What quantity is measu+vi+yb8l 9l2a62 k.vp7zjk g3hs tbapred by a battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow away2o)hgs xhr0 2 qomobum:;tw,- from the negative terminal inbr:x ;hom-wt2u ),go2s om0qh the circuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used oxmhjbu+.-m + up: battery current, battery voltage, batterxm-+ouh .mjb+ y energy, battery power, or battery resistance? Explain.

One terminal of a car battery is said to be connected to “ :cvon5/z3tw5 mf. cfeground.” Since it is not rfvn:3 5 cwemfco.zt5/eally connected to the ground, what is meant by this expression?

When you turn on a water faucet, the water usually flows immediately. Y)f bu3 gj)okgy 6p3q;oou don’t have to wait for water to flow from the faucet valve to the spout. Why not? Is the same thing tgfg 3jukyp) )b3oq;o6 rue when you connect a wire to the terminals of a battery?

Can a copper wire and an alumc0yfo8wqq/e 5inum wire of the same length have the same resistance? Expcy85wq0f o e/qlain.

If the resistance of a small immersion heater (to heat wa8ouhrkh v br.-x-7 h7ater for tea or soup, Fig. 18–32) was increased, would it speed up or xu7 hra-vb7h8 k ho-r.slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, and 3a, how wo;,xm2i j2 yhvmuld you connect the wires from a,y i2jh;vm2 xm 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 lightbulb bura / h; c+a 7msn-hmly,k6/wzzj g1rlm5ns out?

Explain why lightbulbs almost alwaysra 6+5w6sp/s3a0hlg ewit q-z burn out just as they are turned on and not after they have /hg6tea0plzs riw+a65 q - sw3been on for some time.

Which draws more current, a 100-W lightbulb or a 75-W b82 /9om 85ohqbbkqugd8o+ mmzuc:i.a ulb? Which has the higher resistaum ob8boo5i8m9qgh /q ad2mz+ukc8 :.nce?

Electric power is transferred ovek kfs (g,gq1czo/ 5m3+ vde)zcr large distances at very high voltages. Explain how the high voltage reduces power losses in the tq(gd5/kczgk,e +zvo mfc3 s1)ransmission lines.

A 15-A fuse blows repeatedly. Why is it 3nekj fvpdd04m 44vn(dangerous to replace this fuse with a 25-A fusvfdp 4mvk04je(n 3dn4e?

When electric lights are operated on low-frequencgpm/tr 7u7czd8;bu4 h (,nuply ac (say, 5 Hz), they flicker noticeably. Whyuuphl4z;/bu, nmgd7p(8 t cr 7?

Driven by ac power, the same electrons pass back and forth through your -+jj7xxpq0s 2 qvh3wjakz r//reading larx02/va-xqh kq /j+7 pjs3zwjmp over and over again. Explain why the light stays lit instead of going out after the first pass of electrons.

The heating element in a toasterip s-cm7w34ir 2fjrp- is made of Nichrome wire. Immediately after the toaster is turned on, is the currenp jwsrp-i 34m2i7c rf-t $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a rgr9o6e*cr18o ilde y bsl5)r (:k9zilesistor? Explain.

Different lamps might have batteries conngw+7bk:.l mdaected in either of the two arrangements sg+adk :w 7mbl.hown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many electrons are flowing past any podrv(ebw+: zu p5yz/iuia((1 6tld bp 5int in the wire per e(r(ibu+iaz/(z5d1y6 t pldw ub:v5 psecond?    $ \times10^{18 }\;electrons/s$

  A service station charges a ba1nqfhh-k;4jnqhbt88wh7u + shs 0;s uttery using a current of 6.7 A for 5.0 h. How much charge passes through t 1suqh7kn 80 wh4+8 ;nthf-j shs;bhuqhe battery?    $ \times10^{ 5}\;C$

