What quantity is measumdwi/fg; e(. pred by a battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell ns c n+7u6yu:his connected to a circuit, electrons flow away from the negative terminal in the circuit. But within the cell, electnhu:s +cyu 6n7rons flow to the negative terminal. Explain.

When a flashlight is operated, what nrkz*j d0 n 12t)wpw.:c reh7ris being used up: battery current, battery voltage, battery energyh):r w rt01wp dnr2ez.n7 ck*j, battery power, or battery resistance? Explain.

One terminal of a car battery is said to be connected to “ground.” Sinc(0e0 ui *ccobjiz 5z-ne it is not really connected 0*n ji-zoce5c0(i buzto the ground, what is meant by this expression?

When you turn on a water faucet, the water usually flows immn0v7rq63* l (msoy ldqg y7es,ediately. You don’t have to wait for water to flow from the faucet valve to the spout. Why nod7y(*lm sqseyq n6 l7o,0r3v gt? 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 2 jx 2cynmi3;ghave the same resistance? Explainn3cig mxy2j2;.

If the resistance of a small immersion heater (to heat water for tea or soup,fqhi 54ohlph:6s3fywzi- s-(9 + ovin Fig. 18–3nw9l+f-hip(v i yf- hqi:6oh4z3o s s52) was increased, would it speed up or slow down the heating process? Explain.

If a rectangular sol m; ccweq.ix)1g1z6t gcv.k1bid made of carbon has sides of lengths a, 2a, and 3a, how would you connect the wires from a battery so as to obtaibvk).wegczcm 1gc6 x;itq 11 .n (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 lightv m01acb*1w p 4fvx(vqbulb burns out?

Explain why lightbulbs almost always burn out just as they are turned on any; j+c/hpjo(9(2pgw3 wma tqad not aft(mjapg+pj( /3wqc y;9ao w2h ter they have been on for some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which has*jm7w zb(kts)y v1q5z the higher y5v*wqbj1 )(t7k mzzsresistance?

Electric power is transferred over large disvy ob0+qz7m(x tances at very high voltages. Explain how the high voltage reduces power losses+qb mvx(70oyz in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fuse with x) 6avnxbn /k:royoe dk5od;*/ 6s3ka a 25-A fusex sran;:6)k5k a/ od/koy eb6*3xv ndo?

When electric lights are operated on low-frequency a 5ng6 ;z nzsabzpq721sc (say, 5 Hz), they flicker notice sa1bsn;2zzn qp6 gz75ably. Why?

Driven by ac power, the samejyw *rr.fstu ;/fdy +1 electrons pass back and forth through your reading lamp over and over again. Explain why the light stays lit instead of going out after the first pass of elect1 s*jfyd.utfr;r/ +ywrons.

The heating element in a toasters3d)8hm mpi:r is made of Nichrome wire. Immediately after the toaster is turned on, is the cur )8 i:mpd3rhsmrent $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Explaiy3/sk, ige mf4 bld1m mwj/7x3n.

Different lamps might have batteries connected in either of the vrehjawk:55l 8/g 1yqtwo arrangements shown rgv1yja5: q8 we/klh5in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many elec7lef5u zhb j:yk5j 2fn(y60ca trons are flowing past any point in the wieczu6a b (fnf7yl50y:hj5 2kjre per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a cis*s 8ctp 92gnurrent of 6.7 A for 5.0 h. How much charge passes through the bat2 it8*c sgn9sptery?    $ \times10^{ 5}\;C$

  What is the current 8fyti:3ab vry6e1xx..vu( fv in 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 produces a current n.q uw-api- t2b l1:ceof 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of curren weoud ,dp-:k:t through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-V k x p1b6q(x5h9z; zwdeline.
(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 heati*v/9vmv x :7-k6/ hv swqgy4rb4nlqdsng 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 c8 k/w9 eimdc66 ms*ojsonnected 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).h.vi1,uaustzmed lfipo::k12.nz+(2 eb x6i Tof.z+1(lueu21i:ne2dh6 p:s mki. ix ,t zbvahe 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 6ihu joa959c;q v66f7wcy lme).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 causes a current of 0.60 Aq sk 4hh ,z5g1.jqe0tj 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 r-(,i: rgo.vceelax ;besistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m lengthnt,e6 boq+:ns of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance e 5:fwqd lri1tu*z;3 oa;9/x6ha p6s-gm s wkwof 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of coppedaxosa; hkt sfz: 1 lw9-p*m r5i6qw/3;e 6wgur wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a t 4rk 1c np.cesr36kkxflx.p06 ungsten wire of the same length? Gi6c3r1kpcxnerpkf6 0sx.k4.l ve numerical details.    mm

