What quantity is mea8xk5*s fta/rd sured by a battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrla*5 uzlpywo1: vm2- qons flow away from the negative terminal in the ci:*avpqw-ly1omu 2 zl5rcuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battery current,-et-2p 7qtn yw battery voltage, battert-tp2y7e wq- ny energy, battery power, or battery resistance? Explain.

One terminal of a car battery is said tod6k.txfr 0pw7s: gr-jv;qn-p 6ud/ yu be connected to “ground.” Since it is not really connected to the ground, what is jv t 6swg-xydn6.prdk:7uup;rq0f /-meant by this expression?

When you turn on a water faucet, the water8g/qp(,/sckpzg+i -* b znbwt2z uq/f usually flows immediately. You don’t have to wait for water to flow from the faucet valve to the spout. Why not? Is the same thing true when you connect a wire to the terminf,bw /igz -us8 /c2/z* qt+ gp(pnqkzbals of a battery?

Can a copper wire and a/i208wo d we5to aon3wn aluminum wire of the same length have the same resistance? Ex5/otw0 nedoi o3 aww82plain.

If the resistance of a small immersion heater (to heat water for tea or soup, Fij+yu * m ydjx.dil2 +zl5:s m4qio39dog. 18–32) was increased, would it speed up orimd9d*sq5jx2 y. iu +34o:djzlloym + slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths )e.)nomfh7w o a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resistance,)nh ).e m7wfoo (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 4iccjnob- 0h1 lightbulb burns out?

Explain why lightbulbs almost always burn out just as the5o ftu* bobm6:y are turned on and not after they have been on for botu6:mbof * 5some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which has thenn4,fi x8va 2 :ttzhyhcw:u+ 1 higher r 4z81ti y+fh navh:nwt,u x:2cesistance?

Electric power is transferred over largqi,w1kqp:z) **/c)s z r oqb9crcb+wxe distances at very high voltages. Explain how the high voltage rrzzw )cbsi*r:w, c1bqpc/q* qxo+k) 9educes power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fuse wa tsw)3thk1g3ix 6pe 6ith a 25-A fuse?61 )a3 xweph6it t3ksg

When electric lights are operated on low-freqd sy5 t4ay /ypu7j,xn:uency ac (say, 5 Hz), they flicker noticeably. Whyn :u/j5xd 74y p,yayst?

Driven by ac power, the same electrons pass back and forth through your readzknwj5y wmi :dg 0(2otv27;g ying lamp over and over again. Explain why the light stay2 wvgn7:5; z02dgtkoi mj(wyy s lit instead of going out after the first pass of electrons.

The heating element i1fc/vqc 4ee+n n a toaster is made of Nichrome wire. Immediately after the toaster is turned on, is the currenf c4evne+1/cqt $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Ex2qtu(q7qx5-lv(, w ovyet u o(plain.

Different lamps might have batteries connected in either of the twk :0gh8su(zz,rugqff) k,porya uc bl.;k-./o arrangements shownukckl s(0,k.oga8-r:,/zf r ygf qhzbu.u)p ; 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 b2 jkq3(2uiqiare flowing past any point jq232i k ui(bqin the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery k.j v7mi 4rc:kusing a current of 6.7 A for 5.0 h. How much charge passes through the battery.ki v r4mk:7jc?    $ \times10^{ 5}\;C$

  What is the current in 6md9n byvt jc0/ko hv1cum 078amperes 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 4.2 Av/ posl1c.gx +h kc7s8ox1bek,7a+pm?    $\Omega$

  What voltage will produce 0.25 A of current through tua9q s w/ -;fs2gp0:c(aovrf a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when pb a4r7 rprt6h6vo peu:.:qo r0lugged 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 heating element with a resistan l 3z:se5ore.uce 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 whose resistanc8 )7z 2jbzza1yl. akmpe 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 pif0cw5 8.h8uwp *deu carrying 2800 A (Fig. 18–34). Tcu 0iw pdp8feh.8u*5 whe line has $2.5\times10^{ -5}\;\Omega$ resistance per meter, and the bird’s feet are 4.0 cm apart. What is the potential difference between the bird’s feet?    $ \times10^{-3 }\;V$

  An electric device draws 6.50 A at 240 V. g78 q-// nqqxdxgz8t y
(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 throug n9+dag1hf q;s 2ja1kch 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 whose resisag x f.3knv-j1tance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1.5 mm in diakabk/-hzh o+7*am(2hd*n cn 8 d qdfk.meter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m ofa8 z7e7;n+- *f h buz3mfmtkhr aluminum wire 2.0 mm in diameter, to 20.0 m of copper wi7m e z+kf* h7a;mnt-8r3ufhbzre 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as*wkirvz k5,7jlrv:g, ;d4s zw a tungsten wire of the same length? Give numerical detag dkz:vwlwr; *5, rs 7k,v4ijzils.    mm

