What quantity is measured by a battery rating given in (b dkckjfs qht(0lea2a :vf h 06r +.ql:w86jsampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a cir spu-:- qz dsyv((ic8icuit, electrons flow away from the negative terminal in the circuit. But within the cell, electrons flow to the negative terminaluid q:8(svc -z(- psyi. Explain.

When a flashlight is operated, what is being used up: battery current, bato rw:oe v8fz0,7khl3dpjqaxp.+;c9q tery vol, wp:hx097ov +dq3zce k;ra j8qpflo.tage, battery energy, battery power, or battery resistance? Explain.

One terminal of a car battery ik 4a1jbk4o2:c97sujj( qlepw) bpvv f9x l44os said to be connected to “ground.” Since it is not really connected to the ground, what is meant by thi4 : bj os7ja 4lcp v)qxkb2opf14 e9(luk94wvjs expression?

When you turn on a watereq*v:rwl. *4gq:ef xp faucet, 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 thprl*vge.f4qew q* :x:e same thing true when you connect a wire to the terminals of a battery?

Can a copper wire and.b,h/ 8/8 dqb qnowhyw an aluminum wire of the same length have the same resistanceq/8qh dnw.bh8y/wbo,? Explain.

If the resistance of a small immersion herb-u:c( jd6 0zkb)aklt5jj3 vater (to heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow down theb:5ar l6jtv (-ukb jczd30)jk heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, and 3a, how w- ghclgi:. hz4ould you connect the wires fromhg4.zc -glhi: a battery so as to 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 lightbulb burns oau, e+fe co ex12ceu74ut?

Explain why lightbulbs almost always0lli. (o2vzp uxj6a*9civx h- burn out just as they are turned on and not after thex-. u(a* cxh6zol09ivpvil 2jy have been on for some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which has the h im+81ansnm)ldky0 a0 qk;/ taigher resistak10m+0dsna8ym) i;n kt/ laaqnce?

Electric power is transferred over lr.;hd*mu 2luckazz/ci) k+ob :b6 hs 0arge distances at very high voltages. Explain how the high voltage reduces power losses in the transmission l*hu6/zdmk0icuol; .ckazsb: ) rhb+2 ines.

A 15-A fuse blows repeatedly. Wi5 pm-(twtj:,.dh w gjhy is it dangerous to replace this fuse with a 25-A fug- d.m: ,jijhtw wtp5(se?

When electric lights are operated on low-frequ/k;w*2p qitmgency ac (say, 5 Hz), they flicker noticeablgt*w2;q/km ipy. Why?

Driven by ac power, the same electrons passkfa,pcs. ew( 3 back and forth through your reading lamp over and over again. Explain why the light stays lit instead of going out after the first pass of .(3kpf eac,ws electrons.

The heating element in a toas8u.7e,h6d hw2 oqoom jr*z -pu 9+kftyter is made of Nichrome wire. Immediately after the toast phwk7u86uj t 2+q,dyh9zomoofe.* -rer is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Explan a9pc;h19g zrin.

Different lamps might have batteries connected in either of the two arraulji7nay- (q e bn866k2aj tt)ngements s)2n b inl6jqjet76(yku- aa8thown in
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 flowing past ax4 zo ,8zf z*2fjd:hl0rr,7 jssm o,jmny poinmf7djz8o2 j,m*4sz : , rorhzf0sjx,lt in the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery usingtgpm) 2a ha0ho:gsz7b w,0 /k-xgdb9o a current of 6.7 A for 5.0 h. How much charge passes through thh9 xowgtbdskg)hb 0moz7a: 0ga ,p2-/e battery?    $ \times10^{ 5}\;C$

  What is the current in amperefe* 85k .bb))r:e (ksurvosmp s 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 current of a+kx5jh,a* tg4.2 A?    $\Omega$

  What voltage will produce 0. ,tbf86sah k9t25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-V line.5w f7in nh2g/h
(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 dh9r* so+ h2) pqxck1jyryer has a heating 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-xi: pj +f h;(smvh8vb 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 transo6-a;zxc9 ee ( twuv*tmission line carrying 2800 A (Fig. 18–34). The li(ezatec9 6ou ;x*w-vtne 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 d/fto7+g um+ xsraws 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 cwc+eaza7bv xa -*ij 0g,-,qhq urrent 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 whosei9ish(qpp 0vxo+y a 02b1wjg/xf z -/z resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistan29+ b xkgrkxc1spe52( ohd/w lce of a 3.5-m length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the 7j-r g.j hywp7y nv4ib0)ao v7resistance of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 )774bwar-o70vynpgv hij .yjm of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tunb m; lwf2b(e4z6y)a hngsten wire of the same length? Give numerical detai6fam4b;e)b lyn wz (h2ls.    mm

