Whatquantity is measured by a battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow away froa 5wjcs g+nminv0*)6 zm the negative terminal in the circuit. But within the cell, electrons50 ajnm*gwsnc zvi6) + flow to the negative terminal. Explain.

When a flashlight is operated, what+nfo/kre.j to rg/65 y is being used up: battery current, battery voltage, barj o 5t/6o rfyngk+./ettery energy, battery power, or battery resistance? Explain.

One terminal of a car battery is said to be connect6x es3rw--t qued to “ground.” Since it is not really conneu3sq-we 6tx r-cted to the ground, what is meant by this expression?

When you turn on a water fm0eimn/:jj pr62 t q6taucet, the water usually flows immediately. You don’t have to wait for water to flow from the faucet valve to the spout. Why not? Is th60 /6jte:riq 2mnpt jme same thing true when you connect a wire to the terminals of a battery?

Can a copper wire and(u9sig*bv kd dlh)i ; 1vdaq.3 an aluminum wire of the same length have the same resistance? Explaii qhbd3. sv;1lvudk9 g)(a*id n.

If the resistance of a small immersion heater (to heat water for tea or s6b0 azrkmgag ))mp01ooup, Fig. 18–32) was a )ko 0mg zbp)60m1garincreased, would it speed up or slow down the heating process? Explain.

If a rectangular solid mag,k5tv 5y,jhb de of carbon has sides of lengths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resj5,bgk5 hvyt ,istance, (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 lightbulb burns*b. 9 vi0zp 5hc 2v;tav1pvky +brh(rd out?

Explain why lightbulbs almost always burn out jupz k-o :+28g 9mo2qvpn x7bapmst as they are turned on and not after they have m9+ b:m q-o vx ka7z2pnp2gop8been on for some time.

Which draws more current, a 100-W lightbulb or a 75-W buq c943f p1ajydq htf79lb? Which has the higher p 7a194f c9th3yj qqfdresistance?

Electric power is transferred over large distances at very high volta2cw*jo s-km 0uj4/xq6l3 0s:x jjag tkges. Explain how the high voltage reduces power losses in the transmlqgk2jj 4jx*:m sc6ka/-0 0xw jsu3toission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replacb9gmbawa b2; 52 l j cx:.jg7v2gaceh8e this fuse with a 25-A b;:a2 gx572cj ba.a gm8glv 2hc9 bjewfuse?

When electric lights are operated on low-frequency ac (say, 5 Hz)5m*tli( va)rm, they flicker n m5avl)*(ir tmoticeably. Why?

Driven by ac power, the same electrons pass back and forth through your reading 2tsvosq/13pvl weg6/ lamp over and over again. Explain why the light stays lit instead of gt3v 2 svse qp61low//going out after the first pass of electrons.

The heating element in a toaster is made cq 3 4sfi li5lddbj;m0:y 3 c4xps7ip1of Nichrome wire. Immediately after the toaster is tusip5 pq;bj1 d ldl0x yic4s34: fc7i3mrned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? E(s jig+ ra64jkxplain.

Different lamps might have batterib9poq 5qbgvl 0q7cm /qvpgs 1(h/ i7+fes connected in either of the two arrangements shown 1/(0mhs f97q/qcgqv g 5vlbqppo+ 7biin
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 flo+wovuy0zp9 5 xwing past any point in the wire p 0z95yxvuo w+per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a boo t,d2u:xa 1jattery using a current of 6.7 A for 5.0 h. How much charge passes throt d 12xjao,uo:ugh the battery?    $ \times10^{ 5}\;C$

  What is the current in ampereszn pri/fn4((s 3r fr1t 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 nfgb/wn): r5 tx k/l,h1anh3jof a toaster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of curr6)c sb/ nddn)bent through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged o81ypfauo j - 4bi-yy. le9/bminto 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 el/0 rt yy+ .cm 2,hmfg:rd:c4kaj,xzfzement 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 resistan*b3 c-cgs o9q9oc9ds))bfdy sce 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 car 3( pivbt-(n0m) erz9 (h vcwhjkwpg,9x tj97jrying 2800 A (Fig. 18–34). Thekjb9-t3p )gn( mv,pjzt 099 hcvj7hi(we w(xr line 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 2b. )igjou2y*y *bavq;40 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 tl8h4 r u5o:feshrough 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 whosehbn kgv1sqneklh3-w9-*a k11al8g ;o 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 diameter? p*,a+/kmkhxv 5zgtkd )tl-o:    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 1lwb8jitm 925cal83 acsf+5n b0.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m ofw taibm c8+nf l jc35s92bal58 copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wi3cgbua n*t ;9kk5y;hz re have the same resistance as a tungsten wire of the same length? Give numericalnyz* u;a k k5t;h3bgc9 details.    mm

