What quantity is measured by a battery rating given in ampere-hou dlu 3tif1q+3krs $(A\cdot H)$ ?

When an electric cell+9 ezqsb m1flv -0jn0n is connected to a circuit, electrons flow away from the negative terminal in the circuit. But within the cell, electrons flow to the negative terminal. be0 1-zvsnj9ml+fq0nExplain.

When a flashlight is operated, what is being used up: battery currenlbxf zaj 8 u+at)8kn9*t, battery voltage, battery energ +9)t kajz8bx nflu*8ay, battery power, or battery resistance? Explain.

One terminal of a car battery is said to be cobo0s0u4e ko7)y.y gl ennected to “ground.” Since it is not really connected to the ground, what is meant by .oe7 ol y0)y0use4kb gthis expression?

When you turn on a water faucet, the water usu5(, 2ijwt-ple uui/nny d1(wjally 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 trut 51ui(e-iu,2 j/ y(pw dwlnnje when you connect a wire to the terminals of a battery?

Can a copper wire and an aluminum wire of the s8c , o18)maxi8-x ,fiec hjvc l2thzbz-knx45ame length have the same resistance? Explain. x -xmjz,h-c, 2i8kt54hn bc8i1azefvxo) 8lc

If the resistance of a small immersion heater (to heat water for sqdatf.ym+ olu9 ( 12gtea or soup, Fig. 191af( oqs ul+tdm g2.y8–32) was increased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon haxrks7/n4whsg tz8ncd ,nx v17p q69j0s sides of lengths a, 2a, and 3a, how would you connect the wires fro, hc 8q dnx0vnx7kt pnr4j167 zg9s/wsm a battery 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 burns out? cyl*v8cggc+ ta1nq)70n7xst

Explain why lightbulbs almost always burn out just as they at-j.u/74o4u yz9jnmzn; d pvsre turned on and not after they have been ony- nv4 z4zjtn/ojpd s79uu .m; for some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which has tfo6 c.v,ojpf* he higher resistan pv.j *ocfo,f6ce?

Electric power is transferred oveto,-y8ss32zu q,g polacs0x ) r large distances at very high voltages. Explain how the high voltage reduces power losses in the transmission l 3 gu8,opstq-coy,0)2lzsxsaines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fuse with a4 n/ozejn;m 0p60ufjt+lc/td 25-A f+fn un/0j0p ezm;d6ol4 tjct /use?

When electric lights are operatch/vh59o8zdx5rv sc m5a8kq5ed on low-frequency ac (say, 5 Hz), they flicker noticeably. c5v rx5da5m95hkv8 soqh cz8/Why?

Driven by ac power, the same electrons pass back and forth through your vp;c 0eze xg)bzf4g*4s x -nt.reading lamp over and over again. Explain whyz4.pg4 snfxb0 x)tzevg ;*ce- 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. ozua0 7nyk ,;l)7ucezImmediately after the toaster is turned on, is the curreu0z7yao k;cnzu7,l ) ent $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a res )tfxq h98wp9znwl+(r istor? Explain.

Different lamps might have batteries connected in either of thlulo9wa;vsnz5h)m hk. j8pbm) g;n. (e two arrangements ul vj;)nm. b8mplk 5 . gh;)asoh9nw(zshown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many elect+4,g5hl htv earons are flowing past any point in the wirevtheg ,l+a4h 5 per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 Ay) g2* fiwh.vk 9.y6grk teup. for 5.0 h. How much charge passes th.e6igy..p9gr)wuk*2t hyfk vrough the battery?    $ \times10^{ 5}\;C$

