What quantity is measured by a battery rating gidte9v3 w g;six ;5toy9ven in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a cifmo i 3l.+cj8orcuit, electrons flow away from the negative terminal in the circuit. But within the cell, electrons flow to the .f8c io3o ljm+negative terminal. Explain.

When a flashlight is operated, what is being used y);l wq6qk5tyup: battery current, battery voltage, battery energy, battery q)l;qkyy6t w 5power, or battery resistance? Explain.

One terminal of a car battery is said to be connected to “ground.” Since ozwvw/ +o0 o+m:z7mt dit is not really connected to the ground, what is meant:o7z+owzm0vw /do +m t by this expression?

When you turn on a water faucet, the wate s - tsc wywdq2;fla.u.3i1:rxr usually flows immediately. You don’t havw;u..wdxc s2qil1s -a3yt rf:e 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 aluminum wire of the s5k9qze t/x6dt ame length have the same resistance? Explai edz /tq69tx5kn.

If the resistance of.axzuf., (k 6-id* juwm wl,icf; 1mvjb1/hns a small immersion heater (to heat water for tea or soup, Fig. 18–32) was increased, wo ms6wi(mfh,cw- uj udj.axk/l.finzb; ,1*1vuld 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, how wofqvf2z73/ fbh/gcyr *uld /fbf3vrzcqyg* 2 7hf /you connect the wires from a battery so as to obtain (a) the least resistance, (b) the greatest resistance?

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

What happens when a lightbulb burns4q c*08ik/x,ua:j1bz ja sud s out?

Explain why lightbulbs almost always burn 8.gf/a:vclgx9ncxj/jn4 1 tc out just as they are turned on and not after they have been on for someagvg9cn f./ 4 lj1:/tj8ccxnx time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which has the higheak ex8emo, y8;-5lrcdr resistana8 o;cyr-8el mkxe5d ,ce?

Electric power is transferred over l4 vl/m vksg,ln2xr 6d4arge distances at very high voltages. Explain/ vsv4xn,6 gl 24krdml how the high voltage reduces power losses in the transmission lines.

A 15-A fuse blows re* j, zv*7.qbbv i fe,lnpbv82jpeatedly. Why is it dangerous to replace this fuse with a 25-A jn v*pb,*.biz 2fje7vlvq ,b8 fuse?

When electric lights are oizajb (ky- 7 9r3c)qrpperated on low-frequency ac (say, 5 Hz), they flicker noticeabbyaj37 ip krqzr)9 (c-ly. Why?

Driven by ac power, 0t xkzk5q*6egthe same electrons pass back and forth through your reading lamp over and over again. Explain why the light stays lit instead of goinkx05 t zgk6eq*g out after the first pass of electrons.

The heating element in a toaster is mtn x1tkb5(.bi b*n1jtof4j) sade of Nichrome wire. Immediately after the toaster is turned on, is the cu fj n ktbs1*t41oj.)tn5i(b bxrrent $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a :u 0/nqdrd n;5o)gzjo resistor? Explain.

Different lamps might have batteries connected in eith yhvx 1 k7epk9fsg9-s5er of the two arrangements shown inh5-7fvx9 1 gsy9eskkp
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many electrg g- *zu8(ep8m(hexdnons are flowing past any point in the wire per g(8nehpm8gz*x u-(edsecond?    $ \times10^{18 }\;electrons/s$

  A service station charges a bata/bj z8fey ,/etery using a current of 6.7 A for 5.0 h. How much chargee , ae8j//zybf passes through the battery?    $ \times10^{ 5}\;C$

  What is the current in amx r+gr,h p9 6wf-dg4e0aw)uw cperes if $1200\,Na^+$ ions flow across a cell membrane in $3.5\mu s$? The charge on the sodium is the same as on an electron, but positive.    $ \times10^{-11 }\;A$

  What is the resistance of a toaster if 120 V produces xbd6ol1t /mmj 0ah5(pa current of 4.2 A?    $\Omega$

