What quantity is meau u8p-ug6jf m(sured by a battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connt42ux32ro l8n3u8 vwkqq :seq** rrbn ected to a circuit, electrons flow away from the negative te o wur4nr*k2e:3bltu*q 8snqqx82r 3vrminal in the circuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is beit1bc 97 69iz ilnq(h6yvebd e 9ivt.y.ng used up: battery current, battery voltage, battery energy, battery powerbi.9vby 1.dv y9ihln(tt 6ciez96q 7e, or battery resistance? Explain.

One terminal of a car battery is said to be connected to “grov3q y f i25t moi6774nqbyr4okund.” Since it is not really connected to the ground, what isn7 46k2ii3 rftqo 4b ym5yo7qv meant by this expression?

When you turn on a water faucet, the water73v -lneb--v xq6 oewa6f*okx usually flows immediately. You don’t have to wait for water to flow from the faucet valve to the spoe-o*-b6k lx n afv36 vw7o-xqeut. 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 the ok 5qgzlbo-ddf 1jb3j005j rc/.t0xy same length have the same resistance? E ogb3qdr ydb-oj1.00x cfk/lt5j05jzxplain.

If the resistance of a small immersion heater (to heat water for tea or soup, Flu rj(2 zhyob ,;bacy2u7 -c5xig. 18–3bzo(2 u2xjac7lcyy h,-br ;5u2) was increased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon h/q vo5o;agg* bas sides of lengths a, 2a, and 3a, how would you connect the wires from a battery so g;bva o 5gq*o/as 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 lightbulb burns nka 33qxk6g5xw4g vgq2ck75q out?

Explain why lightbulbs almost always burn out just as they are turjl 5ik+z,2entc :r8rmn irc-+ ned on and not after they havn:t rrenc-8r+zm +52 jlk, iice been on for some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which has the higher f(zk9*0 dkkud rukddzfk( *0 k9esistance?

Electric power is transferred over large distances at very high voltage,:md;eshv+j7c5)p oigpf :mb s. Explain how the high voltage )h c,f:i;s mpde5m+ :7 ovpjbgreduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is iaiwp.,-m g/vkt dangerous to replace this fuse with a 25p/.-iga ,kmwv-A fuse?

When electric lights are opev6rh3mca q9j*9i 7hg;ibr d;smh4*clrated on low-frequency ac (say, 5 Hz), they flicker noticeably. W 4hcg6 j7; 3;9m*vhmiaqrbl *sirhcd9 hy?

Driven by ac power, tr/kkbob7 ;f4q(mzx( phe same electrons pass back and forth through your reading lamp over and over again. Explain why the light stays lit instead of going out after the first pass q((r4obkk ;mpz7 f/xbof electrons.

The heating element in a toasae1h++u4jajy xl.d s+ubx )k6ter is made of Nichrome wire. Immediately after the toaster is turned on, is u). 16e+ybj hx++ kaauljd4sxthe current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor?x25vnm0.5 mvf8pyuh,9/jtr ce 1jr ub Explain.

Different lamps might have batteries connected in either of the two arran-qydwkorbfy*el h/8 8c;0 l(qgements shown in hw8qqe/-kl8 fyl cy(r;0dob *
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How t1 xkko0p7nfcng4wbyt:;rf 78 v( 1dq many electrons are flowing past any point in the wire per second?nc:ftt;fdrkv7x7 pw bn 1 y14qog0k8(    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a pns:+s0 ;b;n1/+u u nxfvkq zocurrent of 6.7 A for 5.0 h. How much charge passen uoq 0fbn+ 1+p:ssn/u;xz;k vs through the battery?    $ \times10^{ 5}\;C$

  What is the current in ae*88d s h/g0 aukzfi(vmperes 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 producesr9 q.g2ltjp)m a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current throb/-kmx8sk8+f yoj innj8rl 9 2ugh a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged intoa nr7 f;8dq:- u1gy8k, wbftcr a 120-V line.
(a) What is its resistance?    $\Omega$
(b) How much charge passes through it in 15 min? (Assume direct current.)    $ \times10^{ 3}\;C$

  An electric clothes dryer has a heating element with a resistsmis ac198 .9g.o: )c qezdtokance 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 bulbi+ eyp 3xv7qw-zjs8q 5 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 carrying 2800 A (Fig. 18f:x.i a39a izn-mz k6d–34). The : amf. 3z9k-x6zandii 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 draws 6.50 A h*c): iz4 qoiqat 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 ydsdq4 -)*ozs4 g::xubq gru 4a current 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 resisdn; a.)xkh k.atance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1.5 mm in diameter? da*z7l4poyj:    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance ofz:ko; 28 h ff0(.4pihk czgnpl 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.pkl0ig 28; 4knczfhp f.o z(:h5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have .:1hsf dnglbz:1vf95er7pd p the same resistance as a tungsten wire of the same lengt. 19h pb5z1l:e:dsrv f7dfpngh? Give numerical details.    mm

