What quantity is measured by a battery rasoub7o5t:l ngl ) cu3a+:tgp+ ting given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, e : fqjx*+7wyaklectrons flow away from the negative terminal in the wk*x+:j7y fqacircuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: b)yk+8nw n5vm )m/xczyze/5umattery current, battery voltage, battery energy, battery power, or battery resistance? Explain. zy/wkcny 5 / 8mmzm5n)uex+)v

One terminal of a car battery is said to be conh.w.whtix g2- /o z ,ng0lytyik- y.o5nected to “ground.” Since it is not really connected to the ground, what is mea thoxg -2/lyoi.5.iy.hg twnwy kz,0 -nt by this expression?

When you turn on a water faucet, the water usually flows immediately. You don’t 6i (+ vqe6fyvvhave to wait for water to eyi 6v+6(vvfq 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 length have the same zylk 9p km2++cresistance? k 9+yk cp+2mzlExplain.

If the resistance of a sauz49v kmyf45 mall immersion heater (to heat water for tea or soup, Fig. 18–32) was increased, would i4a4f5vym9 kzu t speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, a 2tbot rjt,eisi8.b;3 nd 3a, how would you connect the wires from a battery so as to ,2is.8t ;otrbt 3jebiobtain (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 burns *fadz w* b20jdgkj5lbtv9. ,jbc1de : out?

Explain why lightbulbs almost always burn out just as they a-fyxgfbj;njap)y50( r y,xw *re turned on and not after they have beejjf,xxp-yy*f ;0r nb w5(g)yan on for some time.

Which draws more current, a 100-W lightbulb or a 75-W 5,w ivk ywrw9i/o, ,cdez/ rzm*r*jo; bulb? Which has the higher resziwoe k/, z5 cmrrw,*r9 ow dy*iv/,;jistance?

Electric power is transferred over large distances at very hig 8l3a br5k.qy5ey lj;i cvr.0yf2,dmn h voltages. Explaink rmfqr2neavdl.jic 08y3,yb y.;l5 5 how the high voltage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dang ni6;u(ihz a:m:m hr/vp7 e;tperous to replace this fuse with a 25-A i ( 7 imuav;:r:mh;ezpth/6p nfuse?

When electric lights are operated on lpx60vt 0sij2b v,/uyz ow-frequency ac (say, 5 Hz), they flicker noticeably. Whb, v06/i0yp tvj2uzsx y?

Driven by ac power, the same electrons pass back and forth through your sy/m 1*9 0uol/(gktmj*kjl xmreading lamp over and over again. Explain why the light stays lit instead of going out after the firsk9*sjmm(0xut y/ jm/ ll *gok1t pass of electrons.

The heating element in a toaste pd1nvhbi (9a6 xyvn-7r is made of Nichrome wire. Immediately after the toaster is turned on,yv 61i7pa9nx( n-d vhb is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a h7)g 3yictun)qnk 1;hresistor? Explain.

Different lamps might have batteries connecterg2)dlzy 8zfm9c .,hed in either of the two arrangements shown in y fz,rgl8cdh9e.zm 2 )
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How maz5/zo;g o1h,y o.fkni9ba-ik9/pixn ny electrons are flowing past any point in the wire9og; ,ko.k/1n iizb hf9/zp5a niyxo- per second?    $ \times10^{18 }\;electrons/s$

  A service station charg q6) q(axho rzsg1a:-ozi5j 3hes a battery using a current of 6.7 A for 5.0 h. How much charge passesh:z)q rg6j3 (qas o1h- zio5ax through the battery?    $ \times10^{ 5}\;C$

  What is the current in a rqb 8je+w4 s93ldwr3jmperes 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 toaster if 120 V p m7az+k *;g6+,jwjxv1w w wi8)pta ttgroduces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current36 mg rj.pb:jg2qos:a through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-V line. pj: nb0dgri mxg4 -s;*
(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 dryerfii:27 ucoz:bt59nw 1 ymlm;c 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 who0s+fs m+esy:,h8ys tq se 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. 1bc v j p;a 7gdhvh3*-:qx;izq/8–34). The line haqhvz;x:3a cdq 7ji -h/;p* gvbs $2.5\times10^{ -5}\;\Omega$ resistance per meter, and the bird’s feet are 4.0 cm apart. What is the potential difference between the bird’s feet?    $ \times10^{-3 }\;V$

