What quantity is measured byibpo:hw/6)0 k5aq iw s a battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connectefrb( l4 d5ikua(0l a9xd to a circuit, electrons flow away from the negative terminal in the circuit. But within the ckxaf adr(l9 0u (5ibl4ell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is beinlvlz-l(i9x3;jwbv i,4;m jjfg used up: battery current, battery voltage, battery energy, battem b9ijjv;w (4 f3v;,lljixlz-ry power, or battery resistance? Explain.

One terminal of a car battery is said to be connectedjnrh4 3m)c85 4( hp/mk vzouuy to “ground.” Since it is not really connected to the gromc( hyn/pk538uh4 vzmju4ro)und, what is meant by this expression?

When you turn on a water faucet, the water usually flows imm7cth9q3 tln:-vs)zkh ediately. You don’t have to wait for water to flow from the faucet valve t:3v-qhhn 97lsk zctt)o 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 wire of the s0i) aa06i r p9-f uqc8pdwh6qcame length have the same resistance? Explc 9w68qic i0qpd6par-a0hu )fain.

If the resistance of a small immersion heater (to heat water for tea 3 p20ic fd;ilfor soup, Fig. 18–32) was increafc l;p02i3f dised, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, and 3y 2vx): gj9ckka, how would you connect the wires from a battery so as to obtain (a) the least resistance, (b) thev 9cjkk:)g2 yx 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 l1tfql/tte7 dia0 7 o73o a+xkuightbulb burns out?

Explain why lightbulbs almost always burnkw re ie,+9iw) out just as they are turned on and not after they have beei rwek,+ 9we)in on for some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which-g /i g;gpivw4 has the higher resistancg /g vgw;i4-ipe?

Electric power is transferred over large disizhznb2 zfkgw:2*:7v) ul ya 5tances at very high voltages. Explain how the hi:5kw2zgiaz)bh y 7nz:l2f u* vgh voltage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is 7 4uorw(ozuni5 r7eabos+ +/lit dangerous to replace this fuse with a 25on+/ az75w(isbul7o +eror 4 u-A fuse?

When electric lights are operated on low-frbtdj1b3tsg1:g2* z qh equency ac (say, 5 Hz), they flicker noth*j q t:3s bg1dg1ztb2iceably. Why?

Driven by ac power, the same electrons pass back 6a3 zm 4i mcyhhbke5wp :3f8z: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 electrons.3i 46k5h3b:mz:p8afwzeym ch

The heating element in a toaster is mads *v)x re(0mwv0vd(q77 mqlkn e of Nichrome wire. Immediately after the toa7q)((r vmlqx0w*s0v 7en dv kmster is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Expldu gbzrtz:6z4 28;bmxain.

Different lamps might have batteries connected in either of the two arranghxrd9 fyo 8m zu6uw4xa)6x:,qements show4a8:uox qh6y,d9m fx uw6)xrzn in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in ajm -an-l:y lq( wire. How many electrons are flowing past any point in the wire per second? -mn :jl(aylq -   $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A for 5.0 haebeoi/2 -n *:bhns9b. How much charge passes through the battb b/h:-2n* es9eiaobnery?    $ \times10^{ 5}\;C$

  What is the current in,n ouyx (.4yvy)b rqmi2hq6-d amperes 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 cur q4dm(m*2 iperrent of 4.2 A?    $\Omega$

  What voltage will produce 0./ zq uw+s-b klq:v*vafkvic4: t:v*9r25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 vya f wv;rwg831y1 ay)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 heatin 3opphdipj/ex;( u d9uhfu**oq3;x*j g 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 resistance itv 9 ,kfv 0qje(w+xym83t9 bnjs $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric tranqgdp80ir2s n / oa1acr zoc*+;r6v5 k8emex5tsmission line carrying 2800 A (Fig. 18–34). The line has +2*cripmor akcv551so;6ee z d8nraq /xgt 08$2.5\times10^{ -5}\;\Omega$ 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,l.,ne wka vrajdd2e,3jl b + y/i7y6h 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 current o; z8 s.mm.y +*v8c3 dlzqaf 6adeexs:rf 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 tqeb 8mzm)m7jfy* i3d4ungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wi( ynf8ksk* d oqe8xkkd) 0cl1;re 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of04v;g yhgv/ym( nk5og aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in yky /4o0nv(; 5hgmvggdiameter.   

