What quantity is mea4tiucbj/ivn *.)z gbn:/ :q vxsured by a battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow away from thelov*z- aoh6 z4u-zhp )re7f (s negative terminal in tozr )* oah(v7uze4z-p fh6-s lhe circuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used ultld 6lb6g2wbzj)+eh yke3;3p: battery current, battery voltage, battery energy, battery power, or b6)gt6wbj+le de2kbllyz;3h 3 attery resistance? Explain.

One terminal of a car battery is said to be connected to “ground.” Sin 4v+nxgq(h t0qks1 g0wce it is not really connected tog0xq0 k 1vt(h +nsgw4q the ground, what is meant by this expression?

When you turn on a water faucet, the water usually fl6d za9z6 si+yh6yu* xtows immediately. You don’t have to wait for water to flow from the fauc+ s6x9hz 6yit6y*aduzet 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 wire of the same length ni;k a a/9tqzlmr(kr)tga0u9w8we/ :r xo 7 i:have the same resistance?iu)n7: 9t r8(9a za: tg /r/wx0lok;kamriweq Explain.

If the resistance of a small immersion heater (to heazcvah hk.;3tfo x38n :a;l tx4t water for tea or soup, Fig. 18–32) was increased, would it speed up or kt;xan3 cxtavz8l.43o;:hhf slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengthpjtg ss2n(..hrb .dp f5j3 a9:jab6o ns a, 2a, and 3a, how would you connect the wires from a battery so as tojfhb nr9 g.s :j.o5ad(.tsn2p3 ja b6p obtain (a) the least resistance, (b) the greatest resistance?

The equation $P\,=\,V^2/R$ indicates that the power dissipated in a resistor decreases if the resistance is increased, whereas the equation $P\,=\,I^2/R$ implies the opposite. Is there a contradiction here? Explain.

What happens when a u-r6ru x :ydj+1ryhh. lightbulb burns out?

Explain why lightbulbs alg*y *wf h63a5xoaucc*most always burn out just as they are turned on and not after they have been on for *wxoh uya* f63accg*5 some time.

Which draws more current, a 100-W lightbulb or a 75-W bulbfvwb *,z ou kv1u.0zp*? Which has the highervwoup*v1bzf0,k* u z . resistance?

Electric power is transferred over large distances atsboav 6civcjo kxa,22 -l/* .r8z tw,g very high voltages. Explain how the high voltage reduces power losses in the transmission lingsw6/iklvzo 2tocb , ,xcavar*.2 j8- es.

A 15-A fuse blows repeate njkrv; /sn awxi*8h3+dly. Why is it dangerous to replace this fuse with a 25-A fush sxka/wn*jr38vni; + e?

When electric lights are operatedj,-lbga1m ig + on low-frequency ac (say, 5 Hz), they flicker noticeably.bm1li+j,g- ga Why?

Driven by ac power, 6h kaobhu au34jpa3(u) s/.mythe same electrons pass back and forth through your reading lamp over and over again. Explain why the light stays lit inst)uu436ybpjohu (.hm 3aaas /kead of going out after the first pass of electrons.

The heating element in ab+f x99eb0orl toaster is made of Nichrome wire. Immediately after the toaster is tur b9l90bf xro+ened on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up ivlb0w95thy x8 *v )9en c5eqjfn a resistor? Explain.

Different lamps might have bat,y(7hy z0yohu teries connected in either of the two arrangements shown iny(uh z 0hoy7y,
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a cg vv, .3(x8.eo/baw/ bwkuk a)zee)va2u h5rwire. How many electrons are flowing past any point in the wire r3z).wvvx8ak(ve5/u uco. abb g w a)/h,ee2kper second?    $ \times10^{18 }\;electrons/s$

  A service station charges a o11ye,o( v(obiro5ack(qc 8 xbattery using a current of 6.7 A for 5.0 h. How much charge passes throug ( ((q8y1acc5kvobeo1o,xir oh the battery?    $ \times10^{ 5}\;C$

