What quantity is mea9wm we2rj -p3vsured by a battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is cogo:n .typcx-9scmi: 4k(sx p- nnected to a circuit, electrons flow away from the negative terminal in the cinx:s( t:9-s4 ykoccg pip-m. xrcuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what i .iv 0 el/j,ao)uofu;is being used up: battery current, battery voltage, battery energy, battery power;)0vi .f,auiol o e/uj, or battery resistance? Explain.

One terminal of a car battery is said to be connected 3btak; qejhvh36 (i5tto “ground.” Since it is not really connected to the ground, what is meant by t3 tej; 3 ht6qvk(ia5hbhis expression?

When you turn on a water faucet, tlq4b +0hrh6y the water 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 terminals of a batt6q+hlt y4r0hb ery?

Can a copper wire and an aluminum wire of the same length h1e kv ,,kk5voyave the same resistance? Expla1kky5ok,vv,e in.

If the resistance of a small immersion heater (to heat water 5qxv15ylxf jh 5* om+cfor tea or soup, Fig. 18–32) was oxyvjh 1*l5+q5xfcm 5increased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sidpayi;7 jxjp9h. :id4ccqb2eh f2;lq:es of lengths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain l 72i ;d; jhppc29jb4hyaqx: fic.e:q(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 lightbeuza1 lqz8:r5ulb burns out?

Explain why lightbulbs almost always burn out just as they are 5e+;,,s8cjyrg x kcgeturned on and not after they have beenxc c,5e g ;+r8geyj,sk on for some time.

Which draws more current, a 1nrejo/(h9p2wq l h,q5 00-W lightbulb or a 75-W bulb? Which has the higher npw(qhrhoe jl9 2/q,5resistance?

Electric power is transferred over large distances at very high voltages. tj9,jz x en1;rExplain how the high volta z;,j1xe9j rntge reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace thist:0 cqj;u;(c4dtdn p;qu0llyt-/ vib rs*r(v fuse with a 25-A 4ijudn;t cr;psy/0c:v*uq (t- br(vl qtd0 ;lfuse?

When electric lights are operatehh -b.6ng q2 q:s,fnnkd on low-frequency ac (say, 5 Hz), they flicker nn qfqs-kghn,b:h .n6 2oticeably. Why?

Driven by ac power, the same electrons pass back and forth through your rzl:(zxu lo t78lkhaz *8:ye7 oeading lamp over and over again. Explain why the light stays lit instead oflo:(h ztz* u7la8l 7xko8 ezy: going out after the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. Imm 5 wk(b6u g4/ebh+meqhediately after the toaster is turnk+/g wheh65qbum4(ebed on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor?1et+gtsto x4i l.w 33a Explain.

Different lamps might have batteries connected in either of the two /2g5d,dgy ttyn8 u1- zsp o/:4ehbftzarrangements show/ottyg ugyh1f -:tddspz/2, 48 5bzne n in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many elec*ht jloy*76kb hhl+ d7trons are flowing past any point7k*j*h6odbh+l7ly h t in the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current o hm(kxagida9 q006c:kp rrfw*s*.7paf 6.7 A for 5.0 h. How much charge passes through the battersp.d fmig9*7xa waa h0(k qrk pc:r*60y?    $ \times10^{ 5}\;C$

  What is the current i tc6a0aw80ms:aq3jq m n 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 g)f*4avx cpt( toaster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current througpo +iy(e(6 ltvh a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged intovp-yolk 7;ia 1 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 heati,njts/dzxi;0q x k4a+ ng 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 whosqm(g7)kzf- gpl wj; f-e resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transmis:bwdin :o/aw a3o h5j6sion line carrying 2800 A (Fig. 18–34). The no o/b::j w5h6a3ia wdline 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 fjk8bw572/ rc ls -kqr240 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 l: rkq 0nlvvka 8:be15resistor.
(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 tg i7rceu::j; tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper zfi jw 4(u-m)twire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of fd k9 xu*da rjc6bww-:t 7-;dh8wv(ujthe resistance of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in diametjh-*vw;8 w r(9ub 7ud-jfc dw6ad tkx:er.   

  Can a 2.5-mm-diameter copper wiry k80wdykz qgwyr2 60-)y,hs0bcrrex* .5 rype have the same resistance as a tungsten wire of the same lengtp*yrs0 5y6rq0k 8w2wy ) kyyzbrc-x rh0d.,egh? Give numerical details.    mm

