What quantity is measured by a battery rati p-d(;.da(ksh ug+sg8rzhle2ng given in ampere-hours $(A\cdot H)$ ?

When an electric cellj8m73qgf q sncrgu -3+ is connected to a circuit, electrons flow away from the ne c jug rg3387+mfqn-qsgative terminal in the circuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battery current, battery v fmmv(k7)8h*o hi ycc5g6fee8oltage, batter 7hgfy8vfk*mh 8mcieeoc) 65 (y energy, battery power, or battery resistance? Explain.

One terminal of a car battery is said tor7mb, jmija mp+o 3jx5je.b7; be connected to “ground.” Since it is not really connected to the ground, what is meai me7 rbj5 ao,7 ;+mj3mjbj.pxnt by this expression?

When you turn on a water faucet, the water usually flows immediatelqubn2m * i,)mpy. You don’t have to wait for m*,piqbu )2nm 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 battery?

Can a copper wire and an aluminum wire of the same leng:;b0kz uw;-hb dwb-qupq 1( 04i fkwketh have the same resistance? Explain.u e4;;0qi: f1bkwwbpz b-kk0dw-hu q(

If the resistance of a small immersion heater (to heat water5l 7.2ju8o dvvg zxqiyz-z1:f for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the lgyjof . 7zz: 5dv2u q-x8z1ivheating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, and 3a, h mr-k;/tuik 6,(ffdvt w)wr( low would you connect the wires from a battery so as to obtain (a) the least resis ( kdul,-t)/6rtfw;m wkr(ifvtance, (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 lig+tqaf6 4elth.r/df5 gvw u7m2 db5j4nhtbulb burns out?

Explain why lightbulbs almost always burnm5dersar s87/jzk 8j7 out just as they are turned on and not after they have bee7/s8j5r a mrz se8jkd7n on for some time.

Which draws more current, a 100-W lightbulb or a 75-W bujlk.vh:9q a;qfe:o(l lb? Which has the higher resistance?:j9qeo qh:.f a( v;kll

Electric power is transferred over large distances at very high voltag en5gpqjw1i111xfn: l0 xymcz x(bf ;6es. Explain how the h bey x0w j xzgf111l:xm 6pq(1;cnif5nigh voltage reduces power losses in the transmission lines.

A 15-A fuse blows repeateq* /. z) x-7hv:jdy adech/eaqdly. Why is it dangerous to replace this fuse with a 25-aeh qa c-zyq.7/*d)v/ehxj :d A fuse?

When electric lights are operated on low-frequency ac (say,2kp1xh8b +/ envbgy4p5 )hunp p:0cwq 5 Hz), they flicker npvkphx wp02cbgn:qe1 bhp5)u+4/y8n oticeably. Why?

Driven by ac power, the same electrons pass back and forth throughgj4u csi9i-qe2ysk4p 9 ;,ynw your reading lamp over and over again. Explain why ts;q4-pkug y ec9 ,w ij4y9is2nhe light stays lit instead of going out after the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. Immediately after*gv7dtnk)bi gqzh+ (6 the toaster is turned on, is th6*v hi( z)dkqtn+g7bg e current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in nnxp*- :d.c;m( z9u koj koo;wa resistor? Explain.

Different lamps might have batteries connected in either of the two arrangemwsnq 8*vjut( *g,vmf- ents showt msw, -8n*v(gqv* jufn in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many electrons are flowing past ze wv* st(/s4+2sux. 2ntdhxlany point in the wire per s 2*s.4nvx(+wehtxt d/ u 2zslsecond?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery ujvo+0hdf;a:y; ed ink/ l1ou2 sing a current of 6.7 A for 5.0 h. How much charge /0nay oj dik:;+u efho;d 1v2lpasses through the battery?    $ \times10^{ 5}\;C$

