What quantity is measured e79pyaau9k.d v wnchm1 581vhby a battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a cpd8l r*y t0yrgk1:cumeng 48/ircuit, electrons flow away from the negative terminal in the circuit. But within the cell, electrons flow to the negative terminal. Expla0crty8mre8 k p*/d:n4 lyugg1in.

When a flashlight is operated, what is being use7h0oy/o cnh/lfsrol;s* ) ( odd up: battery current, battery voltage, battedoosnhf;lch/*0 o(/7yo )l sr ry energy, battery power, or battery resistance? Explain.

One terminal of a car battery is said to be connected to “ground.” Sgd ld58 6m57 -:4.fivaftj o0yhhsvjbince it is not really connected to the gr4o.507 mts6v8 j- fhdih5 afj gdyvlb:ound, what is meant by this expression?

When you turn on a water faucet, the water usually flows immedi wj9qq.3du s6fately. You don’t have to wait for water to flow from the faucet valve to the spout. Why not? Is the same thing true when you connect a wire to6sq3u.q j 9wfd the terminals of a battery?

Can a copper wire and an aluminum wire ocyukb)ix 35r;um(j7fas 3 ur4 f the same length have the same resistanc335sf( )c4ij b uxayu7ruk;rm e? Explain.

If the resistance of a small immersm hzvo4177ld hion heater (to heat water for tea or soup, Fig. 18–32) was incr v7mdho1h74lzeased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides ofsjw+*gy0yngz yh7/:leo u *t0 lengths a, 2a, and 3a, how would you connectuz* gj7y:l*ysg0h0+ o/ tynwe the wires from a 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 burns ou:ltvmh ri2u;w* ql:2pt?

Explain why lightbulbs almost always burn10qbk3/sq *-bumdf d,, gcc rf8e pg8v out just as they are turned on and not after they have been on for some tm/g c,k3ufc d -qr8ef0b18*bqgd,vps ime.

Which draws more current, a 100-W bp/f 1v1ry,l fms7k:dlightbulb or a 75-W bulb? Which has the higher rr lfvyk7s1b/: , 1fmpdesistance?

Electric power is transferredixq 5ah( akz6df /p(u6 over large distances at very high voltages. Explain how the high voltage reduces power losses in the transmis i (6apx6fqa hud(/5zksion lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replaces.d:b9 og apcl w*fo9* this fuse with a 25-A fuse:bg fsw 9**9pool.acd?

When electric lights are operated on low-frequency ac (say, 5 Hz), they flicke t5oh+ nhe*i q5.bhnk5r noticnhk5q +n5*eh.o5 bt hieably. Why?

Driven by ac power, the sam pcrv+1s l1zcg+ n,-kue electrons pass back and forth through your reading lamp over and over again. Explain why the light stays lit instead of going out after th+cvpl u sn-+,g11r kcze first pass of electrons.

The heating element in a toaster is made of Nieo 30lkwr)pg8tj,2;o cc) mpm d(si1l 91skzschrome wire. Immediately after the toaster is turneck1p),r3ceomtws1smg dzki)2o8( pjs 90 ll;d on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a r tzb0ac+1a97yg isw 3d8.osxdesistor? Explain.

Different lamps might have batte5zrt2 s4xc1awries connected in either of the two arrangements shown in 4 c5xw sr2zt1a
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wi +vdv 5naai0k;re. How many electrons are flowing past any point in the wire per second?aian+;05vd kv    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 64 rb ib2qp(hd3gmi7.e.7 A for 5.0 h. How much charge passes throug qi 4bb.37r2ehgi (dpmh the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes c;j erlbti6x)yx3dq(,n4 euvu8:9prif $1200\,Na^+$ 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-t ;t75bu)pj yepx9g1zjp lt7 roduces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 d+26sy,jyd) d govf+b brev4*A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-V line. 2)buqg3q-krihy w3 l t3(ogny l ia236
(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 0r;x( om9ru87jf cmihv-jnb0 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 connecu ql2zz5 iz5f2;dm7 rhted 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 anc:c eyengavg/ oab)3w +.5:carrying 2800 A (Fig. 18–34). Tv)/ ac e gbn.5ocg+yw ne:aa:3he 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 24 :cb.yzz: o24dr3qobv0 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 currew.8 c4er ajtqg-vmf./nt 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 1.00-m length of tungsten wire whose rh/ roj wldc7*4osdx-4esistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance cn.fpn j9/4zza on8-tf8-h6reaofk) of 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 agqwwg3)pb:g* luminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in dg )3b *wggwp:qiameter.   