  An electric device draws 6.50 A at 2 tvv1+ kslb-p q:c4)cy40 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 resi cg4is0rdmt 9 ltwwt6e.; 9jp;stor.
(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 m :*mv+))i ngp dvz1wby.b5gtlength 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 in ody()m -a:ff kdiameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0e7g-t78if,) v- drqkf ouu s1q m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in diameter. )gif 1k tfquru-, s-7ed7qo8v  

  Can a 2.5-mm-diameter copper wire have the same resistance p p2.c,zgh a/obquy)(y0t:vv as a tungsten wire of the same length? Give numerical details.2bq,cuvp pv.g oa()yt z0h:/y    mm

  A certain copper wire h c: l,smiet8/drlhn;i ksi1*;as a resistance 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 (origir8dm(qg olpf il3:a1 /nally at3qa/mfgp 81 (ord:l li $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resisti6xj/yph4+ p zpx6 hmj2vity as tungsten does a2 j/zyp+m4xx6hj6p ph t $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb ha .34an. jks3qippyfhl d7:0cxs 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 along a 26-m length of household no. 14 copper wire (co+ fej, cknh-p3rz2mu i9o. o)6d-wa used in 15-A circuits). The wir upmkow6 ,d+cn3o-o e2)iz-hcr .af9j e 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 cm, 9fcf 9kh1q (fj jigm48and 4.0 cm, lying along the x, y, and z axes, respectff qg hi4jfk98( m9j1cively (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 res wv+sd v;s/i;gcja*r*istance. If one has twice the length of the other, what is the ratio of the diameter of +vr s;c ;idg/wj* sv*athe longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connecteopgp7s8:lc 6 wd to a precision 10.00-V power supply, and a culs7p6gcwp8 o :rrent 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 cogxp./ u +nvn.ynsists of 5.0 m of copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is placed across t /.xgunpny.+vhe 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 not ch0 d 1fvsd94 w4e oh 7ul85(g-ywkxnbhwange with temperature. For ex7n w(9 1y5e0w slbowhu44dk8 d-hxvgfample, 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 producer3-9evw pnp hxd/)v9mv9 o 5pe 3.3 kW of heat when connected to a 240-V source. What must be the rwx/e5h m-v 3vodvpe9)r 9pnp9esistance of the element?    $\Omega$

  What is the maximum dosrj33w ncd-fmi;(8c/rcbl /i6d 0 vpower consumption of a 3.0-V portable CD player that draws a maxi c8r0dwc/ 3d rnvm l o3cijis;(b6f-/dmum of 320 mA of current?    W

