What quantity is measured (szo/9wl j* feby a battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit,naw86 s8ehrah 4xi,2(2nl96o nmc g pk electrons flow away from the nege(rm8 c8n9ha6 hpo l 6 sk2nainwxg2,4ative terminal in the circuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battery current, battery v :gq igq:frr2o8.)sntof b* h+oltage, batteryg q:or+:)qi sf8hgb.ofn2t* r energy, battery power, or battery resistance? Explain.

One terminal of a car battery is said to be connected to “ground.” Since it4abr 0jy2z7sg. n4w iu is not really connected to thj7zn2 g0s ryaibwu4 4.e ground, what is meant by this expression?

When you turn on a water faucet, the water usually flocvo i,.1q d7rmws immediately. You don’t have to wait for water to flow from the faucet valvi7qr c,1om.vd e 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 resi-bf1h*(rcxuy+c iydo/:o e9 dstance? Explix of9:r*yb-do cyec /hd( u+1ain.

If the resistance of a sm rk 6 3pbq4).wvpftpm.kpl5; sall immersion heater (to heat water for tea or soup, Fig. 18–32) was increasekk p6b.l5mppwstp f 3.4 q;)rvd, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengg:u r,yhyelou09hl7 lb +3lb*ths a, 2a, and 3a, how would you connect the wires from a batte+7ryu3*lhub9gl 0,ohy l: bl ery 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 lightbi sq;iu5/q0q 2z1kbui,)co tuulb burns out?

Explain why lightbulbs almost always burn ouxx kth-hlp84)xj6bidr +d 6oc n*8qa5 q.a2pit just as they are turned on and not after they have been 8ir.a- +*)ia65tq c6x4dbqlod8hxxnhk pj2pon for some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which has f( l8 fcib m-wowd,0-wthe higher rfcl--d0wf( ow im8,bw esistance?

Electric power is transferred over large distance. r3akb 45ruh8*g ezstf/ w1kes at very high voltages. Explain how the high voltage reduces bth4 rer3u 1/w 8skagef5z.k* power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replac716sjh7 6mxmccc1n vj7e6opb e this fuse with a 25hjcs7n6c 1ev1 b7mjxc 6mo6p7-A fuse?

When electric lights are operated on low-frequency ac (say, 5 Hz),q(j6-k vt4ki- ufbha38i:d vi they flicker niai6d8- 4k:j vv-fi(h qubt3 koticeably. Why?

Driven by ac power, tnfytn7f2 0 w;ac n w;mk;dh/j7he same electrons pass back and forth through your reading lamp over and over again. Explain why the light stays lit instead of goingw7c 2dtk7;;0 jfn;hnfmywan/ out after the first pass of electrons.

The heating element in a toaster is made ofpt8 e:lh 5ax1y Nichrome wire. Immediately after the toaster is turned e a5:18ylptxh on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in ay8 5ite6t ute 61ds/u)csca, ode:ql8 resistor? Explain.

Different lamps might have batthxxmp+ 1e1fs7a sq(pm**oi y,eries connected in either of the two arrangements shown ini*+x qa p,e 1*1my7 phoxs(msf
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows/irq0; -hxerh z7jac+ in a wire. How many electrons are flowing past any point in the wirrri zqh/c 7ae+ h-j0x;e per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A for 5.0 h.ftg y97fj *sx+ vehk66o.zp4; 7e nnyp How much charge passeetvyy nok7 e467fj+g x.6 f hspz*;n9ps through the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes sqi (pbrp11 qy zu934r-jz r)kif $1200\,Na^+$ 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 q3fho(/z, tz je1hg i:if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current through)+rq0i1ewg l+ qfdol * a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-V linew f+(q t,90(bc44vj7xe 7rujxplicdr .
(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 rei/6k.ea,fn i2vsu3ousistance 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 vdy qek*2j51,b rlyjjt )- ht/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 carrying 2800 A 6ky*1 jq1v7lkx :copn (Fig. 18–34). The vkj x* :6k7nqcp1o yl1line 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 sccbho7 f3gp)ay;ekq- 85j h)6.50 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 0.60 A through a resiq/ ,4iwl* u )pscex4 anfszb0,stor.
(a) What is its resistance, $\approx$    $\Omega$
(b) how many joules of energy does the battery lose in a minute?    J

  What is the diameter of a 1.006smgeif 3u30pv4cdwq4t d* v--m length of tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1.5 mm i4atm /5rk51g9r)xmb jv ugz g3n diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire i0;c/l 9 xai3gy:vwwp2.0 mm in diameter, to 20.0 m of copper ww39w/y;p 0vic lgxa:iire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tungsten wire :-eg,c yc7li*7 v/k(i9l dexd z5 fbhnof the same length? Give numerix9d/h e5,7efvb zc-kci yll g:dn(*i 7cal details.    mm