  What is the current in amperugz(c +i p: s,v;e+zrres 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 toasterk.3ybd3u +rrx if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.+ ,zyvyb0u 8qu25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 Al5+54:*o yzysvcoc6qn-piek d9) but when plugged 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 cxd) h27uxk-t/snj1a dryer has a heating 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 whouq-,wmi2 rp )ow(v,epse resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transmission line carrying 2800 A (Fig. g7g a *,qm9b i.fsqvej1 .ogl218–34). The l mqa.*e i f7bj9g,q2gvlg 1o.sine 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 yuw,cc 3u,q x,2 dsu;s6.50 A at 240 V.
(a) If the voltage drops by 15%, what will be the current, assuming nothing else changes? $\approx$    A (retain one decimal places)
(b) If the resistance of the device were reduced by 15%, what current would be drawn at 240 V? $\approx$    A (retain one decimal places)

  A 12-V battery causes a current of 0.60djc (/ qd5dq9c ezya9. A 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 zex02sg1k7 tm4* twpvqw0+ s x1.00-m length of tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1.5 mm bjw5fqpb/y:i8 rz/t 1knm. 0 tin diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of :r dy3)msz 9mbwc3 c2c10.0 m of aluminum wire 2.0 mm in diameter,wcmc9:b zys)d3 cm2r3 to 20.0 m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter coppeypxrcd2(48 rk r wire have the same resistance as a tungsten wire of the same length? Give numerical dex8 ry4dk2(r pctails.    mm

  A certain copper wire has a resistanceb4/ n8plbxns:6a:g+m 4bhp c q 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 (oru(v6tpn+g)z)ln/w 6 y g 4utcriginally at ( pgug+/6y4trc6uznn l)t w) v$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what tempefu d)b3l dnu(igl 2-mpjp0 1(e,n 2misrature copper will have the same resistivity as tungsten doe 1l 2m(epim,0pb(u2gfn3ls ujnd )id-s at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistancelcejdk3g hn*l3uj w 6..44m zr of about $12\Omega$ when cold ($20^{\circ}\,C$) and $140\Omega$ when on (hot). Estimate the temperature of the filament when hot assuming an average temperature coefficient of resistivity $\alpha\,=\,0.0060(C?)^{-1}$ .    $^{\circ}\,C$

  Compute the voltage drop along a 9gw siy9 gcbnda 6o+6)26-m length of household no. 14 copper wire (used in 15-A circuitywbg96a9insgdo+c) 6 s). The wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm, 2.0 63m 8gc;tcw p.hk:jlr cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for current t j6l3t .wh8gcrkpc m;:hat 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 pjv sm(pr*j )(ed;k8tsame resistance. If one has twice the length of the other, what is the ratio of the diameter of the longer wir ()pjst v (*pek;jm8rde to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-p 8,bf,sec+gdix. c6hV power supply, and 6,c.+x gb, fpie8cdsha current 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 of aluh3g/qpzhd6 b 3minu dhg bq6hp3/z3m, both of 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 noy b vv.e2ky2f3p:l6 vnt change with temperature. For example,yylv v2e:vnf23k b6. p 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 wpiqs 1b 1w6.un(upm. xhen conw1 um(.s6pui1 b qpx.nnected to a 240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD playegv ;si);;8.rm q wcyy z (/fnzbu:*uirr that draws a maximum of 320 mA of currentwz;)rufgc 8 q .;yvr;(yszmi /ubn*i:?    W

