What quantity is measured by a battery rating given in ampere-hou ejn7tezh/f5 g):3 gfvrs $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow away from the nd0r:aaqavt ;l 0c: er8x3 g5hmegative terminal in the circul0:a d30m:8 tx5rgv aqcr;heait. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used u5l j yj + c4v).irlcdgz;p/piy(*a4sxj4z 2myp: battery current, battery voltage, battery energy, batteryjz.l 4g42cszpicl(y jdm xy va) * pyj;r/5i4+ power, or battery resistance? Explain.

One terminal of a car battery is said to be connected to “groubhssbu9:g-cewa dci9z5 )*,bti*u c1nd.” Since it is not really connected to the g: -ba,*c s5gehicb zwd 9)buitu*cs19round, what is meant by this expression?

When you turn on a water faucet, the wr s c0 :sqorn;0koi6b+un;)n ,v+usibater usually flows immediately. You don’t have to wait for water to flow from the faucet valve to the spout. Why nuki)ss;b ;b nr:0i++svuqc rn0n ,o6oot? 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 the same length have the same resistwt(y)k /b 4exiance? y(xiwk4)b/e tExplain.

If the resistance of a small immersion heater (to heat water for te* t01)hx3ec i 6fdszgha or soup, Fig. 18–32) was increased, wouhd z0 6csx*e1tif)gh3ld it speed up or slow down the heating process? Explain.

If a rectangular solid madr lq(gz/ 1nr/ue of carbon has sides of lengths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resistance, (b) the greatest resistlrrg1/ quzn(/ ance?

The equation $P\,=\,V^2/R$ indicates that the power dissipated in a resistor decreases if the resistance is increased, whereas the equation $P\,=\,I^2/R$ implies the opposite. Is there a contradiction here? Explain.

What happens when a lightbulb burns outms*u7 wh *zkj:?

Explain why lightbulbs almost alwayhf.q8zj iu (v8s burn out just as they are turned on and not after they havez iqujfv( 8h8. been on for some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which ;krtt;p,lxk3cgg 9 p7has the higher resistattcrgk79lp k3x; ;p ,gnce?

Electric power is transferred over large dismm*1 tvb5dm s8tances at very high voltages. Explain how the high voltage reduces power losses in b1 5dvst8m*mmthe transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fuse w/uth1a5f bap7ith a 25t a1 fhub7/5pa-A fuse?

When electric lights are operated on low-frequency ac (say, abgbr* yl35n mz(f e/-5 Hz), they flicker notib/ g-n 3*m(zbrae5y flceably. Why?

Driven by ac power, the s3po: )kcxp 6yqame electrons pass back and forth through your reading lamp over and over again. Explai3 po6yq: kxpc)n why the light stays lit instead of going out after the first pass of electrons.

The heating element in a toastn 6.i0h c:xs qywzqybre.s 68(er is made of Nichrome wire. Immediately after the toaster is turned on, is theq6i yxs :ze .0(wry8b6qnh.sc current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistofz p(a 5b.em*c dw h,9gohem7/r? Explain.

Different lamps might have batteries connected in eit2)um- uil 2bhkher of the two arrangements shown in 2m)-2 lkhiuu b
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flowsv 2d(6hsornq*,i u0z*c ;vrrz in a wire. How many electrons are flowing past any point i rq*nud,rsvzc0v*izoh;( r6 2n the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery usxgj4lk-xi *ozs u/g -h-j e/u3ing a current of 6.7 A for 5.0 h. How much charge passes th/iu- ho/-xkj z ggj-ls*4ex3urough the battery?    $ \times10^{ 5}\;C$