  A certain copper wire has a ril2,hai4hscvw t0 )l(esistance 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(eq x(u(m*f(m vpr p/ilpy 3tai)ob, m4nd0f( (originally at()v( db0pm*(f lp3(4(qi,fix u/ aretmompny $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will ha,m/ trei 6sri)6*v;of7c zqnfve the same resistivity as tungsten doe)fsitm fverq; /izo rn,76*6cs at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance l9qh/+8ozm gqof 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 wir*m5 md graz99g*0ig rge (used z*095gg9madrg irg m*in 15-A circuits). 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 pwj+9by 83qhk *)xha ucm, 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 pbxwq 8+)uj3p9 k hy*ahasses 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 tnb-yr .ew8p,j he same resistance. If one has twice the length of the other, what is the ratio of the diameter of the longer wir-bjyrpw.e ,8 ne to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V power supply,u) +d fyixqt4cex38w - and a current of+xix u 384fywdtc)eq- 0.4212 A 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 followed by 5.0 m of alum a+1j lovu2:muinum, both of diameter 1.0 mm. A voltage difference of 85uvmu+loja1 2: 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 important9le9nv,a,qh7lgf mz - that the value of a resistance not change with temperature. For example,zl,qv9eh ml9,-fg n a7 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 exs 6uq.i4(golt k4 9dwlectric oven is designed to produce 3.3 kW of heat when connectedidqku(xl46 tgs9w.o4 to a 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 player t4x( ;zktevnw0)w ylrzku x n9t( s2l00hat draws a max 2( vk wtx0zl n4(txe n0kuz)lswyr90;imum of 320 mA of current?    W

  What is the maximum voltage that can be appl( zi9xyqcg4as.5 b(sbaa 3f o)ied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current ch2kx )e(ot9h/7 v jy pb5lv8kthrough, a 75-W lightbulb connected to its proper 8p9l o7hk/ xb2ct(ekhj)v vy5source 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 e7s d31kw8ldcw0b1 evf/0 uzj110 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 1250v77gcd804qo6 sgd ah joja9a; 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 lightbulrwaz.n a24k1 db in Europe, 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 w 1dazn4 rka2.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 toaster use in the mo-a i.j ,,kf5f1(m 6ecjfpjl btrning if it is in operaabfljfcfe16- ,ipjt5,.jm (ktion for a total of 15 min? At a cost of $9.0\,cents/kWh$, estimate how much this would add to your monthly electric energy bill if you made toast four mornings per week.
energy $\approx$    kWh
cost $\approx$    cents/mouth

  At 0.095 dollars per kWh, whatxz6 e (bq2pn*n9s hs/t does it cost to leave a 25-W porch light on day and night for a year?bxns *s2/(tp96eq nzh $\approx$    dollars

  An ordinary flashlight uses two D-cell 19b;fr*fe n lz0veer43.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 4ebrrfn l*;ee39fvz4 050 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 enerruj3hqp)gj od 9- e04mgy 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, /m9l;;p8wi4 c r mo8+ath +pjgylo8hj can be used without blowinlop;89hwo hi4;gr +8cm j +8lay/ mjptg a 15-A fuse?    bulbs

  An extension cord mad7c85*loeqy:j mxx1 g9y9pf kne of 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 15.0 A on a 120-V line. How much power is 9 y elnx1q8of95jpxc *ym: kg7dissipated in the cord?    W

  A power station delivers 620 kW of power at 12,000 V to a factory through wiresorko t+.) +tyirx.d4u with total resista)yd.tir.++ kourox4tnce $3.0\Omega$ 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 connected9 gvum n,t-.2 pao0)dnp axbl) to a 240-V line is 17.5 A. At what rate must cooli2a),g u0tbpno .vld9nm-xap) ng water pass over the coils if the water temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to heat a cup of water for coffbag6gu*0d, viee or tea. If the heater can heat 120 mL of water6* agiub0d vg, 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 currentix4:cas(pg*gyk/ax,do : . . 9xwalnss5zr c; in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak vwd,.p. pzqji sv:7 ;hfalue 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 thsd d6nm ,; )xo/u:.qy-cbzk fge $120-V_{rms}$ 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 nieqdw35e /3l1500-W device is 5.4 A. What is the rms voltage across it? ndee3i/5w 3lq    V (Round to the nearest integer)

  An 1800-W arc welder is con7op huem2 n)l i(8 /mj*etg*nmnected 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 poweaz/kl7l z m6+wr dissipated by a 3.0-hp pump connected ta 6k+zwlz7/ lmo a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to a xw ms yzh2c 9y c1:apj(o:t,+h$240-V_{rms}$ 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 d;su6 vb tmr0n p1/9xqa 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-cpu,i k a+e2*yopmy ,3diameter wire carries a 750-mA current when 22.0 mV is app,ac*pp2eyyu 3 +m,kiolied to its ends. If the drift speed is $ 1.7\times10^{-5 }\;m/s$, determine
(a) the resistance R of the wire, $\approx$    $\Omega$(retain three decimal places)
(b) the resistivity $\rho$.    $ \times10^{-8 }\;\Omega\cdot m$
(c) the number n of free electrons per unit volume.    $ \times10^{28 }\;e^-/m^3$

