What quantity is measured by a battery rating given in ampere-h kah+fbejt..p; dgd 9 j(d(v,8lw/it mours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow away from tfsc 5f /yy(20ea3zcn the nega3fcnt(zca 0ys2fe/y 5tive terminal in the circuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, whatq(ppvv.h 86ay6 i0vdh is being used up: battery current, battery voltage, battery energy, battery powerv6p8vha p0yh(. 6dv qi, or battery resistance? Explain.

One terminal of a car battery is said to be connected to “ground.” Since tq u q:l1d0ob wavp1qi 3fr05+it is not really connected to the ground, what 1rbqqo0lud5+1a q pf: i3twv0is meant by this expression?

When you turn on a wwn q78a7 wi.aqj2f2;k eu3xde/ 1qzhwater faucet, the water usually 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 when y adz3qu8e/xqkf iq7jwan.;h w2e 1w 27ou connect a wire to the terminals of a battery?

Can a copper wire and an aluminum wire of - zmeo7h:kdd3,x w6a mthe same length have the same resistance? Explaindm3h6oaw mzk,e:x7- d.

If the resistance of a small immersion heater (to heat walf0*pbn4x0y pe3 0xch ter for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the h043pxbnfh lcey0 *px0eating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, /bog,uep*hs ) 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resistance, (b) the greatest resistsbu/*p,h oe )gance?

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 lightbulb burn5t etgvnugo ;45odvr52k; c0xs out?

Explain why lightbulbs almost alwg+ t -7r;28ma opsmitb1fc 5amays burn out just as they are turned on and notmat7 -8pommtg5; r2f1 s +acib after they have been on for some time.

Which draws more current c,5ar,ismkcd91fm 5x*d/tyy r6s v.e, a 100-W lightbulb or a 75-W bulb? Which has the higher resistanc d1ik/sr.r,yse c5xmf,6*yma v5c td9e?

Electric power is transferred ovb h+:4pjfjj b * dcy .z/jl+lzef5o(-xer large distances at very high voltages. Explain how the highj+lx5+ hz/:(fo-zef*.yb pj cbl dj j4 voltage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fuse with a n 2g6emv/m a,)g7xvl h25 gl/mhn6e ,vga xm7)2v-A fuse?

When electric lights are operated on low-frequency ac (say, 5 Hz), they fliek7,6 palt:hp cker noti,k 7ptlheap6: ceably. Why?

Driven by ac power, the same electrons pass backfnbk us u6 9+-cx/g7be and forth through your reading lamp over and over again. Explain why the light stays lit instead of ggk /usc-+ e 67bbun9xfoing out after the first pass of electrons.

The heating element 1vz) xpxa1 9rbin a toaster is made of Nichrome wire. Immediately after the toaster is turned on, is the currenbvp rz x9x1)1at $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resr:qldgdl,ntn7e0n t*v0-x , t istor? Explain.

Different lamps might have batteries connected in eit 1m/vwv m58mu5k1vcuye,4w 1raba8ru her of the two arrangements5kw,ebura48mc1mvv8u1 r5/wuav y 1m 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 electrons are flowing past any po hztm4904nj8eb6e ievint in the w6h9 e ej8bm4 ve0nitz4ire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A fop qe5n gne:2g+hb*m 9dr 5.0 h. How much charge passes through:nmqg+b2e* phn5g de9 the battery?    $ \times10^{ 5}\;C$

  What is the current in ampe, 76ja4c pzs0v,vp ymqres 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 current of 4.2 A? y:)no;x ptz2r    $\Omega$

  What voltage will pros 3d*fu4 ghb8oduce 0.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when pluggedtq2 r,)*xug 3g xwa)zq into a 120-V line.
(a) What is its resistance?    $\Omega$
(b) How much charge passes through it in 15 min? (Assume direct current.)    $ \times10^{ 3}\;C$

