What quantity is measured by a batter2bmlrpw 7,0k vru8 72n vqngfz1*7ni cy rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connec30:/tbpo vb ;okjqwkl43squ2ted to a circuit, electrons flow away from the negative terminal in the circuit. But within the cell, electrons flow to theqousqo/l:bw4b k0pt 3k v3;2j negative terminal. Explain.

When a flashlight is operated, what is being used up: battery c4rkdz t :ga6-pw8 lpmn+i1geo6h 7xx.urrent, battery voltage, battery energy, battery power, o l+r:1 tgw7ao xep4dkp66 h-xzin. mg8r battery resistance? Explain.

One terminal of a car batteryjqlg0h+lb7/kf0d stn q/u/z8 is said to be connected to “ground.” Since it is not really connected to the ground, what is meant b buht 7z0sg/n0/ql/+lfk8 djqy this expression?

When you turn on a water faucet, the water usual+2ob/mry )nhho er6 ,9eaj5ptly flows immediately. You don’t have to wait for/r9ha2,6e tnb 5myj e )+rphoo 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 1j/j8b*dujri b7i j u:an aluminum wire of the same length have the same resistance? Explain bjijj7*j1/:b driuu8 .

If the resistance of a small immersion heater (to heat water for tea or soupfx,+a t-j/vwt, Fig. 18–32) was increased, would it speed up or slow down the heating process? Explain.xtv-+/jf aw t,

If a rectangular solid made of carbon has side z1cg jgl(94dasl-k3os of lengths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) thekcg dog134al-jzs l9( 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 l4ql7zup9,5 i q dmyvs1ightbulb burns out?

Explain why lightbulbs almost always burn out jus12y3a3h alrn2myw+ h gt as they are turned on and not after they have been oyrg wnahlh2 23+amy13n for some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Whichd tvx z; t r9u:iy/b7802nxfyt has the higher retv;y /u8i:7tzry 0n2xftb d 9xsistance?

Electric power is transferred over large distances at very high voltages. Explaitu* :qvvk c3(jn how the h*jvu qc(:v kt3igh voltage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fuse3ujiak *ny2 rhd:8+ iu with a 253 yj2iuha:di r*+n8k u-A fuse?

When electric lights are operated on low-frequency ac (say, 5 Hz), t ;d /kppf0a f-cks*-rphey flicker noticeablp0;--dckp *ak/p f sfry. Why?

Driven by ac power, the same electrons pass back and forth v +yjfjdg a1/-through your reading lamp over and over again. Explain why the light stays lit instead of going out after +g-v1fa dj /jythe first pass of electrons.

The heating element in a toaster is made of Nichrome wire. 8 nz8xxs) f3i0u b2uz1j: wmluImmediately after the toastel)ui szu3:uwbxzf 0 n x8j1m28r is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a0qp808i-6q zo*omnizf cu ya z* 6a2vj resistor? Explain.

Different lamps might have batteries connected in either of thep g6vk*z2 3pdab5, km d,pfs/e two arrangements shownb, *k av3/dkfpg 5sp26medz ,p in
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 flowing past any p9h m3,yi1 dshmoinih yms1,h3dm9 t in the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A for 5.0 h. How mu4+7/zvcjb wm6kcl zg6ch 4 6kwgmcz6c7jv/ bl +zcharge passes through the battery?    $ \times10^{ 5}\;C$

  What is the current in ampe0fh8rw(k8ho ta/q fl at6m4g7 res 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 currn*7 ;4inh0 z7xs w iyi2biu9sbent of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of cur ku5g(th ,9im (quyn )v o+kr;sv1b:hprent through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A whel6:c eqste4l* nd:6nwn plugged into a 120-V line.
(a) What is its resistance?    $\Omega$
(b) How much charge passes through it in 15 min? (Assume direct current.)    $ \times10^{ 3}\;C$

  An electric clothes dryer has a heating element with a resist hyejjb0 7d)b1ance 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 0 u8kh,rqxjrp:(t s(abulb 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 line carrying 2800 A (Fig. 18–34).a9f1d ydl*nnww4kmclbk 265ju8 g)q1 The line h4)dk5l mn2b gnjc k1 *9q16wf8yud alwas $2.5\times10^{ -5}\;\Omega$ 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 Akdht5oqv- /p. :kpr, w 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 curzfcl+ka- 0 bh6rent 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 tu,*8r aokt 5 0ozzc;3ycxt: xjbngsten 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 iovt/6;d2st qz n diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.s/s;uw j.q95-b nq lit0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in dijbtqsiw/u.s l5; -q9nameter.   

