What quantity is measured by a battery rating given in emgha n/927fd ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow awaar fdxah20n:( zr sd96gv6 *6ozq3rggy from the negative terminal in the circuit. But within the cell, electrons flow to the nr* a 6x6r ggdsdzg9 3 2h0vn6azfroq:(egative terminal. Explain.

When a flashlight is operated, what is being used up: battery current, battery 6 3)ec9moac,rzgf gc b c4p8:nvoltage, battery energfc3c), :czag 948ep c6n omrbgy, battery power, or battery resistance? Explain.

One terminal of a car battery is said to be connected to “ground.” Since it in/2y egom)mhw, -j636olwfl2 uz 6xvfs not really connected to the ground, what is meant by thgfj62umnx23fw-ohz l ym/o 6)el,6v wis expression?

When you turn on a water faucet, the water usually flows imme* zz80v qin(cg sw2/ qz.5vle.r af8bediately. You don’t have to wait for water to flow from the faucet valve to the spout. Why not? Is the same t c.l aen (qs85wi.fzz rbeq/z* gv80v2hing true when you connect a wire to the terminals of a battery?

Can a copper wire and an aluminum widsz5 iy ioh1+c a77:,-utm zzjre of the same length have the same resistance? Explai -m:z57uid hyita1scz,oj+z 7 n.

If the resistance of a small immersi( hpx ),i kz3pi(6rcx7v; tgyeon heater (to heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the heating pr6 p(gpxy, kr7t(ii cv;3z)exhocess? Explain.

If a rectangular solid made of carb:ez/ yvqr;x9jlx y).a on has sides of lengths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) they ax.lx q: /9)jvrzy;e 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 ligh+8u5ve xpe r,yfoz9y+tbulb burns out?

Explain why lightbulbs almost alwa7l l(v*iv:yjm ys burn out just as they are turned on and not after they have been on foy*v 7vlim(j l:r some time.

Which draws more current, a 100-W lightbulb or i*t f6hw3q:b-8j( p gqy1upse a 75-W bulb? Which has the higher reqpup -g1y: iwtsb3(e8 *jfh6 qsistance?

Electric power is transferred overf r.8by5j 079cd:z: ,qhou)gdnkv pm p large distances at very high voltages. Explain how the high voltage reduces power losses in vqnd p9 :j5c0b,)k mf doh7:ug. rpzy8the transmission lines.

A 15-A fuse blows repeatedly. Why is it dk3 7nt a8mf*edangerous to replace this fuse with a 25-A fuse38*7edn ktafm?

When electric lights are operated on low-frequency ac (say, 8hh)nw kp2-zw 5 Hz), they flicker hk- ) w8hn2pwznoticeably. Why?

Driven by ac power, the same electrons pass back and forth ty ;7ndspf -nm/hrough your reading lamp over and over agn-/n; fmps7 ydain. Explain why the light stays lit instead of going out after the first pass of electrons.

The heating element in a to+e*exorg(, kpjou/v2 aster is made of Nichrome wire. Immediately after the toaster is turned on, +ro(poue/jke 2 vg ,*xis the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resii: .i:yrz h7v1hyk cp3z3ir1md e2wy4stor? Explain.

