What quantity is measured by a batter h p, hl+wamg5ana5l-.co) /ldy rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a ciqln 0thd3v r6:nk,:v ircuit, electrons flow away from the negative terminal in the circuit. But within the cell, electrons flow to the negative terminal.0v:q3rth l ndinv :6,k Explain.

When a flashlight is opuogv-mz 9i ) g.07t0*obphvfw.u.riserated, what is being used up: battery current, battery voltage, battery energy-b w .i7m.v.u0opzrg )vs*i9fto0h gu, battery power, or battery resistance? Explain.

One terminal of a car battery is said to be connectfzzeu* l: d y(9f5tmgt q282sled to “ground.” Since it is not really connected to the ground, what imdztz* 28e fsy tl: u9gqf2l(5s meant by this expression?

When you turn on a water faucet, the water bdo2uty 9+0ar usually flows immediately. You don’t have to waitryu 9b 0to2a+d for water 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 aluminum wire of the same length have --4nvax52u 0auoliukthe same resistanca-4la uinuok v02 u5-xe? Explain.

If the resistance of a small immersion heater (to heat water for tea 4x. u9) sllfzj)rwodq 6j.j -yor soup, Fig. 18–32) was increased, would it speed up or slow down the heat slx6ql)oj- d9w z4 ry)jjf..uing process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, and 3a, horjr4tyv2/ vj2 w would you connect the wires from a battery so as to obtain (a) the leasjtjvr y/r42v2 t 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 o* 3vs;(euunxkx 75qf lightbulb burns out?

Explain why lightbulbs almost always burn out just as they *: nepdf zxlqw,m-lpp8,l i+*are turned on and not after they have q:ln*p,8p*wl, zpximel +-f dbeen on for some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which has the highel/vlee+ ci, h0irgd1yd5fzvk* 16 zt5r rivz*hz50 vgi+c1yf ,5t6/ ledd1 lrek esistance?

Electric power is transferred over large distances at very 0/ ,oy,lerpp)4*py:7tg n0j vgnlun ohigh voltages. Explain how the high voltage reduces power losses in the p70 nvl*uyy/,j)g4 oprn o ,p :l0genttransmission lines.

A 15-A fuse blows repeatedly0g3zny5 p yqskd-eyu70v-,ee. Why is it dangerous to replace this fuse with a 25-A vy-enseu d3 kgy00 ,z p57q-yefuse?

When electric lights are operat2cv2y9sgy*bf 6 -tffzb brq) px+4f2xed on low-frequency ac (say, 5 Hz), they flicker noticeaxq*fb2s2 y-cf2xy ffrt +pb)69v b4gzbly. Why?

Driven by ac power, the same electrons pass back and forth through your rea is,471w (5ql z:qdj um5ergcrding lamp over and ovzesgru57d mj 5ql:i(wc 1r,q4er again. Explain why the light stays lit instead of going out after the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. Immediately eh;9 l(pmjj4usn6t t26wk7 pz(fhya4rbw+z1 after the toastertb+(h ;(lzpk6s4 rj tfa 7pmew6w94hzujn2y1 is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a wr)d7qvxplt* j;rs h)b (:i 2,o+fwqkresistor? Explain.

Different lamps might hch/8 4h2 6ee- twhvjcoave batteries connected in either of the two arrangements shown6t/e8 hve -jowhc2ch 4 in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A e 6rq55aamkqct/ .ct9flows in a wire. How many electrons are flowing past any point itcq.e q5t5 aa69r/mk cn the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a c1 3jppip- w*xryw b1;murrent of 6.7 A for 5.0 h. How much charge pa-wpy rpp1j*xbi3 m;1 wsses through the battery?    $ \times10^{ 5}\;C$

  What is the current in8ay8 2j6qy6 d-ima4t p 4xv9nxg3x mem amperes if $1200\,Na^+$ ions flow across a cell membrane in $3.5\mu s$? The charge on the sodium is the same as on an electron, but positive.    $ \times10^{-11 }\;A$

  What is the resistance of a toaster if 12dsuqg l5//0. k4 nhsa(dbund4 0 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of cur vz/9fqc. o y:q5a5cstrent through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A v+d ml*fnb;r ,1rbnj: when plugged into a 120-V line.
(a) What is its resistance?    $\Omega$
(b) How much charge passes through it in 15 min? (Assume direct current.)    $ \times10^{ 3}\;C$

