What quantity is measured by a battery rating given:f;pz,mt g (ru in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected toyqt1n8 vbxt)mvix7;7/- tgiu a circuit, electrons flow away from the negative terminal in the circuit. But within the cell, electrons flow to the negative /)t ;qv1-xtixug7i8b nvyt 7m terminal. Explain.

When a flashlight is op uk)t-fvf-ph4cx y-tnkq a/f+ ,m4e*ferated, what is being used up: battery current, battery voltage, battery ener,)f+ yft-h-max- 4tkfknpqu e* v4/fcgy, battery power, or battery resistance? Explain.

One terminal of a car battery is said to be con x0:gbt-l ,qfba8wr3gnected to “ground.” Since it is not really connected to the g0b, -xwfr abt lq83g:ground, what is meant by this expression?

When you turn on a water faucetw ou2h/l1ffbiw39 zt;, the water usually flows immediately. You don’t have b f3fi w h2zl1ut9w/o;to wait for water 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 8eto3 fw ukb12aluminum wire of the same length have the same resistance? Ex kw32tebu18of plain.

If the resistance of a small immersion heater (to heat water for tea or soup,+2y m f vsgyf170d6f9tg vi8dk Fig. 18–32) was2mig6fyv8s dk1gvt9 + f yf7d0 increased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of leng2tqe) y*t2f) 9lg yybyw+a 1ozths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) ez*ftlty y2byoy 921 +))gqa wthe 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 lightb6st)l4meo. y99pz5l4s jhc kuulb burns out?

Explain why lightbulbs almost always buvd.ut2jj )i(d a83xffo*qgj5rn out just as they are turned on and not after they have been on for some time.f q5g d(8.aj2f *uoj)itxj3vd

Which draws more current, a 100-W lightbulb or a x oe pl;w/g023 /r+f,umkxh mgr6:eve 75-W bulb? Which has the higher hx+0gmee:rp3gxow/v ; le6kumf/2 r, resistance?

Electric power is transferred over laj p. /umy1 felegomx7d8;-ns9rge distances at very high voltages. Explain homy l;-du me pe/j s.f9gxon817w the high voltage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. +wdax. 4 -cqx ed v)j4gtpt:o/Why is it dangerous to replace this fuse with a 25-A fuse?:w +)x.4t xjdd-tvqap/c eg4o

When electric lights are operat 7)y +s8qmstaked on low-frequency ac (say, 5 Hz), they flicker noticeably. Wsas7m) 8tk+yq hy?

Driven by ac power, the same electrons pass back and forth through 11p0fkws, bta19d zj yyour reading lamp over and over again. Explain why the light stays lit instead of going out after the first paa t91j sd1fpky wz1b,0ss of electrons.

The heating element in a toaster is made of Nichrome wire. Immedime(2;sdbid ;pomg4 h2ately after the toaster is turned on, is the curm eo2b2sgh(md d4pi; ;rent $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a rg/uw/ nja0u; a xpka69esistor? Explain.

Different lamps might have batteries connected in either of the two a6u)0)8 zcohwp,qq k *,)kctsct8 iijerrangements sk qhkqciz t 80),)uew stjc)ip,6*co8 hown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many electrons are flowing past abax r6th x4+;rny point in the w h4xxbt;+rr 6aire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using k:jerr)r2jm0/wtlz yyc cr 1l+)h+f+a current of 6.7 A for 5.0 h. How much charge passe1rl+0wrck r lyy: cz+jjm etf/r)h+2)s through the battery?    $ \times10^{ 5}\;C$

  What is the current in amperez (oigoit1q+uq/ln-/o 1v i2as 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 resistanci 5wkj*2)zob-entol w zp68z )e of a toaster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current tzdyzw v (z aq-ofe0327hrough a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when0.hdh g jar)(p l(d/8eonef q3 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 re d56(n mexh,132f yloe;0mob0sdqpdz sistance 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 resist:wnh hb1z cj*x-n-,zc 7yyg7k ance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transmissijast +u43ik:dkjuwp; y24i3h on line carrying 2800 A (Fig. 18–34). The linktj2+pui3;dyjiu:s kh4 4w3 a e 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 240 V.,hilu )/-sqc b
(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 him + a/m+nrp.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 wiro .glyn (z1d8ae whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of w,0tnzb4dd 7c a 3.5-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 2e6 sitsjuup j66(h4jl)r0qcmm in diameter, to 20.0 m )seci6r 0uj tlq6s2uhj46(jp of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire havesq(q0- b(xuy b the same resistance as a tungsten wire of the same length? Gb ysxbu-qq((0 ive numerical details.    mm