  A certain copper wire has a resistance of1we o651yuj eah6hn 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 af/ (u,n*h4cikht kd8o copper wire (originally at hc*tn, h4kid8 ok(/uf$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper wilkomnoq.2t*0y,tt g+v y.y*erl have the same resistivity as tungsten does at+0 .qkr,y*2.nyyv tt *eotgom $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb ha qv (.fezn95pss a 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 26du(/ 0r7rwov nnkp, q,-m length of household no. 14 copper wire (used in 15w,dp7 nou0rr(qnk , v/-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 cu+ bm.bjuls- .m, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for current t-u..sl jbbu +mhat 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..mh7i6 xn ptq length of the other, what is the ratio of the diameter of the longer wire to the diameter of .h6 m qip7.tnxthe shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wircjf1z4 u0 y -qnz gqg k6gm7;f8z4.isce is connected to a precision 10.00-V power supply, and a current of 4 n 7gkf0zg8 j1iq6g- z4 fqyc;c.zmus0.4212 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 alumc:es b)8kl) lpinum, both opc)s)k e8b :llf 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 is important that the value of a resistance not cha ncddi*nmnkgr b7je6) h,/uhn(q-* 1 cnge with temperature. For example, suppose you mad(* nn 7r 6*dbqn1ik-,ehum) ccjhdn/ge 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 produce 3.4wqcmey tqx4;nb e 0d7)/krc7 3 kW of heat when connected to a 240-V source. What must be4w7 /0q 7)qeey ;nk4rcbmxtdc the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-yj/+:di7hi1i o5 p vqoV portable CD player that draws a maximum d:qh ioj7vyii/ 1+5opof 320 mA of current?    W

  What is the maximum voltage that can be ap9x )eg yph- ne+n dmfo/ :zdt-+ljy+/mplied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and currerzzh84df0 x w+fpw6t+nt through, a 75-W lightbulb connected to its proper sou f0dp zz4+6 wr+8fxhtwrce 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 ratlqze n44,op )t wu0i:led 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.eh6)3cv swx0y
(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, where electricity is delivered to homes(wg9.wor x,uz1 s1d+v nyzai8gp9 2vs 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 proportional to power consumed.] 1p9 vzviu d+.8ay12wz,nsxs9 gogr (w   as bright

  How many kWh of energy does a 550-W toaster use in the morning if it is in operl )li;ag ..co72i7 dj uap6icpfd*eo3 ation for a totaluoa.e ilal7; gcdii.267 p j o3dpf*)c 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, what does it cost to leave a 25-W porch light on daaaqi0)8*ri-tjf v z)u y and night for a riqazt a j*ufv-)8i)0 year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries conn0b*nx8/wl6auo(ova m s7bo o+ected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when turned on. oo+ob vb 6x/alan7m*0 ( sowu8
(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 amounomolz;,:0 w ljt of energy stored in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, conndzn xxj1*7s,aa4ha. lkdr2 - lected to 120 V as in Fig. 18–20, can be used without blowing a 15-A f 4jdzad,7ks.hn-1l*aalxr2x use?    bulbs

  An extension cord made of two wires o :.kxh4c.j;wo-cld krcuh+hk bn3+8 yf 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 lin hn -+o. lxry cc.d4w8 u:+3;chjhkkbke. How much power is dissipated in the cord?    W

  A power station delivers 620 kW of pow h85 h wia(uf(f94zcheer at 12,000 V to a factory through wires with totaih(u w8ch(9hzfe a45fl 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 electromp/zv* ms:6qz ,hovtd /agnet connected to a 240-V line is 17.5 A. At what rate must cooling wa/o,hdv p zt*6qzvs:/mter 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 coffek38)+an bmzg3vc:i5 e- jg qsxe or tea. If the heater can heat 120 mL+bv zmg)s3kcq:- ng8jx3e i5a 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 current ic oprh:l9su(+ n a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 j4go u ij/o b;s f4gf w.+ulr/.z;btwa1m (v7hV, 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 resistance3j8 l 7ubiu97sd t-tdf 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 cuda-xj 4a+5t 7llv,lv jxhz7.mkq3h i:rrent in a 1500-W device is 5.4 A. What is the rms voltage across it7zlaq jvxmjxk.+i7al4 v5-:thdl3, h ?    V (Round to the nearest integer)

  An 1800-W arc welder is connected to eingwpsy o/90f-9v ) za $660-V_{rms}$ 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 a44dr.jx : yjhv 3.0-hp pump connected .x4r:v dy jjh4to 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;+/ gbxum-viu h.) ipfif1.n s $240-V_{rms}$ 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 cu/6vt+sug e v2jftx2a2 ks*iw+rrent 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 w/vaf)e 280fcp ta rh1iire carries a 750-mA current when 22.0 mV is applied to its e)8e1t f0cfa/p2rvh iands. 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 Eat2mcu3 n9i1wm) wmkt) rth’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 th9 uuoje;x3g *je 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 ach1euix4 r7u+,m8y5(f tw7;mzdf r k gyross an axon membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulatede+bl t 22d cl7l(e0qcj ezv9w2 with an electric pulse. The action 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 fj tce2l dc+l2vbqw97( 02l ezerom 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 required to transmit one action potential along the .s:k2qcn 5 hajnr2b *p jiz)q;axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to thea5qprn b zqhi2nj;s jc *:2.k) 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 potenti4r*9 efplaagkw 6bs:os-2 9abal, $Na^+$ 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 am)1e scno a1b+ o h0o0klhir+:ypere-hour?    C

