What quantity is measured by a battery ratk i7h8v r1+tgaing given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flosdqt99nj /xtui79ok 5 w away from the negative terminal in the circuit. But within the cell, electrons flow to the negative terminal. Expl9kn/ 7qtusd9ti9 jo5xain.

When a flashlight is operated, what is being used up: battery curre96rvx8yq) kc ent, battery voltage, revyk9)xc8q6battery energy, battery power, or battery resistance? Explain.

One terminal of a car battery is said to bet3t qh;plt /vm5+pm 7b connected to “ground.” Since it is not really connected to the grou5tmp;7/ tlp bv3m+qthnd, what is meant by this expression?

When you turn on a water faucet, the water usually flowrrg u pnk danstp o.x3)sy:;,,a1pi/*s immediately. You don’t have * r,1au;dsnatp,pyn)ko i:3r.p/gx s to wait 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 length have eiy 2ynj.o2m3u/prg9k d. b 1vthe same resistance? Exomvy32 ug9.b .1rpenijd 2y k/plain.

If the resistance of a small immersion heater (to sqp.d3k v,o j2ts)nxb15nen;heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow dow5e n)pnkxssotb.2jvq 1,n d;3n the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, and 3a, how w4pkj xaw0 q3s 8fb z:jqm*/y2iould you connect the wires from a battery so as to obtain (a) 4 82jasfkq*b0:yzi qwmp3x/jthe 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 lightbulbqbzxr:/gh)3 dbvul( 3 burns out?

Explain why lightbulbs almost always burn out just as the8i xua6w1 fmt .ph9t,py are turned on and not after they have beenpmpf i ax6.,tt9wuh18 on for some time.

Which draws more current, a 100-W lighh q):m k; de:so(sca1xtbulb or a 75-W bulb? Which has the higher resisac :ds: ;ks q)(meoxh1tance?

Electric power is transferred over lard2;c6 ;un ;pa63dyry-cku1o qgtt5wkge distances at very high voltages. Explain how the high voltage reduces power losses in the transm w nokdk-ar cu c6;tdy61u2g;qt5p;y3ission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to szs:5/oj h-af.e9k uzreplace this fuse with a 25-A:z9h5eu -s.ks/ajozf fuse?

When electric lights are 6 vk(bi4)jawv operated on low-frequency ac (say, 5 Hz), they flicker notv i6w vakb)4(jiceably. Why?

Driven by ac power, the same electrons pass back dh5 0 -xwe7ql r3po*nht+e+gmand forth through your reading lamp over and over again. Exple7d0 l5o+ne rwpth*mhq x3-+g ain why the light stays lit instead of going out after the first pass of electrons.

The heating element in a toaste;) la,yweib -n9ux by8r is made of Nichrome wire. Immediately after the toaster is tun8bie )b wluy,x ;a9-yrned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a remr : jsn6,+tpy*vx5d b9 8slfcsistor? Explain.

Different lamps mightq8e+e1 op7yw e have batteries connected in either of the two arrangements shown in p+ 7yeq 1w8eeo
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flo9j7gmrh qh 5+dws in a wire. How many electrons are flowing past any point in the wire per second?9dq5mr+ 7h hgj    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A fo.;)pa qj g5trur 5.0 h. How much charge passes through the r.)gqt;p ja5 ubattery?    $ \times10^{ 5}\;C$

  What is the current i 1y9pj pd4syg0n amperes 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 produv *z1p;twlaw9pq8dk05m tf2 uces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current t5-)3s xfc-ylz o1xpnf hrough a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged imnq 4t 9 ak,83v vf+fllb8li1snto 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 elemenw3qj/ (wy9i0n7bh ciz t with a resistance of $9.6-\Omega$.
(a) What is the current in the element when it is connected to 240 V?    A
(b) How much charge passes through the element in 50 min?    $ \times10^{ 4}\;C$

  A 9.0-V battery is connected to a bulb whose resistancw p)ykrfob 5i1; 7s6t q9bx0ozo1 vsu+e 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. 1c2,ve.kxn no ftb.4erk5. sz +8–34). The line .bt5kfez e+2,.sc rnn4. kxov 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 V. w6/ej:oh)*b7lgquh h
(a) If the voltage drops by 15%, what will be the current, assuming nothing else changes? $\approx$    A (retain one decimal places)
(b) If the resistance of the device were reduced by 15%, what current would be drawn at 240 V? $\approx$    A (retain one decimal places)

  A 12-V battery causes a current of 0.60 A thjk6go 2i+xdf /rough 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 ofm )5 pkxm 8pj8wbu:+zq tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length (y.,juodso:y3iuf, zv: x2l fof copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of alumib t+jc2e;rn a(num wire 2.0 mm in diamete2(arb; tc nje+r, to 20.0 m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter cop1ro; 7 gk:vfbltv(vyr:0 u*tzper wire have the same resistance as a tungsten wire of the same length? Give numerical deta*v:kob:f(rt gvl1 y;0 zru7vtils.    mm

