What quantity is measured by aod-o4kx t,fq8 battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow away fq79m36gdl 9xr+fx eltd+ lq +womqn4*rom the negative terminal in the circuqq+gdq nm39el t*lx9f+m7 l+x4owdr 6it. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battery current, batteryikv /f(11e.pf awfg.t voltage, battery energy, battery power, or battery resistance? Explain.v.f 1(/.1 etwai kgffp

One terminal of a car battery is said to be-a+fohc-j;s.q r8iojgng nm cyf s.g)/*9ix , connected to “ground.” Since it is not really connected to the ground, w.8y*,n 9a ;h /+ mcn g-f-scjsogfoi.iqgjrx)hat is meant by this expression?

When you turn on a water faucet, the water usually flows0rxa;nv s(rj: pn/q5an;s.tv 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 conne vqp(aja/0n 5 rxss;v nn:.t;rct a wire to the terminals of a battery?

Can a copper wire and an aluminum wire of the same length have the samef(8/e+ssxcsxqdhe x 5h 4..a*qn zvq6x z6ty( resistancx8a 4eseh./x q(. s5xczqz ftv*d+6(x hs6 qnye? Explain.

If the resistance of a small immersion heater (to heat water for tea or sou62:a vc(hejn.ml- xmiz .w eh-p, Fig. 18–32) was increased, would it speed up or slow down the h2wxmz(nhe:. a6 iclvj-.m- eheating process? Explain.

If a rectangular solid made of carbon has sides of lengc b 0cc n(gz7ho0deo.0;en92w pqtvp, ths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resistane9, 7boe(zp.nnq 2gdowc 0 0p;ctc0 hvce, (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 burns+) mmtc //eytk out?

Explain why lightbulbs almost always burn out just as tinx9 a.c 6nk,zhey are turned on and not after they have been on forixz n.9,nkc6 a some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which has the higher/r943pa nqyjbj6 6gyu9jy/4nq jbg3up6 ry6a resistance?

Electric power is transferred over large distances at very high vo;,uba5k r,f4 yp/klpqzkp. l,ltages. Explain how the high voltage rk 5/ y.qf,z,,lkpu;bp alrpk4educes power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it daz /ywg5x 5o+ah*lhn 7yngerous to replace this fuse with a 25-A fuw5 x/ la5hygnyoh 7+*zse?

When electric lights are operated on low-frequency ac (say, 5m9m. eau::la4t sh8)t67xu+ iq bjbor Hz), they flicker noticeably8o6qib ) l.amuhr9tj bu7 :s+a ex:tm4. Why?

Driven by ac power, the same electrons pass dw8jx x,8zept-e*sb/6soo)z back and forth through your reading lamp over andjs ,zzd6)-/wxxopeo8es*8t b over again. Explain why the light stays lit instead of going out after the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. Immediately afteqyh( dzk 0n bv7iavv(*x1l4*nr the toaster is tu0 y(ni(v l71nvv* q hadkb*z4xrned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistoq4i5n -oj)gthi a 24.saqp lr3r? Explain.

Different lamps might haveiz3mq 8:8se ht)xn4vq batteries connected in either of the two arrangements shown in he s83x4q:imv)n t8zq
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wirjd j x1y26+p6j1l*cj gd/wj7r3if jq re. How many electrons are flowing past any poinj jdr66qwlj3cjy11x7d r+j pg2/ij f*t in the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery usfu j/.m,juub. ing a current of 6.7 A for 5.0 h. How much charge passes th.ub/ujm. j ,ufrough the battery?    $ \times10^{ 5}\;C$

  What is the current in amqs 2.:b22i6nwk z):x rcd o7*rj vsclvperes 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 cufv3 v57vjuf)l6t z yk7rrent of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current thra3k/ b6mg66 o/vr4nn ark;vixough a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5ao/1 pgv30ep: zncfvf 7bi/ (p A 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 with a resiwxzy (9h( 7msustance 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.mm txisxv *9lqn8 (y9 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. 18–348:8 jdvrx*sx c8j.ucd ). The line hax*csdvxd88jru 8.j : cs $2.5\times10^{ -5}\;\Omega$ 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 drin. b n/1;beiv-9ls ybaws 6.50 A at 240 V.
(a) If the voltage drops by 15%, what will be the current, assuming nothing else changes? $\approx$    A (retain one decimal places)
(b) If the resistance of the device were reduced by 15%, what current would be drawn at 240 V? $\approx$    A (retain one decimal places)

  A 12-V battery causes a current of 0.60 A through a resistoju/*e cbmhw1h6 -.e llr.
(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 whose rqyc +g5hhi1t *esistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1.5 m h+fr9y2b 07eut5mgk mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the;s isjqrj(lj1w8 8 3ne resistance of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in diametj(s;j8 er 8wqj31ilsner.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tungsten wire ofvy+v 1( c,j5yonh0 j vepqb5x+bl dv3: the same length? Give nuvlyj 31:++ vb0 pj ,(yv5heo5dxcnb vqmerical details.    mm

