What quantity is measured by a battery rating given in sakgz3av/ 9l 9ampere-hours $(A\cdot H)$ ?

When an electric cell is ,g8ack;0oh scconnected to a circuit, electrons flow away from the negative terminal in the circuit. But within the cell, electrons flow to the negativo8s ch0,ac kg;e terminal. Explain.

When a flashlight is operated, what is bd*l2x,f xst e,eing used up: battery current, battery voltage, batf,2x ,tls edx*tery energy, battery power, or battery resistance? Explain.

One terminal of a car battery is sai0z uea7jl ,e-dd to be connected to “ground.” Since it is not really connected to the grouzjel 0 7,-eadund, what is meant by this expression?

When you turn on a water p9xbgycgww4m4old+ 5o n5 t38faucet, the water usually flows immediately. You don’t have to wait for water to flow lxp4cog39w8yn gt55o+wbm4 d from the faucet valve to the spout. Why not? Is the same thing true when you connect a wire to the terminals of a battery?

Can a copper wire and an aluminum wire o7wxw p;b7 j cm /(c0vtmo.5cg krvynp oz55,9uf the same length have the same resistanceyjvwxo um mo;.59rg/5pcz5bc(7,nk 7 wcv0pt ? Explain.

If the resistance of a small ixu hn ;2gc k,usgt1siy*h) ,j5mmersion heater (to heat water for tea or soup, Fig. j;1hg ui ykn)s2,,us*hgtc 5 x18–32) was increased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2aaf 0xmm /q -w)xj.hn0h (xund9, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resistance, (b) th /whn.x0q( 9 0hmxx) ujdn-mafe 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 l iqjve(k(:qr.ightbulb burns out?

Explain why lightbulbs almost always burn out just asz+5tqqy c)w1wdg 5 p+lmy pr8. they are turned on and not after they have been on fw1qrwm. y+pc)ptyz 85+ ld 5gqor some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb?q(,8lcz cm9rdx4jmqc6 zhdiut 9b 475 Which has the higher resistzqj ( bc4,du89c9h5 xmcrtldz qm47i6 ance?

Electric power is transferred over large diss gyks6) x.4x-ulg3bdt;7 q 2gs d9ewqtances at very high voltages. Explain how the high voltage reduces power losy; u xltkqbg3ex-)wq9s 2dgs.s 76d4gses in the transmission lines.

A 15-A fuse blows repeated zhn+7q0nvuxl++ 5yaq ly. Why is it dangerous to replace this fuse with a 25-A f7 nn+ql+v 5zqx+yha0uuse?

When electric lights are operated on low-frequency ac (say, 5 Hz6r cd+-r hjzhwz ;2el(), they flicker nd +(;czrhh6zre lj2-w oticeably. Why?

Driven by ac power, the same + dmjken+abi3vv48 d8electrons pass back and forth through your reading lamp over and over again. Explain why the light stays lit instevv+ m3bd8+ 48indjke aad of going out after the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. Immebsmzxs;0*lb/ dd .fviq (( 0nadiately after the toaster is turned ofb(.0 ms v *i(b0dx;qlnd/ aszn, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Explaxp*ti9j52j fb in.

Different lamps might have batteries connected in either of the two arrangemel/:ld qk ftnryj4+r69pp30x y wbm/5knts shown 90wqkj p3xfkrp6 4 r :t+/l5/m nyydblin
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A n. ( i/)ragrfoflows in a wire. How many electrons are flowing past any pointai/ofr(n .)gr in the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A fortgfu x;36l )nqq 4nuj; 5.0 h. How much chu u 6;qq fn;xjng4lt)3arge passes through the battery?    $ \times10^{ 5}\;C$

  What is the current ip9b zjuy0 tal az5 s5/f7ff1* g5bj.chn 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 of 4.2 + k6,4 teneu+weitfb4h2 ,pwxA?    $\Omega$

