What quantity is measured by a battx1 k2,6ed6- aj:ut bszhidez;ery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow away from tv4*m zkj2g*) ;jheu ethe negative terminal in the circuit. But within the ce2t*)j*u4j;zvekh m gell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being umq3eus /kgdp40zf3u5 sed up: battery current, battery voltage, battery energy, battery power, or battery resistance? Exp5g0 4d e/pkzum3qus3flain.

One terminal of a car battery is said to be connected to “ground.” Since it is64agg6rntpqi8cy5 jyogc+ u f(uy.; 3 not really connected to the ground, what is 6.oq gaf8p g4y;3nrt6iuc 5j(gcy+ y umeant by this expression?

When you turn on a water faucet, the water usually flows immediately. You 5cd:ohk a7 2hmdon’t have to wait for water to flow from the faucet valve to the spout. Why not? Is the samk:o 57hcma2dhe 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 u:ss /ir1sq:7p+6t.iajh6j-km1 hxuufin +r have the same resistanci. pr6q7mr+/ kxnah6 hu:i +s1 is sf1uj-:ujte? Explain.

If the resistance of a small immersijzmo a/kj l.02on heater (to heat water for tea or soup, Fig. 18–32) was increased, would it s0kjl2z/ja m .opeed up or slow down the heating process? Explain.

If a rectangular solid made of caqxxi q0, a( )*nbkr7cqrbon has sides of lengths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resis07q,q(cri bnk *)qxaxtance, (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 lightbfwu gu8bc919a ulb burns out?

Explain why lightbulbs almost always burn out just as they are turd*rsa4j6 uykbm:a:6wi v*mv3ned on and not after j3 kyv6 swm4m:rv:6d i*a*ub athey have been on for some time.

Which draws more current, a 100-W lightbulb okuq )btmxp,*p:gjh i *j ho157r a 75-W bulb? Which has the higher resis* b7,kp 5) g ho*1:mqtjijphuxtance?

Electric power is transferred over large distances at very high volto49pos+u7v va ages. Explain how the high voltage reduces power losses in the transmission pav 7ou+vo94slines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fusejg781f zeuiq*c3ob xksnjy6 2 )n,g:s with a 25-Axy38,k*s:es j) f62zunogj 7ibg1 nc q fuse?

When electric lights are operated on low-frequency ac (sajv t4t + aa,g-uk bdo2s+b61xay, 5 Hz), they flicker notig6k +bx4,-bsu dv aj+oa 1tta2ceably. Why?

Driven by ac power, the same electrons pass back and forth throughv;9rc7 y s t-;f 5hu+hgihc(it your reading lamp over and over again. Explain why the light stays lit in(f y;7 iihvsu; 5cg t-hhcr9t+stead of going out after the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. Immediately after yof9x 1e u+qck9 b;ow5the toaster is turned on, is the curreno wf+ kqe1c;u59 x9byot $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Exp/1 kjgb 4dare0lain.

Different lamps might have batteries connected in either of the two arrangemeolz jddk 6k8/3nts/kl 3kdzod8 6j shown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. Hosgjr/ su8+9 qz3mq u)yw many electrons are flowing past any poimz+3ru9 uqjy s)g 8qs/nt in the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station char6m( aj/vakv)8xgki f-ges a battery using a current of 6.7 A for 5.0 h. How much charg- ji kx)/v8k6a( mfgave passes through the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes if8vlvj0e z (qyt7.0lcg:mt 9 tb $1200\,Na^+$ 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 produces a currentxo q6r:xd;vh 2 of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A sb-rp m p277lqyhix48 of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugt ygec5qd9(mm:1xeq( ged 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 dmo.qz te9-/ flcr z/.mryer has a heating element with a resistance of $9.6-\Omega$.
(a) What is the current in the element when it is connected to 240 V?    A
(b) How much charge passes through the element in 50 min?    $ \times10^{ 4}\;C$