  What is the current in ampeguz66twv zgh,;aw38um f 7j 1ots7jx1res 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 o :n98p1rc ghnq zskd lu5(1*jzf a toaster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.2), 5ul.g nakdoqk .x;a5 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a*)7p0cn ph9c/gngl e+8j ojra 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,5nl f52+wyn *ze x8 tttuqe7m 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 buno8 2riy/o zwv,ldbdgle,,5 y(d1- jflb whose resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc e:ie )k)s /1afj zhfas7lectric transmission line carrying 2800 A (Fig. 18–34). The line 1)a 7z sfeifk:sh)a/ jhas $2.5\times10^{ -5}\;\Omega$ 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-tskgq*2bw ,6uf:/amp bb2 i l 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 currentom edpl8n4hp. )z9 vk8 of 0.60 A through a resistor.
(a) What is its resistance, $\approx$    $\Omega$
(b) how many joules of energy does the battery lose in a minute?    J

  What is the diameter of a 1.00-m length of tungsten wire whosyo 8yclt q1h.xe,i p9:e resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-s 0f 7s-rvu6h:rdc:e kh,n-mkm length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10. m0c2lw/ 3lc5wln/ tyg0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2. c3ln2/gl/w y5lwcm0t 5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have f)ir.n3k6rdxdkj* j; the same resistance as a tungsten wire of the same length? rn ;3jrj d)i.fxdk*k6Give numerical details.    mm

  A certain copper wire has a resi+tgtff q 5d0s/stance 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 (orig)p0:dmeps y 9*vjd3 kyv;i ,bginally at k;esd3 yv 9 ,pdi*vpb ygjm:)0$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the saozdqjcoq.t( ;s c08/l vy3 h2qme resistivity as tungsten dhzqj;0 o vqlqdscct/(.23 8oyoes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has seq0 dg;epyokg 2n4wu m9;v +l+c0.hea 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 along a 26-m le ci9mo*to//l svy 2zkc7tz h-;ngth of household no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm and carr7yvho9sz*m;/t k z-i 2cto l/cies a 12-A current.    V

  A rectangular solid made of carboya-mk)s.ltkd3j 8t6xq z25gwn 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 the res2q8aklgjtm ) wst-y3 kz.xd56istance 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 twicewiw; 0 x smntj:i:elwn**h e,c(hg q2+ the length of the oth :m*: sn hqnw g,*i i;2cxe(tjw0wel+her, what is the ratio 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 connected to al(i0 pf*c+ oiw-owb anigm oru/-2g++ precision 10.00-V power supply, and a current r+-of g /+g*n(pim0-+o2aiwwc boliuof 0.4212 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 d ::y mslm;ftw6t j)9ucopper followed by 5.0 m of aluminum, bymm6)ljsf ud9::tt w;oth of diameter 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 important that the value of a resyzsdz.n*5.a;zz yy3e xn-5g mistance not change with temperaturzzm.y-xyg5n3a5.n;z y zse* de. 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 electrii .hl. dph2kj pu4a06gc oven is designed to produce 3.3 kW of heat when connected to a 240-V source. What must be the resistance of the element?0g api kd.jh64.l2 uhp    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player that drawoi y*zb.p.xvot;( p mwex2(5ody( or8f9 6angs a maximum of xgz6iy(((efyxt a982 m.d5bnv;po.o oro pw *320 mA of current?    W

  What is the maximum voltage that can be applied across ab2b o7szn ,gqo34.sab $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and curdg;pdse e8y9+, lq2ac3z x 2urrent through, a 75-W lightbulb connected to its proper source voltage of 120 V. e du3dx,82 pqcs 9zrla2g;e+y
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heater is rors93g, jlorxm2 3c,mated 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: 850 W and 1250m:-cl3e-8sb c. fwvdw 86jf l pukefzpn(2l3* 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 Eurol if dba1lx.;l7pwt4/pe, where electricity is delivered to homes at 24i l.al/fx4lbdw 71p t;0 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.]    as bright

