What quantity is measured / hrl-hz 3bo (zjadofnh5po)9 y5;lo7by a battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circus o98qto8ukx. m ,kbc uqxcmi57;99g zit, electrons flow away from the negative terminal in the circuit. But within the cell, electrons flow to the negative termi 78c ktuqugscxm x9.kqz;obm 9o5i,8 9nal. Explain.

When a flashlight is operated, what is bk8pm i),)ro xoln 0,o6rin i/geing used up: battery current, battery voltage, battery energy, battery power, or batteryo, i6r0/l,niio)n mr8kxg p) o resistance? Explain.

One terminal of a car battery is said to be connected to “ground.” Since it :qchkm38wo2+nxq 9gj( sqx; k5b lkt 7is not really cxmj 8;+qh k k7sn3l(c 9x2bo:5qtq kgwonnected to the ground, what is meant by this expression?

When you turn on a water faucet, the water usually flows immedo*dt 5 wx;*gu xo;rh/oiately. You don’t have to wait for water togx*ur5* o/;oxt d;woh flow from the faucet 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 wi ecu ft-:se-j;re of the same length have the same resistancs e;jc:fteu--e? Explain.

If the resistance of a small immersion heater (to heat water for t7:a myb:xvf3x7hr) h ir+o bov:7s6 vqea or soup, Fig. 18–32) was increased, would it speed vvb+rs )vy7x:rq7m3 aoi :7h hb:fo6xup or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of length:j0jdoh 1 as8ts a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resist j0th8jods1 a:ance, (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 lightbulbf* ,o. 1aajijrlqd6c ( burns out?

Explain why lightbulbs almost always burn out just as they are turne 85h r,dqhze3id on and not after they haveq5zhre3,d8hi been on for some time.

Which draws more current, a 1005)q d3/ y+t nxgj3fyka-W lightbulb or a 75-W bulb? Which has the higher resistan3 3yjt ak5xgn+fyd/q)ce?

Electric power is trsuz3-gk v s4ef,yr. 0gansferred over large distances at very high voltages. Explain how the high voltage reduces power lossyru s z0kg3,4esgf. -ves in the transmission lines.

A 15-A fuse blows repeatedlyuah 8o; .m8 e/3h0xligzx8ndt. Why is it dangerous to replace this fuse with a 25-A fuse?l 8h/n 83ai.zog txd;muxh80e

When electric lights are operated on low-frequency 9n dvd 8r09sy;wt1m twac (say, 5 Hz), they flicker s09v 9 nm8dwtwdrt;y1noticeably. Why?

Driven by ac power, the same electrons pass back and forth throu.-da /t (l (pg6bv.1 b+dklh bdsj-diagh your reading lamp over and over again. Explain why the lighdt/+s-gjvaid k bh -d .lb6d 1.lapb((t stays lit instead of going out after the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. Immediately af xo kta:kvf :axo4 9m8jvas9*7ter the toaster is ta9vo7 v:9k8*j 4t xxfak:o amsurned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a gam1ux4 g dl-mxj.kl fdf)37:resistor? Explain.

Different lamps might ha ji1i(w-eq6a)ec lm3wve batteries connected in either of the two arrangements shown (e3 -cmq6e)aii 1lw wjin
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.f230 ijjanvf7ys-,((e 2vk hni pqsz past any point in the fziq jiy pj2a(- skvn.2hs3 7v,fe0n( wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of f 7wxn7(ythir87xq6 z 6.7 A for 5.0 h. How much charge passes f( yzh6i8n7xxw7 t7rq through the battery?    $ \times10^{ 5}\;C$

  What is the current in a46qnjs upwk q8). ik *yu-.vivmperes 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 currentynea hvox(ys9v7 56 w9 of 4.2 A?    $\Omega$

