What quantity is measured by a battery rating givej *m* )gdssi9an in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, elevwc;b es+q lvkq3 e0z *ev(s/,ctrons flow away from the negative terminal in the circuit. But within the k v*;q,+sbvz s (qec /elev30wcell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, wh )rk2rn mzn6rnvb: qed: *34 w,da/8ks y-eywoat is being used up: battery current, battery voltagk4s/) e ao yq:w dmrnw-bke3z:drnry8,26n v *e, battery energy, battery power, or battery resistance? Explain.

One terminal of a car battery is said to be connected to “ground.” Sincemr 8 i.e1tl pkyx4,p7o it is not really connected to the gror ,xypel1i mkt .p748ound, what is meant by this expression?

When you turn on a water faucet, the water usually flows immedia-w v4eczd /qs6tely. You don’t hae6sd4 /-wcqv zve 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 to the terminals of a battery?

Can a copper wire and an aluminum wire of the same (3v ja9n1 x leu/twhy3e0d3nelength have the same resistance? Eyuv j/eea d3 (9n331lxen0wth xplain.

If the resistance of a small immersion he6ir4r8at;hi x; z1geeaj0 a)ow t/6cq ater (to heat water for tea or soup, Fig.a06ht 8ee jr/; wcraxaii14t;)qzg6o 18–32) was increased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has side(z; j w*unljhvw*/x )t5 lqt-fs 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 greatest hv;fz*5 /-qtwn tlw* jxl(uj) 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 outq98eddo-1-baofls p)j a) 9 fm?

Explain why lightbulbs almost always burn out just as they are tu.vy 5l5lt13t a t9offzrned on and not after they have been on for some1t otlyt5.lva f3 z59f time.

Which draws more current, a 100-W lightbulb ort m*j,,;p2wmvlvow mq *t m+)y a 75-W bulb? Which has the highermy2*mvloq)m*,;jmt wwp,t v+ resistance?

Electric power is transferred over large distances at very high voltagesfkg b2 g 5bl(i v46fnhoe8t4 )ha5ed/i. Explain how the high voltage reduces power losses in the transmissd)f6(fhg5han84kbeto b42 v5 gi il/eion lines.

A 15-A fuse blows repeatedly. 5l0.do1 4w vd-1 tjyn6of8cen v2d oflWhy is it dangerous to replace this fuse with a 25-A fusefvoow5vcy04fdo tn 1- e 8l6ndj1.d2l?

When electric lights are operated on low-frequency ac (sa p/ , )37ooni+hp6c4lay ytrwdy, 5 Hz), they flicker noticeably. Wr)n,3h6loi w7tc +4p/d yoy aphy?

Driven by ac power, the same electrons pass b ez)m7 +)n.)lebbkkmsack and forth through your reading lamp over and over again. Explain why the light stays lit instead ok lms .b ne+)ze))bm7kf going out after the first pass of electrons.

The heating element in a toassx+ eh:)cwtve 6;8 ph1pn/,zkv b gkj.ter is made of Nichrome wire. Immediately after the toaster is turned o ;b npwje k)+6gtp1xces,zhv. /8v :hkn, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Esoe/j7 1jtqk4 zh rwjd;-2z7caq 69zuxplain.

Different lamps might have batteries connected in either of5h tc8l//zs6 cfc s78cm s0wuz the two arrangements show6fctc8 s mz h78/csuz0 l5/cswn in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many electrons are flowing past any poi m0m,izk ;yz5hnt in the wirih;0z m,zk5yme per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current+g9my9xn /w:p9vxz bc of 6.7 A for 5.0 h. How much charge pasg+nz pm/v 99ybxxw9:cses through the battery?    $ \times10^{ 5}\;C$