  A certain copper wire has a resinshiw 0ed,lsxx5t9z,mz:6:tvix x :* stance 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 tempe + swcf j8b.a)rgs1xq0jqj3j:rature of a copper wire (originally at 1j8fjxw rg . qj:)b ac0qsj3+s$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copu:b) e-q qgh3uek0(lrper will have the same resistivity as tungsten does at lqb0 e )h(u3g:ue-qkr $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has auyka63wep(eg pn8. ,et )ee4j resistance of about $12\Omega$ when cold ($20^{\circ}\,C$) and $140\Omega$ when on (hot). Estimate the temperature of the filament when hot assuming an average temperature coefficient of resistivity $\alpha\,=\,0.0060(C?)^{-1}$ .    $^{\circ}\,C$

  Compute the voltage drop along a 26-m lepbaxnzcy- ;c*xj s 78,ngth of household no. 14 copper wire (used in 15-A circuits). The wire hasxyc7;zs,x 8pa j* bnc- diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made m3 ta /0fl r4;awdem5i+hgd4t of carbon has sides of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determinemwag ;5t+me0rh ilta4 4/f dd3 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 same3l s q yd;o +)*3tj:1ipewyo uxwhw;v/ resistance. If one has twice the length of the other, what is the ratio of the diameter of the longer wire to thej1;l*dqe +w /yy33 p hou:st x);wvwoi diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precisi grvy1)rks ;uy.3c7qqon 10.00-V power supply, and a currenq )rr gycsvqy1;. k73ut of 0.4212 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 followlib*dkb6-s l.t sq4))u1zhhb ed by 5.0 m of aluminum, both of diameter ) st ud- )ikqbhs64llzhb *b.11.0 mm. 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 resistance not c;4 +gw. abukn8 ukdi0 n,bijt1hange with temperaturuiikn1n b0gbu j.;4 ,a+dw8tke. 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 oveii(6nqs mg lr8 x-/sx)n is designed to produce 3.3 kW of heat when connected to a 240-V source. What must be the resistance of-n8x6mg/is)i rxlq( s the element?    $\Omega$

  What is the maximum power consumption of a oztd+yz(v+3 wmc *+xm3.0-V portable CD player that draws a maximum of 320 mA of current? w mv ox+ 3zd+(ym*zct+   W

  What is the maximum voltage that can be applied across a hm 1p.(vpm(jztg9uodkx9fz e0 4i5j i 5n ,z1t$2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current)+f a77k.iu6 q ebm4vuutn -jn through, a 75-W lightbulb connected to its proper source 7bk aenuu7unt6+jf qm.v-i)4voltage of 120 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heateb718ihf+s ieph0g3 yv (2rqk+pm 2arvr 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 settings: 850 W alcidbuq w 4tkb:*bo3z15+ j4 end 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 el(z )lktwfw d4/ectricity 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 relatifwd4) zk(l/wtve 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 in+1soc )bsq (nq operation for a total of 1+q nqs1c bso)(5 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 3rx v+ qi7q 0v0j/ckho25-W porch light on day and night for a yei r+j7qhk3xc 0vqo/v 0ar? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected in series p h73f8,xmqm kas in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when turned on,3 pxq7mk fm8h.
(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 inx 3 f7dezglh*t3( s fo2(iugr+ a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulblr u d k ;p;d)jjv3zfr7e1s5)ws, connected to 120 V as in Fig. 18–20, can be used without blowing a 15-A fuse?prz)l r; js5df13ukj)w dev;7    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 coppev,x y:.l*sf bkr wire) and of length 2.7 m (9 ft) is connected to an electri,xvbkys.f*l : c 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 12,000 dpa w)kx+5g +uV to a factory through wires with total resistance5+duxw+ ) kpga $3.0\Omega$ 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 elect kgfmpu9r. (a e,/h)+yend.mnromagnet connected to a 240-V line is 17.5 A. At what rate must cooling water pass over the coils if the wateerg9)nyp.+(m/d k, u .fa ehnmr temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be u:fomb/v0r5 pco,k -1a fvyvt2sed in a car to heat a cup of water for coffee or tea. If the heater can heat 120 c,v501f: p2by mat vk/ovfro-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 curre 0*4 xmu yxieebjp fc*jx2-06snt in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 18nn dmqk ghg./(/fxk .60 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 resistanc2 5dab degh32oe 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 curh2sfpkbqq9g.j; :6gur u)2 rtrent in a 1500-W device is 5.4 A. What is the rms vh ;2gpqsjurf2r 6k .qt gu9b):oltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is conc 4z bdky4aaj;y2d.)x nected 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 dissipa aum*zp.3;w0p*l cfluted by a 3.0-hp pump connected to alzf w0.m;3*luup pc*a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to 0arli+ycm p )7 1yi6vqa $240-V_{rms}$ 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 x27 ,dj 4wvvyj6q4yipcarries a tiny current of $2.3\mu A$. What is the electron drift speed in the wire?    $ \times10^{-10 }\;m/s$

  A 5.80-m length of 2.0-mm-diameter wire carries a 750-mA current when 22.0 ku1h 0i7 f0ew/ 9bqbtn(smw +vmV is applied to its fvqbu(9m /t 070wesn+kb1hwi 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 thc5sv3 nj,pyt tc7q1a* e 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 

