What quantity is measured by a battery rating gikiyc6(upq( hyk+r 8c. ven in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, sph/u),b1 b 9psdes 9delectrons flow away from the negabdp/1pe ,sd9 )bsu sh9tive terminal in the circuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battv +c1w0 reb5 7xdfnks5ery current, battery voltage, battery energy, battery power, or battery resistance? Ex57drew5 cv 01+nx fksbplain.

One terminal of a car battery is1xxw )( cnw/wrfnv4c0 said to be connected to “ground.” Since it is not really connected to the ground, what is meant bynnwcw/f41crw v() 0xx this expression?

When you turn on a wat6s.ke3qdtk txbo1 c ;;1fq+ erer faucet, the water usually flows immediately. You don’t have to wait for water to flow from the f6kt xe1q 3o crfk1dtse;q+b;.aucet 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 w47w,lcyungw*qjm 0w,6saj 6gire of the same length have the same resistance? Explaq* j swa 6cwnj,mwg4u6l0g7, yin.

If the resistance of a small immersion heater (to heat water xbsj;a+ / 1si .mquf;jfor tea or soup, Fig. ;mb1 ais +f;q/ uj.sxj18–32) was increased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has si5)h.(0szkp;ltgv ps9j1r;chcj b:p o des of lengths a, 2a, and 3a, how would you connect the wires from a battery so as tokcprcvp5:tz9o ;1lsgs)jh .0; bh(pj 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 2ke -me.bf59qt6th od lightbulb burns out?

Explain why lightbulbs almost always burn out just as they are turned ont26dc7w3uz2h grf10zrw,pol and not after they have been on for scorwz 1h g0rfd, puz372t6l2 wome time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Wh6 s af,-t+lt*uk (hwusich has the higher ru h*tl-ft6s ,(uw+ksaesistance?

Electric power is transferred over large distance ;3db 4w1om9 hlaxxix-s at very high voltages. Explain how the high voltage reduces power losses in 3; b9o4xi-mh x xwald1the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to r(yyoi9e3 ov2 leplace this fuse with a 25-A fuse?eo2y v93(oliy

When electric lights are operated on low-frequency ac (say, 5 Hz), theqt n.0:pu0t ekj ;xut 3qlup5aet:r7:y flicker noticeably..r:eklp03uep q5 :0 :ta7 uxjttnqtu; Why?

Driven by ac power, the same electrons pass back and forth through yoy0i+y wt qo9-qamk60 c/q8sqcur reading lamp over and over again. Explain why the light stays litqyy c/6kimqc8 o0 q 9+w0st-aq instead of going out after the first pass of electrons.

The heating element i 0gntt2mxk1r k5(qjm*n a toaster is made of Nichrome wire. Immediately after the toaster is turned ok jqrt 1m2tnkgx0 5(m*n, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in s-t-z)t.wuavo i.h:7tr9 b dq a resistor? Explain.

Different lamps might have batteries connected in either of the two arrant3g r,92sld2texhud 3 m6o po4gements shown in tdt2634lr,3xouem 9hg dpo s2
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 flowig)n0 6e )eycinng past any point in the w6n0)c yg)ne ieire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges apyan9- np/t1(cn(+ psqi)en u battery using a current of 6.7 A for 5.0 h. How much charge passes throun() appeq/ tps1iu nn( y9-cn+gh the battery?    $ \times10^{ 5}\;C$

  What is the current in au2s9ftg; /iel mperes 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 toawv(wph-.l 0z hster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current through a(dw y6a ,pc30walzox : $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-V line) zy5z rz8d58nc a0kxi.
(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 r-r *m1.bwafq(s - mdmnesistance 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 wht+ov4r-;q tgf-gkki4 ose resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric tralfcsou6qk4k5 g3* h7y c:jf) q1g(epvnsmission line carrying 2800 A (Fig. 18–34). The lin yvecj4uo*:sgkq73p5cq6 (glh)k1f fe 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 240): jyweshbv z; 7+apn3 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 resistor.n q;qc 0r/szn+lqt1 )r
(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 1.0kw j5+iq 4 cd57(asmte0-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 inx) sk4,jt 0gdd diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio bs )j3kyi q20dof the resistance of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2db3qy0s) ijk2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tungsten wirz09eu*bd-h +p -a7;muk8z8istyiag7e n.un ve of the same lengea gi+a07-- ve u*p.z79tiyzu8s 8ndbhm;unkth? Give numerical details.    mm

