What quantity is measured by a battery rating given in ampere-houk0y*dbzm 9mza .kv;z;rs $(A\cdot H)$ ?

When an electric cell is c hxmek3u 7cjo/-g s4c8onnected to a circuit, electrons flow away from the negative terminal in th8c /o 7gcmsjxkeu43-he circuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, whhh22 d7s8i) ra +t/nbqmbs1i kat is being used up: battery current, battery voltage, battery energy, batter+b 2ka1t/ )s7 niq8smi2bdrhh y power, or battery resistance? Explain.

One terminal of a car batte8wjdtr lvo-;rubd ra712hi 6dm9ao/-ry is said to be connected to “ground.” Since it is not really connected to the ground, what is meant by t1aodir2t8 ;u69-wo/hm rd7 blja vdr-his expression?

When you turn on a water faucet, the water usually flows immed25ss q pus j,x2z8y;lyiately. You don’t have to wait for water to flow from the faucet valve to the spout. Why not? Is the same thing true when you s5y xjqs2l28; z,pyu sconnect a wire to the terminals of a battery?

Can a copper wire and an aluminum wire of the same le;7dak e 69khew 4tog)vngth have the same resistance? Ex)6 k eaov7gwthekd49 ;plain.

If the resistance of a s6,x* xtkl.( tcxsaa ;uqwlz9/eo hg-4mall immersion heater (to heat water for tea or soup, Fig. 18–32) was increased, would it spees(l9 zt;kaqexh-wx.o4 6l,gc u/*t xad up or slow down the heating process? Explain.

If a rectangular solid made of car9f1o1n9jkoos bon has sides of lengths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resistance, (b) the greatest resistance?onjk9of11 9os

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 o9 wkxeb.t7mocy2 m(.p z4o6jr ut?

Explain why lightbulbs bij0 iut-2lx ,d0rlq; almost always burn out just as they are turned on and not after they hav20 ltjil;drx-b,q 0ui e been on for some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which has 9o.-l bk6ayffkef0.5y4myzq the higher re5omf f qay b9 kz-ye6yl0f.4.ksistance?

Electric power is transferred over large distances at very high voln,-vszpry+2:o ( 9rg(iqx dcctages. Explain how tyspnzr,q(ox 92g cr: i+cd (-vhe high voltage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why e66ett;qwt/bis it dangerous to replace this fuse with a 25-A fu t6/ee wq;tt6bse?

When electric lights are operated on low-frequency ac (say, 5 Hz), tnada*cq:b /afwgx(o8g o ,, -uhey flicker nwad/ c x:ub -a*a,nofgq(8,o goticeably. Why?

Driven by ac power, the same electrons pass back and forth throl24;n9 x0g +oewfi ecvugh your reading lamp over and over again. Explain why the light stays lit instead of g v94ncio 0efxe+ l;gw2oing out after the first pass of electrons.

The heating element in a toaster is made of Nichrome wirp oi7 jghb4lw8/z 6wg*e. Immediately after the toastezig/wb4op*jgh68 w 7lr is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Explr fadnqegp.jr71vt21 n )cg0)ain.

Different lamps might have batteries connected in eit e a*i31jwmwd7her of the two arrangements*awiew d mj317 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 filr/8 mw4m+ u0,z hbxilowing past any poi+mhzwlib8 rm0x ,/iu4nt in the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a cu;fy(ah +wkd oq(u)d0ybuq40t9qqu;c gq6 :hurrent of 6.7 A for 5.0 h. How much charge passes (00q gdyqu4;fkab;wd u yqq:u+69h) t ochu (qthrough the battery?    $ \times10^{ 5}\;C$

  What is the current ik g.nt4z,k+ idn 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 120 V produc,ql+mlxs+b l.+kkd 7 xocx;t f2gn2q: es a current of 4.2 A?    $\Omega$

