What quantity is measured by a battery rating given in a xh,l/ jg cs:c da/yhmw.7:v8lmpere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow ly2y;hp j*;xx away from the negative terminal in the circuit. But within the cell, electrons flow to thyl2yx*; ;hxpje negative terminal. Explain.

When a flashlight is h o+e,fyntm 2x0/b 7ikoperated, what is being used up: battery current, battery voltage, battery energy, batx7o0b /,t+m hye2nki ftery power, or battery resistance? Explain.

One terminal of a car battery is said to be connec+ e y(q6p*0l q40mtab wjul7chted to “ground.” Since it is not really connected to the groundh0mp j*c67q (yb 4lwq e0ual+t, what is meant by this expression?

When you turn on a water faucet, the water usually flows immediatelhui+ ,hw:4jxexeaw8ba. r2 ,uy. You 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 battery? , jh+r 4:xbw.uw2i,eua8ehxa

Can a copper wire and an aluminum wire of the same length have the same re f;b/b715xlqoi kh ry+sistance? Exbqihfl/bko 7+x;r1 y5plain.

If the resistance of a small immersion heater (to heat water for tea or +mjwx,9k3yc tqcjd9+ soup, Fig. 18–32) was increased, would+xmjy,tw 99ck qd 3c+j it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a rir3fd8o e5c3, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resistance, (b) the greatest resi353df oericr 8stance?

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 lightbu2(c4hytae 9 jrlb burns out?

Explain why lightbulbs almost always burn out just as they daav0q*0b,j r are turned on and not after they ha*0ardb qj,v0a ve been on for some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Whice.u6n9mn*hk whr86gc h has the higher rehw6 u*68kcr gm 9n.hnesistance?

Electric power is transferred over large distancp78zv3orx-m 4mh rb ;eo lv+)nes at very high voltages. Explain how the high voltage reduces power losses in the transmissio 7oxrzevr-lm8 3n+m ho4)pb;vn lines.

A 15-A fuse blows repeatedly. Wh3+:y r6d9;sj9jk )itauns;xitf t7d yy is it dangerous to replace this fuse with a 25-A fu79j d9a3y jxs;+;ituyt kti :s r)f6dnse?

When electric lights are operated on low-frequency ac (say, 5 Hz), therzk;0x vsxgbw++o70qg h 9/ ury flicker noticeabsgxwhx7vo+r; 00/b urg9 q +kzly. Why?

Driven by ac power, tk;xy h +vu.rdaqr 7r74he same electrons pass back and forth through your reading lamp over and over again. Explain why the light stays litxqrr+u 4;.k yad7rv7h instead of going out after the first pass of electrons.

The heating element in a toastee ,sfz9 o 1/kaorlx6d2r is made of Nichrome wire. Immediately after the toaster d o,6 /e o1fzlks2arx9is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resisz-0+ 1 sksjubdtor? Explain.

Different lamps might have batterix6dh o- cbaw/(es connected in either of the two arrangements sh(oahd wc-x6 b/own in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flozogi+3 u 2.hul(ybj2 4jux( ajws in a wire. How many electrons are flowing past any point in the wi24uy b(hoau.jl 2j(3uig zj+ xre per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 Ai y6chj(ndwoo(4 2x) y for 5.0 h. How much charge passes thrx w(2o6) ocdn hy(ij4yough the battery?    $ \times10^{ 5}\;C$

  What is the current in ampehb qrpn.gqqj5h)(d; +res 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 if 123q) (51zam j0xxymjccj 4cez;0 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce psu-d8mwu(+ rp 5d7 vlfd8ud. 0.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged uzlmufq r+5*. 48l(rtq d tfb(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 resistance ogg ;3(5bt-f m ;xfe:k :t)etvd 6fewkif $9.6-\Omega$.
(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 wh;er8vlo txq *vj42 d4ms)jf ,0 djnx;jose resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transmission line carrying 280 2, df2b(zapii0 A (Fig. 18–34). Thead(22pz,ii bf 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 6.5)9oepca,/9g je ch3kew-z3 bp0 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 currhqr6jf1 h5zzl3q 1i2f j41h(ipfejt9ent 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 ofmwcx5p 7gfi;m 9vok20 a 1.00-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 copp m8x+;l ogita3er wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the rep (1o,;ovktm26knp 6o+yle losistance of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in di +6ev;,pn(1kp lkt ol6o moy2oameter.   

