What quantity is meay2 tbas-d,cf / zho ri.79bm4bsured by a battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons floc;e8 n:o;as ynms6 0ukw away from the negative terminal in the circuit. But within the cell, electrons flow to the e;ns k:0 a6 ymnoc;8sunegative terminal. Explain.

When a flashlight is operated, wh)4j+ ljgt lbvj a0kwqud+)2rl,0p b,vat is being used up: battery current, battery voltage, battery energy, battery power, o 4r +pljbju+0g)b,0,avqj v w2k )lltdr battery resistance? Explain.

One terminal of a car ba /qunno pr;6wb(n; kc9ttery is said to be connected to “ground.” Since it is not really connected to the ;qp; /w kro6b unc9n(nground, what is meant by this expression?

When you turn on a water faucet, the water usually flows immediately. Yo hhqi2,/oes .f;qngv+u don’t have 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 batgo in, qfh.q+;e/s2 hvtery?

Can a copper wire and an alle875zjh+hrs )nj d t4uminum wire of the same length have the same resistance? Exl8e 4h hjz7jtd)+5nsrplain.

If the resistance of a small immersi5w9mi d(8cd w0ixt p kh 1)f)yea,(owaon heater (to heat water for tea or soup, Fig. 18–32) was increased, would it s(10a)wx hwoif t,()yid wd 9a8cmke5p peed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has qrc 7gu4 ;ze vmoj/ u4e28-lgqsides of lengths a, 2a, and 3a, how would youqe8l go42vgz47u-rmec/ju ;q connect the wires from a battery so as to obtain (a) the least resistance, (b) the greatest resistance?

The equation $P\,=\,V^2/R$ indicates that the power dissipated in a resistor decreases if the resistance is increased, whereas the equation $P\,=\,I^2/R$ implies the opposite. Is there a contradiction here? Explain.

What happens when a l 4ujh+npl0f4f ightbulb burns out?

Explain why lightbulbs almost always 1f4zv.zavj56c . fdmh burn out just as they are turned on and not after thez . h1.cz5ma6dj v4ffvy have been on for some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which has the91kw eftfqg1. higher r1qgw.k1ftef 9esistance?

Electric power is transferred over large distances at very high voltagxdl5scc19 op5es. Explain how the high voltage reduces powl51d5c 9 poxscer losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it d6p4jxy1bhzq (g:.ne eangerous to replace this fuse with a 25:eypej(4qbn1 xz h .g6-A fuse?

When electric lights are operated on low-frequency ac (say,wrf;nvm774:.cdtx:d o utn+g 5 Hz), they flicker noticeably. Whv::tw;gxd.tnmo r+u nf77 dc4y?

Driven by ac power, the same el/0*f dq+n fjeoectrons pass back and forth through your reading lamp over and over again. Explain wh jfq/*+edn0 ofy the light stays lit instead of going out after the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. Immediauek( nx18;:a ctxky.xpa ,,iftely after the n8ufxia,xpy,e1c ka k .(; :xttoaster is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Explain-g4uu4ceiwd6 404dw4s/czakvf / q wg.

Different lamps might have batteries connected in either )1vewe oe q1k(of the two arrangements shown ik(wqe 1e e)1ovn
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows ia5+e0t x * rteo4uh d5zplv3q w:x(t9 be)3zevn a wire. How many electrons are flowing past any point in the wire per eezvepb+5( qt9xx * r 0lwo53de:4)3ht auzvt second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a cu u2-jbudo- ng2fu64y srrent of 6.7 A for 5.0 h. How much charge passessyo26 42u-udj u-bn gf through the battery?    $ \times10^{ 5}\;C$