Different lamps might have batteries connected in either of ce e;ki:l5sn*i dajcj30y+6v hq;y-n the two arrangements sv+6 jqjek3cn- y0sdhl5:c ea;n*yii;hown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A f80sk jstrc n82lows in a wire. How many electrons are flowing past any point in thec 0 88srjksnt2 wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A for 5.0 h.kd x 8eiibcf k.a1;c3z5m7 3gp How much charge passes azx ie p 5im;7.cg83kbdc 3kf1through the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes iou8e i4uoyewj,+ki mzk, )4t.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 3ngq gs pnd5waj.0h /:of a toaster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will proez+jhiw/oka(c j6c 5s7 2yf2x duce 0.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-Vbm zbz,*bob48 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 iqhc.sq:vi5 cvz+n4yzb x.*) ce 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 resistance is ) y c.x8qyx cbkm(;.xn$1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transmission line carrying 2800 A (Fig. 1,p:9n uvj*u ivzsm4 5gzzoc378–34). Tj,:43opz7minu95zvz*sc v ughe 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 24 1qyrnbd-- ,ykc4z +wx0 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 resistor.+sk mk0bjmmq /0) jy9b
(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 resisy2-7o5e 6s,rlq- yxqo,nbusso gf2,c tance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper6y 1lu(n hc/np wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire 2.0 mm in i4p31ts-a el6f h gxn.8.mjp8icq gx6 diameter, to 20.0 m of copper-x.4ia8q6tphglce3 ni p1 fgj6m xs8. wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wir3byr ;p7jtdowq di*7lb:ap mgbm5*0-e have the same resistance as a tungsten wire of the same length? Give numericalt 5bmi ;am*o73gqbj*:dp-rw bp 0yl7d details.    mm

  A certain copper wire has a sfgx k:;avn6z86 m5hyresistance 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 tempn.o4hmiq kw2mr9t) /y erature of a copper wire (originally at wr9tnm)4m2h i k.yo/q$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copjk,2ssmt) m.: /n iwqcper will have the same resistivity as tungsten doe.,tmws j 2)sq :miknc/s at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of ac/ (4 9yfkeevwirj :6bbout $12\Omega$ 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 ekvqrh0(0 i;cs3qca- drop along a 26-m length of household no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm and carries a 12-r 0 qqac3e0 c(h-;vsikA current.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cmf,fp).wbg (iv , 2.0 cm, and 4.0 cm, lying along thg)v(w f.i ,pfbe 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 ,pzw 294 hdkzl.xt:q a;kefi.. If one has twice the length of the other, what is tlxatezw;qhzf92d. k4.ki p,:he 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 15 g*e39svt7qzjr 1hy9 gn;pqj 0.00-V power supply, and a current of 0.4212 A is precisely measured at 20.j seh9zt5p3 7qr;n* q9yv1 ggj0$^{\circ}\,C$. 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 5zl b0q5- v607lb7 wvlxtc )ico.0 m of copper followed by 5.0 m of aluminum, both of dilb 67q0xvoc wb5ct) vil- 7lz0ameter 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 thpym).x43to g )q8kv a4hu )phee value of a resistance not change with temperature. p qy v.ame34 8ukhgt4ox) ph))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 of heat w,no1b+ o,9ilmblgy )h: p7hn jhen connected t j bmh 1nln7),py b,hi9:golo+o a 240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumptxg6md* r1i.ehtwd4 h sj94/g tion of a 3.0-V portable CD player that draws a eg*tg4ht dxd 4w.hs/m i9j61r maximum of 320 mA of current?    W

  What is the maximum volta0h umqa7n+0vrge 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 through, arqabjh;d, 0w l ez1*;s 75-W lightbulb connected to its proper source voltage o, bal*q;0eh;w1 srzdj f 120 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heaz xgo)x,kk/q 1ter 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: 850 W and(bgazk2 8 , 0ksqf4gmg 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 id*/bj-dn ;uosnritr* gb f16/n 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 120-V bulbs? [Hint: assume roughly that brightness is ;bn 1tr gf-/ uo*bsr *6/ddnijproportional to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use in the morning if it is b nbs5h5v; bl9in operation for a total of 15 min? At a cost on ;bbbl5 h9s5vf $9.0\,cents/kWh$, 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 leav dgbo9ukno-c6 au2apij: l1 ,.e6e.j ue a 25-W porch light on day an-.li .1augkb uj 2doa eu6ej cp,:o96nd night for a year? $\approx$    dollars