  How many kWh of energy does a 550-W toaster use in the morning if it oi44t fee9fqq 4b s/8sv6gdq1is in operation for a total of 15 min? At a /eqdisov44egbf6t19 f8 q q4scost 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-m1lheo.ilp3f7 huhgm /*zk1 2W porch light on day and night for a year? 3p2/ih zlmugfh1el1ho. *7mk $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected in ser)xt 3d 5g e1m9l6 kc //j snz5f)prg(arvyqqp0ies as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when turned on. 50rq5 kx1d)elnamg/9p( pz3s) t/cqgrf j6 yv
(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 aml2e2lku i/q ,oount of energy 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 vl)dkf ogfe :vm(/* 3bpw.it; to 120 V as in Fig. 18–20, can be used with e;k3fwfm):.v obg*ip/dtlv( out blowing a 15-A fuse?    bulbs

  An extension cord made1(q ;kntkh5 / c yk9n2l*jnygiog0-b n of two wires of diameter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric heater wbnj-nnq91 /hlyn(g50yg*k okckti 2 ;hich 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, j/-o-n i; hii 48ghya2yib8wund9y 2o000 V to a factory through wires with total resistanni /9o4hiuy-dyabwhjg2-2;i88oyn i ce $3.0\Omega$ How much less power is wasted if the electricity is delivered at 50,000 V rather than 12,000 V?    $ \times10^{ 3}\;W$

  The current in an electromagnet connected to a 240-V line is 17.5 A. At what ravr3 fzmq/23pp te must cooling water pasr3 v/2ppz3q fms over the coils if the water temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car qp4g:t*x t dg0to heat a cup of water for coffee tq t0:gg4p *xdor tea. If 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 current in aym i,-wg o*ym; $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, is acros0z6 4t vuwlfged5/2zbs 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 mmkwm 3k9e hj8 q1t8chy;r++ dof 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 w + 5uv8c0fkrn 0 o p21rxemcp,8qt4mtalternating current in a 1500-W device is 5.4 A. What is the rms voltage across it? 0toxv nw 1ur mtfpck82r05e ,cp+ q84m    V (Round to the nearest integer)

  An 1800-W arc welder is connecs/tb + 5 bsqbdd)k+1tc f+0jilted to a $660-V_{rms}$ ac line. Calculate
(a) the peak voltage$\approx$    V(retain one decimal places)
(b) the peak current.    A

  (a) What is the maximum instantaneous power dissipated by a 3.0-hp pu coqv/(z3;h wjmp connecteovq(; cjwhz3/d to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected vhhzx w4z1y, pore(,:8x cek .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 currcxl4.t k ,euh0ent 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 curr9aa) ( qwx8vooent when 22.0 mV is applied to its ends. If the drivo9q a(8owxa)ft 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 Ear6f1ai6 +7/kwaw svatz7v1viugfhb3:th’s atmosphere, $He^{2+}$ ions in a concentration of $ 2.8\times10^{12 }\;/m^3$ are moving due north at a speed of $ 2.0\times10^{6 }\;m/s$. Also, a $ 7.0\times10^{11 }\;/m^3$ concentration of ${O_2}^-$ ions is moving due south at a speed of $ 7.2\times10^{6 }\;m/s$. Determine the magnitude and direction of the net current passing through unit area $(A/m^2)$.    $A/m^2$  ----待选择----NorthSouth 

  At a point high in the Earth’s atmosphere,ll.y9lec ,xd;+i)pjmgfd gdd 9e346n $He^{2+}$ 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 mems):(c-ln m pq y3n1hhdbrane $ 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(7dumjm,ki ,e potential is detected at a point 3.40 cm down the axon 0.0052 s later. ,mj( ,ud7emikWhen 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 one actionc55cum hw7;igdu;h( w potential along the axon of Example 18–15. [Hint: the en 5whwu;cch(m5u7 ig d;ergy to transmit one pulse is 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 07a ;z3jvhg-qs 1zyacal, $Na^+$ 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 cfmd4 fhmy:fk:5 bso2c l0gem b;* 6.pthere in 1.00 ampere-hour?    C