  What voltage will produce 0.n (+rc w lrk;u2.cm2 v7cc.andd+kjo525 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-V lih:oz9f ;u;tpy,9 vo kvne.
(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 elem)ro gufry*d 4w4xbu7)ent 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 connecghd us x-2 7f.dm(n+qt9uhb x:gj;8*qo wvll5ted to a bulb 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 transmission line carrying 2800 A (Fig. 18–34). ayxnv(8.oy: .hsh l p 5sna./ijonu*3 Tpl*nj a v.5/(hy suyoshox.3 in8 n.a:he line has $2.5\times10^{ -5}\;\Omega$ resistance per meter, and the bird’s feet are 4.0 cm apart. What is the potential difference between the bird’s feet?    $ \times10^{-3 }\;V$

  An electric device draws 6.50 A at 240 V. gyduk.wxpt0s- 8 r h1oa pn,5;
(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 ofm-.hrp5 -dx mk 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 n 1;fihb;g/ xmof tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1 g;zrw+ub t; /r7bv9ij.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire 2.0 mm3)v40hlbfd.nf u -d/jo aci*h yzy;8w in diameter, to 20.0 m of copper wire 2.5 mm in diameter.doaj 3-)*.i4/; zy8hffvl0bc dn uwy h   

  Can a 2.5-mm-diameter copper wire have the same i*m-2t 2lt6)yrrzrhx/ zrw8 xresistance as a tungsten wire of the same length? rz/xtrylw-r m2hi6 xz*)t8r2 Give numerical details.    mm

  A certain copper wirez;u+h9 xe6d7rsw:jbb has 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 tempebxtfq7t/r3/0 kxvghz z6 cv1x1gcnljn(v ; ,)rature of a copper wire (originally at/ nf( 1cgvv0zg 3,z)/ thj76b 1rtnxcx;qxvlk $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivity as o +f;q2 ox ;tca3qp3zqtungsten does;pxotqqc o2q3+;f3a z at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of aboutl )xx-m(9c5z g3dkyp l $12\Omega$ 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 /ust/ (nlecb3 6bt7 fu26-m length of household no. 14 copper wire (usen7et 3lbtuc/ /ubf( s6d in 15-A circuits). The wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm, 2.0 cm;p6 vgqct s:v; 50s+9tnnaagf, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for current that passes through thta0+;n:nf sptg 9s5vg q;6vcae 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. I95 nhw1 ,:p3ug nimwtmt(.ub t,tjb;jf one has twice the length of the other, what is the ratio of the diameter of the longer wire to the diameter om;1w9,uim pn t(jgnjwt 5:hbtt3,ub.f the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 1:f*tpn xtn6 62dsc;n ky 0l./rttxn w-0.00-V power supply, and a current of 0dt srny xtk;n*p t./n0:-tw6cnfx 6l2.4212 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 5.01v.tisz:(h ode4z3ph m of copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is placed across ttp3(vs4e ho zz. :1dhihe 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,tdzo;3f (m9t s it is important that the value of a resistance not change with temperature. For example, suppm ;o3 9stft(zdose 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 designed to produ*98wi6cd5 gr ikk1syul ha q+/ce 3.3 kW of heat when connected to a 240-V source. What must be the resis 89ikwg r5+a/k* d1ilc6hus yqtance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portu6ew qc1)ad u s52cb*dh m0e;uable CD player that draws a 1eu aqdd2hc u;50*wubcm ) s6emaximum of 320 mA of current?    W

  What is the maximum voltage that can be applied acrossh4 titf1- l+l+h4a.z hlikt7x 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 conmwk 5d6b)u c5ru2j *nonected to its pr5b o *k6 rc5dumuwjn)2oper 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 r*2pi zvv1e d gi1)e1e nv.u 1+;j bdyrx.kck,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 has two settings: 850 W (qbx6h9o8j + lwg mham*;k;q qzf,z0xand 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, whh ,hqoomqisxz1d (u*wg2 k1ar c+g), 9ere 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 gack1 hi9hg*1)om(ws+, x,ouqzq2rd 120-V bulbs? [Hint: assume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W to-pkhjz )6ghr qk.ws/7m s 4td)aster use in the morning if it is in operation for a total of 15 min? At a cost of h s/kp)h. mzkq 6)rtsd4gjw 7-$9.0\,cents/kWh$, 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 perth;9nqyd 7jrbf4 *s9y kWh, what does it cost to leave a 25-W porch light on day and night for a yearqt7ydbs j;94 nrh*y 9f? $\approx$    dollars

