What quantity is measured by a battery rating given in ampere-hours rmvwqm:;5j s3sf 9.kx 5:w tlz$(A\cdot H)$ ?

When an electric cell is connected to a circuit,5qdr, ; z ;kcumeyc6lm-tu5t3 electrons flow away from the negative t ku qzytl5 cu emmc-r3t;5d;6,erminal in the circuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is ope 9 orb)rh4e4jdrated, what is being used up: battery current, battery voltage, batter 4o9bdj4)hrrey energy, battery power, or battery resistance? Explain.

One terminal of a car battery is said to be connected to “groundt (5bud*ew/ nvcm:5ys.” Since it is not really co(vnuw 5t/ bs:5edm *ycnnected to the ground, what is meant by this expression?

When you turn on a water faucet, the water usually flows immediately. You donjmst sxz .e7-xq1 )su3’t have to wait for water to flow from the faucet valve to the spout. Why not? Is the same thing true when you cosx3-t1s). zs qum7 ejxnnect a wire to the terminals of a battery?

Can a copper wire and an aluminum wire of the same length h2 -mz9dz*qqjsb9/ st fave the same resistance? Ezz-qf md29b s9jtq/s* xplain.

If the resistance of a small immersion heater (to heav.vz*kf;fjail998whqc r 8q qmx s84+t water for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the heating process? Expv8 lsj4v w8cr98.a+fq;z ikq9xm qh*flain.

If a rectangular solid made of carbon hashb;tkh ss k(9y75(rwd sides of lengths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (ay5s9tsk (brwk h ;(hd7) 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 li d3rc 8gj(alrk/r22ki:4gi jsghtbulb burns out?

Explain why lightbulbs 4f) h-te7l x*lioa l.p 5a.outalmost always burn out just as they are turned on and not after theye -at l.5 oxu) thlpi*o7l.f4a have been on for some time.

Which draws more current, a 100-W lightbulwr8czp ; oo2aj7*g.xl b or a 75-W bulb? Which has the higher resistagw.jzox2cr*a8 l7;po nce?

Electric power is transferred overj4ykkhfc:o j8 ,9 vf6x large distances at very high voltages. Explain how the high voltage reduces power losses in the transmission lines.k: 9846 vjfcjok,xyfh

A 15-A fuse blows repen(h4tzw0i fqsg;. 8g8 j fea7 )fn,ogcatedly. Why is it dangerous to replace this fuse with a 25-A ga4. qt )igon zs n0w;, fgf8chjf8e(7fuse?

When electric lights are operatej, b0vn jv4fm* 4jn+ hhnds2t+p86lkcd on low-frequency ac (say, 5 Hz), they flicker noticeably. Whnjhsj4 mn+vk+vp hn4cd 8 6l2jt0*f,by?

Driven by ac power, the same electrons pass back x+iyd 32ijeu.and forth through your reading lamp over and over again. Explain why the light stays lit instead of goid 2.i+3yju iexng out after the first pass of electrons.

The heating element in a toaster is ma7wy3j4o 5yqup9 ad fj.de of Nichrome wire. Immediately after the toaster is turned on, is the current 5y .pqj 3oyju79fd aw4$(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up ind6 5djl c.vk*n a resistor? Explain.

Different lamps might have battw)z n (uc0)e7 ldlldzc o,w1l2eries connected in either of the two arrangements showlz,ll 2w( e)1u)zcd woc07ndln 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 poivjin)w496m 7 riv1udbnt in the dj1 i76nu4vb)m9wrvi wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a cu. hivm(,eb2n i l5lhewo6nu v i(j,*-lrrent of 6.7 A for 5.0 h. How much charge passes through the batteryh j(boi*nul.,(, vnl hmwe 6v25ei-li?    $ \times10^{ 5}\;C$

  What is the current in amperefc)sl9z 5c0kf*6 clhds 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 of 4.2 A zrn6ffh7d6 wq nf l+bk.2;p2 (ypqam+?    $\Omega$

