What quantity is measured by a battery rating givex:mopg(;:hk(g7z k dtn in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuitigv qv3 k.ww afqw. pr5;312ly, electrons flow away from the negative te5.wkl.y12 v 3aw p ;wvgq3riqfrminal in the circuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated,2r yyaf6y9o3d4 z+ fmzuxxw94-n02n nwwvg1q what is being used up: battery current, battery vol3y2 nnfg-+my x z o164fvwzyqw0nx942 u r9awdtage, battery energy, battery power, or battery resistance? Explain.

One terminal of a car battery is said to be connected to “ground.” Sxb 6 t3u(j)uznince it is not really connectez)x3ut u(j6nbd to the ground, what is meant by this expression?

When you turn on a water faucet, the water ufvmj.g20u(.fav(u6r 3 quuq skn:5 f jsually flows immediately. You don’t have to wait j3vs2 6 (uf0 kmuv :g.a.fjqr5q fnu(ufor water to flow 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 (seuu3r5i2fvwire of the same length have the same resistance? Explauf (isr5e2uv3in.

If the resistance of a smx25sejer, p 5eall immersion heater (to heat water for tea or soup, Fig. 18–32) was increased, would it ssrxeejp ,55e 2peed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths v 0r6l1lqxf,hxtk*zqki9i6qq 5p+ vx; xq w-(a, 2a, and 3a, how would you connect the wires from a battery so as to obtaip6lx1qt0qz9k(x iq ;hfq 65k w i r-+lxv,q*xvn (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 lightbul hy g9d6z8(4wg+*xy.lkjr hbgu f8bj(b burns out?

Explain why lightbulb z5,b-sst8 gnlh16p pzs almost always burn out just as they are turned on and not after they hb8 -n h5,lgsz1zts6ppave been on for some time.

Which draws more current, a 100-W(tvqap;) v)fk 8r2m4wqqi q r+ lightbulb or a 75-W bulb? Which has the higher re;qvf4tawq kqq+r) 2pvm )ir8(sistance?

Electric power is transferred over largeth/.w23kgwy.m)i:qz ij g 9 on distances at very high voltages. Explain how the high vj9:.zw m kw.nti)q 3hggoi/2yoltage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to repl z.7m df )*,kxhnwmx7iace this fuse with a 25-A fuse?z kx.mid7 m h)x7*wnf,

When electric lights are operated onty ap3vj1p *- 3d hquw8p uhx,x20*qne low-frequency ac (say, 5 Hz), they flicker noti2p h0q ej-31wpt 3advu*8n,yp u*hx qxceably. Why?

Driven by ac power, the same ele 5-tz2 fyb tbprk2;g9yctrons pass back and forth through your reading lamp over and over again. Exp; t2ftky- 2r9 5ygbzbplain why the light stays lit instead of going out after the first pass of electrons.

The heating element in a toaster islzu lv8t,tjq6np-;qrv3u+ d *( 3b:zal d9kvq made of Nichrome wire. Immediately after the toaster is turned on, i b3prluaqnt8zjvl kdq3:ut +9(,;*6lv - vdzqs the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a riyzxs z /*( b(b39yis+xcn7wu esistor? Explain.

Different lamps might have batteries connected in either of the twhpnu7m9 rys u27 -o6qp0 fi7ruo arrangementsp7 -i nu6ruf07s9m7p u yqo2rh 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 fonjw jsb1,ze5/b2 2p36ask:z ga(lbb lowing past any point in bweza:oj2gs3jl/b, (2s1 bpbz6an 5k the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a 4lbo.5-l2w8nqsn e 0ve op tv4battery using a current of 6.7 A for 5.0 h. How much chargvl o.ps -qntv2e4e0l8w5 n4obe passes through the battery?    $ \times10^{ 5}\;C$