  An ordinary flashlight uses two Deo xdl206nu aa9u6r- a-cell 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draw6x 6uro-a9el and 02uas 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 :lw+h d fdm0 t.guiox,- h*n;sx*lji2of 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 to 120 V as in Fj*es z/qzzc/j1z*9b tig. 18–20, can be used without blowing a 1q/ *z9/ezz1*tcz bjjs5-A fuse?    bulbs

  An extension cord made oa9r5h 2f ov0ijf 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 which draws 15.0 A on a 1225vai9hr0 foj 0-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 thro. 707cnf rwpfmdsz tm.c4 (v5cugh wires with total revcm7wm.5rcf4nc0 t. dz p( s7fsistance $3.0\Omega$ 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.r*;rw21 xexj4l4n rb (y-wmpx5 A. At what rate must coolin b y2w4rx(j * 1lpmxw-rrenx4;g water pass 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 to heat a cupxtex) a* b 71m/vapcp5k0vqa2 of water for coffee or tea. If the heater can heat 120 mL o )q /7akp e*vtac1 amx2p0vbx5f 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 currev+ lq9 gx7uvkw+c(i )cnt in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose uja0qig;2835 pe 1i f9qkwpq *nlump4peak value 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 resistano6p74 z0*,hrak :c h, rk tdwpzrx;3rcce of the $120-V_{rms}$ circuits in your house as seen by the power company, when
(a) everything electrical is unplugged,
(b) there is a lone 75-W lightbulb burning.    $\Omega$

  The peak value of an alternating tdg4 )s4f hmr0current in a 1500-W device is 5.4 A. What is the rms vol)fst4 0rgm 4hdtage across it?    V (Round to the nearest integer)

  An 1800-W arc welder (48cz cau4eert(;o rwis connected to a $660-V_{rms}$ ac line. Calculate
(a) the peak voltage$\approx$    V(retain one decimal places)
(b) the peak current.    A

  (a) What is the maximum instantaneous +6j(.m3 ngwum+6f -kn 8 yrse:otip5tql(f nypower dissipated by a 3.0-hp pump connected toe(5nju+gt8s mk wr-oy+f3p :fm6y.iq6n ln(t a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connectedv7uhiktqc(lj93.;b , gnbl l-k)* atc 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 tinf3e(v us 5m8k4qi2anfteb,:ty 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 cat -dr.m:3lnw tt auy+4rries a 750-mA current when 22.0 mV is applied t-+rtwtay43n l dtm.u:o 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’s atmosphere, l8nv9prhwc9 / $He^{2+}$ 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 Eartte6es :v h+ :s376zjz dp l;vr;9vlzghh’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 acroypz josaa :( )hs5na, l4:hkbi *o 2z-/nzjb5zss 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 pote, per7d7 /ogdko6tbg0qe 0enzwp i :3,ntial is detected at a p60pe,z : rp0wdi3, d/e n7b7tekogqogoint 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 one action potential along k q4 po+u3wwl/the axon of Example +o /3wu q4plkw18–15. [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 required for $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action potential,gh /ssk6:iv u/ $Na^+$ 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 1.00 ampere-hour? (wea 6h/3 a5ok, wngf+py p0skm3.acs    C

  What is the average current drawn by a 1.0-hp 120-V mozdoom+ f:ghij- f;-8ltor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of the twozqqrbov5 /q2ls ,7kx*u x.q0ft(l.cxeat7, r 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 ico2t7x l tqv .uz .qf,x 5e(skbl0r/a7*xq, rqt is rated at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of a 110-V, 1500-W heater is 5.4 m long. If it is ma-kae(0v qyk/77tq z ndde of iron, what y0ekzqktd-qa7 n v7/( must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the rejm yj.igjv7t5d/l (i8ciprocal of the resistance R; (t y8/m.j ivjg dil57jthat 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 a(i0il2 ye1u.ew14m hwh3 j)sgr ai9t wbout 10 MW of power. Suppose that instead of using high-voltage lines to i)ww(ish y a9g1tr23lwu i1m0ej he.4 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 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 a be6rcma,p98heater $3.0 h/day$ (“on” time), four 100-W lightbulbs $6.0 h/day$, a 3.0-kW electric stove element for a total of $1.4 h/day$ and miscellaneous power amounting to $2.0 kWh/day$. If electricity costs $0.105 per kWh, what will be their monthly bill (30 d)?    dollars per month
(b) How much coal (which produces $7000 kcal/kg$) must be burned by a 35%-efficient power plant to provide the yearly needs of this household?    kg of coal