  What is the current in a u95iufq7 5snfyc- (mymperes 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 a7 mgi,:cf,z8oopq+ tr toaster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current thr2g i4 r.am:)lp0g tlz9x0veaqough a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-V ;lo .u m5t:plnpp0s7 oline.
(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 elemennaf ks qe9 o.5+nccm61t 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 whoseux;oi94gdh qyn +c, w0 resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc eley393suk.x2gdtwnrf gq (/ u9 pctric transmission line carrying 2800 A (Fig. 18–34). The liny./p3(3g d9k qfgu xrn tsuw92e 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 V. y:ni+zt ci .:31hjcmha qiy51gz( t.i
(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 4rbtd0 k 9ocr/yj+m6gstor.
(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 resistance l, 5qlhh;s q (rhi,hn(is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length pjvjf 8i7*-caof copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of /nw 2zv4xym s4aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in diameter. z w4m/2x 4nvys   

  Can a 2.5-mm-diameter 48 vuetyow.,j )l l8ozcopper wire have the same resistance as a tungsten wire of the same o84t l,lwo8j . yveu)zlength? Give numerical details.    mm

  A certain copper wire has 2w5l67) nxuqf jx/ b9 vai.j *2sqgwmqa 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 y wfid-),ps8xnu-9 5q ;cifaz temperature of a copper wire (originally at fawi;xs9-u8 q,iz5yc )nf - pd$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will haveo;4aynww0ph3uqk p3 + the same resistivity as tungsten does at pw 3oq 4;uh yw0+a3nkp$20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resist*a1,gnpe 5 szgance 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.t8frjpai.: 7l 14 copper wire (used i tf pl:.j78iran 15-A circuits). The wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of c5b :;d fcom1aparbon has sides of 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 resistance for current that passes thadfp; 15:mocbrough 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 the length of. jmbxe4x ni*32l ooq7 the other, what is the ratio of the diameter of the longer wire to the diamem 42xl7 boq3oi.n* jxeter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wirh f3pgj.za(. 2pru( aqe is connected to a precision 10.00-V power supply, and a current of 0.az(ppq fhugj(a3 2.r.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 mr+ t(9v,4fm-mlc -xsulvs4v5.0 m of copper followed by 5.0 m of aluminum, both of diameter 1.0 m mc,suxs + m4-9t-(ml rv4flvvm. 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, it is c; bupf8is,w4 mj3e4jimportant that the value of a resistance not change with tempep4e8,wjcb jfs i4 m;3urature. 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 3i x q*wlu rs1gpk+22l g*wof0..3 kW of heat when connected to a 240-V source. What must be the resistance of l+ 2kgl* .1f0gw qur2pwxiso*the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V pfxly p u7v*ber o9n6:+f5a p,tortable CD player that draws a maximum of 320 mA of cun5fape:rlb,x*u 9v7+yfp 6to rrent?    W

  What is the maximum voltage tham/rxcc0 ,cd hdv1fn6,1w j)x at can be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current 3 ,xzj1cy.lhbsu4 xjd;; y pw0through, a 75-W lightbulb connected to its proper souruc 3x. 1lhyj;yd,4w;p x bs0zjce 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 heli zob w mz jvm*6mu;gt1;ox-7-3 nr0eater is rated at 110 W. Calculate
(a) the current through the heater when it is operating,    A
(b) its resistance?    $\Omega$(Round to the nearest integer)

  A 120-V hair dryer has two sg) *n, z6*,numjnxlhaettings: 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 hn wz7txnr/ z/;omes at 240 V. If you use the lightbulb in the t ;z zrw/n/n7xUnited 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 proportional to power consumed.]    as bright

  How many kWh of enerc3.2; dp zarbqgy does a 550-W toaster use in the morning if it is in operati2.p azrb cqd;3on for a total of 15 min? At a cost of $9.0\,cents/kWh$, estimate how much this would add to your monthly electric energy bill if you made toast four mornings per week.
energy $\approx$    kWh
cost $\approx$    cents/mouth

  At 0.095 dollars per kWh,b*- ( 9,nqk3mu1(d ku jryutck what does it cost to leave a 25-W porch light on day and nightt1(,nrmkkd bq3y -u*jcuku( 9 for a year? $\approx$    dollars

  An ordinary flashlight usebj,khsse9n v. w;us)l6/ *su8q3kcnj s two D-cell 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 m 8ss)qn.ewk hl3bu*6 v9;cn/js,jsuk A when turned on.
(a) Calculate the resistance of the bulb and the power dissipated.
$\approx$    $\Omega$(retain one decimal places)
   W
(b) By what factor would the power increase if four D-cells in series were used with the same bulb? (Neglect heating effects of the filament.) Why shouldn’t you try this?   

