What quantity is measured by a battery rating given in ampere 1 nzemob ;m-l(e72obe-hours $(A\cdot H)$ ?

When an electric cell iy ijlu b;n*;0qs connected to a circuit, electrons flow away from the negative terminal in the circuit. But wi *;julqb; 0niythin the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what isqfob n*y8oxzu)5 ioad0;4 o0-zg7k t)nyk8f g being used up: battery current, battery voltage, battery energy, battery power, or battery resistanci0n-oxz45z0 yonkdf7* utgg8q ;f8ba o)ko ) ye? Explain.

One terminal of a car battery is said to be connected to “ground.lwi*q83 z v mx6pit0c3” Since it is not really connected to the ground, what is meant by lpv8w 3 z6xqt3*c0imithis expression?

When you turn on a water faucet7 tm,d; ef.sh.e 8mcmc, 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 the same thing true when you connect a wire to the terminasctmm.,8h.f ;7 cmdeels of a battery?

Can a copper wire and an aluminum wire of the same length have tg:pyogrn s q0 1,u(z/phe same resistance? goqn ,z(ry:s g0pup1/Explain.

If the resistance of a small immersio; x s*kldcm;:pn heater (to heat water for tea or soup, Fig. 18–32) was increased, would it speed up ok:lp dm*;s ;xcr slow down the heating process? Explain.

If a rectangular solid madejix4( 1cvc(kn of carbon has sides of lengths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain i4kj1 cnc v((x(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 lighz78dv0c9i nya tbulb burns out?

Explain why lightbulbs almostnm vh53wi/ /j1rsd qx3 always burn out just as they are turned on and not after they have been on for some tim ns/m35/wj31rqh vdxi e.

Which draws more current, a 100-W lightbulb or a 75-W0zt 5fwt4 e1g.t*fscj bulb? Which has the higher rts ejztft*g1 w0.4f 5cesistance?

Electric power is transferred over large distances at very higjkfb2 :gl dq5 8)gir2lh voltages. Explain how the high voltage reduces power losses in the transmission lingbg5i8 :k qf2lrl )dj2es.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fuse wit vn5 op;516qzsim :bxlh a 25-A vln: x6o5 b1ms;p5zqifuse?

When electric lights are operaa 5pxbq.q*+-z1o yibxted on low-frequency ac (say, 5 Hz), they flicker noticeabq b 1* xozb+y-5qix.paly. Why?

Driven by ac power, the same electrons pass back and forth through your b46n8seqqwgm,;x se)s r0-r n reading lamp ove m 6rens8)w 0 sqer,x;gsn4b-qr and over again. Explain why the light stays lit instead of going out after the first pass of electrons.

The heating element in a toaster is made oaby/j 6/slz 159 wzyedf Nichrome wire. Immediately after the toaster is turned on, is lsb1z/6yzyw 5/ a9jde the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a rfca*had*mw:6 + f/ce gesistor? Explain.

Different lamps might have batteries connected in eitf7 fuj5o.,uvu8 -u ;nel-boj lher of the two arrangements sh.5-nl b; fu v,f-jl8o7uujoueown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many electrocnn (po3 c(ou-1u efq5ns are flowing past any point in the(p non-1(c3ofuq5euc wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charj* 6cwal8- (f plf4tprges a battery using a current of 6.7 A for 5.0 h. How much charge passes through 6(8p lfctawp*rj f -l4the battery?    $ \times10^{ 5}\;C$

  What is the current in amperd qyo:;rsg.j0 es 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 produces a curv f)djzub 685zrent of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current through i5g/ tcih *ux ;kis4,ia $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugge wz i+zfo)o8a7d 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 /q - (4iedcxouelement 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 wqzcde5g;*z z)hose resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc elebngxh tw;y 8x4 duw/(+;lu9iuctric transmission line carrying 2800 A (Fig. 18–34). The du(gtw un /l xbxu;8+h9; yw4iline 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 240qadjm5 ga-q c.+j8ej( 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 -vim sw8+s8rsa current 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* *g1k1.35wdgm apdja9d moeq of 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 copper wire 1.5 mm in diameter?t/ dcdl8yr 7p4    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire 2.0 -fj ,zybmd8ddwpb ye +4kl+6, mm in diameter, j ,p wfbk-+6+ y4e, dd8dmlbzyto 20.0 m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tungsten wire jr v03 psr1.3 wfrvgo:of wgr pj vv: .o1rsr3f30the same length? Give numerical details.    mm

