What quantity is measured by a battery rating given in ampere-hoursz62iy ayk-ib9 $(A\cdot H)$ ?

When an electric cell is connecteddczbvte)+cp x shm;3(3s 3)mq to a circuit, electrons flow away from the negative terminal in the ci+sthc3m qm 3c ebpv)3;xdz)(srcuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, fc lr hmeu8.yj5-be:0 what is being used up: battery current, battery vol05ejm8 :-c hferyubl. tage, battery energy, battery power, or battery resistance? Explain.

One terminal of a car battery is said to be connected to “ground.” Sih - 8 n6acftgqp.i.ef8nce it is not recp.8- at.8nqieg6f f hally connected to the ground, what is meant by this expression?

When you turn on a wate0 do(i7.ut qq6 ny:aldsr9 y, r3)khhjr faucet, the water usually flows immediately. You don’t have urn3 tk9)j y.(irl0q 6:s,dhaq7yhod 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 aluminr:z8nw me-av/u(l8 lo um wire of the same length have the same resistance? Ex/n8v:e( awmzr8o -ullplain.

If the resistance of a small immersion heater (to heat water for tea or+,iify64k qrr soup, Fig. 18–32) was increased, wouldf, k6iyir4 r+q it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, and 3a, ha5t7n6meff pe1+y g y,ow would you connect the wires from a battery so as to obtain (a) the least resistance, (b) the greatest resity ,pnf gmeay+5e671 fstance?

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 b(hv, ;wez oe: h6 bc 7)66ctbq(ymi5b3k rhmraurns out?

Explain why lightbulbs almost always burn out just as they are turned o cspfg;g.4( rnj3jgz :n and not after they have been on for some timg:g gfp jsj.;z3n(r4 ce.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which hau3x4 i4w s(tldhuf*uvhu: 06a s the higher resistadav(4fux 3uth 640 huwsl*:iu nce?

Electric power is transferred ov(qa f/ zokh6a8er large distances at very high voltages. Explain how the high volta8ok z haf/(q6age reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace tsfrqxi4s() (dnu-yv1 :ohn-this fuse with a 25shr qd :ts4( v1-yf-oun(x)i n-A fuse?

When electric lights are operated on low-frequency ac (say, 5 Hz), th1--eaqtsrj6 f ey flicker notf1sa -j-rqet 6iceably. Why?

Driven by ac power, the same electrons pass +ns (kw .)n/rj5jkfhiq xolks3 h+ l23back and forth through your reading lamp over and over again. Explain wh nso /jxjf3.)hk3 n(kw++lh2l kqrsi5y the light stays lit instead of going out after the first pass of electrons.

The heating element in a toaster is made of Nichrome wi/0gjcud8zb4djup03oyt k5w, x 3n 5tire. Immediately after the oc 5,d0 tw3xzn5tygud8 j04j 3u /pikbtoaster is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resivg0yuv f6 ( em;(tk0xzstor? Explain.

Different lamps might have batteries connected7*appj6sb* t q in either of the two arrangements7pt6* p*bsj aq shown 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,)bhmerg3 (nlfq/z a+ 8,me xe flowing past any point in the wire per seco f3h l,aeer/,xgm (eb+q)mn z8nd?    $ \times10^{18 }\;electrons/s$

  A service station charges a battengkn qd7/ xk(u7+drv,ry using a current of 6.7 A for 5.0 h. How much charg7k7ddrvxg q /+k,n(u ne passes through the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes i7 -vr 6+m;dm oriicgc:f $1200\,Na^+$ 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? vtxkg f45-tww4kn 45emjk,p 5    $\Omega$

  What voltage will produce 0.25 A of current 55lxois h0,hhd8nunu6gxx( 2 through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when pluggeo5 rcu0m-r 2jj yru)z+44db r(d o9viad 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 65welg qdj0 2tdryer 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 connects. ,(qhhi-by j2 0vsided 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 carrying 2800 A (Fig. 18–34).wupy4*d:,;d l gwhid;c/f 0yn The line:*dgdfd wwi;p/y;c y, 0u4nhl 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.ev7ae (he/*pgbn l5g350 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 curreqf d6g :**v5vg w;,on2w zjevdnt 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 who., wvjq. vd0hrd agpt63ta,be 2m(p7 sse resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m lexq9 +uwr +:conngth of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0x,arez /vj1+r +c0fyq;o 4et a m of aluminum wire 2.0 mm in diameteqc1j xy 0e;,fta4or /vzr+ ea+r, to 20.0 m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have od*c. vh nu57.vmzll(7jx0ic the same resistance as a tungsten wire of the same length? G 7n..l*mxzlh(d 5c 0vj v7cuoiive numerical details.    mm