  What is the current in amk s/r qd8s;yv,6 bmb7sng(q;ot fz,0jperes 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 toaste) yx dtw6mz-b/r if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will producez4* f7wfg4)gq:kej tt 0.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.51, qetv5xasg3m:l 7mo8 (cubh A when 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 resistvzgpo0)z ;pc2tu8q jh9q gf xjbk537pg*n :5k ance 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 buiw 045qjhg/at4n:qk 2)jpxgnlb whose resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transmix9w; .cfjct aw qfu- *+zv2d0hssion line carrying 2800 A (Fig. 18–34). The line has ;vtj 0uahcxf2zw*d f q-9 w+c.$2.5\times10^{ -5}\;\Omega$ 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 6.50uq.gee- wm ;.v 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 currengro 1kskz+br*w 06/dn t of 0.60 A through a resistor.
(a) What is its resistance, $\approx$    $\Omega$
(b) how many joules of energy does the battery lose in a minute?    J

  What is the diameter of a 1.00-m length of tungsten wire whose resistance mo;28: wr rflbis $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length ow;s 7jlncwem ,539ol+xcw9 fvf copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire 2.0 mm in diameia i oemy nrp 0(52/chbm(/ro0ter, to 20.0 m of copper wire 2.5 mm inor05om02b(yhc i/ n /(epriam diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistanceerw, km,4qe y2.-;b v(kpdzbd as a tungsten wire of the same length? Give numerical d; dkvm,wb.erdk2q , p-4 bzye(etails.    mm

  A certain copper wire has a resistancjz5y3q 7(*5piazs wg ze 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 o(jpwfjo kzb4ad 33zj3o*.w8 if a copper wire (originally at8(z.wdjjb4a k pj3f o3wz 3i*o $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will *y,)/fx fm/c ;bo p 719l+yx crahrpvehave the same resistivity as tungsten d e*f 7hv9cc;rry) 1xmxp /ab+l/py ,ofoes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of about ifgqc5y*:ww5y+ia72a8 xdo d $12\Omega$ 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 le*/j0y8uvm s-mx;ulx l ngth of household no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm and x8y *0sum/-julx ; vmlcarries a 12-A current.    V

  A rectangular solid madhoq srr)kjlzfn 3m*..8w.pd + e of carbon has sides of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes,qrd)k* .zlsp w3nfmjr+.h. o8 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 ca is61)ye8+ d g9xct)wtd i9uthe length of the )e 89ic1 dx aisyc9+wt6)dtguother, what is the ratio 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 connected to a precision 10.00-V power supp8vo5n4o*onyh ctc;8 f ly, and a current of 0.4212 A is precisely measured at8oo5v;no t*8c4fchny 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 o con/ r7eeyjc(/k76s wf 5.0 m of copper followed by 5.0 m of aluminum, boeksc/oj /6r77y( ewncth of diameter 1.0 mm. A voltage difference of 85 mV is placed across the composite wire.
(a) What is the total resistance (sum) of the two wires? $\approx$    $\Omega$(retain two decimal places)
(b) What is the current through the wire?    A(retain two decimal places)
(c) What are the voltages across the aluminum part and across the copper part?
$V_{Cu}$    V(retain three decimal places)
$V_{Al}$    V(retain three decimal places)

  For some applications, it isnk0snx/y*iwq3ugs98cs* ;p8, 1i m -skdnytj important that the value of a resistance not change with temperature. For example, sup0 p*tq,jc*/my1g 8i -3s ndkiwukn;s9ssx8nypose you made a $4.70-k\Omega$ resistor from a carbon resistor and a Nichrome wire-wound resistor connected together so the total resistance is the sum of their separate resistances. What value should each of these resistors have (at 0$^{\circ}\,C$) so that the combination is temperature independent?
$R_{0C}$   $\Omega$
$R_{0N}$   $\Omega$

  The heating element of an electric oven is designed to produc+*i9(d0 ub vpsm )vml*ng8wrbe 3.3 kW of heat wh+dm)sp089(i vl rnb b*vm gu*wen connected to a 240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of /,1lhd 3 grflka 3.0-V portable CD player that draws a maximum of 320 mA of cuf/ld,3 hkgr1lrrent?    W

