What quantity is measured by a battery rating given in amperee3g /gq+,l lo/n(p n7y 7j g4ie9ehxtn-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, elecy6*ln*elm2i9f/ /u l.ih9c opqym;kl trons flow away from the negative terminal in the circuit. But wit *li 9 29qye;mlcn. ily hfo*l/mp/uk6hin the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used f 8/bd3y/yyg d:zl+6 dv9j2mgi 2mzvrup: battery current, battery voltage, battery energy, battery power, or battery resistance? E3:vmz+d892z ly r yjdibg/gm2d/yvf 6xplain.

One terminal of a car battery is said to be connected to “ground.” Since yfh g gytca(1+yd:os*tf z(0/e (x9 vvit is not really conz1yy 9fyt( x+( avt0vge:fhg/ (osd *cnected to the ground, what is meant by this expression?

When you turn on a water faucet, the water usually flows immediately. Yok:vua0 (s.72 quzc3f,f(( zrhykgx z zrjq e7,u 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 (zu,rqsfr7gxv u.(0kje(cz 72qz yz3 :kah ,fto the terminals of a battery?

Can a copper wire and an nkw -d, qwjt--aluminum wire of the same length have the same resistance? Et,-kqdj--w nwxplain.

If the resistance of a small immersion heater (to heat water for tea o1p:+ 0nngyqxzr soup, Fig. 18–32q+ 0yznngx1 :p) was increased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon ha9mmd9wg :pezt7i1 np1s sides of lengths a, 2a, and 3a, how woul7 1wpm:tzm1ed g9ni 9pd 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 burns out?pv1bgd cee)n 0 538nrz

Explain why lightbulbs almost always burn out just as they are turned on and sx y )8ozoml/+not after they ha+ y)z8olm /xosve been on for some time.

Which draws more current, a 100-h7;su.g2 v2qs a5kl;nw9qsbqW lightbulb or a 75-W bulb? Which has the higher res;5 halwu2 gs2.kns;vq7s9 bqqistance?

Electric power is transferred over large dispw2 : x(lrtsf;tances at very high voltages. Explain how the high voltage reduces power losses in the transms2tfw (px;:lr ission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace thi+0 tym:ck,zxzs fuse with a 25-A fu+ xmk:y zzt,c0se?

When electric lights are operated on low-vr6s3so pc 5k7frequency ac (say, 5 Hz), they flicker noticeably. Why?s 3 vs6k5rocp7

Driven by ac power, the same electrons pass back an +u0/t35+gb a4. luhamyx kkezd forth through your reading lamp over and over again. Explain why the light stays lit instead of tb04.35 xyk+mzuah/ +lk egaugoing out after the first pass of electrons.

The heating element in a toaster is ml:ge/8u evke.ade of Nichrome wire. Immediately after the toaster is turned on, is the curkeevu.l g/8e :rent $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Ec - q+wflneu un7a 34i)no2bv)xplain.

Different lamps might have batteries connected in either of thm c k5oev +8(;jizy3vte two arrangements sh3e5k8v+; (j vzm tociyown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flasf(d)* u/ ,4cvhc nixt-n40vk fe.ks ows in a wire. How many electrons are flowing past any point in the wc) 0 -,ucsike 4fxkanst. 4(*fvdh vn/ire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A*7 ;vf/osbon s for 5.0 h. How much charo/n;7s o*fvs bge passes through the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes if; e-t q)fph(jm $1200\,Na^+$ 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 -z( ww8ebx* znw951w ayzdyj7120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current this3 d (do(lfk/rough a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 1u ldj1jv35uaua jaoz 924v6+ g20-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 with a 6 j4luxsk:n i 3y3so6iw+5q wgresistance 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 connectedku9e;p*/a+hoer*rox5 zxt1e 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 electw,e:c9.qz5m(9ixeb,.wr3i z p d iqo ygs9q 2pric transmission line carrying 2800 A (Fig. 18–34). The lb9o (ipz zw.ce952 mqqr.d 9 iqw,y:pegi x3s,ine 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 6.50 A at 240 V. dnx l.w 1f0:1aa:f zg0thrsm3
(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 kpmp06 +o0hked8k l70 4zewskcurrent 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 whose eqdb 9j4dbu f4an1/;c resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1.5 mm in di ;/)2jjpsrhi hameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wiru i r0k j9k -lxjby:r++gvirl0dk((6ne 2.0 mm in diamete vu (rkr(60k bdkji 9rjxn 0i:y+-ll+gr, to 20.0 m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copl(6g o)kuunk 1per wire have the same resistance as a tungsten wire of the same length? Give numerical deta ku(koun g1l6)ils.    mm