  What is the average current drawn by x e(1 l5uh5wt,ipazh1 a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of the twq.ttdc1,bu/ hm-/ sxc2/f svzo headlights uses 40 W and each of the two taillights 6 W, for a total of 92 W, how long wil hc,d2/-xzm/utbqts/ .s1fvcl 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 roy kz qy5p0tt+ u18;jba02zymade of iron, what must its diaa8b5rt;kj2zy pyo+q 0yu 0tz1meter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as9l:pbqu+ eu9oky w 1l, the reciprocal of the resistance R; that i:1l pw+9yeuquob , lk9s, $G\,=\,1/R$. 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 me pf*w.+y0v6k f/wmz,bi5 ms 10 MW of power. Suppose that instead of using high-voltage lines to supply thesm/*f+.zf wikbe,6 m pm y05wv 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 h2o/ k8ravw vh4ym;hq; eater $3.0 h/day$ (“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 cnm+ dfy53(57+pewxe u*-n:ste p ho biut in half and 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 origihx t:web oipy+e p(-+dsnf3e7u 55mn *nal wire?

  A 1200-W hair dryer 3d btlq)9m+ cxis designed for 117 V.
(a) What will be the percentage change in power output if the voltage drops to 105 V? Assume no change in resistance.    % decrease
(b) How would the actual change in resistivity with temperature affect your answer?

  The wiring in a house must be thick enough so it do0 :sdct4*x :v ke)gngpes 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 prodkg p sn:vcdte4)x0g*: uce no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by themg13 y7j 7hyhhxdb1i ; 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 de)4(p5y 8 kg7k+ncgamd ;cf:5rwa zlkxlivers 950 W of energy per second tof4yrckkcakg;(7: z p l55w8n max)g d+ the interior. Find
(a) the power drawn from the source,    W
(b) the current drawn. Assume a source voltage of 120 V.    A

  A $1.00-\Omega$ wire is stretched uniformly to 3.00 times its original length. What is its resistance now?    $\Omega$

  220 V is applied to two different conducto:+ukrfgu yt9v, hm7/hfg3 pt;rs made of the same material. One conductor is twice as long and twice thev;h ff3p 9/k+tuy,mhr gu:7g t 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 1 vavo) sx+oy-3*e + mmzb+tjifx+b(kheat 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)uk5t xq;* z.,vr4rtyep h0yfurce.
(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 my ietpf3xm..,17x1anis o ch2akes use of storage batteries as its source of energy. Its mass is 1560 kg and it is powered by 24 batteries, each p11 coei3si.anfhx , 7y.2tmx12 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 resistancgj.c/jo;y gsl+: 8atxe 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 (Illlmr ht0g 8)b3z266lhs* uok fsis71eainois) is designed to carry an 11-mA beam of protons traveling at very nearly the speh hg zsm8al61 7k s6*u)2rotlseifb30ed 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 coppe65whfd. ajgy 6of j53ar wire with a ajaof6 whd6j f55y3.g diameter 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 4kzi 0e (kne4s*kwsc 9e0b md.to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What is the diameter of the wir9c .z k4s 4diebe0mens*0kw(ke?    $ \times10^{ -4}\;m$

  In an automobile, the syszmv+czq g3bpr91w 75stem voltage varies from about 12 V when the car is off to about 13.8 V when the car is on and the charging system is in ope cq35s1 rb9mv7w+z gzpration, 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 a8krmx(h0 a- t;i lj-dknd 40 W for household applications. Lightbulb B is rated at 12 V and 40 a t-lximd;0- khrkj(8W 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 set1q whhj9aov;2k 2s9bsw 2 7xyb of appliances at 120 V, which draw 2250 W of pow19w2j 2ko97qwabs h hxbsv;2yer 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 dia94qp6 lv)bklm ,ctn7grk.,8p r*u dgc meter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What rr*6tp kd),knql ,v bu79g mc.gl84pc 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 doubles, by t( od ,f2j lcln,r(hk1s-1otdwhat factor does the power dissipated in the wir2s kc(t, o 1d,nfd ltljr(ho1-e change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight z: vh ob1tzeuqu0* 47bbulb operates at 0.20 A and 3.2 V. If its resistancqzbeho :uu0v7z* t4b 1e at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$