What quantity is measured by a battery rating given in ampere-htgc.l.*d5kx*beox7. n lzp6hu 2k hc -ours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons floejnv-t: m kto; udx2,9w away from the negative terminal in the circuit. But witt, u2nk vodj-m9:e;xthin the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: batteu).r2)q bq.hz c0nbe38 bfxwdry current, battery voltage, battery energy, battery pownhqwbd)u 8f x3eqc.)0.z2r bber, or battery resistance? Explain.

One terminal of a car battery is said to be connected to “ground.”9ccg,+.jexs6rkpn8 f z3ys9 w Since it is not really connected to the ground, what is meant by this expre ws, n g9scy3fpz8ek+rc. 69xjssion?

When you turn on a water faucet, the water usually flows immediately. You dpv u4m .lwnazn*3z.fk2n-r;a on’t have to wait for water to flow from the fk *nnr;3ml- naf. auw z2z.p4vaucet 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 andc 1jl8huzb*ggs,18ey an aluminum wire of the same length have the same resistang1y1lzb,g8sh* jec u 8ce? Explain.

If the resistance of a small immersion h6jxsg(ubh33i(xhe 8q w/z4 xh eater (to heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the heating process? Expj8hu(hh 3geb/xzs 6xwqx 3(4ilain.

If a rectangular solid made of carbon has sides of lengths * h (-bfaboyi)ru9rkzi-u2.ya, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least9zfyh( b ia )k-o*.iuruy-r b2 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 oufba tj/rzx.)j vzu0f25b cy6 9t?

Explain why lightbulbs almost always burn out just as they are turn7q0d1 gh1ibv2:lv/scq) (l hlofx8pv ed on and not after they have be1qqbdl fvpv1hghx/:o0) 7isl 82(l vcen on for some time.

Which draws more current, a 100-W lightbulb or a 75-W gyihzp8z(s /g 7fgt 29yy+3bgbulb? Which has the higher resiip( 9szg87gz yygfbh/ y3g2+t stance?

Electric power is transferred over large distances at very high voltages.z9(1pqnydgm; Explain hon9 ;zgqy dmp(1w the high voltage reduces power losses in the transmission lines.

A 15-A fuse blows repeat;qr3 ro dssxlu47bl0 g1+ ;oaredly. Why is it dangerous to replace this fuse with a 25-A fulq+u rg371xs4r; la srbd;oo0se?

When electric lights are opercgufr-,dt vpg7c)a (sv s(7:gated on low-frequency ac (say, 5 Hz), they flicker not,g pgscc((7v as d7:v)ruft-giceably. Why?

Driven by ac power, the same electrons pass back and fxm r s69usjl+x2x1zf29*xxy cr3 z;i horth through your reading lamp over and over again. Explain why the light stays lit instead of going out after the first pass of ele9 jy; zsx2+sfx3*6mlxx 1 crxur2zhi9ctrons.

The heating element in a toaster is made of Nichrome wire. Immb2 ha r)rj z)i-sjaoq7 ykmf*)9)lz-dediately after the2a) iql aj 9sy *fmzhbo-)k-z)r) 7rjd toaster is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resisk1bh /6 7)fo0t flvfgcw r43qftor? Explain.

Different lamps might have b+6wi8u1.w *fh zglou; nlz2vbatteries connected in either of the two arrangements shul .vf o;2iu1nw8+b *zlzg wh6own 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 flowing paszv-/+f qk7rh l tfkud(n,wih8i))0 vpt any point in the wire per s(dv,fwki7)z- q vkhi)8 f lrhn/+tu0pecond?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a cu1yxubrtg3:+ d rrent of 6.7 A for 5.0 h. How much charge pastd g13bxyr:u+ses through the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes ifp1c z mthw-/pu02la.rftyrq qw6)dpc t ,v,2 8 $1200\,Na^+$ 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 resistanbhuhd ny ) )n9trspvbv- -d-(4ce of a toaster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current,9i b5eosm-j8uyz,l s 3 nsl;e through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when prj x 1f5,pytp+lugged 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 heatin95b/ *h yfu/apctx7lx6 w e.wdg 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 whose92s1qrcf,dm5d *m qfoud+(pg resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric t)6gc3:an(jcnep ue)p ransmission line carrying 2800 A (Fig. 18–34). The line ha)an cnug:c6eej pp )(3s $2.5\times10^{ -5}\;\Omega$ 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 drawigu al2l1 oh5(s 6.50 A at 240 V.
(a) If the voltage drops by 15%, what will be the current, assuming nothing else changes? $\approx$    A (retain one decimal places)
(b) If the resistance of the device were reduced by 15%, what current would be drawn at 240 V? $\approx$    A (retain one decimal places)

  A 12-V battery cause8 *ceu6h66cnd-umf tn s a current 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 whose resg k9j3wxj y:/:ac7c puistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of akqko.np i )tlz8e*wf ,xyfr1n0: x )p: 3.5-m length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resiseo -7ra,j*23ps cctp htance of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m ofa7hj2 rsp*e,tcc o-3p copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resin1n1y xirpo(;*y ze*rstance as a tungsten wire of the same length*z(r 1yr* y1 ;nxopein? Give numerical details.    mm