  Can a 2.5-mm-diameter copvxq)tmoo:kj*-dp7qwnrs :- * per wire have the same resistance as a tungsten wire of the same length? Givek-7dm:j: vopx)owns* rq-q t* numerical details.    mm

  A certain copper wire has a resirfcb rb*iwi2l8yyi5 w yd) )5*stance 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 raislowsjab 23 8r y+f, 1n2)dojcae the temperature of a copper wire (originally at jn f8lroa) +22co1jwsd3,ya b$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper wi f0-) ua+ccoxwll have the same resistivity as tungsten doecc )w0-xa fuo+s at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb ha x;5v4gch ye2isg 5x2 yyxw,v8s a resistance 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 householz +8 ;abtt+jjvv3z7und no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.62uzatz78nj +vv3t;b+ j8 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has side5sn 3+esxz:glx /h/87atke tas 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 current that passes through the so/x7+5hxeskzna:t/s8 a e3tl glid 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 twice92/vsd mza3.5lz4nz l y y, 1st6ewvsb the length of the other, what is th.sbs,lnvwz4zz5t e v9 /6m lsy31ay d2e ratio of the diameter of the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire oa 9 4/yhwklr:is connected to a precision 10.00-V power supply, and a current of 0.4212 A is precisely measureaol9r:h w4k y/d 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 obhik+/d hi3 4czxq .xv9 jni3ih+ .+lif copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage i.3 i + xji+.z34b9hi/x qi+hnvldckhdifference 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 thveqosdid+1;6,/m k5dsk5 avv at the value of a resistance not change with temperature. Fora +qdov dk1msvdi5ek v,5s6;/ 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 elexi p- c,tzdpd00p-v73z ni0grctric oven is designed to produce 3.3 kW of heat when connected to a 240--i ip-g70pcz3dn0t,r0dvpxz V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of x vpactwg60u /5vn5-qa 3.0-V portable CD player that draws a maximum of 320 m c/5wvu0ap6gn qvxt-5A of current?    W

  What is the maximum voltag2 wfwhz(jm t6 k vdf.f75z94zpe 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 throu65bu7;+km q o.ng g50j grimtpgh, a 75-W lightbulb connected to its proper source voltage of t5rp k5gq+m7j. u;o0ggmb ni 6120 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. Cal1b:1bol9xk6 mstfx5uculate
(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 Wa9o-*. sbk bdg 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 iudj/v sij41z- n Europe, where electricity is delivered 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 relative to 75-W 120-V bulvj sud-4jz 1/ibs? [Hint: assume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy za cs)rcy t62-does a 550-W toaster use in the morning if it is in operation for a total of 15 min? At a cost y2)rcc tsaz- 6of $9.0\,cents/kWh$, 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 it7c5 q6 :r0vut w 9w;u:mnydxgj cost to leave a 25-W porch light on day and night for a year?u57gjqvxwrm9; :nu6 ct: 0y dw $\approx$    dollars

  An ordinary flashlight f;c 7qli(4zbqc *vql3yb mdsxzx/56 ;uses two D-cell 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when turned onx;q /*3y(x bqq64lmfzdv;l ic sc57 bz.
(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 8 hnvmjui6j..9m6c zp 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 Fig. 18–20, can be used wdpsc8 n-;.ca vithout blowing as-cacp . v8d;n 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 1l 58v5q3g yt*np+xwm g6 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 powl 3wgy+xg*8p vmt5 n5qer is dissipated in the cord?    W

  A power station delivers 620 kW of power at 12,000 V to a fg fblmtf .uqt:(kr3, 1 yr4rt6a//lti actory through wires with total resista(r1ut :fg3 4.lyit bk/rf r/atlmq, t6nce $3.0\Omega$ 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 what rn;5dm ik0-lmg g 8m a7zc9i: nkpfek0)ate must cooling water pass over the coils if the water temperature is to rise by nf90 g-i0)n78e dikag5 nk;mpzmm k: clo more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to heat aw7c xj ri9(,bb14 epzv oky+j1 cup of water for coffee or tea. If the heater can heat 120 pirwevk7xbbj(c1 j+o 9y, 1z4mL 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 currentz(3uw wor-3lcl:p pz ; 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 acrossmns3 s-9/ru ds) wgqhv7sy0w3l ew8-r a $330-\Omega$ resistor. What are the rms and peak currents in the resistor?
$I_{peak}$$\approx$    A(retain two decimal places)
$I_{rms}$ =    A

  Estimate the resistance of ty b 8xqwra75p,csq:)m he $120-V_{rms}$ 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 currenze2 uqxo. 8m;rtn n.r3 ,e1ugct in a 1500-W device is 5.4 A. What is the rms voltcnqnuz r o3m.t,r82u1xg ; .eeage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is s*mv06pseae )x*2qk sconnected 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 instanta5fz+1 (sojvv+yy(a o+3 drowaneous power dissipated by a 3.0-hp pump connected to vwfo v+3yd(o zays rj5oa+ (+1a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to *d07 jy /e fvl9b5e.08p4dlzxauojjo 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 c5u ud 9n qb6x*w6ke-vyarries 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 whenyrnx4l n0z6+h 22.0 mV is applied to itx6z4 yln+n0h rs 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 cq 7u24ts.1z x,aurr8ajjq (d 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 Ear 1(a+jshws5scc +q0ui th’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 1aakd dhb8ez*ldd x+ .s7sn;.of the electric field across an axon membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with an electric pulse. The action potentia.(xto(cfu) -lfb7ip7j0 ld f(eb b u:nl 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 of the electric pulse aluf teb b0(if(f .oj xln)(-pu77l :cbdong the axon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much enercq5dc+ i9tf (rgy is required to transmit one action potential along the axon of Exampl idc5(cqr t+f9e 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 potf3sr*( wuu).ba ic 4gzential, $Na^+$ 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 am z5pj;: b,qlwzt c)cf)pere-hour?    C

