What quantity is measured by a battery rating given in ampere-h2)sh qx.acuy542tic aem 19dkours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electm 9y,3r1fk hu1-vrvy trons flow away from the negative terminal in the circuit. But within the cell, electrons flow to the negative terminay93 -t h1mvf,v1rryk ul. Explain.

When a flashlight is operated, what is becd0d.4:kucq crw7f+ iing used up: battery current, battery voltage, battery energy, battery power, or battery resiskrf70qu ci +w:.c4cddtance? Explain.

One terminal of a car baaf mk; .c(g4s+1jpsxfttery is said to be connected to “ground.” Since it is not really cf;fcsj 4+xa.m psk (g1onnected to the ground, what is meant by this expression?

When you turn on a water faucet, the water usually flows immediately. Y3; 1se5ilxeon cfsw5e/ l *lt(ou don’t have to wait for wateeitl sle*1xn ;ofs5/ecw3 5(lr to flow from the faucet valve to the spout. Why not? Is the same thing true when you connect a wire to the terminals of a battery?

Can a copper wire and an aluminum wire of the same length have the same resis 6m)9qrxj. htbtance? Exh)q .6rx9mbt jplain.

If the resistance of a small immersion heaterlek1m3v hz3 :1a2ot vr (to heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow doo113htezavlm : 2r3 vkwn the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, and 3a, ho215) ,n:mqzh1iyb ubxliwh*ow would you connect the wires from a)zh1 blu*hn:qb1 xyi o,i 2mw5 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 burns o4dz(;qbz.fk(g0m : z p9dqkjs ut?

Explain why lightbulbs almost always(m6aff9cw u/ d burn out just as they are turned on and not after th9m affwc(u d/6ey have been on for some time.

Which draws more current, 1:si 6b.y( jsnobu:jx a 100-W lightbulb or a 75-W bulb? Which has the higher resb b:s (j1y:.jnio sx6uistance?

Electric power is transferred over9+4kp lr.buyp large distances at very high voltages. Explain how the high voltage reduces power losses in the transmission lines.9rypp.b4k +l u

A 15-A fuse blows repeatedly. Why is it dan8w y qdf/o1muwj;ixh l6tt(3s4 gn:5mgerous to replace this fuse with a 25-A 6wi1( uo8; n4lm3 yg:wt5xhqsj df/tmfuse?

When electric lights are operated on low-frequency ac wt3x*z q(hm w0(say, 5 Hz), they flicker noticeably. Why3m*(qh x0tz ww?

Driven by ac power, the sam1jnl wq)5:q.(8dgn iy5 jd-k fo:jygie electrons pass back and forth through your reading lamp over and over again. Explain why the light stays. :kgg)jj-on(81ddil :fwni5yyq 5 qj lit instead of going out after the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. Immediatel+ap44;vf 1a1wq3b ddfe.0 vxa;dpvery after the ta p re4;;0w41b1ved3. fv qaad d+vpfxoaster is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in-w*)6jx tkre j a resistor? Explain.

Different lamps might have batteries connected in either ecey8n5d. (l/kmj ;( jooba4kof the two arrangements 4 konc(j/ 58me.jlekbaod(y;shown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire.uw 4.0 p tenmpm66w7hu *kx1ap How many electrons are flowing past any point in t67 w*4.wmhn 60p1k tpeuuxmpahe wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A for 5.0 h. How wr/u+-fmfv o2 much charge passes through the battery? -r+ uovw/fm2f   $ \times10^{ 5}\;C$

  What is the current in amperes l-.nmya 9fqeu3.w7 jn 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 pfqf .w6v( 62 ;odgwwo+wv n+swy,jm5/ 3ixcrzroduces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of c zn/mzsa*jng euwkx6,l z (79)urrent through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when pluu f(6vi8 sgwxh -4hxu7gged 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 dr99ve3 0cy xlrdyer 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 resistance fh0q1(xjv/k h is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc s4z8fqdgr7t r+/v0 s kelectric transmission line carrying 2800 A (Fig. 18–34). The0qdsr g7/tzrfks v48+ line has $2.5\times10^{ -5}\;\Omega$ resistance per meter, and the bird’s feet are 4.0 cm apart. What is the potential difference between the bird’s feet?    $ \times10^{-3 }\;V$

  An electric device draws 6.50 A at ti-cf :ji+ rirw08:1 qsxwn7 l240 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 an4.rt-pzb y*u 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 rmapa8j4 fnvr5+ ju8n*esistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1.5 mm in diameter?f h y1+pt 4gw- pv+4b9qit8ing    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire 2.0 mm inj0fp zczh) njr1t .e+* diameter, to 20.0 m of copper wij+0zh nzrc* e 1p).ftjre 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copt*5qa rc0qp( h ;*a+bd8fww.th p ah8dper wire have the same resistance as a tungsten wire of the same length? Give numerical*+a fp dwabhptchqa.8*(dwqh5r t8 ;0 details.    mm

