What quantity is measured by a battery ratins0ly 1 *l8(yfgnnb n3dg given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electro, nie rhkfa*)qnq+s*/3)tw5 prqjc)0rllgb(ns flow away from the negative terminal in the circuit. But within the cell, electrons flow p ,n tq)rf)5(h seic *)bqknr0/3qrllga*w+ jto the negative terminal. Explain.

When a flashlight is operatdt- -ewcdtu*8i (jco 3ed, what is being used up: battery current, battery voltage twoc uted3 j8-i(dc-*, battery energy, battery power, or battery resistance? Explain.

One terminal of a car battery is said to be 6c95irwd d)j-/qez8y( h slgg connected to “ground.” Since it is not really connected to the ground, what is meant by this exp y5qrcz9dsgglij-6 / ( e)8dhwression?

When you turn on a wates6j 6usmk 3dx;(j x0pfz1 j,bkr faucet, the water usually flows immediately. You don’t have to wait for water to flow from the faucet valve to the spout. W,fx bm0zs3 6ujj6 x(k; 1kjdpshy 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 of the same length have the same rlf gi ;8origsl6 ,ejfg/,.bhbqxo33 /esistance? Explaifjl6s qbg ,. g/ooli/if;hb xr3, eg83n.

If the resistance of a small immersibqwejt0+*a e iaq3f-7p 6d (kton heater (to heat water for tea or soup, Fig. 18–32) was increasftk-a qe+b(jtw0pe 3iq6*ad7ed, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of ca k/nch;zt irg;s9yz7 4 mrvw()rbon has sides of lengths a, 2a, and 3a, how would you connect the wires from a battery so asg csr(rnym vt/4zhi9 ;k)w;z7 to obtain (a) the least resistance, (b) the greatest resistance?

The equation $P\,=\,V^2/R$ indicates that the power dissipated in a resistor decreases if the resistance is increased, whereas the equation $P\,=\,I^2/R$ implies the opposite. Is there a contradiction here? Explain.

What happens when a lighr;n2ej y 4)t77wayg6 *bkstr xtbulb burns out?

Explain why lightbulbs almost always burn out4y6 y4bz )gbgowepn9kd*z6p7 just as they are turned on and not after they have been on for some y)zebwpgz*y4 4669d bkg7no p time.

Which draws more current, a 100-W lightbulb or a 75-W bul 0ppd o7h: o7-:i1caoxowr-l ub? Which has the higher o::cpp7xau0ldo -hi or o71-wresistance?

Electric power is transferred over large d+twq5zhz c qw5md*)k24ty;dvistances at very high voltages. Explain how the high voltage reduces power losses in the transmissiowqwmzct kq); 4vdz y55dh +2*tn lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fuseodq 8b;1rv ;v)*vwwb s with a 25-A fuse*vo;wsv8bdbv w);r1 q?

When electric lights are opvy,flg;eh9ia(a rj, 3 erated on low-frequency ac (say, 5 Hz), they flicker noticeably. Whja 3(ge ,;rl,ya fvi9hy?

Driven by ac power, the same electror; ij) k3zlpfkeit4ybkd75 + 5ns 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 okzli54yei+j7p;tf5dk r bk) 3f electrons.

The heating element (9w o6gb*m ispin a toaster is made of Nichrome wire. Immediately after the toaster is turned on, is the cus6bgp*m o(w9i rrent $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a r;lu1lv;4k8ywm6zd8 xov d d )jesistor? Explain.

Different lamps might have batteri)eg+rm 2rt3 bx6:ofc)p cgo*q es connected in either of the two arrangements)mc g)26xroq3 epfr b*cot:g+ shown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A 4) .yy0cccyxgflows in a wire. How many electrons are flowing past any point in the wiyyg.0ccy x4)cre per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery 8 v sdkw+ziwyy8c9(*n using a current of 6.7 A for 5.0 h. How much charge passes through twzwc8(nd+9y isk 8y *vhe battery?    $ \times10^{ 5}\;C$

  What is the current in amperesn 8 qp;cb,bwa xcs.a4vt*.0ng 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 curre0f gzjax9:, 4akkut j2nt of 4.2 A?    $\Omega$

  What voltage will produce 0f dgj )l0wa/7i.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-V +4 +m(gbpmf45pyv cep42fh m tline.
(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 u3dnz5eo)pb,:, syka yism; 5dryer 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 con*fz /p1022cxosw lpdynected 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 electrima3 *idim;gy7c6koj v*1zy1c c transmission line carrying 2800 A (Fig. 18–34). Tz yc1* y1gj6;7a ivodmic 3k*mhe 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 atcqw.4:ii sd 8w 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 cur,e z3. u39q kiyib3ypurent 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 ,u. ,ueba ipllc(8r; o/ac;kzwhose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wamfqqm(q ;p8hhj)b1 ;k/nls+ w *5ivr ire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire 2.0 mm in lw5xgy4 k7i.iq/ a16ts fo*p cdiameter, to 20.0 m of copperkg. w76 5*coia/ i1pqtyxfs4l wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as aq/ rp -xwtqc+ 8j/8gvz tungsten wire of the same length? Give numerpgq/jcz +8w-rvxq 8/ tical details.    mm