  A certain copper wire ha-e;kbf v n1 pjdxveeq;ub+4*7s 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 tempeo w:hj v(.i,o0papm b3rature of a copper wire (originally at hb:oa,m vo j0i(p3.wp$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will ha8 w;wx/ut8ci8 ; .xktcmhy7ykve the same resistivity as tungsten doesu t cymt.xwwi8 y; 8;k/xh78kc at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a wbt r*gf1to54v w ) o(lg) hz)x6dlph: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 length of household no. 14 copper x: 9u8se qh z54ab6zvywire (used in 15-A circuits). The wire has diameter 1.628 mm and cb y4s9u v:zqe68a 5hzxarries a 12-A current.    V

  A rectangular solid made of carbon has kzcp:(i* ; bsylp k315p6+5fa mrpaylsides 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 resistance for c(y5pf5 l1:szp;6kl+ biaa p3 krpy*m 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 ha bzan8(t. k mt *o 96ypk/c4pt/z9luscve the same resistance. If one has twice the length of the other, what is the ratio of the diameter of the longer wire to the diam 9 tp(6/4zu.za8mn tl pk*scckob/ty9eter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminumh0b nm2pz vfuvmg.5w52-w p/o wire is connected to a precision 10.00-V power supply, and avg5nw2bw5u2hofp.- 0vm/zm p current of 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 copper8,e6w jujo+ on followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of +jewo8j,un6 o 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 importaae)xep6yr6 bswq*a*:ztizc;9. 5wntnt that the value of a resistance not change with temperature. F.z6w:6qepe) nz t ciyas *w;x5 9rtb*aor 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 el.9 uymb0eg y:hr 1f0kmectric oven is designed to produce 3.3 kW of heat when conn er0h9y0fm ymbg:.uk1 ected to a 240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power r9 :1gd li o2wktoi+f-consumption of a 3.0-V portable CD player that draws a maximum of 320 mA2r i9l:-d1k igo+ tfwo of current?    W

  What is the maximum voltapl rh(:73 xcqmmal8-b(dwn+kge 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-(htrvt83gos4 :jcjx7W lightbulb connected 4 tc:( gxv tj83hr7sojto its proper source 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.,yp 2y hp/c fic,v7k+wvsgl4 2n.qib8 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 1250ldbmq*qf0v:t9 . e cn0 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 elect 8i4ib 6*pcq h;hvf6mbricity is delivered to homes at 240 V. If you use the lightbulb in the United States at 120 V (av ;i*hicqhb 4f6m bp68ssume 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 550d;mcz8dzhcw bw 1r5auf-n; ) 0-W toaster use in the morning if it is in operation for a total of 15 min?md;5 )rz dzw0uc1 abfncw8h -; 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 2r6eyx5 hy2bga 25-W porch light on day and night fo gh rebxyy2256r a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V battlooo)r( . a4ykeries connected in series as in Fig. 18–4b ( oo)y.lak (ro4Fig. 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 sts2qo;w 28h, xxhdk 7ktored in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connected to 120 V as in Fig. 18–20, can be used w6rlsoa*() t*) sfpn ioithout blowingsf)tsa** ni)p r o(ol6 a 15-A fuse?    bulbs

  An extension cord made of two wires of diamete6-)j pvz32g0g84 rn yieiau ,-immuear 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.y e40 p,r -6gu382agevi)j -niuiamzm How much power is dissipated in the cord?    W

  A power station delivers 620 kW of pow)jmwdu6b oc 2mt27v6 aer at 12,000 V to a factory through wires with t67w mmvjt2) a2 udo6bcotal 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 t 3g 3p,9sowvurb 8n7lyq5ve0qo a 240-V line is 17.5 A. At what rate must cooling water pass over the coils if then quq0lsb gr8,3v3 e9w5y p7vo water temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a carfagvsig+,spfyl;6q j ;o //i ( to heat a cup of water for coffee or tea. If the g a/l 6iivfgso ,yq (;/;jfps+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 currzlzs4h5duo0n09 s1is yoq x;/ent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 hrgy8jts21 (i0lcx -pV, 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 *e xuq w6-2wlz/,lxwy $120-V_{rms}$ 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 alteroycf* dl9 e mf5*c a6vn9ss01snating current in a 1500-W device is 5.4 A. What is the rms volta*f s*ycl v nso e1cfs0ad59m96ge across it?    V (Round to the nearest integer)

  An 1800-W arc welder is conn 51. psrp:ffpdected 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-hpz:6)qu jrk 5q+ .u+pwmfs1o2amdxi/k pump connected to a mxsqj r/)1u :25w+ +aqpku.o kifdmz6$240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connecte.v,+d62,c yn/l wp7 wj gagbm8hbj0umd 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 copper7eg92bm;aoyx-h/; p grn. sur wire carries a tiny current 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 kgn n99 -vp9ek22.0 mV is applied to its ends. If the drift speed - 9n9ekg9nvkp 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:bnt 4hp,pkd kn ;:6gp 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 

