What quantity is measured by a battery rating given h7:l+9(n8 y/su9 joezq aerwpin ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, f-rum1 2z qf0telectrons flow away from the negative terminal in the circuit. But within the cell, uf zmtf02qr-1 electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battery current, batteseb yb)exn/ a9j80cqa pi:y6 3ry voltage, battery energy, battery poweraq3c8 s0a6j:b/ieynxe )ybp 9, or battery resistance? Explain.

One terminal of a car battery is said to be connected tohm3 ujf,vs0lha/x; u 1 “ground.” Since it is not really connected to the ground, what is meant by thuam uxfhh ,1 s;/jv03lis expression?

When you turn on a water faucet, the water usually flows immediate/smeu2cadpb,is -o5 5to, /f3dbgs9hly. You don’t have to wait for water to flow from 2 ,ic39aombhs/ 5 dgdse 5btuf/so,p-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 wire of the same length have thlcjrfa m. :wp7j 9:pp8e same resistance? jp .r:7pmwa:c lp98j fExplain.

If the resistance of a small immersion heater (t.dm1w1cqsi+jf j 48 syb 4sjb7o heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow down 4 jdq7j1jbb1 +fyws cs 84i.msthe heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, and 3a, h mj4(ek am7p2vqevg )d+ 2.nznow would you connect the wires from a mqj gpa2)vne7ekm.4+v z2nd (battery so as to 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 lightbulbcm q7e7wqu n/:udtn8.aa; d tlt4) fr1 burns out?

Explain why lightbulkz1k7* as :j5fm mfljy;7qy ,h;pc l4sbs almost always burn out just as they are turned on and not after they have bee,lfz;1 4: qa*s kh yjpy75mck jms7lf;n on for some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which has the ;ud/e er minas7d;:c8higher resistance?se:u8;; 7dr cmnei/ ad

Electric power is transf ebzhui; 5p*7perred over large distances at very high voltages. Explain how the high voltage reduces pow*5pi7peu; b zher losses in the transmission lines.

A 15-A fuse blows repeatedly. Why i+bu.vzjc1s j,lf7 0fn s it dangerous to replace this fuse with a 25f7 1v f+.znsjlcj0,ub-A fuse?

When electric lights are operated on low-freque 0q2x6;auka kot:d e)hncy ac (say, 5 Hz), they flicker notic q:k2 );ak6et xduhao0eably. Why?

Driven by ac power, the same electrons pass back and forth through your reading lh)1yzljwd 6ppr .p i2hjc.+z1hv w;0oiy )/vlamp over and over again. Explain why the light s6j 0vpy/h1lr z wo.).i12i hlh) pvzw;jcdyp+ tays lit instead of going out after the first pass of electrons.

The heating element in a toast) /cki.ub r*xfer is made of Nichrome wire. Immediately after the toaster is turned o xru/if b.kc*)n, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Exj,f fo2p e3xyzx9z. x(vs9h1uplain.

Different lamps might have batteries connected in eit8ils5i,8o nsw hgr7a9 her of the two arrangements5s8 ,nhwigo9a 8is7r l shown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wi,3 b46o3t zak hvk7ynxre. How many electrons are flowing past any point in the wire per hn 73oxkatyz,b vk6 34second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A for 5.0 h. Hd3/g* kd2rnx30 dwhym ow much charge/ykd3dmd*h n3xw g2 0r passes through the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes ifk: 0cs sij1q ao;)/krwxyj82 w j7p-vn $1200\,Na^+$ ions flow across a cell membrane in $3.5\mu s$? The charge on the sodium is the same as on an electron, but positive.    $ \times10^{-11 }\;A$

  What is the resistance of a toaster if 120 V produces a current of 4.2 5lwv1f/y w9jo ;yi mh-A?    $\Omega$

  What voltage will produce 0.25 A o7)st tfhj ;(ra*ksmr4 f current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-V line.vy yr*: 3 ( xmzl*rpl*0dm+evw
(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 h,d6cot7p 93m) ,9dgw rhdxvc6om4k7dp9 rpjras 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 whq2pohn 5v-h z3v4t( d0miqfq;a: l(keose resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transmi0b1e-;qy;qdqag 93 nroeaq a5ssion line carrying 2800 A (Fig. 18–34). Thqq- g d1o3nbqeaa9;ry5q; 0aee 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.x6sj ldyiivzm0:1h.0v b19wk50 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 0.60 A through z.xgtams r 596pew8ro yae4s0 ),xb6aa resistor.
(a) What is its resistance, $\approx$    $\Omega$
(b) how many joules of energy does the battery lose in a minute?    J

  What is the diameter of a 1.00-m length of tungsten wire whose resis wo.rj n4xoe;n;s79hytance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1.5 mm in diamed gt . * 6pexa2u:ntpsjo;co.8ter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resista nh,1z- jpu 0p,pocby(nce of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in diameter. p,yj(u,- 1popn z 0chb  