  An electric clothes dryer has a heating element with a resistance of 9rdss-udf8. l6l- r*jslo/uj $9.6-\Omega$.
(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 whb2w3sqytpk ab8kx * +rnz)5c *ose resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric va:+4; 8:x n9 hrpg ehnhm;ggqtransmission line carrying 2800 A (Fig. 18–34). The li repvn:+8a4g;h:n xhqg m;hg 9ne 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..f*slwwcz0bh v yv 9z9 b-o(;h50 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 l,-6n9 g zy8ht(gwvxjt1ainmd52jv) 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 resistancepm/t1nvnkf,y 2 8dx,y is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m le6 *ckvew-p9 rqngth of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of(i mf)o+4t t,jh1lsvh 14p lsh aluminum wire 2.0 mm in diameter, to 20lj ohf1 4v )sht(m,+sh1il 4tp.0 m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tungsten w mxo;*c ):omggurqew6x,,cp,) ybn);wr9 zghire of the same length?ng,rmougxgo; *,wr)m , 9we;c yhp):b)q6xc z Give numerical details.    mm

  A certain copper wire p-wr(2q cjw5c,ky*5zz o7iw bhas 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 a i.-4dgguwd(k tjl1p kd7k,/r copper wire (originally atlj/,pi kw. u-dtr(kkgg71 dd4 $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same rbl zenl*w7iog+nk5( s, 2a )xhesistivity as tungsten do+ kna5 o7)whnsx(zbgl 2el *i,es at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has 5w a pagkxd: 3:.jxlz4a resistance 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 alonh/b( kh ia(smi c13cw+g a 26-m length of household no. 14 copper wire (used in 15-A circuits). The wire has diame icm1baskh( 3(i+ch w/ter 1.628 mm and carries a 12-A current.    V

  A rectangular solid maha-(fw k/s8df de of carbon has sides of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes,kf/ s dwh8a(f- respectively (Fig. 18–35). Determine 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 resistancyhayny ;8(jrzsjyub5p- 04c+ e. If one has twice the length of the other, what is the ratu 5(ybza y-h4ypj;s80cj +ryn io 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 c9su)kfmydrq w hkh//-:;e.y uvzm-6gonnected to a precision 10.00-V power supply, and a current of 0u6g.s;ehy9z-/mkfy:-) k mwrq vuhd/ .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 .4:9 qbtshknbconsists of 5.0 m of copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage diff . t9n:bkhbq4serence 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 res51) iolh5iykldmxl; 7istance not change with dk lymio5x )h1li 57l;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 oven is designe0mhgsw )k53,.p0 6z iv/gt ccjprqn-td to produce 3.3 kW of heat when connected to a 240-V source. What must be the resistance tp 05.sq-vjci wm k03tgcg,p /zh )6nrof the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V p8 u yi2.fx*oshortable CD player that draws a2 8 *oxiufsh.y maximum of 320 mA of current?    W

  What is the maximum voltagchr nlhw9s, d008wa;h e 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 cog76wa v 3c 2s5jmbh 5ykp2hw5v1wtm(gnnected to its proper so1kj5h 5 t2a3hwv mcw(g6pbv27ygmw s5 urce voltage of 120 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heater isjd/:v3ku:-in x9rq s eo pz9i/ 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 hi s:v:bwv)oq/ as two settings: 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 lightbul(i; lp19uyj,fu+ fuwy x3(tkkb in Europe, where 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 brightness is proportional to power consumed.ufpu;3yjt+k 9lw x1fk (,yiu(]    as bright

  How many kWh of energy does a 550-W toaster use in the 4(dayhr0th6x morning if it is in operation for a thtd04y(6a hxr otal 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, w)) oo-t0c sdxyhat does it cost to leave a 25-W porch light on day and night for a yearto0- xsd)yc o)? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected in qut- u)/ o9zitseries as in Fig. 18–4tto q z-9u/u)ib (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 ends 6nr 7b53pbm)ba y9hergy 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 tc c l-ti0 f kwun9o7kk**ht/,do 120 V as in Fig. 18–20, can be used without blowing a 15-Ahdt*ki*,-c7lk ok /f wnutc 09 fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 copper wire -tahb 4+4bbl,se*yjt5qan58it. dr1 b:zjkf) and of length 2.7 m (9 ft) is connec5f:anb,e8 tj qb5d4k tsl+bjriy4hb1 -a z*.tted 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 620nce uo;xia,b2 :x-p9e kW of power at 12,000 V to a factory through wires with total resistanceei9;2ox:b,ucap ne x- $3.0\Omega$ 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 electromagne5h3ogn7gh9eaxo2;j r t connected to a 240-V line is 17.5 A. At what rate must cooling water pass over the coils if the water temjrn2ahhog 539ex 7g ;operature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to wo)3de . aj)b)vaa7qeheat a cup of water for coffee or tea. If the heater can hee3v)do a.ebwq7)aj)a at 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 in a w6 v ++.xf3dc6qe,nuy pfz+cy $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 4nu xj0tt0j+u5 3 hzsn 6hyjf(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 t6 h2 cpsq259q0 qdq*o ,ghgkbru)hdy+he $120-V_{rms}$ 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 cu sb/8r-gr 7wuq) ni:psfr*ze9 rrent in a 1500-W device is 5.4 A. What is the rms voltage across it? *9/ f)i rqu8s:w7ezbns rgr-p   V (Round to the nearest integer)