  Can a 2.5-mm-diameter copper wire have the ;sc1bm t;:gwme15ro hsame resistance as a tungsten wire of the same lengt:; gr;s51cm ht1meowbh? Give numerical details.    mm

  A certain copper wire has a resistance of 1 r(yt5mr oggj+tmb8 ;$10.0\Omega$ 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 tzcac0ql f* h;1fct;vq+m elg5qb)-) wemperature of a copper wire (originally at a)vefcwlz01 5mfhbt;-;*+q) qccl qg$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivr 0dp31qs*s.t3z q pfaity as tungsten doestszpd31 s.*0rpfa3q q at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb ha)osvtk,.jx qi;v5 m1ls a resistance 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 copper wire (u8gu aq7k-bhb:f9 8ptm sed in 15-A circuits). The wire has diameter 1.628 mm and carries a 12-A hpbfqub9a8 t7 kmg 8:-current.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm0ozg9q8t r1u)x j hk3v, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for curq 8k1)0rthjv3ug 9 ozxrent 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)j,r vog wcp)ckyj5x:it* 5 a; the same resistance. If one has twice the length of the other, what is the ratio of the dia)ij ay5) xto:cj 5crpw gv,*k;meter 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 p8 gasq o)uha09txpg);vm x9r6recision 10.00-V power supply, and a current of 0.4212 A is prexsoag9 qvg 68th0mx 9ur; )ap)cisely 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 hv :2t22fnkb.pbham0m of copper followed by 5.0 m of aluminum, both of diameter 1.hh :2p bb22na k0vft.m0 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 th .gk*yqds i2e5at the value of a resistance not change with temperature. For example,ey.qs2*5 dig k 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 d ll4 an9oj87d,5/ nyyjp/9jhi+if ugdesigned to produce 3.3 kW of heat when connected to a 240-V source. What must be ipg9u 8,ny9dlh74/ o5i+j j/adynf jl the resistance of the element?    $\Omega$

  What is the maximum power y b-nf-(zaq(+ a,;h wwha1ufaconsumption of a 3.0-V portable CD player that draws a maximumyh n(+a-;-,abw w(auza qff 1h of 320 mA of current?    W

  What is the maximum voltage q83 5jnr 62h;pnlsr opthat 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 connee/fyvhg mqzw5 -(k0 3pcted to its proper source voltemkyp5zfq -/ hgv03w( age 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. Calculat3f1,uty ct4;i n *hay/a )dhcxe
(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 settin +hlt*r e/tnv/gs: 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 electricity is delivered to homeep /307 jhxw3y9lsixi0jxk 4bs 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 7540k pj3sy0b/3hxiixwjelx79 -W 120-V bulbs? [Hint: assume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy;c+e0sb lly1n5yqw; gz a:pg, does a 550-W toaster use in the morning if it is in operation for a total of 15 geq;5w 1y:,+l;ypng b 0zsalcmin? 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 leav1e dquv88hel/e a 25-W porch light on day and night fl1e8 vedqhu /8or a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batxd ,5nrc ag:sxnp6gm /s(xz78 teries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when turned on. r (snz 75g,smcxpgnd6 x8 :x/a
(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 amoun+pty 01j:w)htmpz8ij t 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 lightbulbs, connected to 120 V as in Fig. 18z(9w::xa *g jjtmym7 got.kstp2je89–20, can be used without j *y.p:x(s92tajm gtwo ke7mg9:jt 8zblowing a 15-A fuse?    bulbs

  An extension cord made of two wqz+jqvr1+mcy 6znmd j75xt, cu;0 0 ooires 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. How much power is dissipated in thzj +1 0qrqjnz6y,t5 0ocxcu;mo7m+v de cord?    W

  A power station delivers 62fc/g-ug w5e6:4l c2d-yfc su g0 kW of power at 12,000 V to a factory through wires with total rgy gfle-ug c:f 5s2u -46/ccdwesistance $3.0\Omega$ 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 ra;*l+klm. +c i/yuwx owte must cooling water pass over the coils if the water temperatur ko*;/u +l l+m.ywxicwe is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to8 df+iego .:p 5hecfu)nj) 5qo heat a cup of water for coffee or tea. If the heater can heat 120 mL o:f.5i ege))cd+u 85 hq fnpjoof 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 cur7ixv+0u s *96d r+lfg/sek gsv;dzm ,jrent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 18ex*l-yv* / voz 7fj,uemsnb 9vcm+0 5c0 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 resistann wk + xm7x3,lu: a:s.*uivgzj(p-qwx ce 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.d8)9gjkbsa /b What is the rms voldkasg)bbj8 /9 tage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected tansx w7hql ).) g*zm(vo 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 by a 3.0-hp pumyacw 6t(aw33 zkd5.)r d2t picp connected topw aca(rdtct3 .w 3)kz562diy a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connectedchykjc-ayj e5m8z4u39a c2*y 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 carr2x /oqt r*zwjmf0ma14 iq3p*m ies 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 22,3o gx:1j6 ep: raresjkivaqr880; kbnwi-y;.0 mV is applied to its ends. If the ds k;ex vr8ay i ron-ab ,;3wi8j:kqr:e0g6j1prift 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 atmb4l9je gzcr m(,z fi ;kru8e za)3g.r;osphere, $He^{2+}$ 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 atmohq ;c6-t1 fi ;2ojp7 rdzpttipnq:(l9s4vx:bsphere, $He^{2+}$ 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 tho9 0k,uy*lmyc e 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. The action potential is detect7 + f9ulsqhauk +8.n1m etip2hed 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 l+uhp9. hq+ 1san2fkmie 8t7ualong the axon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much energy is required to transmit on1n ex/l-si b2we action potential along the axon of Example 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 requnbe wx-li/ 1s2ired for $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action potey- d+8y vjp3;zhtykk6(/zsx rntial, $Na^+$ 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 1.0jtgy xx 1ww,xa)(g b,,0 ampere-hour?    C

