What quantity is measured by a battes*jn q7sjka m*q;r(;try rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow away from)7 ee7es6 +ww.v *fdjsc0qfa v the negative terminal in the circuit. But within the cell, electrons flow to the negative termsvj)f 0dve+f7ceew6*7as. wq inal. Explain.

When a flashlight is operated, what is being used up: b)6xe m rmd)cy38kflv +attery current, battery voltage, battery energy, battery power, or battery resistance?e8lmx)mc yd k)v+r6 3f Explain.

One terminal of a car battery is said to be connected to “ground.”j6on:g i8gdfcs+.4q f Since it is not rea4. d:n8g+isofgcq jf6lly connected to the ground, what is meant by this expression?

When you turn on a water faucet, the water usually flows immyyyr t*i72w o6ediately. You don’t have to wait for water to flow from the faucet valve to the spout. Why not? Is the same thing true when you connect a wire to the twy r* yy2it6o7erminals of a battery?

Can a copper wire and an aluminum gclac.ju wf i38b2 +5pw 8.exkwire of the same length have the same resistance? Explwia5cj8ex up .lc2gf38wbk. +ain.

If the resistance of a small immersion heater (to hqc4nkw 6mc5ckk.14o 0fciz3n ;*aii beat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the heating procmciao*niq4;6 n zk3kc kbf 14w i5cc0.ess? Explain.

If a rectangular solid made of carbon has sides of lengths 1a 1mlp:venkyw/b; 5aa, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resi1eay:w ; vbmk1a /nlp5stance, (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 ska49b +-0z;g6n d*y emrrblky, b qf,lightbulb burns out?

Explain why lightbulbs almost always burn out j-i ln7jalhm -2ust as they are turned on and not after they have been on for some time2a7hniljl-m- .

Which draws more current, a 100-W lightbulb or a 75-W bux5ub 3u1kulw0ep -qp*gau 3 /dlb? Which has the higher resi lkd0 u*ae5q1u-/x u3 pgbupw3stance?

Electric power is transferred over 9 ox clm+e:g.nlarge distances at very high voltages. Explain how the high volta o9n.e cxgm:l+ge reduces power losses in the transmission lines.

A 15-A fuse blows rep, f/wltpr0lb5-up2)t p0 mnvjeatedly. Why is it dangerous to replace this fuse with a 25-A fus0 bv 5tfj/urw2n0,lptmp-lp) e?

When electric lights are operated on low-frequencyeb dd ;r;, +mmmwxop n1(q2of3 ac (say, 5 Hz), they flicker noti (ef nxpm+mb;d o;2o1qwd3 ,mrceably. Why?

Driven by ac power, the same electronsct1 12yvg/ufn ,zan7e e* v6mwdkyje+w 73)w v pass back and forth through your reading lamp over and over again. Explain why the light jetdvcfgu1ev177z,+n 2y*/3w) enw6mkawvy stays lit instead of going out after the first pass of electrons.

The heating element 3 p(hbb yv(ea:in a toaster is made of Nichrome wire. Immediately after the ( vebapb3y: h(toaster is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a re4wngj p+2 ,/flworl8xsistor? Explain.

Different lamps might have batteries connected in either of the two arrae7 93a7. lombqt 5iiuingements s7e7395 blqiu aiotm .ihown 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 flow 3v/1o/vzk re 04nnwocfwi-1(s; 7avc ge /pubing past any point in the wire per szs( oac1un -nv vg cwwibk 4;f/ee/vr0o31p 7/econd?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A for 5.0 h. q5 zne m*(+ i cydivj9k+hg(a)How much charge passes through the batzn*gjh +vk a5q)i d m9(y(e+ictery?    $ \times10^{ 5}\;C$

  What is the current in+f//pgezi-y1 ewa(zk amperes if $1200\,Na^+$ ions flow across a cell membrane in $3.5\mu s$? The charge on the sodium is the same as on an electron, but positive.    $ \times10^{-11 }\;A$

