What quantity is measured by a battery (;npmeju;6*z3 irtm7smrb2 vrating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circui(l 4vmb .ggx,ct, electrons flow away from the negative terminal in the circuit. But within thl4m,g. c(x gbve cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, wha zh2f) w2gx. /gyr zxvi40iqk7t is being used up: battery current, battery voltage, battery energy, battery power, /7kq0z wxf 2g4iiry2h)xg v. zor battery resistance? Explain.

One terminal of a car battery is said to be connected to “gro)0lfg8u zfl(iq2u l/(a;( uoic4b xtjund.” Since it is not really 4 (quo fblx;/fi)2 0juact(8 (g lizulconnected to the ground, what is meant by this expression?

When you turn on a water faucet, the water usually flows immediatgmlh.jpa e37pts m62wxd v62+ely. You don’t have to wait for water to flow from the faucet valve to the spout. Why nopgs2elxmj 6.m7w2vh td+6ap 3 t? Is the same thing true when you connect a wire to the terminals of a battery?

Can a copper wire and an aluminum w: im(6vd4wotss.a fm+ire of the same length have the same resistance? Exo(.t4v+ :amiw ms6fsd plain.

If the resistance of a s .ij ts366h csip/p.fhmall immersion heater (to heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the heating process? Ex/ct3p .pi6sj hh. sf6iplain.

If a rectangular solid made of carbon has sides of lengths a, 2a, and 3a, he nw7 t8w*gxn2*.)bwl itb3o zow would you connect the wires from a battery so as to obtain (a) the lbe7win) ngwtb z*t3.8 w2l ox*east 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 pp isz;9f-4bzburns out?

Explain why lightbulbs almost always burn ou/gn ,73evaxve t just as they are turned on and not after they have en/a,vx ve 37gbeen on for some time.

Which draws more current, a 100-W ligflqewb/66f5t7* :c oaj.glbmhtbulb or a 75-W bulb? Which has the higher resistanc lel:b/qbaf*wjcfm7 6.to5 6ge?

Electric power is transferred over large distances at ve tn ,b,35t ply46g y.*bvtuoyb5py zz-ry high voltages. Explain how the high voltage vyp*tyug6ytl4b y o t5-z3b5bpz ,n., reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why 2ejd ;tx1blh,.a in0 qis it dangerous to replace this fuse with a 25-A fu0,e ah1tnb qxl2;jid.se?

When electric lights are operated on low-frequency 1us.mbqo kz9ai(f *+qnqc)u-v ly7f+ac (say, 5 Hz), they flicker notic+v) facq*yk9uq i+ fm-zqbo7n(ul1.s eably. Why?

Driven by ac power, the same electroa. ck mjy,bje3:4qr,x ns pass back and forth through your reading lamp over and over again. Explain why the light stays lit instead of going out after te3 ,:j,a kcqbj4 .mryxhe first pass of electrons.

The heating element in a toaster is made of Nichrome wir:9y og-jv 4:dm-cj 0ntm*ode9w;mvi ue. Immediately after the toaster is turned on, is the currentnu0dij9vmc; :e 4 m:tmgvj9o --y* wdo $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up ini zx) j3eiy;/b1e,eph a resistor? Explain.

Different lamps might have batteries connected in eiix4z p/otbj 9*ther of the two arrangements shjo xp4*it/b9 zown 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 pa . npxds8p9 ,)d j4 opoonu9a(8*ovucbst any point in the wire per secp ()9dx4o. 8ponc9ad n ub8o psoj*v,uond?    $ \times10^{18 }\;electrons/s$

  A service station charges a buff osi12 h8y9attery using a current of 6.7 A for 5.0 h. How much charge passes throughff2o8s91yh iu the battery?    $ \times10^{ 5}\;C$

  What is the current in amperexu69+4fssqs6 e s,lq ws if $1200\,Na^+$ ions flow across a cell membrane in $3.5\mu s$? The charge on the sodium is the same as on an electron, but positive.    $ \times10^{-11 }\;A$