  Can a 2.5-mm-diameter copper wire have r6omk g(ajlm1;usz-0/ds fv 7 the same resistance as a tungsten wire of the same lenk-v( ;a 1m7gd z/o6 fjml0ussrgth? Give numerical details.    mm

  A certain copper wire has a resdj.6xaw- 5 sy)leqc3 tistance 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 ah ,g3pn0 g)hn;u2.8zji p2dc aqa:m t xr5gh4i copper wire (originally at ii pn) ahghd3p.hq ; xj8402n agzrm5u:t2g,c$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have th/xnr* ,6ih ce31d6ld kxvjd5ie same resistivity as tungsten does at 66dd d,lxr v*3ihc/ i1 kjnex5$20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of about.)34dyf gm p: ,syrtbp $12\Omega$ 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 (us)ncd( esvj nhx:v11-cy)a9 cj ed in 15-A1 cjdncyv-9(je)ax 1: )chvsn circuits). The wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of leng- y6*txnmo2e9gsjt (q ths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for current that passes qmje yg2n(9txst *6-o 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 twic+zjfb1t+job7j qyy t/ha2 3+ ze the length of the other, what is the ratiq23a1z+y z/+bjft 7h+tojybj o 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 connected to a precision 10.00-V power suppfv+iq l./)/csu bh5b,0woup 4 bnv+e yly, and a current of 0.4212 A is precisely measur b/4+p/ybsev ub,5 i+.v lofqnu )0chwed 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 (jgy5kh;kw7h 5.0 m of copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A v7;kjh wgky(5 holtage 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, it is important that the value of a resistance nodqsl z+,+pg2r t change with temperat2qz sr+pl ,d+gure. For 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 3.3 kW of heat ws t2m,bxhi /adj i*2,phen connected to a 240-V source. What must be the resisti*d,2tx2 si/ b,mja hpance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V po4ss cp-t6.sksfy 8jr0rtable CD player that draws a maximum of 320 mAjpsrt0f 6k-s. y s48sc of current?    W

  What is the maximum 1 6xjv+83k ecsxx2,s bswpmr/voltage that can be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistva, b 11t8)-j*nis clt .bgta7 9yqzx)cap 5nmance of, and current through, a 75-W lightbulb connected to its proper source voltage of 12) 1tnm j bc8yb5t-*x9q1asp)7tiv,.a zlacgn0 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 1ke)sh w+1 lbi:/bdtek: 1yad4 10 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 f ogg-mx t*p9htn854btwo settings: 850 W and 1250 W.
(a) At which setting do you expect the resistance to be higher? After making a guess, determine the resistance at
(b) the lower setting;    $\Omega$
(c) the higher setting.    $\Omega$

  You buy a 75-W lightbulb in Europe, whju::k6aa0nn g ere 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 0:n: ka a6jnugbe 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 mornildn8 pm3pdo0(ng if it is in operation for (o3p 0 8ndlpmda 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 a 25-W porch light on dayiaahb 4u ,e*(w and night fo4uah(aib,e* w r a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected in series a8hb1*fq.5n zjmjo - oke* floafo;6a 0s in Fig. 5z18b;o0f*qok jn ofa 6leajhm of.*-18–4b (Fig. 18–36). 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 in n54f xbm,q2 3t,jpgr6hff o)y0p7tvba 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 Figwoz z6wyyv(8u8 9sb ;.,jmgd i. 18–20, can be used without bl.m(zjw 9yiwbzuo,s;gdyv 88 6owing a 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.12cc;.xf+n+) / sq f o.(xrpirgs9 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric heater which draws 15.0 A on a 120-V line. How much power isg qsofrr/sfp.. )+; c(nxix+c dissipated in the cord?    W

  A power station delivers 620 kW of power at 12,000j xgu7o6ln 3g3-s66gghfpl 4 h V to a factory through wires gg 76fp6g4jho- 3ug6 xlln h3swith total resistance $3.0\Omega$ 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 co7*4fu8yetk+rf2 ep mhnnected to a 240-V line is 17.5 A. At what rate must cooling water pass over the coils if the water temperatureyk*t 2mr+ue78h4 p fef 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 cu(u6hp7p0e zb2tm;9 frgurt/p+ezkb3 p of water for coffee or tea. If the heater can heat 120 mL of water e 72phzm bgft30ur9u 6;kp/rz+e(t pbfrom 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 in(7dowwgk f(bc,ikjl4q +q6 01s 4 fhfx 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 acro8x w)-nsq+k9lqkfi)5-blb x/ ym kc p7ss 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 resistanc zx1u 07gprx3kvvh/i 4e 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 cuknu +v ()u8o j,)ehwvu:d* ppxrrent in a 1500-W device is 5.4 A. What is the rms voltage across i)p8o+)*pdu nve , (uuxwh:v jkt?    V (Round to the nearest integer)

