What quantity is measured by a battery rating given in ampere-hours 4e- blzye*de t7e -u3 1aze/kg$(A\cdot H)$ ?

When an electric cell is connvyq6vqy)(ptg i l,pv3wj()fp /:zl g6 ected to a circuit, electrons flow away from the negative terminal in the circuit. But within the cell, electrons flow to the negative terminzg v y:i(q ,y3lpp6 vp(fl/ qt)v6g)jwal. Explain.

When a flashlight is operated, what is being user.w; yvp)in7rd up: battery current, battery voltage, battery energy, battery powp yr7i ).nvw;rer, or battery resistance? Explain.

One terminal of a car batt-rp2x z:) rk,17bbffjkhcoe v0r2,jh ery is said to be connected to “ground.” Since it is not really connected to the grou7hb,:fo 2rkxjk rp2b-e)jvz,1c0 hr f nd, what is meant by this expression?

When you turn on a water faucet, the water usually flows immedeomk;+lts1gw8 5ri8oiately. You don’t have to wait for water to flow from the faucet valve to the spout. Why not? Is the same t+rwes5 tk go8;imlo81hing true when you connect a wire to the terminals of a battery?

Can a copper wire and an aluminum wire of the same length have the same resistawpdmf;k9*an(g2 e r-q nce? Explaing2q-a ep;d(9w mkn* fr.

If the resistance of a small immersion heater (to he z/ k o k*h4a1q5vl/ne4ff4saxat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the heating process? Expll askxa e/z44*/5fvn 4hq f1okain.

If a rectangular solid made of carbon has sides of lengths a, 2as vm: yzq/n9e6, and 3a, how would you connect the wires from a batt:smv y e/69zqnery so 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 buui +(,)tfdqhurns out?

Explain why lightbulbs almost always burn out just as : ebpjsr(7z n.they are turned on and not after they have been on for some time.:jpn7 z(brse.

Which draws more current, a 100-W l8b.wnz(ape)a rz1 r yy,(j 5cwightbulb or a 75-W bulb? Which has the higher resistancr 8.5yzp zw naj(arc1w)( ye,be?

Electric power is transferred over large distances at very high voltages. E -ssmfm ur *jme,x d:6j*m,6ywxplain how the high voltage reduces power losses sjm d e**6j m:ymx,,uwr6-sm fin the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace thijeg3 .py art*2s fuse with a 25-A fuse 3. yrgja2p*te?

When electric lights are13ygm 5 swd2zz operated on low-frequency ac (say, 5 Hz), they flicker noticeably. zs 13m5dgz2 wyWhy?

Driven by ac power, te.si,cgh* mgl1a(uva : 5*ep z whu4m2he 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 of electr2 1l h4 e,aiaghe swz*gmu5u(.pc *vm:ons.

The heating element in a to iuu7m (uqnv; um ;/:z3r7rp:a sq1ypwaster is made of Nichrome wire. Immediately after the toaster is turned on, is mrq:vi;p qw7 :y3pnuu u/71zu;ma r (sthe current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a res-9hlesafz j2 t5vhy4 mw5 3j a4f.6kkxistor? Explain.

Different lamps might have batteries connected in** ;xs8 fws:i-1bdgmiyhxi7 3 smw-dw either of the two arrangements shown in xsm dify *x7-:-ws igbw dm8si;w*31 h
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A fl9mc) 3pfytf0mp4 jcyhk oivvl)4+7 p0ows in a wire. How many electrons are flowing past any point in the witpjp4iymkho m+ v 3cf4y v)pf07l0 9c)re per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current offwf:j*ch qb (mxu/ j+0xfm(-a 6.7 A for 5.0 h. How much charge passes throf x(jmm+hf /(awcqfxb u0-:j*ugh the battery?    $ \times10^{ 5}\;C$