  What voltage will pr .kwh12o lkxqpopy(bc 5dz(6 435hskgoduce 0.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when p mozx8s,pt0u /dd6t i;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 dryertbqq0z6r n, p+ 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 a2rhnr+ 1 sflt4ykn, gzn449rw 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 cj.4bz rc,(v hvarrying 2800 A (Fig. 18–34). The crh(,vb.vz j4 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.dx zio+r1.i3d9bs9 reim7e 8s50 A at 240 V.
(a) If the voltage drops by 15%, what will be the current, assuming nothing else changes? $\approx$    A (retain one decimal places)
(b) If the resistance of the device were reduced by 15%, what current would be drawn at 240 V? $\approx$    A (retain one decimal places)

  A 12-V battery causes a current of 0.60 A through a resistor. tcev:; 63gkfk
(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+ sd8qksv7p8u6/wyz*bs9 b p g a 1.00-m length of tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of )(o)ff99v l0i)l tmdrq4lgrp/ii za) copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance .8tn ww-pp cfl);h ,hyv-f4xnof 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in diameth-lx- npw 4ph8 ;tf,)nfvwc y.er.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tungstec:9;epyb (oc en wire of the same lec;9eb(oecpy: ngth? Give numerical details.    mm

  A certain copper wire has a resistayrdwm 1pw2lc 1g(7) z dso6m5snce 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 cop d0mxnug, lxhc 907*kpb7v59s0rynn b xw*6qeper wire (originally at 7ehqs00mxdb*gny* ,n0 p97 9 bnl6xrcvk5uw x $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resi/* cv,3a *4rqdow ipxqstivity as tungsten does *w*o q 3xrqc ivp/,4adat $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistaqyfc+wjw-x1u u zwh0,x *y )v;ex f*y-nce 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 coppr imef*+z8)lev )dnt 4er wire (used in 15-A circuits). The wire has diameter 1.628 mm and carries a 12-A cvzn) rid*m)+ 8l4eef turrent.    V

  A rectangular solid made of carbon has sides of lengthm y2i t9vvr:iq/5is -gs 1.0 cm, 2.0 cm, and 4.0 cm, lying alongsy-5mviqi rv /g9:2ti 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 one has twice th9: wja s +rxaqkm42fd9e length of the other, what is the ratio of the diametj 9 kd:4maa9sx+f2 qrwer of the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminumouv z2s23pxm- wire is connected to a precision 10.00-V power supply, and s2mp2uox 3zv- a 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 ofm2pd w(wx0- jf copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is placed across the composite wire.w2j(wp dmxf 0-
(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 resistan4 pcsz c zr-u47v)a n5r;.c/cb6vyqwyce not change with temperaturc 7;)cc rr4b sy65 4.ncwz/-puvvq ayze. For example, suppose you made a $4.70-k\Omega$ resistor from a carbon resistor and a Nichrome wire-wound resistor connected together so the total resistance is the sum of their separate resistances. What value should each of these resistors have (at 0$^{\circ}\,C$) so that the combination is temperature independent?
$R_{0C}$   $\Omega$
$R_{0N}$   $\Omega$

  The heating element of an electric oven is designed to produce33gy8q4 u:0gzn xvl; vvywwt* 3.3 kW of heat when connected to ;t8ly w:qwnvy4vg uvzg3*03x a 240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player that draw0f0 ;tsuf4 -g hv+u8s sfff3 rtr8m3zys a maximum of 320 mA of cus8z3v;hffmu+ fg 0803 y -f tu4rsfrstrrent?    W

  What is the maximum voltage that cws rvd .pjp. /szx*6 85wxjtb6an be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, a 75-W lightbuojup3 u olo(2:1rslp1 lb connected to its pr2rjoouuo 3l1( :p1lpsoper 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 1 cm q,+jdbjw7810 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 1 ws:) ;g:b2ao.isw6rxfhn,u m 250 W.
(a) At which setting do you expect the resistance to be higher? After making a guess, determine the resistance at
(b) the lower setting;    $\Omega$
(c) the higher setting.    $\Omega$

