What quantity is measured by a battery rating given in ampere-j4v ch4n5 7tvwhours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons f/c*fi-u 3 cxtylow away from the negative termina 3yi xt*uc/fc-l in the circuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battery curren0 j(z39 ynuzrnt, battery voltage, battery energy, battery power, or battery resista(3r9nzz0njy u nce? Explain.

One terminal of a car battery ipqv,hur gq0ydo16g c+ ewb 4-9s said to be connected to “ground.” Since it is not really connected to the ground, what is meant by thiupqhvrbw9d6g01ge o q y+, -c4s expression?

When you turn on a wdjw-je:a(a -vds+/h* k9qel w ater faucet, the water usually flows immediately. You don’t have to wait for water to flow from thqwsehk9eaw/ j ddv la-(*j-+:e 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 ahvh/wygn(g5w 8*mf ,xb.q )+ls4sfmxn aluminum wire of the same length have the same resistance? Explanhs/4wxg,sxwh8lmvqyb f +).*5(f gmin.

If the resistance of a small7(yhigalm 2ed9zrg.2 immersion heater (to heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the heating proce re(mg 2zh7i2.aygld9ss? Explain.

If a rectangular solid made of carbon has sides of vhrwlh;xkv;( 0 y h4)zlengths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) t ( xr)lvhvhh40;;ykwzhe 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 lightbulbvp1b mrko q8*fm. ln(5 burns out?

Explain why lightbul-*uatub)y p2d t1n.lc bs almost always burn out just as they are turned on and not after they have been on for some c atlnut .p*d)1 y2-butime.

Which draws more current,v6v:xk i b-g8k a 100-W lightbulb or a 75-W bulb? Which has the highergi k-vx6: vbk8 resistance?

Electric power is tran e:nw fs.zx*ewfj:*qyn6b- 7b sferred over large distances at very high voltages. Explain how the high voltage reduces power losses in tfb wzqj 7f6 n:ey xsb*ew*.:-nhe transmission lines.

A 15-A fuse blows repeatembl7x azl;l /;7b(hitdly. Why is it dangerous to replace this fuse with a 25-A xbltabl; l/7im7;( hzfuse?

When electric lights are operated on low-frequency ac (say, fovtek(lz*(8 ql8 s: d5 Hz), they flicker notvqt :szf( (l8*e8k oldiceably. Why?

Driven by ac power, the same electrons pass back and forth through yoqxzemndg*h /3e- (6a wrh/1wgur reading ladgznr1aegx6 wh(-*/hw e/m 3q mp over and over again. Explain why the light stays lit instead of going out after the first pass of electrons.

The heating element in a toaster is made of 7hvb.w*rf c. eNichrome wire. Immediately after the toaster is turned on, is c f.eh.7*wrbvthe current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resi9.4 3gqb gblnl9hoc/cj:vkk. stor? Explain.

Different lamps might have batteries connected in either of the td*8,2pacz kne0l/fba wo arrangements show l /ndz 2fapkc8e*a0b,n in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many electrons are flowing pa-p,tm9;xi n sast any point in the wire per second x-,anpt9 im;s?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A y vsf-,k)os/j3ez1 xg for 5.0 h. How much charge passes througs1kv/eofj-x 3gz),sy h the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes4bin)3 ;xvw ms 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 g4;gsbqwo xe;s ja3 y. yx8vv87n5u+fV produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current througr7xhqi5n+wag c91im/ h a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-V9 v)*phgmuxrfxp,,k/ 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 aiq/5i-lg e/ ir-eiiub) jq2g* 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 whose resistance iza,4*eowkdfm -d0i k;s $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transmission line carryin kyd9aqw ii)wc fkk;:is* )2x+g 2800 A (Fig. 18–34). Th a)ksy+9dii)k2iw w q ;fk:*xce 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 at 240 V. a-3pc *ruafip 9r41 pa
(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 0.6lbhn j;7) )iy- zbkgzz.2;wqt0 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 lai( qta3+yt1* cfvrcoh22v+dength of tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of cod8llu mub+c22 u qfh857zp8p) gjof- jpper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance ofow2+:ten+i v f7y)jxiqn6 hv+xq u :i1 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 mq y u6tv xfnx71w e+:ii)q 2+i+:vhjon of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same4ude/5iv x cw( resistance as a tungsten wire of txvw4 (de /iu5che same length? Give numerical details.    mm