  What voltage will produce 0.25 A oa q7: mra6:auqf current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-V lhs5 zxu,eh,0cca)7 hk ine.
(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 ha1wyu+ l4ln ppvmp1f8 6s 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 connectnh v4l9wmgby7m 0 lv6,5thky( ed 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 line carrying 2800 A (Fig. 18–34). dfh7p5 uxmqmgb /13, jThe line hasxm,fjg35m d7 q/p1bu h $2.5\times10^{ -5}\;\Omega$ 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 aw)0+ nex 1ll30mp rjgsksp s+w)gc; /rh9*bv mt 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 pmudmnb/2 .f1/rp:xr current 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 wiresrfd6y v- 24qd)yft s)md ;ap7 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 diametm) ;pkzha1. eoer?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire 2yeky: s8mjb , xqj/z.2m*q q/p.0 mm in diamet:p kszqym* mqb 8/ex2 ,qjj.y/er, to 20.0 m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tungsten we0rzv.h v,oc r ljt0)0ire of the same lengr0.to0vr0ljecz ) h v,th? Give numerical details.    mm

  A certain copper wire has a resistance of .zll-0 6*sh*yzaf ijo$10.0\Omega$ At what point along its length must the wire be cut so that the resistance of one piece is 4.0 times the resistance of the other? What is the resistance of each piece?
$R_{short }$   $\Omega$
$R_{long }$    $\Omega$

  How much would you have to raise the temperature of a fb /u z/ueppkf9p2 d7oq+p j98copper wire (originally atpb uppz/9qe ufp2 j+f7k/do89 $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what tempe 14ufoif-h yh 9wd(;4kexflc2* o/m* blrgwd0rature copper will have the same resistivity as tungsten does at **id2rxo9b kd hc/;(wh1 ff4u4-lef l0 ow ymg$20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a ;2 m4vnwdre1rresistance 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 gq qzy6pxc4- 72vlk:3 otr7zccopper wire (used in 15-A circuits). The wire has diameter 1.628 mm and carries a 12-A currqg4: -x77t32zqpyc kvor zc 6lent.    V

  A rectangular solid made of carbon has sidepbrhb y0w 89d;s 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 curd09b;bpwr 8hy rent 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 twice the lenu8bp h3oe j;2ay, xl6wm /9uzigth of the other, what is the ratio of the diameter ofub,lum iw2/ e;z9ayxj86p 3oh the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum(wdb)r vv6+gr /.63lfyxye(uwzh;y9hk n ci; wire is connected to a precision 10.00-V power supply, and a current of 0.42+ebf;96wi nv(rwhy yu3/gdyl6xv . r()zhk;c 12 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 consists of 5.0 m of k)0 gvxo6t4 yk;rv7kd copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage dktox7kyv)vgrk; 6 40 difference of 85 mV is placed across the composite wire.
(a) What is the total resistance (sum) of the two wires? $\approx$    $\Omega$(retain two decimal places)
(b) What is the current through the wire?    A(retain two decimal places)
(c) What are the voltages across the aluminum part and across the copper part?
$V_{Cu}$    V(retain three decimal places)
$V_{Al}$    V(retain three decimal places)

  For some applications, it is important that the value of a resistance not;cjssa 0 41bp)g5c bcc change with temperature. For example, suppose you ma;4sa b)c0jbc1pgc cs5de 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 procg;)8 hwhi8i 8rzxyc 7duce 3.3 kW of heat when connected to a 240-V iczi7 ;gr y88wxh8c)hsource. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player that o3q/j ho:q79igg0q4 uq5p bmmdraws a maximum of 320ui439hq:qqqmo075 bmo p gjg/ mA of current?    W

