What quantity is measured by a batt*)fp0sdmece)p43sy25ax 0f g 3bbipu ery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is cohvg tp-lmhpw 51m,.l0eh;,abnnected to a circuit, electrons flow away from the negative terminal in the circuit. But within the cell, electrons f1 lvp g- a.em,th5b wpmhl0h,;low to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battery current, battery w )1 1ke19 q4evmgks*bswmc.r voltage, battery energy, battery power, or battery resis)evegw mmk14w.q 1kr s9scb *1tance? Explain.

One terminal of a car bxkok:hk4 n -82y m:wvaattery is said to be connected to “ground.” Since it is not really connected to the gr 2:8y4kxovkm-a:nw hkound, what is meant by this expression?

When you turn on a wa.3l*ntprx-: hxbf7+ym o tn( jter faucet, the water usually flows immediately. You don’t have to wait for water to flow from the faucet valve to the spout. Why not? Is the s nf3lxt*rxt mj -7(yphb:+no. ame 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 wt/f0 oe,7bs,zsmk(f shx9 jps*/* ju same resistance? Explain.z,jf*m, *7 xtsspbjhkeo/ u0w(9/sfs

If the resistance of a small immersicb;ura4,+wec-k9 vp d on heater (to heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the heat cdvk,;r wbu9 a+cp-e4ing process? Explain.

If a rectangular solid by )9ozg8c6el17 s ymzw.5dxbmade of carbon has sides of lengths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resistance, (b) the grebz) mc .57l6ob918yswgdx zy eatest 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 ligx3*b q80zzh ec e-pwh+htbulb burns out?

Explain why lightbulbs alml;hn qchd4)/01xtk-g8 b7odnvc+ uzj ost always burn out just as they are turned on and not after 0; jqc)lnz xouh- hkt/47dg1b cv+n8dthey have been on for some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which has the hig 4n2+a y0qqi d4 dlqeyop9r2q;her resistancy2qre4y d qiq lod;4a9+ 2p0nqe?

Electric power is transferred over larj59nvveg ,q :vge distances at very high voltages. Explain how the high voltage reduces power losses in the tran :v vgn9ev5,qjsmission lines.

A 15-A fuse blows repeatedly. Why is it dangerowrm2oi431xp nqw-6 aotb901 e.-z s h.yqtvjnus to replace this fuse with a 25-rpt2h3n0w-1 qj osnbt- 9o. xae6zyqi v.41 mwA fuse?

When electric lights.fkjz ;3 ipq8i are operated on low-frequency ac (say, 5 Hz), they flicker notice38.ijif kz;qp ably. Why?

Driven by ac power, the same electrons pass bac+rkbqachm 5ds)w *52ck and forth through your reading lamp over and over again. Explain why twdasmk5 r 5)2hc+c *bqhe light stays lit instead of going out after the first pass of electrons.

The heating element in a toaster is made of Nichro0;yf35z*a6hizrrg 8 (k tups wme wire. Immediately after the toaster is i38zk0f ( rsg *aw6;thzuypr5 turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up i736te+ ldfoslyu+n2d d*u. qwn a resistor? Explain.

Different lamps might have batteries connecte iwj gk,g,y:q/d in either of the two arrangements showj:ggqk/ wyi, ,n 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 pas19(g tsl dnhjnzv*9 ,qt any point in the wire ,1dtnqgj s v9(n*hz 9lper second?    $ \times10^{18 }\;electrons/s$

  A service station charges a barlm f3c5 hh;s7ttery using a current of 6.7 A for 5.0 h. How much c;5 lhf3cs7hr mharge passes through the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes if6h,x5 4 hxdmp qz5og+d $1200\,Na^+$ 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 120yrtc7 yeyv,3v(0sn9q. ru*qc V produces a current of 4.2 A?    $\Omega$

  What voltage will pr.i :0ntru/) gzp(ftns 5nine( oduce 0.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-V (i*dl6iq 82:* gac0hlfwuxrlline.
(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 qys dc*j4 6 v hltn)9;glh3in/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 conne fq)bgjr:/4m kcted to a bulb whose 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 (nm kkyt- -c c21(zry7uk b4i(iFig. 18–34). The(2k-y ( c kbi-ry4u7nkzt1 icm 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 6.50 A at 240 tdas jf 5v(gr *c2y n(bwi)oi.v y-f;7V.
(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 resist6h(d6wala;qf .ev z fnt bt.z.s6ov44or.
(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 oh)b*3tdhyu v 205g odwhose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance ;36ch nw 6zg i2kus:wrof a 3.5-m length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of anmfxp eb mod93+-vh 05luminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in diamm-de0m5 xnh+pofv9b3 eter.   