  What voltage will producemtjby ,p6.5sx uce4l( 0.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged int.b.0xxgv.3mbv p:wn lo 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 resistancv3fw od yx)lx/a5l/ :oe 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 connec(n o9(r;gl*uldgbuu37yl;z4 my dr 3pted to a 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 transmisk397 w8 wziqhtsion line carrying 2800 A (Fig. 18–34). The line hasw 73wh8zk q9it $2.5\times10^{ -5}\;\Omega$ 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 Vz z;;my2)i7rlv1ikh q dgfs6 .mczv0 7.
(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 xbyx7 t2zc - l*cyw-r;through a resistor.
(a) What is its resistance, $\approx$    $\Omega$
(b) how many joules of energy does the battery lose in a minute?    J

  What is the diameter of a 1.00-m length of j0 v mhv2wcc-8tuwa)) tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of pahb cch6069w*novbm;l 4f1 y a 3.5-m length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 1x*m3mcg p( h30:fas8lc(.oo t lla i5w0.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm io w*0igoh(38sp ll3:mca l(t.mc5 faxn diameter.   

  Can a 2.5-mm-diameter copper wire havjr2r yca ev3c2gy ;.+:sfh t1ue the same resistance as a tungsten wire of the sa a:c2. +cty 3erv;sy ju2r1fghme length? Give numerical details.    mm

  A certain copper wire has a resistancecne;* 7/vi8bv- )kgqosq64aon 0exi y 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 (3 (mz.ziuhebgc:mb +(originally at zmu me.+ib 3( bczg:(h$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper willv3wzoyu go. ((x k sv53:cgup: have the same resistivity as tungsten d: goy.533v:xzp ukg(( wvcsuooes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of abonsu6qzu1cl j8 8 nzix ln40jy522 tl/hut $12\Omega$ 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 wirg.qnmni3k7cl )w v93 we (used in 15-A circuits). The wire has diameter 1.628 mm and carries a 7ni3q lw9)kcw mng3.v12-A current.    V

  A rectangular solid mag88we(g n h/hhde of carbon has sides of lengths 1.0 cm, 2.0 cm, and 4.0 cm, ly88 he/gg(hnhwing along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for current that passes through the solid in
(a) the x direction,    $ \times10^{ -4}\;\Omega$
(b) the y direction,    $ \times10^{ -3}\;\Omega$
(c) the z direction. Assume the resistivity is $\rho\,=\,3.0\times10^{ -5}\;\Omega\cdot m$.
   $ \times10^{ -3}\;\Omega$

  Two aluminum wires have the same resistance. If one has twice the leng h3ngr m77gt;j b5cjm6th of the other, what is the ratio of the diameter of the lonc7m5gm6;jhg btr73njger 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-h f e1,+/xezv zsx6*g7ddt5j 2uyj1m5t(xibtV power supply, and a curren ef6*u1t/ b,jyix 7st(j1zhgd md2zv5tex+x5t of 0.4212 A is precisely measured at 20.0$^{\circ}\,C$. The wire is placed in a new environment of unknown temperature where the measured current is 0.3618 A. What is the unknown temperature?    $^{\circ}\,C$

  A 10.0-m length of wire consists of 5.0 m of copper followed by 5.0 m o2z3;sstob*8 v rat;i df aluminum, both of2;8;*vt3staorbdi zs diameter 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 important that the value of a resistance zm/fvkom*9 *g;pv ) ihnot change with temperature. For example, suppose you mad) ;vfohz/k*ipm v9*mg 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 ovenafa 3(lepap.j rg:21 s is designed to produce 3.3 kW of heat when connected to a 240-V source. What must be the resistance of the elemea2a1aspj3:grl.e( f p nt?    $\Omega$

  What is the maximum poqhk-j sl ;jg*) f+wrc3wer consumption of a 3.0-V portable CD player that draws a maximg;3kshf+-r*jcqlw )jum of 320 mA of current?    W

