What quantity is measured by a battery ratx ak-)6jrx9;k7 ffhkming given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow away from the nejs 0k01wcrom),ai;wj gative terminal in the circuit. But within the cell, electrons flow to the negative terminal. )o cam0 k ri;wsj1w0j,Explain.

When a flashlight is operated, what is being used up: battery current, eg+x5a5 jb b7bbattery voltage, battery energy, battery power, or battery resistance? Expl bj7e5b x+gab5ain.

One terminal of a car battery is said to be connected o2ig,*m-p ) g5cujd ycup c+x:to “ground.” Since it is not really connected to the ground, what is meant by this expresgmpgpy* 2 cc:,)od ux+ui-5cj sion?

When you turn on a water faucet, the water usually fj:h vbsfcs9,f +8gn6flows immediately. You don’t have to wait for wj+ s bf,fgf:8nv h96csater to flow from the faucet valve to the spout. Why not? Is the same thing true when you connect a wire to the terminals of a battery?

Can a copper wire and an alu6v-5w 6pkttbu minum wire of the same length have the same resistank tp-vub6tw 65ce? Explain.

If the resistance of a small immersion heater (to heat water ftn:y*zfr/ n8 /*8wpjnil y(ka or tea or soup, Fig. 18–32) was increased, would it speed up or slow down the heating pn n:l8/a*zpkyfnt(j /*iyw 8 rrocess? Explain.

If a rectangular solid made of carbon has sidef3,nkf d ty6x6s of lengths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) t,xk6y3f t6fn dhe 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 lightb yb2c0t pb5)cujnlj ,-s9miw+o)* hzc ulb burns out?

Explain why lightbulbs almost always burnmvhxg fploso0isclc m1(m+8-ev/ 2,/ out just as they are turned on and not after them mse(x +chvo 1vp2 /8smolc,-ilf/g0y have been on for some time.

Which draws more current, a 10- /s(uiqd,f zav;zter :akh2;0-W lightbulb or a 75-W bulb? Which has the higher tz,qh2asz ak(fi;-;:v rd/eu resistance?

Electric power is transfoaauk5 grnf3o (32m(serred over large distances at very high voltages. Explain how the high voltage reduces power losses in 3a3k 5ausg(mo2f(rnothe transmission lines.

A 15-A fuse blows repeatedly. Why is it danmv0c-d h z 4./mdy/f2wcdnwln - vm8c;gerous to replace this fuse with a 25-cn2 mcv4.m/ dl0/cmvh;zwdf -w-dy 8nA fuse?

When electric lights are operated on low-frequency ac x*p2).tktlg sw a 2*lx(say, 5 Hz), they flicker noticeably. Why2s gxw .lt pkt*)lax*2?

Driven by ac power, the same electrons pass back and forth tho z,y jq93f +lh y;0jusq70zxirough your reading lamp over and over again. Explain why the light st;j3fy0ylqo, h 0qs z7iuxj+z 9ays lit instead of going out after the first pass of electrons.

The heating element in a toaster is6qjz2 rh5o p0vbo/0oy made of Nichrome wire. Immediately after the toaster ir0o6z/pj05 2v qoboyhs turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Ex 6+kmo- sw : h2zs7vcrs1bia7pplain.

