What quantity is measured by a battery rating given iupdxs1w 8c-u:n: yra 3z3s8yu(u,q it n ampere-hours $(A\cdot H)$ ?

When an electric cell is*y *b+awkg +zuh20w ko connected to a circuit, electrons flow away from the negative terminal in the circuit. But withioy+kugza b0 k* wh2w+*n the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battery current, batterjqyp0ge; 5 p;ky voltage, battery energy, battery power, or battery resistance? Exp g;0p5jpq;eyk lain.

One terminal of a car battery is said to- :jrn o*c mdqurvc9: ov)rs*) be connected to “ground.” Since it is not really connected to the ground, what is mea :jcru)*s )mqv v-*ocnrd9ro:nt by this expression?

When you turn on a water faucet, the water usuallac1wex y3 + c:/pk0yamy flows immediately. You don’t have to wait for water to flow from the faucet valve to the spout. Why not? Is the same thing true wh m0yk3pw /ayx e:+cca1en you connect a wire to the terminals of a battery?

Can a copper wire and an aluminum wire oeb;um9j( :5;xtmbm uftk w p+3f the same length have the same resistance;wtmu ;kmt5b9p eub +:( 3jxmf? Explain.

If the resistance of a small immersion heater (to heat water for tea ory c scioikr23ez 8uuu*;bq8j+,c 9d+t soup, Fig. 18–32) i;su yq9c*j38 d iruubtceck+ +z82,owas increased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengthsjq gl6/fz- pnzpn1s ,kwrn15. a, 2a, and 3a, how would you connect the wires from a battery so a-w1rzp 5sq6 npnj/lzg nk 1f,.s 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 ligyq6h4+p mog y9htbulb burns out?

Explain why lightbulbs : b vneme-ip*)almost always burn out just as they are turned on and not afterib-) *en pe:mv they have been on for some time.

Which draws more current, a 100-W lightbulb ocb4dq wlm;0v.i,k ;jj r a 75-W bulb? Which has the higher res.4lb;jw i0dkv c,m j;qistance?

Electric power is transferred over large distances at very high voltages. Exg.n)lt spy)ddn9k; mnfd5s s. b0n(( oplain how d)ds.nbss nnko ;fngdt( m.)0(5ply9the high voltage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to repla2x75j i ivnqn1qn 3wm+ce this fuse with a 25-A fuse nvi 7mw512jnq3n +ixq?

When electric lights are operated on low-fy cou mf hv.7l* wd4g zn2j1y+*vo(ni7requency ac (say, 5 Hz), they flicker no fv2d7 y z*jw(culg.*oh7o mvn+1 n4yiticeably. Why?

Driven by ac power, the sam wl ndoj7m33;he electrons pass back and forth through your reading lamp over and over again. Explain why the light stays lit instead of goilmj h;o7n33 dwng out after the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. Im,e2 t:j ;w.rbwg ckcx(mediately after the toaster is turned on, is the current.w:(rec; b xwc g,2jkt $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a re2gd4ethlo ( )nsistor? Explain.

Different lamps might have batteries connected in either of the two arranzd f e0 v8rj(j3yp,z1mgements ,jfyz 3v(je 18dz0prmshown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How )efkv/ hizjpn- jg4mfkl 16u/5g3gi-many electrons are flowing past any point in the wireigg imvh/nj4-6 -zlu5egk1j f3/pk)f per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a ba/ctwe t8 ea8m;h.71dw 5txh rettery using a current of 6.7 A for 5.0 h. How much charge passes td1/ th 7 ww8etra8mte;e h.x5chrough the battery?    $ \times10^{ 5}\;C$

  What is the current in ecsty s8k,q+r c6d-: famperes 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 cuc7ncd+)f :p ./aau )fuiksis4wc0r(yd ud;3lrrent of 4.2 A?    $\Omega$

  What voltage will produce 0.21 le3l:7smtg7g o k5bd5 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-V lin ja 5r6hq(zd6x9h euq9e.
(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 i cupp7v7 b8lws 8d(ne t),aqlla (2o: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 conn2(6 uhhx;zxc7 xcw)j qf5s;gmected 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 electrie/9p2(npuf;( kqy onmc transmission line carrying 2800 A (Fig. 18–34). The (/ fop2pqn(n;kyeum9 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 A ay zo3exuh:.- cz*hwrq krg+f);ln.5st 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 15nkz6/ kcfk4hr+o vv a 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 wire whose resis avd5-(iq rkrpi7fvwq) q(.7ktance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m lens ewsi6w)v, v(gth of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of td8 sy8 v4dq6/afkub 9fhe resistance of 10.0 m of aluminum wire 2.0 mm in diameter, to dvbuy98a8ff/ qsd 46k 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 tungst6u;d j;jc8ebv en wire of the same length? Give j6dv;j8 bu;ce numerical details.    mm

