What quantity is measured by a batterysb4 rq. piw-.n rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected8v1jg62 exuu orz1 xd0 to a circuit, electrons flow away from the negative terminal in the circuit. But within the cell, electrons flow to the negative terminal. Expla0x2 xe1vru8 1o6 guzdjin.

When a flashlight is operated, what is being :wadd2x(xe u-yt96pd 4 j6fuf used up: battery current, battery voltage, battery ener-dfw9 e x6uf4yd6(udj:tx pa 2gy, battery power, or battery resistance? Explain.

One terminal of a car battv6b v7 qhr y*vnx1,v4nery is said to be connected to “ground.” Since it is not really connected to the ground, what is meant by this expre1h xvb r,6q*v4 7nvnyvssion?

When you turn on a watz)-kh + l* kh+kpx*tzder faucet, the water usually flows 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 connect a wire z+hl*pk +txkk*)zd h- to the terminals of a battery?

Can a copper wire and an alu:gbq jvjw6b e+ xj(a;+minum wire of the same length have the same resistance? Exbx (jgw aqv6;j+be +j:plain.

If the resistance of a small immersion heater (to heat water for4 y1p/f*e 5:zdh2ytxwni)rxo tea or soup, Fig. 18–32) was increp/15idx 2tno:w fyeh 4rzy*)xased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of ce ovu/2(4zphtkez 9f+arbon has sides of lengths a, 2a, and 3a, how would you connect the wires from a battery so aszh2(ukep /oez9t4 f v+ 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 lig(8sli1v84u u;le 9h f 2gbqocghtbulb burns out?

Explain why lightbulbs almost always burn out just as t gj q.pbuwwa:q39.j.v gk0)ymhey are turned on and not afterb)uqk:mw0j gjpv. ..g3yq9aw they have been on for some time.

Which draws more current, a 100-W lightbulb or a 75-W (7/pj;j5xacc:dk;zwzuc lhm23q xg+ g;0xv xbulb? Which has the higher resis;k+cv;c/xa7gwp q (u:j3 zxx0 lzdg mhj;x2 5ctance?

Electric power is transferred oj61hpn 1uk1giver large distances at very high voltages. Explain how the high voltage reduces power losses in the transmissi61nihgujkp 11 on lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace th 8ai2sxyv6hc1*mryg )nu+1 ppis fuse with a 25-Ar1yay*1)ip6m+n gscv 2u8xhp fuse?

When electric lights are operated on low-8t94xp y culus81io ,pfrequency ac (say, 5 Hz), they flicker noti1ply8xuio p 8t9s,c u4ceably. Why?

Driven by ac power, the same electrons pass back and forth through your readinr4m :l6 ml6iebh 6sa3u7om)obg lamp over and over again blmb6:u6sa 3 4i7el6r homom). 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 c.bl5oz b): hk8p ny2nafter the toasb ynhol2bp zc:8.k)n5ter is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistyoi 1c523c6p3 mc. si7 uzndpvor? Explain.

Different lamps might have batterieg1q, h9lhpuft k9fd 2l(qr:n-s connected in either of the two arrangements st1f urq df9lh, g9ln(qh:k-2phown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many s3p ;xg0knbb02 gfrkl5ljq q5g:l3c, electrons are flowing past any point in the wire per second? 05k:n2,pqlf3g b 0rb;c 5xk3lj glg sq   $ \times10^{18 }\;electrons/s$

  A service station charges a batt1q j nrsf2:)blery using a current of 6.7 A for 5.0 h. How much char2nj lb1)r:sqfge passes through the battery?    $ \times10^{ 5}\;C$

  What is the current in qe z(we9 ph6xr7kye4.lote +8 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 iau3p+jlvi wd35 1ma 2V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current 6a b:vmkv3 v6 t )dh*0zj,wafbthrough a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when i)uzbf q+d,,w dx/p:d 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 ezcd7 n;9 ,vavqlement 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 resistancewqwmh3ue lt4fcp dk/l,v7:cgh*q7ghd1 q /:+ is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transmission line carrying 2800 A (Fig. 18–34)hv sa-57-.dzj ec3hqz. Thvec3 -az7-zd.hj sq5he line 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 dr* *4f(ihuvt*vtl fh(jr5yl 5yaws 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 res 1+d2kp n4guuqistor.
(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 whoy+k.lr5rbrdk m+391 +xh jn uuse resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of ao *8 yh) 93enfck2ezkphg: e8x 3.5-m length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of alumi vmw axs)zv312r9,dzq num wire 2.0 mm in diameter, to 20.0 m of copz wz2,mar1v9sx 3vqd )per wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tui2dwjj72d t2bij9 6qcngsten wire of the same length? Give numerical deta c7j ijd2iqw26tjd2 b9ils.    mm

