What quantity is measured by a battery rating given in aqi-- bho5pn k qv/sj(6mpere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow away frd9 a e*z ibsi8yb4g;*jom the negative terminal in the circuit. But within the cell, elec b ;sad8ig*yeibjz*49trons flow to the negative terminal. Explain.

When a flashlight is oper:08n. ysov qjlated, what is being used up: battery current, battery voltage, battery energy, battery power, or batter8y.0 nol:jqs vy resistance? Explain.

One terminal of a car battery is said to be connected to “ground.” Sinc-8gbbjqs+dds i8s: deq3;2 ule it is not really connectedgs8s;q:+i dl8seq3b j u2b-dd to the ground, what is meant by this expression?

When you turn on a water faucet, the water usually fl3r-u tk n99ahzq8a be;ows immediately. You don’t h;a3er- qktan9 z 9hub8ave 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 terminals of a battery?

Can a copper wire and an alel g x ib(rem*ex19/o,uminum wire of the same length have the same resistancl*b(e oegxi9/x1, rmee? Explain.

If the resistance of a small immersion heater (to6p f3-j-tzty+tnwoi* heat water for tea or soup, Fig. 18–32) was increased, wot+ 3iz -ft6njw-y *ptould it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon r*safmebaj35t3 ,k9 9xhe0 vwhas sides of lengths a, 2a, and 3a, how would you connect t5r0 m j,3fx9ahaes93 we ktb*vhe wires from 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 n)ivc+ebzr +2lightbulb burns out?

Explain why lightbulbs almost always burn out just as they 6i dcusjbs;0 xua;(yp cd+22l are turned on and not after they have bexjls6 b cuy+;s d0d( ;ia22cupen on for some time.

Which draws more current, a 100-W lightbu3egk.b,( t tjalb or a 75-W bulb? Which has the higher retjk ,gea3 (.btsistance?

Electric power is transferred over larl6un vs oyln35 s;r01g:0t3zis w+ ltige distances at very high voltages. Explain how the high voltage reduces poweyoz 3g; 6 n:s+00llsvt31inlis t5wr ur losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replali dj/rsem,5gw8 39kvce this fuse with a 25mw/rsvik g 538 dej9l,-A fuse?

When electric lights are operated on low-frequency ac (say, 5 Hzhvd0 nv64c1tk*miu;u atv-9 ud +ytv3), they flicker noticeably. 3 t+vdunvdha1cku*uv49 ; 6yi0 t-tvmWhy?

Driven by ac power, the same e nhe4ragd-e2) ju ):kulectrons pass back and forth through your reading lamp over and over again. Expla4:eke j a )gduhn)2-urin why the light stays lit instead of going out after the first pass of electrons.

The heating element in(vmez3v(7jo5w)rk 8 xh /cnan a toaster is made of Nichrome wire. Immediately after the toaster is turned on, is the curx/zne8rj5m7ck nw) 3 hv(v (aorent $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resis/ vv71wnt v a-b7p)svotor? Explain.

Different lamps might have batteries connected in eito:pqd+ fbks6;)i v cqgj+ (jk6her of the two arrangements shown p6sq6+:gj (fbo d;j+ik)v cqkin
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many e hn66u/8pivk2r h( qeslectrons are flowing past any poiv/h2ukrpn6(q6 8ihesnt in the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a cu ng v7 atzk0k63edut k*swr7 e23cg9q*rrent of 6.7 A for 5.0 h. How much chatu kregn9k q0scz7w6e72 a g**3 3ktdvrge passes through the battery?    $ \times10^{ 5}\;C$

  What is the current in am, .ey8gqveon8yt1wj3h b 7o-cperes 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 4.2 A?zvk.p* ;y6wyt    $\Omega$

  What voltage will produce 0.2)(+- ( xsllumvzctt 8w5 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-V line.ksn e3w *d*+sov cwvfto0n-:0
(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 heat,) 51xsulab5vd7 pn5fau d:bcing 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 bulb whose resista 8vw;m vy5gks s-cg;+nnce 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 carryinv *bc5z9pd.gkg 2800 A (Fig. 18–34). The lin dc.b5gpzkv9* e 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 af) 0ywzn5di;x shk7+at 240 V.
(a) If the voltage drops by 15%, what will be the current, assuming nothing else changes? $\approx$    A (retain one decimal places)
(b) If the resistance of the device were reduced by 15%, what current would be drawn at 240 V? $\approx$    A (retain one decimal places)

  A 12-V battery causes a current of 0.6 ir 34w a7ecl0v7i)ji- *et:zbmth.mg0 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 av bhv;jm*b6 vc; ny-+t 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 wired( uouh7j: b w-wja4z6 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 1s-h:l7zv s ,a 04psmpq0.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in diameter. sq07z,a :- v4 hmpsslp   

  Can a 2.5-mm-diameter copper wire hav hwz)*2q *ioyye the same resistance as a tungsten wire of the same length? Gi*iwzyy )hq2 o*ve numerical details.    mm

