev;)rt chhj)wi 2 +ypg0g 8dv(qnf)t4 er transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a hxxrd.b48 ,ge x 2mmh)q7ac fzb 3/eb5room 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 hookgwn b;o-uetle ,:2c(sed 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 stekesuv98z:r0 hth(.+dxsz 4gd9 ;xfeorage batteries as its source of energy. Its mass is 15d9 :9+g. re hsuf t(dzhx; xs8kv4e0ze60 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 resistanmm(jz gvc*b+ wk9: d4ece 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 designed to carry a;kpknx( *qn72s io,n0( hlhpb)u1zj an 11-mA beam of a(q;nph(lzpn bokj7 x)h 2 1i ,n*0skuprotons traveling at very nearly the speed of light ($ 3.0\times10^{8 }\;m/s$) around a ring 6300 m in circumference. How many protons are stored in the beam?    $ \times10^{12 }\;protons$

  An air conditioner draws 12tpkms89t2dj1 A at 220-V ac. The connecting cord is copper wire witttkj91spdm 8 2h a 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 rated at 95 W when connected to 120 V. The heating lq5ux:4 iyp7tlq 5d7eelement is a coil of Nichrome wird5qi: lxueq7pl7 y 45te. When uncoiled, 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 voltage varies from about 12 V wr hahq+zbk gd3t:c 3-,hen 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 varb+,r d: -cqg3at3hkz hy 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 applicatv cg yf(+6z0x 6aod2nn2zn *ujions. Lightbulb B is rated at 12 V and 40 W for automotive ( n2vd n*yo0zz n2j+6f u6cxgaapplications.
(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 ;0++uple ipw-d q82,k ooehvu cfr prg80/u7 zis used to connect a set of appliances at 120 V, which u w88 0o cifv/p+o -0,hd rpgqe;r2ulpze+7uk draw 2250 W of power total.
(a) What power is wasted in 25.0 m of this wire?    W
(b) What is your answer if wire of diameter 0.412 cm is used?    W

  A copper pipe has an inside diameter of 3;ge(lkf( vm i*;9+(zxeul o xj.00 cm and an outside diameter of 5.00 cm (Fi+ej (;(e;(x *lu lgki zmfv9oxg. 18–37). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistan. efwv 05dp u0yaw4v*fce R is stretched uniformly so that its length doubles, by what factor does the power dissipated in the wire change, assuming it4.uv dpavw 5ew0f*0fy remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operates at 0.20 A and 3 8hcti(tze1bl. h4 ge7.2 V. If its resistan ei4.hhl(e 8 bgtczt17ce at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$