What quantity is measu6f1w hd wg1, ftz4e)9d4u/tid-g7twqm2 abatred by a battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a cirz ;iq r),eq, 5igpvsp..gac8r cuit, electrons flow away from the negative terminal in the circuit. But within the cell, electrons flow to the negative ter85, q ge ),qi.cvsa girpr.;zpminal. Explain.

When a flashlight isl*4gpdlxv wb338l7ds operated, what is being used up: battery current, battery voltage, battery energy, battery power, or battery resistanvlw b*d dx38s3 gl74lpce? Explain.

One terminal of a car battery is said to t6+ume24 bttnbe connected to “ground.” Since it is not really connected to the ground, what is meant by this expretu62 bn+4 mttession?

When you turn on a water faucet, tr/l1,vcp4bs3blad (z+q 1r fv he water usually flows immediately. You don’t have to wait for water to bal1fl,/ 13v+ zb4(qrv pr sdcflow 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 i4 aol wu7+d1y jzzl cq8q5i*+the same resistance? Expldiiw *+a7z8oq jl 1+quc y54zlain.

If the resistance of a small immersion hea bm pw yoq+tn5c-u5:z/ter (to heat water for tea or soup, Figwt:z5op y- /+mqnc5ub. 18–32) was increased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengtvkax5/if /5gm u.nv7e hs a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resistance, (b) t.5veki/f g 7x5nua /mvhe 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 lightbulb burn .qc.iz)w0 +r : h,neoj7rhnors out?

Explain why lightbulbs almost bt zvn)p3d23rb1bn gs773j o q*/syobalways burn out just as they are turned on and not booptbv7sy* 3b23n/ g ndbz1js3)7 q rafter they have been on for some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which has the kr9ta7o 2ni-r3)vwuzbn:c: i higher resistwi :rcn2or :vubkat -in9)73 zance?

Electric power is transferred over large distances at very high voltages oia3qiu rg23xb7ba3/e +*snh . Explain ho uq3gi3 n2r/b*ia+bs7h o 3axew the high voltage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fuse0a;b)y k3jzf c with a 25-A fusa;yzc)j kfb03 e?

When electric lights are ope.vrpskc( z w5 2a46q9npmo)wp8 +pdva rated on low-frequency ac (say, 5 Hz), they flicker notikq9w4nd .op5cwapps )(m p 6r8a2vz+vceably. Why?

Driven by ac power, thex(,qlgttk 4:p/;rx f y same electrons pass back and forth through your reading lamp over and over again. Explain why the light stays lit instead of going out after the fyqt( : lx;p 4rg/x,ktfirst pass of electrons.

The heating element in a toaster irnkx m+6 b(y8ws made of Nichrome wire. Immediately after the toaster is turned on, i xn km6r+bw(8ys the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in 8xl()2fmwut kcq* 3foa resistor? Explain.

Different lamps might have batteries connected ifn - 61dz5ihipn either of the two arrangements shownhi 6fp- 15zidn in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many 8fg k i y-.opqpna8e(t)ojenx)r :) k4electrons are flowing past any point in the wire per je.8kne :( kxyp -)oqit))og8rf n4ap second?    $ \times10^{18 }\;electrons/s$

  A service station charges a; xyr,rj4 baq) battery using a current of 6.7 A for 5.0 h. How much charge passes through the batr abr xj,y;q4)tery?    $ \times10^{ 5}\;C$

  What is the current n o)+:nocdb-kfb/ z62 htqqxcl7 c+5gin 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 producekoqms34b tdtva90 2:qs a current of 4.2 A?    $\Omega$

  What voltage will produce vdub 88th6w+ z0.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when pluggedxxsb;zqzkd+s 5.vv4to ettp8cc; /81 53 pyhh 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 with a ren+j18y ai6yg x8cwo u1sistance 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 reypbd bk 94p)y8sistance 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 (F mfrr qbj8zhb215waxz ; .h;d6ig. 18–34). The wx6;z8 zbjb21dr.haqr 5fh ;m 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 Vk 8,w 9sa 7h f /i0rpgc3ye;hha;d-uvr.
(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 tuidp+7nw h /jnzfd)9n +u a2v(hrough 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 ;ma5.ra +-1 f) bstcdbjdsa:p tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of cd ejpsv6k:s.5opper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistancu hank0y-6eh7e of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in diameter.6-ea7ukhhny 0   

  Can a 2.5-mm-diameter copper w- ptzqi/o3o*dc g ,fe5z2jqa1a7,rwd ire have the same resistance as a tungsten wire of the same length? o ia-r wfc/o,zq,d3edpa7q tg* 125zjGive numerical details.    mm