  What is the current in amx,h; uvxrw,u:n 9s(j;hs bhj4 peres 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 ogg/jrs262tcm i y58nf9) fdaef a toaster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current thm0i :w-r-*vzztp e0 kmrough a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged3gajuvn .sz ddpyf+4.pbw;*z3 fmv3; 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 fwlge*jbhs(x.92yh ) a heating element with a resistance of $9.6-\Omega$.
(a) What is the current in the element when it is connected to 240 V?    A
(b) How much charge passes through the element in 50 min?    $ \times10^{ 4}\;C$

  A 9.0-V battery is connected to a bulb jdx 4yj: 8u f3b0 exrut0xn,-lwhose 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. 18–34)brny5 96 )nj7zdmar a:. The lineanrjn) 6ay br579dz:m 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 Aknd omq ss133a6ua1b . 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(8 ye.osnw zc, 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 lengtc-3 xh)rut9m vr2bu6 fh of tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wireeu9 b4vfd8/tvsg+. x+ gq6:xrxvc6 a y 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminuj47c k9.32 onf6px bhg6 mcndim wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in dia7h96j f6kno.mdic b 2gxn34 pcmeter.   

  Can a 2.5-mm-diameter copper wire have the same r+0v-;kvp1jxcy ;t m2xjznc) vesistance as a tungsten wire of the same length? Give nujcj2x1 )t n;x+ zvvk-pyvc;m0merical details.    mm

  A certain copper wire hasdc.l v96ff juze5v; 8s a resistance of $10.0\Omega$ At what point along its length must the wire be cut so that the resistance of one piece is 4.0 times the resistance of the other? What is the resistance of each piece?
$R_{short }$   $\Omega$
$R_{long }$    $\Omega$

  How much would you have to raise the temperat qxcd dzgy8+23ure of a copper wire (originally at 2c+3 zydxgdq8$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the s t* p;4ppn1n1 qicxen-ame resistivity as tungsten do cn q*px1pinntp1-4;ees at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistb brb g2hoy o .2v;2t;u09wmqfance 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 ab-r e)2ewg )tl 26-m length of household no. 14 copper wire (used in 15-A circuits). The wire brtew )-g)2e lhas diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon hu/h(z(e7ovf ,3 v,xcm pz,tqy;ef9b has sides of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying alon3(7uz,, z h,9qepyvfm; h(bxc ovte/ fg 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 one has twice the length l d bfs8n2je6,e k6eb(of the other, what is the ratio of the diameter of the longer wire to the diameter of the shorterelbn 6e,j6es df28k(b wire? $\approx$    (retain three decimal places)

  A length of aluminum wire 6 :ymp gr6a-ivis connected to a precision 10.00-V power supply, and a current of 0.4212 A is precisely mymg6iarv6p- :easured 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 ofwkds. kup 0pfb6/(,fm aluminum, both of diameter 1.0 m ,supdf(0.kkpb/ 6fmwm. A voltage difference of 85 mV 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 is important that the value of a 7x s .trkd5hp3y ducw.x78zz 2resistance not change with temperature. For example, 5k 8dzc.7d.sh32przuxt x 7ywsuppose 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 sx4l2)*.dwn9ikc a6)ln tcduproduce 3.3 kW of heat when connected to a 240-V source. What must be the resistance of the eleme.cw 9l )n2n4c*ltx u)dkais 6dnt?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player ba*k 8 bd)xu.rthat draws a u b*k.a )dxr8bmaximum of 320 mA of current?    W

  What is the maximum voltage that can be app ig.mkyx (sed0.;x:iv lied 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 ligh..oar: cs 1 xo-vx7bmgtbulb connected rxo- xm 1ac.:v7.og sbto its proper 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:*0;xasre;m 6measyc4, ck e a0a0nys 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 two z stii; r95a-k7dlk2qsettings: 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/52 aso yeve 973jsbfj electricity is delivered to homes at 240 V. 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? [His/eo3sjjya 7ef9 25vb nt: 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 iffoay8tk *+ rm-du;c5 j it is in operation for a total of 15 min? At a cost of 8 5t+;mjar*o-cfudy k $9.0\,cents/kWh$, 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 kW*pqr tj5fr,e, h, what does it cost to leave a 25-W porch light on day and r*,jt5q,fer p night for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batterie d d2i-xs5u-su(hfxd-hi7 l6ns connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 4h l5xif- u2nd 6hu(xssdd- i7-50 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 e3wbg ,(v/ lidqoh7e4h nergy stored in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs9:8m aj3dc m7i s2dryt, connected to 120 V as in Fig. 18–20, can be used without bl82mt9 7 mjsc:raid3 ydowing a 15-A fuse?    bulbs

