What quantity is measured by a battery rating(sz;z;ips;fp given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow aw1f)2oocq l; 1vlj6dgway from the negative terminl;fw)d21o1ovjcg lq6 al in the circuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operatfvtx-0zjd eug4 c:( /a dfd1bdm;9n q(ed, what is being used up: battery current, battery voltage, battery energy, battery power, oqg(dd txb- d0(c9/fj:4n1fdva mue;z r battery resistance? Explain.

One terminal of a car battery is said to be connected to “ground.” Since m:-5fru.se u4*uqzymit is not really f. ze*q 4yruu5 umm:-sconnected to the ground, what is meant by this expression?

When you turn on a wgnp.bvr( sl i07:n 7xqater faucet, 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 thi0pb. qsnlirv7x:g(7nng true when you connect a wire to the terminals of a battery?

Can a copper wire and an al1b a 0:(sknnlcuminum wire of the same length have the same resistan0: lc knans1b(ce? Explain.

If the resistance of a small immersio-k;. vf qhum/mn heater (to heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the ;uhfk -. vqmm/heating process? Explain.

If a rectangular solid made of carbon has sidespyqltxh+scd)22f5 i*t;2 id w of lengths a, 2a, and 3a, how would yo)tdli25 xhfsd w22; py q+c*tiu connect 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 b6/8maq2yh c4cfgsg c:urns out?

Explain why lightbulbs almosjs;cd3e8q*o e)ot :q4qxt2u rt always burn out just as they are turned on and not after they have been one *2 qq:;xuoe3)rsc8tj 4dt oq for some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Whirmmu3t8 ak)acmq9 3 v2ch has the higher resistanc32camk9 8ut)aqr3 mm ve?

Electric power is transferred over large distances at vnpc-c*j c 9 b+j4nk4 qt1sme3dery high voltages. Explain how the high voltkne *b pmn t3qjsc49 c4+cjd-1age reduces power losses in the transmission lines.

A 15-A fuse blows repeatd t4 a0qe)i esk4up+;gedly. Why is it dangerous to replace this fuse with a 25-A fuse?at)e4k+s e gidpuq0; 4

When electric lights are operated on low-frequency ac (say, 5 Hz), they flickt ns4(zhtz0 py i5:a/yer noticehsazy5p(: zy/4 i ntt0ably. Why?

Driven by ac power, the same electrons pass back and forth through your reading2;oij ziqwh73 4hpm+q lamp over and over again. Explain why the light stays lit instead of going out after the first pass of eliihp3z7; +o4hm2q jwqectrons.

The heating element if,9tb+i4hf 7:z hq.hhgzd /krn a toaster is made of Nichrome wire. Immediately after the toaster is turned on, 7 f :rb.ih ,k4hzh+hqgfz9t/dis the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor?(s f-bjg/a (ff( r:j,ptpdaszis- 8 r7vke.0a Explain.

Different lamps might have batteries connected in either of the two arra *,ynruywi 2x*ngements shownyi*rxw 2ny,u* in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A fmp/(kua,ci:kb;4 v tg lows in a wire. How many electrons are flowing past any poia gm(/4kv ;, pciu:ktbnt in the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a currentf6x 8oio5+n5af. uwra/ctf ,i of 6.7 A for 5.0 h. How much charge passes through the batfi5a+ ftocu,oxiw 6/rnf5a8 .tery?    $ \times10^{ 5}\;C$

