What quantity is measured by a battery rating;cqoy8 :idvjnjy-/c; given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connecte1-xdx 3. lvzfs. dlux6id85j jd to a circuit, electrons flow away from the negative terminal in the circuit. But within the .lddv-zxf dju1 38 xlxi6s.j5 cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is beina jlhk,*p, h9lg used up: battery current, battery voltage, bat*ak , l,9plhhjtery energy, battery power, or battery resistance? Explain.

One terminal of a car battery is said to be connw .r z3b5dpu;xe(5nkt ected to “ground.” Since it is not really connected to the ground, what is meant by this exp.(rnxzp teu5w kd;3b5 ression?

When you turn on a water faucet, the w4uuipb6sl8z)/ - ncz rater 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 to the terminals of a batte i/ps) lu6 84-zcbnrzury?

Can a copper wire and an aluminum wire of the same length have the sv2 w 3+xo+kobxame resistance? Expla o3+v2kbw +oxxin.

If the resistance of a small immer3-7el0ezjecw sion heater (to heat water for tea or soup, Fig. 18–32) was increased, would it speede -zew ce70lj3 up or slow down the heating process? Explain.

If a rectangular solid madea5w7fc(vvp )r of carbon has sides of lengths a, 2a, and 3a, how would you connect the wires from a battery so as to obtvcw7ap5(rfv )ain (a) the least resistance, (b) the greatest resistance?

The equation $P\,=\,V^2/R$ indicates that the power dissipated in a resistor decreases if the resistance is increased, whereas the equation $P\,=\,I^2/R$ implies the opposite. Is there a contradiction here? Explain.

What happens when a lightbulb bur kec/:3os)jwnp ee0:bns out?

Explain why lightbulbs almost always burmy xtmyn 7j/2.v ic.axks (bj()v)sy*n out just as they are turned on and not m(/)jkmst )2.ay7ibx.xscn( *v jvyy after they have been on for some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb+;1ws ijyd j6owxa0 y(as4h+ k? Which has the higher resistaw o6ai(x0 d1jw ass++jy4hk;ynce?

Electric power is transferred over large distances af5) +,u6th0wz o.x/jtsqbq u ft very high voltages. Explain how the h.f+u t60jq,5uo)h ts z xwbqf/igh voltage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it da0heorm cj*r8*:co7iurcl 2:f ngerous to replace this fuse with a 25-A fus 7ci *r2fcur:0: oem*cjh8ro le?

When electric lights are operated on low-frequency ac (say, 5 Hz), + .en)qmvv3blo5x jcmv. +6 c 2r:sqbpthey flicker noticea cxqp.ovm:.5bl6m + s3v+n2 rqe b)jvcbly. Why?

Driven by ac power, the same electrons pass back and forth thromu0yb)w;m/ s fugh your reading lamp over and over again. Explain why the light stays lit instead of going out after the first pass of emsfym;0bu) w/lectrons.

The heating element in a toaster is made of Nichrome wire-+qpj 16p9j sii1fc nat2;zjk. Immediately after the toaster ikpq92ij +i11 ajpft n-sj6z;cs turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a oi7y ;vc2ocpkma ,jw6eu 49x+resistor? Explain.

Different lamps might hagd q +.i66mewz va3pv1ve batteries connected in either of the two arrangements shown inq 6 +31vd.igpawvze6m
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. Howm noq/t;l(r (o many electrons are flowing past any point in the wire p(l n;toq(r m/oer second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A for 5.0 h.e 9oct1 *n4nu- s9bfnr How much charge passes throte149n*b cn ourfns9 -ugh the battery?    $ \times10^{ 5}\;C$

  What is the current in ampj a9n 55dw 8(gxj ca/rwmnr o64,mubh5eres 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. w c.kp6 bd4xbcc8:7yt;edv6 r2 A?    $\Omega$

  What voltage will produce 0.25 A of current thr1)9tdd8hga6p erhojws: (d+h ough a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged ila .phyhpp-we, h6a :,m d*pg1nto 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 heating element with0m exro v6 z,fc0jwy9) 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 resistan tagaz31z/uo 3i)g.1fjy ohd+ce is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric jysktrzt) 0;pojn8p lqt +;/0 transmission line carrying 2800 A (Fig. 18–34). The zo r)0sp jp y;l0tnk+/ jq;8ttline 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 f/5n-qlw*k5:*xd o: c7qcag-o7wbkcf) tych.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 of 0.60 A through a resistorz2f5uxeg gr.f m g7y89.
(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 3p4oltpv65cru5)oj h e z,9g dlength of tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a o7xa yn-) 9dsx3.5-m length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 1r6d.uxe2w3kry 0;ysf 0.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 s 3 ky2rwey; f0ud.6xrmm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same r(r6w fqbm d92jssi*k3k2j uku y+eu23esistance as a tungsten wire of the same length? Give nj e3ujyu i*umbf(23skw sr+6dkk2 2 q9umerical details.    mm