  Can a 2.5-mm-diameter copu:paqd.e kn0m1uiz snb,p a;9 dg(o*5em 09t vper wire have the same resistance as a tungsten wire of the same le eqv(d:ou9,epm; um*d90n szg t51 n0kaa.ibpngth? Give numerical details.    mm

  A certain copper wire has uq:tvp7vl-(o 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 tempeoscl*;cw a ,ukp-)3ji rature of a copper wire (originally at*; ,3k) cop-s ujcwial $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will havrscm wlwn)i+5fs: +w26c i9c:cilz,ee the same resistivity as tungsten doeswzn592ew isl: )cf ri6w:c+, +mi clsc at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a /g 6r-oh(w -.vmtlnk*0srdoi 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 r p ,0p(sn(f6oqzyej326-m length of household no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm and carries a e 3sqr(0ony,(fpzp 6j12-A current.    V

  A rectangular solid made of carbon has sides o0r4fgd6 k9 smk3b vmnhd,+p +lf 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 resi+skk6m+mgrhv lnd4, 0f pb 93dstance 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 twice sq/;.2*u - o4 u ( ribxqgsmbpd-8kg3 tcw0flfthe length of the other, what is the *4 xpof8t u .3gswdsgil--qr0f 2qm cb/k(u;b ratio of the diameter of the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is ww6 veeqwi s7i)(kt9e(mlv3e2hd)-jconnected to a precision 10.00-V power supply, and a current of 0jmeiwi6() v t-(2wsdwlkq9e 3 7h vee).4212 A is precisely measured at 20.0$^{\circ}\,C$. The wire is placed in a new environment of unknown temperature where the measured current is 0.3618 A. What is the unknown temperature?    $^{\circ}\,C$

  A 10.0-m length of wire consists of 5.0 m of copp/-6h9urm bk wojhf2m,er followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is placedkmrf hb/ju-om 2h96w, 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 oo :y cm*e,up8gf a resistance not change with temperature. For example, suppose you made a m 8cp u,eg:*oy$4.70-k\Omega$ 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 desig;l1sd)mg /c nfned to produce 3.3 kW of heat when connected to a 240-V source. What g)cn1lsf m/;d must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portab.32 i5mdycbd9 u 5bycfle CD player that draws a maximum of 320 mAubim dy b 5c.y39cdf52 of current?    W

  What is the maximum voltage that can be applied acrlj. 6p +xx2lxm- pte3ioss a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, rgh.i7nlw+; z a 75-W lightbulb connected to its prrg.hw ;n7ilz +oper 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 r8(4bbd1 y siuvg((r jzd28e drated at 110 W. Calculate
(a) the current through the heater when it is operating,    A
(b) its resistance?    $\Omega$(Round to the nearest integer)

  A 120-V hair dryer has two settings: 850 W and 1250 W.65ku vgto +e9l
(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 romp w2 inw7 wz+i uigsu7w9ko(g9 i2+2,i4npat 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 relati4pgm9si2 2wig9k(ow7w w +iniui27 z,+upo rnve 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+c1 b6 t2fkuzk-W toaster use in the morning if it is in operation for a total of 15 min? At a c6tz2+ fkcbk1uost 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 por: 5clq-.q iptb.ne- xvch light on day and night.:tqe -5ciq bx.lv-pn for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected itj czlq263c wo0/ 2stc zi:tu(n series as in Fig. 18–4b (Fig. 18–36). The bulbu l t3tc2w2: 60/icsoqzjctz ( 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 o lknht54d79 bkf energy stored in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connected to 1207bt*8wiu yyu) V as in Fig. 18–20, can be used without blowing a 15-A fuse8w tu7*yyub )i?    bulbs

  An extension cord made of two wires of diametefekb;1h *gkm vaei*2.;im9 jtc -xmu5r 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric heater which dra*u ehv kkbt2a9 ;mce- miix.f*g1m;j5ws 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 throughbs+ irvx7ex*-hwl e9, wires with total reve+*wx si-rb le97xh ,sistance $3.0\Omega$ 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. At what rat(zr1dcw,4i/fdw pa t+e must c,rt4cf w dd/p( w1zi+aooling water pass over the coils 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 t,cvq*si 3c +bntf.:z of water for coffee or tea. If the heat,ccvb t*z ns:3fq.i+ ter 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 k8dibgeb7, r3in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 1)i8u8yn*- q1h -cq ;w vrnhmak80 V, 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 ofyuxiv4a+ y 29*twit1 2 gm(gsg 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 animjmb wli h:y yr-,),/ alternating current in a 1500-W device is 5.4 A. What is the rms voltage amj)l-wyhy m, :bri,/i cross it?    V (Round to the nearest integer)