  What is the current in ammrx 5g74)ioe i(flwd 6peres 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 toaster u4l( mgb9acg-if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current through a iw. 9kzdty25qa7b2f xr;uea0$3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into amuf05sn pdp7xp5 f5v1 haw6q6 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 remi2* f fgl-qy+rkpz 3*sistance of $9.6-\Omega$.
(a) What is the current in the element when it is connected to 240 V?    A
(b) How much charge passes through the element in 50 min?    $ \times10^{ 4}\;C$

  A 9.0-V battery is connected to a bulb whose rex q11,b 5slpj6uo. ickpte0 g*sistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electri/ gkf2bd-1xymh qz(*i c transmission line carrying 2800 A (Fig. 18–34). The l yb/m2*h 1g(kxd-zi qfine 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 20t,i r -e*:obgauea4e40 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 resnmuw:(f s5+v :. zad,wbo4vlsistor.
(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 iwmu mr3/,i2by s $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wkuh)w ; kxce+0ire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire 2.0 mm ngz6 gl5ky6zoc :42tzm34v5jrw 2wf u in diameter, to 20.0 m of copper wire 2.5 mm in dilwo f:n t6w4u g6yrkc554m3jz z22gzvameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tun sv(g.m*so ,9icw wf(vgsten wire of the same length? Give numerical (wvso9csv *(gwm .if,details.    mm

  A certain copper wire has a resistance of t: xi5;gk1pay5r s:lx $10.0\Omega$ 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 (originally a 5e8u1gae l4: v6lsr:a jx1eict:1ule:6e jg 81ix ac 5svle4ra $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivi 6emr1y :7enrlty as tungsten doesey:71m rren 6l at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has amo;f,oy jwh -g7) vbr8az1pn. 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 no. xvdccn7 l.kass l6/9114 copper wire (used in 15-A circuits).1cl9axn dvk c/s 6s.7l The wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of 9ybcw:5qh 0p8/bhbo :0un jedcarbon has sides of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectivel9y0 c bu5 qwj 0ho:/h8:bepdbny (Fig. 18–35). Determine the resistance for current that passes through the solid in
(a) the x direction,    $ \times10^{ -4}\;\Omega$
(b) the y direction,    $ \times10^{ -3}\;\Omega$
(c) the z direction. Assume the resistivity is $\rho\,=\,3.0\times10^{ -5}\;\Omega\cdot m$.
   $ \times10^{ -3}\;\Omega$

  Two aluminum wires have the same resistance. If one has twice the length of th0niey*rw *rydm (a )w*e other, what is the ratio of the diameter of the longer wire to the diameter of the sho)rn awr id*(we y*my0*rter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00* bm b t 96qxhity::b87m:etzqn*t2s r-V power supply, and a current of 0.4212 A is precisely meas8 semrznbq:h9y m:tb* tt*6qt7ix: b2ured 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 8kz9 oas-w l)z5.0 m of aluminum, both of diameter 1.0 mm. A voltage differenk-z8a )os 9wlzce 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 zi sme8d6jbo)vu4pgx9x9) 075vje /rhz su,f value of a resistance not change with temper)8sus 54h jmj 0 )df7v9uxb /,vx9eerz 6pgoziature. 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 oven is de4 gm vg:elc2rx .l5l4vsigned to produce 3.3 kW of heat when connected to a 240-V source. Wh4 grm gx.24levlvlc: 5at must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD playerql1 4d bif ;)6rn: 2ju;bocrcc that draws a maximum of 320 mA oflrcnbc41 2;b:f i) 6jrqcuod; current?    W

  What is the maximum voltage that can be applied acrossazq5niw khv1x / 0wu 8yc7l88u a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current qxeudibk8o(,: c4zfj4e, j 2n through, a 75-W lightbulb connected to its proper 4:j idjf2b,o 4u(c znkeq,ex8source 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 110 zf9m b+z27stwvoe)b mb2k+ kq+l 2z 8mk8wiy6W. 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(mkti x.--66qnzrt qq 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, wherejq kzl ;4b1udr9:u6sa electricity is delivered to homes at 240 V. If you use the lightbulb in the United States at 120 V (ass a1qlzk6:4bs udr ;ju9ume 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.]    as bright