  What is the current in ampg wv8 vi.kx0v gsn-c oc7k+5 .3qtf6ejeres 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 tosjc* ,( h +s*bz96n9ki8eat zlsd 3kroaster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0d84tcbf qp )h2.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when.jgpuf8j32007f nrdyyw:)gic f vw;x 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 hazwj6h4,z,g c:o ,sjrd s 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 resistance is .:/tqqcci3 mguc n; .c.*sscq$1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dlr-le khprm0;04 ,v dwc electric transmission line carrying 2800 A (Fig. 18–34). Th d v0r4,rwekl lh0;pm-e 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 at 240 ot e0 k-s5mgz* t or2up4/so,aV.
(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 curryo.fh stk ot14:k*tz*ent 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 tungl+w)fzqv4sp c-o2 en6sten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1lrt/j x +p q8t-i9qd:z.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance0b.3zqwja l:wonm 5hr wx0zky789- lc of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in diameter0 c9wzb wlmhal7.03r z xyj8onq 5w-:k.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tu1t+sw cecx 8z8ngsten wire of thewtszc 1cx8 e8+ same length? Give numerical details.    mm

  A certain copper wire has a resistancn act9pz72akgvh )g 1.e 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 rais- vh,)i-(/k zgmo ieqhe the temperature of a copper wire (originally at omqvigke,-z (ihh/- ) $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivity as tungsten d a6 d3snh:wzn+ ;bd4jxoes ats ; 4jdbwzdha6+n3: xn $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of ab3t,p cmuse k8 po ;fp.25juo0aout $12\Omega$ 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 lengtowux.1dxydhd m 588t2h of household no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm and carrdo w82h15xdx8tu ydm. ies a 12-A current.    V

  A rectangular solid made of carboey/rr*1ob f 7tn 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). Determier 1*t fbr/7yone the resistance for current that passes through the solid in
(a) the x direction,    $ \times10^{ -4}\;\Omega$
(b) the y direction,    $ \times10^{ -3}\;\Omega$
(c) the z direction. Assume the resistivity is $\rho\,=\,3.0\times10^{ -5}\;\Omega\cdot m$.
   $ \times10^{ -3}\;\Omega$

  Two aluminum wires have the same resistance. If one has twice the length ofc:4fd m g8r6-bj :bsvz8 hmoh0 the other, what is the ratioc:hrm4g6fbj o:0b8-s mvd8zh of the diameter of the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is con4 .uwiu5 bmh/2sbvv*p(vid 8 nnected to a precision 10.00-V power supply, and a current of 0.4212 A is precisely meaimvub.ipw*s/nu 2( 8 vvhbd5 4sured 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 wglmp:/k )fz,7qxk 2m5.0 m of copper followed by 5.0 m of aluminum, both of diag)l p,kk7/qfm: 2mzwxmeter 1.0 mm. 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 importu 1ml i5ofzxo-,.r9dbant that the value of a resistance not change with5uom1.oixlbd 9z r-f, 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 oveng* i.i9 bzz li3qaw7g/ is designed to produce 3.3 kW of heat when connectedag9/*z3qi zi.bgi w7 l to a 240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power co)il1xf9 t55zgsh pp(ensumption of a 3.0-V portable CD player that draws a maximum of 3lx9g(ez5 ps 5pfih )1t20 mA of current?    W

  What is the maximum voltage that can jlvn3/u3u- g owa 2;zebe applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistani oouvyv8y) xtd9xo yn7krl-:tb9-* +ce of, and current through, a 75-W lightbulb connected to its proper snxo-9* ltxvuv7y ) 9-8tdo yiyk ro+:bource 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. Calcul f6wcx8n6 2a-jt e3mc .qp5ewuate
(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 settiahy3kj (js 4zckxq wsuu+vb+1h3a; 7/ngs: 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, whehw bu7-twzwjvfx*.4z hwik2 x7 g6 .blb i6g2*re 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-W6ikwbh 2 xbwx4.6-7 bvw2l gh*wziz*t f.g j7u 120-V bulbs? [Hint: assume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy does a 550*v6rguhl bv 4,lstjwd+e l(0--W toaster use in the morning if it is in operation for a total s0d l6rteuv hg(j,l4b+*l- v wof 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 da(5ahg 3kc u8nc- igrsyo0d )7gy andu 7a h8yd5c-g ngk0rs( gic3)o night for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteri (b7ql6 m0j7cqlxdf8l es connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when turned oc jqd 7760xlfbl8(lmqn.
(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, yf6gdzty **y 5$85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connected to 120 V as in :/ l*rtyq0nhv Fig. 18–20, can be used without blowing a 1 v0ln rqt:h*/y5-A fuse?    bulbs

