What quantity is measured by a battery ratin+-r dme7.1p4t;n bp+ umfo rfhg given in ampere-hours $(A\cdot H)$ ?

When an electric cell ilx, g r,vtpxme8cb)y*pey0 92s connected to a circuit, electrons flow away from the negative terminal in the circuit. But within the cell, electrons flow to the negative te0 yx2pcy,l8x*eb rm vp t,9ge)rminal. Explain.

When a flashlight is operated, wh lxu 3al lu+1.gd3v+h7vh zgz3at is being used up: battery current, battery voltage, battery energy, battery power, or battery reshghlz u3vvzg.l3a++7ud13lx istance? Explain.

One terminal of a car battery is said to be connected to “; tk5f x a;u/-z5j18cuzykwjsm9;rsl ground.” Since it is not really connected to themf9kzz ;ujkc5; uj w5s8at1ls;/- xyr ground, what is meant by this expression?

When you turn on a water faucet, the water usually flows immediat9k b 6nhw (e-bjeo-1gcely. You don’t have to wait for water to flow from the fauce9 1cjhg6e kbewob(- -nt valve to the spout. Why not? Is the same thing true when you connect a wire to the terminals of a battery?

Can a copper wire and an aluminum ws*apil4( u ielj 71;gwire of the same length have the same resistance? Exwilul( 4j7;*epga1s i plain.

If the resistance of a sm3kryo3s-6(vju-v(k ky0 q epmall immersion heater (to heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow doekq(( r-3pjvkm o0y svyu-3k 6wn the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths ag)vx ,,i- yo ycnd )kg2xa9.xl, 2a, and 3a, how would you cong-)ycna2 .)vox9l kx ,y xgdi,nect 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 lightbulb burnb8b /eyk, z /ir92kok/;kfasrs out?

Explain why lightbulbs almostwudr fes, 5d-4hx-l5f always burn out just as they are turned on and not after th ,-5u dw f-lesxf4r5hdey have been on for some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb?x/cq q 0oq od do0bk:axtu (h515yt74g Which has the higher reoa0ok0 5(qhyu/cqttd gbo1:574 xd xqsistance?

Electric power is transferred over lar9fnh/gb1a (np pj/;vbw m9.kskf8.je ge distances at very high voltages. Explain how the high voltage reduces power losses in 8 mghj n a kbf.9s;pnw( /pe9.kvfj/b1the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fuse 8lb/,yh5 jrfy with a 25-Ay/bjf r, h5yl8 fuse?

When electric lights are operated on low-frequency ac (say, 5 Hz), thcfx6s l3ej nn/w82mh*ey flicker noticeabm2sj/ h*fe wxn38nl c6ly. Why?

Driven by ac power, the same electrons tlj4vjx+8 4js pass back and forth through your reading lamp over and over again. Explain why the light sx t 4vjl8js4j+tays lit instead of going out after the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. Immediately av q;nc iypmzjht2(p+kl ,tkp165jc1) fter the toaster is turned on, is thkz (kqj 1 n6ptpcm )5clvjip+yh12t ,;e current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Exr(zhtjq)cz 3p30 )7 jbav 7rzjplain.

Different lamps might have batwmt1;w w rar.3teries connected in either of the two arrangements wt;r wr.3 wa1mshown 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 f ++p1 grw(wchq.ywdw e1qq2 2ilowing past any point in the wire per sedi 2e+21wwcq . (wh+rgq yq1wpcond?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A for 5.0 h. Ho+n1rl)yi)7 vw ;jvj l5oh4 xzkw much charge passes through4v; )llix5 7h vjrjykonzw1 )+ the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes i 0s-pljr,p x*obia 7x*f $1200\,Na^+$ 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 4.2 v.jen wo3v(i 9A?    $\Omega$

  What voltage will produce 0.25 A of currs7 rqiu14bt :xent through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when pluggedvam v-9tat6*j fa(5 aj into a 120-V line.
(a) What is its resistance?    $\Omega$
(b) How much charge passes through it in 15 min? (Assume direct current.)    $ \times10^{ 3}\;C$

  An electric clothes dryer has a hen fp44t)(huwhwngt .tq 8(smi dr 1)p7ating 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 whoseh+ 7l,h .gjpsss/u 9zbvj)pf1 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 mjr.abwzux,4:d ;wgp + fq00 oA (Fig. 18–34). The line ;:mq,j wg04 aw.rou0xdp +fbzhas $2.5\times10^{ -5}\;\Omega$ 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 drrkp n)jn e,d+/:e w7lo cf-,lhaws 6.50 A at 240 V.
(a) If the voltage drops by 15%, what will be the current, assuming nothing else changes? $\approx$    A (retain one decimal places)
(b) If the resistance of the device were reduced by 15%, what current would be drawn at 240 V? $\approx$    A (retain one decimal places)

  A 12-V battery causes a current of 0.60 A through a resnhwd);gw c)s 1istor.
(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 14yfb z; bo;yq3.00-m 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 in diameter? c6gx snt2garl/-+w b ;i /de*f   $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance l-t)9 g:9 t jiw cezti4i7pnm f*ts4:dof 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in dnfitp4 9 gsm:d7:*ti i wlz)c4ttej9-iameter.   

