What quantity is measured by a battery ratin) l3rnt0xh i4l/+eajxufl:x)g given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow avlq(ip5 wq0t9, gkol,ggcsx*a9g)2 dway from the negative terminal in the circuit. But within the cell, electrons flow to the negative termin)lqv*9cog ilggq, sx2p (, w5ktgda9 0al. Explain.

When a flashlight is operated, what is being used up: battery current, b25c;a86 k7 qaux wbw t)dtkb+dattery voltage, battery energy, batte;u )8ww76q5 a kbd kt+cdtxb2ary power, or battery resistance? Explain.

One terminal of a car battery is said to be co yf5,m2zvt/ rtnnected to “ground.” Since it is not really connected to the ground, what is meant by this expryv ,5tfzmt2/ression?

When you turn on a water fau7tt, bkbnpw 5;)8 rzercet, the water usually flows immediately. You don’t have to wait for water to flow from the faucet valve to the spout. Why not? Is the sa,b5p nrb t;t8 r7)ezkwme thing true when you connect a wire to the terminals of a battery?

Can a copper wire and an aluminum wire of the same lengthr oo9w8 ,ybuvn 5t3iljbmn9t5 f. wi:; have the same resistancrv tb3; 95m wi n89u:i,j.tn5f loywobe? Explain.

If the resistance of a small immeklk6:cw+ 1(pk9ht k q 6q fadke+2)recrsion heater (to heat water for tea or soup, Fig. 18k6ktwcq l+)eeck2k khr196f( :+qa dp–32) was increased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of l2 o3 cs6z)wvmp ic-.bxengths a, 2a, and 3a, how would you connect the wires from a battery svo -pm)z32ccw b.six6o 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 lightbulb0)*kj *nba6pmpu 3-hijq0t ue burns out?

Explain why lightbulbs almost always burn out just as they are turned0/c ;l cvt,cuz on and not after they have been on for some timc/vz,lc ;u0 cte.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Whi egjm;ja9 /-b anmp q)w3cjfiwh.0w*7ch has the higher 9j0bmag w h;ciw. jej */n)mfqw pa37-resistance?

Electric power is transferred over large distances at very high voltagey 4.ow8m sj3 gdux(0qas. Explain how the high voltage reduces power losses in s0jy (owd4ugq. 3mxa8the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fup 8hlp(ycp3ob7 dnk m 0l2c.8gse with a 25-A fusk 8.ym pl70pg8h( lonb 32pcdce?

When electric lights are operated on low-frequency ac (say, 5 Hz), they flichqw w9dn;bhf4 6hk1jk9hr(u; ker noh;qfku 1 w9h;rw(9 b64jhdhnkticeably. Why?

Driven by ac power, the same electrons pass back and forth through you+h- jul.6jhfkr reading lamp over and overl+ hjj-6fuh. k again. Explain why the light stays lit instead of going out after the first pass of electrons.

The heating element in atuc 5;by *4z1s8gmz 6- huhokg toaster is made of Nichrome wire. Immediately after the toaster is turned on, is the curr86ht*kcs u1-m gg5z;z4buohy ent $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? E 1 apcmy3uihpv4.m/t ;xplain.

Different lamps might have batteries connected in either of the two arzi*0-hufb* lar*xwt8 rangements shown u zabhl-**ir f *xtw80in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many electrons are f55ket qx l0nf+lowing past any poikt5+0 5 eqnfxlnt in the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a b swx6q.c1t3ht attery using a current of 6.7 A for 5.0 h. How much charge passctq3 x6ts.h w1es through the battery?    $ \times10^{ 5}\;C$

  What is the current in ampere nul7gm:+vqb. s 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 oqx:zy 1-lfs;mf 4.2 A?    $\Omega$

  What voltage will produce 0.25 A odq8qmotj:lv2op . nk*.e )t( 73sl mukf current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged int5+s2dbnm/+ f hk ,o8t,epew hdf 6ivq:9b*h too 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 d 2)fpl.(t 6onag1kuk *mdt 6mifi+fv +ryer has 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 connected to a bulb whose resistan 4ti3gx2mu 5m4diwbi-ce is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transmission line carryingweg2emf7 /) iiq7n+ze 2800 A (Fig. 18–34). Tz )e+m/7 q efi2nwige7he line 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 Axxb(i 5 bd;h9ew0ujf3 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 thro zhs9 wbmfv8/b1 h3dumcc-(n6ugh 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 7,.hxf/hr 6dl c1jzma+wq*se 1.00-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 mm in diamedatldl; c45hmf ;6ey7p aek51ter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio ofq8 oyf,iz)rhqdza yk7/g-91 nl8p j8 w the resistance of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of kqr1no p,8ayjzy d)8w/fz7il q 9h-g8copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tungsten wire o ril1m edypzxy ms5lt9r)ji . z.39l40f the same length? Give numerical9t5.dy31.iy e jsl4rpml )rzxz0i lm9 details.    mm