  What is the maximum voltage thatu6rwf v9* 5jig 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 lightbulb conngwwa*x v3)ik7e; w0 ycwf j2s,ected to its proper soug;),a 7i w3x2s0yw kwevjw*fc rce 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. ikh rfr a-of1y6)7w2yhn8/ sm 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 seuknhc 4kv,y*i/ t2jx8ttings: 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 xrbit j25 c-6whomes at 240 V. If you use the lightbulb in the United States at 120 V (assume its resistance cxwbi -65t2rjdoes not change), how bright will it be relative to 75-W 120-V bulbs? [Hint: assume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use in the morning if it is 2.fezyj(9j owin operation for a tojyw2f9 e.(z ojtal 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-z(up 5udt*f v p-3 z8jp)nldk kWh, what does it cost to leave a 25-W porch light on day and night for 3 pv d-j8l5)nzt(u d*ufppk-za year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries cljw1fq: e363wv+d v yfonnected in series as in Fig. 18–4b (Fig. 18–36). The bulb dr:dj wew36+f1y fqvlv 3aws 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 yyko 7:f6d/6 a7hx mafin a 12-V, $85-A\cdot h$ 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.hzg0r6fd nw , used without blowing a 15-Afg6. ,hdrzw 0n fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (nox6 2a b1 -uxb( 7(8omywphsibw. 16 copper wire) and of length 2.7 m (9 ft) is connected to axpww1iyh8(b (x a2s- bmo6 7ubn 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 620eob1 2*-c9esri mp3vui +pmz0 kW of power at 12,000 V to a factory through wires with total resistanc 0 ebo-s 2p9z1mmiricpv*e+3ue $3.0\Omega$ 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 17.5 A. Apey8mc2: 8e rrx4t+zkf(p c2vt what rate must cooling water pass over the coip8:mek x p(4 +y ze282rfctvrcls 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 c 7u+- u*860dj 8dbs+w,ikifnqld aks ear to heat a cup of water for coffee or twai+6 8 kd8sdu-q+ fild*0n b7sjeu,kea. If the heater can heat 120 mL of water from 25$^{\circ}\,C$ to 95$^{\circ}\,C$ in 8.0 min,
(a) approximately how much current does it draw from the car’s 12-V battery, $\approx$    A(Round to the nearest integer)
(b) what is its resistance? Assume the manufacturer’s claim of 60% efficiency.    $\Omega$

  Calculate the peak currenu7 angk:pww:ooi ./:cd-8 jv7vw1ep yt in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, is 3 lg65jicpvu.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 the g,w f jnvdw,02$120-V_{rms}$ 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 g6 x)ckoec6h0 o8fuk:is 5.4 A. What is the rms voltage across it? 0 6o86)xg uk:ec fkohc   V (Round to the nearest integer)

  An 1800-W arc welder is connjs4i0ff50/ sa qxdl 2mected to a $660-V_{rms}$ ac line. Calculate
(a) the peak voltage$\approx$    V(retain one decimal places)
(b) the peak current.    A

  (a) What is the maximum instantaneous power dissipated by a 3.0-hp pump con psb.:4t4zr;qxas 7m snected to a bms.4:tp 4;x sas7q zr$240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected tof0hnpms1+j sy16 sk;z a $240-V_{rms}$ ac line has a resistance of $34\Omega$.
(a) What is the average power used?    W
(b) What are the maximum and minimum values of the instantaneous power?
$P_{max}$    W
$P_{min}$    W

  A 0.65-mm-diameter copper wire carries a tiny current 2f l+qs:2o cf9hg0h,kty; ap2y fp q4pof $2.3\mu A$. What is the electron drift speed in the wire?    $ \times10^{-10 }\;m/s$

  A 5.80-m length of 2.0-mm-diameter wirf11 h pxt ujh /;/jwgc)mq5n:ie carries a 750-mA current when 22.0 mV is applied to its e1gc/j;h)qmtj /:xw pi51unfhnds. 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 Earthe4kg8qnf7 dj fd.+m/ o’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 om+:wcfc6w 2 mEarth’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 field across an axon m8ns0(+7ds (;rumhb(* tvbfk9nsb s akembrane $ 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 p k8qs+efczm kiu 2h;4 7*z5hjaction potential is detected at a point 3.40 cm down the axon 0.0052 s later. When tf khszk7 *5p+c jh ui8e;zq2m4he 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 are two measurements needed instead of only one?)    m/s

  Estimate how much energy is required to 2 beeycmwtk.-( ,uiw5transmit one action potential 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]. Whew5m,.ueck( it -yb 2wat 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 potentiaio/bj hg(w,4n ihs ca+8wui;/l, $Na^+$ 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-hour? q4nm7myqs c((    C