  What is the total amount of energy stored in a 12-V, 6sr6dxmco8cr .mn bc/, qmhudb6077h 6 fm9wn$85-A\cdot h$ 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 us0acgq)ae 12zped without blowqzce210g a ap)ing a 15-A fuse?    bulbs

  An extension cord magadkw;bny0m*+.o-mr u /i+t bde of two wires of diameter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electr+/ ur;k0+-. bmbt ong*i wyadmic 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 factorybo v.gzs vb+0o w13c1zgixm hh,y,t43 through wires with total resistance sgb.o1gz,cmb3z10hv3iywth 4v, x +o$3.0\Omega$ 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. Ap/,pnphj s h.(q 4ce*tt what rate must cooling water pass over the coils if the water temperature i4 cpp n(sh/qt .eh,*pjs 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 oda54 1,re vwhof water for coffee or tew,rev5o4 ah1da. 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 current in apobl /)ao- i:c072hrwoc izc gfvc9,8 $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, is across a *3bz/ ,opf5xfxubw aqh9 v3yh 5dp96 d$330-\Omega$ resistor. What are the rms and peak currents in the resistor?
$I_{peak}$$\approx$    A(retain two decimal places)
$I_{rms}$ =    A

  Estimate the resista)w ezhto0(/u6yyoyw1 hf9mc*nce 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 1500-W device is 5.4 A. What is th+r, v1l;lalfwluez n *7b9od -e rms voltage across ibudl1-wf, lze nll7*rv + ;a9ot?    V (Round to the nearest integer)

  An 1800-W arc welder is connected to:r d:o5euf.j7 nyibq( a0fgr . 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 pum9d yw+ a2bg2dp:usd / 98rgouyp connected tw 8udgyu:2bdra/p 2s99dyo+ go a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected yjupg 4).syvzbxz9.), gvx+nto 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 ca7 x kj*znj,z6jp21o ftrries a tiny current of $2.3\mu A$. What is the electron drift speed in the wire?    $ \times10^{-10 }\;m/s$

  A 5.80-m length of 2.0-mm-diameter wire carries a 750-mA curia2h6)zqby4 i ,j lbd-b9,rptrent when 22.0 mV is applied to its ends. If the drift s-9b ,rb6tp,ibhy ij2a4 qlz)dpeed 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 2g1t 0hppz+o rln99 gqamzwz k6f -;k2atmosphere, $He^{2+}$ 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 atmosphere,is f*ryfw* rf29n jn;, $He^{2+}$ 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 lp+/qa0 )/q;z w0 rfamtnr o3umembrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with an electric sdrksjcl:dj j*hk25++3,oblpulse. 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, the time required is 0.0063 s. Whatc +sho,s:+ 5rj*dlkb jd2 jl3k 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 potential a n8f.7lxx p4phil*gdmjgq7 ;2 long the axon of Example 18–15. [Hint: the energy to transmit one pulse is el j47hg8xgq; .pil * 2mndfx7pquivalent 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 potetwd z 8 qa7l9)-wjvxp4ntial, $Na^+$ 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 hrh as:49p5g,6ksf + ik 5 6igvfd(bldin 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0-h59 t7co4rj jxnp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. I(6;cn xm eb3bv 6l7 ci(rh-ksaz 4c1tef 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 batte31 7ka(4e 6xb rnice;h(sczlcbv- mt6ry 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 d0a x2fuq6e)z 1 m 1b3y2gvg;eckp6x t5.4 m long. If it is made of iron, what must itgxp1226dkt age; x yqv) 1bu3c6fmze0s diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an/okr n9 pi .tlfysh72abk- ()d object is defined as the reciprocal of the resistance R; that is,. poksdki2)y l(h-ra9nft /b7 $G\,=\,1/R$. 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 -)6 neqfgw.0q)a ac rlof 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 per meter. A.gc)l -)rfn0a qqw ea6ssume the cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular househo1 tw,3rm+oejxld 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 n+fj1ovtot/ xu ( /0ogf1ij3k6gl5 os half and the two lengths are wrapped together side by side to make a thicker wire. How does the resistance of this new combination compar on if/0txg6 lg /t1(5oj+ o1ukov3jfse to the resistance of the original wire?

