What quantity is measured by a battery rating given d)may:355 :fs5mi wejcp 2wyl in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow away from the nsaon s7ab t2 ijor7p5/2g6)yg egative terminal ia7)ao gy /n22jgpsis7br o56t n the circuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operas 61vpej hr5r.ted, what is being used up: battery current, battery voltage, battery energy, battery po6eh5vs 1pj.rrwer, or battery resistance? Explain.

One terminal of a car battery is said to be connected to “ground.” Since it 6kwxavzcr10 upn4063a7j* yhrc ,ypa is not really connected to the ground, what is meant by this expr0,k*yxzhv4prw y auc3 c7n 6pj0ar6a1 ession?

When you turn on a water faucet,7 i ;43uzp 7ly, +zwk:wn)acy sfnfk4b the water usually flows immediately. You don’t have to wait for water to flow from the faucet valve to the spout. Why not? Is the same thing true when you connect azfs7u+yiafwc4 wk l :4 )yk;zp, b37nn wire to the terminals of a battery?

Can a copper wire and an w5su.7k j;sjvaluminum wire of the same length have the same resistance? Exjs;5j7sv wku. plain.

If the resistance of a small immersion heater (to heat water for tea orqur beu34.i b)zjlz; 9wosv;1, 3 cqnp soup, Fig. 18–32) was increased, would it speed up or slow down the heating process? csj.zr43po9 zq) 3 wvnl1 ;uie;, qbubExplain.

If a rectangular solid made of carbo)w rw w2lv6u;-yo9in un has sides of lengths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resistance, (b) the grr ; nl9v wwowi6u)yu2-eatest resistance?

The equation $P\,=\,V^2/R$ indicates that the power dissipated in a resistor decreases if the resistance is increased, whereas the equation $P\,=\,I^2/R$ implies the opposite. Is there a contradiction here? Explain.

What happens when a lightbulb burns outzl k q nqviiu51,f62a)?

Explain why lightbulbs almost always burn out just as they are turned :m jk+:l9f dfbon and not after they have been on for slf:m:f+k9bj dome time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which has th1sr:p .13bbut( pbnkte higher resik3 p.pu n1b1(btb sr:tstance?

Electric power is transferred over large distances at very highb f+3b5ntpn4 k voltages. Explain how the high voltage reduces power losses in the fnbt4k +b3pn5 transmission lines.

A 15-A fuse blows repeatedly. kb,tip;eo4z 7 Why is it dangerous to replace this fuse with a 25-A o,tz7 ;4kebip fuse?

When electric lights are operated on low-frequency ac (say, 5 Hz), they/r5 jm bny-b*sy l+g.it4a 5zi flicker not5sj+.t*iibbr zyy/ l g4m5na- iceably. Why?

Driven by ac power, the same electrons pass back and forth through your readincj9c:ym zq9(p:h42b ia aj h,jg lamp over and ove 2j qi(j:hm,ja hbyc4 a99p:czr 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 Nichromel5pek// l86dy -l chgu wire. Immediately after the toastegcu/yk 8l/hl -l56pder is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Explain.maj + 5phpw0: qppj 6:(ca)yzq

Different lamps might have batteries connected in either of the twoz3: vt)bm 7:mww3navh 9 juja+ arrangements shown in h j3z7:tb)a mvmwu 3:+ naj9vw
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 po n7xusstr yk :5ey5g+-8 dsn10z6yq dwint in dry6qxuz8w y 5+e0 s dkn17-:t sn5sgythe wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using z *.zwm,7n rgyykr(b9a current of 6.7 A for 5.0 h. How much charge passes through the batter (z*r9wym7z ,y gr.knby?    $ \times10^{ 5}\;C$

  What is the current v in5w4cow 0*z1ip*z fin amperes 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 1 f:i4yukdh cw,o6o7oa toaster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A f,foj.ig (z s6 p(-hyuof current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-V line.b htq (jkliri5i9i1o-u883 mq
(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 dryeq2 ;e3sxrc) rnjptv 61r 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 r8 kbd5j8+/c0zuk (v itd p;hakesistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electrmo(kj3f7f tn2veca5+ic transmission line carrying 2800 A (Fig. 18–34). The a2mcn7vko +f (j35tfeline 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 ;2n8 -ojo yjgeA 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 residu+hk9dk r-imn,n q-)stor.
(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 resistan6 r+ ;1sf jb9kn1uztt 7,huqvhce is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1.5 mm in diame2*vet.03 s wzngo9z*3f ig:wgi0 tbpjter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resis:y b(r,is*.iutp0pyiuq. w, ptance of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in diameter. b,yy(piiqiup.0:urt .p,w* s   

  Can a 2.5-mm-diameterl 1t qh9jnf 1v:o3q5ny copper wire have the same resistance as a tungsten wire of the sam9l1 j1v yoqhq3nf:5 nte length? Give numerical details.    mm

