What quantity is measured by a battery rating given in ampere-gnh nyvm5e71 0gkm:q7hours $(A\cdot H)$ ?

When an electric cell is connect qlza-xy, q4eh19cs(qed to a circuit, electrons flow away from the negative ts(4 9 ,xqlaqzh-1ycq eerminal in the circuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battery current, battvgaofr:,sw ;j2x z- 0dery voltage, battery energy, battery poxo,vz2fg a 0rd- jw:;swer, or battery resistance? Explain.

One terminal of a car battery is said to be9vnc,hnaj)qh )wil/ vxk2i 99 connected to “ground.” Since it is not really connectwqvia2vl n ,)/h9j nh)9c9xkied to the ground, what is meant by this expression?

When you turn on a water 0 dlxgob9:367narcwz8,dfur */t nwefaucet, the water usually flows immediately. You don’t have to wait for water to flow from the faucet valve to the spout. Why wrdf dt78,og :urzb*e 9n6cxn w0al/3not? Is the same thing true when you connect a wire to the terminals of a battery?

Can a copper wire and an alumsc- 9vqz:)kp tinum wire of the same length have the same resistance? Explaivq-ktp s :z)9cn.

If the resistance of a small immerxd y2akc2f* g/sion heater (to heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the heating process? Expl*2c2y/d gafx kain.

If a rectangular solid made oa(ley-y( ps;u1 ; hephf carbon has sides of lengths a, 2a, and 3a, how would you connect the wires from a battery so as to ob(pe;yu a l p(1hhs-ey;tain (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 bur j( ph::ek+kkqns out?

Explain why lightbulbs auv1 i*meiuf-b+/n6 z//pbgjqlmost always burn out just as they are turned on and not after they have been on for some /6g1bzub -n /epumj ii v+f*/qtime.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which has theli7 h,v;*f2gd+kl ye p higher resistaklyd, *g7 l+;fhpe v2ince?

Electric power is trell/ ,vlm8sy7ansferred over large distances at very high voltages. Explain how the high voltage reduces plymes8,/v l7 lower losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replanm1 c8qp;lo2accuyn6k(b* v 8ce this fuse with a 25-A fuseo2 6pal(qy;81 c*ck v umbnnc8?

When electric lights are operated on low-frequency ac (say, 5 Hz), they0ld*di-ew.2qrd+k yg flicker noticeably. Why?deqrl d0gw *d -i2.+yk

Driven by ac power, the same electrons pass back and forth through your read()s zy qkmw5a-ing lamp over and over again. Explain why the light stays lit instead o - zm5skaqy)(wf going out after the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. Immediately after th,jktlky/v zg t0s9,.j e tj zkkvs9,g 0jty,./ltoaster is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Ep )*gg6zsf mm,xplain.

Different lamps might have batteries c+8a1.kv5a hdjh/1kw :chnnk j onnected in either of the two arrangements showwk vkdjnk58 h.cna: 1h1h+a/j n in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. Ho60rkj bhn1oi 4w many electrons are flowing past any point in the wire per secon0 rn46bok1 jihd?    $ \times10^{18 }\;electrons/s$

  A service station charges obn;y0olw+gy 4 wp-x,syx2(w .wtn0 m a battery using a current of 6.7 A for 5.0 h. How much charge passes through the battep xboogy w,n4l.xwswy0n+-(w2 ymt0 ;ry?    $ \times10^{ 5}\;C$

  What is the current in ampereq*+/to)x 9gjz5;ntk * vfv egt h+b/ras 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 4.2 A?7hj5c+lvuop +4j3e mszfq 3 k-hda8:g    $\Omega$

  What voltage will produce 0.25 A of current througpyr-lm7v8if7: m b+anh a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugg-qfeb c9u+adj p-.n 5aed 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 elemejknlzx. -- mrcl,dg4:nt 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 whose re; kv45ws g9fgasistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc elecl4ib .wcxm) c4tric transmission line carrying 2800 A (Fig. 18–34). The line hax4li .)bw mcc4s $2.5\times10^{ -5}\;\Omega$ 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 24026pv*e0 igqj de:q,xw 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 throug mh n5-a/uxtm rjgwmq 9h822 ccqc.,x: ds6p0wh a resistor.
(a) What is its resistance, $\approx$    $\Omega$
(b) how many joules of energy does the battery lose in a minute?    J

  What is the diameter of a 1.00-m length of psj)((r/hhc j(gny;wtungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m l 96p ( ywaecd(j:bol dpy093lvength of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminumy /s 3xofqv5. 00aagnr wire 2.0 mm in diameter, to 20.0 m of copper xq05 o 0f./rsa3gaynv wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire h p1bhv v/p+9yk p4g fz+5tyif+ave the same resistance as a tungsten wire of v + g pk 9zty4pf15f/b+iv+pyhthe same length? Give numerical details.    mm

