What quantity is measured by a battery rating given in amp yxa1oi o,; d4xy14bhm 0i8yh j4izr*kere-hours $(A\cdot H)$ ?

When an electric cell is connected to ad2 d7 wvrb)qnz **rjfou-8 ,nv circuit, electrons flow away from the negative terminal in the circuit. But within the cell, electrons ff*v*v)onrwd q8bdj2z-u,nr 7 low to the negative terminal. Explain.

When a flashlight is op*6z n7uf r82)aap xeeyerated, what is being used up: battery current, battery voltage, battery energy, battery power, or battery resistann*rx 2e8f7 auae pz6y)ce? Explain.

One terminal of a car battery is said6)a6;kudif t .pcgpar :lee6- to be connected to “ground.” Since it is not really connected to the ground, what is meantlf ted p:k- a)c6argepu.i;66 by this expression?

When you turn on a water faulzb(rss3+1 mv cet, the water usually flows immediately. You don’t have to wait for water to flow from the faucet valve to the spout. Why3mbss(+r zvl 1 not? Is the same thing true when you connect a wire to the terminals of a battery?

Can a copper wire and an aluminum wire of the same length hrr/b ;kfqf)8 b4th9bjave the same resistanctk;/8r )r bhbqf9fj4 be? Explain.

If the resistance of a small immersion heater (to heat w cw: i4k)aoe tpiu)6m1n,0zitater for tea or soup, Fig. 18–32) was increased4ci tpn)0 a: wm6eo1uii,z k)t, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of leng clc1zuyct.l )7:4oafq( x(loths a, 2a, and 3a, how would you connecttl:) l4cxcoy1u(. c7qz loaf( the 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 lightbulycr/b;d qi- 1yb burns out?

Explain why lightbulbs almost always burn out jusl- b.ys-lgn, at as they are turned on and not after they have beag n.s-l l,-byen on for some time.

Which draws more current, a 100-W lightbulb or a 75-f 3cpzk;zp) zs40 8wk n+uxjv8W bulb? Which has the higher resipw+4 8z kf3vkz pj8 0sc)z;unxstance?

Electric power is transferred over large distances at very high voltages. Exqjli 5kpbik,7xb5/ 9)pfflp *plain how the high voltage r ppjbk*p5lk b f,9i fqi57)/xleduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fus2k - wv8r,dwqye with a 25-A fusevr2yq,-k 8dw w?

When electric lights ar9gstl m)dlp0(y + lme9e operated on low-frequency ac (say, 5 Hz), they flicker noticeably. We m99ylts+( g)p0 dlmlhy?

Driven by ac power, the sameu, bmy k8en447y1bjf35d vrlh9n e2cq electrons pass back and forth through your reading lamp over and over again. Explain why 7yru59bbnv,2q8d m 4c 1fel h k4jeyn3the light stays lit instead of going out after the first pass of electrons.

The heating element in a toaster is made oc (1im-g5,hmz yo+e ybf Nichrome wire. Immediately after the toaster is turned on, is the currente(b +ico yz5,mm- h1yg $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a 4 c4csnm edwak0 m rj/nbfgp.);807pcresistor? Explain.

Different lamps might have batteries connected in either of the two arr xrqo6.p zi(p2angements sho6opq2.pir (zxwn 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 flowing past; v6*tllid9q0tdc8ti any point in the wirel 8tdq*cd6i0 ilt 9;vt per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A for 5.0 h. How mucw mq):(b)caprd ca h pr 9-zh4:x0dupu .d7t:lh charge passes throug:(murzhpaa)c- wb .ddqlth0ru47c): :9 xdpp h the battery?    $ \times10^{ 5}\;C$

  What is the current ih1:ijx flhhe;:5pg huzh+/ ak97/ / xv eph/zsn 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 45*w,m6vabte8t ooe r).2 A?    $\Omega$

  What voltage will produce 0.25 su.ye+ :f-s.c5zulwvpzx8t, A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120- s5+- ms5 mqzyh8nk)osV 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 he *ej2hwvglg -1 i;n4grating 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 dh6x h/mm43 pia 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 carrying 2- z wmv*cnn+l6800 A (Fig. 18–34). The l*cml+ wz 6nnv-ine 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 247 g(/ 4(jgjcfd8b.yfj f( 9jmajmwl q80 V.
(a) If the voltage drops by 15%, what will be the current, assuming nothing else changes? $\approx$    A (retain one decimal places)
(b) If the resistance of the device were reduced by 15%, what current would be drawn at 240 V? $\approx$    A (retain one decimal places)