  A certain copper wire has gqacjp4 )v3r9:xw-l tc9 5dima 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 xm2 fgdd76j1 jxn5- y.or l*bv0s y)dbraise the temperature of a copper wire (originally at*1jsv2yxj0x)5ddn-bo. 6ygm f rd 7 bl $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperatj9epky 1 x.)hdure copper will have the same resistivity as tungsten does19 kd.)p xheyj at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistagm lxp7v6q5bm4al.6zrg4w /7 -ys bbznce 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)+/qcc ue )oz2n 3ar ptwmtl*1-m length of household no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm 2/+w )tl3mzcec*t pu )oqna1rand carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm, 2.0 cm, n +vy a,y7xxh7btv w*nb2ff9;;l8txq and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determa t+bftv xv;yh7nb8;*xw7, l f n9yq2xine 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 zt4l 4nqouve3,u(om ;lv* f2yhas twice the length of the oo*t 3qn4vv (zo4mu u;efl,2 lyther, what is the ratio of the diameter of the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V power supply, anxte9a,zoz -p0: 7 qqlmd a current of 0.4212 A is precisely measured at 2 oxtmzlp: q-0az,qe 790.0$^{\circ}\,C$. 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 con)d 7+qf ,fekoasists of 5.0 m of copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage did ffo ae7,k+)qfference 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 value of a resist /q:k tcyifjp:r(dj 8)ance not change fj: (kq jc i8)ydp/rt:with 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 /;k,g. iowerr oven is designed to produce 3.3 kW of heat when connected to a 240-V source. What must be the resistance of thekro,;g e./iw r element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD u4 yuprqna7l(,1ri.qplayer that draws a maximum of iql 7 pry(au 4un.,rq1320 mA of current?    W

  What is the maximum volta 4bjsle b9duxnn42: ;qge 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 lightbulr2:p;sl (ubz jb connected to its b;zr (lju sp:2proper source 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 rated at 110 W. Calc h,1oq3y :za x5da3iciulate
(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 ze xnq+ k8o :j7k)9ysfsettings: 850 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 electrici n**oaj*:jnm2 -5pp re k7cvjnty 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 it be repoe n*j*m-pjjnv*r:kc7a n25 lative to 75-W 120-V bulbs? [Hint: assume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy doe/qkma3yj) go ;s a 550-W toaster use in the morning if it is in operat mk/;qj)oga y3ion 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 cost to leave a 25-W porch 23cqyvpy.f*/w ) 7h-vxze qhxlight on day and night for a year? vp3wzv.xh-7qc/ ye 2h )qfx*y$\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V ba 9m91 wu*:doe5kezc jbtteries connected in series as in Fig. 18–4b (Fig. 18–36). Theodb c1mwe9z*eu9 5: kj 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 h))lja 9v ,iuen0x eu2energy stored 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, canitg1p 7anbs 3* be used without blowt 1sai 7pg3*bning a 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 copper wiii 3i5o -tz)*kl(d:z4pzztcf re) and of length 2.7 m (9 ft) is connected to an electric heater which draws 15.0 A on a 120-V line. 3otzz(c* :)zz5pk4itf iidl-How much power is dissipated in the cord?    W

  A power station delivers 620 kW of power at 12,000 Vk5-yqn3a gn0 ty1 +dji to a factory through wires with g0ny- q3+ajd kiy15 nttotal 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 k*rmt k ,p7uk3bn5ko,17.5 A. At what rate must cooling water p3 un ,5bkkokk*7p rtm,ass 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 used in a car to hw-ek pes) 8:mdeat a cup of water for coffee or tea. If the heater can heat 120 mL of water from 25em pd k-e)w8s:$^{\circ}\,C$ 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 5- ;b xqx9bfdc+g/dq2ebdyl/in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peaua),8qnpudu9* z e3d wk 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 the suz1qit1 z mc 75w68jf$120-V_{rms}$ 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 cx* 4 hkna1a 8(6jkdoeturrent in a 1500-W device is 5.4 A. What is the rms voltagan6(1ehjtoak4dk 8 x* e across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connecu+e fwled4lj m;,tq 5q;m72,p p(pbzy ted 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 maximu)q;jw 8*utdfk1d1s w7(v yg tsm instantaneous power dissipated by a 3.0-hp pump connected towt1kdvsg *8(tdjs ;fyq u17w) a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to a 2h) fu c/im*w, 2jia3xqt ao58 ,vvoxg$240-V_{rms}$ 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 tiny current ofu 1y bbdsdhsle/g(0cg*hd3:tv tr147 $2.3\mu A$. 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 22.0 mV 3hhn0wd2u.re54q gfh is applied to its ends. If the drifte f.2h4gqn5hhd 30rwu 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 Earx j gt92 2in7v0e((hli3glx gith’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 atmos k uf e::t-kzo0l2(ol.mw le2xphere, $He^{2+}$ 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 axontl61evb, e7pdl 1jrk6 membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with an electric pulse. The a* boww*m m;r5nction 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; w*nomw*b5rm 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 e :b2nhxlc/,ejlr:az 51w/yjone action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored by chargi n,c/x/l5hwjeya rb: 1e 2zlj:ng 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 potent8+c +g+ramhbmza e:y18/blufial, $Na^+$ 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 le1vaz u+rwwkj1))q, 5xbr q h07sizk/s 5o z(1.00 ampere-hour?    C