Different lamps might have batteries connected in either of the two arrangemnlz um te94z*(entsutzlm9e4n* (z shown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many electrons are flowinbs vhifps;p8u5167 i bg past any poin8 1 b7bii 65s;puhvfspt in the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery usiqd 0a 6me/i:nqvp:7ewng a current of 6.7 A for 5.0 h. How much charge passes throug wqd:7i/a0 eemv:n6pq h the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes ggcy9---rcfud6zcmrb ; + 96nh)bomkif $1200\,Na^+$ 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 1c./xtt-y nz6r( rk,dag ee-dif 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of h7 q:7v6q3qaxdtbgmp2 1y c/ocurrent through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into aiamo7i3g.rq , 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 yy,vc g5ntb7 q+n,r d2has 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 bujfc)pr6pw ,w-l- yb2h lb 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 -9offq7ffoqy-. y v ,uuhr7o*transmission line carrying 2800 A (Fig. 18–34). The line has yf9uh yo, qq orff.v7fu7o-*- $2.5\times10^{ -5}\;\Omega$ 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 6.50gvur ja3,xpw/ vi7u32 ufg l2* 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 pf770qo 2;ny61x qzd* pdqklgresistor.
(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 orb+arodq28* el t2gm9f tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length 2t+jp(qcr v+ht,*la she 0 xy8of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of a+ ;kl3.pka3ssb/oz 3qw :ekt3p6pxg nluminum wire 2.0 mm in diameter, to 20.0 m of copper wire ;p k6k stpq g3k3oz3wpne+al.3 xb/s:2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance a1khbo/e m q/x4ab chk/0*ff z(s a tungsten wire of the same length? Give numeck0/z14e x */obmf (bf/hha kqrical details.    mm

  A certain copper wire has9h mctzna0 5)7h s acapg6)o1v a 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 ajy-9: in+fvsxj ;3mr6+w eox n copper wire (originally at +neyrvn6x+;x fw:j 39ijsm -o$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivity as 21 7got/b hvx:kv51, marrwmd tungsten does amrh2v: x/kd t b71aow m5r1g,vt $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of: +d;-qix: tipisfe6/f-qe ic about $12\Omega$ when cold ($20^{\circ}\,C$) and $140\Omega$ when on (hot). Estimate the temperature of the filament when hot assuming an average temperature coefficient of resistivity $\alpha\,=\,0.0060(C?)^{-1}$ .    $^{\circ}\,C$

  Compute the voltage drop along a 26-m lengtg3z 6fjameqo* xvz:/.h of household no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm and carrieaxq*:efz .vg3om6 /jz s a 12-A current.    V

  A rectangular solid made o frr+74hpe3 sq; +vjmrf carbon has sides of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine; 3fr+errp +jhsvq 4m7 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 of thi ,t :d 1 xuxnte1pp1w3cu3n-ee other, what is the ratio of the diameter of the longer wire to the diameter of the tp 1dnuunwt:p1 c-1x,ee i x33shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected t3 :y /jx hjo lefq8wlf3t6w94wo a precision 10.00-V power supply, and a current of 0.4212 A is prec j/9tq43whj:wy e wxl6f l8o3fisely 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 5.0 m8 87w yxyv(eu:h6 gqvz of aluminum, both of diameter h(:7 zx wu6vy g8veyq81.0 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 important that the value of a resistance b4;kxv qwma7bg+ li7;not change with temperature. For example, suppose ygk q4w+ 7vmlia;b;7xb ou 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 produce 3.3 kW o7: jst71ed8qm:t-tscui p6x pf heat when connected to a 240-V source. What must be the resistance of the elxt1d8qj6m-7s:et p i sct7u p:ement?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD plaj qbyngqyn3pbe5kk,i.)+x;0 ap6tw (yer that draws a maximum of 320 nnq0 y()e6ygk+i pjb, 3 k;twaxb5pq. mA of current?    W