  A 9.0-V battery is connected to a bulb whose resistanc vixhm m3jery2e2(n bp. 57m.ce 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 2800c2, vuid 11q ukigre k2-u70fo A (Fig. 18–34). The line h7f2id1,k 20gu-ceou ukqi r1vas $2.5\times10^{ -5}\;\Omega$ 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 Aydgpc(u 3 72q-x-bwmi0 hh7lj 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 resist4r aa l3j7nzxb:4 skd: m-dp:gor.
(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 1.0bjrt2z6 t56tn 0-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 in diametaopom 5;90pv ker?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire 2.0 mm cd(u)znak6 d) in diameter, to 20.0 m of copper wire(nuakdd)z6 c) 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper v87eb)wsk0 u-)qa lwtwire have the same resistance as a tungsten wire of the sl-u)s)0vwaw7 e tq8kb ame length? Give numerical details.    mm

  A certain copper wire has a resistanhc q/6 ,smnk0tce 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 cop-bskc2v t/l1u per wire (originally atl 2kc/-sbv 1ut $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resisl:2m5yuj):dvipu37 ll ;ayq4lf r5/ujk kef9 tivity as tungsten dd4upm/f q7yfry)lik j; k v::35le 5uul2 la9joes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has avau 3c,yw *)me resistance 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 drop along a 26-m length of household no7b 9n07fgm 6tjjy3f zaxlf0b1. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm and carries a 12-A currentj lt 91 by 6mg0bfx3a7z0fjf7n.    V

  A rectangular solid made of carbon has sides of lengthn p0d0 9sk3mm7 wty6bss 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistank9n30bdmpt 0y7 mss6wce 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 lf4tv y6- f0 9mqzhei-vength of the other, what y t9 vv0mqi-fhe4 -z6fis 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 suppq)+ hr-;6 uhqroh wf+sly, and a current of 0.4212 A is precisely measured atq;oq-f 6h)hrw+u +srh 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 mevw4v2jgy; 6h*w+ qix of copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 m h *2xwvqvg64+wyi;jeV is placed across the composite wire.
(a) What is the total resistance (sum) of the two wires? $\approx$    $\Omega$(retain two decimal places)
(b) What is the current through the wire?    A(retain two decimal places)
(c) What are the voltages across the aluminum part and across the copper part?
$V_{Cu}$    V(retain three decimal places)
$V_{Al}$    V(retain three decimal places)

  For some applications, it is important that the value of a resistance not chan8g(1y ksa s;nige with temperature.k81s;isyn ( ga For example, suppose you made a $4.70-k\Omega$ resistor from a carbon resistor and a Nichrome wire-wound resistor connected together so the total resistance is the sum of their separate resistances. What value should each of these resistors have (at 0$^{\circ}\,C$) so that the combination is temperature independent?
$R_{0C}$   $\Omega$
$R_{0N}$   $\Omega$

  The heating element of an electric ov2 fvte, fbp- h4e:.ilden is designed to produce 3.3 kW of heat when connected to a 2tv.hf, pld b:ife4 e2-40-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power coned+8:gwbkv5 f kb l57lsumption of a 3.0-V portable CD player that draws a maximu bbk8:5fdwvllg k+e75 m of 320 mA of current?    W

  What is the maximum voltage that can be applied across a ;p jokmad 9 jbfjvn+vl/f20.-(d ww8 l$2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, ay8z9v lhjn9k 0ok m:(v 75-W lightbulb connected to its proper source voltage v8:9yov(h9zkm knj0 l 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 j,m,y72 u .gzrq:0moma vp:wn : qgr8z
(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 twokbd(p l(ug ( (ar nr2(ef/ifz7 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 in6da-w .r8 c5 48jamox;pn ngnennq .w: Europe, where electricity is delivered to homes at 240 V. If you use the lightbulb in the United States at 120 V (assume its re n6nx-rodnn:m8 5wgjcn a w4q.e8p ;a.sistance does not 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 toaster use in the morning icr6o1xknmkd4x *w x 0,f it is in operation for a total of 15 min? At ax1r6*k xwx0 nmc4dko, 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 toyb0t1 /z xh.wn- z9eohhxzq h..nre23 leave a 25-W porch light on day and nig.yxh/x een.q9z3w2rhnh-10 .z b hotz ht for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell znhb/l . d:bhqpiu +r4 ;7j.n5 mp.qxh1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb dra.lb5zb:.pjd+m; qrpi n . 4xq 7hnhu/hws 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 storr1/,jjgnas rpl)py7, ed in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbpo1io,kn krw y20e4 l+s, connected to 120 V as in Fig. 18–20, can be used without blowing aw,el pny r k21ooi4+0k 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 copper wire8pqoiwl2cw qy3 (ody.i,+cc6p-/ twh ) 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 dissi ch,cy2pl3qp i.+y/(8toq6wwcwi o -dpated in the cord?    W