  A certain copper wire 2xx.k :z3ylzs pd6gw9jf0 iv3 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 t.+9j kjfgcmrh/ efw *1emperature of a copper wire (originally atgkfj9w /ec*f r 1j+.hm $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper wills+gs4nd2m q c1 have the same resistivity as tungsten does a mg14sd2n s+qct $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistanc ugeztg15pfk 6p7zylg b6 8s8+e 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 cop9f- ghqj6w 3gdper wire (used in 15-A circuits). The wire has diameter 1.628 mm and carries a 1dqhjgw9f3g 6 -2-A current.    V

  A rectangular solid made of carbkfvh3;k m-dx.on has sides of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y-kvxk3hm d. f;, 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. Iuf cq4k19ru d6(9tmb wf one has twice the length of the other, what is the ratiocwb1k4m(r9u9q ut fd6 of the diameter of the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum w n44+i(l6 voi* a.ir()0wthqotdg //kf cuqcbire is connected to a precision 10.00-V power supply, and a current of 0.4212 A is precisely measured ak6d0 4o(/h cgi auf )niclo.ti twr/v+ qbq(4*t 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 foll3aend0 wp) wd3owed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is pdpa)e 3wd0n3wlaced 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 impcw c:u-uce6/i 4 0slogortant that the value of a resistance not change with temperature. For examp0w-:/ euc4lcicoug 6sle, 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 t/e5hm /-unfx 8wmgo :r r:ce5electric oven is designed to produce 3.3 kW of heat when connected to a 240-V sou/-em 5xmgernrc/: fu58to w:hrce. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption o27xp ie)dwi,w8ay;v tf a 3.0-V portable CD player that draws a maximum of 32;tipxv iw )7 a8y,d2ew0 mA of current?    W

  What is the maximum voltage that cwnvzz-nv-)c* .m q 6dv5j j5yjan 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 -7muaym :kz8xzkg z30 connected to its proper source voltage of 120 kax :0yzm8gz -kumz3 7V.
   $\Omega$
   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. Calc47depwv v :;bqulate
(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 kc .k2m*c,l,wdlda y-rx ;jh(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 2gi,*nrxhw ev4zr+m c, o(9 uris delivered to homes at 240 V. If you use the lightbulb in the United States at 120 V (assume its resistance does no*,2uxc (mz4,9rerwv+ih rngot 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 t9n him g8 lwxu 5a;l+9u4yjmp0he morning if it is in operation for0i8m5uwj9 yn alph ;xm9u4lg+ a total 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 porl.c 1d-wuxe 6gx0t *c-bk:mfmch light on day and night fotm6gm 1dcxc.:-x *- ewkb ufl0r a year? $\approx$    dollars

  An ordinary flashlight uses two 0hze.* :-22 mudbxv:q t6xqfe syz b9eD-cell 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when tu2:y .:zs -ud9z0t* 6mqbv2f ebxeqx herned 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 ofd e*1,upo6cs lixe(3zf/ m9el energy 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. 1vq d 13n3p1goi8–20, can be used without bln o3 igdp131vqowing a 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 copperhi*;cjt5k.b; mbg8ty uy*mt2 ( zr-cj wire) and of lhi (- c mjmy*;*;j8kbzur.25y t tgcbtength 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 delivchd.p 73yr2zb ers 620 kW of power at 12,000 V to a factory through wires with total resirp cyz 7hd.23bstance $3.0\Omega$ 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-V lin:+3: nzbhk1ltut z )zhe is 17.5 A. At what rate must cooling water pass over the coils if the water t) 3z1 t:uk:t+hbznzh lemperature 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 ws h 6ck,,pw3wx -lps2i)b oo7xater for coffee or tea. If the heater can heat 120 mL of wate)p-sko72o wx 3bh6,clsp wi ,xr 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 c,l*hnys7 7uo qd-;dtyv./vwf urrent 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,j-kflr pe8w. i)dl q+1 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 thec pyuvebd 5q7d( 7qv ai*1qf33 $120-V_{rms}$ 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 i-pjhu/p6jw :eqj71 vxn a 1500-W device is 5.4 A. What is the rms voltage across ix:7e61wjp u- vjpq/ hjt?    V (Round to the nearest integer)

  An 1800-W arc welder zsoppdh::ei ,81hkb 6is 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 inn+hqpwy w v7z:u6zt)3c9+g instantaneous power dissipated by a 3.0-hp pump connected to a 6+c wt+zzgi )yu q: 9pn7n3hwv$240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to amq3lltej2rq0k.l- :2iriy k6 $240-V_{rms}$ 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 curren v+ :j/r rnu (nu5g2srddnz/y-t 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 carries a 750-mA current whgqp si*dr5q42 en 22.0 mV is applied to its ends. Iqiqs 4g d5*2prf 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 zo1 egg15chc (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 Ebv 19f;d ua6enarth’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 elmf (;hkz*yil0 ectric 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 action pot/n.z ih0b),.tmrjgzu ,0 kpi cential 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,/gi,b )zt rm cp,kjn0.u0. hiz 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 recu8p1)br +cww s5 yfp-d0 v4bwquired to transmit 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 capacitance; see Section 17–9]. What minimum average power is required w 1)p c4y pwb50fv-uwsdrc8+b for $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action potentia/ te896 m :gpcrkz(wa x-nxj*el, $Na^+$ 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-hoews/ar8;dmfu.egc 8; g gl5h38yq r i3ur?    C

