What quantity is measurejw(iix.-j + dpd by a battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow away fro7,j1 1eztap(+*m/o ht d lsbyrm the negative terminal in the circuit. But within the cell, electrons flow tj(ap 1 sl toybt,*z+hder/m1 7o the negative terminal. Explain.

When a flashlight is operated, what i6j/q zlolr3o 6s being used up: battery current, battery voltage, battery energy, battery power, oolzor q/6 lj36r battery resistance? Explain.

One terminal of a car battery is said to be connected to “ground.” Sinjc h+aa hzd c/k n1q)667vmte.ce it is not really connected to the ground, what is meant by this expression?va/)+ mnj6dhz ache c167tqk.

When you turn on a water faucet, the water usually flows immediately. grxs6x* /f9y. 4 hj *htos7*kl(miatcYou don’t have to wait for water to flow from the faucet valve to the spout. Why not? Is the same t*m9 y 4/i* 7cfg t.*hhs xjrtxkolsa(6hing true when you connect a wire to the terminals of a battery?

Can a copper wire and an aluminu:rw97qbf/8xeob0 hq5y z vur3/u9 uoh m wire of the same length have the same resistance9 /q/0brr bxuvu:ow 95yh e87 fh3uqoz? Explain.

If the resistance of a small immersion heatf v; wxt95xp7:dy.vx93gmx tler (to heat water for tea or soup, Fig. 18–32) was increased, wp;g 59fxvxd l9:yttx. 3wx 7vmould it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon l a:f/3bac(u:qvhh3t has sides of lengths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resistance, (b) the greatest res3 tab: qa/3:u(hcfvl histance?

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 lightb9x*,ov-jod *+ c gguho8.eabp ulb burns out?

Explain why lightbulbs almost alwayt- skhv8isg e* t3o9q):k; pals burn out just as they are turned on and not after they have been on for8s;l-e ip :a h9kg v3skott)*q some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which ha3ufxzs 5,2n8/oak: kz ( nmscxs the higher rn ,/uosk:3smzckx(an2 fz x58esistance?

Electric power is transferred over large distances at very f8 aljma73)0qrk*h lt high voltages. Explain how the high voltage reduces power l8m0j7tk3a h)fral *q losses in the transmission lines.

A 15-A fuse blows repeat3l r6 *rxi*zhdedly. Why is it dangerous to replace this fuse with a 25-A fuse?**6xr3hd l zir

When electric lights are operated on lfj7) nji;r0q cmpz5i 6p.ccux*7 la 5bow-frequency ac (say, 5 Hz), they flicker noticfmcax 0i.r 5 77cj5z )6p ;qubj*lncpieably. Why?

Driven by ac power, the same electrons pass back and forth through your 7 *g)deb vpo) s-phd7rreading lamp over and over again. Explain why the light stays lit instead of h - b 77op)ddv*)segrpgoing out after the first pass of electrons.

The heating element in3fdr4 - jfb9qh a toaster is made of Nichrome wire. Immediately after the toaster dr9fb4qhfj3-is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a6gc2v7 i3 ehtls r/+1u3hty2 yd ;twyk resistor? Explain.

Different lamps might have batteries connected in either of dnhq039g xvbpx aiqc07k01 s5 the two arrangements3gisxa0 70vq b0xqkchp 95dn 1 shown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many electrons59tvs:;h zkg uc*5fjf are flowing past any point in the wire g:*f9huk;v z 5 fstc5jper second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery uf7 (+qn. n3wvg1 xrqkusing a current of 6.7 A for 5.0 h. How much charge passes through the .ng(17 3 kxwnfuqq+ vrbattery?    $ \times10^{ 5}\;C$

  What is the current in 0hmyadgdn0 .*r: :s;p x xpafry,5,xu 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 12maly: nsk 8rwc-ib4d4( 0rys80 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of currkt9kq u+7jyk 4ent through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged in**)vungts 6bvkv ej,;to 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 drl8 . frvgp h8x-usm)i9yer 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 bulb wh825 +ixqh( iifvhzi2 tose resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric tyve+l w; :mpe pyft9v dt79+h7ransmission line carrying 2800 A (Fig. 18–34). The line p+ f :y+9e9lvdmtwp vehyt77;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 ngb ms:b1)d:z6.50 A at 240 V.
(a) If the voltage drops by 15%, what will be the current, assuming nothing else changes? $\approx$    A (retain one decimal places)
(b) If the resistance of the device were reduced by 15%, what current would be drawn at 240 V? $\approx$    A (retain one decimal places)