  Can a 2.5-mm-diameter copperez6 c mbsh)y.0 wire have the same resistance as a tungsten wire of th)0 me.cb6yzshe same length? Give numerical details.    mm

  A certain copper wire has a yr/-g3r 9c4j/sw h bztresistance 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 (originallk,( e*ohw*rply at wkpo*(h *,erl $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivity as tungsten d,1.tw qr8diz pd8,r1wzp iqt .oes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance ; wq;igccn p.vn4oq, -1scg5 cof about $12\Omega$ when cold ($20^{\circ}\,C$) and $140\Omega$ when on (hot). Estimate the temperature of the filament when hot assuming an average temperature coefficient of resistivity $\alpha\,=\,0.0060(C?)^{-1}$ .    $^{\circ}\,C$

  Compute the voltage drop along a 26-m length of household no. 14 copper3fqcm gv9 zv5b-ns,z; wire (used in 15-A circuits). The wire has diameter 1.zn3; ,v svbgz -f5c9mq628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths 1.l5 efz .gzz25doafh3.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectof2azf35ld. hg 5z .zeively (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 tf22qbf( gg 5flhe same resistance. If one has twice the length of the other, what is the ratio of the diameter of the longer 2 fg 2g5(lfqfbwire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precisy).:vgllpgnh 0k z0dbt g.d0)ion 10.00-V power supply, and a current of 0.421zl).bgyv)k. dg dn0 hpt:00 lg2 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 wi*;rfnx.b d-s xre 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 s r;*x d.n-xfbacross 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,huskq(( lok ;.xgju6m j8 pk8+ it is important that the value of a resistance not change with temperaturh(gmx.j j (8;pkosu qukl8+6k e. 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 is designed to produce 3.3 kW b-2 kr(zr n;mvsxq7i /gn5d:uof heat when connected to a 240-vrgd 7zx2/ mn-uk (in;: sb5rqV source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player that drawjq:*er93j ve ycz()iys a maximum ofcij *qv(z 9jryy:)e e3 320 mA of current?    W

  What is the maximum voltage thao9i ef )u47:6crsyy lbt can 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 lightbulb conx;e;fc9mf (/ul t;axqj.rw +inected to c l/ fxqx(;. fei+atjm9;ru;wits 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 heateh 39lf*ve8ev+ l*mzag5wf 6pmr 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 settings: 85co *4ksejqw *+j0bnv8 0 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 ino;bhal*qkikp kvze (g63 kf,.im*) +t Europe, where 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 be relative to 75-W 13k kfpi.;o6g,k)ki+tlb hq*zev a (*m20-V bulbs? [Hint: assume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W-ow:qgz4zpz fo pe0mau 9:( 6h toaster use in the morning if it is in operation for a total of 15 min? At a costpz h9 oa-:uomwg6z ze0:4pf(q 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 2byon( y0dj rmm7.lhdwz7g0)95-W porch light on day and night for amr0ybd.hy7( 9m 7gd wj)znl0o year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connev yp;fqx; bfuuea9:re x84 ppu8.ck*(cted in series as in Fig. 18–4b (Fig. 18–36). The v8 f4 ue (b. qacp;u uyx*fr9;8:xpekpbulb 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 s(stde-7 xqasy/;nsi 3tored 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 Fia ,.rr h t 7aeit9yjiiev+(8:mg. 18–20, can be used without blowing a 15-A fu,ym. (9: e+e vriajrth87 atiise?    bulbs

  An extension cord made of two wires qq7vz9ynmh rd33dv u- jmku)mb6 :mq8f5c,p 8of diameter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric heater which dr-ucnq8h :kbq)j vm3 79r5fmdmq d6,u8m3zpvyaws 15.0 A on a 120-V line. How much power is dissipated in the cord?    W

  A power station deli ,6lie 1tljb*vvers 620 kW of power at 12,000 V to a factory through wires with tv e6l *i1jlb,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. Aca 2n-owa6 4viq k,/qmt what rate must cooling water pass over the coils if the water temperature is to -,vwn/oimk2a q 6 acq4rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to he1:yn2b2bv pv-u n nakb wrcou(o3ihz0d /;m/8at a cup of water for coffee or tea. If the heater can heat 120 hnc2wi:8n o;ov- bd (0bypaz vu/u/31n2brkmmL 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 cb02btnqs cvy j9.6ps .urrent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, is acroszc )-9q;qs yx( rhlom*s 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 th;1;atdi/-um qqaxy n-e $120-V_{rms}$ 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-W device is 5.4 A. What o7wl.c3mveo)z j; iqph 55yz( is the rms voltage across ilvo (ci 3) mz7oywez.q;55hjpt?    V (Round to the nearest integer)