  What is the maximum voltage that can be applied acr4(0hechvi.tnlb 7q zf ,ti e36oss a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, a 75-W ligv7j.:ikb qa17l y,*sxheu (jz htbulb connected to its proper source voltage of 120 V a 1s7h*qeklbj,7.iju :vx zy(.
   $\Omega$
   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. Calculp,.ovymvr +9 /he :dzzate
(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 twar7sy,5etv+ a g2t 09x mg2zowo settings: 850 W and 1250 W.
(a) At which setting do you expect the resistance to be higher? After making a guess, determine the resistance at
(b) the lower setting;    $\Omega$
(c) the higher setting.    $\Omega$

  You buy a 75-W lightbulb in Europe,lou-a(,fa28u q.emv r 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 is proporti -u2m(,fuao8. reqalvonal to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use in the morninrf , l onei8kgi-fj;sgil nx (e33-hxg;6:uk)g if it is in operation for a total 6h nufjo gleix3,-;i3)g :xfe;-(kg8lniksrof 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, what does it cost to leave a 25-W porch lcgwmv;n;brm wx 3l7-9ight on day and night for a r93lvxmc w;wn-7mg; byear? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected in seriesk9 yo **6:;trwo3mudwc0aeu a as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when em:3cru0o duk*ato6 9w wy;a*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 wla8sl /t o,n*.r x /:frm3brn3bm8zienergy 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 toetp/rw+tc+p2 g0yn3k)r::ozj lr;s g 120 V as in Fig. 18–20, can be used without blowing a 15-A fu w:cp:;gryzp0+lres )n2+3 t/rogj tkse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 1(bj ayg3t2c2 e6 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 dissipated in the cord? g cj32te2(ab y   W

  A power station delivers 620 kW of power at 12,000 V to a factory thrj7u-;q g+ i/ofef*4 gmmv5wl x m)nd)tough wires with total resi+-l)*vfoe)d m/nqx gm;5ftu gm wj7 i4stance $3.0\Omega$ 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 electrost-qvakw +fl01 m3fce v.y/ )cmagnet connected to a 240-V line is 17.5 A. At what rate must cooling water pt0c.s)vffm3 c wy -l+/ev1kqa ass 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 h4ruf6) ddxq3zeat a cup of water for coffee oq 4z3)dxfr6du r tea. If 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 cuaa3vh ex00 kz(rrent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak w6 thw3 h(q: 6avljp*pad0;tzvalue 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 resistan2ojyd q)b.v -4y m /rn3fl74)efnged ice of 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 device is 5.4 A 417 leq1bxo t4oltrk0. What is the rms voltage 4q4 1rl7bx tl0tok1eoacross it?    V (Round to the nearest integer)

  An 1800-W arc welder is connectedf:7 jbw6oa1c7iz5aw w 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-hp io2i-uyr k,7- oy3 jjzpump connected to a y -7o2zjrii ,yj3- kuo$240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected jzcq .c6b)zd- 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 2 z:; wq3.reu+mvrzprof $2.3\mu A$. 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 c7 m k6gp(yb1o zwhw6g(mw4 a1current when 22.0 mV is applgk4a6cpomzwm(7b 61 g1ww(h yied 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 atmospxp:nvr/fp w:o( ,phd-here, $He^{2+}$ 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 atmosp u2(ds ,omyyj)8j2vvf here, $He^{2+}$ 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 mem tln.7)q mo,apbrane $ 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 poten 7 eu3 vvufmp )4iximeq5f59,xtial 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 0.0063ivqmf37 ivuexu459mxp f e,5) s. What is the speed of the electric pulse along the axon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much energy is required to transmit one action pof,mx7::7kjf slgya h6tential 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–hy7k:xs7la :gf,f6jm9]. What minimum average power is required for $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action potential, n f s2nelo vvs yh+:57p1vu7bze;v) 3i k9yr/u$Na^+$ 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-ho*zg*6+-w 8jdjhf *j( ie zcorfur?    C