  What is the current in amper0rhvi(pkt::ydh)f.;t .xueg es 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 ofxi0bgq+x*.s (ud efi+ a toaster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of currt 4ct.rv: gxg0ent through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged intsrtgg, 5tdpuz gow) j)8.ofwx a3n 83-o 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 heating element with a resistance of w06vw5 ;zbhxj $9.6-\Omega$.
(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 c:) nmy ,kkrvl r7k*t+(ffd:s y dlx(+tonnected to a bulb whose resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transmission line carrpxf,j3il9p p+jbhce0hpn 3k 7 *mjj.2 ying 2800 A (Fig. 18–34). The line has npj+7epi3fpj0plbj92k* xc ,h3 .hjm $2.5\times10^{ -5}\;\Omega$ 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 6.50ms.cwnzjmg/l p13-j: ah zkw8 u8e0( n 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 xydb. sbs5h.- +n5 eijcurrent of 0.60 A through a resistor.
(a) What is its resistance, $\approx$    $\Omega$
(b) how many joules of energy does the battery lose in a minute?    J

  What is the diameter of a 1.0pc spk c)5twec1g2;w10-m length of tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5p qo lij0u71qv+ :t8hhklb i)tq/sf8 --m length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire 2.0 mm in : fj7)lxyzmq- fy4u 5fdiameter, to 20.0 m of copp:lj)f 75x zyu4q fymf-er wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resista +o1yt ,wt6e t5oj4iclnce as a tungsten wire of the same leng64+i ct1jl5 y teow,toth? Give numerical details.    mm

  A certain copper wire has a resista q7anrsmr ,r7-nce 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 hpqatdek6 z; *y44 u*zzp1 uku-ave to raise the temperature of a copper wire (originally at 4uuzedqkk4 zpy6*1- *ap; z tu$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature cobf23iy;bb htv9 t 3ju)pper will have the same resistivity as tungsten d; i)3t3 h2ut v9bjbfyboes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance o( zxojp;x ,/ror,z 3u2vq y31vy n6gvqf 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 copper wig,9rll::c hnk*fn* nkror)7hg4m+t u re (used in 15-A circuits). The wire has diameter 1.628 mm al rcolhn rfrgthm+)gu* n7knk:9 ,:*4 nd carries a 12-A current.    V

  A rectangular solid mavh0 :uov8tp8seqxt(+de of carbon has sides of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (hpv0x(8:vs+t ue8 qt oFig. 18–35). Determine the resistance for current that 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 resistance. If one has twice the leng0:mw 5tt,dfv sth of the other, what is the ratio of the diameter of the longer wire tmsd :5ft, w0vto the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wirdc6 x)05 +7sof ytkkh)jcux*he is connected to a precision 10.00-V power supply, and a current of 0.4212 A is precisely mesc*t5 0xd)uh j ok7cyhk) x+f6asured 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 f/s6rx nh103uo 5czck followed by 5.0 m of aluminum, both ofcu5 3ko1hczn xs/06r f 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 applications, it is important that the value of a resista z*t js23 minrjp-(h 0c34r+xwp:qli pnce not change with temperature. For example, supphzlsxjp: t*qw 2ipr+(r3c -j3ipn4m 0ose 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 ofd9a9r2xtfdw/ iddc3 6 heat when connected to a 240-V source. What must be the resistance of the element? 2rcdd9xa d w/3fi6dt 9   $\Omega$

  What is the maximum power consum1lij2ofo ;lg + p1*bqrption of a 3.0-V portable CD player that draws a maximum of 3202ilb ;grqf+*lj o1 p1o mA of current?    W

  What is the maximum voltage that can be applied acf tkfpd(6g(a 4:qzu 9xross a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, a 75-W lightbulb connec/ .xz78s /e l9utmdyihted to its proper source voltage oxe9l d.u8thyi7z/s/ mf 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 110 W. Calc scx(f5epc ef6+b.zk7swxw) *ulate
(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 k3o/wx xkkb*ve.ai. ig+9 tcc6 k)8 xq cj;uy.two 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 electricikt m0q*8obuq8 ty 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 r*k mq08u8q obtelative to 75-W 120-V bulbs? [Hint: assume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energsz dm 2jq483og mqc:i2y does a 550-W toaster use in the morning if it is in operation for a total of 15 min? At a cost of 83g jom2qc2s4:dzqmi $9.0\,cents/kWh$, 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 leavco7-jw jl,8(9tkyflwqmm- 0se a 25-W porch light on day and night for a j wm(,lo9--m0j yw87lsqcftkyear? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected i *b2ce atk.0jm1plbmg fcd9 62n series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when turned o.fb 1g cjp c2el6dk2*b0mm9ta n.
(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 enba )9v g6kihtuzq8 g3,ergy stored 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 in Fig. 18–20, can be used with7awxtua35z *a:r 0 ia skmie39out blowint3awu*rkaea30 izima 957 x:sg a 15-A fuse?    bulbs