  An electric clothes dryer has a heating element vgz,wrnl 4* w4with 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 conne nww+r4-*o f9ywpb(u kcted 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 electric transmission line carrying 2800 x *tvu1r1 baur2k bg8),cj/dz A (Fig. 18–34). The line has zbd 1rc/xtu8v ,kj1grba) *u2 $2.5\times10^{ -5}\;\Omega$ 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 6a3b q,un jd(w2.50 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 curr-4c fy9vopse 5ent 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 diameterz:) h (fbn7qpu of a 1.00-m length of tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1.5 mm in diameti :z ppd1 7hy:bdjyej, 96soi3er?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of r,mxt)qq( b)zaluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in diametmz,(q q tr)xb)er.   

  Can a 2.5-mm-diameter copper wire (zw+ g9czm0k uhave the same resistance as a tungsten wire of the same length?wk(zc9m gzu +0 Give numerical details.    mm

  A certain copper wire has a resistance dv+v 8 jc4rcx5sk+a:j 3k* ogyof $10.0\Omega$ 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 temperatur/ hetsv2w2fcjn 2v 07re of a copper wire (originally at 2erw2 7 /2thfnvj0cvs$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivity as tungstetjvojvf4icw l04 eg x4+l8)z0 n doe4t+l 00vl44 zjj8efx vgcw o)is at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has efle7gj,7a(7 xt xmst,bmk)1a resistance 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 cop twk0do 2s x9:ou7evb-uq*2xe per wire (used in 15-A circuits). The wire has diametu:b2 v7kus*q9o -oxtdx2 0 eewer 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm, 2.0 cm, and 4 k3:rkam 0o9khc:ma+ h.0 hh3am ka09:omc+kr :kcm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for current that passes through the solid in
(a) the x direction,    $ \times10^{ -4}\;\Omega$
(b) the y direction,    $ \times10^{ -3}\;\Omega$
(c) the z direction. Assume the resistivity is $\rho\,=\,3.0\times10^{ -5}\;\Omega\cdot m$.
   $ \times10^{ -3}\;\Omega$

  Two aluminum wires have the same resistance. If u bk:xq1s8zbpn( w:)r one has twice the length of the other, what is the ratio of the diameter of the longer wire to the diameter of the shorter :1ps bqxw zr:uk)b8(n wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precisi-cs6( h/ndlpji, eo-o 8)f ciaon 10.00-V power supply, and a current of 0.4212 A is precisely measured at cion-- ho d)asji8,fl 6ce(/p20.0$^{\circ}\,C$. 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 m of aluminurz b4j (n0fkrs1df9yekz d3f1p 047fy m, both of diameter 1.0 mm. A voltage difference of 85 rf74kzf j ydf31fpner0k9(4 s zdb1y0mV 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 awd+ g0b(cj 8cis important that the value of a resistance not change with temperature. j8g c0+(aw bdcFor 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 to produceh m3kgc69bfa. 3.3 kW of heat when connected to a 240-V source. What must be the resistanca3gf h6.mk b9ce of the element?    $\Omega$

  What is the maximum power consumption of a /b41zftdl:v x 3.0-V portable CD player that draws a maxi: vl 4xdft/zb1mum of 320 mA of current?    W

  What is the maximum voltagw5(6)yqqr x fvqgw6 r)e that can be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resi:vb(:sy+qnc e2l6s e(utt 1 qcstance of, and current through, a 75-W lightbulb connected to its proper source (e2utn q(clb sv16cq:: tey s+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 a ccr)p 7yteba9ixi2cj n:1e+8t 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 andc ubawq:78 q2j 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 0fdnvx-h +ja;qx4+fk is delivered to homes at 240 V. If you use the lightbulb in the United States at 120 V (assume its resistance does not cha +n-+f4hqfa;xd j0vk xnge), 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 :-q* + nzrjyslif it is in operation for a total of 15 min? As*:rqz-lyn+ jt 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 kWuwwi7y4igkjo;1, .qy h, what does it cost to leave a 25-W porch light on day and night for wk,yj4g; i ou 17yqi.wa year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5- y)(. ,s8ux;whx pgezrV batteries connected in series as in Fig. 18–4b (Fig. 18–36). Thwuy;x8 sp r,.)ezg( xhe 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 stoxc p(ee n hr+4q .w/ce t.er.golj3i.+red in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connectedna)rgyd3 8 7y tos5r1e to 120 V as in Fig. 18–20, can be used without blowing ayn8 )toesgr d1r357ay 15-A fuse?    bulbs