  A 12-V battery causes a current of 0.60 A foa vshb/ba (j50 (b(dthrough 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 wire wrfn w 9c 9.xwewp+ 4/xquvi(2dhose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length 7xh)v dswq u-t2v.u9 sof copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio +xaf 2kzwn8.t sxi nulw (1b:0ruy7x7of the resistance of 10.0 m of aluminum wire 2.0 mm in diametrsl2:w xb(k.0y7 t izux8a7unfx nw1+er, to 20.0 m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tungstkb g8jrdx3t *(en wire of the same length? Give numerical detair* 3g8jtd(k bxls.    mm

  A certain copper wire 9 r x lo;r07n5sf*oytfhas a 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 vf37; kly*hylto raise the temperature of a copper wire (originally at flkyy73hl;* v $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the (ycq2-k o -wge*ymmc8c2i0zo same resistivity as tungsten does om2 *o cicg0k8q- 2(cm-wzyye at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of e3zpz2 ,fy- dnl7*jfn 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 l(ez c6mkkvn1cc3 g35zength of household no. 14 copper wire (used in 135v(e6gk3mz c z kccn15-A circuits). The wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths t9 +sv3ug.uh3)*zbuz7aq owl1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for current that pag )zvl9zus o7.+ 3wthuba3u*qsses 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 s;i7ea,a , 0b kex0frwdame resistance. If one has twice the length of the other, what is the rat xae;k,07r0w ,fie dabio of the diameter of the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wicnvbej4ct8)/ c7wzrt)fzh3 : re is connected to a precision 10.00-V power supply, and a current of 0.4212 A is precisely measured aj)8ncc:z 7ht/vtfbre cwz 43)t 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 of aq 9nr vfhb((2sb3l6l fluminum, both of diameter 1.0 mm. A voltage2 9nff(b lrbsvh q(3l6 difference of 85 mV is placed across the composite wire.
(a) What is the total resistance (sum) of the two wires? $\approx$    $\Omega$(retain two decimal places)
(b) What is the current through the wire?    A(retain two decimal places)
(c) What are the voltages across the aluminum part and across the copper part?
$V_{Cu}$    V(retain three decimal places)
$V_{Al}$    V(retain three decimal places)

  For some applications, it is important tha2 j5hmhf/y6l,egcj; dt the value of a resistance not change with t2l 65 ;,/egjhdcyhj fmemperature. For example, suppose you made a $4.70-k\Omega$ resistor from a carbon resistor and a Nichrome wire-wound resistor connected together so the total resistance is the sum of their separate resistances. What value should each of these resistors have (at 0$^{\circ}\,C$) so that the combination is temperature independent?
$R_{0C}$   $\Omega$
$R_{0N}$   $\Omega$

  The heating element of an electric oven ebg85/ xj 0spmis designed to produce 3.3 kW of heat when connected to a 240-V source. What must bem xe/p80sbj 5g the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portablxmj;x5 yw9k4 lxx+1iee CD player that draws a maximum of 32yjw l 1k4e;xxmxi95+ x0 mA of current?    W

  What is the maximum voltage that can;0bwbfo *h6*+eq xce7i yuv u: be applied 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 l ccxqd 9634dkkx;fq p7ny6j8z ightbulb connected to its proper c7qkz98 6kjq4d6nx; x dfc3yp 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. Calcul h1iccpb 93rwpl-vf(+ate
(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 angj0-/1: v*j kokytd,* be ddt bad)-bdd 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 a a)vh)(afq6c 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 it bqaf vh )a)(6cae 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 then,qmdja6p*o:z vf .k g9l96w i morning if it is in operation for a total of 15 min?l .g on v9di,kzqjfw696mpa*: 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 z0 )mgiawl2*g 6+b6fjj (avzpdoes it cost to leave a 25-W porch light on day and night folabjz z+ jg6gwp*av602() mifr a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connesynho ur md*m+e 7 ptj5yx;mbi8i ,);3cted in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when*miyr dn 58mxt;s3,7iuhpe;y+ obj )m 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 12v 6h8zlv 8qg+l,qw-wg -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 use 8ywsbvt. ,vc/d without blowing a./sc wtv yv8b, 15-A fuse?    bulbs