  What is the maximum voltage that can be applied acrzje9hl)8f dkf4*jr;l (dyf 8coss a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and ,sr-(j9 furh bcurrent through, a 75-W lightbulb connected to its proper source voltagehjr-suf,rb (9 of 120 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank he i to93-us na4djr.)inater 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 1250 W. f:pxm9 u+*j(bpb/ jqsmu z/7e
(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 el6pibx-4 3;o/)xbhwffyg w xb0ectricity 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 ro;b4h)3-gixp0/w 6obbf x yfwx ughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy does a 55d7c3g3n+lv2 afp eyp):y-j 1ogor(z v0-W toaster use in the morning if it is in operation for a total of 1z:1n+r ov(gy)l3dyo c-v afj72g3e pp 5 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 por4 lmev3qoq7 9dl sy/.8qio0on ch light on day and night fo.e3l/diqvy 9mo8qlosn4 7 0 oqr a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries coii-2 anv*7o(m um- o )/-omiya vdzvy7nnected in series as in Fig. 18–4b (Fig. 18–36). The bulb dr2 my-)iivzv7iomo -*/a (m7du-aoyvn aws 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 stored in a :ydvxi g2q6mo b7rjbj0,g 29(huxe k:12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connected/(bw10xrdii l i :v(udfr/+3jkd qzc: to 120 V as in Fig. 18–20, can be used without blii(d:frz: x(lbwqrv cdkjdu10 //3 +iowing a 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 co+/ym-ehnxqcr.1z ,i chu 78v0u+xerspper 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. Hoh7xyxse c+ucez1n q+vih 0mr- /8r.,u w much power is dissipated in the cord?    W

  A power station delivers 620 kW of power at 12,000 V to a factory thr wq0t b+c)hk;mough wires with totalcbw)+qm th0k ; resistance $3.0\Omega$ How much less power is wasted if the electricity is delivered at 50,000 V rather than 12,000 V?    $ \times10^{ 3}\;W$

  The current in an electromagntg poled yia /:)fd)/bo, *k;jl50jq aet connected to a 240-V line is 17.5 A. At what rate must cooling water pass over the coils if the watdj*pt)q5/ a lay/j d ,oe;f)0ok:lgiber temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater c 8u)rq2m8 shkoan be used in a car to heat a cup of water for coffee or tea. If the heater can heat 82uhkmorq s 8)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 current in a dvig- 7qxh5 *,ub)mikw2l7 qy $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 Vm3m;x-gj cog+, 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 resistance ofg*h;ynot g:w / 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 alternatiz+zbc) )7jw;pvjz lmg z.)te+nri*s *ng current in a 1500-W device is 5.4 A. What is the rms voltage acrz 7*brpm) +ctzszgj+)vl ; e. njw)zi*oss it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected zpt,)b:k /augto 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 instantaneh19 g+dw hfbbw2qsj 22ous power dissipated by a 3.0-hp pump connected qbwgdh2hw22 f19b +js to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected9dx 0af6g;nhjem j-.a 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 /,v0llcn6zlj5 e - vseqhg8jt,c(z e8wire 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-diameter wire carries a 750-mA current w+ evx4ebqf ,6t1h jh70d hma/khen 22.0 mV is applied toe, 0a1m q7v e+6xt bfdh/kj4hh 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 atmosphere, 5nwe)rk kx3icz qn:6*s3*gnu z xc8 6j$He^{2+}$ 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 ats1rjt e ;f57qkmosphere, $He^{2+}$ 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 a*c )my*jdiw +mxon membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with an electric pulse. The action2i6 ufw cv5 afet529nu 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 arvu22fect5 a uf 9win56e two measurements needed instead of only one?)    m/s

  Estimate how much energy is required to transmit ocwzb/.yokehem .:f2 c kzr+. j7ub.3xne action potential along the axon of Example 18–15. [Hint: thekbccuy erkz:+.wmo7b.f .e. 32hj/zx 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 pot-dbd e63s ulk8ps9paw:e4-qh(ikh .tential, $Na^+$ 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 sdzwy wx sar.7- af.fk*f573r1.00 ampere-hour?    C

  What is the average cubp jv.jmv(+h l4. ;dqsrrent drawn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally jvkqojtx;)84 leaves a car with the lights on. If each of the two headlights uses 40 W and each of the two taillights 6 W, for a total of 92 W, how long will a fresh 12-V battery last if it is rated atk)tvo;4 xjqj8 $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of a 110-V, 1500-W herw)5zokf 2c(jx0 v x0vater is 5.4 m long. If it is made of iron, what must its dia0wv2fcjk(xvo r z0)5x meter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of theil6y-xbb d74+n9pls aw3k7 hhue;j jbvl;n 98 resistance R; tha9inj 6j4pb ;sv;wlk 9y3b7b8hlade l nx+ hu7-t 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 MWc pe5 q1q5uau5 of power. Suppose 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 pu5c p5q 5u1eaqer meter. Assume the cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular household usesr3 fpi8f t50dx 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 leg ,1lykyzb.+:a0ia 0-kdv6qwe k+w o fngths are wrapped together side by side to make a thicker wire. How does the resistance of this new combination compare to the r6 +i -l 0wbk1oa0dgvqyk:faewyz k+,.esistance of the original wire?