  A certain copper wire has a re*9 dvu3c02 ;smb hotstsistance 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 havex:48)m: l jgw qq6.ufu jif3it to raise the temperature of a copper wire (originally at. wgtuq)u8 4ji j :3f:qxmifl6 $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will h+rb(9 8khzbofave the same resistivity as tungsten dobh(f+o 9b rk8zes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resdduvi c-5f.qsbs, 8g.istance 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 lcr zi7+ n;9pgoength of household no. 14 copper wire (used in 15-A circuits). The wire has i pgnc z+ro7;9diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has side 9ul , if82rh(nlq9r0on /ogpxs of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, an igonlorx hr9f9(p02u/ 8n q,ld 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. If one has /9 oqcu -ur e0,.evwvztwice the length of the other, what is the ratio of the diameter of the longer wire to the diameter of the shorter wire? u 90-eezo vqc/ u.w,rv$\approx$    (retain three decimal places)

  A length of aluminum wire/g01urzr8*ft tglilg u7qx2* is connected to a precision 10.00-V power supply, and a current of 0.4 lz r7r*/ ifg gt2u1lq*t0xug8212 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 co 3 ceqlrgq +i h./i)uo eyyj46);b0xicnsists of 5.0 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 theqh y or6x+ c 4q3l.je0;yce)iui/b)ig 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 th8* impll 3(ku26phvo x b8xzl66nu/wpe value of a resistance not change with temperature. For example, p6phn63kl *o(u8w ubl8p/6zvl xm ix 2suppose 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 elect,odqaom,b yki2f*5i5 ric oven is designed to produce 3.3 kW of heat when ,,b *kqo5dmfao2yi5 i connected to a 240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption /7,zmrigb; wq3 3fi)1ka uc kcof a 3.0-V portable CD player that draws a maxim k3;i7i/azw g)f cmkbqurc13,um of 320 mA of current?    W

  What is the maximum voltxky*tky/u /i9+e,06 fckm tgtage that can be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, a 75-W lightbulb conne+de0c6( cngu3(zdyf ected to its proper source voltage of 1 z(d06c+3 gfyee( cdnu20 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heater is rated at 110 ecb9ll d ;ney3v:/hn;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 andtoo;t dd+y6/i 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, whe/l1 a:qi+upp(g- pau7d vkme 4re electricity is delivered to homes at 240 V. If you use the lightbulb in the United States at 120 V (assume its resistance does not chan 7apdpu/mkv-:u e p41ga +il(qge), 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 toaste/ 4m x3vf6zh7 , bvohwhe(ha5rr use in the morning if it is in operation for a total of 15 min? At a hrv5,mhzh4 bvhef(o6 /w7ax3 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 dp m : x:4(dcx+ ddi. c.ps*ocbhxy8m(uoes it cost to leave a 25-W porch light on day and night for a+.4y: c spx8(bhup m:cxd ddxim *(.co year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected in ser j-azmrhfid:o0w;og y5 +,ao6ies as in,5ojmg+ai6z hf:o dyo0a-w r; Fig. 18–4b (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 am use ezet.6a9p 4,mze9ount of energy stored in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbum,m fl y*qxj*8lbs, connected to 120 V as in Fig. 18–20, can be used without blowing a l*m x,yfj8*qm15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.1w 0jqmpp :o,yj lrqxwj8,m:cjp//)5b 29 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric heater which drawsq:/pp,8bjw5y mjj)wcxjl:qro0,/mp 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 a9vo;59cdr.jqi mxyqe sk1 xhy 6*;h 8un7y0cjt 12,000 V to a factory through wires with total r; hcyq89y onh yv.ked;i r*x xu1qm 7jj6cs509esistance $3.0\Omega$ 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 zig0sqi4 *z r8rate must cooling water pass over the coilz iqs*zirg840s if the water temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater cos g2igbg*g4 5an be used in a car to heat a cup of water for coffee or tea. If the heater can heat 120 5g4io gsg*2gb 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 curj 3cgz 3k64qbfrent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak ae +-vxalea9k c845 upvalue 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 resista:mh:zr 2*zpcki7m 4gwt q7 w5mwqz, s/nce of 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. Wha 6z v;.hl3mknnt is the rms voltage acronhk36z lvn;.m ss it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected xkfbf,(/ . rc;u bfj0gto 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 dissipated x8x -ryt+dci. by a 3.0-hp pump connected tot cr+y8x -xid. a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected76s 8a dvdv jg1nbqga0fi o677 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 copper wire carries a ting6 ;i3fqwr,iay 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-diam 877 fgbqtko5lloe61 reter wire carries a 750-mA current when 22.0 mV is applied to its ends. If the drift speed rb8fot7g lq5eko6 7l1is $ 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 th- r9me+mthgg 4n-kyc+e 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 

