What quantity is measured by a battery rating given in ampere-ls/r7q3 x;bpjk0f y.9sq6 tjjhours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow away from tjk qwtsm/joa9mz.w9-o.6gw 9 he negative terminal in the cij-/99ojz.k6ww9 mqamtg. owsrcuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used u)fa.zokov u6;p: battery current, battery voltage, battery energy, battery power, or bazkfo. 6av ;)outtery resistance? Explain.

One terminal of a car battew/4ixj-s(yqqb gomp) ob (ro85hp0/zry is said to be connected to “ground.” Since it is not really connected to the ground, what is meant by this ex8zgmb wos po pb)4x(oi-hq5(r//j 0qypression?

When you turn on a water faucet, the water usually floww zqswtei1n+504 b*wt s immediately. You don’t have to wait wtsi t 40w1qz n+b5e*wfor 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 wire of t tizbw4r7u 8v4thhwd7n7 c79jhe same length have the same resistance? Explainn d7794t 4rv8zh 7icuhbwwt7j .

If the resistance of aoxzmu ce.n g/604ed 2g small immersion heater (to heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow d.eu4n6 dcm0/o 2e gzgxown the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, l3z53bzzf84 hr-0e gw.ozfto 2a, and 3a, how would you connect the wires from a battery so as0l35.b 8o34zo- f hwg tzzrzef 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 lig8 gq q4pea;*jshtbulb burns out?

Explain why lightbulbs almost always burn out ju22l-u;vfk 6 d-efbxdmst as they are turned on and not after they have been on fo bk;6vdl uemf 2d--f2xr some time.

Which draws more current, a 1l) m7.l p bib6lg,et7p00-W lightbulb or a 75-W bulb? Which has the higher resistalg. ti7l)epp7 ,lb m6bnce?

Electric power is transferred over large distances at vu;h rgu*ewf+,/; 2-vyxog ftnery high voltages. Explain how the high voltuf+h/ -rgvx,wu;foeng2* y ;tage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Wh8,xgpmw8e ub181r ozwy is it dangerous to replace this fuse with a 25-A 8 opwxbezr1wg8m,1u8 fuse?

When electric lights are operated on low-frequency ac (say, 5 Hz), they flicker z2.ql4,0r.t g jjcdp rnoticeably. Whyrt.0 cj qgd2r. p,jlz4?

Driven by ac power, the same electrons pass back and forth through your rea(i3k7lff6vo3o; pfubding lamp over and over again. Explain wh63u ob fv7o p;(lfk3fiy 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 ay.cnjbe2 :ye 816rwu ifter the toaster is turned on, is the cury1.:re8yu6 e wjcb in2rent $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? r: -oyi1 mk:ddExplain.

Different lamps might have batteries connected in either of the two pz x*b awg2w:,x*qvq3o*bs9larrangements shown in pa3sw:q * wb o xg,*ql9x2zvb*
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows inoyh4*a j o3a7g a wire. How many electrons are flowing past any point in the wire per ohjg y73oa4a* second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A xbdjzb )ee4 c 0p*/ue:for 5.0 h. How much charge passes through the bbxe pc0j*zeb/d:4 e) uattery?    $ \times10^{ 5}\;C$

  What is the current in amperes ify.04z5l8whi gq2 vid n $1200\,Na^+$ 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 1) s i29ouctd)5vmoq ;i20 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current thri/ msun9rrn+cf;psfjr q q6) dh82**er ,ea2hough a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when pluggej1h)jg d,uyma+ , (sjrd 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 7,i c-mdfgaekom;+ l(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 toxg)( hre9mk.g2ct9 igdk/2b w 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 car p ynx2va-ln7qf o2wbe,/ h7s0rying 2800 A (Fig. 18–34). The e o7-022/ps7 ahn, yxnlfvwb qline 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 drrt d0s,d p7zq1aws 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 cu wnduzp9p 9i7(rrent of 0.60 A through 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 tuaw6 x+.zq 5vfggqe; i4ngsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length 96 qh9mn d9-m*l+cewnui 8gaiof copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance ot w)q/ 3:edvgxf 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in di:w3 dv )xq/tegameter.   

