What quantity is measured by am) jxhc5u hbmn+8f./ z battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to :eg x b*n/s xf )a-ne7bqhl):la circuit, electrons flow away from the negative terminaqn)x -fbsh :ga )*l/eb xn:el7l in the circuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battery current, batteryx2kqf av; 3a1j voltjfa ;2 aqkx13vage, battery energy, battery power, or battery resistance? Explain.

One terminal of a car battery is said to be connected-n8t9-vagw 10ovmps0x3ku osy o;xz 3 to “ground.” Since it is not really connected to the mxxoy30 1vvok8n aw-ptzo3; 0gu ss9- ground, what is meant by this expression?

When you turn on a water faucet, the water usuallqu 813gw os h7,(tgysay flows immediately. 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 to the terminals of q 17tywa ,shu83 gs(oga battery?

Can a copper wire andv, z-jjy 3,m(ofks/fi*yxe 8f an aluminum wire of the same length have the same resistance? Explav femysfyxji, (,z8 oj*3/f-kin.

If the resistance of a smay v jg*q0o23d7wg h7wq)/ qah3xxcd k-ll immersion heater (to heat water for tea or soup, Fig. 18–32) was incredvx)q h wk7q yc023doggh/q7 3ajw*x-ased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a,k: k+ -y7vwz*qa c5bsj and 3a, how would you *q zs yc-vb: j5a7kw+kconnect 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 c,r p6/hh6d8-bi j v(lrz.iyhburns out?

Explain why lightbulbs almost always burn out just as they aro4 8)1sl(zx aed8csz obo q9t*e turned on and not after they have been on for s (dbe oxloaoszq c8*t14s98)zome time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which has the. z4uo1z 6mvl:ld y ;poo;m d2umt/+ct higher resistance?ozmcuo2t m4 ;;u:zd vtl1l+ dmop6/.y

Electric power is transferred over large distances at +tyg2jvushc4w8p;3x46a( cpf j fg d (very high voltages. Explain how the high voltage reduces power losses in the transmissy243p ( jhga(s8f v+4fct;cjx pgdwu6ion lines.

A 15-A fuse blows repeatedly. Why is it dafw oq8m bg)t(,ngerous to replace this fuse with a 25-A ft f8) ogw,qbm(use?

When electric lights are operated on low8usiin lll) 6qe.n3i:-frequency ac (say, 5 Hz), they flicker noticeli)n l n lii6uq8.:e3sably. Why?

Driven by ac power, the same electrons pass back and forth through your reading g 6glb devhs128gvp;. f.7wqblamp over and g8q.h.wsld1 bep g62v fbv7;g over again. Explain why the light stays lit instead of going out after the first pass of electrons.

The heating element in a toaster is made of Ni 37ljl n3.ds1mp 2kgl*g8j yzschrome wire. Immediately after the toaster is jp3jd8ys2l 1lgz7 *mnsk3l.g turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up is 0 tan1:ef7ipn a resistor? Explain.

Different lamps might have batter 8:7k/9 fflew;yoxsvqies connected in either of the two arrangements sho;l y f/wfxvs98q7oke: wn in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A fl s5*52.)kd w7 bpqtyps l2epkiows in a wire. How many electrons are flowing past any point in the wiywp s7e.*k ppt5lbs5 d2)2kq ire per second?    $ \times10^{18 }\;electrons/s$

  A service station chadh,n hb, 6-ukkri:9pk a7rq+orges a battery using a current of 6.7 A for 5.0 h. How much charghd p9ah76,i,qoknu+b kr -:rk e passes through the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes za1/4hhse(p hif $1200\,Na^+$ 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 produ)e qy37b alarp6(p:lqs5aa y /ces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current throwzx+y1z *v jk1ugh a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugge7mx bm9r9qegv6 bg)e6d into a 120-V line.
(a) What is its resistance?    $\Omega$
(b) How much charge passes through it in 15 min? (Assume direct current.)    $ \times10^{ 3}\;C$

  An electric clothes dryer has a h;u2 mn85xm ;mzlyk suwb.4,axeating 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 cs)ufng zi ety7 +y.70x w3iek-onnected 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 ele7a)q8 ;4i9oxdb9f+dtgkffclctric transmission line carrying 2800 A (Fig. 18–34). The lineo ) 8fgkaqxf+t c9 dbdi;9fl74 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 b dez/*ko.u1tsm7+ja .50 A at 240 V.
(a) If the voltage drops by 15%, what will be the current, assuming nothing else changes? $\approx$    A (retain one decimal places)
(b) If the resistance of the device were reduced by 15%, what current would be drawn at 240 V? $\approx$    A (retain one decimal places)

  A 12-V battery causes a current of 0.60 A through a 0b83rin72rdec6 us pi s3egq5resistor.
(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 lenw 5 x;i6neeq9tgth 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 w:wod8bcm8d0 j8v is0 diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m ojdz3rq eo m7c q h3 pt)8;tnp)(b re+:nv9h;xyf aluminum wire 2.0 mm in diameter, to 20.0 qm hy9 vdpb htx8)7jeo(nn;)pre3zct +: ;3rqm of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as ah12b qciu0ua4fa+x p4 tungsten wire of the uqu0a 1bch42apix+f 4same length? Give numerical details.    mm