  A certain copper wire has a resistan*ovarskzb*oyay ti+; 3*g i:w nld; y1 ,i;:yyce 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 oc,7z3vs a id4ejmf6:6baird / f a copper wire (originally at/i eias bfrzj73:6ddc46 vm,a $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper lf3nl 4:up ik a26mvw/ o-rdgf2k:/cpwill have the same resistivity as tungsten does6 n -p2kgaf:/3m2 lpivrw dl4k:/couf at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resist(,xf,lz kg+iowjp b 8;ance 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 noa8 i3s imlg:z)/gjd; g. 14 copper wire (used in 15-/: ; aldjzgisgm3) 8igA 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 -;*y6q dle dfeynv7v+v4i(by.0 cm, 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 passf76-ye4+b vldie v; n qdy*v(yes 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 length0bpivz7f kli2 ;xij.. of the other, what is the ratio of the diameter of the longer wire to tpk li bf2 7zv.ii;x0j.he diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire ic gtt.* hr v-ty(fdm :q;o+,fvs connected to a precision 10.00-V power supply, and a current otdy (vctv;:oq+th*, m.r - ffgf 0.4212 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 oavu oqb qj, v,d r8q:p2x4s6;of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is placed across the6o,qbvjs8:r o; ,xva4qpd 2 qu 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 chatnm mjqh91+c 3x)w3fu nge with temperature. For exampl+f)39n3txc w uqmmjh 1e, 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 produceurg uopu51g : 5iy5qek9-gu 5)-hhybj 3.3 kW of heat when connected to a 2 gyoeg55:-huhk jibuur y5)-p 91uqg540-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumcqo sq8 8utz/5ption of a 3.0-V portable CD player that draws a maximum of 320 mA of curren c/zs58u8qqto t?    W

  What is the maximum vajc 9xcpw3l;5oltage that 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 lightbulbtl)n2wtybo / f; m.8shvg/a;i connected to its proper source voltag/ h8fa;;m/wy btosn)v.2l tige 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. Cal+sig*+nb u-mwo;b9o 7 olygiysp( ,a+culate
(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 1250sdrd4q.qs -qzyj7quk:o6c/ y ; f *2cq 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, where electricity is delivered to homes afmu mew01je.bj5 5ur2t 240 V. If you use the lightbulb in the United States at 120 V (assume its resistance does not change), how brigwbem.e0uj2m5f 5 1rujht 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 tcg.hr/- 7 faldwiy-d -oaster use in the morning if it is in operation for a total of 15 min? A dyr-lcd7-gh wi ./f-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 porj,,sajclg5vm4 5j78 xu k6awo ch light on day and nigaa j5c mljw5x,kgo,7s 4vu8 j6ht for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected 22:o k*w4bnhry/xfuz in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when turned on.zfk2 wbo/nx h*yr24:u
(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 cl vz g.sra-2u c+qdkhj106 ,flz7,ytof 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, connected to 120 V as in Fig. 18–20,ay 02:m hm uu8gqvxl0e n6r4k0 can be used without blowing a 15-A fu2a q0klhe u0v04 n 8mu6xgmyr:se?    bulbs

  An extension cord made of twz95a:32jys v6s cieyo*)fqc c o wires of 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 line. How much pow eo*c svy2i f)cc59zyq:3jsa6er is dissipated in the cord?    W

  A power station delivers 620 kW of power at 12,000 V)dw :slgjyzzf 35 n7v4 to a factory through wires with totazy5jz gw:)n3v4ld7sfl 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 ay,r q/nch6oqm,7fd94rg pr )x 240-V line is 17.5 A. At what rate must cooling water pass over the coils if the water temperature is to rise by no more trxmypf,q6h r4,9c/ qn)7grdo han 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be / vf6jspuw6l-used in a car to heat a cup of water for coffee or tea. If the heater ca 6jpw/sl-6 fvun 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 curreeqjktm70-2d- ntcs .vnt in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value ists.vg/ n; vgu6 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 of thjakoe +e-i4*tj 77 ngz *0jldke $120-V_{rms}$ circuits in your house as seen by the power company, when
(a) everything electrical is unplugged,
(b) there is a lone 75-W lightbulb burning.    $\Omega$

  The peak value of an alternating current in a 1500-W device is 5.4 A. W/:ta+v xoz6mjs tb2i5:iukc7hat is the rms voltage across itmji5i bzs:+26vk:tcx a/uto 7?    V (Round to the nearest integer)

  An 1800-W arc welder is cndze x:c:/mru4f50lm onnected to a $660-V_{rms}$ ac line. Calculate
(a) the peak voltage$\approx$    V(retain one decimal places)
(b) the peak current.    A

  (a) What is the maximum instantaneous power dissipated by a 3.0-hp pump connecfzpuhaa8m eh,)f6 *d6ted tp8 fdahf, umhe6)z6a* o 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 : oijfpf;cb4z;r 5j6xsq/9 lv$240-V_{rms}$ 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 c;vxk/;v4 6ep+ uxngdearries a tiny current of $2.3\mu A$. What is the electron drift speed in the wire?    $ \times10^{-10 }\;m/s$

  A 5.80-m length of 2.0-mm-diameter wire carries a 750-mA current when 22.0 mV is.:r/ 0+ehf 4( ol telf slm;enymam2s; applied to its ends. If thn4l m;t/ary.o le 0ms+ mf;flh: se(2ee drift speed is $ 1.7\times10^{-5 }\;m/s$, determine
(a) the resistance R of the wire, $\approx$    $\Omega$(retain three decimal places)
(b) the resistivity $\rho$.    $ \times10^{-8 }\;\Omega\cdot m$
(c) the number n of free electrons per unit volume.    $ \times10^{28 }\;e^-/m^3$