  What is the average current drawn by a 1.0-hp 120-V y 8:qlwbmr6gqviv 6s c09:r;j motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. 8jh rsm a9r.f/c3zj6y If each of the two headlights uses 40 W9hr msj8rf jc6. 3/yaz 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 at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of axgs*)s;b 0er32ce m: j(ihx/ iuky,vz-jez.z 110-V, 1500-W heater is 5.4 m long. If it is made of ironzu g,h-*vxs(jez)/2e zic;:jmxy rbi3eks .0, what must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the rei1r44f sd6 dw o/7 zw9vu;snt:,hunkbciprocal of the resistance R; ur6:,ohzf4/v;di 7n94udws kwnt b s 1that 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 abouf r/)e8mywt 6qt 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 rw)/qf8t my6e two-wire line of 0.50-cm-diameter copper wire, estimate the cost of the energy lost to heat per hour per meter. Assume the cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular household uses a 1.8-kW heajr v( ix6dl +*t:u4epzt0dh .cter $3.0 h/day$ (“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 cuc+p kt uj a))3cjg3iqy,x9zj :t in half and the two lengths are wrapped together side by side to make a thicker wire. How does the resistance of this new combination cc3jj)u xgkci),9t+pzaj :3y qompare to the resistance of the original wire?

  A 1200-W hair dryer is designed fo(fgc0-alr ,tx 0/ lxlgr 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 th) br65jp(t2hue r n-io8mutq8ick enough so it does not become so hot as to start a fire. What diameter must a copper wire be iuj rm 5) (68 2ob8he-upnirqttf 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 y5zu ;zvvvyc78)h3w p given by the equation $I\,=\,1.80sin210t$, where I is in amperes and t in seconds.
(a) What is the frequency?    Hz
(b) What is the rms value of the current?    A
(c) If this is the current through a $42-\Omega$ resistor, write the equation that describes the voltage as a function of time. (  sin 210 t)V

  A microwave oven running at 65% efficiency-2m.awg,5b-rl kredug pn v)*8w g lc1 delivers 950 W of energy per second to tbgl.v1wgr 8*d ke5cm-- ,ln )pua2rw ghe 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 two different cond2qmd0-x3h.d dl +e dxwuctors made of the same material. One conductor is twice as long and twicdx0d-+mld3w qdex. 2 he 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 du):8i m.ckjk 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 hooked to a 240-V source. 9.o ye b6r+pm igdom/m4hi3tmg,z7 o*
(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 its sourcqu44 4cq2y;lkrjn3ulq(nl 8d e of energy. Its mass is 1560 kg and it is powered by 24yr 3unc4j l du8qlq2 n4;klq(4 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 r8phves9bwo k/rb+wpi y (*8g5esistance 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)7 ,czb ef-uxf3 is designed to carry an 11-mA beam of proton-3ecx7fz u f,bs 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 12 A at 220-V ac. The c 4hh 8k4lr i8psgq ux2rcj*41ronnecting cord is copper wire with a djq4pr4c s 2rh1ruhlxi48g* 8k iameter 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 Vty6-v,oya1; sgy*nu5 gb,eo h. 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 of the wivt1en,; *gy o6b 5ugaoyys-h, re?    $ \times10^{ -4}\;m$

  In an automobile, the system v8 eojd4g3cqk 7oltage varies 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 k gc8j37de4oqdelivered 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 app+3q1ss s8 luwklications. Lightbulb B is rated at 12 V and 40 W for automotive applicatio3s+s81l qswku ns.
(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 tah4 v kw:03lluw:kf y,o connect a set of appliances at 120 V, which draw 2250 W of power0h akvwfwy ,34l:ku:l 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 d76 u/,,.jcfzbhb hkna iameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the resistance of 10.0 m of this 6 ,f/z h,jnch7u.bakbpipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its length double ei:r gax)c6pwg;n((ms, by c;e:r)wi mna g(x(p6gwhat factor does the power 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-0cij u5z zsfn3ln+o l uyq1g/g+3tg(e1wr p. and 3.2 V. If it5 cg0trygzio -g3.uesf/l(pn1+n lq+3uz j 1ws resistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$