  What is the maximum volt92 9daz yos7 k3;c5bgpilmn .aage that can be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current thrl9q6aw.pglvm t 6-8)kixa ,ypough, a 75-W lightbulb connected to its proper source voltage kg8p p, 6)lw l6tiqx-amv a.9yof 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. Calc.q6vn36ma s-d4r pfo o+n3jetaduk27 7fy1j v ulate
(a) the current through the heater when it is operating,    A
(b) its resistance?    $\Omega$(Round to the nearest integer)

  A 120-V hair dryer has two settings: 850 W and cz.c g vt3zm)01250 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 delivered:2,tupl i/uky cl(c-+ pmu7dd 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 willmlupklpu-ity ,(2d/ 7d+:c cu 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 use in the morning(imu.smqd+;(1 a mxh nncfl8 + if it is in operation for a total of 15as8+dhilm1q cm m ( n.xn;+fu( min? 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 does it cost to leave a 25-W porch light on 3j,fzwz74 eyxuuon4 x f73g 5tday and night f 4z njuofxt, ew 4fy7u337zx5gor a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1a a /q,qbf3byf0 8 3/wsai)ikfvgb -o*.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The8b aifswfgvbq*) ,3if /a30o/y -bqk a 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 amount of energy s qxi7a(/l6i mpet4w*ttored in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connected to 120 V as in Fig. 18–20va5 9ricd4zik qo 7.t5jast/6, can be used withctqaiad.6r9 5 s i/jtz5vok47out blowing a 15-A fuse?    bulbs

  An extension cord made of two wires of dxrntdu.atebo0+4253xf / jzl iameter 0.129 cm (no. 16 copper wire) and of lenn+t2.zuabl5 43j etxr0/ox df gth 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 deliveruleimy6g ., 9oz9x5u ds 620 kW of power at 12,000 V to a factory through wires with total resistuxg 6yomu,z5.e 99idlance $3.0\Omega$ 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 linz zfp9qz+g*h .e is 17.5 A. At what rate must cooling water pass over the coils if the water temperature is t. 9z *zzpqgh+fo rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to heat a cup of water for: ;,lqv, qztqp z si,haa5 7rzvn,dw+5 coffee or tea. If the heater can heat 1+; ,zw s7v phq :i5,5 ar,qnqzdz,ltav20 mL of water from 25$^{\circ}\,C$ to 95$^{\circ}\,C$ in 8.0 min,
(a) approximately how much current does it draw from the car’s 12-V battery, $\approx$    A(Round to the nearest integer)
(b) what is its resistance? Assume the manufacturer’s claim of 60% efficiency.    $\Omega$

  Calculate the peak current in amhi;mg0zmiozq-5c7 3 $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, is acbh4+ na dzgo)u .uy(,cross 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 ofg ),5a+iezp 7 ep4eb9x3i wuap 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 15004.1hr tcb lhmf-qb c-5-W device is 5.4 A. What is the rms v4hf c-l-1cm5 .b trqbholtage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is conneb9h cul7jip-,b6+(16 he teqkd0w 7uz l zrm;ncted 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 3rse/ l;7b,m*(9n o 5oqx8bqjz iyaxv 2.0-hp pump connected to a,inrb qz(/ mqob2;7 9oje xa *5xsl8yv $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to awnxu8ck 1ze0 kx0gaw/dv r/84 $240-V_{rms}$ 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 tins9.f+ h,j/nlh d. xmy1nftgb-y 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-diaht a/58bj 6gtj-;i :ilo zf(bpmeter wire carries a 750-mA current when 22.0 mV is applied to its ends. If thezb :fg;b 5(p/l 8ij-a jhtot6i 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’so5:z) ri0qodj 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 

  At a point high in the Earth’s atmaam.) ;2nye weosphere, $He^{2+}$ 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 idep.8(2x q1)yzq+ z a wgj3quaxon membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with an elect7q rav6xmkc+2 sk/) lnric 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 axos ) xv/7 rq+cklka62nmn? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much energy is requirew1:+0+mlw ag k1uqb fxd 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 capacitance; see Sec0u+lmf1 q gb1kww:a+xtion 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 potef9b miz x5)1 t p(/fjzm.i,wnantial, $Na^+$ 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 gdot(j 8*sh o26xq .,jmb1hvzsp9i:rampere-hour?    C