  A certain copper wire has a resis0ut5sk c,/*p3 fhw asmtance 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,z0 t fsdr*.. qutti) lebo-:p a copper wire (originally at ,.ud ttt so)rlfi:pb q-.ez0*$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature cop+xat7hmbvah 5d-8 vpka,q84o per will have the same resistivity as tungsten do7-qh8a pham8+bdx4t ,oavk v 5es at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of abem w;3 eo+flymqx+y- 9out $12\Omega$ 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 2r)y- ./rimot h-rq iz+6-m length of household no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 zh-ir) tiryq.m/ +ro -mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths2 gkxp.ww*,iavnof3ry:8 z a hb d8;;j 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 passes through the s;g.z,abo3 vwhi 8 y f*xa2pnr;dkw:j8olid 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 -vq+h1t 12t/x abv qvrlength of the other, what is the ratio of the diameter of the longer wire to thrvh t2- x +qvav/b1tq1e diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is conneu,aq-tuzpjlv)rrb0b 70b 3w6cted to a precision 10.00-V power supply, and a current of ,aq b l6b-ru07w)ztjbr30 uvp0.4212 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 w8d9bq w spb0f8ire consists of 5.0 m of copper followed by 5.0 m of aluminum, both of diameter 1.0 m8b 890qdpbws fm. 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 resistanz8pmrxg;xlnj,c q w7 w )e1:0jce not change with temperature. For examprj:81mgec;xw) wlj,npx0 zq7 le, 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 is designed 09pz z0 )wprruto produce 3.3 kW of heat when connected to a 240-V source. What must be the resistance of the element?wur0 p) 0zpz9r    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player that lbs()( uh9jnh draws a maximum of 320 s() jhhn(l9u bmA of current?    W

  What is the maximum voltage that can be aymo)z mhta)*i 27kcpl , 27stepplied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, a 75-W lightbulb connect.cm+ts i oal;( 5th +3lnv1asted to its proper so5 tam;n3( lti+sh1 lc.vsa+to urce voltage of 120 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heater is rated at 110 W. m9p: xukbcmn 8-9 /ggiCalculate
(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 setfet9fzs0 r8-i tings: 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 ak1 /vt4a6kzf1ab2)*h ccy8 9ajg lmg electricity is delivered to homes at 240 V. If you use the lightbulb in the United States at 120 V (assume its resistance does not change), 9hcma2/ c16gak gaf )*81j4bazkl tyv 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 toaster use qxo/8m dse e10 ;zq8dtin the morning if it is in operatiod q/dqsm1e 8zo8; xt0en for 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 2 gmuq pv3w/:+ qolkh4.vym 1(exc3k 7a5-W porch light on day and night for a year .ve/:km73qhq1( wkm px v+ 4lcug3oya? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries cns.frty ot ;l:py e/5sm l9a6os-x 0d/onnected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when turned on.-f6.a0d sxnp/tsl9mle/oyyt o s:;r 5
(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 12-V, )w n6k-z4:pj.wtp z un$85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbul1nqa pinaia f(n164y.bs, connected to 120 V as in Fig. 18–20, can be used without blowingn(4in16 1 q.ni fpyaaa a 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 copperbpe 14 4kkw;ny wire) and b4ynek k;pw14 of length 2.7 m (9 ft) is 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 through wiresebcs5j n (*/;kqdc1hu 0jgd6v with total resistanbkc6 h g;q05 d(ds*ecuv1j/jnce $3.0\Omega$ 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 17.5 A. At whaty7b4kaaab4r/cy3 ; hc rate must cooling water pass over the coi/a4rbhk3b 4 y;c7 cayals 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 a car to heat ,knsn/4,l a wzgt9 y,ca cup of water for coffee or tea. If the heater ktsgn4lw 9c a n/y,z,,can heat 120 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 current5*gx7;crzxc dwn-w x +y:k2 st in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak 423n gdy26nrv 8eoyy ivalue is 180 V, is across a $330-\Omega$ resistor. What are the rms and peak currents in the resistor?
$I_{peak}$$\approx$    A(retain two decimal places)
$I_{rms}$ =    A

  Estimate the resistance,1 ) mbkbgasn8)qn,f w 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 alterna,z,fc vzgw4 s8.g xts9ting current in a 1500-W device is 5.4 A. What is the rms voltax9,.48gszstvc wfgz, ge across it?    V (Round to the nearest integer)