A length of wire is cut in half and the two lengths are wrapped togeth9i9 nrcivn*m(er side by nn9i i* r9(vmcside to make a thicker wire. How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 11c9.6- ykamlxtgdj / 4f7 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 9ziwd)*j, 8cv p8 l0 kya7kcdmdoes not become so hot as to start a0admp *v,k ci )z98cdyl87kjw fire. What diameter must a copper wire be if it is to carry a maximum current of 35 A and produce no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given byux q4 eo4 ur:tup.r0np1oy58h the equation $I\,=\,1.80sin210t$, where I is in amperes and t in seconds.
(a) What is the frequency?    Hz
(b) What is the rms value of the current?    A
(c) If this is the current through a $42-\Omega$ resistor, write the equation that describes the voltage as a function of time. (  sin 210 t)V

  A microwave oven running at 65% efficiency deliv emxagu3 -v q-yyw2d,0 t00) ;vbaqhvuers 950 W of energy per second to tvy-t2a0veu0quw)hy0,m3gvb q xa - d;he 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 same materialskt+0*tw m na0. One conductor is twice as long and twice the diameter of the second. What is the ratio of the power transformed in the first relativknms0 +atw *t0e to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room of i;y1 ispp,s-guo-2h f 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 rlp zj ns. qe 6exo/ /mqtr22-bgk+36l240-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 ts k kuu1b14e8storage batteries as its source of energy. Its mass8tk 11se uku4b 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 resists (auaduw/+)u0 jdst.ance 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 (Illinoisz .;oez nn9ub1/ pko5p) is designed to carry an 11-mA beam of protons traveling at very nearly the speed of ligh/e9b;oz uo1kzpnnp. 5 t ($ 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 drq *w4iyiorrnn-rnd el4tgg a e/ .mej: r4366,aws 12 A at 220-V ac. The connecting cord is copper wire with et gy n6ee,w /mlo 6irrnr44*a.i gn34dr-:qja 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 to 120 V. The heating elementlrt l ;/ceb +d5;xj.pn is a coil of Nicp;tb 5 x+nl.led;cr/jhrome 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 sysy :xanaw-8k8f tem voltage varies 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 fr8k8:y-nfa xwaom 12 V to 13.8 V? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for housrtebx d4l(6,oehold applications. Lightbulb B is rated at 12 V and 40 W for automotive a( ldxetb64 ,orpplications.
(a) What is the current through each bulb? $I_A$ =    A $I_B$ =    A
(b) What is the resistance of each bulb? $R_A$ =  $\Omega$ $R_B$ =  $\Omega$
(c) In one hour, how much charge passes through each bulb? $Q_A$ =    C$Q_B$ =    C
(d) In one hour, how much energy does each bulb use?    $ \times10^{5 }\;J$
(e) Which bulb requires larger diameter wires to connect its power source and the bulb?  ----待选择----Bulb BBulb A 

  Copper wire of diameter 0.259 cm is used to connect a set of appliances at 120 5,q34jwm1w 5fj,gbgodhgd -d V, which draw 2250 W of power total3wgq-o m,dd 1f5hw g,jbj5 gd4.
(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 3vj :/vx6tkub p jk 03hzo/:y8w.00 cm and an outside diameter of 5.00 cm3 /u6k y k:o jhbxt/p8:zvwjv0 (Fig. 18–37). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stret9bx1z12ogw)2cts rhsw8m 6ytched uniformly so that its length doubles, by wha1s6zorw )2scbtx1h 2w89m gtyt factor does the power dissipated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flasrm,h4tkxh ;(q:ix-gqhlight bulb operates at 0.20 A and 3.2 V. If i,i:;grhkh4x mtx (qq-ts resistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$