  What voltage will producxg38eo;x przc v0,dm ,e 0.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-V hj fcq/f.o. 1wline.
(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 hak usjz*w*n :g+cr:g0b9b ng q+2uezf1 s 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 connerwi+g jv mlv3//ykg o)1bcq 67cted 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 l- 7ac0a x80inu t3u m+e0z+fxvsc:uajine carrying 2800 A (Fig. 18–34). The li ue+naict0 +a3 : ums-7vz00ac8x uxjfne 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 dr)xbjyn z.1e1qvs 4)o ha1ro a;aws 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 of 0.60 A throughb*;uctlp1 x m ,f1avitl*9qn- 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 ;d.5y sy5zquh.00-m length of tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1.5 mmy oqf3u.z8l 4 *bmq9ve in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminu t67 tlwvg7/z+ej-tt mm wire 2.0 mm in diameter, to 20.0 m of copper wire wmtztt7 g t/6v je+7l-2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tungsten wire + 3dyj3) pyh7ippzd4p of the same length? Give numerical detjpy7 ppyd3 i 4hd3pz+)ails.    mm

  A certain copper wire has a o3-g qj9z p08c2 ir(kgt*v5 dtyemq /fresistance 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 (origiyiv12l/wby- pq :ra ,tnally at-y1l:a2tby/r wq pi,v $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistiviopgwb. u suo) 23lfmem )0es00ty as tungsten does 03mesul)uo 0).peobw m0gfs2at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistanc yjtp/)*lg*;rk uwoe5::w eul5fmon1e 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. 14m zn8-rya.d+m copper wire (used in 15-A circuits). The wire has diameter 1.628 mm anmynd +z a8r.m-d carries a 12-A current.    V

  A rectangular solid made of carbon has sides ofb:b d11 p5abggtztasv6lwua/5c d:/0 lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, 1atzcd/:0b1dwsa l55 t v/ :a6bgu bgpand z axes, respectively (Fig. 18–35). Determine the resistance for current that passes through the solid in
(a) the x direction,    $ \times10^{ -4}\;\Omega$
(b) the y direction,    $ \times10^{ -3}\;\Omega$
(c) the z direction. Assume the resistivity is $\rho\,=\,3.0\times10^{ -5}\;\Omega\cdot m$.
   $ \times10^{ -3}\;\Omega$

  Two aluminum wires have the same resistance. I6 (f; laqm1)pzz+an bqf one has twice the length of the other, what is the ratio of the diameter of the longer wire to the diameter of the shorte zz;lqq+m6na) abf1 (pr wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V power supply,++ -c*uc g b1 s*fqt3 uzkfhgx9cyp0w0 and a current oqcfkuc 3-+guc00 hpt y+wz1g *sx*f9b f 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 consis*+en9ef zjt7bm m82zd z/4gh1qtxvw*ts of 5.0 m of copper followed by 5.0 m of aluminum, both of diameh qj/v98 t 71fedmwbg*n mzz+4z2txe* ter 1.0 mm. A voltage difference of 85 mV is placed across the composite wire.
(a) What is the total resistance (sum) of the two wires? $\approx$    $\Omega$(retain two decimal places)
(b) What is the current through the wire?    A(retain two decimal places)
(c) What are the voltages across the aluminum part and across the copper part?
$V_{Cu}$    V(retain three decimal places)
$V_{Al}$    V(retain three decimal places)

  For some applications, it is important that the v6xx,;pnnyr p(5j74 a6sd tusa-cn se3alue of a resistance not change with temperature. For examplnnrp;txnu yx a75s 6,jpa s 36d4s-ce(e, 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 desny04c (y6agtnigned to produce 3.3 kW of heat when connected to a 240-V source. What must be the (0y 4cy6n ngatresistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable yad:a;zw5h-egx mto,-1w ja) CD player that draws a maximum of 320 mA of curra xz1,jagwe-do 5;mtyw : h-a)ent?    W

  What is the maximum voltage that can be applied vmy( zjj3fb7l9xbhe2e(q g :3across 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 connectd,z rlwb-2 ctoyd+ky+-s 1 x+ged to its proper s2w1kcldyx, ++byg--st do z r+ource voltage of 120 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heater is ;:bio6qq cy7z 4su ke*m: tc*orated at 110 W. Calculate
(a) the current through the heater when it is operating,    A
(b) its resistance?    $\Omega$(Round to the nearest integer)