  A certain copper wire has o 9i f0n2 8 +dnpc*en82nvgpaga 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 (cnh*j+ vwttqu ;6, kti :d3kgwire (originally at wknjc,t+t ui *(6;g:kdhqtv 3$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperat-mlwf;jv +z, 9jih,uyojv l(/ure copper will have the same resistivity as tungsten does / wly f(uolv h,vz ;+jjmi-j,9at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of e8*p+k ez t7nc.vht d7about $12\Omega$ 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 lenqdq/ emzl39wkpv e-; h.g ,un7gth of household no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm and carriegld.q ;9hzpe-wkev q n/3m u7,s a 12-A current.    V

  A rectangular solid made of carbon has sib a):jz;hqli2+y.dosdes 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 re2jbsh ; +i:zq )l.oaydsistance 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 ohr65qq*cu a cvf 1bc3/ne has twice the length of the other, what is the ratio of the diameter5ra/qc 1cfb 36*hcvu q of the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to huwvt70)abg hvj4b 3s(y -6 j;bq /plma precision 10.00-V power supply, and a current of 0bpy 7lv jms)-34au jbh;0/vh6gt b(qw.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 wir:yyu8ov /95pfrkol )f npx:b2e consists of 5.0 m of copper followed by 5.0 m of aluminum, both of diameter 1.0 mm.2y5xpf:/yf rvknp) :l o9buo8 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 th91 7eh(tlra piur7+gle value of a resistance not change with temperature. For example, su r(are197iphg tl+u7lppose 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 electrich1d km7 2ewvo 8f/+hhx oven is designed to produce 3.3 kW of heat when connected to a dh +8mwx1e2okhvh /f7240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portabufsn0 ibnm .+0/qqiv :le CD player that draws a maximum of 32+u 0:f nq.ii0/msqnbv0 mA of current?    W

  What is the maximum voltae-yay-g,i *ce33yj sc;;wvu uge that can 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-W lightbulb connddad q o:uk fsqzk58 957qeu6uve(0v 7ected to its proper sfdq 9evquou7 q0k:86kda( 5us5d7 evzource 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 atrdwv)h:1h qql98u: ( yqynwq- 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 and 1250 W*fpc -:cb7,gecdh a (a.
(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 homergqld9 6nayev(j;kvi .ow,-0s at 240 V. If you use the lightbulb in the United States at 120 V (assume its resistance does nog-.l a6q9rj ;ved ,vyw(i0onk t 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-n5(ih dvut ;7 l7+wnqsW toaster use in the morning if it is in operation for a total of 15 min? tq7;(s+ 7niwlnhd v 5uAt 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 pjyq*m: h6:)y7h aj1xs z*kgtjya7 hd)orch light on day aq gys6h)j)dy*h x mz a:7t:kj ahy71*jnd night for a year? $\approx$    dollars

  An ordinary flashlight uses teuq)vo24 u x4nwo D-cell 1.5-V batteries connected in series as in Fig.nxq424uv o u)e 18–4b (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 stored in a 1 b5/dl nulw9utnx d m9y*)p32t2-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 bppqdyk0+w-86 hadu6pe used without blowing a 15-A qp+d8ppd 66akhy uw0-fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no(flj)8y;onv rd;:wl y4q 1boq. 16 copper wire) and 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 co lb4n; (;qydjrwf ):y8q 1lovord?    W

  A power station delivers 620 kW of power at 1(qq a9pm,-z1mq;c 6z+uw-.z hfagxht2,000 V to a factory through wires with total resiqgh qhfqza cxwpmau9(+-z1 -6, .m;tz stance $3.0\Omega$ 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. y *xm 46n95fe.ykpsf*lhg8dc+zkt(7n: bwn l At what rate must cooling water pass over xzbw97emn.fn6 +fl:k8ct 5p lyn 4*s dyk*(h gthe 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 a car to heat a ch31x1ts4(3 ciabfw*.s kk na 2logv +kup of water for coffee or tea. If the heater can hean133g. k w*1iaxvk(s4act o lb +2kfhst 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 current inyjpqix z:a n z4e*r:5+ a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 16ns;evqd 15 o70tyni r80 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 of theg ld;)92t kn djuvj9z: $120-V_{rms}$ 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 current3gzb wtjy +od ;g/ux 7,k9psw( in a 1500-W device is 5.4 A. What is the rms voltage across ,/zsgu( +dwobw ty3xg j97 ;kpit?    V (Round to the nearest integer)

  An 1800-W arc welder is f hy(jxkr4j*) 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 pu .qq+dkrux/y 0f-7 jzump connected to du quj.zrf/70+x-ykqa $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connecte+1o bpc (fq,h k2z. w3ogmct9ad 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 tiny c*q 90gwzfbjy7 vdi .sv9t)w i8 o7t+umurrent of $2.3\mu A$. What is the electron drift speed in the wire?    $ \times10^{-10 }\;m/s$