  A certain copper wire has a resistu-mhk *i8ine ,xz*4m vw6e7 med0n re/ance 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 ha59 u5fuc 4n.qdtkjy l7ve to raise the temperature of a copper wire (originally at q7.5y nu9k fc4dljut5$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the m2hzy4 cq) yuk0a1s2y same resistivity as tungsten does a0u2a1zc yhqy2) yk sm4t $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of/4oyvak4r pbvtta8l7r7o 6d: 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 lenb,cykm** qf)o0qm o.igth of household no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm and carries a 12-A curren,ybo0* mf .mqckq*oi) t.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm,b2sd zd32j u.h 2.0 cm, and 4.0 cm, lyin2sj 3ubd.2hdz g along the x, y, 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 length of thajxqoor(. 6 1tgk3 -tae other, what is the ratio ofo qxj. ak-ar(6tot3g1 the diameter of the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wve9y49 smhu(vgav:;-d1yst mire is connected to a precision 10.00-V power supply, and a current of 0.4212 A is precid(4h 9y-e v;gtss :amuvm9 1yvsely 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 8 i2pgms2o 0drcopper followed by 5.0 m of aluminum, both of di2 0rpd 2ogsm8iameter 1.0 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 valut.rfs)c* +t zve of a resistance not change with temperature. For +sfz)ttr. v* cexample, 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 desigj** h2pzc bo h,fc94qpned to produce 3.3 kW of heat when connected to a 240-V source. What must bep2*qcj zhf*cbo p ,h49 the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portablenoegr qc zwg)eq8l*vp7dz-tq9k9s x4.is6-4 CD player that draws a maximum of 320 d7 s8e -v)qwqlc4ezg4g r 9psn*6-zi9kto .xqmA of current?    W

  What is the maximum voltage that can be applied av 5+*y) c -lpga89 mdvvajy0vocross 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 connectedrr. c 99wrsr:m l:/gqb 0h8uwd to its proper sourc0: 8w9smr/hrr.qcw:l 9dubgr e 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 rat e 3*rwlv(t,v :khkpf(v 0*bcged 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 1250 W.wmf) s2gnkt2,
(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 deli9zmaa tt0y - mr5;d4mivered to homes at 240 V. If you use the lightbulb in the United St4rti t5 m yaad-;zm90mates at 120 V (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 t+cj60q l6/ame1flz 6lc,opixhe morning if it is in operation for a total of 15 ,lei/q6+a6 6mcjzxo c0fllp 1min? 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 leam6kz:zmhk0;f ve a 25-W porch light on day and:k6zkz mhf ;m0 night for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected in swbz9e.gi zxc ho* ;n:mpx1/8series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA nx.gz:*p/w9h oxcim s 8be;z 1when 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 am v)/zp5 -yokhej:ddr. ount 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, cov55qxsnm( b qq)ud9d9 nnected to 120 V as in Fig. 18–20, can be used without blowing a 1 n59d)(dqs5 x9mbvqqu 5-A fuse?    bulbs

  An extension cord made of two yxq,j +p-m:nujfr)g 5wires of diameter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electr5rjj-:fq, yx mp+u)ng ic heater which draws 15.0 A on a 120-V line. How much power is dissipated in the cord?    W

  A power station delivers 620 kW of power at 12,000 V to a,pmuiy ;h0 3uh factory through wires with total rh3y0hi,umu ;p esistance $3.0\Omega$ 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 8ua35wm+hbf+ 1 beo hze )la5pA. At what rate must cooling water pass over the 8l ha+h fbe1pmb55o+ u)ez3wa coils if the water temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heatu. xa3c (td 18ksg,imeqp c0.her can be used in a car to heat a cup of water for coffee or tea. hxks8cu ,1dg0(cp3e .ati.m qIf the heater can 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 current in a r/ph5f yrjyk+:b6 um+ $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, is acros jtpx+w:-2 wyas 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 resistanlxof-7( xiw+ n26di5 y(g7 mauwa) gduce 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. What isc 4b6 4v.lnsd p*dnqf/g( g7dj the rms volt dj 67d/.( lgn qfnsd4g*4cbvpage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected ckjqp su;1 1.;;u/g ouxsv2 ztto 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 instantanei7fgr;.p; wny:qar7iz 2h51abo( o uvous power dissipated by a 3.0-hp pump connected to a p:yrhzr a ibv; nwu7g7 a.f(;oqi1o2 5$240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connecyf0e7/e3, aw n,crnzkted 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 carries a tiny currp.vk*ug8ry9o i6y4b tvjz w2r(0-uggent 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 22epd q.b8zz.h2 .0 mV is applibz. zdqh.p 8e2ed to its 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 Eartjc0g 6-ul +kxd//kv l5tmtrf/h’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 Ea-*/rpmfnq mcomy mm4m;ls+ g2, 37ijfrth’s atmosphere, $He^{2+}$ ions in a concentration of $ 2.8\times10^{12 }\;/m^3$ are moving due north at a speed of $ 2.0\times10^{6 }\;m/s$. Also, a $ 7.0\times10^{11 }\;/m^3$ concentration of ${O_2}^-$ ions is moving due south at a speed of $ 7.2\times10^{6 }\;m/s$. Determine the magnitude and direction of the net current passing through unit area $(A/m^2)$.    $A/m^2$  ----待选择----NorthSouth 