  A certain copper wire has a resiskw oas+i(w 8:wtance 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 txq0;7os evixubup78*emperature of a copper wire (originally at xp8 ;7 x* eqsvbouui07$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivity ;ebz a (m-nrc 79a/y.cnl,fyias tungsten does am( niznyc.,fl; 9-cyr7eab/at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of abo 4;(o6mx pp3wv)gwte eut $12\Omega$ 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 aloiu0h r+*) fllnu 5hks4u+ l6ofng a 26-m length of household no. 14 copper wire (used in 15-)uu4u+ lsn5ihlrk 60 hl+o *ffA circuits). The wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has side5ja5ubqd9xow j7+h i m9e9ed1 s 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 fei+da1q9 9jj 55 97uxbwoehdm or 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 length of the nhod9u(s(qyd f-f( +f4i7co-kxs(j w other, what is the ratiok+ - jsf y4qi9doufwc((sn 7-fo dx((h of the diameter of the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V poweqyx 2i 2c7mved ;xzi/2r supply, and a current of 0.4212 A is precisely measurqxd/2xyi e2i;mc zv 27ed 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.;*zi sq(6rer:ojv vj90 m of copper followed by 5.0 m of aluminum, both or:6z9 evsj*jr ( oviq;f 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 impt yf)6/qr xbx zp;sd 4 byqcth0-..7rmortant that the value of a resistance not change with temperatur6bs-p bt7;0/.4zyx ftrr.myqdc)hqx 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 pro ah5m5c;he gu)duce 3.3 kW of heat when connected to a 240-V source. What must be the resista) mh5cgh;ua5e nce of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player tf*h tmw9v(iy49 ba 1wwhat draws a maximum of 320 mA of currewwa9wf ybh *1m 4v(9tint?    W

  What is the maximum voltage that can be applied acr1:mw fbk pw1c0oss a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, a 75-W lightbu 1a evxo-,mqx d7,)mjilb connected to its proper source voltage of 12ex,i1,dj avxo-)q m7m 0 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heater isj+rx xrdha8z y,*fq- 5 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: 850 tu9ucgfu ,p q;p1+ k1uvs nz2*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 electricb(f0ra)n7 t- 9yxu i)mvyk+nvity 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 my0 )yun avi-+tv xb 7kfn9)(r120-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 nqe,.x.rugv/gui9m - in the morning if it is in operation foruu qnx gmg.r9/ .e-iv, a total of 15 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 day l4bwqzuw1y atxp g;.8 g4y)1mand night for a yeartw4. lz ypuy;1q1amx8 wb4gg) ? $\approx$    dollars

  An ordinary flashlight q ylv)nzf1 (zhwg o15*8.hw/ e.mawyd uses two D-cell 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when turnevfy*hg mow.dz.q ( 8w5/)1wy1nle hza d 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 energsl+5uafsd . 4gy stored in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightb9nwsy* 2 os;7jlws egyj,-0kjulbs, connected to 120 V as in Fig. 18–20, can be used without blowinw-9*jljjosny0k we ssg72y;,g a 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0 na2 zby6a61i)oto3cc.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 cord? an ibcyo163za2 )6otc    W

  A power station delivers 620 kW of power at 12,000 V to a factory through wirf: -);uhujz 81pbjc l 6qfa3g6dk f+vaes with total resi)jv3lafbqk; 6fh+f6 1 d upgajz-:uc8stance $3.0\Omega$ 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 linppex 40cxc3mft9j ; o+*pibf. e is 17.5 A. At what rate must cooling water pass over the coils if the water temperature is to rise by no more thafco0;px.f49cbt + xiej * 3pmpn 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to heat a cups) ,7w :jg9vjokr04 fwrby3d1siv 6i h of water for coffee or tea. If the heater can heat 120 mL of 9 wr:voysbski4wh6jd i )7r0j,v 31fgwater 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 a 1 3e3bz*vidrqvw :8wo$2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, :v 9ssh(w4:qyh3ufqu 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 resista lid-x.wz ;gp2n6f 0fj)6zdaince of the $120-V_{rms}$ circuits in your house as seen by the power company, when
(a) everything electrical is unplugged,
(b) there is a lone 75-W lightbulb burning.    $\Omega$

  The peak value of an alternating current in a 1500-W device is 5.4 A. What is t(xdygc-/fy7b 5 egrf -.lnmina u4g (/he rms v /nlgbyi/ 4x g5nymuf7-ed-( racf(g.oltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected t12)i v 9osuivwet 3y)po 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 ie5*s5 ct(wqvtnstantaneous power dissipated by a 3.0-hp pump connected q5tt *c5w(esvto a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connectowiw8l0wc/v . 5p d1mi eeatdau::+-jed 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 copper wire carraxro d/km4l i*egg*ylu90-5aies 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-dibrmc2 *wxfb )(ameter wire carries a 750-mA current when 22.0 mV is applied tob*wf(c)xmb 2r 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;7xrv-gszci / 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 thtv s9y0wm22w( in i3b-ees)kf e 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 ahpr.k)0 (h8p g+ hki+fcg nw6l(wr*tucross an axon membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulatui6lnjb+nj1bp uj9 a26d; x,ked 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 time required is 0.0063 s. What is the speed of the electric pulse along the axon? (Why are two measurements needed i xnp+ 6,b ;j jaduli96kn2jb1unstead of only one?)    m/s