  A certain copper wire ha1 w(t+2bwhdw rs a resistance of $10.0\Omega$ At what point along its length must the wire be cut so that the resistance of one piece is 4.0 times the resistance of the other? What is the resistance of each piece?
$R_{short }$   $\Omega$
$R_{long }$    $\Omega$

  How much would you have to raise the temperature of a copper wire (origingj 7 )c*c5z z2d (vjupiy,q.vw an7jr9ally at)7nj(iaqcg z9rc ydj,j.w v*u2vp5z7 $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what tempesuf ++,etzixy *68yq6rf1 euqrature copper will have the same resistivity as tungsten dy z6sey e+6*u if8truq,fq x+1oes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of abousnx;:.q m-.szwhcis f3oblc 5, mpl pw8r(,0wt $12\Omega$ 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 dro5jcsgd;0 u ob .xs1q/kp along a 26-m length of household no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm and carries a.o b x ;g0sqc/udjk1s5 12-A current.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm, 2.0 cm, and 4.0 ,nnauy 18w:kbc;c.p dcm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for current that pas1canc:8wd;.pyn ub , kses 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 hyq: rku6*q6jpa-h 17qf m/dzrave the same resistance. If one has twice the length of the other, what:fzpa jq *q/kurrqyhd 766 1m- is the ratio of the diameter of the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is cot arkai nk3q8t k6 k).-aok49fnnected to a precision 10.00-V power supply, and a current of 0.4212 A is precisely measured at k kr-kokt94n8.qia) a taf3 6k20.0$^{\circ}\,C$. 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 wirplud-.f,4xa e e consists of 5.0 m of copper followed by 5.0 m of aluminufuae dpl-,. x4m, both of diameter 1.0 mm. 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 applicationsf:wr ;p(wqaky vu;7qjq+tpx80j h,c;qlxv; ), it is important that the value of a resistance not change with temp(q; pw:chqujxwk; t0lrf;y7 x+pv; qj)qv , a8erature. 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 *g84:) kbvdoh clf/khheat when connected to a 240-V source. What do*: hvcl fk84k)/hb gmust be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portjkr 3rq/vcn4z a -a/g.able CD player that draws a maximum of 320 mA of curre q3c/ gaj n4-azrrv./knt?    W

  What is the maximum voltage that c p2y;p (impe;san be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, az+pkhcm 4(r eep5x3lr m95ks7 75-W lightbulb connected to its proper source voltak4p75ex59e prmc3 r+zh ks lm(ge of 120 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heate7uyupigbn5 *)r 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 lab ne k*d-+k4d5mr( vtwo 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, whe 9c;oobg 48l c+t 15t(tbvf)ib ol(tture 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 g( 9l5ov ;ot 8+1lt4)o(uitcbfb t tbcit 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 doesxdepdj- fdtur /004 x6 a 550-W toaster use in the morning if it is in operation for a totax dxfj 4u/e 0-pr0d6dtl 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 i*ylwv.kv tu1 6.iy8lgy+s ;gtt cost to leave a 25-W porch light on day and night for a yew18 .tt*lvuy.yi+ lky;g6 v gsar? $\approx$    dollars

  An ordinary flashlight1xyuaoh lb; f+q1s+s 0 uses two D-cell 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bu 0 +a qsuf+l;syhbox11lb 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 noxj3hnle:5. kv- x5y5 x.pe:;whcihstored 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 Vp4 8m)v*nyuha-+ onni as in Fig. 18–20, can be used without blowing a 15-A fuse8)-o+n haivmn4y* p un?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 coppeqj gr 1 0y-gj5st.khk5tz4 iv.r wire) and of leng0g-5sz iv.rk51 gh.ky 4jjq ttth 2.7 m (9 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 throubz d xy(:m-d3n* jw6n1s g.fyzgh wires with total resistfws*-zb n m.gznd :y6xd (1yj3ance $3.0\Omega$ 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 tofts,q m:7h:hb a 240-V line is 17.5 A. At what rate must cooling water pass over the coils itq ,:fh:hb7s mf 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 forfkq.v xg(i,th23or 4o coffee or tea. If the heater can heat 120 mh, 2ok.(4 gofqxtrv3iL 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.3,objikl eaix1(3 (bj1eg,hbf be s( a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, isk-. d/ik;p+wr jexc; 2uef .rn 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 resistanceek7 1rnru*r 3tkbn+sb09pf 4 p 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. s4ry/z2uid55+ l r.4ibj;gspjbb sa is the rms voltage acz. i2rsj;gd5ibp4+bj b /ysrs54a u l.ross it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected to 2v3a4)wp eztau hq, ldtx/:;o 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 maximum8p.fws3atwlnt+b77yyku2qcnm 3)s4fn g 3 l) instantaneous power dissipated by a 3.0-hp pump connected y+)tnkn8sysq lu33)7.mc pw7tfn3 2 b alwg4fto a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to a ; 7 v k27)ctxw9lkanoh$240-V_{rms}$ ac line has a resistance of $34\Omega$.
(a) What is the average power used?    W
(b) What are the maximum and minimum values of the instantaneous power?
$P_{max}$    W
$P_{min}$    W

