What quantity is measured by a battery rating,4i z j h stt9(r,*xm/n4nwm6pc/at8.j bc ymi given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow away fmja;;*mv5vx5ca6w h irom the negative terminal in the circuit. But within the cell, electrons flow to the negative terminal. E5m; vxm;i6jv a5*hcawxplain.

When a flashlight is operated, 2;kj *ps zihu9what is being used up: battery current, battery voltage, ihk;9pjuzs 2* battery energy, battery power, or battery resistance? Explain.

One terminal of a car battery is said to be connected to “6lfdc dk92(:qvvn )7 nsr5plq ground.” Since it is not really connected to the ground, what is meant by this expre lkrqnd27 dncvsp ():qv5f9l6ssion?

When you turn on a water faucet, the 0o*84s kxdhf 4,e tnvgwater 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 tonogxdef0 hk* 4,48stv the terminals of a battery?

Can a copper wire and an al35q:d1p fo fsfuminum wire of the same length have the same resistance? Explainpf: qfd f5os13.

If the resistance of a small immersion heater (to heat water for tea or soupn tgh2-2v,lj.*t+h+( cl3 zleyd uhey , Fig. 18–32) was increased, would it el+h2v+lh, dy-etgch yl(3zu.*tj 2 nspeed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, and 3a,pge:u lk8ps rcsp:8h nn8 2*f+sq2 z.z how would you connect the wires from a battery so cnz+hs fs2uzl p: 8e*r8 ps8: .2nkpqgas 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 li/ nxxxp(h+)ko ghtbulb burns out?

Explain why lightbulbs almost always burn out just as they are turned on ai s2f1 son;:nind not after they have beensiin ;n1: s2fo on for some time.

Which draws more current, a 100-W lightbuac*s o99 fh8ltlb or a 75-W bulb? Which has the higher c*9ofh98alt s resistance?

Electric power is transferred ovz 1p3l:weguho;c492 zqv a* doer large distances at very high voltages. Explain how the high voltage reduces power3hou; z zqeo1*aw4cdpg9v2:l losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is- spoz ;idvn7ce +q*9nmptql 6952adh it dangerous to replace this fuse with a 25-A ndp6c*2p5zl +q9; d9 - ish7aqnetmov fuse?

When electric lights are operated on low-frequency a2yv.3 (p qnkb)6tu umtp/os z,yn8if*c (say, 5 Hz), they flicker noticeablq )n*/8u,2po 6i(3u mksv ty bnypt.fzy. Why?

Driven by ac power, the same electrons pa w-psn ,gue/8p s1ng1nss back and forth through your reading lamp over and over again. Explain why the light stays lit inssw,p1nsgp e/ ng- u8n1tead of going out after the first pass of electrons.

The heating element in a toaster is made of Nichrome 1lxd+ron5hu: mjnbk a5j l.2: wire. Immediately after the toaste.l1x on:5jjl25rhman b+ud k:r is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a res4vrojy29) j yuistor? Explain.

Different lamps might have batteries connected in either :*) bo tzye v4(xf+cqpof the two arrangements4v*ztpx qf:y +cb)oe( shown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows inz w q)*zugh) ywaa-9h8 a wire. How many electrons are flowing past any point w)9q y)8 g-whua*hzaz in the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery u p-jf+ap5i32omd hma ;sing a current of 6.7 A for 5.0 h. How much chiaa-mp+ m 5d;pj3oh2f arge passes through the battery?    $ \times10^{ 5}\;C$

  What is the current inrkc o(7,hl8cw 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 produces a current of :e hbbkueh*ysb8 /)zmtj(l ;n7o t5j okd9.w/4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current through0 kneg)nik 3k/ a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged zx4t4twim h/tf:l(1m2 q;sn:k yd/c minto 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 heati 381xjni p-1fh*(y- olvl 9;jfxpi dwtng 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 connectedb7nu dc4o ,uemzvu(p( -3a0co 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 A (Fig. 18–34a cy/el 0o)tnwsp zl)q/vl859). The q cnll/) wsp y8)v59o a/e0zltline 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.j g+io5isp 0;o50 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 current of 0.60 A through a resistor. wakk-tg(u0v39kdpk1
(a) What is its resistance, $\approx$    $\Omega$
(b) how many joules of energy does the battery lose in a minute?    J