  An extension cord made of two kpzkg1tal; - 5wires 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 1kk;zg5al p-t 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 thrj59qzk;0vyy49k t ubdd 0m4 b4 t8fxqcough wires with total resistan4kvcbqb jf9k; tm4z q5d 80ty40ydu9xce $3.0\Omega$ 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 line is 17.5 A. t+d2e 3*ebj;zhn .nm aAt what rate must cooling water pass over the coils if the water temperature is to risdj*n 3hbte .mnza e;2+e by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to 5y f4f;tvveva j )8j9sheat a cup of water for coffee or tea. If the heater can heat 120 mLfea4v8 f5vs 9j;v j)ty of water from 25$^{\circ}\,C$ to 95$^{\circ}\,C$ in 8.0 min,
(a) approximately how much current does it draw from the car’s 12-V battery, $\approx$    A(Round to the nearest integer)
(b) what is its resistance? Assume the manufacturer’s claim of 60% efficiency.    $\Omega$

  Calculate the peak curren1ao *yboz;5uit in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, is )rm/ tc-rv v2nacross 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 oc*:vsb n1hiay *l l3 *03zxjflf 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 1 j/p 0fhfy:pxvq+( ::ww.bhzo500-W device is 5.4 A. What is the b/p:yh+zqh pf (jwx ov0:.fw:rms voltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected4 ks(1 mvn:w; mtau/5nqob;3 d6ke crn 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 distvi9lp/ f:56y3 qpi p:9 od,rsl e9tnrsipated by a 3.0-hp pump connected3,5vi r9ql6/ptpelt :iyops:rf9dn9 to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected tee(h v(ycf7v0; l:1d ji x).vep x.pdbm3zj k6o 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 copperg -*v2/6at zfx r( /dde4pmrkc wire carries a tiny current of $2.3\mu A$. What is the electron drift speed in the wire?    $ \times10^{-10 }\;m/s$

  A 5.80-m length of 2.0-mm-diameter wire carries a 750-mA )tubqo1ku tdx-vd;f b92ok+ 6v qb4r- current when 22.0 mV is applied to its ends. If the drift spu6-xub) ktkf1bqbr-;qdovto v2 49d+eed 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 Ea a9y.(mwl9rfbgcm i2 ;j(ox (trth’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 atmosphe my0*zt 8fv foyosr.8eb,vh7-re, $He^{2+}$ 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 acp9dx70xuaq u 0ross 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 potential is detectezbd4d : hge1vhao029 ld at a point 3.40 cm down the bzvhhd2d:l1e0a4 go9 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 i je t-d :xehv*lax46c0s required 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 ad x04tvjeac6 h :xl*e-xon 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 potential,0ejuqc-w wnwk5w,) leq.sc:/ $Na^+$ 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 ar sj,ob ( g..5azscl9n)ei1vvl e there in 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0-hp 120-V mot+y7qmv(nbn +i ti m ;2+futetd-rx(b )or? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the .ndyku6 .(dhn3wve ;6 9 7vl zukt1titlights on. If 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 bat.ht et;w7t vn6d3k1udu z9v.klin6 (ytery 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 it is made of enz1 fkjqxj1 e gt:5i*-pjp;,sja6(piron, what must its diampaj *e 6 pe1skizfx ,-qj;tjng15:j p(eter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the recipe .8cv.r ruo+vx l/2rqrocal of the resistance R;vrv8uc. +qr.2x ol/re that is, $G\,=\,1/R$. The unit of conductance is a mho $(=ohm^{-1})$, which is also called the siemens (S). What is the conductance (in siemens) of an object that draws 730 mA of current at 3.0 V?    S

