What quantity is measurepqwov7* 8rh4w d by a battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, eljae .(o 2j;d khy.bhz+ectrons flow away from the negative terminal in the circuit. But within the o. h+ 2khba .d(yjz;jecell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being usf n6gjk5 +9e)ht(dih csb m,n6ed up: battery current, battery voltage, battery energy, bafjnnbt6+9ms6) ed5h(i, khcgttery power, or battery resistance? Explain.

One terminal of a car blrh:4 mc j voa(0icv)w4ge *qdi:9c(qattery is said to be connected to “ground.” Since it is not really connected to the ground, what is meant by thiqahm: 0vco:i9veil4 cdg*rqc(4w() j s expression?

When you turn on a water faucet, t eumq(staw.k+ ad1g7c l36 ;hkhe water usually flows immediately. You don’t have 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 togu 7a 3mqe1;k h(.d+6stkcwa l the terminals of a battery?

Can a copper wire and an aluminum wire of the same lc/tpzioru ,9xa fa/tsy2 0 9j/ength have the same resistance? Expla tia/rfo,/u a99jsztx y /2p0cin.

If the resistance of a small immersioncbldyho 8 )1pos**6 bi heater (to heat water for tea or soup, Fig. 18–32) was increas c1os)pd6 *hyb o8li*bed, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sidecp-q mr7 ,2,8wvnp tgps of lengths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) tcw -mgn28q r7, p,tvpphe 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 lightbulnvx5f: z n3mgbko .2mp9le v10b burns out?

Explain why lightbulbs almost always burlu 9) lis0w4gln out just as they are turned on and not l ws9gl 4u0l)iafter they have been on for some time.

Which draws more current, a f o)xukm,,mzqgch2 e wi,,ry9-d07ta 100-W lightbulb or a 75-W bulb? Which has the higher resimwtfor7 )2g, k,,c0aui-h9mx, yedqz stance?

Electric power is transferred over large distances at ve6p l3g h/eki7bry high voltages. Explain how the high voltage r36 p7 hlbeikg/educes power losses in the transmission lines.

A 15-A fuse blows repekh v*8ip a0 mz 3y6ju7ksm1w8fatedly. Why is it dangerous to replace this fuse with a 25 v3kz1h6mp k7jsw0fy*8 iau8m -A fuse?

When electric lights are operated on low-frequency ac (say, 5 Hz),ss * f*o6zfo5 ozq;8po they flicker noticea6 oz5ofssf *o;8op z*qbly. Why?

Driven by ac power, the same electronsh d:,g(sl8 yvo pass back and forth through your reading lamp over and over again. Explain why the light staysy8l s hg,ovd:( lit instead of going out after the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. I4zzici +2v00wb qhyo-mmediately after the toaster is turned on, is the cur+wv zb40iyhico -z2q0rent $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a mf /rkpo.rk50resistor? Explain.

Different lamps might have batteries co(r* rr1 hxzjxvs(9 3jlnnected in either of the two arrangements sh1rl xsjxr h9z(vj *(3rown 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 arux2*(; zdyfo cspz;c(e flowing past any point in the wire per seconc2z zscydxou*;f((p ;d?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery usd )5fcpp1htq/pr a )ow56 ju8ling a current of 6.7 A for 5.0 h. How much charw86j5fl)doh)p q 1u pt5p/ arcge passes through the battery?    $ \times10^{ 5}\;C$

  What is the current in am( a i9rlnhg52cperes 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 lny.i59em z- xA?    $\Omega$

  What voltage will produce 0.25 A of current throz8,ccai9 n0i muhw:1uugh a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5: iepg*7 vr2wp7lhm)n 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 heatrw; )cwnvnuh 7n* 5bn b98smyb /nlf ,6xf.k5jing 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 reunzrj 0y9 dq./sistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric u/:o( o3e8frq,u8 ytgq)gz.xb.bolo transmission line carrying 2800 A (Fig. 18–34). The line tbbqzgyf8 egloxu .r./o:uo)(o3q,8has $2.5\times10^{ -5}\;\Omega$ resistance per meter, and the bird’s feet are 4.0 cm apart. What is the potential difference between the bird’s feet?    $ \times10^{-3 }\;V$