  An extension cord made og hx :9o435ist+uyc m hqr9ga9f two wires of diameter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric heater which draws 1 u3mco qxyg9 t59 sg+rahh9:4i5.0 A on a 120-V line. How much power is dissipated in the cord?    W

  A power station deliversfpt-z/.a do3nhb nwve0b (44 o 620 kW of power at 12,000 V to a factory through wires with total resistan/ vb-4 noapthn.ew43zof( 0bd ce $3.0\Omega$ 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 whz7 edvdm7va(zm g ,u7 /x;i ryso6,m v:tn(fa4at rate must cooling water pass over the coils if the water temperature is to r7d7vf d y,me ,;uzm:va(7nai6s (r t 4zx/gmovise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used ctuw)ei5tq/)txdc ;c6za5o5qyrn/9in a car to heat a cup of water for coffee or tea. c 5r5dqt n)9ozx6 5/ic/t;e)ct waquyIf 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 ik+c)r8gsdj h,7jd0 1 7urw( sljkox 5tn a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose pe-+g r ,itt+d caw7i o/zr(jld7ak value is 180 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 of thervbj q w2:)vmlv, qd50 $120-V_{rms}$ 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 inrk/a7q fvqan ,/j5xv t.hc2;e a 1500-W device is 5.4 A. What is the rmrnh qvv ekqt/x,a/c25 7j.a;fs voltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connek 4sol )8d+s56 amdnsdcted to a $660-V_{rms}$ ac line. Calculate
(a) the peak voltage$\approx$    V(retain one decimal places)
(b) the peak current.    A