  A certain copper wire has a resistance of ( vvr4e;f ssyn *7: 2mw2zqndh)zn8vemmp0,r$10.0\Omega$ 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 .5; qzp;w(c7*jln mkakj ciy9copper wire (originally at5 k.m;inajykwl (*9 cpqzcj;7 $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temper kwtca tx q/)k88p/k)rature copper will have the same resistivity as tungsten do8kkrpck/q/ xw ))tta8es at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a rethlv-, o q2n9psistance of 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 dqe47,ph lw r(yrop along a 26-m length of household no. 14 copper wire (used in 15-A circuits). Tpl(q7 wrh,ye4he wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengs1,l cf4rm gz:f2fz :sths 1.0 cm, 2.0 cm, and 4.0 cm, lyinml :1c2gfz4 r,z sfs:fg along the x, y, and z axes, respectively (Fig. 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 len6928 w( by8qz 2bkcz3jojsvv bgth of the other, what is the ratio of t9o8z8 sck vqjjwbv2 326(yzbb he diameter of the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wirq g5e clc,z01 nsege o.9n6:yre is connected to a precision 10.00-V power supply, and a current of 0.4212 A is precis z5eg0gnelc6s9.coqnye:, 1r ely 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 wirg3j *x.iuzn k0e consists of 5.0 m of copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is place.ij*k unxz3 0gd 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 applicationjq0 hiyf 7x +mnpnp-/e6n; oj2s, it is important that the value of a resistance not change with temperature. For h neyq xn6n+;f/jiop2m-0 j7pexample, 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 ovo+4t6 3hijh(cibc) gm en is designed to produce 3.3 kW of heat when connected to a 240-V sourc3h( gcioj)6hm tci4+ be. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD play ,cfk mqi92trix j66bl+l.9ks er that draws a maximui6f. si2lql9xcmr btk9,k6j+ m of 320 mA of current?    W

  What is the maximum voltagg tq*8bn 5 m/ea9xex6fb) mw:ae that can be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resiservj/x( c.jl2*r7hkc h;0mlt )z3c d ptance of, and current through, a 75-W lightbulb connected tx7hmjr ce )zvjcr0; hlk/*c.t 32pd(lo its proper source 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 rxgdbzgpz8t i7v 3,c(3 ated 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 two settings: 850 W and 1250 W. tl gsw:j,ydo.:m x g5 .ss6rh.
(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 Ef saco *io cb3;1,rz- at)ujw+urope, 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 not change), how bright will it be relative to 75-W 120-V bulbs? [Hint: assume roughly that brightness iorz ;ja ,usc)3-1ob wc+* atifs proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use in the morning if it is iiv9 s, / v1qfgdilt*m:n operation for a total of 1tv lm:ds/iqf*1i , v9g5 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 it cost to lewji 0a/ xi5o-ln0t-sf j8-+o+gy atvwave a 25-W porch light on day and night for a year?ylatitsaj 0+0v+oi- - n-5gj/o 8 wwxf $\approx$    dollars

  An ordinary flashlight u9+tre -ce8. damxuga8o88j4 tst kjy2ses two D-cell 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb drut et+rdtxm9.oae g 2j88k4c y-s8j8aaws 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 stored in a 12wsa ycb91nlyoz r3fq*o p4854-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connected to 1t:cn90(* vj0zgp6wpizbeu . b20 V as in Fig. 18–20, can be used without blowing a 15- j.zwz*b0 i b:6(pcpu9nt0egvA fuse?    bulbs

  An extension cord made of two wires o7gv0kn q 5c wko(.em;rf diameter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric hea qwmkv5(e.cnr;gk0 o7 ter 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 powto0;e c++ wbyu*o,uga er at 12,000 V to a factory through wires with totalyu to+e*w; u0+ba,oc g resistance $3.0\Omega$ 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 elecvw ez+i7 k 34hmzf;xawwke6*7s8g 0sctromagnet 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 rise b+afizwce mz7* ghk es863 ;4xw07svkwy no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to heat a;tw.k ox 5vy6e cup of water for coffee or tea. If the heater 6ov5txwke; y. 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 ckm3x ;kbtp/)x -cm.zs,zxa 0x urrent 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 across ey lbm6k,8u6ra $330-\Omega$ 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 2ppb y,u ,1woh*um2znthe $120-V_{rms}$ 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 is 0nw+u a-y, pljd6;slzthe rms voltage aclp,azj6;+ nuldwy-0sross it?    V (Round to the nearest integer)

  An 1800-W arc welder is conn23jt(xc -5:eiqbaulm ;e r. uoected 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 3.0-n/ :wp (g9+oiz9 pinalhp pump connectedlpp(za :i9 noi /9+nwg to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected tow8a asynk/crn xkt( tx7x wrfw3o-3o36/+t4b 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 currenttpjiz o7os )de ) sqouyvf;6bxj-2+3/ 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 c1jf*/ ojse y eqm+ *zoi 7j4wsn,h;x+harries a 750-mA current when 22.0 mV is applio 7j+sjhje,i x* mz*oqyhnf1+; w4/esed 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 thih j+8l)plp p-(m2xjn,s)n7 ijtn- dhe Earth’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 atmospherec+ad9jl4,vh2 yeo mnf: g3v3 e, $He^{2+}$ 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 aj-e qt2q,-r fthe electric field 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 action potentiyjqh)ej9 52mh5m :ftk p6p3/ uouotv8al 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? (Whj8omou2 3h qt5 5jefk:6v/pumy h p)t9y are two measurements needed instead of only one?)    m/s