  How many kWh of energy does a 550-W toasterweimvpim t97o .009c f use in the morning if it is in operation for a total of 15 min? At a cost o cp0mftwie7o 9i.v m90f $9.0\,cents/kWh$, 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, whd zd ggk7x/o8)sd;:xoi/m3o mat does it cost to leave a 25-W porch light on day and night for ag/moskizo;/xx3)d8 md 7g:d o year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected in series as ip:asm6(c u ,1xydd( man Fig. 18–4b (Fig. 18–a6(1dc xas myp: ,umd(36). The bulb draws 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 storedgl o-,;zmah3 x 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, can/n7.tqzfb*m:9h (py ht(wxwa 4ru-n g be used without blowing a 15-A fust79zwbh uw/ 4r(fyn*.xtg p- n: (mhaqe?    bulbs

  An extension cord made of two wires of diameter 0.e:n9(b8 h1 anaxl yn,t129 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 linen1y h(n,ba8 x: eta9nl. How much power is dissipated in the cord?    W

  A power station delivers 620 0ny-q1qa6d i bvool*zp6dc +,8s-; za fkqu 9hkW of power at 12,000 V to a factory through wires with too+8az;khfvq -in6 *a cqlo pduys-0q,961 dz btal 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 electromagnet connected to a 240-V line is 17.5 A. At what rapv5i amvu+*xvs*:qo mhoq: z7b)b*(pte must cooling water pass over the coils if the water temperature is to*ibpv*vxsa(qo u :7*qmb zv+:)mph5o rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be uu.eynua;t1(n tn 1j b2sed in a car to heat a cup of water for coffee or tea. If the heater can heat 120 mL of water frot 11 tbnnuja u.2(ne;ym 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 injvtuwbm an 104 0t1w:q a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is * i9mawd0r3 tgol 3zgt/c.u9o180 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 -h5f *a6 qjokx/na mx*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 15ty fh, r0wvp0200-W device is 5.4 A. What is the rms vov,0w02th fr pyltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected dtw .5a+i;mui 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-hp0 h(c1sqov6qk58 d nbf pump connected toqh0f cd8n1qo(5b s6k v a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to rxog93 4qw,h ga $240-V_{rms}$ 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 of 2w p,b clrptfj7i3.9efz+a/n $2.3\mu A$. 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 when 22.0 mV isv np:gedw;r*a4qn+ih-d b9 0 n applied to its ends. If0idb-re*+:d n 4vphgqann;w9 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 E-xcc47qi,p m harth’s atmosphere, $He^{2+}$ ions in a concentration of $ 2.8\times10^{12 }\;/m^3$ are moving due north at a speed of $ 2.0\times10^{6 }\;m/s$. Also, a $ 7.0\times10^{11 }\;/m^3$ concentration of ${O_2}^-$ ions is moving due south at a speed of $ 7.2\times10^{6 }\;m/s$. Determine the magnitude and direction of the net current passing through unit area $(A/m^2)$.    $A/m^2$  ----待选择----NorthSouth 

  At a point high in the Earth’s atmdu 8kz/k s7 z,mz)mh9xjtz30y osphere, $He^{2+}$ 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:zx2sfq 6* ckl axon membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with an eln 8wb/;,hwcal ectric pulse. The action potential is detected at a point 3.40 cm dw ; 8lhcb/aw,nown the axon 0.0052 s later. When the action potential is detected 7.20 cm from the point of stimulation, the time required is 0.0063 s. What is the speed of the electric pulse along the axon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much energy is req.1av- lf:cw eu.pz5hxuired to transmit one action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to t vfpcx.u.z-l 5ew1ah: he 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,d(jq5 j2vh 3+zepec:s $Na^+$ 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 th)o43ah n yjlo2ere in 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0lpi k/n4vymj. (r/y(c -hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of thev4qf h9qqijbl)xr4-; eu5ly( two headlights uses 40 W a9v 4)ri(4x jyl-qfq;eb hul q5nd each of the two taillights 6 W, for a total of 92 W, how long will a fresh 12-V battery last if it is rated at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of a 110-V, 1500-W heater is 5.4 m l:y-h,zj r3afj ong. If it is made of iron, what must its d-z jyfh,j:ar 3iameter be?    $ \times10^{ -4}\;m$