  A certain copper wire has a res*d-xj(fi3mf diy u/lzs- , +vvistance of $10.0\Omega$ At what point along its length must the wire be cut so that the resistance of one piece is 4.0 times the resistance of the other? What is the resistance of each piece?
$R_{short }$   $\Omega$
$R_{long }$    $\Omega$

  How much would you have to raise the temperature of a copper wire (originally atezup8 mnc ++ys97:8aor: v qrd:qr r dup nezo7+sm9y+v:8 8ca $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what tempe llpjos4lhh /r9z72 uv7 g6/vhrature copper will have the same resistivity as tungsten does alg/77v2r phhl9 lh jsz4/ u6ovt $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistat wd/8*wj897sk t:8a .dhla.zlf s7 *zggax evnce 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 lengthaph kevp *k*un7; z3h, of household no. 14 copper wire (usedzv ;k*,k*hn ehu3p7ap in 15-A circuits). The wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon hajlqarj4l5,t4kwabh4 ;trl1 5s 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). Determine the resista 1jart;j a t4l,lk44q 5hwb5lrnce 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 le 8/glvx oh 1u)y*fxp257tiwlf2b*cw ength of the other, what is the ratio of the diameter of the longer wire to the diameter of the sf8c / 1uwlg)fpv l hb*oyw52*x7xtie 2horter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is (; qclal47izs connected to a precision 10.00-V power supply, and a current of 0.4212 A (slc7 laq;iz4is 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 wirisw + w;t9wrg9n6 umi55pwg7 ge consists of 5.0 m of copper followed by 5.0 m of aluminum, both7itrwsg599+ wg 5wnpw;6 miug of diameter 1.0 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 val g0 wt:qbxdl53ue of a resistance not change with temperature. For example, suppose you made twl3g 5qxb0d: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 designe)wkvr3kwr 1 .id to produce 3.3 kW of heat when k1w.wi rv3rk )connected to a 240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0y8r7 )2ra m; .a2 upwbfne,mnx-V portable CD player that draws a maximum of bn y72fw2,rm)nxpu 8 rmeaa; .320 mA of current?    W

  What is the maximum voltage that cas7 jzbo u+td+3n be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, a 75 5 2)ga w0nbk*kpho7wx-W lightbulb connected to its proper source volpk g7 o2aw*hx )b5nw0ktage of 120 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heaterats9la d vj7z8dq8o exw+l*47 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 hasg0 9l; td6t t+0en +ma6 vwij9:zffudc 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 is delivered to homesk)i s h-y,y.tj-0 umqb 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? [Hint: assume roughly that brightness is proportional to p-j0tqyb hm s-i)u,ky.ower consumed.]    as bright

  How many kWh of energy does a 550-W toaster ul+n*:) qsposr se in the morning if it is in operation for a to)s+*q rlns p:otal 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 co p am3j)a8xhy ny6tjh.k;b/k7st to leave a 25-W porch light on day and night fot8j n)xmjhay bk; 7pk6h/.3y ar a year? $\approx$    dollars