  What is the average current drawn 0s/ ctr 1 (l6q3ykv mnsx2rr aa71j)ytby a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally le4 u og.3hhagt loys+-3aves a car with the lights on. If each of the two headlights uses 40 W and each of the two ta.guo3 -salo4g +th3hy illights 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.t:vh+erybq - 94 m long. If it is made of iron, what must its diameter bev-he +9:ytrb q?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of the wl -* xyu,rhj/;v2csuresistance R; sh/xuvy 2*lj,w- cur;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 instead of usingupjlj (f1h:/7 bg u1c1zti)ov high-voltage lines to suctvi(pjhju fz/og b:)1 l711upply 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 cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular household uses a 1.8-kW he)c6nwlc/8d7ob y.fw4rf .ri bater $3.0 h/day$ (“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 together silglm i8b.7hy(de by side to make a thicker wire. How does the resistance of this new combination compare to the resistance of the original wire?.(l gmi7l8hb y

  A 1200-W hair dryer is designed for 117 f t*y5/hus (tyehr 09dV.
(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 a8gsl5a nbag* oli5 nz2a9d.x0 s to start agl2z 0dns a5a xian.b5lg89 o* 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 heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is giveip5v02ge7q6 m p; xt0,ib 3blz0elte on 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 deliv)5rdvvsp/of -rwa4 -mgn 4du-cv -o- jers 950 W of energy per second to t)-rn / pwmvddov--4o5vf-g4 jsc- aruhe 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. Oc q:e+g)kt ,slm/ 5gspne conductor is twice as long and twice the diameter of the second. What is the ratio of the power transg): gclk,q sps e/+mt5formed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to h,b42 ) qsnfhrd3pboi5eat 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 so*2tgfpyi6o4 ji f.;u4/k+oxul tw4erurce.
(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 mak .n jwnw lr7w/qjqr9nwg7/8*res use of storage batteries as its source of energy. Its mass is 1560 kg and it is powered by 24 batteriww 7jw/9lrn7rn. grn*jq q8w /es, 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 lightbulkf*b;i1b qe5. viip1ds hyh80b has 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 accelerator at Fermilab (Illinois) is designed to carry an 11-mA besrh q yj)*el4p994r eiam of protons rqehe 9r4)4lsp j9*yitraveling 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 vgr.z.r1f;.ids yi /pu 16kxnis copper wire with a diameter of 1.g.y zp k;dr vfs1. u./6xiirn1628 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 cv)el7cb y a3n i o050m;xz1zlronnected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has y l7i) 1; nz5erzm0lbxv3aoc 0a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from about 12 V when the car is off 6( .y*/bsmj tk rdi:jzhw53voto about 13.8 V when the car is on and the charging system i3(.5:v 6j*k rshio/wtzm jydb s 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 *cqv /v stnmj /qk6ho ru+(w,6V and 40 W for household applications. Lightbulb B is rated at 12 V and 40 W for automotive applications. q + m,/uhw vj6(ok/qcv 6str*n
(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 app xztun/ystzy.d*nl++,23wm ndx :t h 3liances at 120 V, :+nztnxtn2dx3 t+3/sy.yu* wldhz m, which 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 an2 :kh ,.j fnzbdwjfk;y*p gfnpc uq6m6)f5z :( inside diameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the resistance o:f py.nb m6j*h; :g ) w,zf kfnjd26k5zqcf(puf 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its length doub :zcd,zn /ql6rieo/s:les, by what factor does the power dissipated in the wire change, assuming it remains hooked up to theiqrco ,:zl e:s/d 6n/z same voltage source?

  A tungsten filament used in a flashlight bulb operates at 0.20 A and 3.2 /ai:) xei 3v6qk jbzj0ak5 di:V. If its resistance at 2e/6q53z) baxiivjk da j0:i: k0$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$