What quantity is measured by a battery rating given ik44d5j:imq ujy3d5 dxn ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circkcs*e q npdlbo1)pbu(b2fy3p/7 +2xfuit, electrons flow away from the negative terminal in the circup2 fubcl1fy2 3b+)npqxed* p s/o (7bkit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battex 4+zopix04fqry current, battery voltage, battery enef4x z+xioqp04rgy, battery power, or battery resistance? Explain.

One terminal of a car battery is said to be connected thvlm /5 (qvjo5o “ground.” Since it is not really connlojm q/v5 5(vhected to the ground, what is meant by this expression?

When you turn on a water faucet, the waterzxsj 8() n7ui9ab ,rcf 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 you connect a wire to the termb8srz(n c,aiu 9j7fx) inals of a battery?

Can a copper wire and an aluminum wire of the same length have the same resis qdnwv(4l jkkouq .;,k+6qf8e tance?l;6k8v4kqjk nd,w+u .e qqfo( Explain.

If the resistance of a small immersion heater 2rfihf wf6v,x9mj 1 o3(to heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the heating process? Explain.fo2vfx,6rw9im1 hjf 3

If a rectangular solid made of carbon has1jg+c v cp(mkpmd(o3, sides of lengths a, 2a, and 3a, how wodjmk,vg(c(+13opcm p uld you connect the wires from a battery so as to obtain (a) the 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 lightbulb a *nyh0,tc d:gburns out?

Explain why lightbulbs almost always burn out just as they are turned on andhpibp g5l8n6 u. uo46z not after they have been pg8h6iu.nb 5po46lzu on for some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Whi0 ou y9es,xa /w2si9uqch has the higher resu/xs09 oyiaweq2u9 s ,istance?

Electric power is transferred ob;p)t vx-2u- ze;d +b-khx -nmrgxx2zver large distances at very high voltages. Explain how the -k2 n+2x) evhbx-;;m tpuzz -x- gdbxrhigh voltage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerousth 5n cuww62c9 to replace this fuse with a 25-A fuse?ccw56n tu9 2wh

When electric lights are operated on low-frequency ac (say, 5x702i p5fe a711h cr,ohkwz gqgb+c g7 Hz), they flicker noticeably. Why?+oc7xhgi1cf7a7p ,0r 5bz21gqkh weg

Driven by ac power, the sg1(zjcui(. ,gk6n-v .hvpt wwame 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 f .g(6pwvi ktc1- g(wnhzjuv.,irst pass of electrons.

The heating element in a toaster is made of Nichrome gi)9z9oqb u(b wire. Immediately after the toaster is turned on, is the currenzbb99o(gi)q ut $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a r(6;okr i9vqdany3 e)fesistor? Explain.

Different lamps mighwbh)j,ep kp85rww*7l7y :3x l.p wa hjt have batteries connected in either of the two arrangements shown in 7l5,jw3 .yh8 bkphjw*w)r:a 7e xpwpl
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many electronsz6j: mp2-wtf xll rlh),(jv f1 are flowing past any point in the wire per second? jtf(hjwp x-v,r: 6l1 m2fz ll)   $ \times10^{18 }\;electrons/s$

  A service station charges a battery obmp7yd a e( ;eye:i(7cymx7 0using a current of 6.7 A for 5.0 h. How much charge passes through the batter7o(b; dexye( y7:c 7miyepm0ay?    $ \times10^{ 5}\;C$

  What is the current in amper *m-wcfz q 1eftejq*w9ti2/: ses 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 ofnooo gn(k9)u1u2 f1 ri 4.2 A?    $\Omega$

  What voltage will produg 2t nvnm,d*e7;7oa(km;synhce 0.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A*u9 vg. ic0p6o ys1l a gyuh.qpl;3xo;n0/nyf when plugged 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 withqu m yubnwp/f3v8nzj ,51/4xh 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 abuf ,,4 hxnhs5 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 ca /zkuw /ly+sx ov)9as5rrying 2800 A (Fig. 18–34). Thewz5)xo9 lua /ksys +v/ 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 j /5yoq+so k -. 4. sn0kh7n2dhuarlxpV.
(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 through a resis1gp/wh)nd 2kn,,u z dl)cm m1xtor.
(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 a5w-paw9x 3z5zdf2kw)0k aif e 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 w4so s+z./sw zlire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire 2.0 mm in ditrq rt13lx/ 5iameter, rlqrtx51it /3to 20.0 m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter coj l,x h m9k5a4ytx4)mxpper wire have the same resistance as a tungsten wire of the same length? Give numericax4 xxaml4k,yjmth )59 l details.    mm