  Can a 2.5-mm-diameter copper wire have +(qkw d4;atkm9mluv9 the same resistance as a tungsten wire of theq;(ktv 94m+u aw9dl mk same length? Give numerical details.    mm

  A certain copper wire has a rets fp48x j.0ehsistance 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 c ah*pzuqe 9 ep(vz+-s5opper wire (originally at ee5p-aszqhzu v9p+ *( $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature cud8pmndy7 aj27v .9 laopper will have the same resistivity as tungsten does mv. yn97l8du2dpaaj7 at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb hasj3b grp. sn9-f a resistance 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 alondn0v v6 r wszcd42i7v0g a 26-m length of household no. 14 copper wire (used in 15-A circuits).vwcv4r v0ds7i6d2n 0z The wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made ofgdt r+v95n* lt carbon has sides of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resd9 vr5ntl*+ gtistance 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 twwajnxs/t0vq40i 7 ysgzxe4rdr8 u +lp 3v:0d -ice the length of the other, what is the ratio of the diameter of the longer wire to the w s3p78e/ :-0qrdg+n ua i0tz4lsd4rxxvvy0j diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.0wknj 89 *kyeeu)+pm,q 0-V power supply, and a current of 0.4212 A is precisely measuredjmyp neu9e*w 8k +kq), 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 fo eda+d +f+j wb-ug88lxllowed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage differencj fdd +ue-w+8xl+ba g8e 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 resi **/71trmtxrxi*bz tvstance not change with temperature. For * m*tzb7ix xrr* /tv1texample, 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 dekf:3sfo 54mizsigned to produce 3.3 kW of heat when connected to a 240-V source. What must be the resistance of the elekm z5i3s:fo4f ment?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player td punlfp9idp38cx 9m:ewun, a7.f w/2hat draws a maximum of 320 mfwdfpw 7xm 23nu ,ucn:a8l.9 e/i 9pdpA of current?    W

  What is the maximum voltage that can be appj rkrv*;0oh;vlied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, a 75cr 2v .5d*rkki--yru:gv06z) idnntv-W lightbulb connected to its proper source volta5di vti.)*u0kgyk r-n:dc vn-r6r v2z ge of 120 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heater is rated at 110 W. bqxe8qql9ww:5mu/f7 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 twov- z :: zhw :b-aza-.x4gy9yenpl piy6 settings: 850 W and 1250 W.
(a) At which setting do you expect the resistance to be higher? After making a guess, determine the resistance at
(b) the lower setting;    $\Omega$
(c) the higher setting.    $\Omega$

  You buy a 75-W lightbulb in Europe, where electricity is delivered to homes a+ ruvp,i0 s;g2)wjahtt 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 proportional to power consumed.] th2 wvri,0)s;pgu j+a    as bright

  How many kWh of energy does a 550-sq8/vu t wz7 *d1aby/gW toaster use in the morning if it is in operation for a total awqz bg/ /yvudt*s78 1of 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 co z*x y2exzh69qst to leave a 25-W porch light on day anzh296xez *q xyd night for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V bat y 1;(w7-d2wvwptzpd5x3cno83dgav y teries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when1c8nz 3 (wt2x;wd5opyd7v gapwv3dy- 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 4s *wz-4cu c2ga0lkf s12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connecte w1 xb2 8bcpdlmoo--;jd to 120 V as in Fig. 18–20, can be used without blowbco2 8owlm-;1dxpj-b ing a 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 copper wir qpm9oriag -(q f,g.y2e) 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 dissigy9qfmo r a- p2(iq,g.pated in the cord?    W

  A power station delivers 620 kW of power at 12,000 V to a factory through wirerc (x9 o0x4enm if:m1(c birm5s with total resistance e:4fc9mb x (0rmii m 5crnx(o1$3.0\Omega$ How much less power is wasted if the electricity is delivered at 50,000 V rather than 12,000 V?    $ \times10^{ 3}\;W$