  A 0.65-mm-diameter copper wire carries a tiny curr.ud;4drhl z cn7/)l rgent 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 *4 heemlh.;aowire carries a 750-mA current when 22.0 mV is a.h 4hemeao; *lpplied 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 atmosphere5vn0ian w+ to., $He^{2+}$ 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, cy x xp3ym-31eerapz3sy +n2db85h8n apb*k 5$He^{2+}$ 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 af y,2uu 2 1/kky6sm(e;kq nxuwxon membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated wi6 10mm xkrwm;9,a x iv5nwlwx9xo5up3th an electric pulse. The action potential is detected at a pwrwm30kmxw;nu 9xxoax5p lv651,m9i oint 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 needed instead of only one?)    m/s

  Estimate how much energyd71gv)b e*liz is required to transmit one action potential along the axon of Example 18–15. [Hint: the energy toez ib*17)d vgl transmit one pulse is equivalent to the energy stored by charging the axon capacitance; see Section 17–9]. What minimum average power is required for $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action potentq/kwiq. c; +ig+n/a;wjcf3,hu cm)r zial, $Na^+$ 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 ther pc3v(p1kd6e ne in 1.00 ampere-hour?    C

  What is the average current drawn bwnc.fy;w i(7h fo;mtbf 9nw,dh-f; , jy a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights od p/ gmh5fdj67n. If each of the two headlights uses 40 W and each of the two taillights 6 W, for a total of 92 W, how lopfh m6d5d/gj 7ng 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-Wk0c+ vlq i 2w/okyutqjig76 +9 heater is 5.4 m long. If it is made of iron, what must itsogq ++6 l7ivkw90/yc2tjqk i u diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as 4u(ygbpm3d+m.h wk 4olkki+( the reciprocal of the resistance R; that is, kpo+u( g i4.ymlb h mkd43wk(+$G\,=\,1/R$. 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 inst gm w2ppj u6m.r9)l;auead 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 electricity is about 10 cents per kWhp p2rmju .u)la g9m6w;.    dollars per hour per meter

  (a) A particular household usv ;vew. 3 1u: wwy7li3okkfe.fes 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 wrappe7/v:t ;jmb:0sll fuf ed together side by side to make a thicker wire. Hbvj:e 0 l/s;ulff m:t7ow does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 117/oud 9y ck +,e:mbtx+i 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 doecgi, 3gpw2 uwswb;1a n0fy; *hs not become so hot as to start a fire. What diameter must a copper,b wguh1 ;*3 swiyw2cg fa;p0n 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) r1u1sahpz *9p6 ikti,dsqa4 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 of6wi*/onk dw4 qn1aod 5 energy per second to the intendia5k*d/61owowq 4n rior. 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 ofsc9ou) 9/:gmlo1zoggfxt g) + the same 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 relative to the secon fo )l1coxu)gg9gt:+/mosg9 z d? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat txc.y5u6u rf01x,p aza 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 hooke+qkyya)nall,2 j9m9 ;anyd,n d to 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 make(.o7iig :l2 2 vx4hmfdgnc,rys use of storage batteries as its source of energy. Its mass is 1560 kg and it is powered by 24 bm,n yx girf( 4.ghvc 2ol:27diatteries, 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 resistauyrntl7g 36) fnce 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 (I7zikg 1 awvm v,:)x0byllinois) is designed to carry an 11-mA beam of protons traveling at very gmk17v,:by xwa 0)z ivnearly 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 wi phhm-fahf r34 cc1(g)re with a diameter of 1.c1ch)hgra (-hm3ff 4p628 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 q/k (p jjqnw3bh-tf(8k7c nk7connected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What is the diameter of the wire? f-7qn3k 7b /pjq(kcwh jk (n8t   $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from about 12 V whesat 5)b:q /f l kw,nhml,4g8cdn the car is off to about 13.8 V when the car is on and g:ba/),lt8 klncmdh5 4fswq, the 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 at 120 V and 40 W for household applications. Lightpgp u353u te3obulb B is rated at 12 V and 40 W for automotive applicatio3 ptgu3pe3o u5ns.
(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 appliances at5+c6 rico;whl 120 V, which draw 2250 W+rwicohc l 5;6 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 jf/ ,hrr)eh(:h dlm3e of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the resistance of 1,/e: fr lhrmdh3)(hej 0.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its length doubles,a a;gbdy6p4year 9:j / by what 4e6aad /9yyb agj:;prfactor does the power dissipated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashli9yygumnp :r 2rdy2i;2vfu,h 5ght bulb operates at 0.20 A and 3.2 V. If its resistance a 9fpdgy; 2i,un :2yrh2mry5vut 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$