  What is the diameter of a 1.00-m length of tungsten wire whos 5hlv-1i*h2iq/ ksr4/plh nbee resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistancey5ovvi*ux ) 8((u cpqt of a 3.5-m length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the reh p9u1hda 4r0zky9v0p)i2bi csistance of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in diameter. 4p9 p) r i0iv9chy uk0ah1dzb2  

  Can a 2.5-mm-diameter copper gg *voxcfkx9uf2o,yr6/jv ( 4krsk z1 .j6gx)wire have the same resistance as a tungsten wire of the ss rkrx1v,) 4okg6v62g uj o/9gfx fz.xyc* j(kame length? Give numerical details.    mm

  A certain copper wire has a resistance ohx:))e gotks+qbvk9- 6lzh 9h f $10.0\Omega$ 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 (originally ad n(5hjgt/)wnn o)o uk4rm (q8t (nq /dt (wr )uoo8) mjgnk4hn5$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper wi1hvsl9 pp*e1rll have the same resistivity as tungsten dov9*1p l rp1eshes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of about 6tb2 ) /ewnjga$12\Omega$ 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 copper wire nu 3* byw qy1f q)aquf*gkeb, .e)yu,1(usedbkuq fb.w1u, y*qq *ayu,fn3)) ye1eg in 15-A circuits). The 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 m)ypobqvo/j5s./ol 4 r5zgyz2utr- 1cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determinub//4vrol) zp oyy. -5mgj t125 sqzroe 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 ono9vf0 sn*tc8phg w :7+au /liye has twice the length of the other, wh*:78slohgwfvyinu 0 /c9t +paat is the ratio of the diameter of the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connecttk 9+t efid533-p xtxqed to a precision 10.00-V power supply, and a current of 0.4212 A is precisely measuredtpt kxxdte5 9-3qi f+3 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 b*p)ha l ;aa,v3(ow 5d64lcaa ( lmprzey 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is placed ;o aaedh6l(3) c,aal(v*pzal45r mpwacross 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 important that the value of a resistance nok wguoh6 97)ckmj *p)yg;iwj9 t change with tejcpik) ww y9 m7*;)uoh6gk9gj mperature. For example, suppose you made a $4.70-k\Omega$ resistor from a carbon resistor and a Nichrome wire-wound resistor connected together so the total resistance is the sum of their separate resistances. What value should each of these resistors have (at 0$^{\circ}\,C$) so that the combination is temperature independent?
$R_{0C}$   $\Omega$
$R_{0N}$   $\Omega$

  The heating element of an electric oven is xq8ih:zc48lmht l ,) ydesigned to produce 3.3 kW of heat when connected to a 240-V soux tlc4)q y8hz: hil,8mrce. What must be the resistance of the element?    $\Omega$

  What is the maximum power consump )lwjik75o10 bn,a kfqtion of a 3.0-V portable CD player that draws a maximum wbl, jai ofk1k750 )nqof 320 mA of current?    W

  What is the maximum voltage that c vww;l/ nogru o3r6f*:an be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current thwykq hg(gzt apnjxx44 44/x,0rough, a 75-W lightbulb connected to its prj ,k xpgg/40a4x wqynt( 4hz4xoper 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 heate:vv-5 *ljlk pkr 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 h/zmv8 r5b b.kl; ca(ylas two settings: 850 W and 1250 W.
(a) At which setting do you expect the resistance to be higher? After making a guess, determine the resistance at
(b) the lower setting;    $\Omega$
(c) the higher setting.    $\Omega$

  You buy a 75-W lightbulb in Europe, where electricity)orcmo b z8*h- is delivered to homes at 240 V. If you use the lightbulb in the United States at 120 V (assume its resistance mz8och* rb o)-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/wlhrl tm l73nka-k )8rz7 z5p does a 550-W toaster use in the morning if it is in operation for a h7lp7 - 53/ zr)zak8kt lwrlnmtotal 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 por*60qtx/jn7 )nmpnvrlkp (e erq0.i 4ich light on day and night fovq) 0 /*0.tljmki6nx e7nr4pe (n iprqr a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries c0w7z pvse /wk(onnected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA whe0w k p7v(/szwen 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 energyg 0 ctrcs5)k:x stored in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connected to 120 V as in Fig. 18–20, can be used withh+njnfi/a i 5x7j99el: /2wwos wmq0r out blowing a 15-A+i 9hj/s l j20/ 5fnewwn9x7 rw:iaomq fuse?    bulbs