  An 1800-W arc welder is con nfno366l 8 nz5 tcz*xit3u*cgnected 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 connect(4woa6z 7rie ted to z wr4(toe ia67a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to a n*i:0mivwfia26qtxja1 hb i p 4 m)5.e$240-V_{rms}$ 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 coppeqxo *pr)kv1 5ir wire carries 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 2em2 xu -id hpx4+0m;sp.0-mm-diameter wire carries a 750-mA current when 22.0 mV is applied to its ends. If the dr;+h4i pm sx2x-0pemu dift 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 Earthcqjqg :kw3isf c(*95s’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’sxak:6-ea+0ujpp x sq- 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 ama1w5akn6ol30v gr2f p0r0othe electric field across an axon membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with an electric pulse. The actioicy) n t44t: xwomm19dn potential is detected at a point 3.40 cm down the axn m) twi:xc49y1mtd4o on 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 needed instead of only one?)    m/s

  Estimate how much energy is required to transmit )bmku)d 7 ndwq s*) ed9den,-aone action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equd)eqn nw,)*e bkdms) dd9a-u7ivalent 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 potential, 8cbzl+v 209:f :qeb- nxxnhsb $Na^+$ 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 xa;1vepg jh+j wp9 n)9d8 xit9in 1.00 ampere-hour?    C

  What is the average current qolzwb(.eo:xsc+3 uu9i j/ 0 gdrawn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If evpn5v* l5.f 2p,+e e96c2 p4aoe nquc,cjoz rxach 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 it is rated,2evc l nc fjp o9,e6u4qp5*nx vac.or5ep+z2 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. Ifm 64q w*ro;tu8fwbv5)cefx7 f it is made of iron, what must its diameter bf7f5) xfuw wrvecbq68; *ot4me?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of the resistaofnxy)yt+wqu c 7u3 /4 /ttyz78e;xufnce R; that is, u wxy7 7t ztc )o/3yffu/+;xeuyt84qn$G\,=\,1/R$. 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 us. d o5d)w*qfm3.hp7.ktqavm iing high-voltagw) qpmohfd *37dk.mitq.a v5.e lines to supply the power, the power is delivered at 120 V. Assuming a two-wire line of 0.50-cm-diameter copper wire, estimate the cost of the energy lost to heat per hour per meter. Assume the cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular household uses a 1.8-kW heater *fb2:j3uof rw$3.0 h/day$ (“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 lengths are wrapped togteh1aqj t ;tg.0m gl,2ether side by side to make a thicker wir .te0,m hjtq1tga;l2ge. How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed fqv29e -ll u*hi h;,dvxor 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 housee,nb5bpa0wts 9 sq m v(mv5/f0 must 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 produce no more than 1.8mq9t5e0v w,v 5bs (apsf/nbm0 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is giverm-r,9hwg m-.l2xqmkp yv;zl( j n+y 0n 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 o1u2;p vn ( dvttvh p+;oggo y(4*60w ylcqy.m950 W of energy per second to the interiotytvln; m1vqc2h oo 0o(ygdu pp+6 wy (*.vg;4r. 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 ono8qa djw6dz5e: 85*mjr l-qsf the same material. One conductor is twice as long and twice the diaj d5-rdz6 *q newjqmo85 s:l8ameter 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 a room of volumezws2 kc m1xp g93qp3nj-pr6z9 $62\,m^3$ 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 sourn372. 4e p1aj f.r pcfocal;gwce.
(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 veqa*.y pbgfnug o 5mq,+7en,a5 hicle makes use of storage batteries as its source of energy. Its mass is 1560 kg and it is powered by 24 batterien5 ,b5gq,pa g+ony7 .a eum*qfs, 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 resisb:b.bf5af(m/ we alnhp1ed7 ;b7 mrj q5 ::dtitance 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 acceleratn0o yl)4g/,uswuuv,nje41 k ror at Fermilab (Illinois) is designed to carry an 11-mA beam of protons traveling at very near ,k /,y4) 1lv4eswjurnunuo0 gly 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 noqz;. )vno jk19k1elfzw4y 1 ac. The connecting cord is copper wire with a diametere;q. nk)owvlf4on 1z z1y1j9k of 1.628 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 clcl1dx-q r q0(onnected to 120 V. The heating element is a col0c x1qrq -(dlil of Nichrome wire. When 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 v0pm/yxzcq)vq ; (. vzyaries 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 t;m0 p/(vcy qq) .vyzzxo 13.8 V? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 Wourhy-)4/xah */ f pyx for household applications. Lightbulb B is rated at 12 V andr4) yx poya *hh/u/fx- 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 used to connect a setm 8,d*ehpp65krfhx0 k of appliances at 120 V, which draw 2250kh*xk rdp56m, hf08pe 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 outsitzer n;fj f54)de diameter of 5.00 cm (Fig. 18–37). fe ;nf4jz5 )rtWhat is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so thfx i) jda(6ty;i /7ncwat its length doubles, by what factor does the power dissipated in the wire change,dy7w (icni;fjax/)6 t assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operates at 0.20 A and 3.2qk1 la /r)gtw+;muiajg*x57 w V. If its resistanc rmu l1gt ;w*)a/axji 7+kwqg5e at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$