  At a point high in the Earth’s atcwp 3(u+-wg wkj r)u f+a2ti/xmosphere, $He^{2+}$ 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 across an axon membrannt d 8wkm+f:s(/:ilsw:yms 0q e $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with an electric pulses.+b,c4 : mq6uc5b fs ltyutb2. The 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 measurements needed insteab: u54.+b26 ,scucslbtytqfmd of only one?)    m/s

  Estimate how much energy is required to transmit one action potential along the dp: 4e(sbshn8d oz,5j,z.jvh axon of Example 18–15. [Hint: the energy to transmit one djss,o z bvh8z5e(nd j,.hp :4pulse 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 potzvd ;99wh/*dx3zvy*zhbqbjzrvj,45 ential, $Na^+$ 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 amfy3n+aer4ij gib +olo+dm* * 4fb9;jcpere-hour?    C

  What is the average current dra,.s;4 b fmre w3pm5peiwn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of+tmnjcvm61tt 7i1v e) dwsnk,z7* z3z the two headlights uses 40 W and each of the two taillightt izs7t1v wem,1z7n jmtn *z+)d 63ckvs 6 W, for a total of 92 W, how long will a fresh 12-V battery last if it is rated at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of a 110-V,4on9xsbj 81 8smfp mq0 1500-W heater is 5.4 m long. If it is made of iron, what must its d4mpnfs8819q mx0so jb iameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as thw rm)u/d eca,/e reciprocal of the resistance R; tm ,w/r)uec /dahat 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 of power. Suppose that inklhq 709vnk1l stead 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, estimate the cost of the energy lost to heat per hour per meter. Assume the cost7k9kqlh0 n1 lv of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular household uses a 5,w)rro8ple 9 tzh8 q(6iq zjd1.8-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-: n )pkakaa;*ij re2)-am-jexg,kywr side by side to make a thicker wire. How does the resistae :xjnmke;2 ij*y-)g, aakrak-)w-pance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designedv; y t3.dez8ql 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 stek,wzz 8z);n9 v s2 v7ojf/mno it does not become so hot as to start a fire. What diameter must a copper wire be if it vz2f/8km;wsjonzn z 97 et),vis 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 by the equatio vdg9 1d(l5q0qhfq2ckn $I\,=\,1.80sin210t$, 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 energy per second 4gkgpz)r)ay17u)wz v5jm*ic to tugwm)4c z1 *arz vp))7yij5gkhe 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 tkh+hzkd3h j/xa: s ry 4t-in44wo different conductors made of the same material. One conductor is twice as long and twice k4d hjr:iy4t+ks4h a-3 n/zx hthe diameter of the second. What is the ratio of the power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room opo.un.ql(aa6 u(t p (gf 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 sourcex8wnc xo 3c8bl9+rl0 9;dlqio.
(a) What is the resistance of the oven?    $\Omega$
(b) How long will it take to bring 120 mL of 15$^{\circ}\,C$ water to 100$^{\circ}\,C$ assuming 75% efficiency?    s
(c) How much will this cost at $11 cents/kWh?$    cents

  A projected electric vehicle makes use of storage batteries as idt*qw 2) (b .qaak7cvots source of energy. Its mass is 1560 kg and it is(*7v.qac 2)bao dt kwq 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 has a razx,mqun ;osor+;v 7*c7 :r gresistance 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 Fermi-1gucupzbmu q95 6-zp(d( juilab (Illinois) is designed to carry an 11-mA beam of protons traveling at very nearly the speed of lig1puzcm5uu i9(gb-6uz -jd q(pht ($ 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.vlfd))7qjd ( w The connecting cord is copper wire with a dl (7 jqvwf))ddiameter 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 heating grnva.;saj1c(x3i y 7 element is a coil of Ni.gj7;1nrx3 sa viyca( chrome 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 varih;lf,xzy84d/vfj ks :es 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 power delivered to the headlights vary as the voltjhxfkdv:, 8/4lys; zf age 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 hou y2f )thh2as9jsehold applications. Lightbulb B is rated at 192h tyjfahs) 22 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 set of appliar/9s5hnn90 y rlxq*mo nces at 120 V, which draw 2250 Wmn*9r lr0h xy/5o9 sqn 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 diameter of 7w:uc0gmxn -n lmt9e.5.00 cm (Fig. 18–37). What is the resistance of 10.0 n u c.0 t9:n-xwl7mgmem of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is street4lv60yme f3ar 1*v ptched uniformly so that its length doubles, by what factor does the power dissipated in the wire cte*lyevr v1p63fma 04hange, 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 axihlm9 7cj 1ko4:a a(w0 7fygV. If its resistance at 2aj04wxlm(7hf9 g7i1o ak:c a y0$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$