  An 1800-W arc welder is co.uibdk9y6r+ 5.s ps vnnnected 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 dissipated by a 3.0-hp pump convfj aw8;-r p7q5 3cqmpnected to a cj- q7m;vppa53wfrq8$240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to a fsz8240i3a km ps/ )lho s)hiu$240-V_{rms}$ 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 cu;j0dp6n 1ovbpbo5 fw 3rrent 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-diam*+dr ki 3(*lbsl rn(beeter wire carries a 750-mA current when 22.0 mV is applied to its ends. If the drift speed *lk b*rrns b d3((li+eis $ 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 atmos- ;pvj*/m7 hqduud)b6 6cbud pphere, $He^{2+}$ 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 the4jkumi6swn0 2 Earth’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 across an axon membranc7acd 70q qlp:e $ 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 potential is detectea(dq6efhg8k z-p8i- ed 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 timezid-kefh8gp (a eq 86- 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 along t(7b cnt*.qevi he axon of Example 18–15. [Hin.v( *7cn qtibet: the energy to transmit one pulse is equivalent 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 potrifba ,ayke1+ 4s )f+y 0j(wwiential, $Na^+$ 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 + 8zq):q7 mfc02dni ,wrzwtpa-hour?    C

  What is the average current drawn by a 1.0-hp 120-V motoe g7m +kmdki q3*6d0ibeoh13wr? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a oe0ay-z3jg4 a car with the lights on. If each of the two headlights uses 40 W and each of the two taillights 6 W, for a total oj 0oz4ya3age- f 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 heatri1abw 6ku71ter is 5.4 m long. If it is made of iron, what must its diameter br1k 7t1wau6 ibe?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of thm4x+k u42)+fkx :c 1q5pnkyqftzgjb- e resistance R; that py b1:k m4n kt5jgq-xk2c++ fquzxf)4is, $G\,=\,1/R$. 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 a9yt 0wihfq47zd g-;pi vw*4pg bout 10 MW of power. Suppose that instead of using high-voltage lines to supply the power, th7-q9*f4pht ii ggz0wp d vw;y4e 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 cents per kWh.    dollars per hour per meter

  (a) A particular householx1 xif .jpa/w;d 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 lengths are wrapped to no.,rz mnoc6j/h. n f64k.ydfgether side by side to make a thicker wire. How does thejykon6.f/n46ho.rdfm,. n zc resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed fo9myxd,,lo /znveq3vr 4cqh( -r 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 does not become so hot as tocgv0b rmvf,5(akb dbr)2 d,i9buy0- f -cda9b start a fire. What diameter must a copper wire be if it isc , - bi0b 9mak r9ubv)b5a ,g-2fdfdd(0ycrbv 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 gizvo;yx 8s/m5jdik w6oek cq na7v72 9:ven by the equation $I\,=\,1.80sin210t$, where I is in amperes and t in seconds.
(a) What is the frequency?    Hz
(b) What is the rms value of the current?    A
(c) If this is the current through a $42-\Omega$ resistor, write the equation that describes the voltage as a function of time. (  sin 210 t)V

  A microwave oven running at 65% efficiency delivers 950 W of energy per sehvejx 0 butwp.(,yx9 lnk **p)cond to the interior. Find*xppe9l (0,*jtbu) wh.nk yx v
(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 oa7i/ svkw 9gc8f the 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 first relasg waikc7/ 9v8tive to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room of volumens a;/-u,p g2 iilg c(:kcmoyd dx9j18 $62\,m^3$ 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 240-8 cnatfqw49 av3ly 3ou+6c/xaV 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 oj.f /jt20 1d5pb,/h nan(lpdpubvgh1f storage batteries as its source of energy. Its mass is 1560 kg and it is powered by 24 batteries, each 12 V, 1t(pgj nvp21.0b d,/5 pdau/n jfhlhb$95A\cdot h$. 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 hrmhcgql +(s f: 6znjb)8j6u :sas a 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 designed to carry an 11-mA besu2r)idb6c :zam of prot26d: crbzs)u ions 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 12 A at 220-V ac. The connecting cord is copper wire2ytn b :q b*7tv8dpcr( with a diame* p2qc8 (vbnrytdb t7:ter 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 whd(svqj ty 7dh5yn, q7dn3y3,pen connected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a totalt,,3( ynnd djph7 yqy3qvs d57 length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from about svec1ce,an gm jioe, /.c8*f,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 power delivered to the head 8*seaccg. /n mcjiee1vf ,o,,lights 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.):cpaios0kmt/4gn r 1 :xd (br Lightbulb B is rated at / a:pix mrtdok :cg)n(r140 bs12 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 appliances at wuwm5,obn3.5nblweur. m50rj9i s :l120 V, which draw 2250 W of pow,:nl w srw m39e5mbi..05 wlb noruuj5er 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 3.00 cm and an outside diameter ocy irp7n3g:bnuk/q q;d5r3rkjvm5+ 9f 5.00 cm (Fig. 18–37). What is the resistance o r3cnu 5;dyjrpin9v5/k7 rbmq:gq+k3f 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R q9lh*vs cp0b5 is stretched uniformly so that its length doubles, by what factor does the power dissipated in the wire change, assuming it rema 5*0b qscphl9vins hooked up to the same voltage source?

  A tungsten filament used inm 9o8,dhd*qs :1z hrsn a flashlight bulb operates at 0.20 A and 3.2 V. If its reo*n zs:d1 qrd 98h,shmsistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$