  An extension cord made of two wirz)en8fv 4/esqk ,xxq/es of diameter 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 line. How much power is d//,ze qskxnfxq 8)4 veissipated in the cord?    W

  A power station delivers 620 kW of power at 12,000 V to a 5f9*hqk +ptb s1mu(4r cei7 lffactory through wires with total resistanc *fsck5 tui(r1l+b qp9m7 hf4ee $3.0\Omega$ 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 electromagnewnemrzsuhc ,. o:l:7,t connected to a 240-V line is 17.5 A. At what rate must cooling water pass over the coils if the water temperaturec,w.:7sh zel ou: n,mr 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 cup of water /0-6r:0ntmw ;focpa y csf l/uca3j3ifor coffee or tea. If the heater can heat 120 mL of waterw:fn6ofa3l cs j r-0 ;mpta /y/icu30c 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 j,siy*w;eh6win 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 acr9b+t-p 0n unvhoss 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,j az:yb/q u4bh9rv 1c-a hbe7 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 ar(i:mnz dv feu; 5y,,i 1500-W device is 5.4 A. What is the ri,( edf ,v5ru n;yz:mims voltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder i9vk;ike vr6krd 0vq8js *q /d(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 instantaneous power dissipated by :g6xh8:/c kvu,vgdk y*ch l(d ;u6kkz a 3.0-hp pump connecte:khc6 kuv/6;kc gv:dl kuhydg*8 (z,xd to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connectednzr /jfx*5,p s 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 ci ivu*vr +nj/:urrent 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-didcw h 6d 33 izmp(m0a-0lna/zhameter wire carries a 750-mA current when 22.0 mV is applied to its ends. If the drzh ahcd6mazmn(p/033 di -0lwift speed is $ 1.7\times10^{-5 }\;m/s$, determine
(a) the resistance R of the wire, $\approx$    $\Omega$(retain three decimal places)
(b) the resistivity $\rho$.    $ \times10^{-8 }\;\Omega\cdot m$
(c) the number n of free electrons per unit volume.    $ \times10^{28 }\;e^-/m^3$

  At a point high in the Earth’s atmospa+a sjke jic.cht-14 8here, $He^{2+}$ 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 E vm:rl0- 06ybuue6ab +0y)s;noiay r rqad+x/arth’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 a +wieur03* dbxytzkfg7oz xx/30-3 q zxon 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 potential rp zi cmtd::0+ dap-.equp,cu 3.w s/xis detected at a point 3.40 cm down the axon 0.0052 s later. When the a- p.3xi: +tpc.drucmaz:s/, 0 pwdquection 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 ener8wq -:dls8v d5vtci7 vgy is required 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 17–9]. What minimum average power is v 5cs7tdq 8viw 8-dlv:required for $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action potent:4h :+kmm nbptb+ya 0kial, $Na^+$ 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 /ihhjv8 b(i)c 1.00 ampere-hour?    C