  What is the maximum voltage thaw 8qbpcc/jv03 o2gz:xt1oar/t 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 cbf1yp d.w:./tq4hc ev onnected to its proper sourcwhcvfp eqb/t d :.14.ye 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. Calcuz,i6 cr+w qu/olate
(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 1250cj-tod 2 *ak5g 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 lightb9k3*ycj nwg0yulb in Europe, where 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 change), how bright will it be relative to 75-W 120-V bulbs? [Hinw njy3cy0g 9k*t: assume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster ul5ec 3k4)i hekogn5v )se in the morning if it is in operation for a total of 15 min? At a costk)3n5 l c gkh4eev)5io 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,ued ckmk pe*a9jrm4ks;) uolj20 -a ;/ what does it cost to leave a 25-W porch light on day and night for med r;pka9 24j lu-k a/jk *0sou)cme;a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected in series as inleo788s0eiz8 s:uj5;btib mn Fig. 18–4b (Fig. 18–36). The bulb draws bb87o;i8jnlt8 ium0z:5ss ee450 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 shcql 4x.2he9l -a7jq stored in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connectthso/ r:pl-*os6b9v j ed to 120 V as in Fig. 18–20, can be used without blojb l ssth6/opr:9v*-owing a 15-A fuse?    bulbs

  An extension cord made of two wires 0:biar9 .z fblof 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 lifbb. 0z9:ilr ane. How much power is dissipated in the cord?    W

  A power station delivers 620 kW of power a;nf ccb v6) pegm y/ rvzr4hckj.8l-86,.fwuit 12,000 V to a factory through wires with totacl bc ze;.68frvifw knm/ 6 p-8.uvhg)r j4,ycl 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 conne1v2egev* g, zrcted to a 240-V line is 17.5 A. At what rate must cooling water pass over the coils if the water temperature is to rise by no more thanr ez ve2v1*gg, 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to heat a cup of water for z:tsb-s6ip. ccoffee or tea. If the heater can heas-6z . bpc:stit 120 mL of water from 25$^{\circ}\,C$ to 95$^{\circ}\,C$ in 8.0 min,
(a) approximately how much current does it draw from the car’s 12-V battery, $\approx$    A(Round to the nearest integer)
(b) what is its resistance? Assume the manufacturer’s claim of 60% efficiency.    $\Omega$

  Calculate the peak currec7 wyc tq .0 1wh+wsejt24d;zcnt 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 ac*p 64 n64sk6 ztfpxjrgross 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 theg5tzp 2 7+bxin $120-V_{rms}$ 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 anhw5e;rsc ggcv 31v1t ru(wr28 alternating current in a 1500-W device is 5.4 A. What is the rms vol ew2 cgus 1gtvrvh 5r1;rwc38(tage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connectr05f :payd1 rv(c5k0 crvtvf, ed 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 instax+6/ zce nlt3intaneous power dissipated by a 3.0-hp pump connectedcnz+el x 36/it to 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 a-e c e6zis2l8fxcw/:$240-V_{rms}$ 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 coppe4x +n9lc,btdh:6bq6f4cipcvjv; + mg r wire carries a tiny current of $2.3\mu A$. What is the electron drift speed in the wire?    $ \times10^{-10 }\;m/s$

  A 5.80-m length of 2.0-ajdg 9 es9d2y(mm-diameter wire carries a 750-mA current when 22.0 mV is applied to its ends. If the drift sja 9 ey(gd9d2speed 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 7ho-0c xyb0u qEarth’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 t lc1,zte6s4mo he 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 

  What is the magnitude of the electric field across an axon memn+ y577pas3mj4q ibc / whijp0brane $ 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 j)8ol;z7sqzg:dp3nl 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 thjnp: dl3zosg q)l8z;7 e 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 potential along /op 5,sfjw)+kz nan q*the axon of Example 18–15*s n)5,q+k afjwzon/p. [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 poten pekx1+p)ozx.tial, $Na^+$ 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(q e.irw5/s be ampere-hour?    C