  An ordinary flashlight uses two 5naz r8kil9a 63q ma4rD-cell 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when maar3kn6l4 z8rq5a i 9turned 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 1* 7y qbwy; lzsty4:mc22-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 usl n3vmm2y,o wgh;g3/)qg23k vhduaq8ed without blowing anm3h,y3lg o/ghgd8a2uq;vv2qk 3w)m 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 3m bs1m)qieg, 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is qi 3mes)g1 ,mbconnected 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 powo5hnt n+-nu8e xl+ fjq(z1 ir4er at 12,000 V to a factory through wires with total resistance iernj1+4t8 5+holq-n nxf u(z$3.0\Omega$ 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 n )e(1sx)ta;b taz.fov.4 d wqa 240-V line is 17.5 A. At what rate must cooling water pass ove41ttbna)d.e.) xwfs; aqv( zor 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 .r.eeu f th6+zn fsiw:5, aj90,zju *w)ecvjla car to heat a cup of water for coffee or tea. If the heater can heat 120 mL o t)n *wu srjeev0 fzj 5j6,:fl ,ea.h9w.+icuzf 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 ctqe)x9 d+6c prurrent 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, vq5hw;i.5z.b0w ebqt 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 resistanceoq7lf j e :duoq+ ;gcq/8z*dgwt1a* +bat2rt7 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 in a 1500-W degjg+b/)6c33 (hm q( rdceihzhpq 4n j6vice is 5.4 A. What is the rm zdpjhg hbc+()mh/q63r c3jn ge( 46qis voltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected to aqsbj g9h s6p0 2tutg95: mdla2 $660-V_{rms}$ 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 k jh olq+o-dbrn5.r 7(3.0-hp pump connected tnr or(-5okbjh +7l dq.o a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connectey)p5gp rkg0y( d 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 tinlj 7ngg 601sej9ckx4z y 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 carriesq( g0tl 7lk yx o32/ecbwne.w1 a 750-mA current when 22.0 mV is applied to itslenc 7b3y1e(gt o0qwxl2. wk/ 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 Earth’s atmosphyv1xzisk 8 s q towe*u a2y6pj4(q713zere, $He^{2+}$ 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 atz(2mfnqx k:. b13v y 5g;bycnimosphere, $He^{2+}$ 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 acta0 :jh *xq7uat4 zy6dc5 yv3mross 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 dete itxclw38qb2jv rwk*3e3 tui1c9)9ovcted 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 923*e8o3icb913)ickjqx uv t vlwrtw 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 dp2ro ,my4zff 4cs ,,a)fm6g eis 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 storedezamc,p,ffm4g ) ,46o s2drfy 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 potent xm ;),cjfqn) wdh((wmial, $Na^+$ 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 t/5 gp qya(wpwciy, : e:pj(:c(07 izrdkc:zxjhere in 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0-hp 120-V motork; u apb0mh7y- y9hx1sjd* li,? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If eacpm3g d tyoe v9gs;mq649x0cm 4h of the two headlights uses 40 W and each of the two taillightsmt430ym9de g s9cgmq4p; ovx6 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, 1500-W heater is 5.4 m long. :cz to-hyl4 a-zq22a2 (eyuz61 keqzc If it is made of iron, what must itc-zl4zz qhk y u (ea:22e2ta-o61q zcys diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is :d gfsy0c)25 vf8e rspdefined as the reciprocal of the resistance R; that is,ef )fv2gcsdyr :8sp50 $G\,=\,1/R$. 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 insteadko g dx 2p,;329bxpswq of 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 of3xw22 gpbdpq,;x 9oks electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular household uses a 1.8-kW heatee z8;lpuw jo)25zgsy)k1, 1j s/urxgk r $3.0 h/day$ (“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 azik -hkqi qb ;)zv-m2e r;1m*znd 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 rer1*q -qivkhzz2 - ie;zmkbm;)sistance of the original wire?

  A 1200-W hair dryer is designed for 117 Vcpa dupj83s /d+2r s/y.
(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,ux*mrx3 b7b5k6 rxx hs pl+6a 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. mlxp7uk6*5 rs,hb3+6xbrxa x8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given lzpuq41: 9;eh c5rpl lby 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 8+k5o aa9y;nq mnska4 W of energy per second to the interiorom4a8k+5 sn 9kaaq ny;. 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 materin(;xs7dwzy3 2h rs kk: lqwn;+pbc44aal. One conductor is twice as lo;x(k;pwbyl3 z47nd s:q k2scrwhn 4+ang 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 imr1 uubt0j-r*s used to 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 hookeksc 6/-otnse1 m:s/ixd 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 batteries8f7lbjn7 q w.p2lcado i96/pu as its source of energy. Its mass is 1560 kg and it is powe8 pifo6d 2nwj77/ bupll9 qc.ared 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 5 wsqlbx6/if*1 ;5 s*ekgzj9s h9zcgeresistance 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 gmgq ubn+ csu947l2,uy e/ ax9at Fermilab (Illinois) is designed to carry an 11-mA beam of protonsbn 2 ugeucql7y/m994s,gau +x traveling 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 v xr3elcj32gs)yyp.ll/w*v vwd(+ g /A at 220-V ac. The connecting cord is copper wire with a diameter of 1.628 e/d.2jsrvlyv yp wgx/+cw l3*g() vl 3mm.
(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 V5 xlz0si ycw:wgu+h6 5. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What is the diameter o:w0 lsih y655c zgwx+uf the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varig: v 6haf :ch7tvy2pj2es 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 volchp2j v f:gav2h:6yt7tage 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 fotn ab ab-)lb*g)0alacv4+. n or household applications. Lightbulb B is rated at 12 V and 40 W for automotive applic0an+nv)*ag a al4 blc)- .otbbations.
(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 0.259lod wm5j /o3o4 cm is used to connect a set of appliances at 120 V, which5ol4wm3oo / jd draw 2250 W of power total.
(a) What power is wasted in 25.0 m of this wire?    W
(b) What is your answer if wire of diameter 0.412 cm is used?    W

  A copper pipe has an inside diameter of 3.00 cm and an outside diame h+r*i/2prdb iter of 5.00 cm ihi*d+2brrp /(Fig. 18–37). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly1 o.si9esgbdu*)g-wl n9w+ ma so that its length doubles, by what factor does the power dissipated in the wire change, assuming it remains hookedmen-1 .9w iu*s 9gwogdlb+)s a up to the same voltage source?

  A tungsten filament used in a flashlight 5q guq,2v sgkvgkc. w+ikdh59 1wf8j6bulb operates at 0.20 A and 3.2 V. If its resistance 5sfk iwkg.8 5qqjh 21 9 vwg,ukgcvd6+at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$