  An extension cord made of two wires of(;9o c/x/r-s lr)xs zuiwxu5p diameter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric heater which draws 15.0 A on a 120-V line. How much power is dissipated in the cou-s)5ix;(/x u/rwzlsx9 por crd?    W

  A power station delivers 620 kW of power at 12azt ne0ut6n1hkv+29 f,000 V to a factory through wires with total resis 6va ntht2e+fun0zk 19tance $3.0\Omega$ 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 17.5iu3ai.j3mc r;gi-mxy i*rh / * A. At what rate must cooling wate 3ria*ygh -*xi. uic;mir3mj/r pass over the coils if the water temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to heat a0 bey3f 5f;tonz4p nu) cup of water for coffee or tea. If the hnt) y e3n4;b zpuof5f0eater 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 currz8cvhjfe*w . *5vt pk9nf omxs7 .3.pzent 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 ai uhtzm*;*m q) $330-\Omega$ resistor. What are the rms and peak currents in the resistor?
$I_{peak}$$\approx$    A(retain two decimal places)
$I_{rms}$ =    A

  Estimate the resistancd/mu*h f vy/p;e of 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)o0fg 1ul;ag icc9a .9 4ozfpy in a 1500-W device is 5.4 A. What is the rmafa pg0;u)olgci zf 9c y1o.49s voltage across it?    V (Round to the nearest integer)

  An 1800-W arc welderdi k;4gq41z kiv)ng8lm(4vat is 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 power dissipated byxjkj nz k4;1g7viajfxq s8p15) ct)1g a 3.0-hp pump connected 4f j7g1xt1igjxj8 v)k;pn )5k c1zsaqto a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connec3o:q :shqvqn x*q vdhx5y;2c:ted to 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 copper wire carries a tiny current ofqmi j06;w.gv p9 1cbhz $2.3\mu A$. 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- 6dlm)- xrih.smA current when 22.0 mV is applied to its end6r .lxs-mhi )ds. 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 51qwi nf:,oheqv l -r4d7y+ptz. ek 9vEarth’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 thevr1 *7l r7tobe Earth’s atmosphere, $He^{2+}$ ions in a concentration of $ 2.8\times10^{12 }\;/m^3$ are moving due north at a speed of $ 2.0\times10^{6 }\;m/s$. Also, a $ 7.0\times10^{11 }\;/m^3$ concentration of ${O_2}^-$ ions is moving due south at a speed of $ 7.2\times10^{6 }\;m/s$. Determine the magnitude and direction of the net current passing through unit area $(A/m^2)$.    $A/m^2$  ----待选择----NorthSouth 

  What is the magnitude of the electric fiel jgs 5g(ug7lw: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.384j 1vsrkdxs.hc +41f wqrup The action 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 point8s3vps4k .uwq hfd4r rx+c1j1 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 requirec(jr p1 40c6-lyt vho qs(kc-xd to transmit one action potential along the axon of Example 18–15. [Hint: the enerc6(qcx0tsr-hjl- y vp ck(4o1gy 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 for $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action potential,2s+ qq7vup (2js8lw7qt/f z jx $Na^+$ 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 :naxj q+j17 w+n o3fqr oryh,1ivm-,t.00 ampere-hour?    C