  An extension cord ma(aaq23cxx xr :f8 4lptl2yj6b ep7x2ode of two wires of diameter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric hlaop8x xaxq2 cl7b ft e3 (2r64p2:xyjeater which draws 15.0 A on a 120-V line. How much power is dissipated in the cord?    W

  A power station delivers 626g2eqxaz5 dznx s7f*g7c:*w p0 kW of power at 12,000 V to a factory through wires wi g7 z657q ndc2xa*epgf*: zxswth 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 c: m9g8boltf5u onnected to a 240-V line is 17.5 A. At what rate must cooling water pass over the coils if the water temperature is to ro85lm:gb 9tf uise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion he: lcy)spf 5kf3jt+d*fcj:d( 2,qjy qpater can be used in a car to heat a cup of water for coffee or tea. If the heater can heat 120 mL of water fyq5 *fqjls )p,:+ p3jyct jkd:2f(fdc rom 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 curr+df4 9e. mva79)qp8 h* zupqejgzrrs *ent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value tll q8jr1udd3qir7j:t h4l63 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 5 lnq:1pjihqyo vt(/9the $120-V_{rms}$ 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. ez6po qj7 .uc goi0s;,What is the rms voltaie pcoo60js;. g7uq,zge across it?    V (Round to the nearest integer)

  An 1800-W arc welder is am b3*2n*yq: umode;rconnected 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 by a 3.0-hp pump cosip6hzw z,/ k4nnected ,p6/wzik 4zhsto a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to ai vof ./,rl*sxtpm z9) $240-V_{rms}$ 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 of)rym9me;ou) i $2.3\mu A$. What is the electron drift speed in the wire?    $ \times10^{-10 }\;m/s$

  A 5.80-m length of 2.0-mm-diameter wire carries a 750-mA current when 22.0 mV iclt s,1eyby g(6jvd 86s applied to it8 l1(sb y66 vje,ycgdts ends. 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 Ear 1 cm/j8n73cylqjs v/nth’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’o 8 4wk wn0el 9mv(w+rombho 8 cs98ppoda)/r/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 electr ad*k (/abtc7y qr uo+deufnb 1(,67qxic field across an axon membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with an electric pulse. The action potential is z7 yvls/r3n a1detected at a point 3.40 cm down the axon 0.0052 s later. When the 1z 3/saynlrv7 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 required to rs4h ur-x .w;jtransmit 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; .-w;j x hursr4see 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 potentia3) txmi8*cmw al, $Na^+$ 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 ther-hbndoyh)dx7uv 2 04b v6e *j69lzznq e in 1.00 ampere-hour?    C

  What is the average clp); a25(u(13zsnhschn ehz e urrent drawn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If ;ay5fxlbbg33 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 las3b3bf y5glax ;t 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 heatew :ty4xw q :5s52yoaufr is 5.4 m long. If it is made of iron, what 4 fsu:qto2: ww5y5xay must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprochm, ;y 1bq bskmwpo67+al of the resistance R; that is,o b1hm7+mkwp6bs;yq, $G\,=\,1/R$. 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 of :xka;zd/j14 em7nljh using high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a two-wire line of 0.50-cm-diameter copper wire, estimate the cost of the energy lost to heat per hour per meter. Assume the cost of electricity is about 10 cents per kWh.n:hxaje l;z41d /jk7m    dollars per hour per meter

  (a) A particular household uses a 1.8-kW heateqo14+olgo s 9kr $3.0 h/day$ (“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 cu.qlt g1d7a30 otbra6wt in 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 resistance of the origina0td37 la 6.obrqgawt1l wire?