  A 12-V battery causes a curreilqk(wch6t(d8.qwx :nt 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 resistance isaahs(-+h*e :j *vox8iocpikhj 2 x6i. $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m l x1r9) / h;,k8x 7zzlm/l+l hvagqwyxvength of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the rmruui t0q;4 jjlxm828esistance of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm 8uiujmlxt;2 j 84mrq 0in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance 7 7e fkkiuua.v9y 6:rnat0yv3 as a tungsten wire of:y6.kuaf9 irntku eyv0 7av3 7 the same length? Give numerical details.    mm

  A certain copper wire h)p0vvuflnur jc3 061v(gik ;ias 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 coppemc/k y kc/ e6 ihydhnamr,d2s:.in7./r wire (originally at/.k/ he nam7 cm6n2.rhki yicds/,d:y $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temper. t ct227n-f7cht t bxvb*)u4w)yfaleature copper will have the same resistivity as tungsten doe 2v)-a*wft2yt tlf n ux7.47tbe)cbchs at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resi ctj udh498ba( 63movn: vns6istance 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 nov6 0 ar/-bckxlmd9(l v. 14 copper wire (used in 15-A circuits). The wixamd -cv 60vllb/9rk( re has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has* ctpku0xj co7yi 2e :7siq7q8 sides 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 c*82qu:ck7t7ic xjoq e i 7syp0urrent 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- mv3exjq 50la has twice the length of the other, what is the ratio of the diamet0vxq5-jam3l eer of the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected twl,lf:bnn0o+h7e6fes nt. g/ z5eo 8to a precision 10.00-V power supply, and a current of 0.4212 A is precisely measured azb lhwe75.ge806 o/e+tltnof , n f:snt 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 w:nmu lv4 f8l1hire consists of 5.0 m of copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. Af:4hm1 8nlul v 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 (1upif b/dn g-important that the value of a resistance not change with temperaturegf1nd- (/ipb u. 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 iw:jkuc4 y2ej.s designed to produce 3.3 kW of heat when connected to a 240-V source. What must be the resistance : 4jywekj.2u cof the element?    $\Omega$

  What is the maximum power consumpkmy; he2k8 uk8tion of a 3.0-V portable CD player that draws a maxih;8 kk2y 8mkeumum of 320 mA of current?    W

  What is the maximum voltage that c:*s bq ls9qn1can 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 conneol0 p1 t)3p -n,blr -l:mvyuuccted to its proper source voltage of 120 V.mytn: po -lul 0ub lr)c-vp,13
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heater is rated at :tv t.)) ca;dzdk 6djd110 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 has6n*(j7,2mwl ptvlis m two settings: 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, wh/kbf,h;5d nkq9m 6 kkoere 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 wil kh ,b/dkqkk695fn;oml 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 i+)qqhnn; :oem f it is in operation for a total mheq; )n+nqo: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, what does it cost to leave a 25-W porch ligwu1+ + mewl3aght on day anm+ au1+l 3egwwd night for a year? $\approx$    dollars

  An ordinary flashlight uses two D-ce -mnskbt3e9oq 91o 4knll 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA w3 smk-k eo4o9tq19bnn hen 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 enerjb m 3lj+( (lcg;h 1y;cgwl9xsgy stored in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connected to 120 V as in Fig. 18–20, can be use wt(1b p;r0wyyeqj *.dd without ;(dw1rpb.j *y t0qwye blowing a 15-A fuse?    bulbs

  An extension cord made of two wires:go -upz m8,4rxdcvp0tt:a .d 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. Hc.-:p d0tax4v,tup:mzd og 8row much power is dissipated in the cord?    W

  A power station delivers 620 kW of power at 12,000 V to a factory through wir9v8apta hp)d +ts ;rl.pv65o,xels9ges with total .a)5 lpt8 vtvr6e,axdp;9g+ 9hs lp osresistance $3.0\Omega$ 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 connes6oj u./n f6 kz0brbr,cted to a 240-V line is 17.5 A. At what rate must cooling water pass over the coils if trku z .nsfbj ,6o0rb/6he 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 heat a cup of wateq8ijeeg/u6 oar2ji6k - dwz70r for coffee or tea. If the heater can heat 120 mL of ig qia0 roee6jjk-8/2uw67zd 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 current in wp:azue1mnf.7* uo uvx-*oci*vvx- ,c;fc7ta $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, i +51azjxaez( us 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 9hycy uled691 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 15tfhf or5gc8,,ei+b -v0 y/jiy00-W device is 5.4 A. What is the rms voltage across it+-0yey ji5cv,,o gbf t8i/ rhf?    V (Round to the nearest integer)