  The current in an electromagnet connected to a 240-V line/dx6tt1ia 5y s mxv+6bc yip:/ is 17.5 A. At what rate must cooling water pass over the coils if the water temperature is to rise by no more tha66s:c /+y /bv yxmi d1xttap5in 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater canaf s4;/y5(vn 2hi5qiymbny rsmb2jmv7(7sx 5 be used in a car to heat a cup of water for coffee or tea. If/5vfam5(y 2v ;5jmnysq7b r si2bins hy74(xm 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 current /e4vpj42 qjhtuey 7k;5tt c *xin a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 Vy 9sb) + j5p3jh;i-hvuouh8r z, 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 of twuqq5 7s-(dj: qu1im ahe $120-V_{rms}$ 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 r9t 7.hg5;jpbz6d7lqcur6h l8yfzz1.4 A. What is thegczfu6zz 9lh h t1 .q8rjd7lby65p7;r rms voltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected -ju5zsss3o/+ wulc(k.dq f1ulaz+l 3to 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 instawkwoqr uo87h; up;-* -9hvrgkntaneous power dissipated by a 3.0-hp pump connected wok-qgr hu; 8o-9rkh p 7*wuv;to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connectew +;lyzk3 :wzbku)cp:d 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 carrie 2xkope4lfa:/zycr;fzj z 456s 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 cu 7zofv vqzy l/;o+cx(7rrent when 22.0 mV is applied to its ends. If the d fox/zqcv+z;( vl 7y7orift 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, 0yb9* 1ypmatu $He^{2+}$ 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 atmo a l5qt 7ho9rn505emnjsphere, $He^{2+}$ 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 axon mel c54uby,,nu;p tr*uk mbrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated witz5xh:,h wv2s.xs s,hl n(q1qvh 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 cmnhz5l:vshs1v.x h ,q 2qwx( ,s 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 energy is required to transmit one action potential 0t etali2e a--znx,n8along the axon of Example 18–15. [Hint: the energy to transme -,xanzn08l-i2eat tit 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 poten b a2)sx6qtgll1mnju0zp:hns 2go,/1 tial, $Na^+$ 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 th4cdj cak 8/y y5 hvr-c x4im6qa4ovk1:ere in 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0-hg63qt*pdnhj55rie 5 e -)uv kjp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of the two hph6/ eee- an0beadlights 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 reenpb-a60/ e hated at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of a 110-V, 1500-W heat-t-u3mg (esx aer is 5.4 m long. If it is made of iron, what must its diam s3e-ua-t x(gmeter be?    $ \times10^{ -4}\;m$

  The conductance G of an obk jov/ -u*+ythject is defined as the reciprocal of the resistance R; tjou- yht*+ k/vhat 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 of power. 0b ishi6 (sby)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 copper6biby0si) h(s wire, estimate the cost of the energy lost to heat per hour per meter. Assume the cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular household use;7h ;uwzl+ pw(n- acrls 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 a.xuniq*w-,7 rtj;u swre wrapped together side by side to make a thicker wire. How does the resistance of this new combination co,*7.x ; j-wtnwusruqimpare to the resistance of the original wire?

  A 1200-W hair dryer is des7r )rrux,i1eej7q92:2tb wlv v lepbqe35h 5z igned 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 aolo4 o2 yj4)jthick 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 maximumo4j o4o2 ajy)l 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 hyh1e4lm0m:gqx 6l6 s 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 detf77b g5lw7zet9/9 pnwix+ bd-h) ndxlivers 950 W of energy per second to the5xipz)wefbthwbg7 9 9x 7d- t+nd/n7l 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 differ,v;q 3zdprba4mz c:gubwa/.: ent conductors made of the same material. One conductor is twice as long and twice the diameter of the second. What is the 3 mz rb/aw:,zqdu;.gv bpa:4cratio of the power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used t6 y88l fn*.ptkv8kvw.q(kvf a ngq94fo 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 hookedpafp ,1fx kb8bh-l jw*kv r7:, 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 odbk(n;dki3 j -f storage batteries as its source of energy. Its mass is 1560 kg and it is powered by 24 batteries, each i;kb-kjd ( n3d12 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 lightbulwt1zzb 4 8me5gb 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 accelerator at Fev iv ald3h9 yw7,hqxj0*0h ja1rmilab (Illinois) is designed to carry an 11-mA beam of protons traveling at very nearly the s,hq 0x1dy i*w7a0ah j9 vvjh3lpeed 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 a4gfu; uiibj0;ce7amdp jjv a 0):m3 j2t 220-V ac. The connecting cord is copper wire with a diameter7jb; cmm3jufg4e;i02a):aj v dji up0 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 rateditl )js)wnb+8 at 95 W when connected to 120 V. The heating element is l j+s8n t)wb)ia coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from about 1xbnb 6zarjmos3*. :)st7uqsaxz ; 6u42 V when the car is off to *7n z.s 6um3aar ;:qbxtu)ss6bx zjo 4about 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 resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for housc5)ff3myb3k s sz29utehold applications. Lightbulb B is rated at 12 V and 40 W for automotive appl zck b9sfy2s3 tfm)5u3ications.
(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 diamekt3n/frvlora90g/g co8+3 7 le 4 nlwater 0.259 cm is used to connect a set of appliances at 120 V, which ngv+ f/kra 7 /ra3tn39cell8 wo4gl0o draw 2250 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 out+g4 hqho:1c j/uou 9fqside diameter of 5.00 cm (Fig. 18–37). What is the resistance of 10.0 4 u9goqu/ 1fjh:cq+h om of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so thohqd9: af qygm(p*8 u tos/p8)at its length doubles, by what factor doepfy/o:apm88hgoq9 )*d(tu sqs the power 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 Vlfo+/7tq 1 cmu, zx-xu. If its resistan1zxoct xm/ qf+7-, uulce at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$