  What is the magnitude of thxg dkgn5s+ .t3e 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 le*pdje3+ po, 2hkhco :v4q*g 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 timk o *p:d2* ohgj ql34+vehecp,e 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 6zx+l,yyw)t3 4efijbtransmit one action potential along the axon of 3 y4lwejy6bt,i f)x+zExample 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 poteng+uek.vk (g06me-vqtv8nexpx)- g+e 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 amperhfu9ro4rmgkx 76s8).hx i*q ui5 y(ose-hour?    C

  What is the average current drawn by a b:okmve9nz c09b6/w +angi l :1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a ca9aepjg)cvakl83o *o2 b35,2mj r xiv ar with the lights on. If each of the two headlights uses 40 W and each of the two taillightsve a)pj9a,2oo2lr3k c 8jg5x3mv *a ib 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 1103uotd ud2 a3q6g ti,6c-V, 1500-W heater is 5.4 m long. If it is made of iron, what must its diameter gd26 3du,otut63 aqicbe?    $ \times10^{ -4}\;m$

  The conductance G of an object io:,ef n jqdv*n4ns 5 liwk+y50s defined as the reciprocal of the resistance R; thd ji n:n+ ns4e *kf0,wlq5voy5at 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 pol qyp; pl.87jb6xh2lb wer. Suppose that instead of using high-voltage lines to suppb l8phy2jq7l x;l.pb6ly 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 is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular household uses a +wtjau q9i4vjzf;1 l /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 togc je7amkw- 7x7ether side by side to make a thicker wire. How does the resistance of thisax7mjw-c7e 7k new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed forz 4)gfp(2abwp)f t xo (9z1eaq 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 imtlzco- b-y,(0 -d1a2 c yogkqt 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 than 1.8 W of heat per metbzako-l2do-, q -1gcm (yy0cter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given kq7i5e v0g/oygz (la2by 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 ;: rzy)aqqu v/energy per second to the zq; qvu/:ra)yinterior. 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 differew 677dwjzs 5dxzi 3--rw;r ohvnt conductors made of the same material. One conductor is twice as long and twico wwjsdv-73rzhdx - 5w6 ;riz7e the diameter of the second. What is the ratio of the power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room of volum+3 5a; cizyb.(pra yvke $62\,m^3$ 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-Vzhj;pnl lf)*s.0wo qz16osd (+jn c/k 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 batteries as it ztxppj6cho *f 0,4;uds source of energy. Its mass is 1560 kg and it is powered b 60p,x*4 zohdcj;tfup y 24 batteries, each 12 V, $95A\cdot h$. Assume that the car is driven on level roads at an average speed of $45 km/h$ and the average friction force is 240 N. Assume 100% efficiency and neglect energy used for acceleration. No energy is consumed when the vehicle is stopped, since the engine doesn’t need to idle.
(a) Determine the horsepower required.    hp
(b) After approximately how many kilometers must the batteries be recharged?    km

  A $12.5-\Omega$ resistor is made from a coil of copper wire whose total mass is 18.0 g. What is the diameter of the wire, and how long is it?
L =    m
A =    $ \times10^{-4 }\;m$

  A 100-W, 120-V lightbulb has a resistancez0;3( wm yud(z*w*mr fv; ujbf 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 ()za1cj e0kp- iIllinois) is designed to carry an 11-mA beam of protons traveling at very nekci-jz)10 ape arly 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 wj.vxtcin *, 7f*b3 dc220-V ac. The connecting cord is copper wire with a diameter of 1x7*,3*vi nbw tjf.cdc.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 heating el dfpjgf 91j9j*ezky,0s* ras3 ement is a coil of Nichrome wire. p,eg fs9a1fd9zjksj* 3y0j r* 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 V when o m.+m1wxsf /ithe car is off to about 13.8 V wheo1m+i. /mwxf sn 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 rated at 120 V and 40 W for household applications. Lightbulb B ip* wx;dhgpvjf(z8s9c kr6/9 xs rated (zd9/skp9* xvcg jrp h8 xf6w;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 s(x ts4nl4 x55r93e1e s /lpl-k wffilxet of appliances at 120 V, which draw 2250 W of /4(lx5l lse93n1fw f 5s-4itx xlerpkpower 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 ins5uwir 0sxwfjqqo )7cl b24)( pzf34epide diameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the resistapf34qox eup)fi2) bsqw c47 (z05rlw jnce of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretc o9s44tqjvonwkxq 909l . 7ebuhed uniformly so that its length doubles, by what factor does the power dissipated in the wire change, assuming it remains hooked up to the s4ub79evlxso ntqkqoj9. w940 ame voltage source?

  A tungsten filament usedpc)l(1pvf.a3fmdbk g)h lf k:(:oz(0 s7nlfo in a flashlight bulb operates at 0.20 A and 3.2 V. If il: 0k 7 1 ldkppozhmf((.s:alb gf)c)(3ofnfvts resistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$