  A certain copper wire ha /f5 -zyk.pl:1:pza.cywy jgis 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 to raise the temperature of a copper wirem 7 oj/v1 s(/ue-nccyq (originally at 7o1(jcn-s/e /u ycvqm $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the sam9y):rc o wdbt8 q;/bjme resistivity as tungsten dtqwb)9 / m co:d8yb;jroes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of aboukr6 tx2,yu+ udt $12\Omega$ 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 copper wirtv fo;s g06ftttv18r2 e (used in 15-A circuits). The wire has diameter 1.stff821 tvgt6 0 tor;v628 mm and carries a 12-A current.    V

  A rectangular solid made of carbos6hw;rop1.a pn has 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 that passeha; wspro6 1.ps 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( qi5/ x7)ltppuwee xk7 -jmh1. If one has twice the length of the other, whatu)xm k w5lq7(-x7/ itjpeph1e 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 16 7pzwfad8)cvqzqf),x-t a+ c0.00-V power supply, and a current of 0.4212 A is precisely measu-f xc)7aq vpc6 d8zq,z+watf)red 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 copperquq, yd2rp; b3p jak2, followed by 5.0 m of aluminum, both of diameter,; b2jqpd ay2pqku3,r 1.0 mm. A voltage 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 imppzmr d:v+ i/(o-lgemty.w:cp- /he/portant that the value of a resistance not change with temperature. For example, suppose you made y.p p:twpcdme/- /gz/o h r:v-+l(miea $4.70-k\Omega$ 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 pc53 1si hf4tluroduce 3.3 kW of heat when connected to a 240-V sou uc1hls4t35i frce. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player that draws /h 6yclwo0zzee-2;sn3 p axs9a maximum of 320 mA of current? pxschen9es/;y2 6azow- l03 z   W

  What is the maximum voltage that ccko, 1p((9wibentq0 ran 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,mb7 h5zfx-q8h5gof; yy k/d nightbulb connected to its proper source voltageqmzy7 ngf8/5 , yhh;x 5fobdk- 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 ,- kt5:wzryugbmn9c .y v(pb/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 s +a+)hus(fvgv ettings: 850 W and 1250 W.
(a) At which setting do you expect the resistance to be higher? After making a guess, determine the resistance at
(b) the lower setting;    $\Omega$
(c) the higher setting.    $\Omega$

  You buy a 75-W lightbulb in Europe, where electricity is +fni;zl (io/n delivered to homes at 240 V. If you use the lightbulb in the United States at 120 V (assum(+;in/zolnif e its resistance does not change), how bright will it be relative to 75-W 120-V bulbs? [Hint: assume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster us9h ioam qy) y)wl:o-8te in the morning if it is in operation for a total of 15 min? At y-:8mwoaq))9 oyitlh 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,lnb2aqt()rqx q5 :u- j what does it cost to leave a 25-W porch light on day andn(q 5:t)ubl-xa rq2qj night for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected in series as 6qa btg+8;sz t*9c xmyin Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA whe 9tgc+8y z qtb6xs;am*n 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,j hns*dr -mofhvvf*frn1* () 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 ure,zyf (if,n6 8 d6gqas in Fig. 18–20, can be used without blowing a 15-A fusee6u6zy,8 grindq(f,f ?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 cop9nzsdpyg 8ke6av r0+5per wire) and of length 2.7 m (9 ft) is connected to an elect eray08 5 spzkvd9n6g+ric 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 a factory through wire0lh o:; mpr*wgs with total resistal0* p;who:g rmnce $3.0\Omega$ 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 2ct7v5hsx k6q xl (85vlczv,k17.5 A. At what rate must cooling water pass over the coils if thl 8 5sv5klv(cv zt7cq6k x2h,xe water temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to heat1q6)xdsnqb 5wlz :ecg/v *f f2 a cup of water for coffee or tea. If the heater can heat 126qw1 f5x*)q:fe zd/2glcvn sb0 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 currenya p1jtke1 ywoi ,9u47t 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 across a j.a7rhp p b;j 101mysf$330-\Omega$ 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 bu9 3+ pdwto*h h 7vb-0mcug*jthe $120-V_{rms}$ 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 currenoi dqls 1,o7.bhq1 ca-t in a 1500-W device is 5.4 A. What is the r 1cso7ah-,.qb1ql o idms voltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connectedlxz5mp : 8 jbwu)3ga5 .nz2b z.oqww7q 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 bxazprbj nryoyn8s 1 owck 6ht 4;q4q726l542connected to a ynszwoy ohn4cqbkjl r rxa45qb 1p2t;2 48766$240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connectej i he6)eox c*4dw3moyk62, 3exwj ww4d 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 coppc6l .0n3gkav2 t;vpbpzs ucw, vrb+/sn2;7u ser wire carries a tiny current of $2.3\mu A$. What is the electron drift speed in the wire?    $ \times10^{-10 }\;m/s$