  A certain copper wire has a resistancet);w jn,y 4ccklfmxb(f 2sn75 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 copper wire (orijp3x; .e)ljsl ux+;qiginally at xe xs j;i);q ullpj+.3$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the sampi h8ntwc73h 8e resistivity as tungsten do8n7 ip whh83ctes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a rel/6gq.mq oi7r+mp.k2kp; b tysistance 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 hou,advuf7ztcmk3in6ms m )1)u2sehold no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm and carries a 12-3va7msdmuzic, knu6tm 21f))A current.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm, *xpm:kz rpg9.xxr 5q-7n sz hge0-8ah2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for curxzp07nhr-5pzkh x:m. 9xaqg * ers-8grent 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 resistancea5jzj*ees pv7 7x2r+x. If one has twice the length of the other, what is the ratio of the diameter of the longer wire to the diametee7vj 2rps *7ej+zx a5xr of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V power slv9 14 +hp l;0krk bt wd6.kmhwxef:b8upply, and a current of 0.6.mv k x;ed 8+:4wh9pfbkt1bl0hlr w k4212 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 m of alumin+xvpf 0z*q +pfpr5ze 3um, both of diameter 1.0 mm. A voltage difference of 85 mV is placed across the compospexq +5p *ff3pr +zz0vite wire.
(a) What is the total resistance (sum) of the two wires? $\approx$    $\Omega$(retain two decimal places)
(b) What is the current through the wire?    A(retain two decimal places)
(c) What are the voltages across the aluminum part and across the copper part?
$V_{Cu}$    V(retain three decimal places)
$V_{Al}$    V(retain three decimal places)

  For some applications, it is important that the value of a re ehjwdj(l).2ril * yxw)e2 r0asistance not change with temperature. For exam x.i(rle 02d)a*j2we ry) hlwjple, 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 q2av di .)cs0d1y)ctn an electric oven is designed to produce 3.3 kW of heat when connected to a 240-V source. What must be the resistance of tvnact)d) c 2 i1y0ds.qhe element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable2v sznhb). oes9+ /rgl CD player that draws a maximum of 320 mA rln+ hs) vzb29/o.s geof current?    W

  What is the maximum volt. o2 dhndnn)b 6mb+j36nhx md5age 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 lightbb:x+m ll4t -ae)4h awvulb connected to its proper source voltage o )e+ 4m-4wvth la:labxf 120 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heatv +/awbv n;i3xer is rated at 110 W. Calculate
(a) the current through the heater when it is operating,    A
(b) its resistance?    $\Omega$(Round to the nearest integer)

  A 120-V hair dryer has twoq 1ql y80bkiz;pe kmuczn.32+ 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, where electricity is delivered to h. y:stwp yaay93ozi7, omes at 240 V.:. awyzos i,3paty 7y9 If you use the lightbulb in the United States at 120 V (assume its resistance does not change), how bright will it be relative to 75-W 120-V bulbs? [Hint: assume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use in the mornin o:4:fqwzwqg*i+g rz0 g if it is in operation for a total of 15 min? At a cost ofr+: wzgf*:i w40 qqogz $9.0\,cents/kWh$, 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 doeasmbeb+ ek rf98l7g 5.s it cost to leave a 25-W porch light on day a89+7eg5s mbkbaf.el r nd night for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batterie5n- cha iti8s ;k(m7xes connected in series as in Fig. 1sicx;5k8 i aeh7m t(n-8–4b (Fig. 18–36). The 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 stored in a 12-V,87vadlk(e 8/pedox tz 5s 67ktuj5rh9 $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connected to f h7oc tibr9nm .5z18,bpdr 5q120 V as in Fig. 18–20, can be used without blowing c hdn75b9opz.1 5if qm,rt br8a 15-A fuse?    bulbs

  An extension cord made of t j;6jn a: uz3u2t:ova30/huggw9 cm gxwo wires of diameter 0.129 cm (no. 16 copper wire) and of le0c z:wg 6j juuv9u:mxg aoa3tghn2;/3ngth 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 delivers4 chf3ii )g1vaxdkshap7e8. --dtq u* 620 kW of power at 12,000 V to a factory through wires with 3g 7*pih 1d-i.)asv4 kt-duhq cx8eaf total resistance $3.0\Omega$ How much less power is wasted if the electricity is delivered at 50,000 V rather than 12,000 V?    $ \times10^{ 3}\;W$

  The current in an electromagnet connected to a 240-V line is 17.5 A.po3 (txxtjlj /-l25h+xf z- zo At what rate must cooling water pass over the coils if the water temperaturezj ltoz+ 2 h-jptx(-xo3l/x 5f is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater jl//qlkqdxmk /00) md can be used in a car to heat a cup of water for coffee or teaq kqldk)0 m0//xjd ml/. If the heater can heat 120 mL 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 currentz.(d7cq e8mxz 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 across a5i9m liryv-4k $330-\Omega$ 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 2b:hj32 mysgcof 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 1500-W device is 5.4 A. What q, (mc ghb1xybgbd9 :(3 rusu/is the rmss( q:gdy m bbr(/bh93xcgu,u1 voltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder hb*p pfxw)9m wf8e;2)om2 basis 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 p7a eraaljs 1;/y n4pl7ower dissipated by a 3.0-hp pump connecte4ayas /ne;r7la1p7jl d to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to a u3fg+4/gzsy u-;f l iv$240-V_{rms}$ 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 hv)0wiuv il-n4da; /sof $2.3\mu A$. 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 curre** 3buaw +ijbfgvtmm 6ru 48c1)1ilh fnt when 22.0 mV is applied to its ends. I1 *gfv+umthlfc4 i j6ir*8b3a)1mwbuf 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 atmosphere,3u,glpk kew,p p+mewu7:ok (, $He^{2+}$ 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 Eu*dzrm32d g q4y-2f63lyo wufarth’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 electric fielir oss3+aq-k1 d 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 actionm4ilvi64i2bvbh hfsx 3bkq1 n:5p6h - 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 stimulation, the time required is 0.0063 s. What is the speed of the electric pulse along the axon?64h1mb s bqihivkxl23pvh :i4 56bn-f (Why are two measurements needed instead of only one?)    m/s