  You buy a 75-W lightbul). hgmkv ,9iz+49nnzfnq+vjl b in Europe, where electricity is delivered to homes at 240 V. If you use the lightbulb in the United States at 120 V (assume its resistance does not change), how bright will it be relative to 75-W 120-V bulbs? [Hint: assume roughly th+z n j)lv,4 9qm.hnf g+vz9inkat brightness is proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use zyf6e 8(a, xkf,jn*r 3cjra ;ein the morning if it is in operation for a total of 15 min? At a cost xn (ckzf3rrjf ;eay6ae, ,8j*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 oe5+ezfb +0(e. bqvlka 25-W porch light on day and nievo0+5kf zl+(beq b. eght for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries c km s8;* u,uom dx88+vdwxh k:)myko(bbp49hoonnected in series as in Fig. 18–4b (Fig. 18, so+mo ;kh:budh89m*xk u d8k4xmvop( y)w b8–36). 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 enlpdmr2t896ifo q z:u 75haz+ mergy 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 Fig. 18–20, can be used wi-k3,ab-pl y3r:pg qlrthout blowiyq3bgpl -3arr:pk -,lng a 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 fxzgg (6g)m z:3f)9s,knvsjwb c p)r.copper wire) and of length 2.7 m (9 ft) is connected to an electric heater which draws 15.0 A fc: )vsgg.pzm w(xgrf)ns6zj ) 93bk, on a 120-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 fac 8uhr 1koy2ysb -ngn(m,/r+;op: m/cf9k ruyrtory through wires with total resistancebcm9(ryu,gruo yknhr:r /ys1-82fn +m; kp/ o $3.0\Omega$ 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 coa qga746l+db rttp ;p+ 06ja wveyb:3annected to a 240-V line is 17.5 A. At what rate must cooling water pass over the coils if the water temperature is to rise by no more than 7.5a6 +vpbqdb :tt73yw eal4pjara+60g;0 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to heat a cup of water for,7)f+/t ozvxcez-acq z5gq,x coffee or ,)oq cf,q-+xc ave5gzt x7zz/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 +4q (d(tnhy md:df2ga in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak m(eac8zuyj.:up2 n,q 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 resistance of w yk;ul;bmteo41ksym: plbhtp4m: *ck5:2.s 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 altern0 kdh 5c3 5sg(vh)b( rgdgx2emating current in a 1500-W device is 5.4 A. What is the rms voltage across it? c(r3vmx s 5kg(0g 2b5)dg dheh   V (Round to the nearest integer)

  An 1800-W arc welder is connected to + ly0os49i3zy,y kmav 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-.z 9umdogk(r9hp pump connected ru(z.md9 k9go to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected tldv0 y ,((rxmwztt* z3o 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 currezaw7lcb 3lsu q(h.7hvl s8)/xnt 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 currenti 66+ . fe-yngpdfib4z when 22.0 mV is applied to its ends. If thfg6die. 6zip+-bynf4 e 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 bm+gmvwyu/9j,fa-r : tf t,gm7wl 4t/’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,6g*v)w z-wf7brnj;r1k8o 0+dldx xf c $He^{2+}$ 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 acrbtu 0 *d): -wx*/c,acg rdiorjoss 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 2 j3b6yco m,cipulse. The action potential is detected at a point 3.40 cm d m,cboic326j yown 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 onzc -. uan-vx w s-dtx;tjc;iv1(4a-xxe 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 capacita- -;uvx;xac x-tiwsntj -v41cz.da (xnce; 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 potenti8ne- -f/ ejr9jdv.cdmwj+e 4yal, $Na^+$ 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 amp-dc0qvev ;2 ggere-hour?    C

  What is the average cuaf q6rz9;luh +rrent 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 eachudhzcq8mk5 cbo(/ph- 8)bcc 7 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 rab u(/7cp db-m8cc5c)qhkoz 8hted at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of a 110-V, 1500-W heater i, 5 49lafdqtahs 5.4 m long. If it is made of iron, what must its diameter b,d45fq al th9ae?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of the resistanceh/r j: 6g)dryj R;:jrrjh 6d/y) g 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 MW of pa;a0 v6kp ;eisower. 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 meter. Assume the cost of electricity is about 10 cents per kWh. s6a;a ;vi 0epk   dollars per hour per meter

