What quantity is measured by a battery 6uccq-piu1cj 0o 0q dy)ea3-zrating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow away3 :32za xjmovxz l0z;)svxog- from the negative terminal in the circuit. But within the cell, eloz-m;lzxo j3 vzvsg3)a 0:xx2ectrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battery current, b 55o1cv rk)zh ,rwvj(d qf7nc+attery voltage, battery energy, battery power, or battery res kr j 5)dc5oqrv,v1n+7 fzc(whistance? Explain.

One terminal of a car battery is said to be connected to “grr jl1sde ao4zes 8(5e2ound.” Since it is not really connece zd5e4osle1j(28sr ated to the ground, what is meant by this expression?

When you turn on a wqf :l mllah61.6y6; rwux7dmygx.k ag;j)+k jater 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 t; uh6 7mmy6x ga:la kg)l+yqwj 1; .lxkjf.6drrue when you connect a wire to the terminals of a battery?

Can a copper wire and an aluminum wire of thkwh -y h,a ;1kat.vn.ye same length have the same resistancew;vaka ty nhk1y-h,..? Explain.

If the resistance of a small immersion heater (to heat water for tea or s(9em c1ef)pf* gd byhialp -,;oup, Fig. 18–32) was increased, would it speed up1mliga(p ;f,e )c byd -p*9hfe or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides mrw xgn4lv1i2 4or30 iit0 ad5rbb/ .gof lengths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least t nbd3ir 0g v24xa.5bri1/0w li4 rgomresistance, (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 burnvet h0,us:k o7s out?

Explain why lightbulbs almost always burn out just as they are turned on uzocf9p-mo .dy 5 ,ga ,x30rzcand not after they have been on for some timad0g.cx5 9fuz, oz rmco3-py,e.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which has the hf5 66gucmtpg g2*vdg )igher t p 562u6cgv*gggfdm) resistance?

Electric power is transferred over large diie1:f foc, ggk+8al7p stances at very high voltages. Explain how the high voltage reduces power losses in the tglf1kp 8oeicg +:a,f7ransmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fuse 3rd9lqlov jq y1 l)s0+with a 25-A fuse? y+rlqqso )v 9lj3dl10

When electric lights are operated on low-freq.b.l rv.t8bj7es9dm 1 uagc+q uency ac (say, 5 Hz), they flicker noticjmgl91b . +.q.esurtvbd 8 7aceably. Why?

Driven by ac power, the same electrons pass back and forth thrdt) roeyh q26jkmiuw;tq8+z 6 g; p;)xough your reading lamp over and over again. Explain why the light stays lit instead of going out a8 rto)6+d;ze 6 2uqhwy;gimptjq x ;)kfter the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. Immezn/wtd iz;mak, * b6ejr43p,idiately after the toaster is turned on, is the at3dr 6 ,m,zij k/n;zw*4bepicurrent $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistorzzfzm46.w cnj4q mpqr92rc.im- c* s,? Explain.

Different lamps might have batteries connected in either of the two arr bzclpu0dl 3i110bu .)rcgjl3angements c)3 b0b 13d ilul10.lurzjpgcshown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How mqns3ck u0 n,w5c37 1snav 7vsmany electrons are flowing past any point in the wqk sv s307v3wca7u1,nsnc5mnire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a curu: 3be h bn:r,/7vraiqrent of 6.7 A for 5.0 h. How much c eahb:n3:vui7/rr, q bharge passes through the battery?    $ \times10^{ 5}\;C$

  What is the current in amper zn )jpyf;4uhvd (*cz3es 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 /z1pn8pp9z y sV produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current through 4 uqxa iix d+jp(cb5qu9p 84c*a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into alb9ehy-z2caax) u/ de5dajmge 7b.+. 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 dm06r l b,((zt k+znecdryer has 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 to a bulb whose res2ff0 r.: tkuyizp/g- qistance 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.3s-4jp)jgi vor*oa* cqroc /. 18–34). The linc*v/i .43jo)aoqocpjrr sg* -e 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 drawsym2mg5l ; qz2a 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 res2a4pyk ps 6s5cistor.
(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 tungstf bq*4e6h*e+n d4b5odakkyk0s/p wm/ en wire whose resistance 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? 6 htg v4:csfj 5m8gkyro+av:gs1dv*7   $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wi9).4 6emksfq-v c ybpfre 2.0 mm in diameter, to 20.0 m of coppefe64-ymv9pbq fk s.)c r wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tungsten wirevf4zt 5nu791lq/ v xsl+b)wvt of the same 4+ ux btqfw)nz5l7v9tlv/ s v1length? Give numerical details.    mm

  A certain copper wire has a resi7 y+ r;rq-pqt 3cgpox n/xfn3zst4 j+7stance of $10.0\Omega$ At what point along its length must the wire be cut so that the resistance of one piece is 4.0 times the resistance of the other? What is the resistance of each piece?
$R_{short }$   $\Omega$
$R_{long }$    $\Omega$