  What is the average current drawn by a 1.0-hp 120r:stzqav2-w- 3 ev8,i kt 9yah-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of the two head3xx+h8(os n imlights uses 40 W and each of the two taillights 6 W, for a total of 92 W, how long will a freshm( xi+on 38xsh 12-V battery last if it is rated at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of a 110-V, 1500-W heater is 5.4 m long. If l r-k h/5;jsjxp/fnx( it is made of iron, what must its /l5jrfhk-x(ns ;x p/j diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of the rex- pqh /q .i-k7eqfuy1sistance R; that i-up/-kqfi7 1y.hx qqes, $G\,=\,1/R$. 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. Suppose thate)t+anx;e4*j1qpa atj yj : nlp 2f7-b 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 electly7a*+ -) b q ;xtnp4eenja:tp j2af1jricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular householv 69 vlg(b 0vszfj5/med 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 t; b 1.gmoipf5hi*oauhd *17u ehe two lengths are wrapped together side by side to mph;1iou 7 *mfb.u5i1h*do e gaake a thicker wire. How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is desig 0b0h6 oov.4omn ttw (-g5lwzjned 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 noedkdrc,35uuz g r7t5c45ho a7t become so hot as to start a fire. What diameter must a copper wire brd45h7 t ,z a5doc3ruk eucg75e if it is to carry a maximum current of 35 A and produce no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current iscrcv 4(tj7. vnui:y3w 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 delivers ias f8br:b9m fo hronf;75m-)950 W of energy per second to the interior.r;ni9 f: h 7r-ffbbo5om)asm8 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 ma/+hy5hy -1gzycda a6j de of the same material. One conductor is twice as long and twice 516 cgyydyaz- ah+/hj 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 o0ta* z8:3t wza xyi;r:)l;z0tcut m croom 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 24o d+j0irah3c 20-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 souys2alb/s1tge 0s c ;a8rce of energy. Itsy8tca 0 s;aeg12ss /lb 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 rebyay rmuzq 4bu9 h(;v0y-yf.7sistance of $12\Omega$ when cold (20$^{\circ}\,C$) and $140\Omega$ when on (hot). Calculate its power consumption at
(a) the instant it is turned on,    W
(b) after a few moments when it is hot.    W

  The Tevatron accelerator at Fermilab (Illinois) is)pomsq (+wg b1 e0ii4i designed to carry an 11-mA beam of protons traveling +io (sm)q 0bigp1i4weat 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 12 A a5jgfsf ;,wka:/ pw5kst 220-V ac. The connecting cord is copper wire with a diameter of 1.6k5gkwjwsf s/,; 5af: p28 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 connect/vzb-cv 7 bs1r7ddb: *9n imqfed to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total length od/9ncb:sbqd 1*zfm viv7r b-7 f 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage vq: )jg*hr rb9r9lbd5 naries from about 12 V when the car is off to about 13.8 V when the car is on and the charging synq r gr59rbl):9 bdjh*stem 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 120 V and 40 W for household applications. Lightb ofw:ya d/3*mku2t6pz6t 4 xenulb B is rated at 12 V a ut3d 6n* 2 6xpawokf:mt4ze/ynd 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 0.259 cm is used to,/s sp 0mlmzcd,hry3+ connect a set of appliances at 120 V, which draw 2250 W of po 3mr0,/shpd,c+s m zlywer 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 di6dqwhkrak ,( +e3x5xygu,k)gameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18ged5w+axx uh6(y,kkrk3g)q, –37). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is th ku )i9(r ynscp2+w4 l:-z ag8j rm+w1xwzq)stretched uniformly so that its length doubles, by what factor does the power dissipated in the wire change, assuming it remains hooked up to the s+x( z4):lw pig) cht j+mywsaurw2knr8q-z19ame voltage source?

  A tungsten filament used in a flashlight bulb :2pmfwcko216-n8b5 ;t ) lqoqk kvogxoperates at 0.20 A and 3.2 V. If its resistf6 )bg8o ok5cwvx; -qk2tn:2mq 1lpokance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$