  Can a 2.5-mm-diameter copper wire have the same r vjpj b)pcl1 c5(h*e-cesistance as a tungsten wire of the same len lc1c( b-v*p)5pecjj hgth? Give numerical details.    mm

  A certain copper wire hafm)z cj31ry /7ezq.kk59 zdfxs a resistance of $10.0\Omega$ At what point along its length must the wire be cut so that the resistance of one piece is 4.0 times the resistance of the other? What is the resistance of each piece?
$R_{short }$   $\Omega$
$R_{long }$    $\Omega$

  How much would you have to raise the temperature of a copper wire (or8yvcl4m:npgm:d mo8 0iginally at0o8pm ydm: cm8l n4gv: $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper wipu63; r +jdhtrll have the same resistivity as tungsten does at ; +th3rrj6pu d$20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resista ;q fc4.gqbmx9gqa)7ince 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 26-1 hwoi+544 ytd-egoxgl7j rv) m length of household no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm +oy hrx4getvgil1ow7- d 5 4)jand carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm8jbs773zijt lo6 yb.a, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for current that passes through the solid ij. jso7iz6 87byta b3ln
(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 sam+a0f amlu.r uw1.drg- e resistance. If one has twice the length of the other, what is the ratio of the diameter of the longer wire to the diameter r+ lra g-m0wuda..u1fof the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V power supply, an+ xfa(bsl2-r bt:dmk2d a current of 0.4212 A is precisely measured at 20.t +bf2xkra(mdslb-2: 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 onm)qrum,, vo8++l rol f copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is place++,o, r8)nrqlummvo l d 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 a0g:76n:zu euaol ,r lwq jz(p9 resistance not change with ter9q( o,uluj6 7az gze::wlp0nmperature. 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 designed to produce 3.3 kW of h:vo5vy;u3 d1gbatat,6t 7lwv5 /pu sceat when connected to a 240-V source. What must be the resistance of 6p 1v/tto5,5luw 3agu; ytcsadv:v7 bthe element?    $\Omega$

  What is the maximum power consumption of a 3.0-n i2hnbn2 zw-8V portable CD player that draws a maximum of 320 mA of curr-hb2n8w i2zn nent?    W

  What is the maximum voltage th9s +k4j6y wwxjat can be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, a 75-W lig/lz j,wlm:g uoa7x7j3htbulb connected zl: 3x7g7m,ao/ljjuw to its proper source 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 W. Calculate k 0b9bcpu(y4e1js4ocv s 3,cg
(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 az93ebaeje 5 ;und 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 lightbulpq:k/cr.j+ 6a8 sgso :f r8tcwb in Europe, where electricity is delivered to homes at 240 V. If you use the lightbulb in the United States at 120 V (assume its resist:8ofc:+csr wja6 k ts8g.qr p/ance 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 mlh+ +j/2cih2yy8t-qze sn+pyorning if it is in operation for a total of 15 min?n zyq8 h+ylpct+/ -y22j hesi+ 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 dvqy2ix/w n0 y,ay and nigyy 2 ,vqx0n/iwht for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V baty q n6mf8q5 kh1v)zs0nteries connected in series as in Fig. 18–4b (Fig8n1f5 6y0qk )hzq mnsv. 18–36). 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 stored in qkos1:r(9-lpup nb: *a:jykva 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 /2xunqg. e3bg1xx1gs in Fig. 18–20, can be used withoutg2geqxx.sng 1x1b u /3 blowing a 15-A fuse?    bulbs

  An extension cord made of f.qe nor 7/(emtwo wires of diameter 0.129 cm (no. 16 copper wire) an.rome7/ ( qfend 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?    W

  A power station delivers 620 kW of power at 12,000 V to a fk5-fo 3eq.g yvlm63z8j icti6actory through wires with t5tjq.z3 c-goyei v6i fl 8m3k6otal 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 connecta x ez*hs17wn4atmei:1xh6 .m ed to a 240-V line is 17.5 A. At what rate must cooling water pass over the coils if the 1xe tm s1wnim.ahx6z4* a:7hewater temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be use.pi xs3 w 4(x0lfzxxe2d in a car to heat a cup of water for coffee or te.xzl(0sx3xi 2fe p x4wa. 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 cu3gnrz k/ mzi-md03 vs(rrent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak valanzxhnu7/ i8 6ue is 180 V, is across a $330-\Omega$ resistor. What are the rms and peak currents in the resistor?
$I_{peak}$$\approx$    A(retain two decimal places)
$I_{rms}$ =    A

  Estimate the resistance *l.m u.q9b h:tl+fmqv 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 dev,(msu3,q3h ej ;mt+* lytgfgeice is 5.4 A. What is the rms voltage 3t;(gm3l ,ys *q+g,ftjmue ehacross it?    V (Round to the nearest integer)

  An 1800-W arc welder is connectede-mk+8ve, e 7 cedsy.o 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 0)7(zjz jsfqd pump connected to a q)d0 js7zz(fj$240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to a (/ty f/qyuzx:s b7z). bhlz .;w1ebxy$240-V_{rms}$ 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 curren9d7j89vxyfz-e4+mlt kf75pm/b,(yeqo zv imt 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-m/k v4wn6 ;px ,hr +ylpgrx:0xsA current when 22.0 mV is a ;xwns p:/xk6v gyxrl,+h40rppplied 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 29rw0( 9bdsa/, u) diy hjutsqEarth’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 E2)ju l) fpri2tarth’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 magnitudc vgh3t8u -sv)oa59pge of the electric field across an axon membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with an electric pulse. The action2a j,za6xo. ob:gjmnre: q. 0g+lefr; potential is detected at a point 3.40 cm down the axon 0.0052 s later. When the action potential is detected 7.20 cm from the point of stimulation, the time required i2rje ajbge:ao 6qfg.r0, xlzom;:+ n.s 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 actioj *n:op6 syb4on potential 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; :p bo*4sn6yoj 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, u w2,*lc7b q99 iz(urtjfv (li$Na^+$ 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 5u)b.r ij 3aqi :bxw)yfs 7v9iampere-hour?    C