  A certain copper wirs:f:byzx 6p,c e has 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 ofzr( fq)okc lh+a: f:6o a copper wire (originally atc:o (ffk)q azl6o+h r: $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same 2(fz6ajy wv 4wresistivity as tungsten does at v2(4 a jwy6wfz$20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a , y ),hinilqiznq-d (3resistance 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 wxzq9pb 4wci1gz/ hm)fc+h e+k 1)(oq yire (used in 15-A circuits). The wire has diameter1c/x ih 4mzq bf o)ekqwzp g9++1)cy(h 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengte .29oj1 hfcemhs 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 current that passes through the sh91eo. c2jmef olid 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 twj,sw 8pes5 o9wice the length of the other, what is the ratio of the diameter of the longer wire to the diameter of the shortjse,5spwo w9 8er wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V power supply, az k6p 3lxl*u/ck.vfdqjs 0+v jv0i; ewi;44u ind a currentl+qv/usi; ekpzjx jv6d43040.k fiuiv* cl;w 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 consists of 5.0 m of copper followed by 5.0 i/ bp1w:fj se8m of aluminum, both of diameter 1.0 mm. pjs/8ibf: ew1 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 icdxe g n9-na8m) i s8i9rt35ob.;ivz /9pzln ks important that the value of a resistance not change with temperd9prn; tvie-z k 89xai5l8g o /iznb3c)sn9 .mature. 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 electric2imstj1 5 ig6*yf2p xy oven is designed to produce 3.3 kW of heat when connected to a 240-V source. Wy 265miyipg*fst1x j 2hat must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable C)cu6/tk e6 yjjD player that draws a maxk cye)t 6/6ujjimum of 320 mA of current?    W

  What is the maximum g)nbo9ud b;)z voltage that can be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, a 75-W lightbulb co+0 52k nxh*iw uvtl 9yga.ej1lnnected to its proper source vol5tw 2g+jl.h1 i*ale k09nv uyxtage 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 -e,1mycch+ ah. 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:5;-rcj*ca-kzk b;)dh p aprs 6 850 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 home- wgs/a0ofqma4mz 7s *s at 240 V. If you zsoag/wqf s* -0m4a7muse 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 brightness is proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use in the morning if it i )53pdnx3vfvh s in operation for a total of 15 min? At d 5v3fx3)nhvp 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 ze i*; jeps34nit cost to leave a 25-W porch light on day and night for pze*e;s i4jn 3a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries c.cq. qm g 4dea1p.m1xronnected in series as in Fig. 18–4b (Fig. 18–36). Tha mqd4c.q gem.1 1pr.xe 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 stj gj -qp80tr6dwkb6x ,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 120 V as in Fig. 18–20, can be used wiu4d q380j36e/ . 8ckpjxvw-iop umuckthout blowing a 15-A fuse? icu.qk- x0dpmk3co j6wvp3ue/ 8 48ju   bulbs

  An extension cord made of t9 7 3viv kfjfw:+hleq iy17+crwo wires 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 dissi+3l h f :kc9w7r1qvviy+7 fejipated in the cord?    W

  A power station delivers 620 kW of power at 12,000 V t4eq6c1r2f b riyi9krg.t(c.9znwff6 o a factory through wires with total resi tf.cb6e 6czfi2gwr ri f9kq(4.nyr19 stance $3.0\Omega$ 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 electromagyz *5ed.iqn;s7umkq- net connected 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 ris.mez5- sn ky7q;qudi*e by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be usee s k- s(tl)p)r: j+(xgr)0 mfkw,ayzmd in a car to heat a cup of water for coffee or tea. If the heater can heat 120 mL of ws ayr -esw)((mmkz+)x:)rpfl, gj 0ktater 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 current in ariq :t7.e)05o2aon7ltsln w k $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak gdlcq(2oum,bp+jek : 2,a2 xy value is 180 V, is across a $330-\Omega$ resistor. What are the rms and peak currents in the resistor?
$I_{peak}$$\approx$    A(retain two decimal places)
$I_{rms}$ =    A

  Estimate the resistance of th ;p nng.0clb24n-o:s6nno s afe $120-V_{rms}$ 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 ) 6c/qjabo *hmff*:b6*lqh/syfmx *rcurrent in a 1500-W device is 5.4 A. What is the rms voltaglqmr f/ajx/qc**y mb*o)h: f6h f*6bs e across it?    V (Round to the nearest integer)