  (a) A particular household use9 6: zpc b*lbp,qb.g hcpz2m(9fou e7rs 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 i;1lbtx bx0byl * +h)ypsp( nzam- tyoa25y- 0in half and the two lengths are wrapped together side by side to make a thicker wire. How does the resistance of this new combia-h0 a2syml5*b+lytp)i o0 1bpxy n(-t;byzxnation compare to the resistance of the original wire?

  A 1200-W hair dryer is design2fx t*:wk c6f(pgo jv+ed 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 sk5:g uzxpppgu k :(8z1tb/g(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 of ug sg(8k /p( kx5ppt zbz::1gu35 A and produce no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given bygt/zvbwug+ ( *rb4s tv 2xg-x/ 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 q9 (peo34 cbf*pdqj,39o jvaw at 65% efficiency delivers 950 W of energy per second to the inter bj9qda 3fe(94p qo3,wvj*copior. 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 i;w *dp*+tmm;qw z gx1* k1nkhconductors made of the same material. One conductor is 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;g1hik+;1 w* mqmw*tpnkx* zd? $P_1$ : $P_2$ =    : 1

  An electric heater is used to hk.ig;jlm k :g7eat a room of volume $62\,m^3$ Air is brought into the room at 5$^{\circ}\,C$ and is completely replaced twice per hour. Heat loss through the walls amounts to approximately $850 kcal/h$. If the air is to be maintained at 20$^{\circ}\,C$, what minimum wattage must the heater have? (The specific heat of air is about $0.17 kcal/kg\cdot C?$)    W

  A 2200-W oven is hooked to a 240-V source)lt9fn3o 4dnm3j ets: .
(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 1zky y /r:rt.ustorage batteries as its source of energy. Its mar/ y.u1rtzy:kss 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 resistancc/kw z bw67jb)e 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 designeatw(+6.i g5b2obeo 0lhtfcl 1d to carry an 11-mA beam of prote1 ao(0gwtllic t56fh bo .b+2ons traveling at very nearly the speed of light ($ 3.0\times10^{8 }\;m/s$) around a ring 6300 m in circumference. How many protons are stored in the beam?    $ \times10^{12 }\;protons$

  An air conditioner draws 12 A at 220-V ac. The connecting cord is copper wire wip wy87ojcva 8:th a diamp 8j coyvw7a:8eter 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 heati3m tk; by1thq/ng element is a coil of Nichrome wire. When uncoiled, the wire has a total length of/1 ;khyqt 3tmb 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the systeml+ax1 -zdkhynpr; ;dj nm5.7 q 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 perchnp7ay.r n- q m;; djx+1d5lkzentage 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 120 V and 40 W for household applica:w wq78o;w )cflqgy* htions. Lightbulb B is rated at 12 V and 4lwy:cq) qf8;7 * oghww0 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.s,:7 mksieg.w 6-8rma+ x:oiabo /tp p259 cm is used to connect a set of appliances at 120 V, which draw 22 psaar:o:+ s.6btm-8g 7i wkxmi /op,e50 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 ankru fbm*u9 ac-z xyc (6 n:,sz11ewp-r inside diameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the resibr( mufeu-xs6y r1 z,zcw:n9k pc1-*a stance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R /uk5kpi5 mm.;36 lu. nviulugis stretched uniformly so that its length doubles, by what factor does the power dissipated in the wire change, assuming it remains hoouvmp5 ;5kug .iulk/in3. ml6u ked up to the same voltage source?

  A tungsten filament used in a flashlight b76t)9 tjmuz/ hdyw5a3kn h)yv ulb operates at 0.20 A and 3.2 V. If its resk5 y)/ t36 z7mhyu n)dt9ahjwvistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$