  (a) What is the maximum instant(z,+s9pw . 1 azsxgqqr;qj2 gyaneous power dissipated by a 3.0-hp pump connected y9p + xzq12swrjg.qs,zqg;a( 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 q9fe*x xsm98pi 0;pela $240-V_{rms}$ 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 wirej-k9p +x yo-sk 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-diamtr,kp *vbu21vve/q ;f eter wire carries a 750-mA current when 22.0 mV is ap1 / v;,v2rvu*qftbp ekplied 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 Earthpyo 14 xogl,i/r+eff5’s atmosphere, $He^{2+}$ 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 atmosc4w/cmj-ca 3a h8y.fe 4ymv0ed(ed y(etb5j,phere, $He^{2+}$ 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 0kr -x,zwc0b.,bgdxox gp1 g 3field 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 electric8w5wed, t0 uuql o7f1c pulse. The action potential is detected at a point 3.40 cm down the axon 0.0052 s later. When the au, f0c1 qe ow78u5twdlction 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 required to transmf,l5asbg.v;dg b : po/it one action potential along the axon of Example 18–1 /pgl:s,afgd5bv .; bo5. [Hint: the energy to 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 potential, m3* 83th 2fbrkpmzi 3a$Na^+$ 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 7 g)l +hx-ivebq:v z)pthere in 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0-7q5 o2lsnhrex5y l5* nhp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of the x0 x5ct6ic, :fp5)yg7 exjnfvtwo headlights uses 40 W and each of the two taillights 6 W, for c: g65, exf 5jtv7)0xx ifypnca 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. In-wu g3hqu -x(f it is made of iron, what w3x -( uqughn-must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined a42xr):x6o(x,z4+tenx wyare 2o ww cm s the reciprocal of the resistance R; that ir4xw+w: w,zx m)e 2xxtyocn2are(4o 6 s, $G\,=\,1/R$. 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 t h4uh;;l/wprbhat 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 thehlu 4w;rhb/;p cost of the energy lost to heat per hour per meter. Assume the cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular household uses a 1.8-kW hea :hf/j iqp-+d0 r+rfprter $3.0 h/day$ (“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 torxabr2o.cbsy34y2 , t gether side by sid o 2 rbsbty.4ra3,c2xye to make a thicker wire. How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 1cnn8dn*v3/n2(tjrqkb .5 o gw17 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 hous +rewgr5/k t b0:kxa+ee must be thick enough so it does not become so hot as to start a fire. What diameter must a copper wire kre0r5ktxea + gw:b+/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 equa1dy4d +(ijptuo(z(gbsg eya*r7,7k b tion $I\,=\,1.80sin210t$, 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 ene7 thz4hs(q7y/d 2p/b x6+qnjwc4juyu rgy per second to the interiors chy unj+/q7w(64/4xjpqu27d yhb tz. 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 cw;s b6hp tjkj d*.y1xk( ( c2dwbluuv0e*o).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 re0jtkk.wj62 vhdlc u *.uydcxb o(b );*(p1ew slative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heatdg pjlq-;oo7q ez31 dlun,vr6.1:ta n 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 toj6w jk c66.tme 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 makvn8vf/,hit p( px/ua y95iv3g es use of storage batteries as its source of energy. Its mass is 1560 kg and it is powered by 24 batteries, each 12/(ui hvt/5fia ,p v3y8 vxn9pg 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 of: c8uvh8 2 :aa6tkwnub $12\Omega$ 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) is designed to carry an 11f t1:i xw/mnsaqam f.6swuo+0a /og53-mA beam of protons traveling at very nearly thomsfsamq.1u50wx6a 3t/aiof: n +/g we 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 Ah/b, ogl0j5g y at 220-V ac. The connecting cord is copper wire with a diameter of 1og lghyb0/j 5,.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 akjp9;znh2rb z.o3f0xtoh6, connected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total le23rokh,f;hjp0bz. z6on9a txngth 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 ofr e8.z))3qxqx s8bpd3q 5 ntnbv.:bjif to about 13.8 V when the car is on and the charging system is in operation, a difference of 15%. By what percentage does the power delivered to the headlights vary as the voltage changes from 12 V to 13.8 V? Assu8ebix3r53zqv:q pn8sjq. ntx )) b d.bme the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for household ap7bmsm 7n(4 tn8sw-p ub,fi+x bplications. Lightbulb B i( +-8s,7xwb mnubpt 47bsnmf is rated at 12 V and 40 W for automotive applications.
(a) What is the current through each bulb? $I_A$ =    A $I_B$ =    A
(b) What is the resistance of each bulb? $R_A$ =  $\Omega$ $R_B$ =  $\Omega$
(c) In one hour, how much charge passes through each bulb? $Q_A$ =    C$Q_B$ =    C
(d) In one hour, how much energy does each bulb use?    $ \times10^{5 }\;J$
(e) Which bulb requires larger diameter wires to connect its power source and the bulb?  ----待选择----Bulb BBulb A 

  Copper wire of diameter 0.259 cm is used to connect a gzon(keg8wh, 8 wpk.4 set of appliances at 120 V, whichn8h k,w gw4o8gk pe(z. 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 outside diametp64/wm q dk 8yydv-/zier of 5.00 cm (Fig. 18–37). What is the resistance of 10.0 m of thismq6 8zvy/d pk ydiw/-4 pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its lengyz*up5 j+)e prth doubles, by what factor does the power dissipated in the wirpuey)* 5pj+rz e change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operates at81 ub)1 cz8t5qqqac tvh/15fvo yo6pt 0.20 A and 3.2 V. If its 5 pqaf/ocy5q6 t 8bu18h vqt11vtco z)resistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$