  What is the average current). dsa0c-oe gs drawn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights4* rr/ )d5f*/t5ixfaci tlss o on. If each of the two headlights uses 40 W and each of the two taillights 6 W, for a total of 92 W, how long will)5oxif4ar rc /ts/5tsf il**d 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 is 5.4 m long. If it is mkxl,j v8t ,s3sp :ef,ovt 4.m.xt2qinade of iron, what mus4ln,,jvq,t3ox.sx kie ttf vsmp : 2.8t its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the rec cgr:b r qo; md91suopk /e.naa5-oz;(iprocal of the resistance R; that is,uoab(9m g;ecro:p kq/. n-s azrd15; o $G\,=\,1/R$. 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 powmo ) 33wdpsb a-ysg6s.4hn- mjer. Suppose that instead of using high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a two-wire line of 0.50-cm-diameompsma3w gh bd3s)6-j4 . sny-ter 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 heo61 xzbp fd9nj0ni rj 2n9;z4pkx4, tgater $3.0 h/day$ (“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 togem kqpb a 59fkd*zwip ;/qvoh(-,vup19 ther side by side to make a thicker wire. How does the resistance of this new combination compare to the resistance of-maqobp;v/p,q9k*f iw5zk1u v h(9dp the original wire?

  A 1200-W hair dryer is designed fmwlsh4/ohg. 3 6:kt blor 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 not/ l-s5w tx-ogm 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 1.8 W of heat peo s- l5-gwmt/xr meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is gi x*2 9gcnvlab8ven 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% efficwc g.:2+xp lm*hn2c hgh8ru4 tiency delivers 950 W of energy per second to the mtxr8 +p2 uhhl*c2.ng:hg c4w 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 different conductors made of the samn7ib7e1 87loj lswg 2me material. One condumis e7l2 1oblwj7gn8 7ctor 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 c( o5 6oo *e4hbpdpf,oto heat 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-Voy,d7f9orlgl9 ,l bv2 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 qkdna.l7. y d3z7jj -st:9i masource of energy. Its mass is 1560 kg and it is powered by 24 batteries, each 12 V3.z7 97 ajlmd nsqa.y :dkjit-, $95A\cdot h$. 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 resib*r,nuv krbliqu1 46*oea(pv2j/ bh 2stance 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 eg3w1cy e+ytnuu p2-8 u 4lk8qFermilab (Illinois) is designed to carry an 11-mA beam of pr upwk2 8ey yn8cegt4quu 3+l-1otons traveling at very nearly 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 connectingzs gi5z5v(ie 5 cord is copper wire with a diameter of 1.628 mv z(si55i5gzem.
(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 connectec5gyd,q3qq8 x+memuch v75 9nd to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m.cmdgncq, +9q8eqv57y3m5 xhu What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from about 12 V when theu-b-x/)zl os hkk1 6dq:mnsv-lfkr9 , 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 dhuqs-zl-/f,b91kxdov 6l-)kmn k:s relivered to the headlights vary as the voltage changes from 12 V to 13.8 V? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and m/m +hk; jy8pn40 W for household applications. Lightbulb B is rated at 12 V and 40 W for automotim myn8k/h p+;jve applications.
(a) What is the current through each bulb? $I_A$ =    A $I_B$ =    A
(b) What is the resistance of each bulb? $R_A$ =  $\Omega$ $R_B$ =  $\Omega$
(c) In one hour, how much charge passes through each bulb? $Q_A$ =    C$Q_B$ =    C
(d) In one hour, how much energy does each bulb use?    $ \times10^{5 }\;J$
(e) Which bulb requires larger diameter wires to connect its power source and the bulb?  ----待选择----Bulb BBulb A 

  Copper wire of diameter 0.259 cm is used to connect a set of appliances at ; z 4n+c23jvv s(3pvcqj.+ gkxmhm(xy 120 V, which draw 2250 W of po.cvsxhy+(kc4+; v(nvgp zj 3 2 xmqjm3wer 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 tnr sxo410bj szi2/t ,5.00 cm (Fig. 18–374bns1/oi rjt zt,02xs ). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistancemx mz6j y+*t;a/xa lqp6efi(5 R is stretched uniformly so that its length doubles, by what factor does the power dissiplea ix6xmm6 tj*z(+ a5/pfq; yated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operates at 0r4xs ij ((6.r9yfqa-pag 0ij z.20 A and 3.2 V. If its resistance at 24js0g f(qr.r z-iaa(x j69ipy0$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$