  A certain copper wire has a resis6hs6c6 afjtmu: .8p vttance 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 (originallt( b1,r, w+xcsfxa bmvjm(fc5 5 (dv.ny at r(cwxxdmcv,fbj .as+ ,mt 5n v(f51(b$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature cop j7zh6w,q6fopper will have the same resistivity as tungsten d6fqhw j ,p6zo7oes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has.x l* ebtwz9ja(i +s7k 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 copperc l3 q j aftz+b1)u3wbyb3k+5r wire (used in 15-A circuits). The wire has diameter 1.628 mmtr1wj3z+3c u 5kb)bl+3qf a by and carries a 12-A current.    V

  A rectangular solid made of carbon has sides ofrv ow3oqk xt 94:v1mi8 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 thwtv1qi3 :m89r vkoox 4at 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 refk q5s6 g8etm2/ viqn.sistance. If one has twice the length of the other, what is the ratio of th sgiv/f e8nm2qqkt.5 6e diameter of the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connsaz /: do:n8atected to a precision 10.00-V power supply, and a current of 0.4212 td:zason/ a 8: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 copper followed (ca :6o+ezwrbby 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is placed across the composite wire.6o:eacrz (b +w
(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 1cqam:* is(z8ezr4 xbaavm 7v7;j)xgthat the value of a resistance not change with ez;7zg7sij avc)x(vbam*qmr84:1a x temperature. 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 ofcr6rp vub908j an electric oven is designed to produce 3.3 kW of heat when connected to a 240-V source. What must be the resistance of the element? crb jp6 r9vu80   $\Omega$

  What is the maximum power consumption of a 3.0-V portablegomswae8 lzxlk,9. n67 we /i* CD player that draws a maximum o oiee7aw k8z/l 6.wn*9 xsg,lmf 320 mA of current?    W

  What is the maximum voltage tha07z)w o;ghaq2a +ujz vt can be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resisk9eu)t0treu7 9 pn sc2tance of, and current through, a 75-W lightbulb connected to its e7nuke)rttc9 20up9 s proper source voltage of 120 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heater is rated at , j(yq ii*) ginybi60zqv kgfi(s. ;h1110 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 222dpzo*xde me i9 govv--c . ajfg8a9W.
(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 Eurol27z v8 ajd;ka y c8vd6rrqu,nh44) mdpe, where electricity is delivered to homes at 240 V. If you use the lightbulb in the United States at 120 V (assume itscuv44hlrzy dq;d ,karv 2)d6n 8m78ja 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 energy doenw-farab g2( iwz- i f*0fexa0a ,2ti8s a 550-W toaster use in the morning if it is in operation for a a2i zb2ae 800 fg,rnxiw fw *-fta(ai-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 seu)paf :xvk4 p gpia939g(* 0rt4ntalight on day and nig4up9) (t a*f40:genrkps39t gpivaaxht for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 18uba b9 ww.p/-ovy0y f amis2br4p, / ne-cx6g.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when turned on. 2e0i6.,f8p/ rvy b9ox/ mwwnu -pcsba ayb4g-
(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 kv2dq5cy 0bj6u *d nylvd:0:ya 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 aq a(t2 wgv :rju*d2 eeaej9/la 9qi8v6s in Fig. 18–20, can be used without blowing a 15-A fuse?a8djw2 *:v etul6/rag 9ve2q(q9 jaei    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 copper w/ yld :vw0t p0ttmf*6mef)up( ire) and of length 2.7 m (w*0 u )d/f0 fmt(6:ptyp tlemv9 ft) is connected to an electric heater which draws 15.0 A on a 120-V line. How much power is dissipated in the cord?    W

  A power station delivers 620 kW of power at 12,000 V to a factory throu.vy 7jit) 8ko lo9lc+vgh wires with total riv) 9l+yv oko87tl.cj esistance $3.0\Omega$ 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 1ac ov a5q4ad+n/ +-gsx7.5 A. At what rate must cooling water pass over the coils if nd 4ag v+x-acos5qa/+the water temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to heat a cup of wm9*iyao0s-9j qes 4dasvj6 2later for coffee or tea. If the heater can heat 120 mL of water from 25j a vldjq46m0s as-9isy*9o2e $^{\circ}\,C$ 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 insk2bamrox9(02p ginmn55 4yj a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, ib) i5r:n8h5nkh ay0vm6t h 3pgs 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 resistanc9nk avyipsl. pr,k;c;+ )v :mkup+uxd3qb a8 -e 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 coyeaxz bsoyngk 3slh7s9/+.p0/ 3i+ the loi yax9bg.73ck /s ps/n0zos+y+h e3rms voltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected to a z /hvc.k/3cuf$660-V_{rms}$ 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 d2dhcysr+0enx 72zab ; vn(9zzptu/d/ issipated by a 3.0-hp pump connected2x0rudtz zaz (hpv 9+y/7n cb;/s edn2 to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to vqwc+arz:1q o2x2fb: 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 tinyhslt1p (xkbz64v-wmpz*c2wh 8m h- z( 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-mvmf yg0maqa/mu; /4 9nig6wolhh,8tb):lr 8dm-diameter wire carries a 750-mA current when 22.0 mV is appliedg)b0/8;4 w8:h6 dnfl,lymoi q9ut gmhr/aa m v to 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 atmospgoboc6wk2/a1t gte 08here, $He^{2+}$ 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 - 5(akzws0pvndmy,7y9 waz t 9atmosphere, $He^{2+}$ 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 elex 9 e5vv,r*rmmctric 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 po9;us bcx)vp s6tential 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. What is the speed of the electric pulse along the axon? (Why are two measurements nv s9bsu 6xcp);eeded instead of only one?)    m/s