  Can a 2.5-mm-diameter copper wire have v;rndkh fx*;dn9 9a;* j+leqlthe same resistance as a tungsten wire of the same length? Give numerical d;ln*d ldjvf9;hq 9en+x;ra k*etails.    mm

  A certain copper wire k b r25ksfy*j6has 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 temperature of a copper wifh5k 1y3r;dl pre (originally at13rlh pyd k5f; $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the zjt6 uv 2x(1js/q(cmrsame resistivity as tungsten doesj2zq6stv u j(c/r x1(m at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resxt08n+pt+qok istance 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 jg4:etsq royluc;,03g l04bmlength of household no. 14 copper wire (used in 15-A circuit rej4cg ql043;sgyou: t ,l0mbs). The wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of x2 eirgzys::g)o5x8j 2ep:vecarbon 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). Dxgpg:je8 o 25 zr:s2ev: )ixyeetermine 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 thgbk 6i; u:o, iw+yhb7de same resistance. If one has twice the length of the other, what is the ratio of the dia6hu;gi:bki +d,7bw oymeter of the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V power*h.e3xo3z lu .i;.rcaojc :e f supply, and a curr3o u:;xfcacor. *e .elhj3.izent 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 w*,hz;jt tsl h7ire consists of 5.0 m of copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is placed acro* j ;,t7tlzshhss 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,fqx/8 s1+ thek it is important that the value of a resistance not change with temperature. For example+tkx efq1hs8/, 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-qc;ll9 lj *a2r auuf9 electric oven is designed to produce 3.3 kW of heat when connected to a 240-V source.r-lu9lj qc;9a2*a lu f What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption, n twy p4w 4g,2/bpiu-ju4diz-otxw6 of a 3.0-V portable CD player that draws a maximum of 320 m,x, gw j z4to-6u24ndbi p/tiwywu-4pA of current?    W

  What is the maximum voltage tha ndeeuy22j :1b :7d: ctvv(v)srkao,z t can be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and currzh kf w86hj(xya.*qx8 ent through, a 75-W lightbulb connected to its proper source voltage of 120 V.h 8qfxkhj6 8y*xaz.(w
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank he kh7huhs7.bsy 4tq.oym c8j 3-ater 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: 850ks1l/r 8urwl.j10a wsop;r) s 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 i fio lxmdx/. /,pjepf/7 (sc-bs 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 rela/ bs7-f( p xxepifcol//j,dm.tive 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 inbh msp.gb*ds* t f79y, operation for a total of 15 min? A h sgmst**df7b,9 p.byt 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 porch lighta iq6fv*( + .dm8uvqu/qkbrs; on day and nightf/vdq+;(kabqrmi.u 8q u*6vs for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected in series as i*9 hsddpw1cg 3z: kmxj2d9z 6rn Fig. 18–4b (Fig. 18–36). The bulb drd1d3jhcp m2d 6sw k xz9:g9*rzaws 450 mA when turned on.
(a) Calculate the resistance of the bulb and the power dissipated.
$\approx$    $\Omega$(retain one decimal places)
   W
(b) By what factor would the power increase if four D-cells in series were used with the same bulb? (Neglect heating effects of the filament.) Why shouldn’t you try this?   

  What is the total amount c 8e tie k+i)g75:x8hasswk6j of energy stored in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightb9j cq1; vb)3u nrp:adhulbs, connected to 120 V as in Fig. 18–20, can be used without blowing a 15-:vbj)nd ap ;h93 1uqrcA fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 (d5 (xtao5eq dt9w7jicopper wire) and of length 2.7 m (9 ft) is connected to an electric heat(5q5i edat7jodw9x ( ter 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 V to a factorywzwb3myri 5+:xg w2g5 through wires with total resistance :gg+5 w3zwyr2x5m wbi$3.0\Omega$ 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 17.2 uogsqwlrii j je ; 81 ,u,/n1flgo8zw,7if.r5 A. At what rate must cooling water pass over the coils if the water temperature is torgfzw j,n.2u7ojf8,l iuls 1wiq;rg8/ei 1o , rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to heat a cup of water for coc)wko 4 b6yaj8av se/rvg)w v/:pw/ 7yffee or tea. If the heater can heat 120 mj )o6k/aevpg:4b v/8 vsarw7 ww/y)yc L 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 current in ace b,z+wc 9t;j $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, et0,qq(y(g3 l 9nfrpuis 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 thef+ml*8/6wa t5 esnxgqc(8 s,sdx5ti2mp 8lna $120-V_{rms}$ 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 1v ny8qa bio06d8wa /sd1fi )l(500-W device is 5.4 A. What is the rms voltage across n)a/a0idbl61 (ydqifo 88vwsit?    V (Round to the nearest integer)