  A 5.80-m length of 2.0-mm-diameter wire carries a 750-mA current when,iq -t9sgl)c hor4l9f 22.0 mV is applied to its ends. If the drift spe tfi o9lrs9hgq4,c)l-ed 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 Earthdoss(wd* /s)9k b k9pm’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’s0c3nx . b)vrqcv de8y0 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 fi g0b1v-1khxn8j 3bhw neld 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 action p mc6-29hodm asotential is detected at a point 3.40 cm down the axon 0.0052 s later. When the action potential is detected 7.20 cm from the point of stimulation, the time required is 0.0063 s. What is the speed of the electric pulse along the axon? (Why are two measur6oamc- 2h9sdmements needed instead of only one?)    m/s

  Estimate how much energy is red wzsn sp7qx9w ;, d(g7m9+a)sdufon8quired to transmit one action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored by charging the axon capacitance; see Section za8usdd +s (osnwd977mw)x fnp q;9,g17–9]. 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 potentiacc+ f ,lixexrmc -h5:j. t+8mll, $Na^+$ 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 amsbvm + gau*1f03y/8ds8 qrbnwpere-hour?    C

  What is the average current drawn by a 1.0-hp 18*jk y6bq,5scl6rfhz s :f5 es20-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If eg5 ml/el/; y s i6eildz61,ysxach of the two headlights uses 40 W and each of the two taillights 6 W, for a total of 92 W, how long will aglmyy6, le 6s s5/i;ei/zx l1d 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 +u6 *( dlwstgca 110-V, 1500-W heater is 5.4 m long. If it is made of iron,+tgwud6 s( *lc what must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal mge:c elz5o/ 3- is.hiof the resistance R; that m-ceo/3.ehi5 silz : gis, $G\,=\,1/R$. 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 thatvq1p.t yu s;v. instead of using high-voltage lines to supply the power, the power is delivered at 120 V. Assuminy v.t1.u;spv qg 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 h4qb; *sp;zr fneater $3.0 h/day$ (“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 l3dl qjrl7,yau/ 0slhy:7den5engths are wrapped together side by side to make a thicker wirela7 e:/ds3 0yu jd,qnrlyh7l5. How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is desih3 (.b*,d7ipc4et qiv 1 yat.,zhngvkgned 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 must be thick enough so it does cas cp ) vl*68ttw+tl +sz2gp0not 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 prs)cltcts80 lppv *+ z+ awtg62oduce no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by the equationil )06.-)kv; puf f9gee3ltspk- mr st $I\,=\,1.80sin210t$, 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% wnx:s 2k/;s.cf;sjt oefficiency delivers 950 W of energy per second to the interior. F:n./sj f ssx;k tow;2cind
(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 ma wd63ce9 /rkdede of the same material. One conductor is twice as long and twice the diameter of the seckde/6w re9dc 3ond. 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 o8jeh8p+/ 3q ke;lvaf1(h hko 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 hooked7c 81laflg sb1 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 batteries as its source ofze zg,f22ot /u energy. Its mass is 1560 kg and it is powered by 24e2gut,z of z/2 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 riqznw9 t-r* s+esistance 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 designed to carry an 110nbzw yo: 1u,b af*)bq-mA beam of protons traveling at very nearly the speed of light qbnbaw*:zu 0f)1b,o y($ 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 a q2y9).eil twc f6kws0t 220-V ac. The connecting cord is copper wire wiic2fe)l690.sqyw tk w th a diameter 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 connected to 120 V. The heating eleme,f;0fo1iucs u x6xsm6nt is a coil of Nicofxm ci6, u1 xfsu0;6shrome 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 systela4nb e ,xsh7ek mkq 1cut;s2ri /*.u:m 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? qamix12 b ,e k:snsclru.*h t;4uk7e /Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated g+)v mg;nu ut, g5)hem)po fk4at 120 V and 40 W for household applications. Lightbulb B is rumkvego)+5ug)) t4h,;f n mgpated at 12 V and 40 W for automotive applications.
(a) What is the current through each bulb? $I_A$ =    A $I_B$ =    A
(b) What is the resistance of each bulb? $R_A$ =  $\Omega$ $R_B$ =  $\Omega$
(c) In one hour, how much charge passes through each bulb? $Q_A$ =    C$Q_B$ =    C
(d) In one hour, how much energy does each bulb use?    $ \times10^{5 }\;J$
(e) Which bulb requires larger diameter wires to connect its power source and the bulb?  ----待选择----Bulb BBulb A 

  Copper wire of diameter 0.259 cm is used to connect a set of appl(aw: m ,;p7jr*cjh7ueri:f cciances at 120 V, which dr 7 cir 7pjeuhwm,;:c ra:c*jf(aw 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 ane2gjmq+/t:j+4ak,d g ejhssz( 6sa 0wd an outside diameter of 5.00 cm (Fig. 18–37). What is th:e sj(j+ma,ga6 +0tzeds2hksq 4/jw ge resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistanpe.gynyx-mx 0,51 xovce R is stretched uniformly so that its length doubles, by what factor does the power dissipated in the wire change,p1m n,gy 0oyxv.5x-xe assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operates at 0.20 A and 3.2 Vzm1s*z-ihg62,shxxj mg 1 tg7 . If its rx6gzhxs7t z*ms g-i2mg1 j1h, esistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$