  What is the average current drawn by a 1j9xel-mjvj*/1. y pnsq,z v5v.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of the two hqe9pz:s pw*zq( r 3s8-a iyv4veadlights uses 40 W and each of the two taillights 6 W, for a total of 92 W, hovy 84w ri*zsq(pp -v s9:aeqz3w 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, sg c)/kxsw.a-lby 2n;1500-W heater is 5.4 m long. If it is made of iron,a-s)sn/ ; xwc2kb.ygl what must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is ;:i)fbx/ l wm,7(su / 7pnlbj tyyoabo(23ll udefined as the reciprocal of the resistance R; thatjsulal/ o 7:x)(bp7yy,l ;b3 u nbfl/ (otm2iw 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 3q (4t(w1fwwqun zx1w. Suppose that instead of using high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a two-wire line of z1 fw4 n1tqu(qw3w(w x0.50-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 househol)r5l6xw trj+1o2mb u. tgjq2yhh82bk d 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 togetz(rpg*2yg. *4hppa h dher side by side to make a thicker wire. hryga . p4p(h2zp**gdHow does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designj6 6nj;02/stqavxmy sed 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 does not become so hot as qt7t.ggl 7+z 0sclzu-l 0g 8rephce;2 to start a 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 gt8t+0prul-g7ls0q hc.z7 g2; ee lczof heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is c-dc1k5 jpx sr6b,jn 4given 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% e0 - j8pa(x/q3: ttujgonqgn-4x-umal fficiency delivers 950 W of energy per second tox -gun tj 4xnmu 3pa-(q-0jlq :/goat8 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 conductors made of the same material. One wv5d2q 0l,l-nrof5 z dhq /mf/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 sec5 qm0fzl2/w fno, 5v/- dqlrhdond? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room of volijjii9 l4+dzbx;2f 3dop).giume $62\,m^3$ 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 hoo83u)lkw+7mscy: jn7 cwg qmd* ked to 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 vehicle makes use of storag.vdakyr/bk is:7 *es0e batteries as its source of energy. Its mass is 156sa.7*0d/ykebrvs: i k 0 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 resistance ofncz:5 )xtqhq0 $12\Omega$ 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 acceleratorxr al(dx++0iy q, cge0 at Fermilab (Illinois) is designed to carry an 11-mA beam of protons traveling at very nearly the speed of llrxy(c+q,0ga x di0e+ ight ($ 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 r0zcj:d*:p,0x cz-ezbv e 7ot220-V ac. The connecting cord is copper wire with a diameter of 1.62: cv,00dzjez ro* e7x-ptbc:z8 mm.
(a) How much power does the air conditioner draw?    W
(b) If the total length of wire is 15 m, how much power is dissipated in the wiring? $\approx$   W(Round to the nearest integer)
(c) If no. 12 wire, with a diameter of 2.053 mm, was used instead, how much power would be dissipated? $\approx$   W(Round to the nearest integer)
(d) Assuming that the air conditioner is run 12 h per day, how much money per month (30 days) would be saved by using no. 12 wire? Assume that the cost of electricity is 12 cents per kWh. $\approx$   cents per month (Round to the nearest integer)

  A fish-tank heater is rated at 95 W when connected to 120 V. The heating eo .m; lc/ou4+nvuiwir7e6ri2 lement is a coil of Nichrome wire. When uncoiled, the wire has a total lr+2 /4oiuo iewci u.nv7rm;6length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from about6ykk 8v5c1 tnu 12 V when the car is off to about 13.8 V when the car is on and the charging system is 8c1kkvtn5y6 uin 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 and 40 W for house6ybu kwx+t d,p-t3u 4hhold applications. Lightbulb B is rated at 12 V and 40 W for automotive apw,+tdh tp6- uukx34 byplications.
(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 diamethofwj1 5pijh..nmrt3, q6ro 8p( fbb 5er 0.259 cm is used to connect a set of appliances at 120 V, which draw 2250 W of powe (q61orpfwhf 58h 5tbrnjp.j3,bi.m or 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 d- ,a9qcpt:zcqm,f:w9g ruk f,iameter of 5.00 c,wq:f qg czctma,fu9k :r9-p,m (Fig. 18–37). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformlyq,lfi;wlu1n1)i1 o or so that its length doubles, by what factor does o wlu o,1 qi);r1lnfi1the power dissipated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb xh +j,7geiq1wx+db:ec ro:6g operates at 0.20 A and 3.2 V. If its resistance at 2d+gc :r176igoebxqh:,ex+ jw0$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$