  A 1200-W hair dryer is designed q a1ptl;a en;/for 117 V.
(a) What will be the percentage change in power output if the voltage drops to 105 V? Assume no change in resistance.    % decrease
(b) How would the actual change in resistivity with temperature affect your answer?

  The wiring in a house must be thick enough so i n n+asqel,l)p3evf +5t does not become so hot as to start a fire. What diameter must a cn5+qfe n)l ,s l3paev+opper 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 equa(a,gbqv; gtm 2tion $I\,=\,1.80sin210t$, 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 eneriq)dtc7qk+. ot: o il3gy per second to the interior. Find tqq)li7ito. 3c:o+ kd
(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 mat 3x6 z:jvmku+b5 oliv4erial. One conductor is twice as long and twice the diameter of the second. What is the ratio of the power transfv3b+k z6 4m:olv5 iuxjormed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to hea bmcq3hp5t t..t 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 toh o ihnics v,)s6(,pk. a 240-V source.
(a) What is the resistance of the oven?    $\Omega$
(b) How long will it take to bring 120 mL of 15$^{\circ}\,C$ water to 100$^{\circ}\,C$ assuming 75% efficiency?    s
(c) How much will this cost at $11 cents/kWh?$    cents

  A projected electric vehicle makes use of storage batteries as its source of en. q -ill,xu6jv)hx7ucergy. Its mass is 1560 kg and v-h .,x6)uc7lqu jxliit 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 resi. x e 8zmh z:i)tj8itse/ f,(*6hofkqvstance 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 Fermilabcb9pyq0qm i t 746ibe5jc r7/x (Illinois) is designed to carry an 11-mA beam of protons traveling at very nearly thi7bje 9y746r 0qt cx5bm/qpice 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 9p t+p.4l *xgcwqim-dcopper wire wi lcm-d4q*xpt+9 ip.g wth a 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 connart1m 7,j5u c)esdd1g ected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total lenu) 157rd smdjg eac,t1gth of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from afx60;m :p q+cwnfzm a(bout 12 V when the car is off to about 13.8 V when the car is on and the charging system is in operation, 0aznf;fwpq(mm+cx : 6 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. Lightbulb B i 68+ zu okonmbz4h:3tvs rated at 12 V and 40 W for uknm bzzo3o4 :vth68 +automotive applications.
(a) What is the current through each bulb? $I_A$ =    A $I_B$ =    A
(b) What is the resistance of each bulb? $R_A$ =  $\Omega$ $R_B$ =  $\Omega$
(c) In one hour, how much charge passes through each bulb? $Q_A$ =    C$Q_B$ =    C
(d) In one hour, how much energy does each bulb use?    $ \times10^{5 }\;J$
(e) Which bulb requires larger diameter wires to connect its power source and the bulb?  ----待选择----Bulb BBulb A 

  Copper wire of diameter 0.259 cm is used to connect a set o+fm) : yabrgv/f appliances at 120 V, which draw 2250 W of power total. ) ba+r/ vgm:yf
(a) What power is wasted in 25.0 m of this wire?    W
(b) What is your answer if wire of diameter 0.412 cm is used?    W

  A copper pipe has an inside diameter of 3.00 cm and an outside diameter of 5.gl n-3j3d8wkxn9l xx4 00 cm (Fig. 18–37).33w8nx9jll x 4 nkdg-x 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 lengtj+qu 3n4zsc /:( 30wr 2yhon7mldtbvgh doubles, by what factor does the power dissipated in the wire change, assuming it remains hooked up to the24 l3hm:d(cosn73b/wtvr+qny u0z gj same voltage source?

  A tungsten filament used in a flashlight bulfzch1 o yyxp8cc1;/b 8b operates at 0.20 A and 3.2 V. If its resistance at 21 ;8/fzc 8yp1ccobxhy0$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$