What quantity is measured by a battery rating givennvt-c g,r2yp1 in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a;ef l 7b-xdy t76u+rs(sgw qm4 circuit, electrons flow away from the negative termi4yl (qd77x6; srse m-wbfugt +nal in the circuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: batternc+4vqc-s f5 xu6jwq7y current, battery voltage, battery energy, batterx+6jf4s5 ucq-wq7v cny power, or battery resistance? Explain.

One terminal of a car battery is s2 1:q(gymdvt iaid to be connected to “ground.” Since it is not really connected to the ground, what is meant by thiygti(q2 m:1 vds expression?

When you turn on a water faucet, the watn+tybk w /,dycz0 i(c;er usually flows immediately. You don’t have to wt+y ik c(yndw ,b;/zc0ait for water to flow from the faucet valve to the spout. Why not? Is the same thing true when you connect a wire to the terminals of a battery?

Can a copper wire an6e0waga (3so b4sq-jt d an aluminum wire of the same length have the same resistance?3(o6g 4etsq- aa bsw0j Explain.

If the resistance of a smalvq: gg454fxhclpx(md-k7v k* l immersion heater (to heat water for tea or soup, Fig. 18–32) was increased, would it spee4*l qd-7:xx h vm 5vkfp(ggc4kd up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lovc2su yqd: /33 6d(ggi ,xfypengths a, 2a, and 3a, how would you connect the wires from adiovgyqy,/3p2cx d (u fg:3s6 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 lightbulb burny+b b/w * vtogm* yhvu1p fy0)-0-dxlys out?

Explain why lightbulbs almost always h ;e*ksuyl9 jw/y -il*burn out just as they are turned on and not after they have been on for soyjhw;il9y* slu/-e* k me time.

Which draws more current, a 100-W lightbulb or a 75-W bulk +ue bb.ka52):iduj/ zp2 utgb? Which has the higher resisa2 .b5bzeuujt:/i)k+2uk dp gtance?

Electric power is transferred over 4xiwec gz6dkn/)+a+l large distances at very high voltages. Explain how the high voltage reduces )k/ g6 zxni 4eawcdl++power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fuse c1g1+ u0rja +2d onbhefm u.ufmwl /53with a 25-A fuefw ghnu51/u m0 jro3l +dmf+.c21ba use?

When electric lights are operated on low-frequency ac (sa. n 4k ssgjr958ejhk-cpc) y(ay, 5 Hz), they flicker noticea e9k p(4cnay8)rjh-.ks5sc jgbly. Why?

Driven by ac power, the same electrons pass back and forth throuel-4m8l i e1u/kzq3bl gh your reading lamp over and over again. Explain why th-/b1k e4u8qm 3ill zlee 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 thedn 6, ;.u:fjnsn.gc 6fj3c cgbt2q-tf toaster qf g:c t6f6s3bnunjc;dfg. jn.,2c t-is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Explai(5tp3h+ a)vjupe j+ pin.

Different lamps might have batteries connecxiij0h,/b vo1wzj p.4ted in either of the two arrangements shown in . ibj0x 14/jpozhiwv,
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 any po9jy4k9ss0pd j eje+6 fint in the wire per second? j+90j4sp9y j e6fedks    $ \times10^{18 }\;electrons/s$

  A service station charges a batx:cl9k mts8 ici6:nzdqb- -fi-7uwq3 q/ 0knetery using a current of 6.7 A for 5.0 h. How much charge k:l i7x--u ncb-ek9:3 m0 f q/d6s nwqiiqtz8cpasses through the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes ig6k91p)n0ll4-jmd wvvm8 hl je wl3-m z6dw(wf $1200\,Na^+$ 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 12mv+mes):dq 8,dh3yv d0 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 cuy 33p*fubks9 ;a(hs A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged ; p(2(dc d8-z)t2uekiyxnpcj- eb,v iinto a 120-V line.
(a) What is its resistance?    $\Omega$
(b) How much charge passes through it in 15 min? (Assume direct current.)    $ \times10^{ 3}\;C$

  An electric clothes dryer has a heating element with wr1f -sbcmgb9 rebvc(6w7,3r 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 resigjaq1f2q1 nf 6stance 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. 18–34-ax/fufb14 sz). Thez b f1-su/fx4a 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 drawszj9:u-lf4)ff prz) v(wds 2t r 6.50 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 0.60 A through a resistor.)l. c4b: wtirqtdy0 1w
(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 whym g,ahf sl8lqcjrcn( de1/m /s 0f72,ose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m lh;m zznz;wit.+1sw.nength of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0/aguxb4dg d09 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in diamete 9uddxg4agb/0 r.   