  What is the current in ampereso i6c9k rw/l o pftu/08fe*ff- 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 ofj8 tk k(3h/hv*;-mf qe vr/ycx a toaster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25*s-ay9tp p9tu bpow5 1 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-V j(9bwnt (i f9gline.
(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 heatid qie;j09knsi 9 8;ae.tw0vbing 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 whose resistance i65 jcukp2pc zuio; * osya/*8js $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric trann2n q)un)r) n 6arka6tziw,by8m1 h*fsmission line carrying 2800 A (Fig. 18–34). The line has 1ta))6 r kfnihwmnr a6zu2)ny*q8bn,$2.5\times10^{ -5}\;\Omega$ 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 a l-3d wz,wy vm20-fher 6j/gllt 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 currenljb-r29fyz bqux::x5 t of 0.60 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 1.b s7d,ycrw,u(wiw i -: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 1.5us w:k(p1er+l mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resifjxy 3hsbw r.2:s1l/wstance of 10.0 m of aluminum wire 2.0 mm in diameter, to wj3ss21f xl.wh/byr:20.0 m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diametevnv5 qmw 9mt7( uv5-)gv/1.pdk aavxrr copper wire have the same resistance as a tungsten wire of the sar 9)1-vvkxv mw5 5tnapv7q/mgvau( .dme length? Give numerical details.    mm

  A certain copper wire has a resistance o kasv21a,u; ,) raojkaf $10.0\Omega$ 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 (ori9wr w)7q soqa(goz +s/ginally at 7o/az s q)( r9gosww+q$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper wi u-rene1hyi)7ll have the same resistivity as tungsten doesur)yi h-e71e n at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of ar;r. uxbb+ mx3bout $12\Omega$ 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 h;1w0sp . ivkydrop along a 26-m length of household no. 14 copper wire (used in 15-A circuits). The;ys i1whk .vp0 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.mg :otf+o8jwzw 3tyfxp 6 cd(3k1jr0/0 cm, and 4.0 cm, lying al+0r:dtjjw1 k3 o yp(fwfg xoz/3tc68 mong the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for current that passes through the solid in
(a) the x direction,    $ \times10^{ -4}\;\Omega$
(b) the y direction,    $ \times10^{ -3}\;\Omega$
(c) the z direction. Assume the resistivity is $\rho\,=\,3.0\times10^{ -5}\;\Omega\cdot m$.
   $ \times10^{ -3}\;\Omega$

  Two aluminum wires have the same resiszn pwvx 3 n/mzp0*y,r8a-e1b mtance. If one has twice the length of the other, what is the ratio of the diameter of the longer wire to the diameter of the shmverp *mzy/ wx3a 0 z,nb-p81norter wire? $\approx$    (retain three decimal places)

  A length of aluminum fr jla- .j o7*ehxw4b8wire is connected to a precision 10.00-V power supply, and a current of 0.4212 A is preciselojlfx4ae.*7r j 8-hbw y 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 lcv/sfgja7oy311/ tt followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 87c3/ftv /1gasl ojyt1 5 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 th4o 8pv sdftpve2rv9fei6q/u5u le (./e value of a resistance not change with temperature. For example, suppose yo iv 6epqoed u /8s/u4p9t52.erf flvv(u 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 elezrs9sd+p(p- ictric oven is designed to produce 3.3 kW of heat when connected to a 240-V source.-pzpdi9 +(srs What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption hs.(nu9zk u 6g d/fdz*of a 3.0-V portable CD player that draws a maximu6 d.zukg(hns9z/ufd *m of 320 mA of current?    W