  A certain copper wire has a resista vlk6 p37n6mvince 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 (origina-yly9y xkj dq( z4wxoc3jh;)(lly atx4 jd(o 9kcyjxy;3(lz)wqy h - $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivity as tung5ejp i3,k rsjuc3 t:y8n x(nj0sten does a 3p,kr3sxyjin085et u:njj( ct $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of abunw4 mafhsi./ f. 0p2gout $12\Omega$ 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 alo zd- l4 7t yepgp9 ..e*zoykgrayj2,p1ng a 26-m length of household no. 14 copper wire (used in 15-A circuits). The wez7tdr2 lo,p4 g* z apj ygk9e.y-p.y1ire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides p:utfxf35j2v o6i /cbof 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 throu2boivujx f6p 5t3c:f/ gh 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 h2vgf nclcf r6 t0u350has twice the length of the other, what is the ratio of the diameter of the longer wire to the diameter of the shorf032u0ft cv 65 hlgcnrter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is conn0ao34/dfe3vpf zml h-ected to a precision 10.00-V power supply, and a current of 0.4212 ozmeff3l/h p -a0 3vd4A 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 vfn-h5b83 h4 d dsd6lg5.0 m of copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A vogn6l4 dd-h8sd35v hbf ltage 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 of a resistance wx 4+ 3bey-lqiudkw0oka4j/1b db0.j not change with tempd w4dbb0 lo3 q0-xjakyk e/.4bjuiw +1erature. 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 designed5 6ahp: rlr 6rzptz0n8 to produce 3.3 kW of heat when connected to a 240-V source. What mustpzr8rz656 nta:phl r 0 be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player tcsxb) 5ozzlsy 3f(. f6hat draws a maximums f)(l o6fy zxz35csb. of 320 mA of current?    W

  What is the maximum voltage that can be applied across a c9k9zs *zt8zt $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistancywy1ud4lt7dhb 7o46 je of, and current through, a 75-W lightbulb connected to its proper source voltage of 12d17w hulyty4db6 jo470 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank hem+ lc 3 -ioxnh1.rbif,ater is rated 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 twj l qkq:lef2cm/l ((1ro settings: 850 W and 1250 W.
(a) At which setting do you expect the resistance to be higher? After making a guess, determine the resistance at
(b) the lower setting;    $\Omega$
(c) the higher setting.    $\Omega$

  You buy a 75-W lightbulb in Europe, where electricity is deliver8.z n.md,x sqrihw2q4u;e g0+ct,tro ed 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 7.4q.u8 2;sm0cnzo ihxgr ted qw, r+,t5-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 if6uo8+oe7 xh: pl5c xob4*xq kh it is in operation for a total of 15 min? At a co co 6uekpq78 x:hxo+o5l*xb4 hst 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 rmx; fc/2vnisfh+v-. porch light on day and nightnh+cv ;x2- vfr fs./im for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected in series as icp( 2i v1gxs 6e6tff:vw gkr)6n Fig. 18–4b (Fig.t c k6v 2 gwefgfxvi)p1s6:r(6 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 amount of energy stor e;eh3w,f bxheo0ib6*ed 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 re) t;) e*.sgahelojbr,c8u 0 V as in Fig. 18–20, can be used without blow*l. uerja ec8 0, )eo;bsrgh)ting a 15-A fuse?    bulbs

  An extension cord made of two wires of digklll, e tg1( 0zo -rsot0 btnu6n91g9ameter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9sob,1k0e69gu1nlorl9l t( g t0-ngzt ft) is connected to an electric 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 factory through wires;n 8sl4n skhreia6/,l with totr slkn en6,sl/8;ia4hal resistance $3.0\Omega$ 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 w y50yl+5joi h5goit q +mor((a(bel,z hat rate must cooling water pass over the coils if the water temperature is to rise by no more than 7.50 z5+,oog5(5amyry ie oq0+(ljth i b(l$C^{\circ}\,$?    kg/s

  A small immersion heater can be used in) *wcy m,,.xg.bpufmc a car to heat a cup of water for coffee or tea. If the heater can heat 120 mLby,pm u .mfcx),*gwc . 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 i+h fau/ep l/n/)tzycp4e08d qn a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, 9p/x p wrtg+lygx.wzvau+ -42is across a $330-\Omega$ resistor. What are the rms and peak currents in the resistor?
$I_{peak}$$\approx$    A(retain two decimal places)
$I_{rms}$ =    A