  What is the current in amlb-c. zn zdj8x:5go; bperes 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 toefi8.7k1nj3r/tq hv(: qy,e0r nhagxaster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will prodq5 z6qv5n1wos uce 0.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.cq9dzjx(*xt:jm0al vx1i :j 45 A when plugged 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 he.q3l sp3gstc+a tmsu ::r(n2gating 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 connectjn91um f0hu:1 7ch:q d+hsmjued to a bulb whose 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 carryie +zyr6)d.i yegx7.pl 5d.t 4z0igugb ng 2800 A (Fig. 18–34). The line.z670+pgu4y i5t).yx ge.gl diz rbde 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 ah 9 yp-icd:zux1gb/56fp. o/y d f:flw. q9sm240 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 causesm p* m zva+kk0a f7tx2y+*prj: a 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 of a 1.00-m length of tungsten wire whose rk,:;yze eo+zqxe iusfjb ::7*k. afg-esistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1.5 mm in diameterqb,koj+,y )qgyio 7e9, 1ffsq ?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of yno;ate)tn*t,n0i s7 the resistance of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in diameten;t0,a ti7ye on*snt)r.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tungsten /dvm+s).u dt:toz 5;dh3 iyl zwire of the ssdoh) td3y:.d+tu/ lizz;vm 5ame length? Give numerical details.    mm

  A certain copper wir :n7 v+qy9b5.y ts)h,h dqxmdke has 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 (originally at3dm7,s ;7 le)f rihrvf e7fr ivh7sfl)3m; ,dr$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivity as tungsten ddevp55dm5li ;zd, ,s toes ,zivl,5 s dmd5d;te 5pat $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resista vg/f*mn e ;5z 1phz5qhvyg;(xnce of about $12\Omega$ when cold ($20^{\circ}\,C$) and $140\Omega$ when on (hot). Estimate the temperature of the filament when hot assuming an average temperature coefficient of resistivity $\alpha\,=\,0.0060(C?)^{-1}$ .    $^{\circ}\,C$

  Compute the voltage drop along a 26-m length of household no. 14 copper wire (u2)iymzg: c9ivkt c ni:9.,m chsed in 15-A ctnmc9:kh . gim:z2iycc,i) v 9ircuits). The wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sidf-oi+a, .ko oxes of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for cao+.xoi o,k-f urrent that passes through the solid in
(a) the x direction,    $ \times10^{ -4}\;\Omega$
(b) the y direction,    $ \times10^{ -3}\;\Omega$
(c) the z direction. Assume the resistivity is $\rho\,=\,3.0\times10^{ -5}\;\Omega\cdot m$.
   $ \times10^{ -3}\;\Omega$

  Two aluminum wires have the same resistance. If one has twice the length of a pzgi8qcbj5 0z i;7yr)f9:is the other, what is the ratio of the diameter of the longer wire to the dias5pf0g9jc :a8yqiz ;b7riiz) meter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V powerk fc ll+g2:,-l(duzx w supply, and a current of 0.4212 A isz-:kldl2( flcu,+gwx 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 orychr524qsgp ;yx 4tq76-l:zjrb( ttf aluminum, both of diameter 1.0 rbs ( pt ;zcyq65:4qtgly74 xthj2rr-mm. A voltage 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 the value o9 n y*rh isoihrs.ni0r);x50d f a resistance not change with temp50*ir.n dsrhi h0o9i ns;yrx) erature. 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 ofp:gwac*ft4ct96li8 d heat when96dtfl4w* t c:cgapi8 connected to a 240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player tfm8)a ysngx0 iy2y6g/ hat draws a maximum of 320 mAag8)2mx ygf0y6ni/sy of current?    W

  What is the maximum voltage that can be appliedj c8a.w1 emmw2 across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, a 75-Wklv7b1004zf+zf lnao lightbulb connected to its proper source voltage of 12v n+o1l0kzfzlf40 a7b0 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 ,0dfcw26/w l8*iac yvc0iefh
(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 a6/ p*qc +s mwz29b fhpbn,n vp.zx5iy4nd 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 Europe, where electricity is deliver7 cjd4xif vp+6t, 5wljed to homes at 240 V. If you use the lightbulb in the United States at 120 V (assume its resistance does not change), how bright will it be relattifv lj,x6p +5w7jc 4dive 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 in w; rfgrbg 5c:6operation for a fc :r6 b5r;ggwtotal 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 25-W porch lightnj:ieablx k8o9o1 )bs42d jn5 on day and4j)9l2jx8b: obnesd a1no5ki night for a year? $\approx$    dollars