  A certain copper wire has a resistimrszw+ hcgx1 7j:c *mj wg/5pag)v2; ance 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 rypnvmqlxkqu(1b u0 .u; q73(yaise the temperature of a copper wire (originally at 7nkmxb ;yl 1u0 3puqq.uyq(v($20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have6fucky/ )k6ek(ohppdanx0e4 vax )8 ( the same resistivity as tungsten does at/hn e( cofxy d)v(p xue0kp6ka)486 ka $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resisb/2 3*e6m) 5oqs lmnga md+yzatance 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 hoimpf (-tj 8: *e9 cdh j31gyppivu0tz*usehold no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm and carries ae3pvt1jmt9 pzfc8-* iy( p:hgi0*j d u 12-A current.    V

  A rectangular solid made of carbon 7gv oyq:qc*o ubz+7.nhas sides of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying alo qon*7b.guy:c7z+v oq ng the x, y, and z axes, 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 resistance. If o .j u/.r,b-l ter d80ocqv1ruane has twice the length of the other, what is the 1qbvuojr ae08rlt/d., r. c-u 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 connecte2-8aqn3a9a ;n4 j,u bo+8x nxi jkakujd to a precision 10.00-V power supply, and a cuoan au9n-84i q;bkjx n,akjj3 +xua82rrent 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 copper1 z0 5lt hex:dyzfzrsl(o+3itkl63*f followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is placed a e3 kx 36dhifz1 :yor(st0z+flz*t5llcross 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,oa dn6f6u+lp au1x5r2 it is important that the value of a resistance not change with temperature. For example, suppose you made a 6u l62nxo1rp5+audaf $4.70-k\Omega$ 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 electrf yx6m 9 yena587eb/9w +cbhuuic oven is designed to produce 3.3 kW of heat when connected to a 240-V source/hecyb95a8y97emw b 6u+xfn u . What must be the resistance of the element?    $\Omega$

  What is the maximum power :ifft;c/.hy .hu +d4v tk0kl u4:fzic consumption of a 3.0-V portable CD player that draws a maximum of 320 mA of current? fi:/lh :.c4fkit4u k.hdz cf0 ;vy t+u   W

  What is the maximum voltage thmmlw58pia8qr) z:u m)at 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 7o32zxmujv/g.f0lcfiuux zpx) (/6d ; 5-W lightbulb connected to its propupzjx 3i(zd /u6om/flc0. v);gxx fu2er 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. Calculat ek/u 1kqydk:3e
(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 two014m2d y 7.v hvuzb 0mkfsfvi9 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 lightbulb in Europe,w 9 g,;(i qri/zz+ zmo*3vbcqp 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,o zvqp39;(+br/ zmwc gi*qzi power consumed.]    as bright

  How many kWh of energy does a5)n7 qqe+qc6sowtkkidf*j e: 8,tlw;6jpd(c 550-W toaster use in the morning if it is in operation for a total of 15 min? Ap klq j(j* wesk7nwi:;,tqo5td +866 d)efccqt 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 j2wpu1f7 vk7fcost to leave a 25-W porch light on day and night fo7 fuwkp21f7vjr a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5- .hwp1 4gpndu4V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when turnegnwdp4u1 p4h .d 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 stort c e0./8 ktg+:p/njcx izlg glu3lvxk5a 094jed in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, e* dts(*qk;+xaw8-pz7d vkw2 x)p +vq4iu gepconnected to 120 V as in Fig. 18–20, can be used without blowing a 15-A fuse+-ag4udxxwkw(k* s)p+q p qt2zv7; e8i e v*dp?    bulbs

  An extension cord made of two wires of diamete)z+uh :ikxp c3hux54nr 0.129 cm (no. 16 copper wire) and of length 2.7 m 43z +:uxkihphn) cu5x(9 ft) is connected to an electric heater which draws 15.0 A on a 120-V line. How much power is dissipated in the cord?    W

  A power station delivers 620 kW of power at 1 u b dah3vjn+29hof e-fj:,j+b2,000 V to a factory through wires with total resistance j- ++,2 fvjb9jhueho 3nbadf: $3.0\Omega$ 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 jx)do ((5 wk2)xfanpo17.5 A. At what rate must cooling water pass over the coils if ta2(fj dpx 5)xo) ow(nkhe water temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used s9pv(ds4 n92/pdx:d w/blx fgin a car to heat a cup of water for coffee or tea. If the heater can heat 2nwg(9d vf49 d pbs/d:/ xpxls120 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;(ivj ;inpfm6 a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak va5x;n,y hn7g yblue is 180 V, is across a $330-\Omega$ resistor. What are the rms and peak currents in the resistor?
$I_{peak}$$\approx$    A(retain two decimal places)
$I_{rms}$ =    A

  Estimate the resistance of thec7jtgfbtcs5u -.a7u 8y*kbpfz 2f6i)i6y7 al $120-V_{rms}$ 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 current in a 1500-W device is 5.4 A. What is thd 0ltlh6 j46yo,puh e.e rms voltage ayoel6 p.tu,dlh4j 6h 0cross it?    V (Round to the nearest integer)