  At a point high in the 7l+6kd( qe;g5)htcadlho +fy 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 an axon membr-eurnx nzln *kr938h-ane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with an electri +-mhl4q2ws1 iqhvgn 8c pulse. The action potential 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 a4sqwignv 1 +qhh -28mlxon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much energy is required to transmit one 4* tkmdzfehy k-7t16 x;wqv0d 2 stzq8action 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]. Wtzs0 2et x;-1khqwt6fdqkz ym4 d7*8 vhat 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 potential,. *m gcc4bgzn, $Na^+$ 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.z5qxq,j+ n59fkf r6 k:.ubhik1 xkidqh( 8.za00 ampere-hour?    C

  What is the average cunqsx*+i )u zmmim71g l83x+v grrent drawn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of the two hegdqd-c t .cm7-adlights 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 iqdcm-c.dg -7 tt 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 iskhhu g));rgq6h4cd a p.5 .zto made of iron, cou t)6zh4gag ;h.kdh5qr. )p what must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is de3fi;y 6r-orq tfined as the reciprocal of the resistance R;q6;t r- 3oryif that 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 requires about 10 MWpw 6ieo1:xsucb 7 n(/r/q.lnl of power. Suppose that instead of using high-voltage lines to supply the power, the power is delivered at 120 V. Assumingiw/.q /rn7u( 6 bello1cnsp:x 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 household usesu99 i2ofj hsk9s; vcd3 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 len dk yr i,dw/m5)n,l hevi-bf;j87fs 7rgths are wrapped together side by side to make a thicker wire. How does the resistance of this new combination compare to the resistance jh,7v ; y-w)l,k5bifn7fr/8 ridmeds of the original wire?

  A 1200-W hair dryer is design1 1cf8g*lr kiiuyh52y1f( ht bed 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 be r5fj;*igt2w (7tid 0k gy;adycome so hot as to start a fire. What diameter mk g2 *7y;t;w(grya50ijfdidtust 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 per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current isssjr ,)9utj6xdfdx 90il.p, j given 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 runnintlq5akcge1 5r,pv9e0g at 65% efficiency delivers 950 W of energy per second to the 0va5pkecg 1l59q, etrinterior. 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 same mang om:5 qxq7fs ad5+6hterial. One conductor is twice as long and twice the diameter of the second. What is the ratio gf5q h6:5oaxsm7+dqn of the power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a ro )o49zu0,hc k,0 d6ldjfchj gwom 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 2o rt2y 7bo)q(*wjz6lg40-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 storaee -n/c vgu8if;zq.3,ok fzi :0i cly3ge batteries as its source of energy. Its mas:n ik/-; ei 3zecf0vzyqf.olu, 3c8igs is 1560 kg and it is powered by 24 batteries, each 12 V, $95A\cdot h$. Assume that the car is driven on level roads at an average speed of $45 km/h$ and the average friction force is 240 N. Assume 100% efficiency and neglect energy used for acceleration. No energy is consumed when the vehicle is stopped, since the engine doesn’t need to idle.
(a) Determine the horsepower required.    hp
(b) After approximately how many kilometers must the batteries be recharged?    km

  A $12.5-\Omega$ resistor is made from a coil of copper wire whose total mass is 18.0 g. What is the diameter of the wire, and how long is it?
L =    m
A =    $ \times10^{-4 }\;m$

  A 100-W, 120-V lightbulb has a resistance (f58cj6r3 g:nv qut lpof $12\Omega$ 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 (Illh a4 ryk(qug(67 4ricm e.lj6ninois) is designed to carry an 11-mA beam of protons traveling at very nea(6n4(y qu647.clir e agrmh jkrly 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 conneag5zs-m c34 f)w pt)0( hkzcqwcting cord is copper wire with a diameter of 1.628 mm. (3aw5zc)kgqs m -p)f h t0wzc4
(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 a849ke mxdblzp w:x+ 5gt 95 W when connected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total lew:bz xg48x ed+mp9l k5ngth of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from abowt 8-,ymg tr+it *ji(- 3fdwwtut 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%- i(tw*8ytwg trtfj3 +-w ,dim. 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 1s1 3ahw.pej:d 20 V and 40 W for household applications. Lightbulb B is rated at 12 V and 40 W for automotive applicatio3adw.js1:e hpns.
(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 isq(8 bsh+ta/ jye+:yar used to connect a set of appliances at 120 V, which draw 2250 W of power total/ey8:a s+hbrjt(+y q a.
(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 insidejfa8vd*s*-.n w -e aonu(bw-l diameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the resistan(nn aj-we-*da olswb*v u.f-8 ce of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformlw7n6yuf5xhkc6dpg r j ,w/d72y so that its length doubles, by what factor does the power dissipated in the wire change, assuming it remains hooked up to the same volfdgykn66 h5j2uwpcrx/ ,7wd7tage source?

  A tungsten filament used in a flashlight bulb operates at 0.20 A and 3win3tjn x+ 9/x.2 V. If its resistance 3n9 njx+t xwi/at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$