  A 120-V hair dryer has two settings: 850 W and 12bs;k6d8iyv )su h 7-.o2ivxfs50 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 electbpc.rnj.fqn 4qp4v7 ,ricity 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 it4qjc .nqp4.7,v fb pnr 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 :cn*mvfh-14 i ky1ah stoaster use in the morning if it is in operation fo4*cv :1h1manyis fh -kr a total 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, what does.pi29yhj, / o0obleft it cost to leave a 25-W porch light on day and night fo0.tf2e j/hoyip, 9olbr a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected in seriea( lscl1*a0)cockts( s as in Fig. 18–4b (Fc t1cals0( kac)ols* (ig. 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 energj6ojpj1a: 4t sxp7k ot-kk 6u;y stored in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connectf,wc5*y r3p eued to 120 V as in Fig. 18–20, can be used without blowing a 15-A *,w35eufprcy fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16gqke1 km-s5h- copper wire) and of length 2.7 mk--1q gmsh ke5 (9 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 powetxpp3mw:pv4 i+u ga o0w:y1 ;ui-qif*r at 12,000 V to a factory through wires wi 1muxu v3:g :*w +fqptii w0oppy;4-aith 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 rn- 9rvz/q. 7yssaky+to a 240-V line is 17.5 A. At what rate must cooling water pass over the coils if theay/r.qs97 rs zkv+y- n 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 ,co2dmj (li2e: j7 kizto heat a cup of water for coffee or tea. If the heatkj (,dil:72ciozmj e2er can heat 120 mL of water from 25$^{\circ}\,C$ to 95$^{\circ}\,C$ in 8.0 min,
(a) approximately how much current does it draw from the car’s 12-V battery, $\approx$    A(Round to the nearest integer)
(b) what is its resistance? Assume the manufacturer’s claim of 60% efficiency.    $\Omega$

  Calculate the peak current in a 2 h) +ci,vwbeseov7xlm,;7k w$2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose w6fv,v5knix6p-kmv + peak value is 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 of tskjx)p 1w.umzd t-w9mz )n d;lh2c:9uhe $120-V_{rms}$ 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 curren; s 9+yxlptd2wt in a 1500-W device is 5.4 A. What is the rd 29xwp;ts+ylms voltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected to (7. kkw*de4d oxa /naw7w4rq ba $660-V_{rms}$ ac line. Calculate
(a) the peak voltage$\approx$    V(retain one decimal places)
(b) the peak current.    A

  (a) What is the maximum instantaneous po -cutd6a* l 1mxd/xog(s jrl m)tp07 e9g)wx:ywer dissipated by a 3.0-hp pump connected to (uo7/dda- 1s)mpygx lwj x906 )rt:*etlgc x ma $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to x,osz l,/q/8e1ye7jh xm,mrbma*sg 8 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 wir7o/-o wwsh 1fke 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 cgo-dry65os 5b arries a 750-mA current when 22.0 mV is applied to its ends. If the drift od5s5rb -oy6gspeed 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 Euj 0zzm r)+y-lj q coki:uhhl6*5 /ae2arth’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 a:1-nb*hh9 dglven aj2tmosphere, $He^{2+}$ 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 ofkuwtt h6n 0(+blko p6. 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 electry zsyqdmpk( g6wjo/m* 72*68rt1rhud ic pulse. The action potential is detected at a point 3.40 cm down the axon 0.0052 s d/uyjw6 qk8o7tzy21h sg6p*mmr( *drlater. 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 action potent (f) nhti6bis(m-+dgmial along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored by charging the axon cap(mdi-(sh m )t g+nb6fiacitance; 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 potentiafk70rp(e ohyptc -4 q;+-nxw kl, $Na^+$ 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-hour?9k1,r5mkb+ pu /ojudu    C