  What is the resistance of a toaster if 120 V produ zr9op h8x4l *)ywxjs.*lz: arces a current of 4.2 A?    $\Omega$

  What voltage will projy ;s0/j,hd;qyz u8jpp1nm a1duce 0.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged intohixb)9zd 8xfc e6+j/r 6far a* 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 ha bw*e4u8kjnuq:z-v 5bs 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 y(cr3/ ef)n1quszt d;. 9z yjyto 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 l9gu 9uq8ip+l)y+t6 url+xxdhine carrying 2800 A (Fig. 18–34). The liiyhlr uxp+9+g8)+ xdq6ulu9 t ne 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 A at 240 V. kp p09qk ahlwd3ub-;/
(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 currentn a2yc 9(cgbn //ju.pf 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 tungsten wire whose resistantl pqsg ca fk--+:9:nfce is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5w c*dcp.z1+3h3mp)s 4t3e sqjvy z jy*-m length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of alumiarc.3e r1io2dcv 5 1zrnum wire 2.0 mm in diameter, tz5.red3cra 12 1ocriv o 20.0 m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tungsten wi n 7nw 9gpawe/ih,3,lcre of the same length?cih9w /ap 3gnlewn,7, Give numerical details.    mm

  A certain copper wire has *oc*o ewwqbs/d ,y i8s9+mc0pa 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 (b p e2bpbv5kbe9-dv5 z+m;thcopper wire (originally at mpzed;bbb b-52 k(htp ev+5v9$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature co6*k-veag 1gshpper will have the same resistivity as tungsten do1a g vgs-*eh6kes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has ay5g /w*ryvptb* as lf7 -npf(2 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 lengwgr4 ll4+a g+*r eeiho ;c)io2dd )*mkth of household no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm and carries a 12-A current.gdl +hcrg eml)ew2 4*ko i4;r) *di+ao    V

  A rectangular solid made:gsx55i 0g 5vjv8z pkudik3z5 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). Determine the resistance for current that passesdg8gzxp0uvi3k55isv j: 5zk 5 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 len tggukn9/3gj(:g zyl4gth of the other, what is the ratio of the diameter of the longer wire to the diameter of l yjg(3 t9zgknu/4 g:gthe shorter wire? $\approx$    (retain three decimal places)

  A length of aluminumytcs yy53f c/7 wire is connected to a precision 10.00-V power supply, and a current of 0.4212 A is precf7 /ty5ycy 3scisely 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 *ashnu9+.4by)+ drm;wsraw x of 5.0 m of copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A . +rxumy 9sdr) ;hw*s 4nwba+avoltage 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 ah.p1xwpc-w/d2 s)nj qnitcfqe9 4(*pg :9 teresistance not change 4c9q-ppf .t)eqt1( 9s/:wj *pe2x h iac ndngwwith temperature. For example, suppose you made a $4.70-k\Omega$ resistor from a carbon resistor and a Nichrome wire-wound resistor connected together so the total resistance is the sum of their separate resistances. What value should each of these resistors have (at 0$^{\circ}\,C$) so that the combination is temperature independent?
$R_{0C}$   $\Omega$
$R_{0N}$   $\Omega$

  The heating element of an electric oven oce5uo2r 2 ;msis designed to produce 3.3 kW of heat when connected to a 240-V source. What must be the resistance of the eleerc uo 22;5mosment?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player thatzjs5m6 sfrj 5q6fcs(ap. ..dp draws a maximum of 320 mA o .6s .jzq fr5msfp( d5acp6s.jf current?    W

  What is the maximum voltage s)1n 4ruq bdoxjpr2; 6jn5(dfthat can be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and k-b s2f6ij.damz b :b0current through, a 75-W lightbulb connected to -bk .bf bi s0:za6mj2dits 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 heate)9kuyc0 po)oo r 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 andxd)x6 q izt7m75cpcue0ky 8o;uapx-2ak ( p y8 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 electri5o,/vd 2ye hf5+ awrlqcity is delivered to homes at 240 V. Ih5q+way/d vr fol2,e5 f 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 power consumed.]    as bright