  What is the average current drawn by 3bt*rk :g i nx(t-j2 yy/b/ykca 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lighipndts6(v;u51b o+ pm.uy6a x ts on. If each of the two headlights uses1b s6p5(m;yduo. uvi+ant xp6 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 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,qsav8y gfnqj27j:,4kc jwd* it is made of iron, what must its din*jwdvkq: 27 fajs 8yjq4,c,gameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal1-c ucz2 z-xb (ibyh4l of the resistance R; that is,c--(lby2 ic4z1xhu z b $G\,=\,1/R$. 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 MWq2ji, kb27.c5 jvmppyp,9 dwv 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 per hour per j .pdpyq,,w kjic9b2vm vp725 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 6wvyuw ,-4nzwheater $3.0 h/day$ (“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( jgksw(inq.9 x6cn0z two lengths are wrapped together side by side to make a thicker wire. How does the resistance of this new combination compare to the resistance of the original s ikj zqg0( (.nc9nwx6wire?

  A 1200-W hair dryer is designed n / m av(l8jeono,ei oi).qcj0j5;4ntfor 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 thind w+7,0kzm +qcqjjx v5zdd*)ck enough so it does not become so hot as to start a fire. What diameter must a copper wire be if it is to carry a maximum current+kdxq znz0cw+57djm j*qd) ,v 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 the equat7+mn 0lnjh8p iion $I\,=\,1.80sin210t$, 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 6r 21s eeud,lidelivers 950 W of energy per second to the inted er6s12eul i,rior. 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 dif:/ d i-t);j2ebai*i sgudfeh)ferent conductors made of the same material. One conductor is twice as long and twice the diameter of the second. What)ef i-jd;duegih)s :2 b/i *at is the ratio of the power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a r,*3tj-di rp ;pcdg p4uoom 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 hookezf .eapu e;.3id to a 240-V source.
(a) What is the resistance of the oven?    $\Omega$
(b) How long will it take to bring 120 mL of 15$^{\circ}\,C$ water to 100$^{\circ}\,C$ assuming 75% efficiency?    s
(c) How much will this cost at $11 cents/kWh?$    cents

  A projected electric vehicle makes use of storage batteries8 yjl*st-a) kdvmu d;kt4,ch4 as its source of energy. Its mass is 1560 kg and it is powered by 24 batteri4cl,m;t*hj)8u-da t vdykk s4es, 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 f: mhg u4trpj6,3l5z- nsa q*nhas 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 11-maft0e*-,tr dw: 9ags cA beam of protons ,a-rewt cs*af 9g:d0ttraveling 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 cop(q/cbwq7vhi 3 per wire with a diameter of 1c v37hqq/ i(wb.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 to8do -,)atng gf 120 V. The heating element is a tg,ag-ofd8 n)coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage i-jx rc6uxb;)dw 9 c9wvaries from about 12 V when the car is off to about 13.8 V when the car is on and the charging system is in operation, a difference of 15%. By what percentage does the power delivered to the headlights vary as the voltage changes from 12 V to 13.8 V? Assume td;9jc b-r6uicw w)x 9xhe headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for household appf r y9xzv+uyh/9h o-e /)i8rqhis:ff7lications. Lightbulb B is rated at 12 V vif 9f y)+iy7r//hfru o se8z9:qhxh- 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 app d jki-rg;z. y(kqx2uk 0:8sj14zn :a:dtlykqliances at 120 V, which dr 8xj( dzi0zntq;2:gs:kajkkkyd -l41ryq: u. aw 2250 W of power total.
(a) What power is wasted in 25.0 m of this wire?    W
(b) What is your answer if wire of diameter 0.412 cm is used?    W

  A copper pipe has an inside diameter of 3.00 cm and an outside diameter of 5.00 o-iaa 0 .z6kpjjm zj(pi9:5tecm (Fig. 18mzj 9j o0(.:ti-k6aazi5 eppj –37). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched unifo5tg :qhim, )oxrmly so that its length doubles, by what factor does the power dissipated in the wire change, assuming it remains hooked up5): mgtqxh i,o to the same voltage source?

  A tungsten filament used in a flash;b cfcpb ee kl1724iq;light bulb operates at 0.20 A and 3.2 V. If its resiklf;1q4;72 cbcpi b eestance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$