  An ordinary flashlight uses twolz+4q z8 )yrrh.0p uk;atvq)o D-cell 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The;a.kv0 r+yup)8q)tl qz4 zh ro 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 st2(kmdgv3s7 ebj)zg )lored in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs,ci b:t 0dvuhy,ro6g*. connected to 120 V as in Fig. 18–20, can be used without blowinyt vbi.dor:* u, hc0g6g a 15-A fuse?    bulbs

  An extension cord made of two wires of diamozrhwk0, ta55p3yjs v1dii k l,e49+meter 0.129 cm (no. 16 copper wire) and of length 2v,a94m0 etk ijphlw ,+ kior15dsy z53.7 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 delivers 693cqd ctt 7q 4j)e(dqkrylq8120 kW of power at 12,000 V to a factory through wires with total req(qd7 t9r3qe 8dyc41j lckqt)sistance $3.0\Omega$ 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 electro dztr( b:( sruxx+wq,h)yl,9 xmagnet connected to a 240-V line is 17.5 A. At what rate must cooling water pass over the coilrh,zt:d)uxx9rbs,w+ qy lx ((s if the 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 heat a cup of water fouv)x(hi sjgk7gdh1lulm0 lfa* f94l)7v ln24r coffee or t ( n*il afuhf0hsg1)dulgv )l4m4l72j9xvl7k ea. If the heater can heat 120 mL of water from 25$^{\circ}\,C$ to 95$^{\circ}\,C$ in 8.0 min,
(a) approximately how much current does it draw from the car’s 12-V battery, $\approx$    A(Round to the nearest integer)
(b) what is its resistance? Assume the manufacturer’s claim of 60% efficiency.    $\Omega$

  Calculate the peak curreoy pa ,k tz;s 1/tl7v,afgn/5, 9zdznvnt 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, is1f1 s409fmh7wcuv qjx 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 resistance hkujjop( 0 o5+nqu44uof 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 altejbw r,7-qrbi c0o0d 5tb zc3+9 c1bueirnating current in a 1500-W device is 5.4 A. What is the rms voltage ac+qb z73jc,t0b0 9 rcd5eb1-ri iwucboross it?    V (Round to the nearest integer)

  An 1800-W arc welder is connecy:8q qppqk5y .ted 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 pumze yz i7s.n: /wifi,h5p connected to yie 5fi 7n.szzi:/hw ,a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connectv w(c sjx-yj6/ed 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 carries a tiny currexyc k7s 6-n5pm:bp r)ynt 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-diameter wire carkct f-ae7xv ( mfi2.0iries a 750-mA current when 22.0 mV is applied to its ends. Iffvf(t0c- 2x kmi7 .eai 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 atmospherwd rkhogh0 ol5+kko-yi6j ;+9e, $He^{2+}$ 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 atmosphe/uf c ;8eee;kgre, $He^{2+}$ 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 , fok4ei2 ois6y(x v;j +cpfunfmf+72of the electric field across an axon membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulatn ng 9;e(tq2hved 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 dengq9(vnh2; tetected 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 instead of only one?)    m/s

  Estimate how much en16 sg0p;vnkezm1a1.rg/ +*lp bsmi wnergy is required to transmit one action potential along the axon of Example 18–15. [Hint: thewgk1 e nag 6 n +sm*10isb1mlp.p;/zrv 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 potep5i zb ebyfxdao; l(y1i 46d.8ntial, $Na^+$ 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 aqfhtw9:+8y c3lu6 m+ ot7unw umpere-hour?    C

  What is the average current drawn by a 1jf, pcq2*qu7 w.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the ligxpn) 0f5 (chywhts on. If each of the two headlights uses 40 W and each of the two taillights 6 W, for a total o fhyncx(50p)w 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 h rd sfr.lau91v84ftx3+tfg 5),jjxb d eater is 5.4 m long. If it is made of iron, what must its diameter btb) rv 5f 138ax f,lxdstf+9du rj4.jge?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as iqu8)m y0/jev,d qis 1the reciprocal of the resistance R; e)vqy,u is 0/ q8md1ijthat 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 o; q9jvdep9n( q,6kp/f8qtg uof power. Suppose that instead of using high-voltage lines to supply the power, the power is68d;tqjnkq 9pgfp,e9 (/vquo 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 househo o3xnagrto /)7u bd;ilgl1w:7ld 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 tr0ua y*o xyip te0z fv.b+(1x/ogether side by side to make a thicker wire. How does the resistance of this new combination compare to the resistance of the o(b/*1 exzytr00aiop u+fy.v xriginal wire?