  What is the maximum volt5 eehv;qjvi*bna86d)wg f . o:age that can be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the re4onp nly62gh7ui l0muw w1dy/f oa,9.sistance of, and current through, a 75-W lightbulb connected to its proper source voltage of 120 V. myhano d9 u/n,74ywu0f.o6 l2gw1 p il
   $\Omega$
   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. Ca4cri1 ayf haynsm-7 +3lculate
(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 aq bm+p sm xdfm/,.bk55 7so)lfnd 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 electricity is delivered ,dctqj 24,mh jp ssw27ihv:p 9to homes at 240 V. If you use the lightbulb in the shpwi mt2v9 j 2,j:q7h4c,spdUnited States at 120 V (assume its resistance does not change), how bright will it be relative to 75-W 120-V bulbs? [Hint: assume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use in the morning if hyq l64)wc :c;trfj (git is in operation for a total of 15 min? At a c wf c4ljr (c)gqt:6;hyost 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 leav9 cn9vo u8cqhb(-p dm3e a 25-W porch light on day and night for a v8dmb o9c c(q3-hup 9nyear? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batte(0 s1iqpy+s59y4n iaqrer7ab ries connected in series as in Fig. 184qr n ay 9(bieys5a70s1+ rqip–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 o6*a;5tr cfy;is,g*f a vb3oj in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbsa,m, amm.css+*h sxm(, connected to 120 V as in Fig. 18–20, can be used without bls,m,ms sa (+mm.*cxhaowing a 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 c0h lnbto4p5g, m (no. 16 copper wire) and of length 2.7 m (9 ftg pob,h04t5ln) 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 lt1:3 m, j sq:bfrxuuwgdc24 ,qcj n+8l:udq 0through wires with 4 dlfumq1l s bx:2:,,8+quw3ujcd:0grnqt cjtotal 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 line is 17yko7 (x( h6 -5vixmi fy;-vhfs.5 A. At what rate must cooling water pass over the coils if the water temperature is to rhih(vimx-;o-sfyk( 6 f5v7 x yise 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 wat+-x1uhg7 ups9 bpsf.ver for coffee or tea. If the heater can heat 120 mL of water from 25p7g b u1s.fhxs-+9puv $^{\circ}\,C$ 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 infe hz:i8:/my eooyoo3916f yj a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak vadmo ,)tsfnx ,v:qdg3; lue 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 of the sab4ak+ dipc zu.r7 /3$120-V_{rms}$ 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 alternara cy8 lfln4iv 9/6 wf-x)gav4ting current in a 1500-W device is 5.4 A. What is the rms vo6cr)/ll va 4vxwfg yan48if9-ltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connect-bee6. jk7g.trez 5jc ed 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 p:kr+y8 xdfrgx:(o* roump connected to a+:r o(oygr xrx kd*f:8 $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected toy:-ey b )(nqru 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 ck 76op9 anc*5c qzmbs rrwwj/.+d+e1a 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-diameter wire carries a 750-mAf0on;kjnjx3(+ 13 twd/ ljtsz current when 22.0 mV is applied to its ends. If t3xsn0 wdt3n lf;kzjj /(to+j1he drift speed is $ 1.7\times10^{-5 }\;m/s$, determine
(a) the resistance R of the wire, $\approx$    $\Omega$(retain three decimal places)
(b) the resistivity $\rho$.    $ \times10^{-8 }\;\Omega\cdot m$
(c) the number n of free electrons per unit volume.    $ \times10^{28 }\;e^-/m^3$

  At a point high in the Earth’s atmosphere,i;.fd zp lova0xl1)2v $He^{2+}$ 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 thrj h-oq8a ,pg5f-w t5se Earth’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 hxk:8hmu)t9jrx1 ihk8 , 8 klpan 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 potx: j h(n4nl 9 mt;/ifie aw.qaox1lnc;9s36kkential 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 a3;4kafcjnhl(i xix6; ws: / n 9otq9k1ne. mlaxon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much energy is required ta o1)94cpbo uf(d9s-b7kwn lio 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 rep)c1o b99n-7u4(wko blds aifquired for $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action potentialk1 p2ckm:cdq 5, $Na^+$ 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 1.00o ;9;o.pllebpkn, cd 3jtgh 0s.vs 9k0 ampere-hour?    C

  What is the average current drawn by a 1.0-hp 120-V motorw(e.u0w;wzgu7.w cds ? $(1 hp\,=\,746\,W.)$    A

