What quantity is measured bv,(nhtl( evdk6vb87gen5psoh2g)-m y a battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a cf kk. ab3jc tn;p0m21xircuit, electrons flow away from the negative terminal in the circuit. But within the cell, electrons flowk3.bkn0pt x2cf ;mj a1 to the negative terminal. Explain.

When a flashlight is operatx7eq z),x d.t8,bqgw yed, what is being used up: battery current, battery voltage, battery energy, battgtd 7, xqe )wzx.8b,qyery power, or battery resistance? Explain.

One terminal of a car battery is said to be connected totwegn08r4 wtr/ +gpo- “ground.” Since it is not really connected to the ground, wtw+og/r-8pg4r 0enwthat is meant by this expression?

When you turn on a water faucet, the water usually flows immediately. You don’t: paon6gu8hf 9 have to wait for water to flow from the 86nfoa 9g h:pufaucet valve to the spout. Why not? Is the same thing true when you connect a wire to the terminals of a battery?

Can a copper wire and an aluminum wire of t8n x8 d9p+; eitq qoxm+v+kne2he same length have the same resistance? Explain ne qtnqpexik+; +m +28xd8o9v.

If the resistance of a small immersion heater (to heat water for tea or soup, F8 1zy7toilz ) y*p (5iu8nnjs8 tfrmb3ig. 18–32) 5)t8 7u3fb z(ri* onziyml1j8p8ty snwas increased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, and 3a, ho x tkj-+((nssuw would you connect the wires from a battery so as k (ts(+nxj-usto 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 z0l9 )uod)veelightbulb burns out?

Explain why lightbulbofs07gy:(7 or0 wbujv 5) :vkj(eb ok9sglg: us almost always burn out just as they are turned on and not after they have been yl v5: bj9esoosr 7uo:g:0gkgbvk(0w f(uj) 7on for some time.

Which draws more current, a 100-W light /;f3feyi5r9kxgct 5 rbulb or a 75-W bulb? Which has the higher resisr5rff9 y3 ke/gt;x5ictance?

Electric power is tranba2mtsz - 8n.vsferred over large distances at very high voltages. Explain how the high voltage reduce .abmt8sn -v2zs power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous tlurn j7bz7iw 3fts 8)5o replace this fuse with a 25-A fuswuz 3irtj7)snl8bf 75e?

When electric lights are 3py82nn-q.k ;1rm2jq-j,ld jbsihr ar/cr r5operated on low-frequency ac (say, 5 Hz), they flicker n.ry38-cr;-q1h dq, jjr 2b2 sljrrkn /a5mnipoticeably. Why?

Driven by ac power, the same electrons pass back a/ 7xe040fg:fyngjg u8myw+x jnd forth through your reading lamp over and over again. Explain why the light stays lit instead of going out afg :u+ jgxf8e mwn/7jfx4y00ygter the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. Imn+2/ yrck zzm2mediately after the toaste2 k/2cyr+mz znr is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Expla4xgnpl yxs 5jpks-a;3(hs k38 in.

Different lamps might have batteries connected in either of thecu .ezg(0ya,t two arrangements shown ie,cg.uz yt0a(n
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 flowino2h/n 5/3vdkk bdc ),s iius,eg past any point inuoibssk,/5h /ie2nc ),d3v dk the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a e *jtl7t4p8lqe,w /gbcurrent of 6.7 A for 5.0 h. How much*bqe/lg8jt 74wp,tle charge passes through the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes ga30 0xbkt d9w s-az,dpacg:0 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 120 V prodpbj 2a1y fh::y/zsm/q uces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current through w;k9p*g wl9 lha $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-V linevqw4mt1a n5; kqn .l+n.
(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 (seyq te)es4p xg/lo:x258g i 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 bulbcig .m+t9yg,d whose resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electria*do1 ea2;hce o+s/wwc transmission line carrying 2800 A (Fig. 18–34). The l+21; w o*adecho/eswaine 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 drawxr1t 9.thw0:l th*ewms 6.50 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 current of 0.60 A thre lny l88*(ke7 +iz6j ddqu*yiough 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 )mbm;c 9ib7l f;c b)qowhose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1.*/ tedxcz+ e1e5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire 2.0 mm in dxw3-uq1mxx nr 4h zy,8iameter, to 20.0 m of copper wirexqw 4mxu zy38-hnr x1, 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resie4df)aj 2*0h:jmbixo stance as a tungsten wire of the same length? Give numerijoam d0b i*j f4h)e:x2cal details.    mm