  A certain copper wire has a resi w4waiv6l8 e,vstance 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 wirewlaxh74:l+h:cizw,pxsn ,1q k, c-pr (originally at c:z+qsw 4px7 k 1, nlicwxh,p:arh ,-l$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what tempenis:)w ct8kou nd9)9fv 6i3wrrature copper will have the same resistivity as tungsten do6fs9)8dwownt v:u9)3i rinck es at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistancf1gvok g xkd-t5s ppv7/:g-q )4)pxr (xmosg;e 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 household no. 14 copftca0(38 offaec ;r lw(5kcg:d5 3vctper wire (used in 15-A circuits). The wire has diameter 1.628 mm and carries a 12-A 58 t3vloc at3f(ewc cdr( gffc5;ak 0:current.    V

  A rectangular solid made of carbon has sides of5.xaurb t5, 7-o ybol8wbru6l lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine th ub wb6la5 7lo5x yo8rubrt-,.e 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 l b-g 6e u (xbc;iw+v9yz,kmf)7pw 6oqthe same resistance. If one has twice the length of the other, what is the ratio of the diameter of the longer wire to the diameter of the shorter wcb66iy9,)qpzl7o(+g fme vbu w; kxw-ire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V power supply, a: /z9qc-4b,a v: ckryi;kqci ond a current of 0.4212 A is precisely measured at 20ki4icv c:/b,9a yzc:q;-o rqk.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 ofx. whn/s4o 3al 5.0 m of copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference oow a4.shx3 n/lf 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 img9w+xs7khg : tb6bas/ /4ve:du,axvalue of a resistance not change with ,xb/u4am:b+7w6ixa:st d k9shgve/ g 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 of 5e iqfgea3q sjoz 8a3,9;ipo9heat when conzjso5 3q89gi9qa;3e,f pe oianected to a 240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consum +gl8 lyxdx8v,ption of a 3.0-V portable CD player that draws a maxilv8x 8x +d,gylmum of 320 mA of current?    W

  What is the maximum voltage that can be applied acrfm32 jklc04:1tyq4zu 7njbvpo )b m g(*qvxz:oss 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 conn c(s: lb. ,maxdx;h(p.ahjdh7ected to its proper source volm .aphcjdx alhx:(.ds7( h;b,tage 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 rated aspas583a g/wz*d,x pjt 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: 8:geym:d;l oa4*-s bds0wx(wc 50 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 iqq jq(h hpgk8j-b puhq7:10(ws 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 bulbs? [Hint: assume roughly that brightness is proportional to 7 -1(upkqjwqh0bghh8 jpq: q(power consumed.]    as bright

  How many kWh of energy doi83 f/s:lol7 :)wf*xeyc xj-afp c+lges a 550-W toaster use in the morning if it is in operation for a total of 15 min? At a coly e-fl:si +3c/g*o cf 7wlj )p:8fxxast 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 25nxz8 wo9++/x 0 k;sm yvwmc+ee-W porch light on day and night formk/e 8 09+xwno szy+wmxev+;c a year? $\approx$    dollars

  An ordinary flashlight uses twfwkvald n466 1o D-cell 1.5-V batteries connected in series as in Fig. 11nda6 wlv6k4 f8–4b (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 energy storedag(3 8t4xqob1.jj +dax4ss sk in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connekbx0y z3q 3t tum8v2x:cted to 120 V as in Fig. 18–20, can be used without tby30 qx 2txm8v:ku3zblowing a 15-A fuse?    bulbs

  An extension cord made of two wirez *thv (3gb7g l 7jha:dmjt74ds of diameter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric heater which draws 15.0 A ojh7j* 73gbmtg da:l zhdv(74t n 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 fac p2yce71uir(wi7ojxqad7 t.3 tory through wires xi p qri tdju37y12w7oc(ea.7with total 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 i3(;3.xx ev0qmi rb7*rzs ailps 17.5 A. At what rate must cool0.;plrzi mar7xe(si3*xbqv 3ing water pass over the coils if the water temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be u )e9l8garl4xt sed in a car to heat a cup of water for coffee or tea. If the heater can heatltg xl9)e4 8ra 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 currenf/ n;ke/ ;p9(btsjkrwt in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is5 nx.o2qqr*b :lcsuen h;i86v 180 V, is across a $330-\Omega$ resistor. What are the rms and peak currents in the resistor?
$I_{peak}$$\approx$    A(retain two decimal places)
$I_{rms}$ =    A

  Estimate the resistance okv9+lh;9 hmr9lbva8e ; zipg.f 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 15i*5w ni4vhanses 2we*3du 3 wa67:vvi00-W device is 5.4 A. What is the rms voltage across it? a6n3i5:hvin3e iw2s *4* duvs7ewwva   V (Round to the nearest integer)

