What quantity is measu,jjyh4 +o d;bered by a battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, e,z*th:t1 fmx1c,c y+5 itmae plectrons flow away from the negative terminal in the circuit. But wii m,t* c:1+t e1ptxamhcf ,y5zthin the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battery current, bat.-zdto8 w.ark r:j mwjr.+p /ztery voltage, jpw.z /-a.wrd.rzm8:jktro +battery energy, battery power, or battery resistance? Explain.

One terminal of a car batteryvupb-/hp./6l;qmh8 q dy- hwi is said to be connected to “ground.” Since it is not really connected to the ground, what is meant by this expressmi dhlb;hp8y6/vp h/wu qq.--ion?

When you turn on a water faucet, the water usually flows iuv 8 (w8n tjcm.;b+8sw az5qr:fovs2h mmediately. You don’t have to wait for water to flow from the faucet valve to the u:cznw;8aob vsm+f(8j2 ts8vr h.5qwspout. 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 lengt 2oii vn6ul/u(h have the same resistance? Exi(n6 /uuov2 ilplain.

If the resistance of a small immersion heater (to heat water fo dj9o;m3xqy6rn* fje2r tea or soup, Fig. 18–32) w fjx29qjm*d3 y;nr6 oeas increased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbonrcw8aghpfw)b6ua k4 95-c +j1evam *e 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 greatest resistance?e 8r5jauvakc f- 6+)hwc wp*4gbem19a

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 mv+wdpr cw2.3np+ ccgxd2mj bax-4,h) -k b3xout?

Explain why lightbulbs almost always b+;viu1t p vi*turn out just as they are turned on and not after they have been on for som+ti*v t1uv; ipe time.

Which draws more current, a p1:ldte11 sl j100-W lightbulb or a 75-W bulb? Which has the higher resit: 1d p1j1ellsstance?

Electric power is transferred over large dkbb1 d41y- 1nhd(u(jeai 7h2oxf -nuqistances at very high voltages. Explain how the high voltage reducenhfj dx21eu iq1b d oy-h(nb147 -(kuas power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is ithu02d)s z yur8umd +a357:hd1glon ca dangerous to replace this fuse with a 25-A d ad+1c2uun 30l7ad5yho8 grzs:mu )hfuse?

When electric lights are operated on low-frequency ac (say, 5b2zvq70b)hhw ;z4qshl-/( q uf0nvo f Hz), they flicker noticeably. fhz0(q qz n/0b)4bwl;uf-2v7hsh qv oWhy?

Driven by ac power, the same e n2l+0 w(5d/ilqbamxn lectrons pass back and forth through your reading lamp over and over again. Explain why the liixn 0 /qll(w52d b+manght stays lit instead of going out after the first pass of electrons.

The heating element in a toaster is made of Nicnc/xnz34mmawc :wt1 4 hrome wire. Immediately after the toaster is turned onw :34t/cncmm4xzaw 1n , is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Expla0:4o)bxxtji qt g9)ccin.

Different lamps might have batteries connected in either of the two arrangemen pbb7 h 7l;(gljet +zomfg;(fm,3fu 8sts shown in ho 8,z;mm(fe but7lb+; sfjf (pg3 gl7
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 n+c.1lzg: wm*ip*xtm,k +iuunkc7 a7 point in the wire per secokn gi+kwt7.,u*cz p:7a1 *mc+xilmnu nd?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a curr.nqv-7e 9k jiment of 6.7 A for 5.0 h. How much7vkmj9n iqe-. charge passes through the battery?    $ \times10^{ 5}\;C$

  What is the current in a3 sb2ed5lur xckk153f mperes 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 prodqu; 9m3gtrpv1z4 yj9t uces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current through a *f3x.z-lmkap 8ck , /byzihs0$3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A whe.x5 yfbc6tai ywp-wvq5bpg3q3swj.08q v* 9tn plugged into a 120-V line.
(a) What is its resistance?    $\Omega$
(b) How much charge passes through it in 15 min? (Assume direct current.)    $ \times10^{ 3}\;C$

  An electric clothes dryer has a heating element with a resistan+ 0.zt7v2j y9p bdrpeace 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 whkda u24nti 7y71,fub rose resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric b71 c wf:0,-dq; cqzrb vsczkc3,vn6 etransmission line carrying 2800 A (Fig. 18–34). The line b - kvce0c6z zswr cqc13;vn 7,:fqb,dhas $2.5\times10^{ -5}\;\Omega$ 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 6.5 xn(;kg3.y7 bu/wkdlc0 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 0.6ja8 ,-2qsya7km 7b ;qg8povh *wd gc,t0 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 resistancewfl7csqs,v wraf)9hx) - , 7dg is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length ofegkgl8b ,m+- 4e;wa5mg -rrgl copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m ofqn:c.x/b7 n uo aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in dcu7n : oq/.nbxiameter.   