  Estimate the resistance of the u k0uv:4fqnu+k6 wz:; sfvcu6 ,0bpzz$120-V_{rms}$ 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.7uhm8y fqo *b8 What is the*mh7yf8o8buq rms voltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected t3lgl x a(- (gch.hea7to 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 dissipathz3yg+h 1of+fi8 a dv8ed by a 3.0-hp pump connecte ifyd88g 3+avz +f1hhod to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected o7;w:a m:xpkj 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 c.st-lr1dlydd8q 4i ( tbyp m83ufsm .-opper 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 when 22.0 mV 8px q2ngc /vvkypd-/ q91n7ikis applied tovqn 2kxvnd/7yi-9qk1p8p /cg 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 ay mcv:ad 85)itr5-)jg2pdr52ht ur yEarth’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’s atyg-s/dc uz377njhco *mosphere, $He^{2+}$ 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 /1 hdi;/lfbjmb p n6i;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,v 5uqcei9fh9 34vb zkx)m)ub detected at a point 3.40 cm down the axon 0.0h,k qxiu9cbvf34me9 )u)b5vz052 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 along the axon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much energy is required to transmit one actionb )xhrv mpp6t. k3/qupl)ok23 potential along the axon of Example m)pt kb)k2v3x36 /o pphqu.lr18–15. [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 potential,*o ;2yu5p g pccimol52 $Na^+$ 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 inv rpnh9u27zb g/5 i6fs 1.00 ampere-hour?    C

  What is the average current drawn by a d,(jkhtwq s4-gty kz1b pfu51vl qg,i+ *81 kx1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentallyui/l hy*)wapws- aq-5)q 2xfh leaves a car with the lights on. If each of the two headlights uses 40 W and each of the two taillights 6 W, for a q lhqx)5fw haay /isu*p)- -w2total 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-Wx51.0e y jex yy*a;asl heater is 5.4 m long. If it is made of ir 1jya*y seex;ly 5.x0aon, what must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the r6d0vyos+jh1d0 yp 0u 2k7kxz feciprocal of the resistance R; that iz 20dyskokxhpd6+ j0 70y1 uvfs, $G\,=\,1/R$. 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.k)x5xhvnt 5 fd -hc5-d Suppose that instead 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, estimated-n55-dv fhx xtk5 )hc 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 useg igu :do 8g49ocz t; b)p7gzc(fr)bu(s 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 /6qbje6qmb k77( 9wxtpspm-ohalf and the two lengths are wrapped together side by side to make a thicker wire. How does the resistance of this new combinatwo/ j9x7( mm6qqktp 6be7pb-sion compare to the resistance of the original wire?

  A 1200-W hair dryer is de3priuj j.1v a2.nwlg4signed 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 so it does not mxbl,am- c 02mbvg8d 0become so hot as to start a fire. What diameter must a copxlb,mbgc- m 280ad0vmper 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 g+ksj4z :e4ss c),wg(q dlt/ oaiven 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% efficienkf)i fo)fp7jx;.kc; +k 9rgf lcy delivers 950 W of energy per second to the int) 9)7f i;f kxgkcof.lf;pj+ rkerior. Find
(a) the power drawn from the source,    W
(b) the current drawn. Assume a source voltage of 120 V.    A

  A $1.00-\Omega$ wire is stretched uniformly to 3.00 times its original length. What is its resistance now?    $\Omega$

  220 V is applied to two different conductors mahqw-50e 4sv qf r/,zmxde of the same material. One conductor is twice as long and twice the diameter of the second. What is the ratio of the power trawx-54 qs0vf/ m ,ehzrqnsformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater isj5t fzx50d ifhe*o2t;ttx c(-bqp 44j 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 tocka a,b ,ae24w 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 batterif,jm/t .3rs x yq3pgv2es as its source of energy. Its mass is 1560 kg and it is powereqt s3g .v3xryp2j,mf/ d 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 0w*gsznq -u:e has a 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 accelerat62uj/3di +vxr mwu,xbor at Fermilab (Illinois) is designed to carry an 11-mA beam of protons traveling at i j uxm2brw3d x6/,vu+very nearly the speed of light ($ 3.0\times10^{8 }\;m/s$) around a ring 6300 m in circumference. How many protons are stored in the beam?    $ \times10^{12 }\;protons$

  An air conditioner draws 12 A at 220-V ac. T of43hnc;vne4 he connecting cord is copper wire with a d; v44ohecn fn3iameter 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. The hea ea0u31 4-z8d p l.0clrak:euh6+ydj5pgvsj u ting element is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What iylae hzu d5v34rd 0ls-gua pe 80cu1+.pj:k6js the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system wb-28d g/sss ql/ccn1 voltage varies 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 pow1s8ldbs /w-s qgn2/ ccer 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 1kg.7 t .0ojgpcsyj8o320 V and 40 W for household applications. Lightbulb B is rated at 12 V and8o3j7t0ojc .g kpgs .y 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 r x4;6qwnj buxc8+c)hused to connect a set of appliances at 120 Vbc4xu8;wrqxc + )6j nh, which 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 outside di*ru k4k,u m0 rtep8c/rp1nfurft:09 qameter of 5.00 cm (Fig. 18–37). What is the resistance of 10.0 m ou0crn 1fkure*ttpf8p ,m:9qrr/4ku 0f this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly5yox:8u * yycn so that its length doubles, by what factor does the power dissipated in the wire chaoxy y 5ny*:cu8nge, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operates at 0.20 A andyhu6j1j; kju*bc u:q; xy y-h* 3.2 V. If its resuhu1qu :;j yhy6*-;j*jxcykb istance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$