  How many kWh of energy does a 550-W topstu5b7 a; bge4c8:fl,gt w )baster use in the morning if it is in operation g,)7t bbse; 45ta8uwflb:cpgfor a total of 15 min? At a cost of $9.0\,cents/kWh$, estimate how much this would add to your monthly electric energy bill if you made toast four mornings per week.
energy $\approx$    kWh
cost $\approx$    cents/mouth

  At 0.095 dollars per kWh, what does it cost to leave a 25-W porch light on day aawj t g0t: hmjlg)8.j)nd night .mg0j j )wgat)h:8jtlfor a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connecu) cm4)3b,nyltqzp-v ted in series as in Fig. 18–4b tl,cmv )zn3q4bu p)-y (Fig. 18–36). The bulb draws 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 of energy stdig+fo xozx4m*6 -y4 gored in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connv6kyo n u05p/ xkytk 7shgyw7.r41bz*ected to 120 V as in Fig. 18–20, can be used without blkzkh/uo6*n. gtryp40vy k717y5 x wsbowing a 15-A fuse?    bulbs

  An extension cord made of two wiresbha p)liz4lk88 y :ap) of diameter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) ispaiplb48h: kly) za8) connected 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 power at 12,000 V to a factory thr14a+k9pltrwm c q5,wrough wires with total resistanclw+5tp9rmrw c4q1, kae $3.0\Omega$ 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*uakdo*d7 +op 4tuoajcf+g0 q 6z.ab3 line is 17.5 A. At what rate must cooling water pass over the coils if the water temperature is to. j*bq406au odkdu +a3ozo*acf+pt7 g rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used inesmgdmw1gv *q s7- 03t a car to heat a cup of water for coffee or tea. If the heater can heat 120 mL 317*g 0qdgsm t-mwe svof 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 +s6dt ) u v*l3jcich;sa $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V,g) k ms eh53lkzjx.:l8h:1r+txa xx8d 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 resistaq*fu) )bethsca 7 9fv3nce 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 a5 b:*i,w6i i:vkbqvo8rm 1 p;beht4x i 1500-W device is 5.4 A. What is the rms voltage acrv,tmkbqw;*bi:ro5i x6i ibh18e 4 v:poss it?    V (Round to the nearest integer)

  An 1800-W arc welder ,ndl b:3er+ 4k2dz tqzis 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 / yx12lg.7c,gl 3g2ia ggifvgdissipated by a 3.0-hp pump connected to aggg x7 i2. glvic21lf ,gy3a/g $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected ti ngqxqnj, *;9o a $240-V_{rms}$ ac line has a resistance of $34\Omega$.
(a) What is the average power used?    W
(b) What are the maximum and minimum values of the instantaneous power?
$P_{max}$    W
$P_{min}$    W

  A 0.65-mm-diameter copper wire carries a tiny cursy .v ;6yx9gvnvf66 4s bcb5knrent 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 c cacb0+0bukle. rn9f7urrent when 22.0 mV isb.c9 luf7 bea+cr0n0 k applied to its 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 Eabu7ip9p3boj3ro 1s ;chem) w2rth’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’s atmoqo1gc.9jw*f r9 ts y7osphere, $He^{2+}$ 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 axo qyoouo .,e( ol83tb8gn membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with an electric puluy30q )aw- pbvse. 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 speq 3u)p-yw a0bved of the electric pulse along the axon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much energy is requxexc5)kb*/jd m+ qoi1ired to transmit one action potential along the axon of Example 18–15. [Hint: the energy t jcxekmo5id)1q/ x+ *bo transmit one pulse is equivalent to the energy stored by charging the axon capacitance; see Section 17–9]. What minimum average power is required for $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action potenttbui z., .aoq hz;*evlu;n31m ial, $Na^+$ ions move into the cell at a rate of about $3 \times10^{-7 }\;mol/m^2\cdot s$. How much power must be produced by the “active $Na^+$ pumping” system to produce this flow against a $+30-Mv$ potential difference? Assume that the axon is 10 cm long and $20\mu m$ in diameter.    $ \times10^{-9 }\;W$