  What is the average curre mizk8n:m94itnt drawn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. /kctaurvhe a.iq 53.ed7)mn9 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 bat e.k75.9dvciu)3 mahn r /qeattery 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 is m9a0z vwpbo 5bl-/.pyzade of iron, what must its diameter be? wya59b0/-b ozz .vppl    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of the resistan3(pmumyf n (:tce R; tput m:3 f((mynhat 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 , dd*pg;yrp1w qi(x(rthat instead of using high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a two-wire lindw x* dpr(1(pr,yig;qe 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 uses a 1.8-kW heater 4ay sax ).w/ul y,oi7o$3.0 h/day$ (“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 to i s1)v3bebu cs//)ur(veg1+)aganikgether side bye)r k3bi)avg n(e1/cigsu 1usa+ b)v/ side to make a thicker wire. How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is desi(8yoxugd.5 bs(lzy3w gned 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 hous 3kqcy1hz oq+6e must be thick enough so it does not become so hot as to start a fire. What diameter must a copper wire be if qyk31cho +z6qit 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 give72fy 8hjev3 izn by the 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 W of energzi m.u)pj80tr y per second to the intetr.i p 0jz8u)mrior. Find
(a) the power drawn from the source,    W
(b) the current drawn. Assume a source voltage of 120 V.    A

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

  220 V is applied to two different conductors made of the same materia,4 o(gdhvsh)hl. One conductor is twice as long and twice the diameter of the second. What is the ratio of the power tro h)hgsvh,(d4ansformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room of volum( cuejx7qfc 3 3pab-0v 3ll/the $62\,m^3$ 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 sourdaqi )v kh+7xl713ug :iz ri4oce.
(a) What is the resistance of the oven?    $\Omega$
(b) How long will it take to bring 120 mL of 15$^{\circ}\,C$ water to 100$^{\circ}\,C$ assuming 75% efficiency?    s
(c) How much will this cost at $11 cents/kWh?$    cents

  A projected electric vehicle makes use of storage batteries as its source of e6 hd; qkbuw8)pa:y:g rnergy. Its mass is 156wy:ud 6b;p):h8qkg r a0 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 resistance of b+a unimj0zos*1t 1mnae2x14 $12\Omega$ when cold (20$^{\circ}\,C$) and $140\Omega$ when on (hot). Calculate its power consumption at
(a) the instant it is turned on,    W
(b) after a few moments when it is hot.    W

  The Tevatron accelerator at Fermilab (Illinois) is designed to carry an 11-mA 7dud. -ur 4flwh6mvt en2+ce1 beam of protons tr2ce -n+6durt vdh71l e.u4mfw aveling 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 connecting cord is copper a;9mb,j,xt(h g*u-uh)vk hu5uftk/ l wire with a g)9(5hht;vtmuaj , u, bflhkuuk* x-/diameter of 1.628 mm.
(a) How much power does the air conditioner draw?    W
(b) If the total length of wire is 15 m, how much power is dissipated in the wiring? $\approx$   W(Round to the nearest integer)
(c) If no. 12 wire, with a diameter of 2.053 mm, was used instead, how much power would be dissipated? $\approx$   W(Round to the nearest integer)
(d) Assuming that the air conditioner is run 12 h per day, how much money per month (30 days) would be saved by using no. 12 wire? Assume that the cost of electricity is 12 cents per kWh. $\approx$   cents per month (Round to the nearest integer)

  A fish-tank heater is rated at 95 W when connected to 120 V. The ato8d ea+np-ese.ytl,+4ja;heating element is a coil of Nichrome wire. When uncoil.yj8e4aeln; pa oes+a ,td -+ted, 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 vouqc-4 gd0trt) ltage varies from about 12 V when 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 percecdt grqt40-u)ntage 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 10m-ifo5c43myra b26ngjs a-axby8.umg e.t +20 V and 40 W for household applications. Lightbulb B is rated at g 8y.3c.m0emsa5tmiyr b2jo4b a6ganx-+f u -12 V and 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 df4 n3zuo5vk7d+ m2t;by) tdr.259 cm is used to connect a set of appliances at 120 V, which draw 2250 W of power totalknz52dot +dty rfv)u;md7 b 34.
(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 2xh(ud8hkt a4 diameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is axh4u(2dt h8k the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is swc hu308y 1ihitretched uniformly so that its length doubles, by why8h13uwi0i c hat factor does 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 Am i8 no98bg(ub phgej8v(x*j( and 3.2 V. If its o98 vji*(gbm8(x8ngbe ujhp ( resistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$