  A power station delivers 620 kW of power at 12,000 V to a factory through n25ezi.e)ubjc/ b;q5e tn4 ac wires with total 25ue.ncbe a bizn45 ;/t) jceqresistance $3.0\Omega$ How much less power is wasted if the electricity is delivered at 50,000 V rather than 12,000 V?    $ \times10^{ 3}\;W$

  The current in an electromagnet connected to a 240-V line iz8 /3)sg 92xxzsj c y6oydilg.s 17.5 A. At what rate must cooling water pass over the coils if the water temperature is to rise by no mo 3)2xs8x/y c6dzz.iy jlsg o9gre than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to heat a cup of water for cotikz4*pqm ,su m2kfg m5l5;r0ffee or tea. If the heater can heat 120 mL of wam2z*mm ;tpiu0l 5k4rk5qs fg,ter from 25$^{\circ}\,C$ to 95$^{\circ}\,C$ in 8.0 min,
(a) approximately how much current does it draw from the car’s 12-V battery, $\approx$    A(Round to the nearest integer)
(b) what is its resistance? Assume the manufacturer’s claim of 60% efficiency.    $\Omega$

  Calculate the peak current in a-ac0 ej0 nkqn-nswilttj e12-)d7z j, $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, is across9s ncm9fi-iv 4g.xz+b 2j 3sgh 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 resistanchdy 2-vk23lmns 6m zb)e 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. Whazzlu;xrkr9i50s6)7yjwhz+7h*nr1 nnd tg v 8t is the rms vo* sxd7u0tgr zhnz7ylwn1;j5 r6i hrzvk8)9+nltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder qdbew78x )j:- c3w dx hgw23ns*1ij tlis 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 dissipated by a 3.0-hp pump+8ysi 6r6x .rxao02bbbe.u yg connected .br 2rgb8u6+ex b yx 0y.aos6ito 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 yo6q7)vx;s yi$240-V_{rms}$ 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 cih(dxq --qqz :opper wire carries a tiny current of $2.3\mu A$. What is the electron drift speed in the wire?    $ \times10^{-10 }\;m/s$

  A 5.80-m length of 2.0-mm-diameter wire carries a 750-mA current da wzkmjx2rgf /ha6:*pw.c : .yldg--when 22.0 mV is applied mw- wrad : /:.g px-ga*26cjfl.hdzyk 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 atmosve0 yrogikl.v ; 1ad9;phere, $He^{2+}$ 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 atmolk,g+zbee;y5fxgc : zxj-5xy/2b(y dsphere, $He^{2+}$ 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 a2rpn;o: tayxy7tl m:j*7aqa )ep0hq4xon 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 potential hhet+l pbl.ea+lqvor :0o+(+is detected at a point 3.40 cm down the axon 0.0052 s later. When the action potential is detected 7.20 cm fv+qooeh(lr+:ha0 +p t+ lb. elrom 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 energy is requi; s) 4hguj,gmhred to transmit one action potential along the axon of Example 18u gm;,jg4sh)h –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 potential) y iu oo9i:vox5-mmbf52kdv(, $Na^+$ 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 theg1le o/16ptrm v,1hh/w31,ghkmkg dn re in 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0-hp 120-V md q/dc0.cn q3aotor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each ofm w cgb7q lo4.ezc61h0 the two headlights uses 40 W and each of the two taillights 6 W, for a total oc 7z0beow6.lgh q mc41f 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 11m qfj,rop5sl-p/:t 3rr sb-v50-V, 1500-W heater is 5.4 m long. If it is made of iron, what must its di,q5 -blr/rf st:r os p3-pvmj5ameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of the resistanjrm3rg(jyp; i7 e*h6 -fri3kdce R; that is,hgrpke;-fyrdmr*37i6j( j3 i $G\,=\,1/R$. 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 ins-* bplll(k// :mk(:jtpjvk d ntead 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-diameter copper wire, estimate the cost of the energy lost to heat per hour per meter. Assume the cost of electricity (llbn-kkd*m: l p//kj:(vtjp is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular house2hao:wz1bl 1xhold 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 and the two lengths are wrapped ub0qki0vux:n1s*4hr together side by side to make a thicker wire. How does the resistance of this new combination compare to the resistanckux 4 00*ub1qvrs:nihe of the original wire?