  A certain copper wire has a resistance ocu::bqi5lzp4, rqf jh6+q zz510vz tsf $10.0\Omega$ 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 (originap2*z.o 3wo)kty eyto8 vi,9 oclly atk32i z9oc).w,o8ytpeyv too * $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have theul /6pp2;3 h60l:ue; jofi-i kctnyaw same resistivity as tungsten doescujti;;a2-/op wln: f0 36iu6 yekphl at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of aboxl )4b*ks/uex b: bl,5bz4 )1byo0uotwf i8wuut $12\Omega$ 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+ rlirg8r: n2a 26-m length of household no. 14 copper wire (user: r8+a2nlir gd in 15-A circuits). The wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid maj+uzq9xmk3e: n*o 84 +ecscdrde of carbon has sides of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axue9*+q mcxsz cr dk:o+j38e4nes, 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 resis/ v (s6lseul0+w+y gbgtance. If one has twice the length of the other, what is the ratio of the diameter of the longe(vwgsyg6e /+ 0ls u+lbr wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V power supply, andpo9)g, ub*qnwyj o9a ti ,7)so a current of 0.4212 Aao,sy)j p )9uiqo,g * wn9bt7o 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 gz5i ovbyx+,xa9 h y27 qu3mc-of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV 7x ,9y2-bv5gcmh qiy3u+x aoz 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 application*/52rbubdary s, it is important that the value of a resistance not change with temperature. For example, suppose you madr*au2y5bbr/d e 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 oven4ud2tk joz 9.v,m zlz2 is designed to produce 3.3 kW of heat when connected to a 240-V source. What must be the dzuvk2 4,o mlz 9z.2jtresistance of the element?    $\Omega$

  What is the maximum power conslna050 aj;7 rhg2tkor7h bh9sumption of a 3.0-V portable CD player that draws a maximum n0 o0hkbh;rtl2aa97hj g5s7rof 320 mA of current?    W

  What is the maximum voltag;ma05ups1 6qdh;xv e ue 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 thro qh b:5ek5m2tdh;b0io+e si i8ugh, a 75-W lightbulb connected to itsq52 kho +be0 :8s5tmih edibi; proper source voltage of 120 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heater is ratedpe4 1 mmwdzf11--k /lbroxtq7 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: 850 W and 125g07qnqh,q z f. a)cqx*;a 0pnw0 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 hoe;t.r0zm fs 0sv d+a6xmes at 240 V. If you use the lightbulb in the United States at 120 V (assume its resistance does not change), how bright will s ;dme0x0s fa+vtrz6.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 th a +kzj1 l2bhz7moo *t:+csh4de morning if it is in operation for a total of 15 2s tcljo z4ahd+:mz1*ohk+b 7 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 v,zld10og+6bgj+ eei a 25-W porch light on day and nighl10e j+,b6e+od zvgg it for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.eh8:r* w o,bqj5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when t:oq8* rh, jebwurned 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 sto;t k3dv(ewr-wa.z ;ws red 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, can bemr6j6 - ftre5hg j9 . +qdizot(sh84vw used without blowing a 15-A f5rd964- e jzvhwf8j 6trqt o.+i hmg(suse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 csdna u0+a5/ hiq xw;/copper wire) and of length 2.7 m (9 ft) is connected to an electric heater which draws+d 5sauqc ai/h;0 xw/n 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 factory through wires w m,diw3rf9-jwith total resistance wwrj3i9 -f,md $3.0\Omega$ 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 17.5ytlb/7cs;f: r A. At what rate must cooling water pass over the coils if the water temperature is to ris/s bf;yrl7 t:ce by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater cab5 3(,wtw tzvo,(i rb4 zvvzs+n be used in a car to heat a cup of water for coffee or tea. If the heater can heat 120 mL of water from 2is rbv 5zo,tv,+v4 twzz3(b (w5$^{\circ}\,C$ 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 currmave (*oaf +(kjr6)prent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value i pur4fd2ajhenw .4 wrw /v7:82n0gmors 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 resista t hmz:3-hk0m7e58fu5 ts.2r wafqd yance 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 1:mf;nn:m(n9u i ihz 7o500-W device is 5.4 A. What is the rms voltage across it: i 7(ihm9m: f;nznuno?    V (Round to the nearest integer)