  What is the average current drawn by,i4fo e m t5k3l,: yst1i6cgut a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with thevxi* ,rea eve:r l;76nnbda9+ lights on. If each of the two headlights uses 40 W and each of the two taillights 6 W, for a t9 d ree ab,vl+n;r6aiv*nx7:eotal 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. w ptt*gcr(cakcp a27 +6+ko cany2,yfua0 8r1 If it is made of iron, what must its diamet6 fpr ac*ac1t+yc2w8k 0 uky7agn ra t(o,2p+cer be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the recf, dcvhd., ,fniprocal of the resistance R; that in,,dfv,cfd .hs, $G\,=\,1/R$. 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 abekk 5tee bi(o/t:js50out 10 MW of power. 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, estimaki te0 b(jt:55s /eoekte 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+ cdn2,c/qojc uses 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 togethba.y4- k9a j b1mght1ger side by side to make a thicker wire. How does the resistance of this new combination compare to the resistance of the 1ag4tj.ygm 1abhb -9koriginal wire?

  A 1200-W hair dryer is designed for 1bghymg: -vp83ww+60zm fz ft: y4 o,qe17 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 enab k*bbf/3 e)zough so it does not become so hot as to start a fire. What diameter must a copper wire be if it is to carry a maximuz3abbe )b/fk *m 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 by the equatio zuo5qd;ni2+-,vncrx n $I\,=\,1.80sin210t$, 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 gsighg5 4alm jxur9:y85y- , /m+o cui65% efficiency delivers 950 W of energy per second to the interior. Fm ,-5l9ju5+8rg/gi4agu i ys oc hmxy:ind
(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. One z0 jniqj-btl3 y.ay1678snnpconductor is twice as long and twice the diameter of the secondl b68pas0z1.t3yin nnqjjy-7 . What is the ratio of the power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater isvvo,o+*r (l-mh;ek)c:bn wnf 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 hoo,tkriy3 fko,o s,+e-+vto v,eked 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 lqn;jx w:jc35 cplg48as its source of energy. Its mass is 1560 kg and it is powerqgj3j l5ncxl8 :;c 4pwed 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 has a resistance o phfdfghr*-16f $12\Omega$ 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-ih8u 6l qfi1xok / eep(gba0:8mA beam of protons traveling at very nearly the fi iu(ao e:1b x gp/88klqhe60speed 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 connecting cord is ;;h3u ek fetj6copper wire with a diameter of 1.628 mmk; tfe;h e6uj3.
(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 af74 q-tm/g5g jqpz. bat 95 W when connected to 120 V. The heating elementgt5zjfq /bm qg7a -4p. is 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 voltage varies from about 12 V when the car is o;cpt golxpl6yz . h78/ff 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 po7zpghyl6 8o p/lt.x;cwer 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. Light9 fk8vfvisn inhj82 f*7 l*whyi9p2me4gzy;.bulb B is ratipgywvs*i fn7 zi 8h2m4f28j y.k9e*fln;9vh ed at 12 V and 40 W for automotive applications.
(a) What is the current through each bulb? $I_A$ =    A $I_B$ =    A
(b) What is the resistance of each bulb? $R_A$ =  $\Omega$ $R_B$ =  $\Omega$
(c) In one hour, how much charge passes through each bulb? $Q_A$ =    C$Q_B$ =    C
(d) In one hour, how much energy does each bulb use?    $ \times10^{5 }\;J$
(e) Which bulb requires larger diameter wires to connect its power source and the bulb?  ----待选择----Bulb BBulb A 

  Copper wire of diameter 0.259 cm is used to connect a se p w3frm2tk8)c *4jbket of appliances at 120 V, which draw 2250 W o2 4te pmkr*8cfkj3w)bf 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 andp0xq6.cd)ne(v oscwly 2ox5+ an outside diameter of 5.00 cm (Fig. 18–37). What is the resista(ls5o0w2.xy) c6veq+p onc xdnce of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so t h,cy ka+iqsd 5b7sftze/ x 3v3+w+n8 pz4n8awhat its length doubles, by what factor does the po3vk3dc+saqx,i wn78w++/z f4a t 5s8nez ypbhwer dissipated in the 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 and 3.2 V. qw+(;7 tx 8- ngwgc32n,,mynmswbbg3 bba n)jIf its resistance at 2yxagnct2 qb m3b,),nm73bgw-g8w; n+bwjs ( n0$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$