  Can a 2.5-mm-diameter copper wire hrfmn58s 4,0-rgakdxw ave the same resistance as a tungsten wire of the same length? G k50, wdx8msf nagrr4-ive numerical details.    mm

  A certain copper wire has a 75ura t/e2:tw n+bl uwresistance 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 temp os, 0v1jomck0 ci*6xuerature of a copper wire (originally atjc 0i ukx o0vo6cm1s*, $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have t5uqmj e zc m:15cs c8zoly7*2qy 54csfhe same resistivity as tungsten does at ccyu*s7lf12zs8jq c o5:yc q5z54 emm $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of axvzcp cmyp-+f; ze+*3bout $12\Omega$ 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 h ,y5.:wni tbshousehold no. 14 copper wire (used in 15-A circuits). The wire has diameteriwh5ty n.,s:b 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm, 4yem4.f ekto, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for current that. m4e4yo ,tfke 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 la kr2vi,( q/d-i :dqathe same resistance. If one has twice the length of the other, what is the ratio of the diameter of the longer wire to the diaq i-(/kvral: ,addi2q meter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connectt9h+f, 7sw ohhed to a precision 10.00-V power supply, and a current of 0.4212 A is precisely measured at 2fos whh ,th7+90.0$^{\circ}\,C$. 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 wire8z uk ryri8trv* :*8xs consists of 5.0 m of copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage diffr z*vrs8t8*yx k:ru8i erence 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 resist;w16 ct*9z lojxjc k9qance not change with temperature. For exampxtc;qjl 6 o91zkjc9 *wle, 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 ove6dwt9ozy oiq4+a9tba o f07) ohim/ 6ln is designed to produce 3.3 kW of heat when connected to adwqbfy zh9 l46)aa+7io/6 tomo t0 9oi 240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD pl8;rik. y do,rg kzz-u4ayer that draws a maximum of 320 mA of currku,yz-r4 8.ir; gd kzoent?    W

  What is the maximum voltage 3cj7m t5d 3txjs (p7vye9r5ae that can be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the res/gb4ika(o rb+istance of, and current through, a 75-W lightbulb connected to its proper source vob+gk 4orai b/(ltage 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. Calculate yksa*koz3 .gmx3 m/rbdp e,.0
(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 setti ,udnh eqz(:4moi.3lrngs: 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 E) jm6r*1 a.sigfpy 5l-z: dxbqurope, where electricity is delivered to homes at 240 V. If you use the lightbulb in the United States at 120 V (assume its resistance does noypj.x*l)z1fmg-dq b :5sr 6 ait change), how bright will it be relative to 75-W 120-V bulbs? [Hint: assume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W toastc8qr7 t5;b+ g /cothkwer use in the morning if it is in operation for a total of 15 min? At a cost k5htrbgoc q7cw+t8; /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 per54qrtl/9 2jub - g0nn-v/ lz8 rntxkwb kWh, what does it cost to leave a 25-W porch light on day and night foj5-rx8k g- 2btnb 0vqll /u4ntrwz9/nr a year? $\approx$    dollars

  An ordinary flashlight uses twoz/7fy,lb /r jh D-cell 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when turned on. l/fh7, b zy/jr
(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 a*x5 n,f lw9f7o+mv9 bx,ijzr f 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 us3hgx4x-:n- agq,z puzed without blowing a 4-pnaxgxzq,-3 : hgzu 15-A fuse?    bulbs

  An extension cord made of two wires of diame 89. hmkn.gb*m 3zn amq.o.awdter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric heater which draws 15.0 A on a 120-V line. How much power isom b .zd3a*.nwha 9gnqmm ..k8 dissipated in the cord?    W

  A power station delivers 620 kW of poweqx 1 07kid slx,nb(/9q wjk3zdr at 12,000 V to a factory through wires with total resistdkb9q,x73q nx10k/ j(sil w dzance $3.0\Omega$ 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 electromiwc xpav c2 ,k-y85toq3-vm *hagnet connected to a 240-V line is 17.5 A. At what rate must cooling water pass over the coils if the water temperature is to rx 28h-iqcyva53w ,*mcptv ko -ise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used lruo;7p-a 92admsfrpy(fbr11:,pfyin a car to heat a cup of water for coffee or tea. If the heater can heat 120 mL of ,(l-2 f:rffppo79sar1bpydr1y; au m 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 c /s pg(sk38fhaurrent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak b6uy zt2r*4 r *b-h+(r yiizrkryl72lvalue 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 thya0g1mm a *lvuq-v 05oe $120-V_{rms}$ 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 inm2vq r+8*p;g1auw jan a 1500-W device is 5.4 A. What is the rms voltage across it? q munvrjp;2 1g*a8a+w    V (Round to the nearest integer)

  An 1800-W arc welder istywnz) w;(+ho8.*dgv 4 r rcjh connected 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 dise 2cj0: 8bl v2hk6rbvesipated by a 3.0-hp pump connected to bkble v2 0c8jve6r:2 ha $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connecka :n:ee./bj hted 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 wire carries a tiny current of tms;ba7f3l.e5v9k*s+mv i yb$2.3\mu A$. 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 a 750-mA current m)t7kivb90t-fqry fi:ds 5s: when 22.0 mV is applied to its ends. If the -: ) iytqr0kv:fm57 fdit9 ssbdrift 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 atmospherge+:f*n;7xu uc ;lainn.b4lxc4 a/ hfe, $He^{2+}$ 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 xmrh s(s: h)5wcfv6j7’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 