  An 1800-W arc welder is connectedx)tzixnq 0duy339jz9 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 powew*lm.kh( 6h)rjf 20 t3orheg wr dissipated by a 3.0-hp pump connectedwo.20 t6mw* ) hgrjer(3flkhh to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connec+n pm/y: n.nor;j i67n c19gpv i6esj)sq-nwated 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 carries a tiny curre 6l :yby - le89dhpksd)bo(6hont 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 car +)neyf-/ihg x 937jsuf. rgawries a 750-mA current when 22.0 mV is applied to its ends. If the drfgr /. fynj ugh3 +waie7s9x-)ift 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 at7 tff; rjdj(b:mosphere, $He^{2+}$ 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 atmosphec5k1gd3p9gnn 4; db7oo z/uk wre, $He^{2+}$ 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 acrb h6il53pr,jih in(9n oss 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 pulsz cmq7v7p ira//u 5*fye. 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 cm from the point of stimulation, puc/ /qi7zr5m7yf v *athe 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 requirbcfq/1+x*gz zed to transmit one action potential along the axon of Exa/zzqxg + b*1fcmple 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored by charging the axon capacitance; see Section 17–9]. What minimum average power is required for $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action potevcl/;9 prrg:gm +we;gntial, $Na^+$ 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 argt -w0k+eps, ge there in 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0-hp 120-V mot)a,g)oybn/ 4 sxgldh p9)hx9yor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with*t))h5 v.7vdhxu1 eklbfiq8j the lights on. If each of the two headlights uses 40 W and each of the two taillights 6 )ub5tlf) vdqkvi xj he71*h.8W, for a total of 92 W, how 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 is made y *712w:1u;q0 xcc fnjl5/rtdnsl)mukxwgb* of iron, :wln u /yclc; )1nkrut 2d75gmbwxqj*f*1x s0what must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is dc w rn0,jo80amefined as the reciprocal of the resistance R; a,0w 8r0 cjmnothat 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 +l eic)ch yl/(10 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 perlci)l ey( h/+c hour per meter. Assume the cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular househ8rs3 2eb8y( .zquav w :u4ukpjold uses 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 togecsj86*my xvn;ther side by side to make a thicker wire. How does the resistance of this new combination compare to the resistance of the original wire? sxvmy6 ;cnj8*

  A 1200-W hair dryer is designed for 1+ar+p+txrma y 106 xm 0s1xwgg17 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 become sodipos ftq 89a8n 4cy55 hot as to start a fire. What diameter must a copper wire be if it is to carry a maximum current of 35 Aq5 o5f8i9cdany ps8t 4 and produce no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is givenjt, ms y/, r0 pgar7*-afs,gmq 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 aln8atx1fa0 /at 65% efficiency delivers 950 W of energy per second to the interior. 8a1lxan 0a/ ftFind
(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 ma: 1s 1*re4zv.aboyjvf terial. One conductor is twice as long and twice the diameter of the second. What is the ratio of the power transformed in the first relative to the sev*fory.z svj:1 b14a econd? $P_1$ : $P_2$ =    : 1

  An electric heater is us59 nijsek 09qu9ak( e(ri*zlsed to 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 hooked to a 240-V sourc0ayqx2wyw kc291e d v+hbi b*hoqx9;i5pvf,2e.
(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 make2+a/w2b n x0jpogt*z ms use of storage batteries as its source of energy. Its maanm +gtbzp/22w*x 0joss is 1560 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 uy4 xn7egh -8fs8oe7ka 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 Fermilab (Illinois) isdw3p /(w 91mucxf *epg designed to carry an 11-mA beam of protons traveling at very nepfw3p1m c(/ dgx*we9uarly 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 z1t 2v4cec s+vcord is copper wire with a diameter of 1.628s2+vz v1 cet4c 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 i; i1bn.i) ortu.yi9c95 W when connected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What is the diameter 1ciour .yin ;)9.ibitof the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from about 12 V when the car is offqro.6)pr, ly x to about 13.8 V when the car is on and the charging system ir ro)px6y .ql,s 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 applications.xgv1)8 lm) sghbchbr27 m,q8jkdg9e+,+sss c Lightbulb B is rated at 12 V and 40 W fg+9+,7m82 8csjg)hsgl),cx drvhqmbks 1 besor 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 diamed,demdag50jan :z / 3lon 5yjw pa(:0zp gf;/tter 0.259 cm is used to connect a set of appliances at 120 V, which draw 2250j0dy ,ao:dajl0(d 5azptn:/z3mng/e wp;gf 5 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.2c *k3lef dizhbixx/7y3 cc* of 5.00 cm (Fig. 18–37). cfx3 dz*x *cy ke 3i7cl/2hbi.What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its length djhp0v;l* )vkf hm*7meoubles, by what factor does the power dissipated in the wire change, assuming it remains hooked up to the same pk;j*7)l vmvfeh*m0h voltage source?

  A tungsten filament used in a flashlight bulb operates at 0.20 A and 3.2 V. If 6j-fa5 +n 1pt;ryvknlits resistanc;vy n p-1n+jt 5l6kafre at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$