  At a point high in the Earth’xk42 1ngz0tzf 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 field across an axonrsolbv3xr 9f1urn+q.s o1)y.6 y.kap membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with an electric pulf4 v-*s- v -cziiy(ngese. 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 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 needsi*4v(yvg z c i--nef-ed instead of only one?)    m/s

  Estimate how much energy is required to transmit one action potential alongd.y. /h jgint8 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 Section 17–9]. What mi8dg/.hjyt. n inimum 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,dxx eta:k c3cmy ) *5khn,d5:k $Na^+$ 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 theru.zoxg 2r)s, ee in 1.00 ampere-hour?    C

  What is the average curre8dxs-0+ 5.xilhut so znt drawn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentallr,decs9zsbv 7/ 4hh1 cy leaves a car with the lights on. If each of the two headlights uses 40 W and dser h/zc,b1s 7 c9hv4each 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-V,hpqu5 (.6mv l,zsa xa3 1500-W heater is 5.4 m long. If it is made of iron, what must its diaa 3.lv, pmq(zh5xas6u meter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the recip(ed p02 y5i:bwlr)wof rocal of the resistance R; that is, irdbl()0wyw oe2 p:5f$G\,=\,1/R$. 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 usinjw1k(bgxy/ ip l;0 dc0g high-voltage lines to supply the power, the power is delivered awb1 dp /g(clyk0j;0 xit 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 1.8raease6y , r58-kW heater $3.0 h/day$ (“on” time), four 100-W lightbulbs $6.0 h/day$, a 3.0-kW electric stove element for a total of $1.4 h/day$ and miscellaneous power amounting to $2.0 kWh/day$. If electricity costs $0.105 per kWh, what will be their monthly bill (30 d)?    dollars per month
(b) How much coal (which produces $7000 kcal/kg$) must be burned by a 35%-efficient power plant to provide the yearly needs of this household?    kg of coal

A length of wire is cut in half fzuc1zn2 vog m()ja2eo;x )x :and the two lengths are wrapped together side by side to make a thicker wire. How does the resistance of this new cex21;o m(z)2cov) ung:jzxfa ombination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 117oe1tu816yl: m khhoot2;svz( 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 s1v)njm dn 8km 7+twq;mo 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 producem;)+1 k87mnd njt wvqm no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by tejzyh*t 1e- u8he 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 enerhv ya r::jowj()ae1s19 bio i5gy per second to the inoe1)jow as5hja91i by(v:i :rterior. 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. One t8we h6zw0(g./mbyyt1 ervc/conductor is twice as long and twice the diameter of the se6 z 8( tm/y/0etw.weyhc1bvrg cond. 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 voluzts+syx0kyr, *jvl cg v6x8 0/me $62\,m^3$ Air is brought into the room at 5$^{\circ}\,C$ and is completely replaced twice per hour. Heat loss through the walls amounts to approximately $850 kcal/h$. If the air is to be maintained at 20$^{\circ}\,C$, what minimum wattage must the heater have? (The specific heat of air is about $0.17 kcal/kg\cdot C?$)    W

  A 2200-W oven is hooked to a 240-V so ppn*r*gw5m.whzm; (e urce.
(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 v,wjsk 1wt3)q storage batteries as its source of energy. Its m3q)ks jw,v1twass is 1560 kg and it is 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 resistanceo4mo. e4 k1b ssd f2pih);ml :war3nd. 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 (Illinoza23 1+;k+ g eoazwhwx mjz69rp--ocf is) is designed to carry an 11-mA beam of protons traveling at very nearly txz9-mwkp+a zoej; ogcf- har1 2w z+36he 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 co4ek s9f.z xxh jtgv*, fb 69dzy9p*ud7rd is copper wire with a diameter of 1.628 ex9xp 6 uyfk9s*dh7*,.g9vjzzt4d bf 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 suqs 8cqmr0 - / kw3)rfiz85zt73gvywconnected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total lengtwmkvi3z8q3rrz/t q -7 cfg 5sy 8u0)swh of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varimvnt ki+d(0h6es from about 12 V when the car is off to about 13.8 V when the car is onn imdt (h+v60k and the charging system is in operation, a difference of 15%. By what percentage does the power delivered to the headlights vary as the voltage changes from 12 V to 13.8 V? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W foc d-ieju/ :+csr household applications. Lightbulb B is rated at 12 d/ +c -eiuscj: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 cm is us( oudfb)nsj +)mce m0.ed to connect a set of appliances at 120 Ved.(mj+o0m s)f ubc n), which 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 o79xy- aa9aasq.teub6 f 3.00 cm and an outside diameter of 5.00 cm (Fig. 7-q9ayae9s6aux a bt.18–37). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R isuns2sgtoi9 i19kf)-i stretched uniformly so that its length doubles, by what factor does the power dissipated in the wire changei1s)t - iniug9o2k9fs, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operates at 0.20 A and 3.wy9p7h:;pyo bm p+cy (2 V. If its resistay oy(+bp9 c;ymp:h pw7nce at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$