  How many coulombs are there in 1.00 ampere-houl ri70+a/v/ 4s)pnvvs)ily wo(h 4feqr?    C

  What is the average current drawn by a 1oic7 emzz4lg*5 *r x-c.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If eacdk 3mi5x;r3)nvove 44jrby a 2h 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 laj n iae )kv3;5bdrrym 3vo4x24st 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 x*rnjjar m* 02long. If it is made of iron, what muj 0r*rmjxn2a *st its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of the resistanc:, xpaa ug 4iiwrm*p8:e R; that isi8x w4m,*r ipap:g: ua, $G\,=\,1/R$. 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 cd 52iih)*kix 0nm-t /au+bo cMW of power. Suppose that instead of using high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a two-/ k2*ibu io xh)tcc +d-mi50anwire 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/ 31gdj8o;ldnt53daurjw r 6 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 lengs-s2 ul/3 eiqwths 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 original wir l32wuqsi-es/e?

  A 1200-W hair dryer is des ov n2(7xw9dcnsy q 1xzm39nn0igned for 117 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 md0q wq 6zat(5ktx w2 ob:8 mks;l8u,eoust be thick enough 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 current of 35 A and px2,sat:; 86eko u5(ol8 ktqdb0zqm w wroduce no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given :u,*fpn1qq msby 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 95;6 zai5fr9 rqc0 W of energy per second to thefz95 cr6;ri aq interior. 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 diffe k -v4puhl28cdmv(j ,qrent conductors made of the same material. One condud k(vq-cv28pj 4mu,lh ctor is twice as 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 to heat *lbpx7c /lru4a 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 hooked to a 240+pi(u jz (nlqh/g7l7j oje42c,zc /ux-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 eb7-edxc38aian:m/ k v)sd)3ni1afquse of storage batteries as its source of energy. Its mass is 153xa ) ) ikea1bed7f -3n i:nqscm/8dav60 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 lightbul8hqoy2wzw 0 5vb has a resistance of $12\Omega$ when cold (20$^{\circ}\,C$) and $140\Omega$ when on (hot). Calculate its power consumption at
(a) the instant it is turned on,    W
(b) after a few moments when it is hot.    W

  The Tevatron accelerator at Fermilab (Illinb cfm: .asd05uois) is designed to carry an 11-mA beam of protons traveling at very c: 0fua.5msdbnearly 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 connec4( ,/rfn, .q4wemj3t ejposseting cord is copper wire with a diameter of em,srj3wo.psnqe/ ej 4t,4 (f1.628 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 codkiw;2cbg * u3nnected to 120 V. The heating element is a coil of Nichrome wire. Whebwu;ic32d gk*n 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 jbc;b;,cxe9y, k pk .lsystem voltage varies 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 voltage changes from 12 V to 13.8 V? Assume the headlight resistance remains constantx,bkel,pb9cc;j k; y..    % increase

  Lightbulb A is rated .1r17uevzui4 b y;cro at 120 V and 40 W for household applications. Lightbulb B is rated at 12 V and 407uy ori4;rzvb1. ecu 1 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 used to connect a set of appliancesr9ymgb8: zqjij ,xapo2 38oh 1 at 120 V, wh928go xyi3m1ojzahqj 8 :rb,pich 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 diameter of 5.y2acgh:0ar-*9 tqi je 00 cm (Fig. 18–37). What is the resistance of 10.0 m of this pipe?t2ag9 jeqyih-:ac0* r    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that igxjxy 75 2 a6o7nlmpa6ts length doubles, by what factor does the power dissipated in the wire change, assuming it remains hooked up to tag5jy 77m6 nox6pla 2xhe same voltage source?

  A tungsten filament used in a flashlight bulb op kc5p(dyhx n 52qj29yzerates at 0.20 A and 3.2 V. If it j nx25dykzh5y9(qpc2s resistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$