  A 5.80-m length of 2.0-mm-diamet6 s1elgds hkfo72i4;ver wire carries a 750-mA current when 22.0 mV is applied sg64 klfd 127s vhei;oto 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 a /f4dvjy5rv 2xtmosphere, $He^{2+}$ 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, * vxkvtu4*u5:gfg;tl50xn3a o jm ) yu$He^{2+}$ 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 fie( 6euk81b4jvdgb9n qg ld 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 elefjecd wgvg,uo (aw n07i*3.0md * acy/hh:j) cctric 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 0.0063 s. What is the speed of the electric pulse along the axon? (Why are two measurements nei(g dnwwhc.0f,hu7 :a oe03c/)g* vd myjcj *aeded instead of only one?)    m/s

  Estimate how much energy is 2x thf0f m(x-trequired to transmit one action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored by charging the axon tf f2x-0 txhm(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 potentifuj9 b; )+obxc (:kk t(x-8rk dwt;vy7l t.fpual, $Na^+$ 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? kg j xrgzz7-;tuw )h()   C

  What is the average current drawn+s otdo0n2 mn; by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lighty(.z5lrqc ee/l4g ls jfo9crw ++k3s6 s on. If each of the 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 batteryj e e.cl6++y59sr(r wg4lolksczf/q3 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. Ifo whv+3dqwm2+z+mkn;-yf w .h it is made of iron, what must its y zw kf+q;+m+ .od-2nwhm3v whdiameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the recip2g45fyn1 kh ia8dw)kh rocal of the resistance R; g5kwfh4kad1 i28) ny hthat 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 fpuxmz)mv4 kv .u26xuy 25cx+ of power. Suppose that instead of using high-voltage lines to supply the power, the power is delivered zymu vx5+4p xku2 6f .2cxmv)uat 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 household uses a 5qn q a(*ri,(7alc fsb1.8-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 tw028m/dp- , oddppuzlpo lengths are wrapped together side by side to make a thicker wire. How does pp,z/do02 upm 8pldd- the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 11f-.vdgkmx v v( (3px e-*wut/r7 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 )br2w hulf6t;does not become so hot as to start a fire. What diameter must a copper wire be if it is to carry a maxiuh6l fr)2w; btmum 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 giy5z :+ftmmds0 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 05pjvkf 3,wtgc4 gf0s950 W of energy per second to the ic s p0,tf jvkw354fg0gnterior. 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 conductorsv5ly*lx e) p9m,gpa(u made of the same material. One conductor is twice as glv*m, a l)xpyep( 59ulong and twice the diameter of the second. What is the ratio of the power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room of4dp09g;evnh .8kx hlb volume $62\,m^3$ Air is brought into the room at 5$^{\circ}\,C$ and is completely replaced twice per hour. Heat loss through the walls amounts to approximately $850 kcal/h$. If the air is to be maintained at 20$^{\circ}\,C$, what minimum wattage must the heater have? (The specific heat of air is about $0.17 kcal/kg\cdot C?$)    W

  A 2200-W oven is hooked to a 240yn tjltcy0jgd ; 0y5j86,ril1 +hf:l m-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 +n*nhak 5svk ,as its source of energy. Its mass is 1560 kg and ,nank hsk v*+5it 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 resi3 g-n/tor/ g*b-ybkbwstance 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 labd+5mv 4:y ,m:qf lf11-mA beam of protons traveling at very nearly th 4 :ay5f:fql+mbdmvl, e 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 cb:j (k1 zzmp8 eyfe;6jord is copper wire with a diameter of 1.6pyb;m1zk8eje (z fj6:28 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 -epku/iz 9lv:- nxs5ewhen connected to 120 V. The heating element is a coilv-pl9ke-sez i u5x:n / of Nichrome wire. 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 asg2)c 0g jd5vz* exc5ibout 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 headlights vary as the voltage changes from 12 V to 13.8 V? Assume the headgis5cj*5 zv e0d 2cgx)light resistance remains constant.    % increase

  Lightbulb A is rated at 120 V a5oe+6f jxe y4g( m zxt/ *c,jmdag2gf+nd 40 W for household applications. Lightbulb B is rated at 12 V and 40 W f/x jx4mof 6fadgcg,t+eye(+ m 2*gz5jor 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 connectkz- el*rm4fni2 n9.pj a set of appliances at 120 V, which draw 22jp4-*n leifrz km.92n50 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 3.00 cm and -w:ztrnz2o,k an outside diameter of 5.00 cm (Fig. 18–37). What is the resistazk-:tn 2w,or znce of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistanc+iwge*)zc dt gi,r- o,e R is stretched uniformly so that its length doubles, by what factor does the power dissipated in the wire change, assuming it remains hooked up to the same voltage sour i i,od, g+rzewtg)-c*ce?

  A tungsten filament used in a flashlight bulb oj *3l) +rzytmvg *d)scperates at 0.20 A and 3.2 V. If its r yslr)dtmc g+3j )v**zesistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$