  A certain copper wire has a resizremhdl) am3-ml pi(w l:oc ap/o794 ;stance 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 (o5dmm dg.a .4rdriginally at4.d d5.m ragdm $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copnroc9)4vz5p n) st cn0per will have the same resistivity as tungsten does acs)c9ronn zp4v)n 0 5tt $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of about 7irn52e*zj c; fjw18n ipvay4 $12\Omega$ 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,c4dx opo1(*mq4nn3 f0awouw along a 26-m length of household no. 14 copper wire (used in 15-A circuits).1wu(, qc*f pnxam o4o3o0dnw4 The wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm, 2.0 cm, anj:xmdu9g6b6t d 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for curr gbt9d66jux:m ent 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 lengtpywhq. swsn,+q9oz:s2 gp 2e .h of the other, what is the rae2z gp9 n:w2pys.. q+sqsh wo,tio 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 connectey78u6b5zc5vj g 1mabe d to a precision 10.00-V power supply, and a current of 0.4212 b55v67uym je a1gbzc 8A 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 follzj n 4y866c7p7sthz0mr w 3qxdz;p0y zowed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference zwh36mr0 d pt y0x;jqn7z4zypz6 s7c 8of 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 resistance not changsljlg a;e1j9ylk a/jx,(p9 .r rhqr*;9;qjfee with temperatu.jpl*;9ra /krl; jef9ea1 qlhsx,; 9ryj j (gqre. 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 de,yab4rd0r+p p signed to produce 3.3 kW of heat when connected to a 240-V source. What must be the resistance obry0,d 4+rpap f the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V poq k+n(m(g / nji5 zggf5tre,(krtable CD player that draws a maximum of 320 mA of currengk5gtk/nmzr((5+ ,eiq( jgf nt?    W

  What is the maximum voltage that can be appliednnsxz m r65w*ttobd/.r.5km 1 across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, a 0/q-tk9rxok+f x0 vif 75-W lightbulb connected to its proper sourcq/t90xk+ i0-ok ff vxre 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 110 W. Calcula;(wqzds+ 3) gmqs5 i1u5wjntqte
(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 settigequr2bi+1-08n gidtq.q rj 2ngs: 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 elu3/h ;wve um(* apa8d-r j(qc9usvf.dectricity 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 8(f9dsc mqj w*3.uh-uv(d aru/ev pa;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 does a 550-W toaster use in the morning if it is inf(c a9/3ewnisd-+pl g operation for a total of 15 misw dp(9f+e / -cani3lgn? 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 t6jt ) qj5ytfb 11rz(fs ywb( y(f.x,ito leave a 25-W porch light on day and nightty51fyx tjb fr,ij s yb(w.((zqf1t 6) for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cesbw(ve6o:*dcrpi e 9*bp qs(-ll 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA wp 9(wicv*d( :b b-poe*qre 6sshen turned on.
(a) Calculate the resistance of the bulb and the power dissipated.
$\approx$    $\Omega$(retain one decimal places)
   W
(b) By what factor would the power increase if four D-cells in series were used with the same bulb? (Neglect heating effects of the filament.) Why shouldn’t you try this?   

  What is the total amount of energy stored in ah k kxc5w)9ir0qw++6.gnid p e 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightb7++ br3fuv w n.b2ezxdulbs, connected to 120 V as in Fig. 18–20, can be used without blowing a 15-A fu+vwn +e.72 rfzbb xd3use?    bulbs

  An extension cord madebtr0 t:6fg8sqs-us -m of two wires of diameter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an8:f0u tsb6sm-r-tq s g 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* p3p,;inv6sv7bcb*hej l4av at 12,000 V to a factory through wires with total resistancc,jpvs 7i a 3;heb4*6 lpvbv*ne $3.0\Omega$ 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 g+o.,v. zmc4/ :c8ykvk) uz3uq mkpreis 17.5 A. At what rate must cooling water pass over the coils if the water temperature is to rise by no k gmr:83u/ pc ).ke.k4vqvzyuz,om+cmore than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to heat a cup of watil;:q ri(-cr or gl*7yg,zfc*er for coffee or tea. Ifl;cfg:r*yr,go-z c7qli( ri * 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 n-4 r7poe mhutds+a7*in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, is /fhc/d6 j(z fy3:ciqvacross 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 ruv+ r;p8 bh8wof 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 deoy3 x(kqy;wteib9xf s u.5*m v.: 9fshvice is 5.4 A. What is the rms voltage across it ku3x;ff wb tq9 m*:v5yh9..y eois(xs?    V (Round to the nearest integer)

  An 1800-W arc welder is connected.4( -.dqji(ytdita pch0 9psz 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 instantaneous power dissipated by a 3.09.n 2jbmaj 3ck+r p 3.j6wjvpy-hp pump connected to a 9 y.3jm p2ka .rjbjnp36c w+vj$240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to y8u lbv.-c 5acx 8a) h*gd6k +i /d2lgpuejt7ua $240-V_{rms}$ 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 carr/bls qvke67zlbmy- i4+nt. )yies a tiny current of $2.3\mu A$. What is the electron drift speed in the wire?    $ \times10^{-10 }\;m/s$

