What quantity is measured by a battery rating given in ampere-hou7:i m 3)ge8 wdroj30rnsv xefbj,j7e2rs $(A\cdot H)$ ?

When an electric cell 2nbs5: t g-6*,khyasd4m k xbfis connected to a circuit, electrons flow away from the negative terminal in the circuit. But within the chb- ss*m 456ykag,kn 2:bftx dell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battery current, battnfkfg(sc1y ;mi51 ; xiery voltage, battery energy, battn 1mi;xfg;f is(y5kc1 ery power, or battery resistance? Explain.

One terminal of a car battery is said to be connected to “groundn u cn7m-h(j92qh8 byn.” Since it is not really connected to the ground, what is m-ynub jhn28n m9hq7 (ceant by this expression?

When you turn on a water faucr2 31aoguc umyq827gd et, the water usually flows immediately. You don’t have to ogg2r uauq7 328yc1mdwait for 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 an aluminum wire of the same leniqi8vhk0er u/) wd zmzwc2 j; 3ud(0q4gth have the same resistance? Explev uqch/d (md2kr8 i4)w3;wz q0ui 0jzain.

If the resistance of agbp +*kd3 4f2v kqu4dd small immersion heater (to heat water for tea or soup, Fig. 18–32) was inc 4bu3gvdk*q 4 +kp2ddfreased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of cq 8vks5jt2jp,arbon has sides of lengths a, 2a, and 3a, how wo,j j52v pst8kquld you connect the wires from a battery so as to obtain (a) the least resistance, (b) the greatest resistance?

The equation $P\,=\,V^2/R$ indicates that the power dissipated in a resistor decreases if the resistance is increased, whereas the equation $P\,=\,I^2/R$ implies the opposite. Is there a contradiction here? Explain.

What happens when a liuo/ (xlrgs* s;w6r yz4ghtbulb burns out?

Explain why lightbulbs alcm/ 7yp b*oo7mh3( jchmost always burn out just as they are turned on and not after they have been on fomh ( hooc/3jcmb*p77yr some time.

Which draws more currenpv hx4vg5coh3o( t)u,t, a 100-W lightbulb or a 75-W bulb? Which has the higher resistanch5uh4t 3, v(vg oxo)pce?

Electric power is transferred oyb4(imm 9jzw5v40wf kver large distances at very high voltages. Explain how the high vo45 vj z 4m0fki(wy9bwmltage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why ispk73j47t ukby it dangerous to replace this fuse with a 25-A p kkjb4y7t3 u7fuse?

When electric lights are operated on low-frequency ac (say, 5 Hz), they flicker a7d3j v e;e+/q8hwetu noticeably.;+uha8 3/qewtv j7e ed Why?

Driven by ac power, the same electrons pass back ah5kjjjkd25 226c gkgind forth through your reading lamp over and over again. Explain why the ljd62ji5h c jkkg25k2gight stays lit instead of going out after the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. c5mdpc8. ds;edxs0lt+qyd 1uz.:*ba Immediately after the toaster is turned on, is thepdud0mle ;t*yaqxss:1..+cd d8cbz5 current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up ina h ak,ky.kgifq;u* ;; a resistor? Explain.

Different lamps might have batteries conncm1 b- xfy4w3nected in either of the two arrangements shown in xywbn31fm - 4c
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flouok7- t/n 044q awzei2 k4:u)zbxbxuiws in a wire. How many electrons are flowing past any point i07w: inxubt44 iae-uz x4b o 2kukqz/)n 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. Hoa35 jybfj;2 gew much charge passes through tg53aj;f2bje y he battery?    $ \times10^{ 5}\;C$

  What is the current in am nuj5h; -ly+ zcq7lo3speres 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 l;fj nvr5hkam+ 4ka(3if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 te7m7ryh/;ej t 1x qwy87t9pk A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A :zjt8lur;9.m 7l2n 7vkkibxm/a t k8fwhen 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 dryernw2pxyb s2yp ku2,wm+tag2 -7uk 7bo7 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 fp. 6wsafiwr;irq)o-5abn ( .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 carry(, azuf+ o0jbplhz4o4ing 2800 A (Fig. 18–34). The llj4f oohu, a+z( b4z0pine has $2.5\times10^{ -5}\;\Omega$ resistance per meter, and the bird’s feet are 4.0 cm apart. What is the potential difference between the bird’s feet?    $ \times10^{-3 }\;V$

  An electric device draws 6.50 A at 240 9e1jg ij3 pa9nV.
(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 0.60k;fp k7kn 0sr0 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 1.00o3k9xxis l)c7 -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..-k qru)/l/nsf4 tezd 5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire 2.0 mm i,o6d2- npo leln diameter, to 20.0 m of copper wire 2.5 mm edonlo-l p,62in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tungbnf 1vg6l:ygg zacs/5 2y:)xmsten wire of the same length? Give numerica)5ynlg a :2z6/1 fcxs ymbgg:vl details.    mm