  A small city requires about 10 MW of power. Suppose that instead(e)(yb4 qju sj3 j b*hxvit4x: of using high-voltage lines to supply the power, the power is delivered at 120 V. xsi vy 3j*jh(xj4tu)b :4(beq 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 electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular houem:lhgee a640q;s 9n isehold uses a 1.8-kW heater $3.0 h/day$ (“on” time), four 100-W lightbulbs $6.0 h/day$, a 3.0-kW electric stove element for a total of $1.4 h/day$ and miscellaneous power amounting to $2.0 kWh/day$. If electricity costs $0.105 per kWh, what will be their monthly bill (30 d)?    dollars per month
(b) How much coal (which produces $7000 kcal/kg$) must be burned by a 35%-efficient power plant to provide the yearly needs of this household?    kg of coal

A length of wire is cut in half and the two lengths are pc8xr ,y .wk:pwrapped together side by side to make a thicker wire. How does the resistance of this new combp.r cyx:p8wk, ination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for ae.haeb8mh ej-: w u/f:uoc55117 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 y5ir 99(f1ysf;f hem pnot 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 hesy1(;mfp9 5r ih y9ffeat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by the equath,jdb4ree+jqph65 8wtfeqn p8 , 7:bl( duol8ion $I\,=\,1.80sin210t$, 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 per second cuvtmk hue68r q)3 cg+ r8mm09to the interior. )m t0cuk6 r8+qm vcu8g39 ermhFind
(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. On8 jyue))2h fgt5evt-xe conductor is twice as long and twice thet5tgh)8je 2) eyuvxf- 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 voluy2lp6t6qd mm e,vgo.6me $62\,m^3$ 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 sour22g7am8yz9yrtxq5x.k mt hv.ce.
(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 stttg9t y5-nftm1wmv 7s,r t 7y*orage batteries as its source of energy. Its mass is 1560 kg and it is powered by 24 batterie5m,7y n9ttvywg *m t7t1tr-sfs, 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 resistaqud5dh x: 8i,knce 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 Fermitn.l a c(gl46zlab (Illinois) is designed to carry an 11-mA beam of protons traveling at very nearly the slz (nt 4lc6g.apeed 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 copqx :e894mfcg bnpu(;x per wire with a;bpg(fm:xe8c x9 n 4uq diameter 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 conne a62n).f3ae kli 4ulc3smnm)qcted to 120 V. The heating element is a coil of Nichrome wire. Whfs u.ml3q6lk4m a)e)ca3 n2 nien 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 90+gfv nnzimr,e p pn cg;+3i2varies from about 12 V when the car is off to about 13.8 V when the c2;c+ pn03ipgne+f,nz9m vi grar 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 120 V and 40 W fo4 (4iyi c,vzhor household applications. Lightbulb B is rated at 12 V and 44iio,vc h(y4z0 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 connect a set z,3sa herlqs 3+b),f,1d ra 6gm+idytof appliances at 120 V, which dd ,mby as+df,h is+3r3 rg)z,1a6qetl raw 2250 W 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 3.00 cymr i7h5c:alj5el( 7ym and an outside diameter of 5.00 c5cly7ile : ra5myj7(hm (Fig. 18–37). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R iskcj *hh+ gww6- stretched uniformly so that its length doubles, by what fw-kj* wg+ 6hchactor does the power dissipated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in e gv/u yy0d6t7 )symeb+6rn3ya flashlight bulb operates at 0.20 A and 3.2 V. If i3 )sev6guyd e6+0yy/tn b my7rts resistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$