  An electric device draws 6.50 A at 240 V. .q 5ysz6mfmw. 8cj0 mq
(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 0.60 A through a 7 ki ce;-q7sfcresistor.
(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 tungst hpqprts)p5 +97*eyscen wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3 hbu:3+taixvv l)0bs;tt 8jt:ld9. il.5-m length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of thfz h r..wk0a*x*w1ek me resistance of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0e.h*1 amxw.rk *wzfk 0 m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tungsten wire ok d9:6bjh.dpgyn/o.tf the sam .pnybdtghj:dk6o .9/e length? Give numerical details.    mm

  A certain copper wire has a resistan+s:myr2c ao2 t,o r4jjce 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 (originallye5d2mpsa :0tvrp .1 bp at 0: edvt. b1rp2ps5pa m$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature jusz 3i) 5kn;p0tfly7copper will have the same resistivity as tungsten does p;ln705 zj fty) isu3kat $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of v9cdb07 roid. about $12\Omega$ when cold ($20^{\circ}\,C$) and $140\Omega$ when on (hot). Estimate the temperature of the filament when hot assuming an average temperature coefficient of resistivity $\alpha\,=\,0.0060(C?)^{-1}$ .    $^{\circ}\,C$

  Compute the voltage drop along a 26-m length of household no. 14 copyz1s0hr j 6.vkper wire (used in 15-A circuits). The wire has diameter 1.628 mm and cakzyr 06j 1hs.vrries a 12-A current.    V

  A rectangular solid made of carbon has sides of length3ru3q. 8lp:ot (iwrz*cz g gt lcx+04ps 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 thro :8t (.*cg+wq3l3lg u0crzt 4z prxpiough 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 8qx41n/:dk+wcsb- q 1dk lotsof the other, what 1wkqq sc+/l4onsk1 -8x dbd:t is the 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 is connected to a precision 43rxygi;q,5h0tlfcp 10.00-V power supply, and a current ofpt3,l4yxrqh5gif0 ;c 0.4212 A 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 5tg1us2/lrd0e )xh y 6btd;di,.0 m of copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is placed across the composite w1dhy/udext; ,sl) i2r0btd g 6ire.
(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 iw 93w sy0khj p7c9w x3*wz1epbs important that the value of a resistance not change witp1 zphkw ww0e9s3cy7 b3*jwx9 h temperature. For example, suppose you made a $4.70-k\Omega$ resistor from a carbon resistor and a Nichrome wire-wound resistor connected together so the total resistance is the sum of their separate resistances. What value should each of these resistors have (at 0$^{\circ}\,C$) so that the combination is temperature independent?
$R_{0C}$   $\Omega$
$R_{0N}$   $\Omega$

  The heating element of an electric oven is designed to produce 3.3 kW t: a:wm4 ixv 6v1.p6pxyvs t /,hsgo3yof heat whens3a/v1, xviov:.:pyg6tx htpm 64sw y connected to a 240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player that drammh76/g)0 5agcmx3kqrcy(e uws a maximum of 320 mA of/a)u6(5h0qyxggmkc7c mmre 3 current?    W

  What is the maximum voltage mpoj *z4* m v:ks *pme7)mnfp7that can be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and po n8;qdvzhl, :my-v:izwa 42gz,kj 6current through, a 75-W lightbulb connected to its proper source voltage 6: z-o ;ip,ghj4n v2ykv:z,d8alz mqwof 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 rag (+o0 ,nr1fdhzf6 u.m adnew9qt: gn)ted 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 Wn0 ty830) xbh j9xd 3v4ychemi 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 Europe0fmz7 6hzr5uapro63vt8m6 y *gt*5 bgl h 8ecd, where electricity is delivered to homes at 240 V. If you use the lightbul7g*68 *m5rd8ct h zt5gehaly3rfp6mb6 uz0 v ob in the United States 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 uritw15 jahlyo+j1sdu e *. u)28yexc -se in the morning if it is in operation for a tot 5li1t* +dhwuj ryoeus)8x.-ya2 1cjeal of 15 min? At a cost of $9.0\,cents/kWh$, estimate how much this would add to your monthly electric energy bill if you made toast four mornings per week.
energy $\approx$    kWh
cost $\approx$    cents/mouth