  What is the average current drawn by a fzt*.,pfjc.8 z.h mch1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each ob.o8q(wr pf+b1t2;+c juhvxc s21i vc/os3ci f the two headlights uses 40 W and each of t c8ij.2 1c+p2rc vh+v x ot;ucbwfso31sb(iq/he two taillights 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, 1500-W heater is 5.4 m long. If cg qo/v5x* a *uezm- fm*0f0xq yg16pxit is made of iron, what must its diameter 1xzm 6g -gq5c/yqf*af0*vo *m xx0uepbe?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the rfwis7x,-:bg j u6-w gaeciprocal of the resistance R; that iswg7fg,6 -x-b :waujis, $G\,=\,1/R$. 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 powo :*i3 1 jgjawb uq87h9jplbee:c f4-uer. Suppose that instead of using high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a two-wire line o-fb7h3blu:*i u 4:ewqe cpo 1j9g8ajjf 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 useu xeque 8n(b2.pb6t-ong v:-es 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 lengti2re .yn .n+1eqgbpk6hs are wrapped together side by side to make a thicker wire. How does the resistance of this new combination compare to the n1n py6b qeegr+i2k.. resistance of the original wire?

  A 1200-W hair dryer is designedb* u b7vsk/2ma 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 ha c3-8xdubmy,cs )3qxp2)fz so it does not become so hot as to start a fire. What diameter h)- u 2cxzsbcfmy)3q p8, xd3amust 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 givei :mvdb n75.pdn 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 6;um2 kx:mo6p4we mt-3 fs ,wdm5% efficiency delivers 950 W of energy per second to the interior. Ftds6 xf2op;:wm -k 4mm,mu3 ewind
(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 sau**iu9i+f:n agx:5a6try*kke:zr;ha:pt c dme material. One conductor istiay; 6 u5ze:k: hgad r:+9c**:xukanrfp it * twice as long and twice 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 tolg-zm,h a/ge,7a ex4, yg ncc; 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 hoo.nfg57kcm gubhh -.k,ked to a 240-V source.
(a) What is the resistance of the oven?    $\Omega$
(b) How long will it take to bring 120 mL of 15$^{\circ}\,C$ water to 100$^{\circ}\,C$ assuming 75% efficiency?    s
(c) How much will this cost at $11 cents/kWh?$    cents

  A projected electric vehicle makes use of storage batteries as its soue/i8 +p k,lindz ip4pujx1ml8.t4 s4j rce of energy. Its mass is 1560 kg and it is powered by 24 batteries, e/1+st4p4jx8p, mi il.ez 4duipkln 8jach 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 res:u( e -jzcw5opf7bvq9istance 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 (Illinoii*dosl-jsfj) 78w a8 gs) is designed to carry an 11-mA beam of proton alf ojg-8sds)w87i *js traveling 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 ac6drziw9hr) v 6. The connecting cord is copper wire with a d wrdizvr66 9)hiameter 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 120c.c8/d/ .lxhf28a)nncavj qt V. The heating element is a coil of Nichrome wire. When uncoiled, the w8fajx c.ac2vqn n/hc) /tdl8.ire has a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltagab qtg3q1 -w;q)gn 2raz,ii-je varies from about 12 V when the car is off to about 13.8 V when the car is on and the cagq-q1 iqgn3w2z ibj ; r)ta,-harging 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 appli cxd/q( kwti1 wwx06f)cations. Lightbulb B is rated at 12 V and 40 W for automotxfk60tc /w wdq(wx )i1ive 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 us;q::e) s lgcpwed to connect a set of appliances at 120 V, which draw 2250 W of swqe:): l pcg;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 outside diameter ofhb2:yjpe x* u2e7zjx, 5.00 cm (Fig. 18–37)ju hxp,2e:y jz 7b*2ex. What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so thkmc94 oopln.p1s v9- ye/;s eeat its length doubles, by what factor does the power dissipated in the wire change, assuming it remains hooked up ty/po4ml1ec ; 9nekvp- se.so9 o the same voltage source?

  A tungsten filament used in a flashlight bulb operates at 0.2b. ,g3q5lmih* wmn;+t, kqmy d0 A and 3.2 V. If its 3*qm qm.ikb5nmlgyt,d, ;w+h resistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$