  How much would you have to raise the temperature of a copper wire (origin,2;2 wor2lp1wljitdz,j o9 qj ally atr p2wi; lq2jj9zdj o1 low,2t, $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature cope 03, dnlw1:6acp gzyzj( a+daper will have the same resistivity as tungsten doesdga3 zn1,cza + 0:(ly6ejapwd at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resisu, wcp7 v1:vpcre5;zqtance 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 aq n7bb fa3sqs0jf 1h blq9*:(nlong a 26-m length of household no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm and carries a0bfnqa:( s hf s7n3jql*bqb 91 12-A current.    V

  A rectangular solid made of carboxx1rn4eb /kkpz c0v .m2 -djy.n 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 thmvc je2d.yb/0k 4x1zxnp.- rke 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 the same resistance. If one has f1q/grro 798wjla 1cvw+7y cxtwice the length of the other, what is the ratio of the diameter of the longer wire cvxwq9/71 yjrgf+c l 7ao 8wr1to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.c slc6(g2qc8 hbwr2,c00-V power supply, and a current of 26rh2s,gw (c l cccb8q0.4212 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 wire consists of 5.0 m of copper followed by nd g2b.mp)c c.5.0 m of aluminum, both of diameter 1.0 mm. A voltagm). .cgncbp 2de 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 application5aes;*)j9arkacu do q )7 /ka,eeol xk6:d.sws, it is important that the value of a resistance not change with temperature. For e;o. aeq)ksde7w) kaca,a x*9rls o/djuke56: xample, 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 to pgp3u7iy hxqgt5+ 61b vroduce 3.3 kW of heat when connected to a 240-V source. What must be tq5ty b7 3g16x ipvhgu+he resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player t0te gtu 0/pj9uhat draws a maxt/e9 t0j0puu gimum of 320 mA of current?    W

  What is the maximum voltage that can be appl ++bfkx(i lwy 67eu4z;aremva z-/k-died 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 li7f+qvg: zvw+6l2dc;b9ak /l g: cll jvghtbulb connected to its proper source volt:7vd+;l/vagvwlzq: j6bcfc g9l+ lk2 age 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 isc0 ykd i)f3t:z 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:6bp a 8oy-+klh 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, 1jue tg+ br70vi*ry mv6*wl1zm5b8 y g6udg/gwhere 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), how bright will it be relative to 75-W 120-V bulbs? [Hint: assume roughly that bri0irt7 *ug mb b8du5m/g w1rjvev*l+y6 61zgygghtness is proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W t2jfk)4g urb ,y3sq e(7rt;eug oaster use in the morning if it is in operation for a kf);3ye7jbe u4r qr,( gstg2utotal 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 ligh:c owwk;r 1lpr k9fx+;- b0emzt on day and night for l-xkof9 mkz:wr r+ wb;c;1e0p a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell :eg5u sjw:i)w 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when turned oneg u)w5sw:i:j .
(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 enen4cg* 3g r-tq2uj p,ewrgy stored in a 12-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. kv8udtu4 00mw18–20, can be used without b uuwv8t m04kd0lowing a 15-A fuse?    bulbs

  An extension cord made of two wires of diame i,mj1:n1hjpmy m0xk vqb-;*fter 0.129 cm (no. 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 linejm-iqf1, y:m;kx bp 1v*mj nh0. How much power is dissipated in the cord?    W

  A power station delivers 620 kW of power at 12,000 V to a fact)ukg18o k ily4/2f(en)eiaud ory through wires with t l1eiiyukku)ao2( n4d8feg)/otal resistance $3.0\Omega$ 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 lin0mg.wcry r9v x/,fxe:e is 17.5 A. At what rate must cooling water pass over the coils if the water temperature is to rise by gw.:,f/0vrex xmr9 c yno more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a 5rb( 2aq.kz jhcar to heat a cup of water for coffee or tea. If 2b.jqk rh5z(a the heater 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 currepm h.2iw1je ) pn)md1mbr* ;xdnt in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, is across g4gg5;d6ao exp 4j), yxxg-wba $330-\Omega$ resistor. What are the rms and peak currents in the resistor?
$I_{peak}$$\approx$    A(retain two decimal places)
$I_{rms}$ =    A

  Estimate the resistan7:iczw3nq guz:s h9l*8uo,rl .j, iu gce of the $120-V_{rms}$ circuits in your house as seen by the power company, when
(a) everything electrical is unplugged,
(b) there is a lone 75-W lightbulb burning.    $\Omega$

  The peak value of an alternating current in a 15/2ubtuta3+n)x jh s:m00-W device is 5.4 A. What is the rms voltage xjt +:as n/3u2)thbm uacross it?    V (Round to the nearest integer)

  An 1800-W arc welder i gmq*n:9y. j-aivn mch, j)ax.s 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 insu:rra ( aun,qn;:sv d/tantaneous power dissipated by a 3.0-hp pump connected /us( d:unra nrq va;:,to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected tlvv ;sv, -vya+2vtx 2go 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 curren* lseuj k.-7n(ctgf.qt of $2.3\mu A$. What is the electron drift speed in the wire?    $ \times10^{-10 }\;m/s$