  An extension cord made of two wires of diamsg 41;hren t7heter 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 dissipated in the coh e7;s1 trgh4nrd?    W

  A power station delivers 620 kW of power at 12,000 V to a factory through x e a*2k2hgy(hc:m,px2q zn;b wires with mhx2a p:(2c2x*en z;yk,q hgb total resistance $3.0\Omega$ How much less power is wasted if the electricity is delivered at 50,000 V rather than 12,000 V?    $ \times10^{ 3}\;W$

  The current in an electromagnet connected to a 240-V line is 17.5 A. At whclk6vb+ nn1(+ i81/ crkao uxfat rate must cooling 8 caf/o +1u lk (vc+6nx1nikbrwater pass over the coils if the water temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heatzg*7b85 7t jrh eidb)ier can be used in a car to heat a cup of water for coffee or tea. If t zr)7bebt5d j* h78igihe heater can heat 120 mL of water from 25$^{\circ}\,C$ to 95$^{\circ}\,C$ in 8.0 min,
(a) approximately how much current does it draw from the car’s 12-V battery, $\approx$    A(Round to the nearest integer)
(b) what is its resistance? Assume the manufacturer’s claim of 60% efficiency.    $\Omega$

  Calculate the peak current ino9i dsgi7v 15fs,.twa a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak g )n8s92p 9rxe gwz9povalue 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 resistafy+oet 5 d1h.i a+tuc9j p*b.cnce 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 4in5.hsc,aa9py fe-ocurrent in a 1500-W device is 5.4 A. What is the rp.ec yo ia,f- h49ns5ams voltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected to a hljrqg,i3 lodw7be e46 g-d05$660-V_{rms}$ 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 pump co/ ijg 0rel;( dlwsl j7c2-by)xnnected;bwd)l l2/erxg -il s(j7j 0cy to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to a n58 dwg)anedf fd g;2t tj;-f4$240-V_{rms}$ 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 current ofzv;,bzt j y9tlxs0 3c-y-u ot1 $2.3\mu A$. What is the electron drift speed in the wire?    $ \times10^{-10 }\;m/s$

  A 5.80-m length of 2.0-mm-diametfk:)x ,m. qtpter wire carries a 750-mA current when 22.0 mV is applied to its endsm xtp.qfk:, t). 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 atmo ecg5o ir/l)c-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 atmospher m whxo*,c(3zoy-lljs:,mf8 re, $He^{2+}$ 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 axon m 1:;nwt)okmkaembrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated nfn5 p2q)fhu+ with an 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 t n2q+)ffh5unpime required is 0.0063 s. What is the speed of the electric pulse along the axon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much energy is required to transmit one action potential alowik+nna5 3sj)z4 )8x epf ( ghv3dwanme8oh2 *ng the axon of Example 18–15. [Hint: the energy to transmit one pulse is eq3)8 f s oehx+ g a*dj5nwe2z4avnimp8nhk3w )(uivalent to the energy stored by charging the axon capacitance; see Section 17–9]. What minimum average power is required for $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action potent) k7 no f.0:ocggef;; ufbi/soial, $Na^+$ 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 thl( n+c/vw 4odyere in 1.00 ampere-hour?    C

