What quantity is measured by a battery rating given in a *r-gvmo3j go2mpere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow away froqh (8kpwg6g 8pm the negative terminal in the circuit. But q8g(gk ph6w8pwithin the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated,dc61, *+nu( gqcszlkz x;u j+(i(tw dr what is being used up: battery current, battery voltage, battery energy, battery po(w q+ujzks 6+uzdcnd,( rxtl*c;( 1giwer, or battery resistance? Explain.

One terminal of a car batt+517u.-otp3t/sfe m wueq s roery is said to be connected to “ground.” Since it is not really connected to the gmtu5 swq .eot 3p-e/+o rsf7u1round, what is meant by this expression?

When you turn on a water faucet, the water usually flows immediately4px (boq56xwr . You don’t have to wait for water to flow from the faucet valve to the qx oxr w56p4b(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 same length have tht ; qp//lc8/+ f0s.qltay jteae same resistance? Exflta0/t;plte.aj8/y+s q /q cplain.

If the resistance of a small immersion heater (to heat water for tea ,rk pmz5j1mw5 or soup, Fig. 18–32) was increased, would it speed up or1m,5rmpzwk 5j slow down the heating process? Explain.

If a rectangular solid made 10hg5gbtp no. of carbon has sides of lengths a, 2a, and 3a, how would you connect the wires from a battery so as to obt5p0no gh.1bgtain (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 l8efs 5*ug8 wo; gqn6su; 7qnieightbulb burns out?

Explain why lightbulbs almost always burn out just as they are turnp;sk6djb4 )i3 nvq 7cfed on and not aq pf6 s 7jk43vb;)icdnfter they have been on for some time.

Which draws more current, a 100-W lightbul oh p eqeg3wzacuxu:5)2.u3z5b or a 75-W bulb? Which has the higher resista u5ep2: 5gaux)eo3h3ucq zzw. nce?

Electric power is transferred over laaex9 :ubv :ry:0okn.crge distances at very high voltages. Explain how the high voltage reduces e ovbn 0:x uk:9c:rya.power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to rmyfq-u x7 9r7xkig+/ aeplace this fuse with a 25 y if m9/q7-karxu7gx+-A fuse?

When electric lights are operated on low-frequency ac (sk+;5sa9un2dqh: hgm ray, 5 Hz), they flicker nor: qakms;hh+5u2 ng9d ticeably. Why?

Driven by ac power, the same electrons pass back an8qc avr l-+5ve3lioc7d forth through your reading lamp over and over again. Explain why the light stays lit inc r7li 83q-vcev5ol+astead of going out after the first pass of electrons.

The heating element in a toaster is made of Nichrome wireeb2wh6 hw,e0w . Immediately after the th,e h 2eww6b0woaster is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? E.zxz53 db adr*xplain.

Different lamps might have batter0kmqmz bicc3uf n b3 iaz1:k 1b4qk189ies connected in either of the two arrangements nk :bm q1u 1m i31bqcz 49ab3ic0kfzk8shown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many elecl*vv 70.k8emwaqyxqs*/b2 +p6 d jurotrons are flowing past any poi*6lmb7. vrpdqoyuw *x +sjq08 ke2v/a nt in the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using 7kvw- f5a hsxv ,os6tn9 4dev1a current of 6.7 A for 5.0 h. How much charg6e h7f9 ao-x,sd15sn kwt v4vve passes through the battery?    $ \times10^{ 5}\;C$

  What is the current in amperesrcm0o bx6z)0z 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 1ip6 pll/2ml s120 V produces a current of 4.2 A?    $\Omega$

  What voltage will pro.p q/wxx7ijt qg(z4y3duce 0.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged intoigzy3 8, mjt*: fuq;fc 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 he4(ij/x l v ar.1bef3mrating 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 conneck8 6n oq7*sr5k l,+mmvkjol)u ted 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 se brq 55i2+ jy;vovk1jkm7 y*line carrying 2800 A (Fig. 18–34). The linsj oy7kjv;i51 +k2vqybr5*e me 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 an0g1e5pua+ rdcr wtfh5 :/*oA 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 0.6r rax3 2qx zuvo)8hc1ym**d)u0 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 tungybl8bi(jf 3x3sten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistanceqc2h sltykf7 p9px/2( of a 3.5-m length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of m76 t2 hmtqld.aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in diameter. mltmt7q2 h6d .  