  An 1800-W arc welder is connectedlf.f s89*hzhj 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 power6b,pv rvbq1)hz;kjk 9o.mji( dissipated by a 3.0-hp pump connectedj6(jikb.hpz ro ),91qm;vvk b to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connect5j wopk5q5-y ked 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 tif/b c5+ecca-b ny 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 -0y 4 ecwbsp ao:2mi+ncarries a 750-mA current when 22.0 mV is applied tsa-o i2m0c+yb:n pew 4o its ends. 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 Earth’s atmosp b6g8jxgf, ) 99o c)i(sisfubrhere, $He^{2+}$ 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 ahbr;fx(a k bwb 6:4e7wtmosphere, $He^{2+}$ 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 electri- +qg;jtl. m)3owptvo c field 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. The action potential is detected +zt24 jzz4 ;hr pfx.gfat a point 3.40 cm down the axon 0.0052 s later. W 4z.h+rt;p4gxfz 2fjzhen 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 the axon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much enevj6q jjvt6,e/ rgy is required to transmit one action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored e v tj6qj/j,6vby 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 pot rwb-bw8: 5jxyxv se0;ential, $Na^+$ 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 i2gh36 m3e apg n;hha7r)miu(ampere-hour?    C

  What is the average current drawn ny,;mcr wp3-06q)h1ujl 6 prt 4yrv apby a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car wie rj4tq g)zztr5r3yl18z (fo+ th 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, how long will a fresh 12-+( z5 lzrf81t)3gezq tjrro y4V 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, 15;1/eh.oqqo/c1 emk sbxjg +4o 00-W heater is 5.4 m long. If it is made of iron, 1; mejo +e //oxo1bqhckgs.4 qwhat must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the f1 8 rns h:xl -cut7a)jx19umoreciprocal of the resistance R; ts -89c l7muj xou)x 1f:1hrnathat 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 of using hpw vnsq k,+l4 3f5g z7shrw uhq19:8zmigh-voltage lin9h g:51 ,q rz7skupfhnlmw84qz3sv + wes 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 per meter. Assume the cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular household uses a 1.8-8eftvh.x- -bp7jw* lp 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 m8m l)/:bsnc sr,ca9d in half and the two lengths are wrapped together side by side to make a thicker wire. How does the resistance of m: s8)b,lrc/dn9acs mthis new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 117 V. euwz2zdfnb8 y1 ;,b,7qeayd ;
(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 n 52bh2912+nl c*upe9izfevfrw kvl s6 ot become so hot as to start 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 vehznu2p9 2 rkie f1w+ 2s59c6lv l*fblength?    $ \times10^{ -3}\;m$

  Suppose a current is gio*ky2;9k bbs/ewygjy3 k:h. g+i ebw ,ven 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 energbx. .m9wlbo z2,xwu29w-s emiy per second to thezlwwu bsx229 .m iwm ebx9-.,o interior. Find
(a) the power drawn from the source,    W
(b) the current drawn. Assume a source voltage of 120 V.    A

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

  220 V is applied to two different conductors made of the s*iofc;m1 ( v+ jcyl7oqame material. One conductor is twice as long and twice the diameter of the second. What is the ratio of the power transformed in the first relativcmc y;o i*o(qf17j+ lve to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room 1si/k;7b3 ol-ctu )u+)veqqed b-ogb 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 s ;5w*)ovpz ourource.
(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 vehgd qds0; wc*y- xdq(,jicle makes use of storage batteries as its source of energy. Its mass is 1560 kg and it is powered by 24 batteries, each qjg c,d(ddwsx;-* 0qy 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 resistu:,jw0-bsvs mktf ig6( /my w5ance 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 Fermyh5gz9ot.ii 1/7a/wms0wj q d wlj0j8 ilab (Illinois) is designed to carry an 11-mA beam 0 wi 5y jqi.tshm/0jj8dawg wo1/7l9z of protons 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 connecting cord is copper wirn-c3 k7 6lrwc;0 sdvghe with a diameter of 7lrv kc scdwn6;h0-3g 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 heating eleml n,;e,9/j7 ;ssfn t/ l*dpmuwhwob 2nent is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What is the diameter of thnsw l hf,nt;m dweu2nsl9;7// p* jb,oe wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies frof1gv-7iqk d4lm 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 percentage does the power delivered to - vli47fqdkg1the 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 Wz j ;:j: (eao*hm9dsji for household applications. Lightbulb B is rad ;:a9*e:z jomj( isjhted at 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 0.259 cm is used todkl9yu7t*l 1f connect a set of appliances at 120 V, which draw 7yduft*1 9lkl2250 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 55 vz7k*pqx 1am.00 cm (Fig. 18–37). What is the resistance of 10.0 m of this pipx5qpk7*zvm a1e?    $ \times10^{-4 }\;\Omega$

If a wire of resistazb 3(zttsau6ys3 fjfgty 3 (:i*dh-/unce R is stretched uniformly so that its length doubles, by zg ju/azytt bs(ud -(:6fihsf *t3 y33what 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 A a 3( 5fypgk2fq7aa:c jcnd 3.2 V. If its resistk 7jfpf ca qa(2cgy5:3ance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$