  What is the average current drawn by a m,l--qzf5g e.w p)kl clg5s3 d1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of the.-bg0 s;2cpao sv v:moe pw d+vs337tv two headlights uses 40 W and each of the dps.oog;:vm3-vbav2te +vc 30wss7p 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 a 110-V, 1500-W heater is 5.4 m long. If it is made of n3-.kcw/gr e/kskut/ iron, what must its ds/w k3n.krgu-c // etkiameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object m vd01iro/cuq9(, zvuis defined as the reciprocal of the resistance R; thuqdzu1 i,0vr/9o v(cmat 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. Suppluooht-(/ p d(g(6mmt ose that instead of using high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a two-wire line of 0.50-cm-diameter copper wire, estimate the cost of the energy lost to heat per hour petho tm(o-/ l 6(g(dupmr 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-k,r2 -a: 3 )nqp8h* fkbtp)ozywak5cgq(9jb mzW 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 at04mgys -r-oy re wrapped together side by side to make a -smy o4rygt0-thicker wire. How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 117 V.wqf.hbvwv1: i.xk/p1 y,ge n1
(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 thmf:f3-ddn su;ick enough so it does not become so hot as to std:f-; 3ufsn dmart a fire. What diameter must 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 gz14pyljyyf(sx, i1 5f k,5 qk9tkaj +riven 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% e2al10x, ggnxe+ur t goj7- .pi,2bfqqfficiency delivers 950 W of energy per second to the interior7. u+,pnq22ij-r elx gfq0 gb,tg1oax. 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 conductors made of thecsq91 czeeqwfka1pp1 nw(hc -/ 9+x* f same material. One conductor is twice as long and twice the diameter of the sea+qcz( 9kpw/f9p1n s*11ecefxc hq-wcond. What is the ratio of the power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used6- tju)dbu7dj 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. 66o stkx q3twkth7.5t d2-(llf)ck2fpd 0kgn
(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 battoa ;72+ymrpc meries as its source of energy. Its m 7cmma+; yopr2ass is 1560 kg and it is 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 remr+ o7, f ndkw9b-xlb::nsr6 qsistance 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 carry an ). -yg ocgnmmyay:..e11-mA beam of protons traveling at very nearly the speed og.ncmoaeyym -. g:y) .f light ($ 3.0\times10^{8 }\;m/s$) around a ring 6300 m in circumference. How many protons are stored in the beam?    $ \times10^{12 }\;protons$

  An air conditioner draws 12 A at 220-V ac. The connecting cord is2nhm10 cxsld9 copper wire with a diameter of 1.62 cdmx9l20s 1nh8 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 con8/k7m,bl tyc*6 tyvyo/q9mah nected to 120 V. The heating element is a coil of Nioyatm9 8l,tm6/ q cy7v* b/ykhchrome wire. When uncoiled, the wire has a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from about 12 V when the car is ofcxh19 egy wkli:j82p2f to about 13.8 V when the car is on and the charging system is in operation, a differej c2wg89xihe:2 1 kplynce 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 and 40 W for household applicat:2ca4ytj3 mh2dbmu w0ions. Lightbulb B is rated at 12 V and 40 bhw3m0 tyaj 2u42 mc:dW 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 appliances at 120 v-w0e0phr:wxc.i-my2 z 2zbp V, which draw 2250 -2r .zb 0mwx e :pyhi02v-cpwzW 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 diamet(a5yc,h +uuwp5xq-fw :vuo4aer of 5.00 cphq - xfuu,w:55yaucao+ 4v(wm (Fig. 18–37). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is strexxxl-s/j3 3ih tched uniformly so that its length doubles, by what factor xi3 3hj xlx-s/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 oped4;k9 c +k7y-yr. xe(kjidg hcrates at 0.20 A and 3.2 V. If its resisi -kdkj (4 g;xykh9 7y+dcrce.tance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$