  Estimate how much energy is required to transmit one:k 9nh(syyu:4 hstfn8 action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored by charginnn9tuyyfhh :(s4s : 8kg 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 potentiawuy (zm(jca (1 eh.st:l, $Na^+$ 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- c*516w nrh9mu8n k8-lm ttdynhour?    C

  What is the average current drawn by a 1.0-hp 120-V motor?bjd 2ka9ebcm: i j157v $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of the twxf9tr12k hun;d - zm6 uqp)6ipo headlights us)utrq2hixu-mfpkn9 6 z16p;des 40 W and each of the two taillights 6 W, for a total of 92 W, how long will a fresh 12-V battery last if it is rated at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of a 110-V, 1500-W heater is 5.4 m long. If it is m ur5fiv hfxv6:qg:12made of iron, what must its diamete5ghfxqvr: fu6m i:12vr be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of the resistan4wzlokjn48uj t9;r4 oce R; that inzr48owuko; t9 j44l js, $G\,=\,1/R$. 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-.4a6y /qy:k ,e ezyy torja(fpose 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 energy lost to heat per hour per meter.(ye yayfeoy4r 6t: z., ajk-/q Assume the cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular household uses a 1.8-kW hm,z z+jhf5)ljeater $3.0 h/day$ (“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 a4* z )nbppldl8cfy1)nre wrapped together side by side to make a thicker wire. How does the resistance ol ybf1 nnl48p) c*dp)zf this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 117 V. g 1 igbi/ nh6is/ad,/i
(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 zkz.5jy vx*c) ; oudh/enough so it does not become so hot as to start a fire. What diameter must a copper wire be if it is to carry a maximum current of 35 A and produc/x.kov z5 zyc*;u)j dhe no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by1)kk1 - kr) ffgc1+n qsn9mj.o7zcyx k 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 x0j1 h fre1kvd;5i2dk950 W of energy per second to the interior. Fxev5k 2dhd0 1i;r k1fjind
(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 matxi6u-9+e6f/ xqj jupierial. One conductor is twice as long and twice the diameter of the second. Whi pi/x6e9ufuxjj +6- qat is the ratio of the power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used tob spy:c*no6a, heat 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 hookedjfnj)f2h9(d g to a 240-V source.
(a) What is the resistance of the oven?    $\Omega$
(b) How long will it take to bring 120 mL of 15$^{\circ}\,C$ water to 100$^{\circ}\,C$ assuming 75% efficiency?    s
(c) How much will this cost at $11 cents/kWh?$    cents

  A projected electric vehicle makes uv3g:xe, l): ob .fusdcse of storage batteries as its source of energy. I,flubeg ) oxd:vc3s.:ts mass is 1560 kg and it is powered by 24 batteries, each 12 V, $95A\cdot h$. Assume that the car is driven on level roads at an average speed of $45 km/h$ and the average friction force is 240 N. Assume 100% efficiency and neglect energy used for acceleration. No energy is consumed when the vehicle is stopped, since the engine doesn’t need to idle.
(a) Determine the horsepower required.    hp
(b) After approximately how many kilometers must the batteries be recharged?    km

  A $12.5-\Omega$ resistor is made from a coil of copper wire whose total mass is 18.0 g. What is the diameter of the wire, and how long is it?
L =    m
A =    $ \times10^{-4 }\;m$

  A 100-W, 120-V lightbulb has a resistance d hvgy8u2s 89 +mpr/f 9czty1vof $12\Omega$ 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 Fermila)ew87 , qf8(keulkcb tb (Illinois) is designed to carry an 11-mA beam of protons traveling at very nearly the speed of 7 8e(uek8tbfc l w,)kqlight ($ 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-Viit:0+iwv2dspb i fx)v w* )+g ac. The connecting cord is copper wire with a diame igvwd)+xv:0+ iwp ft2)sbii*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 is5kj )w(p 1zkg7ia1t dd rated at 95 W when connected to 120 V. The heating element is a coil of Nichrome wire. Whi5d 1z k(1pa7k)tdj gwen uncoiled, the wire has a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from about d9*(g *qtxc epp2+kd j12 V when the car is off to about 13.8 V when the car is on and the charging system is i jdcx(ep+gq*p2 dk* t9n 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 headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for household applications. Lightbulb Bzwr lcb9-(k 4tv5mo6z o rr(/m is rated at(rm(-oow r4v5b /ltc9k zmrz6 12 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 diameterukc gih5o;:q ( 0.259 cm is used to connect a set of appliances at 120 V, which draw 2250khi(;gc:5uq o 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 an outside diameter dk.y: o msx8u0of 5.00 cm (Fig. 18–37). What is the resistance of 10.0 m of this p8o0x.suy k:md ipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is fm 0iits(tu, 1stretched uniformly so that its length doubles, by what factor does fsi1(t,0mit uthe power dissipated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashl7 yub5pazwm;;xb, vm6ight bulb operates at 0.20 A and 3.2 V. If its resist5 uz,xmm;ba wbpy7 6;vance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$