  A certain copper wire has z -fatg(vf6l petjitgx140 1/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 temperature of a copper wire (originaio- ; aq5e,qlllly atl oei,-al;5 qq $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivity as tungste:9zp v 0fb2 wk(0kkecun does:pfwke0 9 ( c0uzkvb2k at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistsel, ,:qrc;nv p(xx a6q -l6dtance 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 le2byv agj )vo2v1(h2vt ngth of household no. 14 copper wire (used in 15-A circuits). The w21 v(g 2t2vv)vy jhbaoire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengtisstw+a 8* 8ojs:tqi0) ny oh-0,caxnhs 1.0 cm, 2.0 cm, and 4.0 cm, lyincs-it 8 *wqj snyax0so+:0ah8oi)t ,ng along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for current that passes through the solid in
(a) the x direction,    $ \times10^{ -4}\;\Omega$
(b) the y direction,    $ \times10^{ -3}\;\Omega$
(c) the z direction. Assume the resistivity is $\rho\,=\,3.0\times10^{ -5}\;\Omega\cdot m$.
   $ \times10^{ -3}\;\Omega$

  Two aluminum wires have the same resistance. If one p6ru bmr;jk )0has twice the length of the other, what is the ratio of the diam6r kj mp;)ub0reter of the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is e*j+y xew.n f :i/x*jrconnected to a precision 10.00-V power supply, and a cifx wej./ yx*njr*+e:urrent of 0.4212 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 consistq 9c lk9 gnb(i//iwu c+1)zxvss of 5.0 m of copper followed by 5.0 m of aluminum, both of / c( z+gi9wn cli/ u)sxqbk1v9diameter 1.0 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 that the value of a rp1xhbcn m0k:jta*,l*x6a-o zesistance not change with temperature. For example, suppose you made tn-xak oam hl1pb,0*xzj 6 *c: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 of xz7rinr) s8e,h (iss0heat when connected to a 24 8x i 7reinrshsz)s0(,0-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of 1ho6v7rjs8v g a 3.0-V portable CD player that draws a maximuh68sv7gjr1 ov m of 320 mA of current?    W

  What is the maximum voltage that ca d2satjkkk: t7 nfsms2pa8n,52+v, pan be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current t uulv /jzd/:jh1s 5yo5hrough, a 75-W lightbulb connected to its proper s sudu5z1/j/yolh 5jv: ource 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 heanda lxou+,odmk7r9 4 :ter is rated at 110 W. Calculate
(a) the current through the heater when it is operating,    A
(b) its resistance?    $\Omega$(Round to the nearest integer)

  A 120-V hair dryer has two settings: 850 W and 1250 W. fn:be:ejl 1e l *7fs.e
(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 ntn,fpx b 1(4c*xzn e;in Europe, where electricity is delivered to homes at 240 V. If you use the lightbulb in the Un p(x4 cf1zex*nbtnn, ;ited States at 120 V (assume its resistance does not change), how bright will it be relative to 75-W 120-V bulbs? [Hint: assume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W vp7jl7 xkt)x7og)k q5toaster use in the morning if it is in operation for a total of 15j)7p xqg7tk75lkxv o) 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, wcm r31mo0(zec k:iq g*hat does it cost to leave a 25-W porch light on day and night for1 c30 c:mmz*r(ioq gek a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries c9cu mu xfl4*6zonnected in series as in Fig. 18–4b (Fig. 18fxu46l* ucz9m –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 stored in u(d g*4v9jnb. .aaa. .wzvdwq a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connected to/:y5 1zkz4 ;xem w1dpm2q elnd 120 V as in Fig. 18–20, can be used without blowing a 15-A fusz1m;p /d neexlk4yd1w 52 mq:ze?    bulbs

  An extension cord made of two o55-6xv(emkl ntwa, b;gr8;y k0pft hwires of diameter 0.129 cm (no. 16 copper wire) and of lengto5 ; 8wtb5tkxl 6hmna,y-rg0v efk;(ph 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 the cord?    W