  An 1800-W arc welder is b :1m 54tcjm0nss+h:na(t sdyed vd, 0connected 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 pumpjdo6r 8o*myz( connected to a d*y68 ojromz ($240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to a 40*qvc ln,8h u+ 97iv1wrfaa:k(p 9oeevk exa$240-V_{rms}$ 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 sy :t c,-xuh/qtiny 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 carriescv 8 gro3t(630ywz1hgf c)ddx a 750-mA current when 22.0 mV is applied to ivhg ydr3 (xtf8g0wo)zc63 c1dts ends. If the 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 atmr601 h.czr n8ar;8s75p 8 jcyhwibz/rp mo p2nosphere, $He^{2+}$ 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 thj7p,a2 w kc1hce 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 elec: k5 /1wdcieqhtric field across an axon membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with an electric pulse. The acbx1f u:z; wr8jtion 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 st r j:1;b8uzfwximulation, 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 t3onv 8t:q;rtc h 9h8mwransmit one action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy 8 htv t;8orm9q3c :nwhstored 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 potentia 6xlaouy6ajjkqit 17)s 851yb+zblh :l, $Na^+$ 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-hourdr4,; dfd/ lb8u 4wyak?    C

  What is the average current drawn by a 1.0-hp 14bpj oh ru -d+ lwhhq9q*y)p7)20-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. Ifpc,3em + v7s gqg-3ztwo4-f fq each of the two headlights uses 40 W and each of the two taillights 6 W, for a total of 92 W, how long will a fresh 12-V battm+-4gpqfsw z3e gf3vo, -7ctq ery 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 kr k( hazx7b46)jz*mo-W heater is 5.4 m long. If it is made of iron, wha) 7jazk 6(k*xhr 4mbzot must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is define.w k, ranxii*d (/.copd as the reciprocal of the resistance R; thai/,x(.c .knpadwo *r it 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. Suppt/fw 3sexw k,)ose that instead of using high-voltage lines to supply the power, the power is delivered at 120 V. Asss/ktfe ,w3) xwuming 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 electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular househol3hy(m/ao wzvy(3hb6 bgt8 .n qd 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 ck;gu ,sna--h-,5tv lh4lq nzaut in half and the two lengths are wrapped together side by side to make a tha,-g-nnl-q 5azhv ,stl;u4 khicker 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 117z0zz;bexo8y)pw xi, -ccn )t(vl9n x8 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 ip)l0v lkyf jr0 l:9w9become 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 producjpw:i 9 lvylklr)009 fe no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is givend o86t8s)0o 4nme )yy/iuf /htkfa7vk 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% e8-u nd9gchs )jfficiency delivers 950 W of energy per second to the interior. n-hcj)sug98d 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 twvnsuiflt;ax/:/* 1 zy)q j wa-o different conductors made of the same material. One conductor is twice as long and twice the diameter of t f:a ;/nxtyv )zaqj1s-*/lwuihe 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 roomjd66;,. xp1xewdvn k g 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 -vbo,r2,;i. j;h pewxyrqel3 to 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 n1xmis 5prm) 9use of storage batteries as its source of energy. Its mass is 19 5xmsp1r )imn560 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 of n+t(e5n- i52 lect-*ws aekac$12\Omega$ 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 desjg;n5n*su jq7voc0xp;hi/ 9 jigned to carry an 11-mA beam of protons traveling at very nearly u;;7v9o5/q* ci j0 sx hgjnjpnthe speed of light ($ 3.0\times10^{8 }\;m/s$) around a ring 6300 m in circumference. How many protons are stored in the beam?    $ \times10^{12 }\;protons$

  An air conditioner draws 12 A at 220-V ac. The connecting cord is copper wq4b :9aa8uusv 6bs jp9n60gh cire with a diameter 6acubha8b9p0 nvs9 64qsuj :gof 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 V. The h8be/kbbr. n6yrz 8c. de .4hcneating element is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What is the zned84 brb.hnc8y .rc6/b ek.diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage var1rlk/ wl1v d5fies 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 thell5/d 1v kfw1r 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 householdk oeb.ws4envr-p1q y23 sh7-p applications. Lightbulb B is rated at 12 V and 40 W fov2ph1-q 4e p3nr7e wb.sks-yor 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 f(1or cxz ,hq nq5yz))of appliances at 120 V, which draw 2250 Wq1c ))5foqnr (,zyxzh 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.ijt oxy/q41yii2ah k63-vs; m00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the resistance of 10.0 mym /hyt ijsa123 4qvik6ix;-o of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its lp tb7+3z(yzi4qz bir:3f,* q;pefms n ength doubles, by what factor does the power dissipated in the w;3 z(+n zqy:fbp3ei,q z 7*trp4fimsbire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb opdpwp:egqi*4 9p+h r 0u8sxsk4erates at 0.20 A and 3.2 V. If its re:p4pe 9084 +rsqhwgxduk* ips sistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$