  An 1800-W arc welder is coh0 s6p .-2 vwakg6exqdnnected 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. p 7bkj)(*vrhc8iu b8s0-hp pump connected to ar(887k uh v*bisb )pjc $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected tojc xs)qm:7t/0i9 jbey 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 currcd)i defmp f.4+*8qk: nao5krent 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 22.0 mVhjayim5nbo7e)5 i7 ber.qh f9;qi(w9 is app7qh7;if o ii9haey.b5(em5n)j9rwq blied to its ends. If the 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’f jzhx/3/m jrz3 cp8sy0 l.mk0s 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 Exl q+qp x7:.m;y)oq4tlev my3 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 ac l+,bdb. 7/ nq1sjogk:s2rb xcross 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 potential is dete/5zj. buhrx, p1yzz. hcted at a poin rhp,zz uzb5.1h/jxy.t 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 energy is required to transmit onwp82 walbu 3p uo+y;.xe action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is ay w+p.382bu;wolx p uequivalent 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 pott/t; j n8duxz-ot11plential, $Na^+$ 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.t 93c:henn yov9--vyh00 ampere-hour?    C

  What is the average current dr) wch+7n/f,x6 acyw rtawn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves ub*on8t:t 468q secxghhke;.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 last if e:q;*tcxesn6 uho 8bk.h4g8tit is rated at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of a 110-V, 1io0 40 yrva4yv500-W heater is 5.4 m long. If it is made of iron, what must its diameter be? vvoiy4 0y4ra0    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal *(s ;f ,tkozn;7 xc+*.rtxx pq6dgj mtof the resistance R; that is,*jzpn ;sm6fgc * xd7t.oxr;x, tqk+t( $G\,=\,1/R$. 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 MWwvn *jifztm4:*d b1k-dybw-ld j( - t9 of power. Suppose that instead of using high-voltage lines to supply the 9v:k dlt-n*d- mjjfwzbt4w y- 1d b(*ipower, the power is delivered at 120 V. Assuming a two-wire line of 0.50-cm-diameter copper wire, estimate the cost of the energy lost to heat per hour per meter. Assume the cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular household09w, l5 xcmi00ady hic uses 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 wrappyeen296/7rh /;dpd .xj wwabced together side by side to make a thicker wire. How does the resistance of this new combination compare yre7edc h ad nwx62wp;j /9/.bto the resistance of the original wire?

  A 1200-W hair dryer is designed for 1178vhhjy s6jm6 .k(gz4hdp ob93 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 as to o f37l yso8zb;start a fire. What diameter must a copper wire be if it is to carry a maximum current of 35 A and producobz 7 fyl8;s3oe no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by the equat-44 7wq oqui;wi* xbhflv): haion $I\,=\,1.80sin210t$, 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 deliveanc9x-) , vqpow5v)wsl: jvd(ou5m :qrs 950 W of energy per second to the interior. Find -q,ax9 n5 mwosvw v)ud5(v:pol)q :jc
(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 same material. btw(mg3 bxm0:b :1uuv(n8 hov One conductor is twice as long th1 3og0b:vmxbwumb :u ( 8(vnand 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;z esnn0 ps:f/ 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 8 i,:eejcg8dw240-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 swx2 z0/yzj)4 q)icdh makes use of storage batteries as its source of energy. Its mass is 1560 kgz i/w4)s2y qh0)c jzxd 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 has a resistance o3,:, kyco)b1s julonkf $12\Omega$ 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 dep2rrmd1 jggyr- xo,-)signed to carry an 11-mA beam of protons tra p1r )o-g2rydjxrg-m ,veling 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 connecting cord is copper wirjv)we-vvu, q6i 5zcke h -0m4s c:mz;nl,usv8e witz4:;)5uivse6cm ze0vjw, vc s8k -,u vhlmq- nh 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 t1.1rf u -wk3bqda+q bwv d)90wvrn d9po 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What is the diameter of +w0bq qvu-dndwwbf rk )d1vr9pa391.the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies frq /zsd b7y+( ch7b6ohwom about 12 V when the car is off to about 13.8 V when the car is on and the charging system 6zw b7(sd+oqh hb7/cyis 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 8kry fo +d;tqs k u/u:-f+lvi(at 120 V and 40 W for household applications. Lightbulb B is rated at 12 -y+ /sdv8t( u;qkk lu+ri:o ffV 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 appk 2p:uw+z bj3xliances at 120 V, which draw 2250 W ofjz:xp+3wk u 2b 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 insiyago25ikepr : ;5ji(x de diameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the resistance of 10.0 m of this pipeoae rgi 5 xp(2;:5kjiy?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is:(d3 senp5 e5ggh v,fi stretched uniformly so that its length doubles, by what factor does t d ifp(n,vgheg5:5s e3he power dissipated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operatetem zz) qs(*kws2)h1es at 0.20 A and 3.2 V. If its resistance)m (*st2 e1q kswzeh)z at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$