  Estimate how much energy is required to transmit onkofaljj c8/+9 - 2dbsqe action potential along the /8d9jo -bj qs+2fkl acaxon 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 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 potli0f 9hykh bpk) 7j;s0ential, $Na^+$ 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 are2+2wcybr9i2bolq;s2 g ,eog c there in 1.00 ampere-hour?    C

  What is the average cur pua96lo rns,av;* it6rent drawn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lid5k3muc7d o,mi+/mf t3ker (qghts on. If each of the two headlights uses 40 W and each of the two taillc dqk 3 e3mo57,mid krfm/+ut(ights 6 W, for a 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. If it is+jq32)yhfy d)blnw- v made of iron, what must its diamete jhd+3)f-2yn q vb)lywr be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of the resistangglf-v) ti 0i5 e6hfg-ce R; that i)egft5l h vgi g6--f0is, $G\,=\,1/R$. 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 instead of using high-v ) fjbz:og2,b;d8qpmholtage 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 copq;2):8obhmb,dj zgf st of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular househ93whe ) ngjj kn-2;2mq1qxcct cm8n.bold uses a 1.8-kW heater $3.0 h/day$ (“on” time), four 100-W lightbulbs $6.0 h/day$, a 3.0-kW electric stove element for a total of $1.4 h/day$ and miscellaneous power amounting to $2.0 kWh/day$. If electricity costs $0.105 per kWh, what will be their monthly bill (30 d)?    dollars per month
(b) How much coal (which produces $7000 kcal/kg$) must be burned by a 35%-efficient power plant to provide the yearly needs of this household?    kg of coal

A length of wire is cut in half a+2g zrt 9i4hsmm4qh, znd 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 wire4 s2mizr+hh, q4z9gtm?

  A 1200-W hair dryer is designel6opm;46v.9zmprf+i e-. h uu7gbvs xd 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 eoq//f )/qjt2 7as,xvw ;rhpt cnough so it does not become so hot as to start a fire. What diameter must a copper wire be ,/a)hqs /ofx2v r c/qtw t;jp7if 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 equatiydh 57 c:0hyueon $I\,=\,1.80sin210t$, 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 oi orv2p 3 ;/ltb0brrx+uh5c9tf energy per second to the interior. Fr;ov3btibpt 9uh05x/2c+rrl ind
(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 differexl.-( /h1n zx zji,0vbvtl pcw69tf 8tnt conductors made of the same material. One conductvh.pvc9blzt16lt xnx8f -wi0 j(,/ ztor 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? $P_1$ : $P_2$ =    : 1

  An electric heater is used to he x9 fe-vazo8imey1g0*nb) cu )at 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 to a 240-V source. h)-k-5mmgthc / nl1vt
(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 source/qmn34 ) t3p;b uw uf-k3dpj.f -ydxbs of energy. Its mass is 1560 kg and it is powered by 24-n3d3.umft;3wb ufksj/)xpb pq -yd4 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 ezx,-90dv)qu 9 vw( l gq5dvjlhas a resistance of $12\Omega$ when cold (20$^{\circ}\,C$) and $140\Omega$ when on (hot). Calculate its power consumption at
(a) the instant it is turned on,    W
(b) after a few moments when it is hot.    W

  The Tevatron acceleratbo ser9j (n*u(t7fgfxdeu;p ),8:ydi or at Fermilab (Illinois) is designed to carry an 11-mA beam of protonss(j97u:itef, y8 n;g(uf*) drop exdb traveling at very nearly the speed of light ($ 3.0\times10^{8 }\;m/s$) around a ring 6300 m in circumference. How many protons are stored in the beam?    $ \times10^{12 }\;protons$

  An air conditioner draws 12 A at 220-V ac. The connecting cord 008 qz gfc2ly8diy gi/is copper wire with a diameter of 1.628 mmq8dl8iy20zc gg /y0if.
(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 connecte.cnb .ah3o wsvh4s( n;d to 120 V. The heating element is a coil of Nichrome wire. When av(b .; nno .hsc3s4whuncoiled, the wire has a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from abou4e/cii.vnyq7rb :jb ho m:s +;t 12 V when the car is off to qri jb; +:ys em: n74vcbi/oh.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? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for household applicatio40 hx,ohs p5pdn(;1zt eeis x*2edld2ns. Lightbulb B is rated at 12 Vdze5l1,*2hdd ( s4po;2s0xpti x hene 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*wrwr 5gnkyi 04 /,sjm is used to connect a set of appliances at 120 V, which draw 2250 W of power tw*nj4iyrk0 s/r g m5w,otal.
(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 diamet-rny7nc x5n.9 bq2pws8hiw.her of 5.00 cm (Fig. 18–37). What is the resistance of 10.0 m opwichn9 sw5b-rhxn .8y.q7 n 2f this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its length doub( 2oy.o 68trvr ehc3iyles, by what factor does the power dissipated in the wire change, assuming it remains hooked up to the same voltage sy3hy(o .co rv6re2it8 ource?

  A tungsten filament used in a flashlighpp4m4ixx( 6,i9 kpfxc t bulb operates at 0.20 A and 3.2 V. If its p(m4cx 6 x9p ipkf,ix4resistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$