  What is the magnitude of the electric field across an axon membranq. p/u*tzp6t eu, i*mfe $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with4gs:.r z m6vp /z , mh(epb18sq6dqcja an electric pulse. The action potential is detected at a point 3.40 cm down the axon 0.6 dzhq. qz6s(8p /1p:jbermag mvc s4,0052 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 en32 b*xkpcuq8x ergy is required to transmit one action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy uc x2k pb*8xq3stored 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 potenm2 (; hhi msvv8 naai;;4qsl5gtial, $Na^+$ 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 arecxa5y7s9b +dz there in 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0-h( yh(aw1kol) ydm a3x,p 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on-a4*x6fh bfbz. If each of the two headlights uses 40 W and each of the two taillights 6 W, for a total of 92 W, how long will a fresh 12-V battery lastfh a*f-bxz6 b4 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 lonh; va -h7ki9y;keipl5r, 3r udg. If it is made of iron, what must its diamep5;lha uh39y,dvreki k;r7 i-ter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the recipro(g1n3fis30wgb vty49t kk. xpcal of the resistance R; thatgtt 01i vw 4kn. kxgsfpy3(39b 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 MWr *vpx: nz*4e4 en+* f1(dyxnbuwtn2 d of power. Suppose that instead of using high-voltage lines to supply the power, the powe2nb *:(*nndw4 x+tyn dreezx uf 1pv4*r 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 kWh.    dollars per hour per meter

  (a) A particular household uses a 1.8-kW c3p.mzd/t+,gt 69hquytqqj( 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 torwxf /z8 p8 (fh-*zjgygether side by side to make a thicker wire. How does the resistance of this new combination compare to 8hg- zf y/w*z(frjxp8the resistance of the original wire?

  A 1200-W hair dryer mf2. ,cim*dr mis 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 . az3b(0yqmu vdoes not become so hot as to start a fire. What diameter must a copper wire be if it is to carry a maximum current of 35 A and produce no more than 1.8 W of hea 0a.qbvm3y( zut per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given9stp )yr8 cg(n 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 runh* ua i/dmvy0 r08srn/ning at 65% efficiency delivers 950 W of energy per second to0/*ry/ ashvi 0 n8dumr the interior. 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 material. One csg,y (s+36ze uf)sb ubonductor is twice as long and twice thez)bs3f6y+,ue ( sb sgu diameter of the second. What is the ratio of the power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room of volu7ipiw2 ea:;bo me $62\,m^3$ 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 sougt:,tc ; r. ofxp,mvq)rce.
(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 stor g,v6*e wjs7tdage batteries as its source of energy. Its mass is 1560d wtjgv6s7,e * 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 resistance 9t5,n64tevf rl8sn 8eid5 cpvof $12\Omega$ 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 acceleram w,70ffgs5nztor at Fermilab (Illinois) is designed to carry an 11-mA beam of protons traveling at very nearly the speed of lifzw50 s,fnm7gght ($ 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. ,c 8 fn gaud2:crhgx7rr s(b+4The connecting cord is copper wire with a diameter of u s8dr(g n+r:grbaf2c47xch,1.628 mm.
(a) How much power does the air conditioner draw?    W
(b) If the total length of wire is 15 m, how much power is dissipated in the wiring? $\approx$   W(Round to the nearest integer)
(c) If no. 12 wire, with a diameter of 2.053 mm, was used instead, how much power would be dissipated? $\approx$   W(Round to the nearest integer)
(d) Assuming that the air conditioner is run 12 h per day, how much money per month (30 days) would be saved by using no. 12 wire? Assume that the cost of electricity is 12 cents per kWh. $\approx$   cents per month (Round to the nearest integer)

  A fish-tank heater is rated at 95 W when connected to 120 V. The h..qpgcbo63dyh . 5;a vcd-e qceating element ive dc.qc6ya.b 5ph-g. cdoq ;3s a 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 v p dn).aiib chm.kp,*9oltage varies from about 12 V when the car is off to about 13.8 V when the car is on and the charging system is in operatiop d.h* p)k.acmi9, binn, 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 applicationsmle7qd 7e b) ns2(,tfd. Lightbulb B is rated at 12 V and 40 W for automotive 7ef27nldq)t,s b(dme 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. +2p7rgf hy(nq259 cm is used to connect a set of appliances at 120 V, wh+7 rgyp nfh2(qich 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 3.0f0uvk 8 j,cy4itz j5v,0 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the re0j vfk 4c5ti,y8ujvz,sistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its length doubles xc 1tbx9+nap)lg5s2s, by what factor does the power dissipated in the wire change,2ab15nct ps +) g9lsxx assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operates at 0.20 A and 3.2 V. If8gg i- w:er+2yyjnth 7 its resistance +nwj g-ei2 :thyr8gy7at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$