  A 1200-W hair dryer is designed for 117 Vmf/(peu 5lq,q.
(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 rl)5be icd4*mi).znw )b( i eeso 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 current of 35 A and produce no more than 1.8 W of hemern i() e *blcwb)ed.zi4 i)5at per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by the eq* 3gkddz7,n.iph1b euuc n pz:o9,jo( uation $I\,=\,1.80sin210t$, 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% efs0-auhel cf b /zn2s,(jw 1d.dficiency delivers 950 W of energy per second to the inte/,adf0.ucw(1 snjhl d - e2bszrior. 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 the same material. Ogmk no+ t-/q1mne conductor is twice agq/ onm-1mt+ks long 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 t,xc1iji7dl*eb4 c xv+9 k+v yeo heat a room 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 hooke 5.-zt axsqnw(d 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 b.w2 7 * np36(5m se4d, nrkxlqlwebaxeatteries as its source of energy. Its mass is 1560 kg and it is powered by 24 batteries(edxn,* aeres7l 3mn lkw b4wp5q.6 2x, 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 7do;( k,m9*nmoye wmiresistance 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 c+bgk s*o*ghv)x./woq u n z)4(Illinois) is designed to carry an 11-mA beam of protons traveqhus o/.+vn wc) )g xz*b4gok*ling at very nearly the speed of light ($ 3.0\times10^{8 }\;m/s$) around a ring 6300 m in circumference. How many protons are stored in the beam?    $ \times10^{12 }\;protons$

  An air conditioner draws 12 A at 220-V ac. The connectin.s.n6 :qnrw q mv3 lqc+vyec3h/ gd6wuv,k8c 8g cord is copper wire with a diameter of 1.628 mm. +w:6rm.3cd,c 88s6vueqqyhn n g/.vvc lwq k 3
(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. T*1sd16;l umb.qrp2jl4jtss0x 9 iayb he heating element is a coil of Nichrome wire. When uncoiled, the wire has a total lenl1u .xjqa0ssr s421bijdt;6p*l yb9mgth of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from about 12 (7ujpil waw)o i6-4e cV 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 6ljwa (u)ii47e-ow pcheadlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for househyql;l 6d7p mbh8fv :s/old applications. Lightbulb B im8pqd f6s/l7;byv:l hs rated at 12 V and 40 W for automotive applications.
(a) What is the current through each bulb? $I_A$ =    A $I_B$ =    A
(b) What is the resistance of each bulb? $R_A$ =  $\Omega$ $R_B$ =  $\Omega$
(c) In one hour, how much charge passes through each bulb? $Q_A$ =    C$Q_B$ =    C
(d) In one hour, how much energy does each bulb use?    $ \times10^{5 }\;J$
(e) Which bulb requires larger diameter wires to connect its power source and the bulb?  ----待选择----Bulb BBulb A 

  Copper wire of diameter 0.259 ctx+p/sm:pp yqc ctqh,i;e-sf- 93c l79k 4re qm is used to connect a set of appliances at 120 V, which draw 2250 W of po -9p;iklx: h4 s9/yeq qtst7c+pr3cec-, qpmfwer 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 r c(i1m /6 0u-evcidgr 9tr)qtr9bqm5inside diameter of 3.00 cm and an outside diameter of 5.00 cm (Fi0g tve6i(9cqmru)im/ t qb 9rr-1rd5 cg. 18–37). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that it82b pinzdklg:m9w7 mu l /i:-gs length doubles, by what factor does the power dissipated in the wire change, assuming it remains hooked up to the samewi:89lgz/n :diulbmk2 p7gm- voltage source?

  A tungsten filament used in a flashlight bulb operates at 0.20 A and 3.2 V. mug)j2m g-j +avr l2y)-jloi:If its resistance at l2: ojmvryja+ui)jggm- l)-220$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$