  What is the maximum voltage tha8i+ *lk1tvwes;la vr/ t can be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current throug(zgo6w w j52:m+ bsbtf5nxx :zh, a 75-W lightbulb connected to its proper sourcmwnowx56 5t z2fz s:j:b+x(gb e voltage 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,vhuh1b3-hz cb y7 v7tater 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 setti-yw4 8f*dio cmngs: 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 rcny8p-7(u. gn ogdkt-m 9j;n in 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 bri (dn;gn 9m-uo 8rc.n7-pgk tjyghtness is proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use in the mo zu3o)0 egzjx*rning if it is in operati3x0 *o)juz zegon for 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 ( -wmxuv x5pwl--5gpc,8ojkaz / 3vzi a 25-W porch light on day and nig / j3gvzk5oucv5 -p-zx8 iw,mp-(wxa lht for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected ni 4d8:bezm7)t.xb zn in series as in Fig. 18–4b (Fig. 18–36). The bulb draws nx4 .ze bmt)7idz8bn: 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 12-V,gpjub,.xtq5 9 $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connected to 120 V as in Fig. 18–20, can be used wz+.xsmd s*nv: ithout xd szmns.:+*v blowing a 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cmo((/ 1*ywhjf sxa8 x r3lorrt/ (no. 16 copper wire) and of length 2.7 m (9 ft) is connected trlr/*8a jx o/ (wsrf o(31txhyo 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 620 kW of power at 12,000 V to a factory through wi0 1yfq+7r8 f 5xlmhbtpres with total resist+q y hpfm518fr t0xb7lance $3.0\Omega$ 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 ixok4 lb t+z21bs 17.5 A. At what rate must cooling water pass over the coils if the water temperature is to rise by no more than 7t2l1x kzobb+4 .50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to heat a cup of water for c8/b i *q.u(gmhfw dv+ic4wyn7 offee or tea. If the heater can heat 120 mL of watumby/ q i4 wd* vcn+8ig7.fw(her 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 iqtv3eled/ss6z/w q/ 1n a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, t564 l mi fh y97zh*uo i.ouowyfyj2c7.c 1u.eis 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 fhbw) ,i+iv, mk:skz bn9g35ence 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 alternv4hxczb - k*(5x6 ylspating current in a 1500-W device is 5.4 A. What is the rms voltag kcs6l-(px54*b h zvyxe across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected to a 5cvj+ 2bwafe ;2o*as( + ysvlo$660-V_{rms}$ 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 h(om)hwwyj d033u1ca .0-hp pump connected twc33u0jwm1ho a h(y d)o a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to a i 5ay+xg;e8.v)z yyba$240-V_{rms}$ 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 coppeakn u) a*dup+0r wire 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 when 22.0 mVbc 85kanbnjrw8; fr, ipu)0mmm* n,6t is applied to its ends. If the drift speed 6u0km*r fm,,ra n8w8cni5jnb)pmt ;bis $ 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 atmor) 7szu-uysr2v qsz-8 sphere, $He^{2+}$ 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 k2*y1uzguivm r;w q65Earth’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 fiel86axf5.n +mnbf b w;,bpgn px(d across an axon 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. Theadd8 gvo3**zg 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 thev3 zdgag8*o*d axon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much energy is required to transmit one action potentia7t2sqc7y 44n4(qu 4mftnip x0 a6 zghol along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored by charging the axon capacitance; see Section 17–9].ga6447 h cntizyn 472xutqp4smfqo0 ( 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 potential, ,03rb ;cjwjrq $Na^+$ 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-hg.s;t0y ki c-uep j38your?    C

  What is the average current drawn by a 1:g4r5 qsyu)f ghk8re+: myl s7.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a cz 7l 7ni)y4yjk utb:3ear 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, 7 ely :kinj)uty3z7 4bhow 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 idhmapsp s(bx6dqhr( k9 -1-u.s made of iron, what must i.px sd6(ku 91asp--(mr hb qdhts diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of the re. v ahmcf7ud4c.do4 kot m8*7esistance R; thh .7 4mctd *o7muco4 8dfv.aekat 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. Suppose that instead ygadk6 +r lwi 71y;nn,of using high-voltage lines to supply the power, the power is delive 1+7alkyr6n d,;wy nigred 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 household ur+xlo8:w+3 d(pji na2 zpl)k pses 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 tog8z +5r:tzmetgether side by side to make a thicker wire. Ho gzrez+t: 85mtw does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is dez-ljy yy(-wi7signed 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 becopm du fc-t ,0e4+w2in,c jgy)eme so hot as to start +e4c uf0 mdjpg2en,iyt,w)c-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 of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by the.loh 85w5o ab aclc(zit 9)7pt equation $I\,=\,1.80sin210t$, where I is in amperes and t in seconds.
(a) What is the frequency?    Hz
(b) What is the rms value of the current?    A
(c) If this is the current through a $42-\Omega$ resistor, write the equation that describes the voltage as a function of time. (  sin 210 t)V