  An 1800-W arc welder is con1;n. u x8 i v-nz7meshvx*8 .zocyybp4nected 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 instantanq:)r6y c ;n :pvs9bl/u tk2fxneous power dissipated by a 3.0-hp pump connected sk/9u2lx)fn yqv;: t6r: bc npto a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected 7aj, m3j6f,5qr oxgyoto 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 82b s;qdlv m5wcarries 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 q;p gu /ao93kacarries a 750-mA current when 22.0 mV is applied to its ends. If the drift g3 aoak9/uqp; 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 atmospheegf u+ro)iur zm,6 4d1k a36apre, $He^{2+}$ 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 t0n wj88 i jcx0a-h+sll(mrgy2he Earth’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 elecfz8 l,)qo ot3ctric 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. Thr;q3vb ptkh4)ons0b, e action potential is detected at a point 3.40 cm down the axon 0.0052 s later. When the action potential is detected 7.20 cm from 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 meas4 p),kb3vsq n0robh;t urements needed instead of only one?)    m/s

  Estimate how much energy is requir07pq1vx i9ca u o-08fqhuo 0vfed to transmit one action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is e01 00uvhxvfqoqc o p7f8 i9-auquivalent 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 potentim1 2ud**mg/ewqx -*- xp5ruji tpdi(e al, $Na^+$ 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 ampere-houd s.lyc: zh4(vw,-vekr?    C

  What is the average current drawn by a 1.0-hp 120-V mz.2 -h.kcijupn8h zw/otor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a 839ilv)tqgm45 antxz5j9eo k5hk hu/ car with the lights on. If each of the two headlights uses 40 W and each of the two taillights 6 W, for a total of 92 W, he9mno3ti qv/5zjg )lu hx8k hkt954a5ow 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 it is made:co-x 6cbrp + :g-uyak of iron, what must its diameteoccxbp --:: +ay6gku rr be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of thjvp1 kf) q+rs6 q)t7e du+qx2me resistance R; k p)6s)qqr7e1q++md2j txfuv that 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 ofn5 r*wp hnp(2z power. Suppose that instead of using high-voltage lines to supply the power, the power is delivered at 120 V. Assuh *nw(52rz pnpming 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 x9e;5vhtfu (l 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 togethe)x. ,bl dld:pwr side by side to make a thicker wire. How does the resistancbxldd.:, )p wle of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed forg77jj mkk/m )w5n9k/kj zx/w x 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 enoughwz6lscv8: /ae wwnj l)w,vw *+ so it does not become so hot as to start a fire. What lvwn: *w)wwles,c /a8+w z6jvdiameter 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 meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given 0g eh mkxfgj;yg 2 t4:4n:jn:cby 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 iit vgkmys(b(378e is(jc:m5 65% efficiency delivers 950 W of energy per second to the intertk3m(g v( (: im5icbes87syj iior. 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 diffeh.mv,*no *qcq rent conductors made of the same material. One conductor is twice as long andmn*.chq,oqv* 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 oyj zaf ud1.z 9)*359exlb eadused 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 to a 240-V sourceo ,+ abfb+,ujpo9a 9crw07msj.
(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 bt09crufc8f e1+ 5bxz/a4fx d tatteries as its source of energy. Its mass is 1560 kg an 9x ca10zetuf48ffcd xr5+tb /d 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 lightbulegn)n-bnlzo 9 w8.o.kb 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 accelerator at Fermilab (Illinois) is designed to cq mu3rilml seh8)yq+, g d82*/dxryx6arry an 11-mA beam of protons traveling at very nearly the speiqm +rylrxdxu y,/ gqme268*dl )s8h3ed 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 dr )rn3wyb5(iy w7pi phgd3 7(connecting cord is copper wire with a di 7 (wiwy)3dn r(pdhg53py7 birameter 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 heatv (h3 j b,h/n6t5s(pr:v x0 guqsxw3bying element is a coil of rp y /vh w:vs(336xxsq0 u(jbgh,5tbn 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 voltage varies from about 12 vuu9mi4-a:e ic z.0ot 5t:pm oV 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 power delivered to the headlights vary as the voltage changes fr4:9 m5zo :atcmuvp0io-e i.utom 12 V to 13.8 V? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for housd0 7awo.eu55y g:h /zvf,xnos ehold applications. Lightbulb B is rated at 12 V and 40 W for ns fzg0:o5 /ae5huyxo wv.7,dautomotive applications.
(a) What is the current through each bulb? $I_A$ =    A $I_B$ =    A
(b) What is the resistance of each bulb? $R_A$ =  $\Omega$ $R_B$ =  $\Omega$
(c) In one hour, how much charge passes through each bulb? $Q_A$ =    C$Q_B$ =    C
(d) In one hour, how much energy does each bulb use?    $ \times10^{5 }\;J$
(e) Which bulb requires larger diameter wires to connect its power source and the bulb?  ----待选择----Bulb BBulb A 

  Copper wire of diameter 0.259 cm is used to connect a set of appliances at (2xqsi9vie86wzslp c ,pe)k 2120 V, which draw 2250 W of power total. z9px2esq, c6l 2s8 vi )wei(kp
(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 i xreeni8 7i w0e,9jg2snside diameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the resistance of 10.ie j7gew ne,8xs r290i0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that it / y4im/j w2lrwihnn6(s length doubles, by what factor does the power dissipated in the2mwj4rw6 y// inl(nhi wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operates at 0.20 A dw+qb/pupvvoz v//;, wnk-r 1 and 3.2 V. If its resistan r 1- wvuk ,p/w+;//qnbvovzpdce at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$