  A certain copper wire has a resis,y l (n)u.rtzttance 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 (original9s /aw bb9xib)ly at 9s/ bxbw)i9ab $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same ress8rz k713hx fjm5b4jgistivity as tungsten does 3js7f1m8rk jx 4b 5gzhat $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance oj.jay kfk7j:u,ko5 -vekf:, ef 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 dl 9-mmqu +x44/bcwgq nye 3ng/rop along a 26-m length of household no. 14 copper wire (used /n qcm4mn9-xqb wg/eg 3 +u4ylin 15-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 cm, 2.0 cm, and 4./b6e2p) t8 3 mrghe2hzit* zqv0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for current that passes through the soli v*m2i2tbpq)zez 6 er/38ghthd 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 resistanm3zu96ly kp i;ce. If one has twice the length of the other, what is the ratio of the diameter of the longer wire to the diameter of the shorter wi9 u6pk3zym;il re? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V poiv3sc)jy lw)i8ju1o2 wer supply, and a current of 0.4212 A j1 jiyow8 ul3)s) 2vciis 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 al5 s fiy+ip*/*mvt jlsr65o0 sln4) xoruminum, both of diameter 1.0 mm. A vjs4+ irs*spfi y*nt 0m)lorv 5lo65x/oltage 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 the4j-1nvddvy - zo.7g y9 mz+fdi value of a resistance not change with temperature. For example, suppose yonz+i4o9j .7g dmvf ydd- -1yvzu 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 heat vj0 2hq mrewxq /c(;;fwhen connected to a 240-V source. What must be the resistance of the elemeqhc ;m;(re/v fjwq2x0 nt?    $\Omega$

  What is the maximum power consumpx.ndq7:f:q0i-s 8b;z63d w1yg bhxonndj z5mtion of a 3.0-V portable CD player that draws a wnhyb q:7i0xdbf6 zjsn83xqz:dg5 n. o1-;md maximum of 320 mA of current?    W

  What is the maximum voltage that can be appliz rkegt1c6aewt7a+(- ed across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current thrzpsqh5x.) -; 7aj1vaji fv3khough, a 75-W lightbulb connected to its proper source voltage of 1 z q)vaaxhp-1jv;7 ij3hs k.f520 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heat . sfn1 ;t+*yinh4xupger is rated 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: ;pcihh/iv+b1. h nc0b 850 W and 1250 W.
(a) At which setting do you expect the resistance to be higher? After making a guess, determine the resistance at
(b) the lower setting;    $\Omega$
(c) the higher setting.    $\Omega$

  You buy a 75-W lightbulb in Eoj( w ir)b1:ig(uku. ourope, where electricity is delivered to homes at 240 V. If you use the lightbulb in the United States at 120 V (assume its resistance does1ikb r. go):oiuu(w(j 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 kk(:q kvc; s)-xl/j nctoaster use in the morning if it is in operation :k/jkv(-c)c sxlkq; n for a total 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 25gbu m-4lg/prugj v9/: -W porch light on day and night fob /mpu:4ugl9g-gvj/ rr a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V bt,,5wb y4k,dw9va qqmvls9 aw-v5t4oatteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA why-wl,d 59v,b5 av, 9vawqm4t4qts kowen 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 a 12-vm9 6w1zhvo6 h0cyj/nV, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connec inzx+jq5i-a*ted to 120 V as in Fig. 18–20, can be used without blowing a 15-A fuse?ai+x q *5jzi-n    bulbs