  What is the average current drawn by a 1.yv73w/c gkl+yqcg 52b 0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a c+oly 9ul j)cw1ar 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, how long will a fresh 12-V battery last if it is rated cwylo)l1+ju 9at $95A\cdot h$? 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 wmm7ayh m42:;nbz2j7ylvyr .it is made of iron, what must its diameter bew lm4n.v 2:a7yj r;m yzbh7ym2?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of the resisth1 qd*e2w-jhc ance R; that iqd ejhc1w2*h -s, $G\,=\,1/R$. 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 abou8 b y2t2wtgf,yt 10 MW of power. Suppose that instead of using high-voltage lines to f2y,tygt8w2b 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 cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular househse -)qzac/yt a9p;bp yq:-li* old 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 andg,.ltyms kjp7 q+ p0g: the two lengths are wrapped together side by side to make a thicker wire. How does the resistance of this new combination compare to the resistance of the original wire?kqg7.g :psj0y ml+, pt

  A 1200-W hair dryer is designed f-ymhh 9x++xrc+ 5un)zmn sln*or 117 V.
(a) What will be the percentage change in power output if the voltage drops to 105 V? Assume no change in resistance.    % decrease
(b) How would the actual change in resistivity with temperature affect your answer?

  The wiring in a house must be thick enough so it does not becom6r.q1 w. lkl5dn vn,oge so hot as to start a fire. What diameter must a copper wire be if it is to carry a maximum current of 35 A and produce no more thanqkn51d gvllr. wn6o. , 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by the equ8c3e)gysl.u ,/ nyuxr ation $I\,=\,1.80sin210t$, 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 95 /cokpc8 ,2iff0 W of energy per second to the interior. cpo ,i8kf2cf /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 z4a0slr+no av jv,sc;2uotr qpo1/6-ni9on : different conductors made of the same material. One conductor is twice as long and u6s0/2z t9 o:o;v1nvq ,ri 4a+noa-ro nlsc jptwice 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 usedtb* (-yp1rwc5nke lb+ 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 240-79g;g:/ abaopqe4qttt u:x 4oV 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 batt8tq54s *by br,2 imorneries as its source of energy. Its mass is 1560 kg and it is pow5m4 bnby 8r ti,rosq2*ered 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 lightbuhs kn:gh6p5r 7wc(+hzlb 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 accelerx s3agm,ez1+fator at Fermilab (Illinois) is designed to carry an 11-mA beam of prots a fzx3g1,me+ons traveling at very nearly the speed of light ($ 3.0\times10^{8 }\;m/s$) around a ring 6300 m in circumference. How many protons are stored in the beam?    $ \times10^{12 }\;protons$

  An air conditioner draws 13q(grjcom+wxsda)d r8y mzxf 3u;4 )sj1t 9i:2 A at 220-V ac. The connecting cord is copper wire with a diameter of 1.62d+x q usz)m(ms d:j 9j3 y g)r;84ofaw1xrct3i8 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,wrqw6,u dlw pf nu x/g;/h2fjg6z5;c at 95 W when connected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What is the diameter or 6 j ;fcg5nlq,wd//f;pzg2 xu,6hwuw f the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from about 12 V when the car is off 7ram)iq5mmmnr*)9gi;e q o;a to about 13.8 V when the car is on and the charging system is in operation, a difference of 1i men7 *m)i5 mg9r)a;rq;qamo5%. By what percentage does the power delivered to the headlights vary as the voltage changes from 12 V to 13.8 V? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for household applications. Ligeek. d4*-bp pzhtbulb B is rated at 12 V and 40 W for aub pedz4*ek. -ptomotive 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 uscrj+v /kx1o43 ae5xyfxa63 qsed to connect a set of appliances at 120 V, which draw 2250 W of power c5ef v3x /oyskx634 qaxa1+rjtotal.
(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 3.0hz5qd 05cx*0ev3 1 m7kxyo*c vgnimy(0 cm and an outside diameter of 5.00 cm (Figv(yczm v505ge13*mid 7hx0xk q n y*oc. 18–37). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched ue ixdzl-sq ;3/niformly so that its length doubles, by what factor does the power dissipated in the wire change, assuming it remains hooked up to qids 3;xe/-lzthe same voltage source?

  A tungsten filament used in a flashlight bulb operagyd1wcut7a +1tes at 0.20 A and 3.2 V. If itt 1u c17ad+ywgs resistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$