  A certain copper wire has a resistancw70g1frs 0px8vd78 c1lb rqdee 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 rai ck)ych* rz:b8se the temperature of a copper wire (originally atc*kbhr yz:c)8 $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will7 jkmeav91djx jw --zw6,w ,e8;yy sqv have the same resistivity as tungsten does at v jz ; a1,6xw -se-m e9kww,jyjy7d8vq$20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of aboutej5 5 84ugouj e1glgahtbg )77 $12\Omega$ 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 ofq-d)s(:7hquk8 imy 37zjcr ex household no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm and carries a 7 (q-z7 dqye)i:mru ch8js3kx12-A current.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm, 2.0 cm x2plm r*epx/9, and 4.0 cm, lying along the x, y*lx 2ppmer/x 9, and z axes, respectively (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 length3/6ndajo:nk)ra;x gd of the other, what is the ratio of the diameter of the longer wire to the diameter /agodnn j);:3 x6da rkof the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V power supply, ko0zn t ,j(,,te. pn6/rwfbp aand a current of 0.onbpa,6er, tfw(n0.jkt p z/, 4212 A is precisely measured at 20.0$^{\circ}\,C$. The wire is placed in a new environment of unknown temperature where the measured current is 0.3618 A. What is the unknown temperature?    $^{\circ}\,C$

  A 10.0-m length of wire consists of 5.0 m of copper followed by 5.0 m of apu*d n7v7tpp 1 vi,j /ypoh/6xluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is placed across the composite wippn7ivp jpx/o* v1y6 /7,hd utre.
(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 import:jwq t-+ s3vzo8q3dvm ant that the value of a resistance not change with temperature. For example, suoz vj3v-t ms+qdw3: q8ppose 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 electri;0hb j wm .ua)p),ms 9fty2vuec oven is designed to produce 3.3 kW of heat when connected to a 240-V source. What musts j.a;u0y9)mt wb)vue,p2h mf be the resistance of the element?    $\Omega$

  What is the maximum p ff)jwbbq:h;s6t 6yw+ower consumption of a 3.0-V portable CD player that draws a maximum of 320 mA of curren+wbwf66syb:q)t;hj f t?    W

  What is the maximum volkm .f9)a dg0kjtmgqxu9b9/2 dtage 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 lightbulb ( dn2 caq6 vn4 3xzdllqu03 .veme7o5dconnected to its properxq3 e2 d4emod.nlvlv0cn6( 5ud7az q3 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:;pcn;)px0qrx d8j oo 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 hiku.0kst f g lu)nx:*.as two settings: 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 m7) 8bid9t m9p : rikst15rvjnin Europe, where electricity is delivered to homes at 240 V. If you use the lightbulb in the United States at 120 1i t d9rv)p59nk i7m tsj:8rmbV (assume its resistance does not change), how bright will it be relative to 75-W 120-V bulbs? [Hint: assume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use in the morning if it is ilhuj ux(*2xs(s+mfls-jc;e 79y ggd* n operation for a total of(+m jxc2u9e(*d;lj*s7husfl yg s-gx 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 25c.wzr y/(33o avbe7xf-W porch light on day and night for a year?.bxforwz37c / 3 evy(a $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected in y4k8mnqwaa(mgw8; 6 yfq33tr series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 y3tqm gmwn(34 wfkr8q6;a y8 amA 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 oftv,k 6gn(p n)fiu- 7oa energy stored in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbw+fkocb;7d 2e; ,gki julbs, connected to 120 V as in Fig. 18–20, can be used without blowing a 15-A+;f;i c72,db kkwoegj fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm-)m*pp ,cwz p6ghq,ve (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric heater which drawzh pq)w-*6cg vp,e ,mps 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 fs,a9+. r*oy ;dxz.f n ox8qa;op5 tmgsactory through wires with total resisyn9*oo;pr,. .; gdxqazssa8o t+ xmf5tance $3.0\Omega$ 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 wm0r8,dluh8 xnhat rate must cooling water pass over the coils if the water temperature is to rism 08xun8h,dl re by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to heat a cup of water for coff) vkfb bz+vuk8k w8 9 ,5r9xir,zqy)zkee or tea. If the heater can heat 120 mL of water fror8vq,u))z8 +,b9k wxybf5kzz k9rv kim 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 izkf/ 1h4 d/:hv(0hpkxafr m2pn a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is-2)zx xxl3qcbddv; /g 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 mzdc *l9ifk;+ 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 device is 5.4 A. Wh)ifiwl05 a.cmp9 oih 3at is thc5 o p3) miilh.iwf0a9e rms voltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is coam/w t (yl)z 5qkj 0su3r.yc(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 instant0 mtuyi,*/vof3h+kea+s uz9taneous power dissipated by a 3.0-hp pump connected tt9f+3 tyou0hsi+zeu/vm, *a ko a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to,3v2 unixj xy,ks9-s n 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 current oyby:d (ju+q spao6e2 :f $2.3\mu A$. 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 mxeip l;;c .0d28 qudra)l/oru V is applied to itsql e ;)p 0o2drr/lx;uc da8.ui 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 Earth’s atmosphhl k49 xa/.d qag(vs7cere, $He^{2+}$ 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’v/kej8fd6z jt9 56lfts 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 ofdzuhc0 6ta41 x 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 elect*c5tefiuatf; 2 s..rlric 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 ;.*e.sruit f 5lct2af of the electric pulse along the axon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much enernz 3h.0pt5* kub*rzr fgy is required to transmit 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 ftp* zr5kr3h0b*un.z17–9]. 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 potentiaw ;xd0irr;irbm dp2 o 4l,*mdh ;8eg2ql, $Na^+$ 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. :1v9usay n6kz00 ampere-hour?    C