  What is the average current drawn by a 1.0-hp 12h k7)yxkz9nrh*zk 2 4u0-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights o/yn0, tbkn*f cn. If each of the two headlightsyfc/*bn0n tk, 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 is rated at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of a 110-Vr)8c7cuah5 qw , 1500-W heater is 5.4 m long. If it is made of iron, what muq8wc7r) 5 uahcst its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of thecxg7,t/9gv jwo .0iq u resistance R; g/ji09vq.t,ug7c o w xthat 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 ofy b+ jo92kf0mo using high-vomyoo2 0 jf+9kbltage 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 electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular household uses a 1.8-kW heatjost (u 0xrt0)/hs.cm er $3.0 h/day$ (“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 wrapped togwblwx5 3 n(pf(ether side by side to make 5pxn(3w(l fbwa thicker wire. How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 117 V. f ;8yduct,r. x/v+cjl
(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 hot as8x3 :(hirh8bsmm9msb to start a fire. What diameter must a copper w(3msmrbx9:sbhh m8i8 ire be 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 is give7c7ye9)b/ kp*s7 laxferbo -kn 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 950 W of energy per secondxzpwh,lq37 sd i 2rk:bkr k-dogw, /4- to the int7 3dl/hi,kk r dsqb2 wok4,p -:r-xwgzerior. 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 d * 2fw,*gnubri,1vtfamn(8 vxwy qt .)ifferent conductors made of the same material. One conductor is twice as longuawg,x t *q)vf(bw*i f 21n.n ,yv8trm and twice 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 room of volum;o:u3 x)ztpt he $62\,m^3$ 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 hooksg aizt y 16/20)tftr+pvahj)lj4 6yfed to a 240-V source.
(a) What is the resistance of the oven?    $\Omega$
(b) How long will it take to bring 120 mL of 15$^{\circ}\,C$ water to 100$^{\circ}\,C$ assuming 75% efficiency?    s
(c) How much will this cost at $11 cents/kWh?$    cents

  A projected electric vehicle makes use of storage batteries as its source of enryetj .tjt 18 m8.f,oizsg7 y6ergy. Its mass is 1560 kg and it is powered by7ifj6zty8o,yr e gjm ..ts t81 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 haw ysce0 ufz9f71 at8c,kgbdwgu fx-4bm1*0c/s 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 accelerator at Fermilab (Illinois) is designed to carry an 11-gxq/r n0) on+wmA beam of protons traveling at very nearly the speed ofw/ nqx+nr0)og 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 ):r)yk0ukmq w /xtj16rm7iji with a diameter of 1.628 wr))jut0q6ik jm iyxr 1m:k7/ mm.
(a) How much power does the air conditioner draw?    W
(b) If the total length of wire is 15 m, how much power is dissipated in the wiring? $\approx$   W(Round to the nearest integer)
(c) If no. 12 wire, with a diameter of 2.053 mm, was used instead, how much power would be dissipated? $\approx$   W(Round to the nearest integer)
(d) Assuming that the air conditioner is run 12 h per day, how much money per month (30 days) would be saved by using no. 12 wire? Assume that the cost of electricity is 12 cents per kWh. $\approx$   cents per month (Round to the nearest integer)

  A fish-tank heater is rated at 95 W when connected to 120 V. The heating eleor vrr4*b,h)7q15 x z7yhttyement is a czyqryh, obr*4hv77 )t 5e1t xroil of Nichrome wire. When 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 varies from about 12oh /hl(x-c xt1 5 zedez; cw**yyab1i) 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 voltage changes from 12 V to 13.8 V? Assume the headlight resistance remains constz / 1*h -ct;(xzoedc5* yei awbl1hy)xant.    % increase

  Lightbulb A is rated at 120 V and 40 W for household applications. Lightbulb B 06akl,1sxjs 6yab-us1 e6j pkis rated at 12 V and 40 Wy0 e6j,sk- s6 jk 6a1uaxlps1b 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 0.2:8nrhz+pqg;) drkr *e 59 cm is used to connect a set of appliances at 120 V, :)hr;rqknpr+d *e 8 zgwhich 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 cmb:cq:1s ej a4y and an outside diameter of 5.00 cm (Fig. 18–37). What is the recq1:yas:j4 be sistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is suja1t6 o8p qfg4 q:s6ptretched uniformly so that its length doubles, by what factor does the power dissipated in the wire change, assuming qt1 p6g:8qajs op4f6uit remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operates at 0.20 A and 3.2 jh7y 9uvk1k mh1r ;pp0V. If its resistance ;hp19v7h0ku jpmyk 1r at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$