  An ordinary flashlight+1n/ .g (;sgddtd x.mzjk,mf d uses two D-cell 1.5-V batteries connected in series as in Fig. 18–4 fgg/.d,x ( d1ndjm;+t.dszmkb (Fig. 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 amomhu)36m-pixq -xf- fvunt of 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 Fikbq3+apq *c +jg. 18–20, can be used without blowing ab3+p+ *aqkcj q 15-A fuse?    bulbs

  An extension cord made of two wires of d nbz1.igl(jgqnn./1:c l2yv u iameter 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 power bl(q1zn:1licn.g u2.yn g/j vis dissipated in the cord?    W

  A power station delivers 620 kW of power at 12,0q*7(ugny r0t c00 V to a factory through wires with total res*7r(qt nycu0 gistance $3.0\Omega$ 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.p- qo8 eyvitr 9l7bf0:gxb0 .a At what rate must cooling water pass over the coils if the water temperature is to rise by no mopgblebiv8. ot:79 q-f y0 0xrare than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car tojh g.esfoxm:5 j +m3-z heat a cup of water for coffee or tea. If the heater can j:eh5m.xmg +sfoj -z3 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 curgfna(xe:0k 3g rent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, is,bqwez0u gwv8t; xz/ *aml b8: 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 resistancexspntz5*ns6g-),vbqn ) mvuai) ti 48 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 1o 7/ q.;kfgdmk6po- vk500-W device is 5.4 A. What is the rms voltage across i ;g7q.kfmkkp6-v do/ ot?    V (Round to the nearest integer)

  An 1800-W arc welder is connectede i+(cq- o jc9:dgovv) 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 instantai; c 4zxaa66cwtoest7rea(b)2 m8 0 wzneous power dissipated by a 3.0-hp pump connectedmz a4 a;xw8cs2 )7e0( io cttare66wzb to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connectxgrh zcs4l6q; ni+u19(c-gqped to 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 co p h*q ,+38fobtfs-kkja+uq 6opper wire carries 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 wez q1 5.s 0or1t;nqajqhen 22.0 mV is applied to its ends. If the drift speed ;11 0qsj5eqoztarqn. 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 :d9dxo/ hcvx5Earth’s atmosphere, $He^{2+}$ ions in a concentration of $ 2.8\times10^{12 }\;/m^3$ are moving due north at a speed of $ 2.0\times10^{6 }\;m/s$. Also, a $ 7.0\times10^{11 }\;/m^3$ concentration of ${O_2}^-$ ions is moving due south at a speed of $ 7.2\times10^{6 }\;m/s$. Determine the magnitude and direction of the net current passing through unit area $(A/m^2)$.    $A/m^2$  ----待选择----NorthSouth 

  At a point high in the Earth’si j(sw 5esn6 -*ks+wjq 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 across an axoy2/2k d-zn-f /wvu0,o . gjwm4wbhaj ok-fpv. n 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 oszu4h 3np+k(j6ey0iu pv.p 9etected at a point 3.40 cm down the axon 0.0052 s later. When the action potential i6 p9k.y3uj40+isu ez( onpvph s detected 7.20 cm from the point of stimulation, the time required is 0.0063 s. What is the speed of the electric pulse along the axon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much energy is required to transmit one acrxcv9+/inv1wj9(3 htvknggfwdap:q5 q)+m )tion potential along the axon of)3x(5+mhcvvwg:a 1 k q+qd n /tpv)9iwf9jngr 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]. 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 potenti2k6jjru3 f44 0or+ pds/x6n7 twctds aal, $Na^+$ 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 areveki h)w)bg 0p;wjz4 )ym+b/ w there in 1.00 ampere-hour?    C