  A 1200-W hair dryer is designe jjwevefhx1dy t7j02j8;,8p yd 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 enough so it does not become so tv7kscp8anu)8h+: w5 9zc txuhot as to start a fire. What diamsvx 8p9ac 5)7tc: u zh8ktwun+eter must a copper wire be if it is to carry a maximum current of 35 A and produce no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by the equas9znz )jnr1d 4zc:4 sction $I\,=\,1.80sin210t$, 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 sec q9s pkk83a a5u/j-t dihz)d t*/av.fbond to t5*8 haka/u- tba9ktq.3fzd/ ijv sp)d he interior. Find
(a) the power drawn from the source,    W
(b) the current drawn. Assume a source voltage of 120 V.    A

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

  220 V is applied to two different conductors made of the same0s2zg cbl7ibkr fpv 0q463+wq2wyy*d material. One conductor is twice as long and twice the diameter of the second. What is the ratio of the power transf2c2 flbyw6k+qz*rip yw b00dvq4g3 s7ormed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a a((. esgc. rgmtkd76u)3s jauroom 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 hooked 3(x*ym;0mv7rdbughfor)84 k qkmjq7 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 use of storage batteries as its source of en5kou d/-njp 6aqz9(wn ergy. (n6n apzq9do/-wu5k j Its 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 p9m l b6xf2qe*ud)kak0 .llu9rvo7- o 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 pg au j7;:nig,11-mA beam of protons traveling at very nearly the speed of light ,;:7aigp jnug($ 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*,bo-id k6dn- km qi5v is copper wire with a5b6 d-*dqn vkmk,-ioi diameter of 1.628 mm.
(a) How much power does the air conditioner draw?    W
(b) If the total length of wire is 15 m, how much power is dissipated in the wiring? $\approx$   W(Round to the nearest integer)
(c) If no. 12 wire, with a diameter of 2.053 mm, was used instead, how much power would be dissipated? $\approx$   W(Round to the nearest integer)
(d) Assuming that the air conditioner is run 12 h per day, how much money per month (30 days) would be saved by using no. 12 wire? Assume that the cost of electricity is 12 cents per kWh. $\approx$   cents per month (Round to the nearest integer)

  A fish-tank heater is rated at 95 W when connected to 120 V. The heating elemen he5l;t+0 aumpt is a coil of Nichro 5p;lt0mhu a+eme 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 05wjn17w hc1mg wju 1m2/ 3rdrpyc7ogsystem voltage varies from about 12 V when the car is off to about 13.8 V77c n1 mowrjh3jw /ugyr 5gc0211wp dm 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 headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for household ap3h )hf g)sguyze+s1 r4plications. Lightbulb B is rated at 12 V and 4z+f g4hysgr 3h 1u)e)s0 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 0yoq)b41 s1 daq.259 cm is used to connect a set of appliances at 120 V, which draw 2250 W of power totaq14)o y1qdsb al.
(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 vx/. 7rnmxn*u cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the resistav*nr.uxn7x /mnce of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its lenga*8m s atr4m 2bjgr9b4th doubles, by what factor does the power dissipated in the wire change, assuming it remains hooked up to the same voltage sourcer mrs 428m9aajbgb4 t*?

  A tungsten filament used in a flash;-kw,dj m;a+o +q2jd gwxl0m3/f+fxlr)noaj light bulb operates at 0.20 A and 3.2 V. If its resistad+nfk+ xojam)l;fj 2l0 d3 xmw/waq j+;go-,rnce at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$