  What is the average current drawn by a 1.0-hp 120-V motor? 7qssfgm0 qvh 7(3dvwa)) 6xrn$(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car witv 4nnm8g.9zzth the lights on. 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 fres .mg8 4zzn9nvth 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 lwoy ha2s 4) /avi8c9zm long. If it is made of iron, l9chaaw vso)z2y4/8 iwhat must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is def fz;lo+q9 nho8ined as the reciprocal of the resistance R; that is,;+ ofl 9ohzqn8 $G\,=\,1/R$. 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 using hmsc)): ayq4le igh-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 qa)l4emsc): y 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.s0p;t3kr0s y( cffe(*lf d ep)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 lengthstegt v0ls. w99 are wrapped together side by side to make a thicker wire.wtl0.9sg9et v How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designejxm, oi6g /ngg u,o1qz/m(av sv*10bnd 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 c0(pc9q;m yrnzy6zqn l2 u,x+so it does not become so hot as to start a fire. What diameter must a copper wire be if it is to carry a maximum current of 35 A and procply+nc,x n2my 0(qrqz u ;z69duce no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given bye;y i7 l8a2sus 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% efficiency delivers k /emt29.fbf ka48nz r950 W of energy per second to the interior. taf/m.ekbzfnr8 294k 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 materiaaxaa5o*tx4 (co x5h9 gl. One conductor is twice as long and twice the diameter of the second. What is the59x5x(a4haa c otx *go 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 room of volumtc) p,,n rkga-e $62\,m^3$ 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 t dw 4,h.bjd8d+b-ms qwo 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 magr qmu.q mr,uc 7h81mc:5eq 5ukes use of storage batteries as its source of energy. Its mass is 1560 kg and it is powered by 24:m erq, mmc.5q ug8huqr5uc71 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 ren-yse4 gcnsew8 g.br*vb3.u7 sistance 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 y noevn4 4:wl*at Fermilab (Illinois) is designed to carry an 11-mA beam of protons tvnn4lweo* y :4raveling 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 ac. The connecting cord is copper wire uw df8fe 58* zk(gqi)c(m3gknwith a diameterwgkdzg3 k(m*unec(f8 8q i5 )f of 1.628 mm.
(a) How much power does the air conditioner draw?    W
(b) If the total length of wire is 15 m, how much power is dissipated in the wiring? $\approx$   W(Round to the nearest integer)
(c) If no. 12 wire, with a diameter of 2.053 mm, was used instead, how much power would be dissipated? $\approx$   W(Round to the nearest integer)
(d) Assuming that the air conditioner is run 12 h per day, how much money per month (30 days) would be saved by using no. 12 wire? Assume that the cost of electricity is 12 cents per kWh. $\approx$   cents per month (Round to the nearest integer)

  A fish-tank heater is rated at 95 W when connected toi8pkm*(bd ,e*wv0nbgi*f h*e;td lt6 120 V. The heating element is a coil of Nichrome (ib df8v,ek**6htbnmg0lp;dwi * e*t 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 from about 12 V1oz5fsd uaa( + when the car is off to aboafz +(sado15 uut 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 12 V to 13.8 V? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is ratedx +*y 5myizbn;aehdo2p ;hl11 at 120 V and 40 W for household applications. Lightbulb B is rated at 12 V and 40 W for automotivnpm;51hd+i1ah;l z ye xbo2y*e 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 pkje*yts 0l ,9kfwuj(4z,vp 3 is used to connect a set of appliances at 120 V, which draw 2250 W of powekpsu4p j z0k9lf*(jt3,v, ywer 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 outsid 4m.g eu0pm ys8//)d3.yap5towubr tie diameter of 5.00 cm (Fig. 18–37). What is the resistance of 10.0 m of this pipe5 dum r4 etim83/..oytwyp/aus p0g)b ?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so thear,62yby mykfh 7/f,at its length doubles, by what factor does the power dissipated in the wire change, assuming it remains hf,fkye7 y ,ma/hyb6 2rooked up to the same voltage source?

  A tungsten filament used in a flashlight bulobi*0yk t3 jq(:jeh6qb operates at 0.20 A and 3.2 V. If its resistance at 2o6*(jyqkhq :0 i jbte30$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$