  An 1800-W arc welders (pvitd31lu ko3b. t4 is connected 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 disqm h59 ub3ah syom373osipated by a 3.0-hp pump connected to h7u3s9yahmmb3o q53oa $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to 7pykbn;d ; +ifa $240-V_{rms}$ 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 (u9-e wb9gcf eof $2.3\mu A$. What is the electron drift speed in the wire?    $ \times10^{-10 }\;m/s$

  A 5.80-m length of 2.0-mm-diameter 5 wtww79wcrt. oowy1s;/m3kcwire carries a 750-mA current when 22.0 mV is applied to its ends. If tww5/9 t1cwtsmcow. 3 w;7 koryhe drift 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 atmnd4sxc ( o7wi7d 7kbv-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 atmospt*1xi/19k2 d yxb4 hqgh0; ahddzmzv0here, $He^{2+}$ 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.-p1hfr,cv tw 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. Thi cqdfro2nz3 *8 itvk1t/- 8 asi*:hkpe action potential is detected at a point 3.40 cm dow fok qvtz *-sp*ri32d1 ii /k:hc88atnn 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 the axon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much energy is required to transmis;t:ddu:e(j 0ikxu.it one 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 cap xeu;sj u(i :.tdid0:kacitance; 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 poten6-,o4ums6pua pc5m n xtial, $Na^+$ 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 bz a2ahy07:qv rw:ta*there in 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0- wtt,u:fsmr6 :9zhgr *(js.zvj, g/ ythp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves .rgdf p)uk u *nnc2:z+a car with the lights on. If each of the two headlights uses 4gf )crzdu.kn2un*p +:0 W and each of the two taillights 6 W, for a total of 92 W, how long will a fresh 12-V battery last if it is rated at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of a 110-V, 1500-Wbw7ori)la (o q2l;en9 heater is 5.4 m long. If it is made of iron, wh ownai ;(l9lb2)o7er qat must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of the resistance gu p buu;5id;e2a wd -0i0*pleR; thala0gi iue;5 -u *dpbupd0;2wet 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. Sev7t9vlmh wr ,i-mao ,dx:2ytih-4c-uppose that instead of using high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a two-wire line of ri:4 o,,amy2d- cvmvtx th9h e-ilw7-0.50-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 hous c.rkga5 x:;v iebn/v2ehold 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 hm4 :,zmihme*0ie *b ikalf and the two lengths are wrapped together side by side to make a thicker wire. How does the resistance 0i 4 i*m,h*memzkibe:of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 117 V. hzpke0 3h4+ud( q7 rgq
(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 become ky7l28yit*lw so hot as to start a fire. What diameter must a copper wire be if it is to carry a maximum current of 352 ltw7*8 kyyil A and produce no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is fk8tdrqee.+ . 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 d19kdd9g cpl88- lxcxh elivers 950 W of energy per second txhl 9d8 g9lc8-p dxck1o the 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 conductors made of the same material. One convr 9 gde4+,gvve3:h9 opkg,lqductor is twice as long and twice the diameter of the second. What 3g,9+,pv4he vlog9e: qvkgrd is the ratio of the power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used t9g c-b.xgnq .xo 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 sou*a(wdnc8y+0etb19rk l lk6ukrce.
(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 v )nkh 5ape1(hmakes use of storage batteries as its source of energy. Its 1evp ahhn 5)k(mass 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 resistance ofww yjxg0 il*;; $12\Omega$ 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 caikpn-s9e172qye;y c f6tlh:kt* itze s + i7i2rry an 11-mA beam of protons traveling at very nearly the speed of li*pz7 7:tsieks-tl t2c nh;6i1ek feq 2y+iy i9ght ($ 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 is copper n;(ycxrqd9goy w(.m6s;l;a0ywjy + twire with a diameteqcsoa+g6m.0(; dwn;yw j(l t ry;y9xyr 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 Vty,05azrh at:(xv hh5 . The heating element is a coil of Nich5: (th5,a xhyr hzt0avrome 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 i9( nxf,ur5maqzce); 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 to the headlights vary as the voltage changes from 12 V to 13.8 V? Assume the headlight re;n)5e rz9ic,(xfqum a sistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for household applicationsy fh e3py4cx5m (cx psh*:;.ql. Lightbulb B is rated at 12 V and 40 W for 5xlf4:*hyyhmp (3 x qps;ce.c 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 1ywyc)9 .eo +ag20 V, which draw 2250 W of power w+ay eycog)9.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 diamej n34s*ea- 0fojr* cwster of 5.00 cm (Fig. 18–37). What is the s o-rfws*eac3j4j0* nresistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly socach 5hzj6f cg a114,g that its length doubles, by what factor does the power dissipated in the wire change, assuming it remaina165h, fc1 g gjazchc4s hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operates at 0.20 A ana/dm8d5vm73 wjt/f o vd 3.2 V. If its remf7/jvv3/dm w 8od 5tasistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$