  A microwave oven running at 65% efficiency delivers 950 ngn6a: s kho: ,44:;nxomlaow W of energy per second to the interior sa4m4k :ln:,xno;wn oghao6:. 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 conductow.( rlri.rr8i rs made of the same material. One conductor is twice as long and twice the diameter of the second. What is the ratio of the por (..r8lwirirwer transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room of volume 2-7-u* sxxaeng/f qlb$62\,m^3$ 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 hookel(:c acubm : yrfr39fb+r 0vp+d to a 240-V source.
(a) What is the resistance of the oven?    $\Omega$
(b) How long will it take to bring 120 mL of 15$^{\circ}\,C$ water to 100$^{\circ}\,C$ assuming 75% efficiency?    s
(c) How much will this cost at $11 cents/kWh?$    cents

  A projected electric vehicle makes use of stor ur)c(b14ftwdmpdb 1,age batteries as its source of energy. Its mass is 1560 kg and it is powered by 24 batteridr du4(bmbcw 1t, f)1pes, 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 resistancokifx) mt / +y et kw b2)s;;/2t*vtn0vn2tuxte 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 carryztol;sc-lm/rfkhx*5 8 kro07 an 11-mA beam of pf ltr;cz/0* rmsxo8o kk 7lh5-rotons traveling at very nearly the 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 connectivb/sh g )0zk-nng cord is copper wire with a diameter of 1.628 mm.- b)ngs/zv0kh
(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 qs)-b.qbkl/t bm(cgl -) bjx.rated at 95 W when connected to 120 V. The heating element is a coil of Nichrome wire. Wh)mx-(/.g kjt)-lb s qqcbbb.len uncoiled, the wire has a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, thes,e8tlc:p c )a system voltage varies from about 12 V when the car is off to about 13.8 V wheas,pc8:)l e ctn 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 househ-kl g..q ;vsm5gvm).z otz no1old applications. Lightbulb B is rated at 12 V o5z) ;soz..gm-vq nkg m. tvl1and 40 W for automotive applications.
(a) What is the current through each bulb? $I_A$ =    A $I_B$ =    A
(b) What is the resistance of each bulb? $R_A$ =  $\Omega$ $R_B$ =  $\Omega$
(c) In one hour, how much charge passes through each bulb? $Q_A$ =    C$Q_B$ =    C
(d) In one hour, how much energy does each bulb use?    $ \times10^{5 }\;J$
(e) Which bulb requires larger diameter wires to connect its power source and the bulb?  ----待选择----Bulb BBulb A 

  Copper wire of diameter 0.259 cm is used to connect a set of appliances at 120 );ul4xmtxfy7ycgd1a 9(ngb n+ 5h/ww V, which / lynh9wbd;7g1mxfn +)cgwy( a45txu 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 outside diameter of 5.0p5nb *w:gse/ts .e ,hzd5e1iw0 cm 1si hpg,e/ww 55btde:n .esz* (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 uniformiji- 5+h( yut ajiue4 w3::gminqkn8. ly so that its length doubles, by what factor does the power dissipated in the wire change, as ie . n:u-iwhmqiiuk34a8 t5 +nj:gy(jsuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight buxdve6/,* e nhs3sp6h ylb operates at 0.20 A and 3.2 V. If its resistance at 2ne6 ,/ 6y s*s3hvexdhp0$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$