  A certain copper wire has a rec ,26aao9eq pgsistance 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 : x f;yh/bybrlfjts.7-h5to7copper wire (originally at :xjlt;/t 57hbsb h- r7ff. yyo$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature cf7g1;r.jrdv o3 dlk5 t2rzy2v opper will have the same resistivity as tungsten doe2;v v3yrl 1td gd o7r5z2jrkf.s at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resist1lm4; ct+cyr7w qy 8rl+ pb:z y7;wzlmance 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 l hv k*v8r+l,ulength of household no. 14 copper wire (used in 15-+v*vr lh8 luk,A circuits). The wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides ozyhypx5 l(v(1w:po l6f lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, 5( (xwlhypzolpv 1:6 yy, 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 hasoi; ro/byl hshw);hn-+zc4, s twice the length of the zh-;c hs,b+ no4ylhir);/o wsother, 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 l; lw/it d,d+bxq5p- ,gh t(rcpower supply, and a current of 0.4212 A is precisely measured at 20.,d tqdg ;lxt(ibpw-+l5h,c /r0$^{\circ}\,C$. 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 c .fqx:b226juqg( qhmhopper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85qfjh2 qxq mg b:.(6uh2 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 resiaw8j (p:p y1postance not change wit(op y:1jpa8pw h 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 oven is designed tof hdq/c8j4d *w avy;-o produce 3.3 kW of heat when connected to a 240-V sourcewhy4-q aj*oc 8fd/ ;vd. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.03b 7khto5zkj3hqqi 37-V portable CD player that draws a maximum of 320 mA ob5ho3 qjzt7k q7ki3 h3f current?    W

  What is the maximum voltage that can be appliejz*qq39,sbj kd 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 connected uuhz.d imp512 to its propei 1md.5zhup2u r 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 l:q wpy.)+ds r9wyj:s 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 1250e ;su -ve;tn*la- tddf-.p4mz 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 delic p s8ut) xl.uj/ tsy/yac3e08vered 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? [Hint: assume roughly that brightnestax0csypcle/3 8y )sju/t8.u s is proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use in tk*v7fad b3*is anbcf ;n(uat0y 1r 0z,he morning if it is in operation for a totn73n0,( t bfab; kdcuyi10arsa**zf val 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, wht mlmabg:o ;yl.(:y4w at does it cost to leave a 25-W porch light on day and night y a(;.mwb:t4:yo g mllfor a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected y3sh bf8+c s*vli 0xz/s:ma+gin series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA/*s0:s+b cvmx hz8y lfs+3agi 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 stu .k ;rmz9hpw0w:1 5dwaepnq ,ored 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 128 z:uamz,+jeq ug29qq0 V as in Fig. 18–20, can be used without blowine: jamqzu+,8zq9u 2q gg a 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.qf g8iibaucrv) d7* +9f8x ra9129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connecte8 i9q fuaf8i*cd7rabgr+ 9 vx)d 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 delivers 620 kW of power at 12,000 V to a factory thro jpnb)e-4n 5du .-tnirugh wires with totann. 5dprnj-)-tu 4biel 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 electromqg 3h 8y 0rpojn3cyu(;t;1tw cagnet connected to a 240-V line is 17.5 A. At what rate must cooling water pascq g;o 8h0yjwnruct3;p y(1 t3s 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 hea.lj4s9d(s9/( jhl9 of mor ahut a cup of water for coffee or tea. If the heater can heat 120 mL of water rdj/omuf(lahl9 sj4o9.( h 9sfrom 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 curp5hky0-x(m;gke. cx rk* 4ufg rent 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, iv*ur; vz. 8tp mxm6u;ks 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 c69mp bqi/ga h1es9(f 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 1500q(ffltq 9pzl t,h 08t2-W device is 5.4 A. What is the rms voltaget 0pt(htl,lf9 2q8qz f across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connect7ojuk7 cq) 7fkwk- gd3ed to a $660-V_{rms}$ ac line. Calculate
(a) the peak voltage$\approx$    V(retain one decimal places)
(b) the peak current.    A

  (a) What is the maximum instantaneous power dissipated by a 3.0-hp pump connz dl/crs* 73:2 wjtzewected tr72 z w:lje/cs *d3wzto a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connectdu0ksh/e qc 6: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 copper wire carries a tiny current of+o. b; mkuws)l $2.3\mu A$. What is the electron drift speed in the wire?    $ \times10^{-10 }\;m/s$