  Can a 2.5-mm-diameter copper wire have the same res-sm xy(em)0dtm:gi y2istance as a tungsten wire ofimx )y:y-(mds mg t02e the same length? Give numerical details.    mm

  A certain copper wire has a resistance of eu. : c;luoxu8k/- 1ab2rzeyk $10.0\Omega$ 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 ww:gal/ rq 2wwkmz1c .7xw60ua copper wire (originally at xc.k7wzlr 01w:ww/ 6w qmga u2$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the q hdst 4bob8,/same resistivity as tungsten does atqbt8o,b/4s dh $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of ab) +,kntoucbgc 7k3tmalr6cv-3a yq) /11lvkz out $12\Omega$ 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 26-m length of household iv +)2le4q , ;jw,0b b1lrh,c5qgrvr-m txypdno. 14 copper wire (used in 15-A circuits). The wire has diametedly2rr - e+,1 v,g 5;mwbiv0q,rlj4b q)pxc thr 1.628 mm and carries a 12-A current.    V

  A rectangular solid made b z /tf3,le9exof carbon has sides of lengths 1.0 cm, 2.0 cm, and 4.0 cex93e/,fblt z m, lying along 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 resistance. If one hs.z x* us+;xo jkpt8ps9fia 14as twice the length of the other, what is the ratio of the diameter of the longu1spoaxz f;*sx9tski.+j p48 er wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precisr,k.h d moqp8es5*vm7kv,wb ;ion 10.00-V power supply, and a current of 0.4212 A is precisely measured at wksq8v b*me, 5ph 7mdr;,v ko.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 m2t:n sl:y.i kq of copper followed by 5.0 m of aluminum, both of diam:kyi. ltq ns2:eter 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, ddrzl9k4)a3 bit is important that the value of a resistance not change with temperature. Fo b4r )dzd3a9klr 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 3fh: w-en:z:o)etv f3u .3 kW of heat when connected to a 240-V source. What must be th wetzu3n:v-ff: e:oh) e resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD playefn v*jqbg rxx0x2k2 +.r that draws a maximum of 320 mA of curgnk+x*x0x2jr2. q bfvrent?    W

  What is the maximum voltage tea0 2lri(95p (hhc/yxk yg6 ywhat 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, a 75-W lide u+layg(15lghtbulb connected t5a(uly lg e1d+o its proper source 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 heater is rated at 110 W. Calcul4b l;egyzx4k.qetg( / ate
(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. gwi)cb//d rk-
(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 tbzlb9 /w 3)r6 ij5yxnno 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 prowj 9n)x6 zi/3bbl5n yrportional to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use in the5jru2x( gq sa2 morning if it is in operation for a tqr5ux j(s22 gaotal of 15 min? At a cost of $9.0\,cents/kWh$, estimate how much this would add to your monthly electric energy bill if you made toast four mornings per week.
energy $\approx$    kWh
cost $\approx$    cents/mouth

  At 0.095 dollars per kWh, what does it cost to leave a 25-W amm2nk zp2*y*qngi)(/ y7ob dporch light on day and night22i/(zdq obm m7ynga*ny*k)p for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connect(yc-7d -i bwueed in series as in Fig. 18–4b (Fig. 18–37(ydb -ueiwc- 6). The 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 stored 5;.mnpk ce 8 bbqn j,-gs*wss*in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connectygm.6 or ir9hi9;ix w/ed to 120 V as in Fig. 18–20, can be used without bl oiyg/ .;irhxw6m99ri owing a 15-A fuse?    bulbs

  An extension cord made of two wi0-ga9cj5n ocygkih4f*wc2p:jc* 5jkres of diameter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connecte5 jw-:k9c cgc g0a5yfojn4h ik**jpc2d 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 620 kW of power at 12,000 V to a fo. w,c67q tzwcactory through wires with total ,.oq ct6wc 7wzresistance $3.0\Omega$ 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 is 11tcpmq5 .kw sm8 dri4/7.5 A. At what rate must cooling water pass over the cotdp4kmr5wsmq1./8i cils 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 for r 6:n ,nfy-p;ko7p;mi q jkeo ol4iu5.coffee or tea. If the heater can mei o; 54y;oolfi6ukpn- :npj7 .,qrk 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 ifke qpxk+:f414e 3ntm n a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, is acros.. ap 1cmi-lhrfz+o2qs 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 resista2de x d.rd0x .ya84jdqnce of the $120-V_{rms}$ circuits in your house as seen by the power company, when
(a) everything electrical is unplugged,
(b) there is a lone 75-W lightbulb burning.    $\Omega$

  The peak value of an alternating current in a 150jr ( 3 ab7d+caw)w-u3dnyrot*vp okd:1 u.i7b0-W device is 5.4 A. What is the rms voc.k+d*-1a: ou wvwr3r t7 u(a73bddno)i jpy bltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is coi1zghjpe5 8x0 nnected 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 dissu *hr- vw7x7mtipated by a 3.0-hp pump connected to au *v7rx- wmth7 $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to a zw69h,wjwm 6l$240-V_{rms}$ 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 ;0atqkk1;fc t 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 ca beob06s 8(l;)ivr9 ihzrll6 arries a 750-mA current when 22.0 mV is applied to its ends. If the drift speed is 68 ;0e)9 i6b (zharirvlslo bl$ 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 n nt3 2u r3x6bvd.klh:Earth’s atmosphere, $He^{2+}$ ions in a concentration of $ 2.8\times10^{12 }\;/m^3$ are moving due north at a speed of $ 2.0\times10^{6 }\;m/s$. Also, a $ 7.0\times10^{11 }\;/m^3$ concentration of ${O_2}^-$ ions is moving due south at a speed of $ 7.2\times10^{6 }\;m/s$. Determine the magnitude and direction of the net current passing through unit area $(A/m^2)$.    $A/m^2$  ----待选择----NorthSouth 