  At 0.095 dollars per kWh, whatk o4tdobbc xzn,8u: .jh:3o1b does it cost to leave a 25-W porch light on day and night for a year?b1ook .nb :zj bx4uhc8o3,t:d $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-:fmvhbx 7hv/2 V batteries connected in series as in Fig. 18:hbvvfx/ h 7m2–4b (Fig. 18–36). The bulb draws 450 mA when turned on.
(a) Calculate the resistance of the bulb and the power dissipated.
$\approx$    $\Omega$(retain one decimal places)
   W
(b) By what factor would the power increase if four D-cells in series were used with the same bulb? (Neglect heating effects of the filament.) Why shouldn’t you try this?   

  What is the total amount of energwz) 3ty 4icai0tt;8jwvc 5 zy3ifo;f/y stored in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulm5,) djtv6v xa/siub/ bs, connected to 120 V as in Fig. 18–20, can be used without blowing a 15-A fuse?,65uimb/ v s /)tjxdav    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 copper wire) ay/wlx ff61qblk+h:. q9 j m,gynd of length 2.7 m (9 ft) is connected to an electric heater which draws 15.0 A on a 120-V line. How muchq6,q kx1 9wbyjg +.fml:hfl /y power is dissipated in the cord?    W

  A power station delivers 6wnkwxfn/dr6x j:u))j0-zo: dk l/pr920 kW of power at 12,000 V to a factory through wires with total resistance pd9w /:)ndkluxo0/6r:k-rj)zwjxnf $3.0\Omega$ 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 rat3atlc, trs-pe 6-t ob6m bi5/qe must cooling water pass over th6tbb-sr6ime,lpq t3- c5 ota/e coils if the water temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car;f 6l8r-a cgj)wh+:m fd1gj yk to heat a cup of water for coffee or tea. If the heater jd-kgmh;+) 1r caf8j w6:gylfcan 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 smc4ia-+ j/ora $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, is ace7qwxf,e (.xiyq7;w 1fv q0pgross 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 of0y9i7xh ,v ycv 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. W4oz;,7 dv sseqhat is the rms voltage ev;q7zsd o4,s across it?    V (Round to the nearest integer)

  An 1800-W arc welder ip*-7xo /u.eq0ilkwcsz +w 1 )ahe hp*ys connected 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 d; r zmx+gj4h7; y0pgbxissipated by a 3.0-hp pump connected to;hg0j4m +r;zbxp g7xy a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to a liuc4fvp9( ;y$240-V_{rms}$ 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 wireq 9ir.(cxni .q 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-m)3fkooks nx2q+kgw /k q;, 5nym-diameter wire carries a 750-mA current when 22.0 mV is applied to its ends. If the drift speed +kkos qxn), 53/y;w2ogfkk qnis $ 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, gh 6 k7gt8p/+d/s 0rg rmw/eqvn;ns y/$He^{2+}$ 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 Eart14h;t j5dpuubx86g ojh’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 the electri 3n)sjn+ngv1a 7n*a9n 3z rjazc 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 potent3 brb)9 a*lxowial 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 along the axon? (Why are two measurements needed b 3l)*x9ao rbwinstead of only one?)    m/s

  Estimate how much energy is required to transmit one action potea 1yrz 7tlm2p4 j:q: oxw9epw/ntial along the axon of Example 18–15. [Hint: the energy to trrp9 aq mjpy/o2:z4x1:wt w 7leansmit 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 pot1g26.ot jufqeential, $Na^+$ 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 aremvg9uiw7/57o6*weh n vos e. c there in 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0-hp xdwrrco9k4e: by))d7 c k,c6-9tjpzxa2;flz120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the ligha3yo)-z b-1vc ddr-lits on. If each of the two headlights uses 40 W and each of the two taillights 6 W, for a total of 92 W, h)dz-d yvbi-3l-1a cr oow 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, 150, ay/lxraygby8t g-j 3od5.s; 0-W heater is 5.4 m long. If it is made of iron, what must its diameter be?/5 .3 xg,albyj ytgsro8;y- da    $ \times10^{ -4}\;m$