  What is the resistance of a toaster if 120 V produces a current s1c q 8:3tqlv hh6js/uof 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current throuly n0kna,4t).3lrg f cgh a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged intoop8 joimer :khp6 75 z2tbm(-h 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 dry+p7us4utu(7 gr1 oma tuaxm/5ohzmw .u.v+b4er has a heating element with a resistance of $9.6-\Omega$.
(a) What is the current in the element when it is connected to 240 V?    A
(b) How much charge passes through the element in 50 min?    $ \times10^{ 4}\;C$

  A 9.0-V battery is connected to a bulb whose resistanc:4(b 70k8pk htldf rohe 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 (Ft;02,q6-e jtxzkf2sb bhg x -fg*3u0wtiz-zeig. 18–34). The li tz geqf0es3-t ujw f6;,zi20z-ktxb2*hbg-xne 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.l 1xm i4o1l;it50 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(usjt 0.ck g;l2hdv0 2(gnwjc 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 resistance ijzw- 5w1tj, huog9 5fns $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper)qv ( e+rbn5l,n)covpt- 5vtd wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resic4f6wm62bu io(g s2.pn6j h pfstance of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in diam fui .c h2f2(pb66ngjm sw4p6oeter.   

  Can a 2.5-mm-diameter1 4,bmx; - eqg(rdfwsq copper wire have the same resistance as a tungsten wire of the same length? Give numerical dwm -qerq1x ;s4f(dbg ,etails.    mm

  A certain copper wire has a resistance4omuq1az,(xzcto 5 vf ig0h *eh0 r87s 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 (originally1n5ml6 1w2ic9, kuflehokl g8 ath 2lm5unwlk1cfek1lg,8 6 o9i $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will ha*4g ihxf-sb.2 7nqvi5 7slunove the same resistivity as tungsten does at siis-glhf7xo *2nvq5 n 74 b.u$20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance ofc,s: w.x0 wae6 s) bvnul:mnu) 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 leng9ki*dtn32w gvj :m82+ior o lmth of household no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm and carries a 1vm: ntg +irl83i*2d29mw kooj 2-A current.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm, 2.0 cm,akf)+ohpb 6nhk0qg . m8bp39i and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for current that passes throughihbb+q 9f)kap 68 h03on pg.km 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 resistancd76+iqa 4 oesfe. If one has twice the length of the other, what is the ratiqde6a 4+ f7ioso 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 1of+s, m*7 uazn*i in3 2nm7jih0.00-V power supply, and a curren2z3iu7na ,7* mni+io f*mjshn t of 0.4212 A is precisely measured at 20.0$^{\circ}\,C$. The wire is placed in a new environment of unknown temperature where the measured current is 0.3618 A. What is the unknown temperature?    $^{\circ}\,C$

  A 10.0-m length of wire consz 0dspbqx8- lewq4 .b3hy.fmf lf9 ,x:ists of 5.0 m of copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage differencx3-.0 pd8qx fb: hly.b mzlf4wesq9f ,e 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 resisudnp) 1vz 57zttance not change with temperature. For example, suppose y z p5)7d1vutnzou 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 pro ox/h6 )dhr:1mya,z a 0;yrqchduce 3.3 kW of heat when connected to a 240-V source. What ;a) 0rr/ohdy hz cx:ha16 ymq,must be the resistance of the element?    $\Omega$

  What is the maximum power consumption olg dcwq1;9jt(agi g ;,f a 3.0-V portable CD player that draws a maximum of t1(dgg ;aw9lgi;, jq c320 mA of current?    W