  A person accidentallyvh gdij+ /hu(3n7xa s*5vzd u:,rins- leaves a car with the lights 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 a fresh 12-V battery 3g+ njuv:ax/s5,r(-u dsi*nzv7dhi h 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 et ++ror 1-1fhq uqjiv-7j (ip /do:ixis made of iron, what must its diameter 1x7 dov+qjp/ioi- 1jheqr r:(+f -u tibe?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciproghn i.mj 2t(ui17yi+tcal of the resistance R; t (ni+t2t igui.y7jhm1 hat is, $G\,=\,1/R$. 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 require f6zyz- 2-hm8ew b2ojnhp4q:bs about 10 MW of power. 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-diameter copper wire, estimate the cost of the energy lost to heat perqwzf8nz 4ho -bjb :2m 6ey-p2h 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-kWwp,lz ,8 kx; uc*qm*j*pc5uis 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 8 vu+hjqr uha3k,ufoa 0 .+z,stwo lengths are wrapped together side by side to make a thicker wire. How does the resistance of this new combination compare to the resistank u+a8+o vu ahqj0fhuzr.s,,3 ce of the original wire?

  A 1200-W hair dryer is designsn9 mx ck9 -tntq:4.rged 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 not become so hot kwngc :e ,. /cp5y3mshas to start a fire. What diameter must a copper wire be if it is to carr cmek 3:,/sh.5gcp nwyy a maximum current of 35 A and produce no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by thgo pe3c*o/sqoexn15f1i8j: r e 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 aa.9yy-kl7 zxd*edzv*t 65% efficiency delivers 950 W of energy per second to th.-k*9v y*zyad zed7lxe 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 sa6ce i,xca,1 o/n(ov zame material. One conductor is twice as long and twice the diameter of the second.xc ocie(/ a,o1z6 nv,a What is the ratio of the power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is j,+s;ciqihni n*e rh900q to6s9zkb:used to 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 240:56vz o gn783eltfjau -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 oqdhchsha pab*m7 ) 041 ikv5)vf energy. Its mass is 1560 kg and it is57hk )a hbs q1)ah*cpv40mid v 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 has a resiscrbp1v, b;ya -tance 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 acceleraty:.7l a/rp6nxrh b.lq or at Fermilab (Illinois) is designed to carry an 11-mA beam of protons traveling a/ ar x:q7 l6plb.yrnh.t 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 .+i9e,fwadz+ a 1tsgh connecting cord is copper wire with a diameter of 1.628,ds+h1 +aie gtfw.9az 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 10zay .rk6 u*xx b5gu5j20 V. The heating element is a coil of Nichrome wire. When uncoiled, the wi6gubayk5 xx5 z ujr.0*re has a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from z q/83+8iamarwa/ p5 n*vj gkqabout 12 V when the car is off to about 13.8 V when the car is on and5awa38/vqa+mz j rp*ngqk/ i8 the charging system is in operation, a difference of 15%. By what percentage does the power delivered to the headlights vary as the voltage changes from 12 V to 13.8 V? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for household a*al 8rwuq0w ,bpplications. Lightbulb B is rated at 12 V and 40 W for automaww,q0 ub*8r lotive 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 yr:u8i,jshko g)s;; zzk n*5zto connect a set of appliances at 120 V, which draw 2250 W of power totazks*g i ;o,z);k 8sujzhr5y :nl.
(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:fl-nycndv (,kx uf ;( of 5.00 xd uf;(-lkcn: f(yvn,cm (Fig. 18–37). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistantd0frm*sjp s tvr::- 4qc-2 lsce R is stretched uniformly so that its length doubles, by what factor does the power dissipate: mrv*lqdjpf2r-ct s-s st0:4d in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament usa 4t5f9 drt;,)/jom m-fvrc vxed in a flashlight bulb operates at 0.20 A and 3.2 V. If it cmr)dtv4x 5mfjt oarv f-,9;/s resistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$