  The conductance G of an oboryya i1bms20zr, r0n*(c)j lject is defined as the reciprocal of the resistance R; that isrs*n a, mlybyr0r21c(o0i) jz , $G\,=\,1/R$. 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 aboud*,l2zvk- tm;/kx 5ixs0y cct t 10 MW of power. Suppose that instead of using high-voltage lines to supply the pockz2v0mikx-xc l*dy ts/;t ,5wer, 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 heats; :jpeas7qa ag /ts17+c2. vymzcuu 1er $3.0 h/day$ (“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 kmdqin:*/xa)7m d:o d ky 3i8mare wrapped together side by side to make a thicker wire. How does the resistance of this new combination compare to the resistance of the origi:oqx:)/k7a3ddm y8m k*dnmiinal wire?

  A 1200-W hair dryer is desim+ ;abki, l3rw eds3(jqo3g,agned 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 3u5+xg aupyykz:qk.yn- 5 fd.so it does not become so hot as to start a fire. What diameter kz.qg53py ky +a:-u5dunx.yf 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 eque0 -guwj 5) c3cqsxxj/ation $I\,=\,1.80sin210t$, 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 2- le lg02+scn ,nuwog*jxn-r65% efficiency delivers 950 W of energy per second to the interio,j nexrn2os2-llgc* 0 w-+ng ur. 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 :dd8,j o2oy.nv bkw u2material. One conductor is twiceko.2 vd n:w 8oubyj,2d as long and twice the diameter of the second. What is the ratio of the power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used y +:8ayzq8r roto 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 td/0) b tkgbp3jk28e9u)nbem:oqjdh 8o a 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 veh;ph+ tml0s:amm:lr 0picle makes use of storage batteries as its source of energy. Its maat ll m0 r+:;p0:hsmpmss is 1560 kg and it is powered by 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 lightbulb has a resistay57d 7ptj221jsi tnsff)n4d bnce 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 e ugv6nq0 vk8wx1d b,j c(hl;+11-mA beam of proxk86 (jwb+,len1dcuvq0 hg; vtons 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 1 tof:ah8vkc3fy9c(0a3 g1zl83 ua vkc2 A at 220-V ac. The connecting cord is copper wire with a diameter of 1v:zkac3cau g3y ov(8 f0lh3t81fka9c.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 z9jjeju)jm 8 9 v/v7gcV. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m.e)jv8 vj7/cz 9jmg u9j What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies frommrlv5vc;wi 2t kmp.-, 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 thevrl5m2,.m pwickt-; v voltage changes from 12 V to 13.8 V? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 4t hvui9z 18i,tp 9u1ja0 W for household applications. Lightbulb B is rated at 12 V and 40 huzju8i9,9 i t1vtp1a 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 use1*t:henv 5d1xonakce t 1h+akc7y7+ ed to connect a set of appliances at 120 V, which draw 21 xvk+ee:n7nc*aah5t+et7yh ko 11cd250 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 diameter of 3.00 cm and an outside diameter of 55:go0)vi z wmvi+cfe,.00 cm (Fig. 18–37). What is the r0 fc5)ge: wvm,+ zvioiesistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its lq 1fvht:h4 bj(ength doubles, by what factor does the power dissipated in the wire change, assuming it remai4(:1jh bhfqtv ns hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operatecmtg (i2w- cm n3)i uy+2+ckwws at 0.20 A and 3.2 V. If its resistance c )m23ywwu++c2i t wc(imn k-gat 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$