  At a point high in the Earth’s au1 r /o2.y+ut*u jzzautmosphere, $He^{2+}$ 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 thh 3roru*a s1t+e 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 ofx vru 8+(vven0c,uz z8 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 action potential is d.amsi6d k kn;5etected 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 pulse along the axon? (Why are two measurementsid;sam. k5 kn6 needed instead of only one?)    m/s

  Estimate how much energy is required to transmit cpm2ur/gq5j 1xlvy57 one action 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; see Section 17–9].jxlu7 m5/yv5g2p c1 rq 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 poten5hn0ie5lm- mv00 qlcl tial, $Na^+$ 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-h4 bwjj1l8:/d0bdd r zwfm4de2our?    C

  What is the average current drawn by a 1.0-hp 1ips g/( j7n( hb+9nhhk20-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a a styr sc81 4p00rwm*kcar with the lights on. If each of the two headlights uses 40 W and each of the two taillights 6 W, for a tota8*r pkr40wsam1s y0 tcl 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 skl0;j8k-gfb:fk 0 .qgzd u) ym long. If it is made of iron, what must:0 ;fsz0k yg kk-bufgl8 .qdj) its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as qmdz2jo-g8w .. jkm 3 bdk8f0lthe reciprocal of the resistance R; tha3kgw.jjkdl q2db8m o f z8.m0-t 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. Supphz 8jt 8fz5h xqg;ln u/dj9c3;ose that instead of using high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a two-wire line of 0.50-cm-diameter copper wire, estimate the cost of the energy lost to heat per hour per meter. Assume the cost of electricity ist8 lcgjq x d h5fznzj39u/;h;8 about 10 cents per kWh.    dollars per hour per meter

  (a) A particular household uses a 1.8-kW heaj)hklay,5mk6iu qt a8,yxg*q8:f qx;ter $3.0 h/day$ (“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 wrappedjvgdn j*/2kg: zdap-: together side by side to make a thicker wire. How does the resistance of this new c v*d2pjg/nd:ajzg:- kombination compare to the resistance of the original wire?

  A 1200-W hair dryer is desi9: sfdcfysz( *gned 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 :7n6 mija3 tdee;a)oh to start a fire. What diameter must a copper wire be if it aet 37 m;aij:ond)6heis 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 e g-f gi.tvgx7 ,xq+bhexzctn0*4n3n.quation $I\,=\,1.80sin210t$, 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% efficiencyaw e +/v *ztr43/jkld7x9jngj delivers 950 W of energy per second to the interior. j*+3j k lnadg/rv4ewxt/ 7zj9Find
(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,dj8 se s)cx,5j7qh:yll1o bz t conductors made of the same material. One conductor is twice as long and twice the diameter of the second. What is the ratio of the power transformed in the first lxs q cy5sodz ,87)j lh,be1j:relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heatu )4gwm92i4xx :fg nld 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*.b jf zisdr9)utk6o82gh. vd 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 storage batteriq m. c*/hz qhip-80v1.sebvmges as its source of eneqz s*i8hmmeb.v1h gq-./0vpcrgy. Its mass 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 abokr/ 2a17zh,l-xznx resistance of $12\Omega$ when cold (20$^{\circ}\,C$) and $140\Omega$ when on (hot). Calculate its power consumption at
(a) the instant it is turned on,    W
(b) after a few moments when it is hot.    W

  The Tevatron accelerator at Fermilab (Illinois) i+iy rfn s+qg;.s designed to carry an 11-mA beam of protons traveling at very nearly s ;iqfn++y.rg 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 ac. The connecting cord is q:m;:vzgefmkk2 fk62copper wire with a diameter of 1z6e:kv mq2f2;k gm:fk.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 V. The heatinf fpqlf/- q4i(76sqnuvvo; d* g element is a coil of Nichrome wire. When uncoiled, the wire fq dq/4 us6vfl(q;v*fn7po i- has a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the 3vl,e e98 he*k *u;mna,r lfqrsystem 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 operation, a difference of 15%. By what percentage does the power delivered to the headlights vary as the v ru8e*9qhl vmefaen, r*3k,l; oltage 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 houv 6chq tlow.;,sehold applications. Lightbulb B is rated at 12 V and 40 W for autl;o, w6htcv. qomotive 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 0.25eczia(hla( hga fhk(nt5 2l48,6 ply/9 cm is used to connect a set of appliances at 120 V, which draw 2250 W of power totpaa/k(gyalh ( lf 846ht(,ne2h 5zil cal.
(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 3.00u0o:tabgu 37j cm and an outside diameter of 5.00 cm (Fig. 18–37). What is theu j a:bto037ug resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that ab.+bxrq(pq + its length doubles, by what factor does the power dissipated in the wire change, assuming it remains hooked up to the same voltage+b xq brpa.+(q source?

  A tungsten filament used in a flashlv s3. fwazh*k e6jb/z-ight bulb operates at 0.20 A and 3.2 V. If its resist w6bkja3*f ev.hzzs/-ance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$