  An extension cord made of two wir h.*h6;z4osl xkdfb1u i.kt;ues of diameter 0.129 cm (no. 16 copper wire) and of length 2.7 m*4 ;u.s;o u6kk1l ixb htf.hdz (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 1 z mdg0o5q;f, c.+czva:pj5 sn2,000 V to a factory through wires with total 5mvqd; g+.z cj,o pf0ns5a z:cresistance $3.0\Omega$ 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.boashzl 416k 85 A. At what rate must cooling water pass over the coils if the wate1a6bhoklsz 48 r temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion he5ldr)w mo 43wztdj6 c,ater can be used in a car to heat a cup of water for coffee or tea. If the heater can heat 120 mL of ww )ocdm,jl63 4wdtrz 5ater 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 curren.yqpj)*dvw +v t in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value )yc42ugpq e0xis 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 resistanu26mp.h)x :)qtzxl1; 0fk0g) s dr vbh bw(vxmce 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 15*emh , fwizh2,00-W device is 5.4 A. What is the rms voltage acroshzi*h2, e mw,fs it?    V (Round to the nearest integer)

  An 1800-W arc welder is .dn8eft taq90s7u x,econnected 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 instantaneo(:nhm xv:)/8b:uzy6 ej ; u1if2tnib+ rsf yveus power dissipated by a 3.0-hp pump connected t(ev) :t8;nn 6uy x ru/2ibsj:fv1ybh:fzme +io a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to2*n ua3qw ee1t+puj3h a $240-V_{rms}$ ac line has a resistance of $34\Omega$.
(a) What is the average power used?    W
(b) What are the maximum and minimum values of the instantaneous power?
$P_{max}$    W
$P_{min}$    W

  A 0.65-mm-diameter copper wire carries a tiny currx1)oalfe87v p; mxrrn (k4dq7ent 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 wir6;fd ocns/y n1e carries a 750-mA current when 22.0 mV is applied to its ends. If the drifto6s fnc; y/1dn 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/mhr, mj /mxb6y-xvcxzq f1v *wh; ;s1 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 

  At a point high in the E u/c vwy)2sgltv 4c6db,e12vxarth’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 *s v6bwx4sf57 h9 rv0mfibhv(xv6i.l + (bhfxacross 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 ,) q owfkvy-j, uzja11electric 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 from the point of stimulation, the time required is 0.0063 s. What is the speed of the electric puzk,-f y1uov,)jwa1 q jlse along the axon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much energy is required to transmit o7u3y zib hpnx4;r5fx)ne action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulsz;bnuf4r py 7x 3i)h5xe 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 potentialaw 2k 8f3;sh5jz.uw ch, $Na^+$ ions move into the cell at a rate of about $3 \times10^{-7 }\;mol/m^2\cdot s$. How much power must be produced by the “active $Na^+$ pumping” system to produce this flow against a $+30-Mv$ potential difference? Assume that the axon is 10 cm long and $20\mu m$ in diameter.    $ \times10^{-9 }\;W$

  How many coulombs are there in 1.00 ampere-ho sh 57b/n/imzqtbc/ m5tcr11dur?    C

  What is the average current drawn by a 1.0-hp 129i tf1-pqb a1m.i v6tr0-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights onkx:cydvtp24wj7r * -l. If each of the two headlights uses 40 W and each of the two taillights 6 W, for a total of 92 W, how long will a fresh 12-V battery lasktj4w*c r2yv7l-d :px t 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. -:j l-jp 55tg1qrkols If it is made of iron, w -l-po:sqlt551gjkjr hat must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of anyi 4mol k2p4o6 object is defined as the reciprocal of the resistance R; that ioyp4o24i6mkl s, $G\,=\,1/R$. The unit of conductance is a mho $(=ohm^{-1})$, which is also called the siemens (S). What is the conductance (in siemens) of an object that draws 730 mA of current at 3.0 V?    S