  What is the maximum vov(g x+s /9huvxrq( ui(ltage that can be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and currenu4hf7 hb dk15m;o.6+ ru nzaq*p)egpb t through, a 75-W lightbulb connected to its proper source vohqu gu)z +4 k am1*6h5e.dnobrb;pp7fltage 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 sln 1 u255o*cac,/ltx rko0w)( rxwjkrated 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 ty4c6v e, oy2b3v yjavl.nv1z 8wo 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, where electricil4tp qwtb/i.1ty 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 be relative to 75-W 120-V bulbs? [Hint: assq/.wt bti1l4pume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energyd*(.:ftg;p ks ,z0 znf)poz0rxr vo;o does a 550-W toaster use in the morning if it is in operation for a ton0ppz*;,otgz;. )kf vszx 0oodr r(f :tal 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 kWsoro 6*q4vionq6k3 .jh, what does it cost to leave a 25-W porch light on day and night forki3q66o*.nqorj 4sov a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batterip8cmwdnf j,;k /xm6u+es connected in series as in Fig. 18–4b (Fig. ; /fm 6xkjd+mwp8nuc,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 stoixws,(g e n8k ,xzc 7f txs.x/t0n3-xured 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 120 V as ga a l53km-5 cbv0gcl:in Fig. 18–20, can be used without blowing a 15-A f3kcv-5 5 alcbl:g0m gause?    bulbs

  An extension cord made of two wires 6 294t vhi-jd5xma+(q7vj mwm nz (vlvof diameter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric w-lv2hmtjx 9i(mqm5v (n+ 4z 67avdvj heater which draws 15.0 A on a 120-V line. How much power is dissipated in the cord?    W

  A power station delivcq.h6p 4 u0me 1huwogdyrspp.jg),:6ers 620 kW of power at 12,000 V to a factory through wires with total mewgc u14y:od66u gp pjsrh, 0.)q.hpresistance $3.0\Omega$ 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 w7mn-c 9tb:lkxsgf- -hhat rate must co sh-gx9b-7n:tlm-f k coling 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 of water for cofo+-+s; n8va i2ts0nq egra* cwfee or tea. If the heater can heat 120 mL of water oqsc0 +ast- e2 win8g+a*v; nrfrom 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 cur9nlu;sr6k 5 zc3bhj0rrent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 18f +gwillq9;8 i dj*pi:0 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*nxwfmxcmpd )f11( w7 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 i qrt 6j07yqnva.6-wmtn a 1500-W device is 5.4 A. What is the rms voltage acrj.vqt 066yw rt 7mna-qoss it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected to +2g, ar2-6 plj cs+)yjnculp(qms)e ma $660-V_{rms}$ 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 3.0w-+rg 58a;n6qkap s ue-hp pump connected to akq;gwps+ 8e 5a6run -a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connecte;/.meq0fdj 1oij7ghy d 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 wirei dh82xr g6/mh carries 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-1k 9ki 4 ap ynoyrqk4 a+vcjt0p *d5*)skzvt62diameter wire carries a 750-mA current when 22.0 mV is applied to its ends. If the drift st0yq51p*v 46 rzsdok9nj kpav*kk i c2y)a+4tpeed 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 atmosphere, w vrp 503a je5-igt-dvb4pm7y$He^{2+}$ 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 atmosph,e-ozi w0s:bb ere, $He^{2+}$ 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 suz+iqu ;(, c4 hqcon;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. Th ih r yyt-yppge3)g2d8-os :lg.jt.e i-s94mhe action potential is detected at a point 3.40 cm down the axon 0.0052 s later. When the actgh pi83l. rmye-o 9p)ijs s-.gyd 2 4httg:ye-ion potential is detected 7.20 cm from the point of stimulation, the time required is 0.0063 s. What is the speed of the electric pulse along the axon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much energy is requiredp;,+3o d) q rt3aigejnup8.s y 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; see Section 17–eyg3 sd .n +i83a,t)oupjqpr;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 potentialq, cc e k:e/ukh1x/-8by 3bgm+vx 0xeh, $Na^+$ 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 1.06b1ni9* t u-1s0swr0 qezryb-mw/ bhr0 ampere-hour?    C