  What is the average current drawn by a 1.s6+ x -.af*9 uglz(kmbubr/ze 0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the:t0uk/n - zp 5cbhxghj*o /qq; lights 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 battery laj phu/t5q-/ h0*;:cb xzongkqst 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 4ci es,uc c5hs- 9j0qhheater is 5.4 m long. If it is made of iron, wh5u he,4i-9ccjcs sh q0at must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of the res(n-o wdyu1p*r istance R; that isw-(u1r p *ynod, $G\,=\,1/R$. The unit of conductance is a mho $(=ohm^{-1})$, which is also called the siemens (S). What is the conductance (in siemens) of an object that draws 730 mA of current at 3.0 V?    S

  A small city requires about 10 MW of power. Suppose that instead of usinhr0u d,gew o26g high-voltage lines to supply the power, the power is delivered at 1o ,hgu w2e0dr620 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 hou-u yzp(ufaj o1+7 j-d u4huji(sehold 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 lenu+a7gjm7uwt.p: pv t8 gths are wrapped together side by side to make a thicker wire. How does the resistance of this new combination compare to the resistance ofg u +t:mpapuw7 8tv7.j the original wire?

  A 1200-W hair dryer is ;)mflhzvtmr8.gfc) x-th v ;e m 62;redesigned 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 enou3qv x6 hq-am*; 4wqbn.e(aegwgh so it does not become so hot as to start a fire. What diameter must a copper wire be if ib4gw 3m*evh-qaw6;qe x(a q.n t 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 ta9li* ;m x6wlkhe 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 secoqib t;jc1o2k+nd to the interior. Fko2+bq ;tcji1ind
(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 materialfxcdo.ixm4xzx. 0: / q. One conductor is twice as long and twice the diameter . xf:.xq0xim 4cx/o dzof 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 hea, ralan tv-q1hz48s j.-n khb7 62etedt a room 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 hooke sdh)ga s (prkp985dc3t eis cb8n9z8peig72/d 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 make47xz5j se77(jot olles use of storage batteries as its source of energy. Its mass is 1560 kg and it is powered by 24 batteries, each (e 7jojx s 57tel7olz412 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 resistanc3o8r mn17/c*7rpotiv5er ny le 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-my3 xi aju+qnf:qd+8-rA beam of protons traveling at very nearly the speed of ln+i3daf: q xjqy 8+ru-ight ($ 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 connectin1c6)/b ot 3r bmt(wuqbg cord is copper wire with a diametermrc3o6 qbbu1tw( b)/t 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 wheew:*9w ai nz9in connected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total le:*iw99eizna w ngth of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the sy7ytu 4z4gw(ic stem 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 poww4ug( i4yct z7er 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 househ *t jzxx8.n1w,quacu5 im. u6xn(c;kbold applications. Lightbulb B is rated at 12 V and ka jctu.xxwm q(xzu.b*516n ;c uin8,40 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 gfnpv3 o+7kwvig:e i4q)h/bi( 7nyr+ appliances at 120 V, which draw 2250 W of power i)w4rpi7 vqko+( n/gybv+n:fie7 hg3total.
(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 of o5 nhe ;xa3cdmnk b) q)9i/o7d5.00 cm (Fiin)kom7)xab o;ne/39dd5 hcq g. 18–37). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its leng, y v*isliaa99g5r (gith doubles, by what factor does the powe(yri*l ai9gia 59,vgsr dissipated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operates at 0.20 A and 3.2 mmokw5;zy6un47; h om5/l eh;zpwp 0eV. If its resista0k;pl p6w/yo 5memu5o h7h z4e;n;wmz nce at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$