  Can a 2.5-mm-diameter copper wire have the s t1orxz6kjv 9 1;1xi,*zipqyuame resistance as a tungsten wire oftquyj;ivz* 116 po 9z,kxr ix1 the same length? Give numerical details.    mm

  A certain copper wire . jm1 .dh(gsuphas a resistance 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 temperatub k1;tvxh)*y52hlmnn9wf *7 e thq cp6re of a copper wire (originally at fbmpxh )vn cwy5h6ke921h* *t7qtln;$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivity as tungstenhxyt u6d3y3v5 does6yd3hy3t vx5u at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance-y0h+m( (yhgbc;y,xzyc+jks rzpq; ; 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 coppig;5e n:e o;n+fq/9veeigi v2(f 0hoyer wire (used in 15-A circuits). The wire has diameter 1.628 mm and carries a i+5v i0 nyef2 vohgoeeq/f;n9(;:gei 12-A current.    V

  A rectangular solid mk c.,riq9ul.8yeqwu6 o2rp2 made of carbon has sides of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for currenr2keyc piq8ulq,.6u2 .9rm wot 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 resistac,q w8q4d npjtu 7;y.zj6do s5nce. If one has twice the length of the other, what is the ratio of the diameter of the longer wirep j8jz5, y6uq;cdd.qnow st74 to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precifng3f w,jsy 5zxeuv 50h: yt3-sion 10.00-V power supply, and a current of 0.4212 Av 03fuye s zfx5n,y:h-5tg 3jw 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 5.0 m of copper followed by 5.0 m bz/b4rrw1 yj. of aluminum, both of diameter 1.0 mm. A voltage difference of 85/w4rzryb. j1b mV is placed across the composite wire.
(a) What is the total resistance (sum) of the two wires? $\approx$    $\Omega$(retain two decimal places)
(b) What is the current through the wire?    A(retain two decimal places)
(c) What are the voltages across the aluminum part and across the copper part?
$V_{Cu}$    V(retain three decimal places)
$V_{Al}$    V(retain three decimal places)

  For some applications, it is important that the value of a resisb)bdx/ wqnh. :tance not change with temperature. For :xwq/ . ndb)hbexample, 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 96giqqeqv.jy kdzm n.c)f /: :of heat when cg::k/) i .yn6me 9qqcjdf.qvzonnected 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 draw5 uqcr50tyon *s a maximum of 320qt0ou5*r5 ycn mA of current?    W

  What is the maximum voltage that can be aeh ww fnc4)m14pplied 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 lightb-l:)x+xd;d paap eihd3xi2q +ulb connected to its proper source voltage l3ii:dxad+e -)x x; p2dhpa +qof 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 at 110 W. pk bbmv e*8ncqa2+eg5, y c-c+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 1250 ipc30tsbjdc i+gy958 W.
(a) At which setting do you expect the resistance to be higher? After making a guess, determine the resistance at
(b) the lower setting;    $\Omega$
(c) the higher setting.    $\Omega$

  You buy a 75-W lightbulb in Europe, where electricity is d --cowzy:q xhp3qtbx958.+y8s tl zwpelivered 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? [H.x8: o -wpq +qw9t3lcszx8z-yyth5 pbint: assume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use in the morning i.p)b*o agm -. -0pst o9zyqqkxf it is in operatioqt*yo g-o9pq .xkm-0.zab s)pn for 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 it co 0jd.(fys-kv yst to leave a 25-W porch light on day and night for a year(v0k-ysd fy.j? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected in series as inmhtp bap0m 8jc7k:(+j)ih a.e Fig. 18–4jeh+bkt i.ampcm ja07: h8( p)b (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 storb6*g4icl -0l17 vlsmpxvp8 lx ed in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connected to 120 V as in Fig. 18–20, can be use,c9e8 cvh;jo3, x-0h g dnzbzc:e2essd without blowing a 1,3e,; : cz xcnhbe2g sdoh0s8-cjz e9v5-A fuse?    bulbs

  An extension cord made obha9 * z*x*ebqf two wires 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 on a 120-V line.eb h **baq9z*x How much power is dissipated in the cord?    W

  A power station delivers csdja;-b23xhrkd3 z:4im e ,b620 kW of power at 12,000 V to a factory through wires with tota24d3, d :-bi hx azcbrmjk3s;el resistance $3.0\Omega$ How much less power is wasted if the electricity is delivered at 50,000 V rather than 12,000 V?    $ \times10^{ 3}\;W$

  The current in an electromagnet connected to a 240-V line is 17.5 A. At whhmg2rlu 44zuga w70 m82 au;dgat rate must cooling water pass over theguu0r;g 82ha4 amw l472zdmgu coils if the water temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater ca wqz1q1ion40an be used in a car to heat a cup of water for coffee or tea. If the heater can heat 120 q iow 40nzq11amL 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 coca fyyd n/6:yt+a (6v /(hdqrurrent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, is aczcj:h ;r og7fi a0xgt2pg/.x;ross 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 thecapfp v8f+ . x(7 zyokag6lx26 $120-V_{rms}$ 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 awp ww;i3g(no4 1500-W device is 5.4 A. What is the rms w4oi gw(w;3np voltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connecte1eyzf4vf+o j5 d 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 dissipa-r8js47jeuef gn)h* sted by a 3.0-hp pump connected to sn 8sfjgh j47ur-ee*)a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to 0k-5f/zc2s1ib1 l pokasb 4lla $240-V_{rms}$ 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 ca5 q4 3 qhcjlmodpoqgu42u7j7:rries a tiny current of $2.3\mu A$. What is the electron drift speed in the wire?    $ \times10^{-10 }\;m/s$