  The conductance G of azd;n nn nz.h:tri )4d.n object is defined as the reciprocal of the resistance R; that i.n)n.n dzth:iz;4d nrs, $G\,=\,1/R$. The unit of conductance is a mho $(=ohm^{-1})$, which is also called the siemens (S). What is the conductance (in siemens) of an object that draws 730 mA of current at 3.0 V?    S

  A small city requires about 10 MW of power. Suppose that aew xi79kmp0 3rxyzs2l7ins.+p5u i +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 7par x+nuy 7s. m xi+e32i wiz9lsk5p0wire, 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 v uta*d8vox *+t qq(o6uses 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 together side b+ n ys3p08ip,sk oqe*ry s0*sp ,ye3skipn o 8r+qide to make a thicker wire. How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is desigg x)z6tff 1oz+zjq(wqpk i8 ,5ned 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 become so hot as t*l p (lsb f4xzss04yk-o 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 1.8xl0bkf-(z4p l s*sy s4 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by the6++nm n4is,jy+zueob 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 e( s0*cv rkq 5xfa,l9cgnergy per second to5 qfk*x,lcgs0a c9( vr the interior. 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 made of the same material. xsl+z cie)rsq8of.o2h, k5x9One conductor is twice as long and twice the diameter of the second. What is the ratio of9.xq)k5 erhc olxssi+2 z8,fo the power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a rghqv ,f d-l 9yr, v gneokv7sc1:*0 d8w9kbui)oom of volume $62\,m^3$ Air is brought into the room at 5$^{\circ}\,C$ and is completely replaced twice per hour. Heat loss through the walls amounts to approximately $850 kcal/h$. If the air is to be maintained at 20$^{\circ}\,C$, what minimum wattage must the heater have? (The specific heat of air is about $0.17 kcal/kg\cdot C?$)    W

  A 2200-W oven is hooked to a 240-V so xbgpiyf gygntuy:.5)io9; -/urce.
(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 u b8 (zp, p9oykj79cryese of storage batteries as its source of energy. Its mass is 1y8b7r,yzkpo j9e(p c9560 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 fpy*3b6a dr/2uo)ms vhas 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 accelerator at Fermilab (Illinois) is designed to carry an 11-mAg:3+g9jx4om unv3mt e beam o 3+n4e:93xvmgjt mo guf protons 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 ac. The connectsim1.(37t)l2 sbcb; ye fiirding cord is copper wire with a diameter of 1.6s2y; ili msf )3t br7e.d(1icb28 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 ro; o ek cx5vcu74qzm;f)kw*h )ated at 95 W when connected to 120 V. The heating element iu kv 5mf )oczo7eh;c wqk*;4x)s a coil of Nichrome wire. 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 volash :yy1.3 0.vbjynlljtn:y9jfat 1;tage varies from about 12 V when the car is off to about 13.8 V when thevan0 ; :at.9tjfjh.llsynjy3 1y :1 yb 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. L uh/w53de72yrjoj9lwightbulb B is rated at 12 V andj9o2 7wy/rj dwl 5hu3e 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 0.259:6qdlo,o j tg7 cm is used to connect a set of appliances at 120 V, which draw 2250 W of power to, :golt 7jq6dotal.
(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 of 5.7kj5ej nit k:+nei4cxp9cd39 00 cm (Fig. 18–c x+ 5 k9ned7p3it:nj 9ji4kec37). 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 length doubdb *k2+zdod fj5n9fl0 les, by what factor does the power dissipated in the wire change, assuming it remains hooked up to the d5 dfbdz9 +lon2*fk0jsame voltage source?

  A tungsten filament used in at /hd;fwkhh(xbssb ec /z:.t)(2;xhs flashlight bulb operates at 0.20 A and 3.2 V. If its2ste /h/zkbc (h;w(h)tfh;:ssx. b dx resistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$