  An 1800-W arc welder is c14b.rc.n lo b2xi,qz monnected 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 dissiun(jc n:7) w2ri;orcm q g/ol0pated by a 3.0-hp pump connectejnc /on :rw orcq7gl2 im;)0u(d to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected ztf- qt :wk2v( ky,c+5smpev/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 copper wire carrij 4e0pqov otr:-v +t6tes 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 carriza6/8mz 0h8p3csk(svnae )qaes a 750-mA current when 22.0 mV is applied to its ends/ s0 aq hnvskc88epma36 a)zz(. 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 atmosphere,(ot83s .etc8vvbb.uq $He^{2+}$ 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’s atmo2rxjtkfjym g*8k; s(i8b 7w7osphere, $He^{2+}$ 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 fielpy-r9u lus 0skz9g 0:u/jy xu2d 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 spg1 po+8od:bpulse. 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 spg81oo +:bdp 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 action potential along thea+werp i n7jz vd -d+m*+93s+dv4 tdkg axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy storep7+k4 d-w 9sd+ v*n+ edrv3zgmtia+ jdd 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 potential,uz)z7* o25tys6 mpcvz $Na^+$ 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 ar1-sxcmilx( s 8e there in 1.00 ampere-hour?    C

  What is the average l;xh1j t;c akc,6xvbqm. t;6wn)(huo current drawn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on./i o1uai,l v:e hbv7w xa6 /vbwzq/**g If each of the two headlights uses 40 W and each of the two taillights 6 W, for a total of hlzw//i1w*b a/av:xe*qvi,u vbg6o7 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 heat60 hcf-yxxl3 her is 5.4 m long. If it is made of iron, what must its diametehxlyf0- 3h6x cr be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined og9z. itie c.b3+0 9jm5v ljsxas the reciprocal of the resistance R; that es+ 9.i5 .lbz m0j9jc3viot xgis, $G\,=\,1/R$. 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 avszl h26 2jlb0bout 10 MW of power. Suppose that instead of using high-voltage lines to supply thejlvblz s 0h622 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 is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular househo f. lsp.**egihld 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 toge v)g 3jed:cx77u bpix+ther side by side to make a thicker wire. How does the resistance of this new combination compare to the resistance of tbdu xe xgvcp3j+):77ihe original wire?

  A 1200-W hair dryer is desigr5bvjprc q kb6pzvn9+sx 1)d*un/o/5 ned 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 -fxyq;;+yb e-ah* z enbe thick enough 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 produce no more th-; y;hean+f z* -yeqbxan 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is k,.)55nk2prf - ulbd,xadhubgiven 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 runslm(eu+ 4x g hih-m6q3ning at 65% efficiency delivers 950 W of energy per second to the int+um(im4q-xe h l3gs h6erior. 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 differenaovw t+0m xqlk(u29+ mt 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 relative to th92 xl+0oqk (mvmtw a+ue second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room of voludw /c g965jl7uh5 efmmme $62\,m^3$ 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-V sx 6v1vp 4yf/opource.
(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 batteries4om,+ db w:xvi-4gebyuxf24u as its source of energy. Its masv4xuobbi+4d mw:gx2-y , f eu4s 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 kz;n h j4 pfeo0hw6cu5(g6xi3a 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) is designed to c*vq :xu9a uk)rarry an 11-mA beam of protons trxu v9q kar):*uaveling 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 a2l9 8,c:qr mb 3ru(hzvj dahw(t 220-V ac. The connecting cord is copper wire with a diameter zd h2ra(: m(ch3vbu jw r9q8l,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 120 V. Theuemoet4 83s;i/gw za) heating element is a coil of Nichrome wire. When uncoiled, the wire has a total l4o/ tw8g; usi3)me eazength of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies f x4trlz v31y uexgq6m9;*0v wbrom 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%zy93 1gxetx;*l 4muvq60vrw b. By what percentage does the power delivered to the headlights vary as the voltage changes from 12 V to 13.8 V? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for household applications. Lightbulb Byihuq;1mp7 h;v /)c5y gw+z ax iyw5/xm)qvz ug;y;a 1hc +7phis rated at 12 V and 40 W for automotive 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 appliances at9an6rdv( )q)odd (cp c 120 V, which draw 2250 W ofc))6n(r pdqd(vod 9ac 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 insidnpsq n6e60p n7e diameter of 3.00 cm and an outside diameter of 5.00 cm (q6spnep76nn 0 Fig. 18–37). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its lengely,;g,cozw5 d,q rl( th doubles, by yo wd ;,5lg(qzelr, ,cwhat factor does the power dissipated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flash8pjp+nkpab8vz 9(2tp. icmask6*jk 5light bulb operates at 0.20 A and 3.2 V. If its res p*tp8j p( j9ip am.bkv6naks25c8k+zistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$