  A 5.80-m length of 2.0p o 8 udmlh)-29m zciop;i+y8t-mm-diameter wire carries a 750-mA current when 22.0 mV is applied to its ends. If the drift spe8doh mty2i)p-z +8lupo9c;i med 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 Ea.m(pf(6 lrkty 0u+dn2q ycs .brth’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 Ea5-c0u;qcj7t,i (wwih;aqs zqrth’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 field across an axon mejh jf) l 38zly;g3knk*kcxj19mbrane $ 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 potentc.*fnfunttwo;t.)m hp)tzu8c d1y2 :ial is detected ;o*:htttp)u8)n c.zft cw1y nm.d2 ufat 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 measurements needed instead of only one?)    m/s

  Estimate how much energyqvjqcs/1) qr vjc0d9: is required to transmit one action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is vj9: vqs1d/ q 0jcrqc)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 potenti)(f rh eh-zfpmysf bk(v /:/5s.u m2awal, $Na^+$ 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/ go0op1idcn iliq ;0-h1dh dw3;ulq9 1.00 ampere-hour?    C

  What is the average current drawn by a 1.03,.v 08c4f9*ttmkx kxonqtiq -hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leavesso (te. ypu2d9 a car with the lights on. If each of the two headlights uses 40 W and each of the two taillights 6 W, fo9u(2dtoy. pe sr a total of 92 W, how long will a fresh 12-V battery last if it is rated at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of a 110-V, 1500-W heater ig+a)1lkhre 9f s 5.4 m long. If it is made of iron, what must its diameter be)e1gfk+ra 9 hl?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of thckz3 xlqoucd2c247c, e resistance R; that i c24o,cqz73cl2 dx ckus, $G\,=\,1/R$. 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 uv:nwqn x0/u-9 ,-) ztty jfcxosing high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a two-wirejt/qywz uf-:t-,xc)nv9o0 nx 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 ui5rnhh 7+ va(n,/nen vt1,tmmses 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 lengths are wrapped together sides7j 2if d:ov0hv5rhd l)l1q8v by side to make a thicker d 7)8vl12r os5:h jv l0vhdiqfwire. How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 117 l 4c.cjr2f9egn+a oy9V.
(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 not become so hot as to a+ +pk3 f1hxdastart a fire. What diameter must a copper wire be if it is to carry a maximum current of 35 A and produce no more thanaxf+3 h 1a+pdk 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by the equation (gxvf wt 14aiz 9(/xui$I\,=\,1.80sin210t$, 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 delu4t 5l;ees, .zp5a milx8 b3lsivers 950 W of energy per second to the i puz. 3l 4blltm,xsise8e5;5a nterior. 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 the6:gxniq)g2cy u2pv 7lj: * clf same material. One conductor is twice as long and twice the diameter of the second. What is the ratio of the power transformed in the first relj lvgf6iq7y:)cg lu*:22xpc native to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heazsmav -v(u4my..n z h*t a room of volume $62\,m^3$ Air is brought into the room at 5$^{\circ}\,C$ and is completely replaced twice per hour. Heat loss through the walls amounts to approximately $850 kcal/h$. If the air is to be maintained at 20$^{\circ}\,C$, what minimum wattage must the heater have? (The specific heat of air is about $0.17 kcal/kg\cdot C?$)    W

  A 2200-W oven is hooked to a 240-V :m ayyf d( x4jtk/e+cg04: 3ox;p dttisource.
(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 batteriesq)sj-+k6 9lro nvm ys3 as its source of enerrnsm s ovlk+qj6-)9y3gy. Its mass is 1560 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 lightbulb *+wev m5kmjq+ 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 (Illinois) is designed to carry an 1ix8y (l tuu/5iec8rz)03ag 7e fpy;p f1-mA beam of protons traveling at very nearlyiguriefpl (f3 t7pce x5;a y)/08zy8u 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 connecting c65kt9qw vubn6a:g ) az9u9dc iord is copper wire with a diameter of 1.628 5az96t d9 wc:bi 9 uu6)qvankgmm.
(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 el4pnyh09h erjz(at3fj iy/3, fement is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. Wh9yj4rjniy /ea(03,t 3p hzffhat is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system r:5a ly*3 xblhvoltage 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 var3l bx: haryl*5y 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 andl-g1 tmy)qplhc z(+ 7f 40 W for household applications. Lightbulb B is rated atg h1 c7pz (lf)mlq+-ty 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 use1nr;trd ad s6)d to connect a set of appliances at 120 V, which draw 2250 W of powerntradd s16); r 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 diamet22tk4b4yp rbcm2-0xkqmnyu7er of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the resistance of 10.tnkybm mr q y-74x2p4uc2k2b0 0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its length doubles, o,3it.3uzdc9 n+ c xywby what factor does the power dissipated in the wire change, assuming it remains hooked up to the same voltage sonu 9td yx3o+w3izc.c,urce?

  A tungsten filament used in a flashlight bulb operates at 0.20 A and 3.2 V. Ifl4d 0ivjud5 2w no)pw) it vup 5n02w)ldj4odi)ws resistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$