  A certain copper wire o)xrjny, dk; 6has 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 tioo ;r8fk86m njj5vj w,-oe i6he temperature of a copper wire (originally ati ej6,ji mnjo8- kf5;o68orwv $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivity as twev ;.0l6b p/gnh1ilco6fp g(ungsten does atbn6eill6hgvcf;w.g( 1p0 po / $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of aboutmt bc9fuo,9b p fe0rkuza*9;* $12\Omega$ 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 aloj6( phg)6p9srzo:x3(v lik k tng a 26-m length of household no. 14 copper wire (used in 15-A circuits). T6:(3os zkjvtk pi6 rhxg(l)9 phe wire has diameter 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 f.z rd45 uc.9skotlh.4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for current that passes through the o9zlh.4rktc .f u.5sdsolid in
(a) the x direction,    $ \times10^{ -4}\;\Omega$
(b) the y direction,    $ \times10^{ -3}\;\Omega$
(c) the z direction. Assume the resistivity is $\rho\,=\,3.0\times10^{ -5}\;\Omega\cdot m$.
   $ \times10^{ -3}\;\Omega$

  Two aluminum wires have the same resistance. If one has twice the fu7 :a;i-l qajleg2*l length of the other, what is the ratio of the diameter of the l :fua-gea 7qll*2 i;jlonger wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V power supplyia jlb3xdpc ns554( z1)m6pus, and a current of 0.4212 A is ppn5x(ui jmz6541pbd 3acs sl)recisely 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./ej/5 qlov ooayffdpr 14i 5, +ja46jj0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is placed across the compoja q/e6,1f4/j5o pj+d5 rfl4ijaov y osite 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, ifn -6oa sjzg85t is important that the value of a resistance not change with temperature. For example, suppose you made a -5g nz j6fa8os$4.70-k\Omega$ 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 to0edkf gy 1yw52x2c7o u produce 3.3 kW of heat when connectedeyo 27c ug2d1 0y5xfkw to a 240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player that draws xon 6gix)i3m6w c1pxy-: kzm+ a max)p6w 1gx kio6xy3m-cm+:zn xiimum of 320 mA of current?    W

  What is the maximum voltage that can be applied across a 7 a2jd;ryti02 40w nelr zva;d$2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, 9+:ovte gpc vk()ep5 j pg5g 5dq/6ylland current through, a 75-W lightbulb connected to its properv5:)5/k e p v6dc9ptg( +qgpo gl5jely source 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 at 110 W. Calculah;rb ;r/pn1ibfs pd6) te
(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 and 1250 W. u- -no2xmu+ncyvq ox+f8 zl1+
(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 lightbulr gb5pzo1 -x*ib in Europe, where electricity is delivered to homes at 240 V. If you use tpb1i r5z*oxg-he lightbulb in the United States at 120 V (assume its resistance does not change), how bright will it be relative to 75-W 120-V bulbs? [Hint: assume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use in the morning if it is inpbx ;8mts ymj,rn h;; tg8zy)r:5p7b s operation for a total of 15 min? At a cost of m;s zjy prt8:s 8r;7tnhmbb xp;,)gy5$9.0\,cents/kWh$, 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-Wzpgvrm- /: wk2l*+ ls54ibyiq porch light on day avzy2g5-4l r i:/lw*sbmi+q pknd night for a year? $\approx$    dollars

  An ordinary flashlight uses two D9tfi kxwz1b 93-cell 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). Thezx1ti3 w k99fb 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 12hxix9a-/ik4 4yd ig14feknk (-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.dpn 8eu3o2w1u fc*k7g*w+ qu g 18–20, can be used without blowing a 15uw 1 gfe8dg k7*qnwuocu 3*p+2-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cvppf4nx9krqy .d6 2g*m (no. 16 copper wire) and of length xvpqnrfd4 *gpk y2 6.92.7 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 delivers 620 kW of power at 12,077 qhnkxcv 3znug,.e(00 V to a factory through wires with total resi( 3xh7 uqgc 7v,knnze.stance $3.0\Omega$ How much less power is wasted if the electricity is delivered at 50,000 V rather than 12,000 V?    $ \times10^{ 3}\;W$

  The current in an electromagnet connected to a 240-V line is 17.5 A. At what ratk8sp f7c9w9.uzr04 6gra1y griz*l f le must cooling water pass over the coils if the water8w7 uciz90 l s9pfkay*.6 rzrgl4f gr1 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 water for cof2 +yd 6.uwn4yg1n frnrfee or tea. If the heater can heat 121nudrfy n6y+ g4. wnr20 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 currentl 3s* dg:m2dxg95qnk d in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whoseb 1tt)vlhs t 9c;xa(g+st k(:x peak value is 180 V, is across a $330-\Omega$ resistor. What are the rms and peak currents in the resistor?
$I_{peak}$$\approx$    A(retain two decimal places)
$I_{rms}$ =    A