  A small city requires about 10 MW of power. Suppose that instead of usb o:sc-j(tmx,ing high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a two-wire line of 0.50-cm-di c,-:o(mt bxsjameter 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 heat9 hfo0*vu2ixhv (+tq-zx 5 zvjer $3.0 h/day$ (“on” time), four 100-W lightbulbs $6.0 h/day$, a 3.0-kW electric stove element for a total of $1.4 h/day$ and miscellaneous power amounting to $2.0 kWh/day$. If electricity costs $0.105 per kWh, what will be their monthly bill (30 d)?    dollars per month
(b) How much coal (which produces $7000 kcal/kg$) must be burned by a 35%-efficient power plant to provide the yearly needs of this household?    kg of coal

A length of wire is cut in half and the two lengths are wrapped together sl6e;0gy /taoim)b85i 0gazir ide by side to make a thicker wire. How does the resistance of this new combing mib8oa/zeg 5;tay0i) rli06ation compare to the resistance of the original wire?

  A 1200-W hair dryer is3vy l97za-cn+j1ol p y3qw7k l 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 en5 kf fbpk-6 w+irml+qakmqvw)v*x (*9 ough so it does not become so hot as to start a fire.k*5a (+m6m xf+pi)qqr 9 kwvw* lk-vfb What diameter must a copper wire be if it is to carry a maximum current of 35 A and produce no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is gid4j7;8ac 4swo3p2n9d ef kjkrven 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% efficiency5i1 r pzk4zrm- delivers 950 W of energy per second to the interior rzp14rmk-i5 z. 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 differen kqizkp:-. sy9t conductors made of the same material. One conductor is twice as long a p9q k-zyks.:ind 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 to heat a rovf/:/ rpdn9by om 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 24cg np sco53/6u0-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 sthzvs6qzshl6l r34tkr i*0-4eorage batteries as its source of energy. Its mass is 1560 kg and ir-*6hq tzlsiv40k6rzhe4 l 3 st 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 resisx+i8w ;s4)m6mxh8c0fei ds *v sws.jx tance of $12\Omega$ when cold (20$^{\circ}\,C$) and $140\Omega$ when on (hot). Calculate its power consumption at
(a) the instant it is turned on,    W
(b) after a few moments when it is hot.    W

  The Tevatron accelerator at Fermilab (Illinois) is designed to carry an 11-mA)bw ,kp 2 ;yrowboh ;:e98wwl;w +zzc sfp96wr beam of protons trav br,p;);9w2;owzly:9wprw zshok+bw we 6f 8celing at very nearly the speed of light ($ 3.0\times10^{8 }\;m/s$) around a ring 6300 m in circumference. How many protons are stored in the beam?    $ \times10^{12 }\;protons$

  An air conditioner draws 12 A at 220-V j+mifjt j538(d5:n xyn)l jczac. The connecting cord is copper wire with a diameter of 1.6ixdnj8 tnm 5y)+ cjj(3lf5j:z 28 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 elementtlk+kc+b c9s6*q) st y lf7f-v/rrdw / is t-7l df6w*lsfy 9ctqs+v )r+brk//kc a coil of Nichrome 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 varies f)6sex, +q;a:uysuc q srom 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 the voltage changes from u6ax q:qs+e,ucy ss);12 V to 13.8 V? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for household applications. Lightbulb Bzl cydjebjv p,p9e fx),-e81 af*7 1mo is rated at 12 V and 40 W for automcf9pz)1b *l,yjemd-7 f,oj 1eav8xe potive 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 appli 4ydznv a3vf+.s)6p xmb 3toy9ances at 120 V, which draw 2250 W of power totmx+p v4asnbo63y ft9. 3zdyv)al.
(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 inside44rfrmzlg )h2n r tb8v;c72i5glhji* diameter of 3.00 cm and an outside diameter of 5.00 8i* 4mjrrf2cnll5zh7 ih bvtgg; 24r)cm (Fig. 18–37). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretchns ,:ua ,(-k fs bmb0,rtbd;zhed uniformly so that its length doubles, by what factor dor0mf (uds ,b,;zshk a:n-bb ,tes the power dissipated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a* a/n44bluxy rr*;s+ e+ulqn j flashlight bulb operates at 0.20 A and 3.2 V. If its nye4+ba*xlsr l;/ ruj*+q4u n resistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$