  At a point high in the Earth’s atmospherr3-h )t anopt,ud .3mle, $He^{2+}$ 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 memb l8bmd:i5 eu+p . :bkqwdvkv91rane $ 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 action potenhzp qk+hac) ch(6bmir3 *7 yc2tial is detected at a point 3.40 cm down the axon 0.0052 s later. When the action potential is detected hhmkh)26p c( 3briya 7c*zc+q7.20 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 energy is required to transmit one action potent66tn*)lbdks q64cqw5j wl ;hd 07ohiyrcp /0 pial along the axon of Example 18–15. [Hint: the energy to transmit one pulo 0ipl)d* jq hr yspw/4l6 c76n;qdwc6hkb0t5se 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 potentiavg 8 vu5eb/vcz:b ,i fxty; -qccfi i,)z:h.)xl, $Na^+$ 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 th0pp6l t(t7kq7xt+ mpo ere in 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0-hp 120-V m,grg0n /sj1i jotor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each0 ;pc g9yd v7j;jxo0ne 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 y 7j 9vgd;xe;p0o0cjn at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of a 110-V, 1500-W heate t0 xc6,+(gr 4zwqif rok z*g-f:zzr7lr is 5.4 m long. If it is made of iron, what must its diameter be? ,:zlg tz0k-fxogz i+(4 6q rwcrf z7*r    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of the rp(w6 6 n yab6j*;bctxresistance R;yxbr(;a*n6wj 6 cpt6b that 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 10vuke26uy 1pv ( MW 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 pe6v1vu(pye 2 kur meter. Assume the cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular household uses a 1.8-kW heauxm64h zd:5b 4 jrp,ezter $3.0 h/day$ (“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 wr 5lit s4si 551xtaqo,rapped together side by side to make a thicker wire. How does the resistance of thir51io,x sia s 5t5qtl4s new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 11hba8d*pd2.ap sgr ,yd*7: tl,rdw ;jb7 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 no,p,.aobb rk yg 1j95ctt become so hot as to start a fire. Wk ,t 9bay,j5cgob p1r.hat 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 equation dx9;i-y dtts 69*fagi$I\,=\,1.80sin210t$, 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 dex fn:k33,5 qptezp,g alivers 950 W of energy per second to the interior. Findx,ka3f: z,5ng pp3qte
(a) the power drawn from the source,    W
(b) the current drawn. Assume a source voltage of 120 V.    A

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

  220 V is applied to two different conductors made of the same material.- xw;y5jjf kleff *2)f One conductor is twice as long and twice the diameter of the second. What is the ratio of the pj - yk5wff;f2ef* )jxlower transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room h/ z 6y8ne xz8+m474bu1rtlkhnijt;f 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 to a 240-V source. cde5)* .rnyf8hj/g iasc +ty0
(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 zh+hi9v 9xna; of energy. Its mass is 1560 hz;vanhx+i99 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 rescg58 hbrmi1( ,.:cdhsoz kms3istance 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 Fermilagzwwv9j2 28m,rvndsvv q8tp:- hb 5a7b (Illinois) is designed to carry an 11-mA beam of protons traveling at v bn8vds7tj pw:zr,h 9qv5w -2mvga8v2ery 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. T+347/ trvrwhx sm9s; rq/*gwt+vuppg he connecting cord is copper wire with a diameter of 1.6t/74th;wqgvw xs3mr* u9+ g+vprp /sr28 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 hede 339h;u q1bnh hj e.z+t3alhating element is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What is the diae3ehudn19.jbht+q3ah; hl 3zmeter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from about 12 V when the car is l xz r,3lridy-ucy0zr 932 lmp4 zb6p8off to about 13.8 V when the car is on and the charging systl92,cu6b z z30dyxl i 8prmpr43y-rlzem 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 appq9bxgsoh ylp32o: o()vv- m d2lications. Lightbulb B is rated at 12 V and 40 W for automotive applicationss o g9hxo2dp2l b:qvo)v- y3m(.
(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 app)8p ny1zkgt56 gkodu9be d 94uliances at 120 V, which draw 2250 5t 96u9ge1uk nygbo4d8z k)dpW 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 inse o:)rq,f 8g/a+)hxon+djzcj ide diameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the resistance of 1,)nj a+go:xz8 fq d )rocj+/eh0.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched unu k6uso9i r/,iiformly so that its length doubles, by what factor does the power dissipated in the wire change, assuming it re,/o9ik6u siu rmains hooked up to the same voltage source?

  A tungsten filament used in a flashlightjejxk k;,5, w (phu(ou bulb operates at 0.20 A and 3.2 V. If its resistanckhw ;xjej(o5 (k,,u upe at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$