  Estimate the resistance of thrjd) +cq.geby z *od-q- ;,mwne $120-V_{rms}$ 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 devip8b2 yo(+e7pz*du zh xr7.q3 nceqi1 lce is 5.4 A. What is the z 7 yed*ihrp7+82o np b czx1luq(e.q3rms voltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected (s v lwq 9s3:f-n;:lqibvaw5zto 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- m8l tlmzyg9.+hp pump connected t.tzlg+lm98y mo 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 2wkkmak 9(veea*q94) rz9vpo$240-V_{rms}$ 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 coppe eeksj:6 lx-l*w:fv 5vr 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-mAvus 98fnao l., current when 22.0 mV is applied to its u9l.8nvsa,f oends. 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 E 1 am5/xx/vahoarth’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 atmosphere,(dusk1ts3q (x hmw6b 2 $He^{2+}$ 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 acrosss,n u:ogo8 3ip 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 ac(a n;yishd;2stion potential is detected at a pay ;nssi ;(d2hoint 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? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much energy is 10j 01do5kd.j9 zcawt)0g( egliq8 rzdlj 3oo 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 axon capacitance; see 5lg() oj eka00 i8.czozg d1j9rqt3d1 ld w0joSection 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 poteng yyy5ia,i+ in6l4xcqdm8 cw60 q8 6bdtial, $Na^+$ 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 then enxx*7vt2.l0xkx(obzp :z)re in 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0-hx- 2x3xjk3 bv,bxe ;cjp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If -0s3nlz2 aylfleyd1(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 any lel1(sz0- yf32 dl12-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, 15l ( g8pdse6q5(sda6ty00-W heater is 5.4 m long. If it is made of iron, 8s d 6y(lspegt56d( qawhat must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined asp i(;6zst6+w lb,oiof the reciprocal of the resistance R; bo(p6so i+l w6fzi,t;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 vewwalf d4ie9b)7 oe)g;s7-uof 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 o;w) d lvweb7f )s-ieoeg9u47af 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-ey)svu5+ pyonx,f )o4kW 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*7fr my/ aoo6.m 54pg uwrt.sq half and the two lengths are wrapped together side by side to make a thicker wire. How does the resistance of this new combination compare to the resprfagmq7s*/..t ou y 5r w46moistance of the original wire?

  A 1200-W hair dryer is designed for y,4.0ur acm; ikbxz3f 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 eno gwel-007vqtk t5p bd*8tktk3ugh so it does not become so hot as to start a fire. What diameter must a copper wire be if it is to carry a maximum currentl0wkp bt tk-3g8e5q7v d 0ttk* of 35 A and produce no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given b 4qaq0tg7pnx7y 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 950 W of energy per second er q7b u5f8b:tn3 p1cbto the interior. Fru7 nc e p5fbb1t8:3bqind
(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 conj-c +5cpqh ey*ductors made of the same material. One conductor is twice as long and twice the diameter of the second. What is the ratio of the power transformed in the first relative to the seconde5*pchj-qcy+ ? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a rooms u9akj2-e do* 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 ae0nsoai9 -us4 qe rh+9 240-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 mayob/y 9okw /9f. tmn8okes use of storage batteries as its source of energy. Its mass is 1560 kg and it isybwf8ktn/m/o9 y.o 9o 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 lightbqbe2 4 tc: 0senat0z 6qh7mn+lulb has a resistance 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 acceleratoru/lmlx s3u w4l5 jo*r( at Fermilab (Illinois) is designed to carry an 11-mA beam of protons traveling at very nearly the speed of lig5(jw lm*ox3u u rsl/4lht ($ 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 is8t,n1r:m rji:-rk/ crg:q bca copper wire with r:rn, r g1c- tqckrmaib:8 :/ja 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 k x;iq stcpue70*aw+0 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. Whatec*qpktxs+ 0w 7ia;0u is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the ssak .a90sew7ak9e d/pystem voltage 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 power delivered to the headlights vary as the voltagd ak 79 /skaew9.pse0ae 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 honak( gv69ookd57c9 ai usehold applications. Lightbulb B is rated at 12 V and 40 W for aoc 7vgn95o( adkki 69automotive 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 vy.p,0f*pamji6 u4gt cm is used to connect a set of appliances at 120 V, which draf*6jt0 ,g4aumpyv .i pw 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 andtind 04jb69xx pl.;;hyk,ysl 6p feq- an outside diameter of 5.00 cm (Fig. 18–37). What is theq;lf.x0;h-p6ldnb k 4xsyp,ejit9 6 y resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly i4oabw.c/h shd16dsc hl;)7a so that its length doubles, by what factor does the power dissipated in the wire c 6lh4) hdo1icb/a d cws;ahs7.hange, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a fla sbx-/c;3edc ishlight bulb operates at 0.20 A and 3.2 V. If ib se/c;i xd3-cts resistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$