  What is the average current drawn by a 1.0-hp 12pvg9r8+ 1tytkxs8 m8n e1u)qmhal +t*0-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each ofdk,r,empf- 1ur8k/kx the two headlights uses 40 W and each of the two taillights 6 W, for a total of 92 W, howexk,drpf ,ku -r 1m8/k 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 heate llc0wq1a(1ufdxo l mxv:9 /bmnu,m -4r is 5.4 m long. If it is made of iron, wha 9x1ulon4(1bc:l /lmmaqw 0x-v,dmf ut must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of the resistancm8yac2dyp+jpt +l/ ra d2y) 3we R; that is,)22 mtw pay/dpd y+ l3rca+y8j $G\,=\,1/R$. 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 M6 6uhwtc+ yol-W 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 per hour per meter. Assume the cost of l-uc owy6+t6helectricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular househo*(uo0boq xza/0wkog (ld 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 tog*4bu uhjj+ j u:e4 m(sr,y4nawether side by side to make a thicker wire. How does the resistance of this new combination compare to the resistan4+*,4h4 jb aj wuu:ynmu(srejce of the original wire?

  A 1200-W hair dryer is amagd25s6 )gi+. tpb ghic85g 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 beco ks+iqoeby6+ /q(sj7 yme so hot as to start a fire. What diameter must a copper wire be if it is to carry a maxi67oe jsbskq +i+y/(y qmum 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 y qf9d z:66t1:poykq- qn 6uttthe 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 energy per sec,7k,yt szrkiaq3ndt s p:/d;7 ;w8 aslond to the inte tqs 78t;s dw kanrp3 /sad,:yk,il;7zrior. 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 materiakepna 3plj ua9uz/j 7.f7,ro0l. One conductor is twice as long and twice the diameup/ ej9 rp0ja7onl kz a,uf37.ter 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 zstf 7f ya7a0,6hi;,m9ywaffa 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 sons.ltbps1 k9: urce.
(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 ve,q:2ouf bds(jsg,u ):ceagg:u:pp p:hicle makes use of storage batteries as its source of energys a ,g g2:::ed:ubfjopc,uppsqg ()u:. Its mass 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 hlxj)akh04i :nt -k -dbas a 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) 6vgm.(hp9xa lv5w3 x ais designed to carry an 11-mA beam of protonav.lpxvm9wa(3x g h 65s 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 -utww02;ttl4 v pdt.akpj;l ;12 A at 220-V ac. The connecting cord is copper wire with a diameter of 1.628 mm. t tw0u2v-j a.k ;dp;4ptlwl;t
(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 heatingox .i,th(x;hhpdsv4d pw 2l:; element is (4dhipdxt2h: ;;shwl vp, x. oa coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from about 12 V when the car is offm) svjpz; (mh/ to about 13.8 V when the car is on and ts z;vp(/hm)m jhe charging system is 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 7a,wj;qysf -(r xnvlv/u, f;n at 120 V and 40 W for household applications. Lightbulb B is rated at 12 V and /,jlf-yx;f vnqw( 7a;unrs v,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 to connect a set of app9u h8 v*e1etqpd/ff ocrr/7m7liances at 120 V,198mectp oue7/h rqdf /r*f7v which draw 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 inside diameter of 3.00 cm and an ,a-t.m f w)jshxvj y)za:3n +woutside diameter of 5.00 cm (Fig. 18–37). What is the resistance zv)y:a x+sm3. ,w t-)whjna jfof 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its6(xbaa 5 ry;rwp0 (ne v4,v4ambed)p e length doubles, by what factor does the power dissipated in the wire change, assuming it remains hooked up to the same voltage source?em vap5y( d ner (pwbe4a4r)xv6,a;0b

  A tungsten filament used i d4x2-xwbg;wb ntge.0n a flashlight bulb operates at 0.20 A and 3.2 V. If its resisexbdn.2bwtxw -g4g0; tance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$