  A power station deliverryq p+b hud1zy fzt))7-0bvt)s 620 kW of power at 12,000 V to a factory through wires with total red)0u1t7+r )v-p fbq )zhzybt ysistance $3.0\Omega$ 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-V4n*8jw c3axyg g89lor6dxw6 k line is 17.5 A. At what rate must cooling water pass over th *lk4a66jyd 8g goc9n8wwr3xxe coils if the water temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater ei ewa xyde7 j6:;g8j5g,60yvcka f3 ecan be used in a car to heat a cup of water for coffee or tea. If cy a:g360vjaj5,e exkiewe7d8fy 6g; the heater can heat 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 co + p0-bvc-4q movp*dfurrent 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 acrug f/wusf,7 +wie9k:*x svca3oss 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 p rnflk2 1;dq8ox /xr7of 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. What is t*tyz ip46 1 +/cal.fhrzbgu )ghe rms voltclg4aug.y +pz/ i)*bhtz1r f6age across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected to dqt( e;f+(fz /uohbak5vx(q , 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 bhe* :8k ecu4wkn*xstgkis 98t*1oeu +y a 3.0-hp pump connectedu1kni t wg keo8shu 4c** kx+s9e8*t:e to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connectphn+f dyj x;6asj-9 0jbsq1g, ed 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 comr6c 2ebnma m,+xgai*7kli z536b,hji er:a 5pper 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-mm-diameter wire carrie j1oryi7 2i2jbs a 750-mA current when 22.0 mV is applied to its ends. If the drift jyo1ibjri22 7speed 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 pj t)3t,f-xnzj*f t ru z*7*1kdt(v ulatmosphere, $He^{2+}$ 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’s4xqr *d:n)xzv 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 lwskh y 1y58/oelectric 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:yjm, i1 qtxi; pulse. The action potential is detected at a point 3.40 cm down the axon 0.0052 s later. When the action potential is detected 7.20 cm from the point of stimulation, the time required is 0.0063 s. What is the speed of the elexqy :ti, j;1mictric pulse along the axon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much energy is required ns; fzr79l-i :qvjdr7to transmit one action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the r7n-i 7dlj;f9s qrvz: 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 pot g h3av9iiq: wbr;g0lo1)u 4xfential, $Na^+$ 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 ampere-hourgtahfvc e h,ahgom +-/1ym 41)?    C

  What is the average curoicuv t;(;/1v98.qaj z2lwm9hxs db xrent drawn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of the t2; cq+pm7g dthwo headlights uses 40 W and each of the two taillihc7q ;dgp2t+mghts 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.:ctrvy:bor3w dw5p 71 If it is made of iron, what must its diam1dro :3y5r7:ptb wcwveter be?    $ \times10^{ -4}\;m$

  The conductance G of an objeo(v0ajljieii/6(n x it3 . 5btct is defined as the reciprocal of the resistance R; o.(j( 0/ivtaix3li i5 nteb6j that 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)vu*j vh+w)vo about 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 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 electric*)o vjvw vh)u+ity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular hous yhlx51 *tggh4 */jmcoehold 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 and the two lengths are wrapped together sxfys7 (x+pq e4ide by side to make a thicker wire. How does the resqe ys4p (f+7xxistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is desip0k/( vo1cfw kusqd u-:xe5s6gned 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 not bzf+r;gsm-w 7zu8uj g s-:2 cav,yyn2 eecome so hot as to start a fire. What diameter must a copper wire be if it is to carry a mga 2 r ys8fg;eu--7:j s n+uz,v2ymcwzaximum 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 ta-n1ec vhe6 7equation $I\,=\,1.80sin210t$, 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 delisf kieh50 qaxo.9) gw,vers 950 W of energy per second to the interior. Fifs.hweqa 0,k9g5x o)ind
(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 conduc(bnb s),*vzmbm 6s6mre ong23 tors made of the same material. One conductor is,s6en vbsmnm mg 6* )(ozb2rb3 twice as long and twice 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 used to heat a roomd0pxcl(0g:leko6 tp2 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 lcz2;8*(x yxsy acm- xsource.
(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 usevz-*6mttc 6t:7l uidr of storage batteries as its source of energy. Its mass is 1560 kg and it is powered by 24 batteries, eamr*i:utt6 t6 7cvd z-lch 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 resistance of qcpj(2meyn -dn1ttf4)s -f o7$12\Omega$ 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 (Illinoi) ozbdc1 8mur9s) is designed to carry an 11-mA beam ofbm 8)c9ozru1d protons 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 12k1x:v f chrj-0 ci:qj8 A at 220-V ac. The connecting cord is copper wire with a diameter of 1.cv:0jc1:fq8 jk xh i-r628 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 connev5 ;ghfia7lv*0or; s;n m4ldh cted to 120 V. The heating element is a coil of Nichrome wire. When uncoilvfgr0 v4;*5sdolm7l a;inhh ;ed, 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 varii6d+fcr,e1tckxp8 g1es from about 12 V when the car is off to about 13.8 V when the car is on and the charging system is in operation, a difference of 15%. By what percentage does the power delivered t ftge1,8xi pcr k6+c1do 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 application-v eok1q+eem7s. Lightbulb B is rated at 12 V and 40 W for aute kq+ 1moev-7eomotive 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 Vq+ud,:7;s5cr d ghuuhrz v+3n7b4ib e , which draw 2250 W of power tuhb3b7g7+u ;cn4 q+ ,shd:iru5e drv zotal.
(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 anrc kjzc,7kc(xt0a o39 rh6idjk/+ ly0 outside diameter of 5.00 cm (Fig. 18–37). What is the resistance of 10.0 m of this pipe/drtcjkxcar, j io0 kh9 +c63y(zl0 7k?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uni wjxbn xx2f+x7zco4y -53kg h.formly so that its length doubles, by what factor does the power dissipated in the wire change,.zxw j3yb+ xocg2- 4x 75nxkhf assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operates at 0.20 A an 8ov9nk.da bjt3 gui96d 3.2 V. If its reidt8bovan u .99 jgk36sistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$