  A 5.80-m length of 2.v83g tpu0/,afsx0oz- * d miid0-mm-diameter wire carries a 750-mA current when 22.0 mV is applied to its ends. If the drift speed i3mxpo,t/0u8 *di-vzia fg0d ss $ 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 Exo-*w wyrv- ;uarth’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 atmospka 2 z8. zokf0tb/wkg/here, $He^{2+}$ 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 membran ;45loxyz7u due $ 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 deto,al v;y (h3 8ix-3rlswkk* xyected 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 along thavr38wh oks(ll3yk-;*ix yx,e axon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much energy is required to transmit one action potent3d..c0d k;qsd qu; f; nbdzwa1ial along the axon of nbk s03;qfcddd. w1zua ;dq ;.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 required for $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action potentc,xg2 qn :ssvw6ate): ial, $Na^+$ 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 ti51ucl+zpd /rtt 5aq 1)sk, cuhere in 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0-hwxp/ 2lawl3 a; 2zx by, c(cd+/i(yojwp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of the two a -if,o(z on:mlx0f-iheadlights 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, ( z:i-il0o mnox-aff is rated at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of a 11+ysyp)z c m*+u0-V, 1500-W heater is 5.4 m long. If it is made of iron, what must its di+* zmpyucs)+y ameter be?    $ \times10^{ -4}\;m$

  The conductance G ofi)6,b q(zl :ihw2hhwh :er ,iv an object is defined as the reciprocal of the resistance R; that is,,2,i:beivqh (z )i ww6rhl:hh $G\,=\,1/R$. 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. Suppos7cbi(psbh/2 ae 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 costahcbs27pb i (/ 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 ugi,kef3b *5 hrses 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 cut9 ,siiqy6ualy 5l6n*x in half and the two lengths are wrapped together side by side to make a thickey xnlia966 * uls,q5yir 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 m0w 6li30to/ome ) enl117 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+mud)3er livu:i;9h k does not become 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 than 1.8 W of hv3: 9r)lmk;ehuui +d ieat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is givenhi 2f1ixzgi ox x+jbfcuw/6,pg; q475 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 delivers 950 W of energy x *zgj/)o7cila- obsjwrd2 z9*5gq 5cper second to the interior.5d ) *cxjijq7/rl-z*g9 soba2 zgco w5 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 t+ggo6acd x2t5wo different conductors made of the same material. One conductor is twice as long and twice t+ oaxt2c6gdg5he 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 room of volume w;lpd)xka e4v7 7 g5jz$62\,m^3$ 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+ 8qd3 xrzzk9xh7-ypaye:( be a 240-V 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 batteries as its 5ap/gxoq +vn4(ckag( source of energy. Its mass isnax 5(c+kapq/( 4ovgg 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 haa0wzjg)nc lo39laty,n+d liyd, v2 .8s 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 accelerator at Fexc67s)hr meo+gs 50 txrmilab (Illinois) is designed to carry an 11-mA beam of protons traveling at very nearly the speed 57 0xcsox+er6 m)t gshof 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 d7* taj*n n.qsiraws 12 A at 220-V ac. The connecting cord is copper wire with a diamejnia *7.tn sq*ter 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 1k s3whq8a+h2x 20 V. The heating element is a coil 8kw3q2 xhhsa+ of Nichrome 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 thl/8p(md hohk;dw-mz4p iq q5- e car is off to about 13.8 V when the k(4/z -pqmw5dq ol-h; hmdip8car is on and the charging system is in operation, a difference of 15%. By what percentage does the power delivered to the headlights vary as the voltage changes from 12 V to 13.8 V? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120xfs+ vxhx:,pf: y:r lg+yf+:,roze sav6q*1b V and 40 W for household applications. Lightbulb B is rated at 12 V ,:*sq++re f:y1+b vg :sf 6vxz:lrx oax,yfphand 40 W 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 0oitbctl5goc) q.)eph*d3 8b ).259 cm is used to connect a set of appliances at 120 V, which draw 2250 W of p oedtch*tglbb 8)c oq53.)p i)ower 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 outsi ,f:k+1 rm-dr4twrper de diameter of 5.00 cm (Fig. 18–37). What is the resistanc,r: drte m f-pr4+k1rwe of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistanc x2pye83 pcag1e R is stretched uniformly so that its length doubles, by what factor does the power dissipated in the wire change, assuming it rema81 ac3epgp 2yxins hooked up to the same voltage source?

  A tungsten filament usqb+ 9-rlv*qr pq el58xed in a flashlight bulb operates at 0.20 A and 3.2 V. If its resistanbex rq *8ll9-r5 pq+vqce at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$