  A 1200-W hair dryer is designed for h/5kk1 oh7;zwq fztz. 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 j7 khva.4xfr 2thick enough so it does not become so hot as to start a fire. What diametehk 42a rv7fj.xr 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 given by the uiwz3 ie/ufuls;3x )6equation $I\,=\,1.80sin210t$, 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% efficil x5gpg9g -r /t4lifh9ency delivers 950 W of energy per second to the -9 g9glirf/p4 5lgxt hinterior. 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(:rxf6a wul9y o het(0 of the same material. One conductor is twice as long and twice the diameter of the second. What is the ratio of the power transformed in the first relative to the second rl fo0:9 yhx6(we(tua? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room ob,05l/;cq e. jjsvqjcj cgx 4o, yyy+4f 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 n 5 akj3v2gpin- z 62gcl0okf:240-V source.
(a) What is the resistance of the oven?    $\Omega$
(b) How long will it take to bring 120 mL of 15$^{\circ}\,C$ water to 100$^{\circ}\,C$ assuming 75% efficiency?    s
(c) How much will this cost at $11 cents/kWh?$    cents

  A projected electric vehicle makes use of storage batteries ah /yp3 hu:s)s flb 6 l* 72e0bf(sojomg3mbm/gs its source of energy. Its mass is 1560 kg and it is powered byump37mhg2se/f/ 6 sb )l:lyg ohjbm0 (3f*bs o 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 light 56enm,o cbpc0- e(u nk:gt6ff;oyc5tbulb 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 cab r9 ,om2oku t,jhmn1vk o r,27ki4.*vqg)ojprry an 11-mA beam of protons traveling at very nearly thk4nk oko t,r1gvom*972.uqmij ,rhvpj,o )b2e 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 is c)tf9)i r8*i-* vvj2 fmksjjt qe l0a.zopper wire with a diameter of 1.628 mm f*l 8mvvj9i )0z*ts) fieq jra.-tkj2.
(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 heating k-m6tf(0g tx)jnk3v85jol:w rfjk 2w element is a coil of Nichrom j83n6tf:m2) jwgrvo -wxkl50f(kk jte 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 voltage v8 ekwvl(90w fvaries from about 12 V when the car is off to about 13.8 Vv 9w lk08(ewvf 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 andmf9) zzcb ;ep7 40 W for household applications. Lightbulb B ip ) ;eczf9bzm7s rated at 12 V and 40 W for automotive applications.
(a) What is the current through each bulb? $I_A$ =    A $I_B$ =    A
(b) What is the resistance of each bulb? $R_A$ =  $\Omega$ $R_B$ =  $\Omega$
(c) In one hour, how much charge passes through each bulb? $Q_A$ =    C$Q_B$ =    C
(d) In one hour, how much energy does each bulb use?    $ \times10^{5 }\;J$
(e) Which bulb requires larger diameter wires to connect its power source and the bulb?  ----待选择----Bulb BBulb A 

  Copper wire of diameter 0.259 cm is used to connect a set of appli0f0-c 5fa8klihv- pvcances at 120 V, which draw 22c -v8v afhkilfcp50 -050 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 insidecu cn.wv :b)2.l 8at-bqz,kwq diameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–ku8a ww)qvbbt- 2.clc n.q:,z37). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its length doublesfk ry270cnx v;, by what factor does the power dissipated in the wire change, assuming it remains hooked up to tn v2c7fy ;xk0rhe same voltage source?

  A tungsten filament used in a flashlight bulb opers9sg8zi 9p 6zrates at 0.20 A and 3.2 V. If its resistance agz9 ir9s86zspt 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$