  A 5.80-m length of 2.0-mm-diameter wire carries a 750-mA current when 22.0igd8dsd 4j9 a0y r3ct, mV is a rcj0,d sa i3gt8d49dypplied to its ends. If the drift speed is $ 1.7\times10^{-5 }\;m/s$, determine
(a) the resistance R of the wire, $\approx$    $\Omega$(retain three decimal places)
(b) the resistivity $\rho$.    $ \times10^{-8 }\;\Omega\cdot m$
(c) the number n of free electrons per unit volume.    $ \times10^{28 }\;e^-/m^3$

  At a point high in the Earth’s atmospheu1 6g* 8fm8humeeqtr. re, $He^{2+}$ 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 atmospherm.ycem1*s vc e xow57pjfk:/ ,e, $He^{2+}$ 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 od bk.m;v.x2 )zjdb,dlf 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 electric pulse(e- ;kekh w0 ohgq;3li. The action potential is detected at a point 3.40 cm down the axon 0.0052 s later. When the action potential is detected hog;(wlk q0eh3i; k-e 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(y*csg 9 falx1 potential along the axon of Examp* 9cg1yfa(xls le 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored by charging the axon capacitance; see Section 17–9]. What minimum average power is required for $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action potential,)u), k ,tga0:ncman4wm-fvwq;luy a- $Na^+$ 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 arem)u )*3zv mrn9okv zc(+ fa;rv there in 1.00 ampere-hour?    C

  What is the average current drawn bycgbb:g 69b kb- a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car w z pm(-znsudk040s 3snith the lights on. If each of the two headlights uses 40 W and each of the two taillights 6 W, for a tota ( ns4szs-pnz 030mudkl 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. If it is made of i57 l1 kqik;ldoroqd 1i l;kkl57on, what must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of the rex5 zdhx 7x5a6yrxcxfvr1 s /0+sistance R; t 0+15yr6rxax/xhdxs5fcz v7 xhat 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 instead of u;3g)rmk1l)3 fbvlwpjny s/9sx s:gv4 sing high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a two-wire line vlsxbp s43sg;n3)r/m w :)kf l91vjygof 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 i)btpl(b;4 b84z ,sy+wrnzyza 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 tw a1-v c ygcvc1zsfb+d94*8h qcc5cg/co)+ am go lengths are wrapped together side by side to make a thickecozc+f)8*gvda1y/1s9ccq-4 m+c ghc g 5v acb r wire. How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is desigejlc,7k) 6jluned 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 nrrtyuu,ke509lk+/ tw ah0a1 6ueea7 qot become so hot as to start a fire. What diameter 9aur00au,t / r tu6ek5qe +1hwek7ly amust 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 by the eug3/08 k sdkw6-n 7kbkmqdur:quation $I\,=\,1.80sin210t$, 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 tp*jfnvx-18;1h;*mkemo xl xenergy per second to the intef k-n 1xhjpe x;mlt*v;8o xm1*rior. 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 diff;wcm.l z +6qhcotq2m3ratd 03erent conductors made of the same material. One conductor is twice as long and twice the diameter of the second. What is the ratio of the power transformed in the first relative to the seconco w.mrh2t;mt q dl q0ac+33z6d? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room of volug ;l*3 z q(xpsak-bng/(sz:dime $62\,m^3$ 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- h 4wvz,)oz)dnV 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 battef + zgq3q2.4eodqo9fr ries as its source of energy. Its mass is 1560 kg and it is powered by 24 batteries, eac q+3 4orf2fqzgdqe 9o.h 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 resiefw*zl1x0q* +zgmx, qz(; anjstance 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 caur /if,sx202rhwbu h ,5rw/furry an 11-mA beam of protons traveling at very nearly w2fh5b/, r /hwrsi 2xu u,r0ufthe 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 connecting dmzp)pi1 i,j4zh1l8hhi sr3; cord is copper wire with a dri8hiiz; ,14zhp)dmjl 1hp 3 siameter 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 hv1;gv 9kfm6mat 95 W when connected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire 6fgmv;hvm 9 k1has a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varoa jg.jovakh w0,4-h )ies from about 12 V when the car is off to aboj0kw .g,4ahv jah-o )out 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 from 12 V to 13.8 V? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V an9swlsjp pu+6;sy(dbe0k q3s (d 40 W for household applications. Lightbulb B is rated at 12 V and 40 W fo ssy 06wsd3kp(+9uj (s;pe lqbr 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 appliances at 120 V rizrd6:cj,6 gml 0:oq, which draw 2 jmr6,:g0o lrid 6z:qc250 W of power total.
(a) What power is wasted in 25.0 m of this wire?    W
(b) What is your answer if wire of diameter 0.412 cm is used?    W

  A copper pipe has an inside diameter of 3.00 cm and an outside o6ui. z lg 7vutg6fst;;wf0h.diameter of 5.00 cm (Fig. 18–37). Whatsu.gvtli76h fu t ;6w;gz. o0f is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that itsf:-0qslyvfq *y 2 v:et length doubles, by what factor does the power dissipated in the wire changefq:ytq:y sf0lv*2v- e, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a-o9g xy 4kt7fk flashlight bulb operates at 0.20 A and 3.2 V. If its resistance otfkxg 79y k4-at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$