  A 1200-W hair dryer isqr06q/ mi: 7jla,h/mk,pt.dqr-tc b e designed 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 thcu p*kf w,1g0lu ddea/o*0+zv ick 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 produce no more than 1.8 W of heat per meter egp+ku c0f1/law zdv*,o d *u0of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by the equdq hcm(2 ) cmwy1h 7-ws3cnw-fation $I\,=\,1.80sin210t$, 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 energyux4z 9n5 .,,m2xiwa :oqmoodwf,hu1u per second to the in 9x1u:mh.mu wxo qow2o4,zu a,d5,finterior. 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 cond2vl(tj 7a 3s-x1zp grwuctors made of the same material. One conductor is twice as long and twilg (vs p27x31art-jwzce 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 of f776,ygscny kqr;a7n +snvu 5volume $62\,m^3$ Air is brought into the room at 5$^{\circ}\,C$ and is completely replaced twice per hour. Heat loss through the walls amounts to approximately $850 kcal/h$. If the air is to be maintained at 20$^{\circ}\,C$, what minimum wattage must the heater have? (The specific heat of air is about $0.17 kcal/kg\cdot C?$)    W

  A 2200-W oven is hooked to a 240-V sourp.z)ne7bs twrrm02;zce.
(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 mahlnm0u15 t cn jo-,7kokes use of storage batteries as its source of energy. Its mass is 1560 kg and it is powered by 24 batteries, each 12oul-jo 1h tn5c,07 mnk 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 lightbul98yu pat8lunac4):q6i asqv,atx)gu ws (94xb has a resistance of $12\Omega$ when cold (20$^{\circ}\,C$) and $140\Omega$ when on (hot). Calculate its power consumption at
(a) the instant it is turned on,    W
(b) after a few moments when it is hot.    W

  The Tevatron acceleratonhdlfk 3 mzr+p40; 3ekr at Fermilab (Illinois) is designed to carry an 11-mA beam of protons traveling at very nearly pzkm+de0h n4frk ;33lthe speed of light ($ 3.0\times10^{8 }\;m/s$) around a ring 6300 m in circumference. How many protons are stored in the beam?    $ \times10^{12 }\;protons$

  An air conditioner draws 12 A at 220-V ac. The connecting cord is pf; kjltr5r1+1(;p h .vmsuyak (ir3ucopper wire with a diameter of jrh ( (1+pr kku;r i1up5y;t3lv.afsm 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 t4k--g 2 z/1fkhvmc2lqxl ;bowhen connected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has l; /k1l2-b4 vh t2mqk-xozfcga 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 12 V when 1ck496r vll b as vge3u/kot;/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 headlight resitc 9/3lle /savvrukobg14 k;6 stance remains constant.    % increase

  Lightbulb A is rated at 1e/mgo0g c;wsg:*,zlv 20 V and 40 W for household applications. Lightbulb B is rated at 12 V and 40 W for aute z:*o glg;v/g,mw 0scomotive 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 diamete363 :2 s hiwd ;yy-ke8ucasijer 0.259 cm is used to connect a set of appliances at 120 V, which draw 2250 W oski 6;ju he8ce2wiys: 3 a-y3df 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 od1o(5-aqhc k ff 3.00 cm and an outside diameter of 5.00 1h kaqd-ofc5( cm (Fig. 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 l(1e mzoz/ l/inn2h0mm ength doubles, by what factor does the power dissipated in the wire change, assum0(mm n/ /noe12izlhzming it remains hooked up to the same voltage source?

  A tungsten filament us4.yyg 5bjj xrge 9s;;jx0s fy8ed in a flashlight bulb operates at 0.20 A and 3.2 V. If ity58;gsgjf9x0ys4jy;b . jxre s resistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$