  At a point high in the Earth’s zdz i:k fkxaz:3wm73: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 jig 2 flc;blv7..jhi* 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 

  What is the magnitude of the electric field acrob z5zpyiv6;2gss 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 sg x8 5xim-kp)ahk9q;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 t5ps)8h xkxgk-mq i;a9he 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 transmit one action potentzl m8c6eb oju7u9r xbb 97s *zydcq*-/ial 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 average power is required fdquceb8z 9xzsr67cyu7b b -l *o 9m*/jor $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action pote(u; kj+r5rejihu8e /l u.vgd +ntial, $Na^+$ 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-hou,r5wr8 yq/ arur?    C

  What is the average current drawn by a 1.0-hp 120-V motor?vz 3* ,v70f9koz lqhjm $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights: 6;uddt5ou)q )o7m3u)yvj sog qhz;j on. If each of the two headlights uses 40 W and each of the two taillights 6 W, for a total t :j)5ozodq6ju 3hs u)u)qvo ;7dgm;yof 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, 151+vu 9csa862lv p8cm e*u qprp00-W heater is 5.4 m long. If it is made of iron, what must its diameter be?6+qu1u28l8 c svvcm r9a epp*p    $ \times10^{ -4}\;m$

  The conductance G of an object is defined dt v.wfw z0.r9vsnj- (as the reciprocal of the resistance R;v9f(vd r-j.ts.z0nw w that 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. Suppose that 2t lo yw5h7xw8instead 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- hlt7w2oxw8y5diameter 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 )z0rd0u) kxps1.8-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 hg gouv(;xm w- a ely3r6)uo(2salf and the two lengths are wrapped together side by side to make a thicker wire. How does the resistance of this new combination coga-2ug(woou;ys r6 x(lmv e)3mpare to the resistance of the original wire?

  A 1200-W hair dryer is designed for t qn5f(3zr,5r5uob9f po 4tid117 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 s q;+ek/tp4 dcbo it does 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 p;tk+ bd/qp4 ceroduce no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by thelpa5/ l ;zr j//+xleeh 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 deliveat3fgvzgbdc0k8 +( 93n1ppq iatf)+qrs 950 W of energy per second to t( 8 +afd9pq31k +bcitn)za3f0vg pqgthe 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 sax1 p- wfes,p8kq0xz1vme material. One conductor is twice as long and twice the diameter of the second. What is the ratio of the power tfw xk8-q zspv,1xep10ransformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is v2cnei4wx2y12x (xu9a j7accused 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 hooked to a 2409;wf+b).8i3weozxkzt o /whw -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 batte **on/2x t9ynj:vnqmwries as its source of energy. Its mass is 1560 kg and it is powered by vnnjw2 9omn*y/:* xtq24 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 rer4 lqrw(gq *0psistance of $12\Omega$ when cold (20$^{\circ}\,C$) and $140\Omega$ when on (hot). Calculate its power consumption at
(a) the instant it is turned on,    W
(b) after a few moments when it is hot.    W

  The Tevatron accelerator at Ferm+;dxry( 9s2 n)cr uezikt90dyilab (Illinois) is designed to carry an 11-mA beam ) y9kc9ndz;du +t(2yrreix0sof protons 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. T gi3cc yabh*8kge4n u:5c8gk *i h;kk)he connecting cord is copper wire with a d :c g kg 8i5b3ia yeck)u8k*ckn*4;hghiameter of 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 r8m/3:yx8snnyn+qo q sb:/ rpeating element is a coil of Nichrome wire. When uncoiled, the wire haq:xnrnr/qny 3/b: 8y8m+sps os a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies *ukejb/zm/6px6 s t*2 w as;xcfrom 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 difference of 15%. By what percentage does the power delivered to the headlights vary as the voltage changes fro mpksj*zsu 6/xbaect ;26*xw/m 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 applicatig a( j6fdwj(*dons. Lightbulb B is rad(*gjda(w6jf ted 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 i - nd b64f/hc7c0fg exqp/ux4is used to connect a set of appliances at 120 V, whiccfgc b7u 4-/xdq40exh fnip/6h 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 dq7b 63f0ez1wzh:wacz b-ew d* - f/ftmiameter of 3.00 cm and an outside diameter of 5.00 cm (F :h3mzf0e fb1ec7w-6 wb fq*z zd/twa-ig. 18–37). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so t n3g7igl ,p8zl a1epj(hat its length doubles, by what factor 3eln1zpji g7a ,8gl( pdoes the power dissipated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlighuv7pa 0g rz(u.t bulb operates at 0.20 A and 3.2 V. If its resistgpur . v7az(u0ance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$