  A 5.80-m length of 2.0-mm-diameter wire carries nehac ln 5(/4*uvi t(ya 750-mA current when 22.0 mV is applied to its ends. If the drift speeh *t4 uv5yca nil(/(ned 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 atmop ui5qj5s0gwyf,a ,hrw6o6 xvo)f+0osphere, $He^{2+}$ 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, qp92a :db3.uml) k-vadby6 mf$He^{2+}$ 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 t,,4 )b kvaj -tm0)auk;jgry ifield 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 actiha,,tsv4x .cnme+s/r gr2f:h on potential is detected at a point 3.40 cm down the axon 0.0052 s later. When the action potential is detected 7.20 cm from the point of stimulation, the time required is 0.0063 s. What is the speed of the electric pulse along the axon? (Why are tvt +: 24,,h.rrfesxgahm cns/wo measurements needed instead of only one?)    m/s

  Estimate how much energy is required to transm)wss-s1 xf( + zkjpip:rp4 d5jit 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 17–9]. What minimum averps)5( w-is+1 jspx :p4 jzfrdkage power is required for $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action potentia)n7cy lcg38 krl, $Na^+$ 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 ampere-houhbc;04ka;c/ gdmn ;xpomcm3v3zc- 2 qr?    C

  What is the average current drawn by a 1.0-hp 12u 7/r/hjp4 aou4aa xml 9.f2re0-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally le t5a*2 io-nxgwaves a car with the lights on. If each of the two headlights uses 40 W and each of the two taillights 6 W, for a total ow* n2xigto -a5f 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. If it is mads9yjli: 7ijm1:q gk/d e of iron, what must its ds mk7/ jdi:qly19ij:g iameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as t 29vs f1biuz;jbn-t7the reciprocal of the resistance R; thattub sivb7 z-2n j;9ft1 is, $G\,=\,1/R$. 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. ;h9,/c5v e.fh9z q 6n jmqbhytSuppose that instead of using high-voltage lines to supply the power, the power is delivered fm5/ ,jby6qec n9h;tq 9hh.vz 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 kWh.    dollars per hour per meter

  (a) A particular household uses a 1.8-kW heateqwbs8ir5iu -pqi1bd - u0j;1kr $3.0 h/day$ (“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 a.. w 7q5.ija r22r 9aazdktsgund the two lengths are wrapped together side by side to make a thicker wire. How does the resistance of this new combination compare to the resistance of the original wir.97w2rt qjs. gu5azr.k2i daae?

  A 1200-W hair dryer is designed fos2- 1h(xoms owgflp ut: :v/ep. nb:j2r 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 so hot as o)*ob u6bgk r6to start a fire. What diameter must a copper wour)bg* 6bk 6oire 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 3d1z2*rq2u-fh p tifugiven by the 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 4qok; - 6zsth6ophv5- / y4s7lcojvvqper second to the intersv j kq;q4h6o/-67p5shlov-oz yv4 tcior. 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 diffhxd9 sf6.vbla es1/8herent conductors made of 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 second? 81evshxa9h/l d f .6bs$P_1$ : $P_2$ =    : 1

  An electric heater is usedm r3b y2j6afq.ous ( 9ebh9md3 to heat 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 hooad v*e v c- :djkwm80)m)6ktthked 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 makes use of storage batteries as its sourag h+io +at:j-ce of energy. Its mass is h-ogtaj+ a +i: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 has a resihoklu j)w - (os8c83i8c rcap(stance 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 xu n+iw y3mg;5r 7j+geat Fermilab (Illinois) is designed to carry an 11-mA beam of protons traveling at very nearly the speed of li+7irw+ geujx3; 5ymng ght ($ 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 dr8pf v uebg)e.es :x/2gaws 12 A at 220-V ac. The connecting cord is copper wire with a diameter of 1.628 mm./xvge e:.fu e28sb)gp
(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.g5u/k - emrxmw x02wa:l2d9 0viaijo( 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 tmv(a:5o-maw0e9 x dik2 lgri2j x0w/uhe wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies fr(1x-s noxo 9/hrw .zpwom 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 differen.o /1owhzp-xxw n(9 rsce 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. Lightbulby(m3dnu+p+dyv*0 p vi B is ratypvip m vdu(n0y 3d+*+ed 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 set of appliances at 120 Vx y yks:is/yi arvjwy70gk)8 si007-e, which draw 2250 W y j7a vi:kk ws07xs y0-8ge0s)/ryyiiof 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 diamtccdy3c 9 :(ir/ ohx1jeter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). Wha1ihr:codjy/ c(xc9t3t is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its lengq zg v6qf9fb607 -wqnbth doubles, by what factor does the power dissipated in the wire change, assuming it- vfz0qnfqbb69w76 g q remains hooked up to the same voltage source?

  A tungsten filament u/h2n* drfmn0)p;:wa ( lmyt dqsed in a flashlight bulb operates at 0.20 A and 3.2 V. If ith/d()rnqwtm;* ap :l2f mn 0dys resistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$