  An 1800-W arc welder is eqi1gfqg2mio7 0 7;fy 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 by a 3.0-hp pump 3- 3o; 1iwrztjv1 isvnjhb ,y:connected to a ,tn 1:iwi3v3;jjbrhsozy- v1 $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connecte 3sck59b)p3kgrf8:a* eybvfs 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 1i5/6rjjga h rsl-rkv,/7f6wg ol4 u rcarries 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-mAvm0znppmjj 6 2+ e0a2rjxo-m 4bdu,7a current when 22.0 mV is applied to its ends. If the drif a +0o,x247-jave0 m mjb mp2unj6rdzpt 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’sx() 1lwk e or(tar2zc+ 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 E71vkbr l(w; l:3tmarwarth’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 fielp*c-lp l(ph7td 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 eluf1x3 ,b: ouin;7.y/a hkwpf xclh-z5ectric pulse. 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 l-o:w fhp15xyib/3 ca f,.zn u ;uxh7kis 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 transmit one action potential alongsjo/rb ;o 25labs1m1t the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the ;s5/jmbtolsa1r bo21 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 potentialx;gwsa.y 3 ye, 9o+r 1.j(v ob qqjry9envo-x1, $Na^+$ 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 thpj3-q5i5qo5,6 5iymxmbb /jfm g y z-qere in 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0-hp 120-Vr7.pc / krstv- motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each .z+vjyaz+ty)rt lba2c :6 3al6od ye)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 last if i3r 6ty jaoe2cz )+lytl a.y:)ba+dzv6t 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. If it is mafbo1 h xs9x8h8b *6ddide of iron, what must its dhbsfh o8i 9d6x1bdx8*iameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object i ugwfy a58r5rkd6/e87v7 t5wbe0 zvvhs defined as the reciprocal of the resistance R; tha5 ry v dga7 bhkv7w8t6/ee5ufwr8 50vzt 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 wo)wp9r ,yx7s about 10 MW of power. Suppose that instead of using high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a two-wire line of 0.5p7o s,wywx )9r0-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 ury: soqa0(i )ises a 1.8-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 and the two lengthsw0x pt+)h k5b5m6*j7ibp74thkc n kfz are wrapped together side by side to make a thicker wire. How does the resistance of this new combination compa bw5kjk5t0p 7 n7 t*hb+4h)xc6kpf zmire to the resistance of the original wire?

  A 1200-W hair dryer is designed for 117 V. vr+ov*4)x fvrvv+ e6f
(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 enou7wg5 nptlq g-rpo0nz+*w 4duie*a5s7gh so it does not become so hot as to start a fire. What diameter must a copper wire be if it is to carry a maximum currentwp q*-a 5t75sl gwerp0i47*zu +dgnon of 35 A and produce no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is giv:mt+ ;c 2j9evfiy z.jqen 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 pr./xkdqw);an f hb:6g er second to the i; r.xb )wka gq/dhn6:fnterior. 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 materi7 nmo/rb 3on.zal. One conductor is twice as long and twice the diameter of the second. What is the ratio of the power transformed in the firstb.o/n mr3oz 7n relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a ron(gut t q0dw81om of volume $62\,m^3$ Air is brought into the room at 5$^{\circ}\,C$ and is completely replaced twice per hour. Heat loss through the walls amounts to approximately $850 kcal/h$. If the air is to be maintained at 20$^{\circ}\,C$, what minimum wattage must the heater have? (The specific heat of air is about $0.17 kcal/kg\cdot C?$)    W

  A 2200-W oven is hooked to r.m n.8/u-svufzs:h)rt n9wt 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 en;akr6 s 34s)z:sngyfbergy. Its mass is 1560 kg and it is powered by 24 batteries, eagss : nf4kz )y6arbs3;ch 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 resistanc*5tp 0d 5sx 0ixcb4ftlyn 81tie 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 d1q( 9/n ppukucesigned to carry an 11-mA beam of protons traveling at very nep/uqn1ck u9 p(arly 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. Thef1e ikgri;qe;x7z:j 2 connecting cord is copper wire with a diameter of 1.628 mefrqjgk7x:z;e;1i i2m.
(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 3)js h,ibi0 hsV. The heating element is a coil of Nichrome wire. ijhbshi,03) sWhen 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 var476 ovokk c(: rok7bfyies 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 t7 c(b yfv:7or6ookk4k he 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 40xyzw1n+-*gbh3g sn egwa )*33ss: gbj W for household applications. Lightbulb B is rated at 12 V and 40 W for +nb3j3*g sxwwzh nb:e -3gs s)gg*y1 aautomotive 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 used to connect a set of appliances at 120 V-q.+lokwy :twn5xd0q , which draw 2250 W of power tow +-t. ndqql5 xk:0ywotal.
(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;x 7 qlj+l:qgbl:x f,f of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the q,;l g: x7lf j:qbfx+lresistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that jy396uv2u0n0ye2ab-soc nu k its length doubles, by what factor does the power dissipated in the wire change, assuming it remains hooked cs3 n-b2 nu uuyjayo26v9ek00up to the same voltage source?

  A tungsten filament used in a flashlight bulb operates at 0.20q ;o+:t3xy7e ulsf z(t A and 3.2 V. If its reoy s (:;elxz3tf uq7t+sistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$