  What is the average current drazs (7r(zvcn vbp(p(v 7191fq3udvg auwn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If 3c*qe e t7kw: 4n ea em8r,t5lj0nz -ueezl(f2each of the two headlights uses 40 W and each of the two taillights 6 W, for a total of zez32ekmcnr,ul l0j8 etefent - a57* 4e(:wq 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 long. If it +s au5ftdvey7)*2o6hw:ksh ; lzd8eeis made of iron, what must its diameter be? ye2hud7e;6*oe85ks fdh )l:+wt zvas    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as th:uax+;b.zhkio2 q n*-d2*4 tpy ltcobe reciprocal of the resistance R;ty;x*c 2ih koo :4ba+z p.u*db2ltn q- that 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. Sup/a( jqhf(*phtve2yviua0*r/pose 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 yhfrat( h*q ae *pu/2vv(/0jienergy 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 househol2ltg;c(my s*mho2 jjf 9o+n,rd uses a 1.8-kW heater $3.0 h/day$ (“on” time), four 100-W lightbulbs $6.0 h/day$, a 3.0-kW electric stove element for a total of $1.4 h/day$ and miscellaneous power amounting to $2.0 kWh/day$. If electricity costs $0.105 per kWh, what will be their monthly bill (30 d)?    dollars per month
(b) How much coal (which produces $7000 kcal/kg$) must be burned by a 35%-efficient power plant to provide the yearly needs of this household?    kg of coal

A length of wire is cut in half and the two lequl-cr2 .rpe *ngths are wrapped together side by side to make a thicker wire. How does the resistance of this new combination cop*rqlu 2.r-c empare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 117 np1qi o8;tq z(ql2a z+kn. gm37l7 vmrV.
(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 does not become so hot as to 0+k vmdiw/vpq f(-0vm starv0 mwq0kdfvi/+( vp m-t a fire. What diameter 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 lb ufpua(v:pd 4g5 .51e:kjuyequation $I\,=\,1.80sin210t$, where I is in amperes and t in seconds.
(a) What is the frequency?    Hz
(b) What is the rms value of the current?    A
(c) If this is the current through a $42-\Omega$ resistor, write the equation that describes the voltage as a function of time. (  sin 210 t)V

  A microwave oven running at 65% efficiency delivers 95b2aq7/ wew7w8 1b u8n4usbqj k0 W of energy per second to the inw buw u ke72 7b1j8n4w8/abqsqterior. Find
(a) the power drawn from the source,    W
(b) the current drawn. Assume a source voltage of 120 V.    A

  A $1.00-\Omega$ wire is stretched uniformly to 3.00 times its original length. What is its resistance now?    $\Omega$

  220 V is applied to two different conductors made of the same material. One co5ekhr) 8;w(iz isg(cf84 ub aknductor is twice as long and twice the diameter of the second. What is the ratio of the power transformed in the firaufc; ker ki 4ih8b(wz(g5s8)st relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room oag+x 66ves9w7 u zbn3vf 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 hooke-kr99pcc v9q.e h)rq :hl6wjod 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 mak4q rjoflvac;i()w dp.f(ej )wp,j 48mes use of storage batteries as its source of energy. Its mass is 1560 kg apavqjm .cw 4)4;(wifl8) rdfjp,(jo end 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 av/ mq6yb e. y+jvos a(lcr4)0x 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 a+2 rrygtehz-/zr 0(qx t Fermilab (Illinois) is designed to carry an 11-mA beam of protons traveling at veryrygz2zte/x+-qh r0r ( nearly the speed of light ($ 3.0\times10^{8 }\;m/s$) around a ring 6300 m in circumference. How many protons are stored in the beam?    $ \times10^{12 }\;protons$

  An air conditioner draws 12 A at 220-V ac. The f uuaj; ;2b:er+6zck d s/meg4connecting cord is copper wire with a diame:r k/z2fbuge ; dj+as;cemu46ter 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 e(hhg68nzqy4 w lement is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What iw(h qynzg 68h4s the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system2ph0vge +: gsl voltage 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 s ve02:h+gplg 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 h+ttd/ +fvx1 ka /p:acew6p .fzousehold applications. Lightbulb B is rated at 12 V f.ap6vwp1+ /a /e:k+tzfxctd 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,13sy srihie1 0.259 cm is used to connect a set of appliances at 120 V, which draw 2250 W of poiir1sye3, h 1swer 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 w3+c ;xev dq8mdiameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). Wxe8vqd;3 + cwmhat is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistanc;*o 0m9*vgvlwo/gq tge R is stretched uniformly so that its length doubles, by what factor does the power dissipated ;*gg0*9qvgwo v/l o mtin the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashligh 4o4fq/ g/xde /be ,u8mk)y0w0dwvpzt t bulb operates at 0.20 A and 3.2 V. If its resistance yku0w/)4,e4zpdvm0x/wdet b 8o gqf /at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$