  An 1800-W arc welder is c w :mjvno *lp+4k hl4lv,iii:/8 h/essonnected 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 dissi0)-ibm y*,, iqpfpfatnpv4 uqgc p,(8pated by a 3.0-hp pump connected gqpc4i,p pfi)uy0bqma8 f t p* vn,,-(to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected tou0 ,6 bl myck,0n.yoav 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 wirdtppx( 5:.+,-pcqbqo zz jw5 pe 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 cu8f3j:ydsaa*f6 ghdq7rrent when 22.0 mV is applieh68y: fa3s*fdg q7 jdad 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 j vwixh:it j;wlc ;/8. n:bd*hEarth’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 Eartd*1tm-x fel0 qky0/ksh’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 axszf1 n9rq9:vxon membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated witpol07hk4*s/eazq5 fg h an electric 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 axon? (Why are two measurements needed instead of onlyop z4*as7qhlg0 /ke5 f one?)    m/s

  Estimate how much energy is required to transmit+)rga-j)alqgb )w q/u one action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored by charging the axon capacitance; see Secj) guq-a/ + )gblqaw)rtion 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, * cgtt/*ntsr 6qmo2 a1g0kb8ka wbr +($Na^+$ 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 amper .dt+i pe5,7zc w5uz48syqsrre-hour?    C

  What is the average current drawn boc;*k,amgde c4z cxb g /gik)0/w:t5gy a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the sf9if .i sdp5dc*g)b /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 it is rated at gd5)b 9 d*cffiisps./$95A\cdot h$? 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 madeu(p t)g1 r:ccg1ys 3wqagw( 2 wcjbbed,q)2y0 of iron, what must its diameter bewcgtusrg)y)w2(byp2wbc qa q 1( : 10jce,gd3?    $ \times10^{ -4}\;m$

  The conductance G of an object is de(4l e 2aft ;ksu i,iq9hfkm--ufined as the reciprocal of the resistance R; thqam,- l;94st2kuiu h (e-fi kfat 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 MW of power. Suppose that insteadyjx)yot 2b/(b 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 meter. Assume the cost of ele2bb( ot)jy/xyctricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular household uses a 1.8-kW od 50 skte+3tux z/fb8:wil8qrgpp /(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 tzhas l9an6mcv5i3h*3 2xai1x wo lengths are wrapped together side by side to make a thicker wire. How does the resistance of this new c9c *xm36sn3h v ix51 2ahaliazombination compare to the resistance of the original wire?

  A 1200-W hair dryer is desig/p5-8afi+ 3mfzelncgk3u ix6ned 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 be1cc rk5v 7 urlt.y)rzuw8sy v,z.5zn(come so hot as to start a fire. What diameter must a copper wirsvkc 5 vt.8)r.1ylnzu5cz7 wur,yz r (e 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 by f(vrb 75yv1rlthe 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 delivers 950 W of energy per secowf:4yk m xdtphx7ao yt(8:f vt3se*46 nd to t w6hf 4d(4tfvptey::*s x87tkyaxmo3he 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 materia3 nvwl)c ; dkh6iqo( 8ae(x-5+jm bdhvl. One conductor hm-+ e d(lbd3kiaq( j ;c)o6 5vv8nhxwis twice as long and 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 to heat a room of v 5n2..5fw f1l0bg,n nsnqh ibgolume $62\,m^3$ 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 240hlyeu4-oz wq) 5 7zq6q-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 vehiclt3u8*)zjozcy 78ik:t n lv b:fe makes use of storage batteries as its source of energy. Its mass is 1560 kg and it is powered b 8n zcf73o:)i ulk 8bjz*tyv:ty 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 resistancev 4* b7ytiscld:7 l(aa 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 Fermii(xq nep* :jpk nywk64e *d8+zd1xw. blab (Illinois) is designed to carry an 11-mA beam of protons t jike(n dzq1+yxwwdn*4kx*6b. :p 8epraveling 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 nm,rpab*o*/: vzgi (o ac. The connecting cord is copper wire with a diameter of ioavo* :r z(/ m,nbgp*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 wv.x1x mvct,p4hen connected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What i1 v4t p,vcx.mxs the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from about 12 5-me4jms gav ng9b8 (j+,w.esfyv4u fV 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 he,(g8y 4uvjvbssm94.w+jaeff -g5 menadlights vary as the voltage changes from 12 V to 13.8 V? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for household applications. Lightbulb B j)gzv(/y t i56oil i9mi9mi) ivtyij6go /z(l 5s rated at 12 V 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 appliancepa xa j2ac6s(9idu4kbjky5( -s at 120 V, which draw 2269ba2 4u 5 pyaxkcs(jaj( -idk50 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.glggg;tit+(0 00 cm and an outside diameter of 5.00 cm (Fig. 18–37).tgt ;g+0g g(li What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its length doublt 6gqjx/6t wafkg+( y7es, by whaxa gj wy6t /6k(qgtf7+t 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 flashlight bulb operates atbxsjee+;bh w e2 qua5h12y*1b 0.20 A and 3.2 V. If its resistan5+e*aush1b; xjby21q w ebh 2ece at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$