  Estimate how much energy 4w9/so k-jnetp5y4t nis 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 by charging the axon capacitance; se/9knjeop st4t- yw4 5ne 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 potenti7ho(rqsvh t *;6lc vh3al, $Na^+$ 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 auc27w+umxw34pmdx e 6mpere-hour?    C

  What is the average current drawn by auqm52ix16: hr7ng2fo d3m , ugnyuw)j 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of the (ew4.ivnf/rctwo headlights uses 40 W and ef4rwvic . e(/nach of the two taillights 6 W, for a total of 92 W, how long will a fresh 12-V battery last if it is rated 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. I-ri.bsu)r 9rm w7a h.if it is made of iron, what must its diamu-rm7)s.rb ihar.i9 weter be?    $ \times10^{ -4}\;m$

  The conductance G of an s0ph7 nkd4itps625 .jzgz0uuxhq t g 2e/2,gaobject is defined as the reciprocal of the resistance R; that ipki u h42gs27 0 qt,ag.dzjg/enz6t0 u2s xh5ps, $G\,=\,1/R$. 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 ctq*, ymt0:;j5c bs3c c+ibenMW 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 e0 yc*5qn; c:ms3 bj,i tctc+blost 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 1.84 pdqh.z+ye:f -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 hkrdb 9atuzb3y1 l2-,calf and the two lengths are wrapped together side by side to make arlackd3b y9-b1,uz 2t thicker wire. How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer ioqr0f5-pwwg0u q imycwf249/ s designed 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 it does not become dpyw0xw 10 1ae vc+h;tso hot as to start a firp11ecthvwyx +;da00w e. 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 length?    $ \times10^{ -3}\;m$

  Suppose a current is given by the eq47k+lajn2pz)gt +a nnuation $I\,=\,1.80sin210t$, 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 energyr,mnln xx8z -+ per second to the interiorxm+, nnl 8rx-z. 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 maqe:y92 3ee;4ra+ht*ugb z )i v x7xatoterial. One conductor is twice as long and twice the diametx ;g7aib ue23ehtv)tz4 qaroex+* y:9er of the second. What is the ratio of the power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room nwr 0 ).*5l, wnoz;-msimikm0 t zc1zrof 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 240bl30t v)l4c ) 2d sjyo.)32wgw3gqjaf7qmcc c -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 batteri rkku(g:oadc-/dohj ;;s1:na es as its source of energy. Its mass is 1560 kg and it is powered by 24 batterie/dchk ( g-rusdj ;:1 ko:na;aos, 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 oka 9tc f qt3(xtocmm*53)ez u*f $12\Omega$ 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 po355, i6rduezne91n t4 dlsr hg*8ec Fermilab (Illinois) is designed to carry an 11-mA beam of protons traveling at vesidrt59 nhp6n,z35e glo eud4 ec8r1*ry 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 co0pfn8/ p.t eth*crw 9gnnecting cord is copper wire with w .pne0t8hp*cf/g9r ta 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 95dav++. ge.r i2 lg)gfo W when connected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total len)rl. g f2ade+i.gov g+gth of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system vj1 ht: azs(8k -(mrkmxoltage 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 percentage doe(k1:krxa8m ( hj tsmz-s 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. Lmnl3; tlc8i2bo- pvam e ;)1ttightbulb B is rated at 12 V and 40 W for automotive a 3ipe1;b2tvtctall8mm -);no pplications.
(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 i fm-5qx6k ,;bt7bry kti8 rkd)s used to connect a set of appliances at 120 V, which dk kbmi rbf d;rk56t8t,7)x-qyraw 2250 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 .k450ylmzg:27tr fmmu 6 rogsrrw 0j3 inside diameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the resistance of 10.0 m 67 w rk0fmr.jy3m5 l0urogs4gmrzt: 2 of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so thatj.,owoq ;(zezkid : u; its length doubles, by what factor does the power dissipated in the wire change, assuming it remains hooked up to the sameoz: ;u,dwzki; q.eoj( voltage source?

  A tungsten filament usege-gm)nc5r2ja meic9 ii84p+d in a flashlight bulb operates at 0.20 A and 3.2 V. If its rere8c nc-)ie mpaj mi5g+2 ig49sistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$