  What is the average current drawn by a 1.;p v02i;ka2a*cx vu .jzc )qhr0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of the two hea gb+stb3kp+e zn:7+sv dlights uses 40 W and each of the two taillivkszbb7get :ps+ 3+n+ ghts 6 W, for a total of 92 W, how long will a fresh 12-V battery last if it is rated at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of a 110-V, 1 ztzf)+tm 46 y)2kdsdw500-W heater is 5.4 m long. If it is made of iron, what must its)2t f6 zstzdydmkw) 4+ diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the r9r.zll(-tzh(v bv d1o3co;up1 u9 whoeciprocal of the resistance R; that is, b c-(o3row1z hv.lovph(9;d1ut lz 9 u$G\,=\,1/R$. 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 6 -l,ufc m k*h-b)*sui8j hcq 9ccqpp: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 co q9m*-cshfb :lk6iu cp*u 8,-)pchqjcst 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 house+c(4ftpst08 qzf ohw 1hold 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 togetmsdpn +)1 e3lxher side by side to make a3) dpsxml1ne+ thicker wire. How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer i:f 7-ktjhstm )s 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 thickmna d:j0q-:jq enough so it does not become so hot as to start a faj-mj0q: n :dqire. 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 gh-h;;vtros o1iven 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% efficiency delivers 950 W of energy per secondo 0 :9(xvxyzbo to the into(b9y :xvzx0oerior. 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 conductjnm;hbya+ 71bp;* np yors made of the same material. One conductor is twice as long and twice the diameter of the second. Whatnyb ;jy *phnb+71 p;am is the ratio of the power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is+tc czaq s )u:co-4hl3 used to heat a room of volume $62\,m^3$ Air is brought into the room at 5$^{\circ}\,C$ and is completely replaced twice per hour. Heat loss through the walls amounts to approximately $850 kcal/h$. If the air is to be maintained at 20$^{\circ}\,C$, what minimum wattage must the heater have? (The specific heat of air is about $0.17 kcal/kg\cdot C?$)    W

  A 2200-W oven is hooked to a 240-) mw ty3hvtrpxiwr;*(d*/t*i r p(oc 8V 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 of2n pnc3n g1qz4 storage batteries as its source of energy. Its mass is 1560 kg and it is powered by 24 batteries, e1 npcnnq 4g23zach 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 resis/8 vuttberap(9zk :dgf+(r*9jl l8bw 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 ca tahrps opst1(x2- 07*.yd hhyrry an 11-mA beam of protons traveling at very nearly the speed of lightt12 (ss. phdo p a*y7-xtyrhh0 ($ 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 5yz rw *.w)*4hq hu rtjowav,:220-V ac. The connecting cord is copper wire with a da.wh qtrwuh *r5,: )yw*ovzj4iameter 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 to 1an x9kg1 zr/ z,/dry yqfvv36(20 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire dnyzfx(,6q a v9/rgk /v3zr 1yhas a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage v4 si639;mvw qnj6 xofsaries 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 voltage cha64;3ixs6nv9fjw qm s onges from 12 V to 13.8 V? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 1nyupw9 3g7ec/i ,+zk tk3vc-l20 V and 40 W for household applications. Lightbulb B is rated at 12 V and 40 W for automotive appni/v3ukz7y3g9ckw-l,t p c +elications.
(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 syzvwp;o:()yko;kp 8iet of appliances at 120 V, which8 k)v wpooyi:zyp;; (k draw 2250 W of power total.
(a) What power is wasted in 25.0 m of this wire?    W
(b) What is your answer if wire of diameter 0.412 cm is used?    W

  A copper pipe has an inside diameter of 3.00 cm and an outsideaz1a uy; xk--e diameter of 5.00 cm (Fig. 18–37). What is the resistancauxz e--k1ay ;e of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its length dovqt1 z- w p ,irsm6nl)fw* sgb85o) i0rp0+occubles, by what factor does the power dissipated in the wire change, assuming it remains hooked up to the same vo6,rbl wg 0 qof*i -scm8piwn c)t0rz+)1povs5 ltage source?

  A tungsten filament usejhgetqv 9e041,pl mv h2k/5 ycd in a flashlight bulb operates at 0.20 A and 3.2 V. If its thq, mk4e 1j2 gvp0yv e/95hclresistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$