  Estimate how much energy is required to transmit one action pote(uz7hd.8uj4z j bxhx1ntial along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equiva.zxxu7 81u4(hbdjzh jlent to the energy stored by charging the axon capacitance; see Section 17–9]. What minimum average power is required for $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action potential,0b6ar) rru xpmx*45ta $Na^+$ 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 5mz (dx3a1kxqw .mi z51.00 ampere-hour?    C

  What is the average current drawn by a 1.0-hp 120-V m0vjd1p y d0yi9:3fmx wotor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on.* gx8dxnj0ei 7 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 battery last if it isxe87gd0 xnji * 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 ph hwft -:)kq)of ironpk:twh )) qhf-, what must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal o5du-y2t c88+,rowzx 9pn4dnaggl0dqf the resistance R; that is,rcd-d l+ 8dtg,q9zxnog8u 24 pn a5wy0 $G\,=\,1/R$. 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 instef-+t* ia eqyxe1 5bc9ead of using high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a twoefe a+ 91t-qe5bixcy*-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 household uses a 1.8-kW heatwdt9 c(46hutvhpt 7s c33x (mner $3.0 h/day$ (“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 aswmw3kr 8+dc 2re wrapped together side by side to make a thicker wire. How does the resistance of this new combination compare to the resistance of the original wire?8r2wd cm+ 3swk

  A 1200-W hair dryer is designed f ,umw6cx41 wsk4jowka1 1d7enu c j-l4or 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 not become so *nvx2. ai,g 1ngbes v8hot 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 hea81nveg v2b *.i ,xngsat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by the equationb brdt2)9l k)k $I\,=\,1.80sin210t$, 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 w(gi;)dib sk: second to ki; s: wi(db)gthe 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 thgbn q m5l;y:;he same material. One conductor is twice as long and twice the diab; nm;hygql :5meter 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 r9bmmzgvi u : tai2-,c.oom 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 t n3 pe4hv,vrov,+0f.q5 a8djw -ttoma 240-V source.
(a) What is the resistance of the oven?    $\Omega$
(b) How long will it take to bring 120 mL of 15$^{\circ}\,C$ water to 100$^{\circ}\,C$ assuming 75% efficiency?    s
(c) How much will this cost at $11 cents/kWh?$    cents

  A projected electric vehicle makes use of storage batteries as its source odlr b2; j4o06re4rh)yai4b.nso q6s(y ,urskf energy. Its mass is 1560 kg and it ).r4y4jar;e2o ub yd6o h,sq rsn6i( l ksr4b0is 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 yu*z e6lh3 mm2resistance 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 designed tbt8ag l ,nld:h( v q r ybhy-am3h9xmnf:(*6a+o carry an 11-mA beam of protons traveling at very nearly th(l,lf3-*yraxnn: v abqd agmhmt : y8( h9+b6he 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 wire wikrkj5a;(zaz -wx w 6m8th a dzm;(rxwakk w8a-65 jziameter 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 rdx-*t)do 5iupl f p+m*ated at 95 W when connected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What is 5ipmf)*ldo- tdu*px+ the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltvn)4:wg(solzm k(n5 u age varies 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 the powe4 ):l5n w (zosgnmkvu(r 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 ageqtc:e5ujbvlwb1 b/ * 0o50w nd 40 W for household applications. Lightbulb B is rated at 12 V and 40 W for automotiv0t*g ju/w5oqlv b bcew5:b10ee 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;/au kd jf)2tdrn qq-5q j)-no is used to connect a set of appliances at 120 V, whirdof-jjn )nad k5tq)2 u;/ -qqch draw 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 cm l qnf/7;tqz 4yns6o(8k5zpwy and an outside diameter of 5.00 cm (Fig. 18–37). Wh(8w;zoz4l7n k/ qs5 fypny6tq at is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly h8mtjg4q pg9d96v.atso that its length doubles, by what factor does the power dissipated in t8g 9gq m9jptd.hvta64he wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a fl4 0r(ad9jdldx ashlight bulb operates at 0.20 A and 3.2 V. If ia dr90l jdx(d4ts resistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$