  A certain copper wire has a resistance ;gqls *s mn+(iof $10.0\Omega$ 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 y y2(n,d- w5,iggy:cinh ghh*copper wire (originally at *hih-yg,5hc2( ni ,w:gdg yn y$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper wifuk wqvc/ (kk -wpta/ at( 0cj*ai;i-:ll have the same resistivity as tungsten does ik jktc//wi ;a* v0q(tpf-c-w(a :ukaat $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of about la1ug+6 y c96 dzerzi4$12\Omega$ 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 copa-,)3oq; i jhkxsm7c qper wire (used in 15-A circuits). The wire has diameter 1.628 o7j qx -ska3)i q;cm,hmm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm, 2.yh o9wr.rhme.f9sm.qpob : / l w/,)tn0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistan/mer/t,lworf ybw)9 h.n9smq.ho.p: ce 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 resistanni: 1ycgf.ucj;wbe. s 5i ,mze/k43zjce. If one has twice the length of the other, what is the ratio of the diametcjf5e.4i.mcw3/1 gk;n:,s bzzji ueyer of the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire e h55e4lbd2 w3iwj+gt is connected to a precision 10.00-V power supply, and a current of 0.4212 A is prl4dg eeh5 jb+w5t 23iwecisely 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 com w +xce7y32s cxuf21cpper followed by 5.0 m of aluminum, both o x7fcxmcsw1c22y+ e3uf diameter 1.0 mm. A voltage difference of 85 mV is placed across the composite wire.
(a) What is the total resistance (sum) of the two wires? $\approx$    $\Omega$(retain two decimal places)
(b) What is the current through the wire?    A(retain two decimal places)
(c) What are the voltages across the aluminum part and across the copper part?
$V_{Cu}$    V(retain three decimal places)
$V_{Al}$    V(retain three decimal places)

  For some applications, it is important that the value of a resistance notmq *a/y ej*j u;f(udr84ibo9ezbzi1 *0d 3vxo change with temperature. For example, suppo8zmedfuejdxz*iu9bq4b1*a io j3( rv*oy / 0 ;se 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 produc4f c3ihxdx(j3 e 3.3 kW of heat when connected to a cx (3d i34hjxf240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum ,9bm*2 nmtisnpower consumption of a 3.0-V portable CD player that draws a maximum of 320 mA 9b ,ms2tnnmi* of current?    W

  What is the maximum vg 27t7m2 b9 f evitg6b-xivbv,oltage 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 ,u;(3f21-yoa gukgk cyvz p0h-W lightbulb connected to its proper sou 0a;uzk-3y2u 1gv,k(g cp yhofrce 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 heatpjm 35 k6*2,knhi4k le4fni czer is 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 tvu pb;dkm9s +3wo 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 lightbulbok y .b1(cbm*ooz1 wh- in Europe, where electricity is delivered to homes at 240 V. If you use the lightbulb in the *zc.hoow(o11bk b my-United States at 120 V (assume its resistance does not change), how bright will it be relative to 75-W 120-V bulbs? [Hint: assume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use in the morning if im+ilc 3m;bvl3t is in operation forlml 3 mc;bv3+i a total of 15 min? 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 coy kbjr4upin 79m5 f)9a.i)pjist to leave a 25-W porch light on day and ni j9umb4 f i59jp.) np7ky)riaight for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries o tv;kh9o3)*jco/jkxconnected in series as in Fig. 18–4b (Fig. 18–36). The bulb dr;vh 9oc3)t/jx ko*kjo aws 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 energyp4 0kd /pth b9uiq-lz( stored in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, conne 0 hb4h2xqm (0i/dg:ikkjt) yxcted to 120 V as in Fig. 18–20, can be used without blowing a 15-A khx 2tih b yd0q/x)ik(m40:gj fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 coi(0 4zvhn8t 5cj ylk)nlf7*pcpper 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. Hoj* n 847iczcf h(vkyl0tl5)pnw much power is dissipated in the cord?    W

  A power station delivers 620 kW of power at 12,000 V5tr;o n7g,pm i to a factory through wires np7 ,5g;o imtrwith total 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 to a 240-V line is 17.* h1h5eg0he *thhpj o0/0w guc5 A. At what rate must cooling water pass over the coils if the water temperature is to rise by no more t0t*hw 5e0jhhphu/*1c eg 0 gohhan 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heatev mbq4*q:hz amei+ sln6tk55hx ,st /-v2r2bor can be used in a car to heat a cup of water for coffee or2 :l4 - svh5*n xaq/e2 mtzikr+6m,sbvtbh qo5 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 izz-nd2l7.q /qh b6yazn a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peaknwkx6p(v7w n--:d roy 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 occpoony(w ig3 87+(iyi7ny e*cfq :v8f 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 current in a 1500-W device is 5.4 A. Whaze*v9,6i 2 0mi cw x gt,niw3f9dvqpa0t is the rms volwvde3p06 0 g m,9zt*2,fi9iicwan xqvtage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connectedd -u.*q. nmpil,nh+wd 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 powebe+coeo +0 p8ci gcv+2r dissipated by a 3.0-hp pump connected to av+ e2 0i++eobgcccp8o $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connect7job-m-ugc/cb nsp+:/ ) :iz, jgktsted 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 al ,c9 mdpx*(di 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 75 3cza(w,w bmi40-mA current when 22.0 mV is applied to(, ibz 4acwwm3 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 atmospherey4 zrf/s/6idz, $He^{2+}$ 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*r(4 r +rmmeti 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 el( ue x8v/(dldd k5vs(dectric field across 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 potential is d h 3gz(f enr1yw)uppd/0*xt: n6t i*tretected 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 insteat he)xp/wpdz*g n1rf*t6r: un30 y(itd of only one?)    m/s

  Estimate how much energy is required to trsrv.ctvpu t xnag)c 6pd::21 /ansmit one action potential along the axon of Exc1nu 6.c:/xrvtv2 p )tdga :psample 18–15. [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 potentia v05k;k zs qu:iw2rhs( ;nqg)zl, $Na^+$ 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 izie cr5 evr3c)ijd). 6n 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0-hp 120-V mof. xonjh13 t51dodgf u/db ;3etor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of th.ddewd:*q5 vz j z(d:o ,t-cnxe 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 l-d5z(o vx: *dwztn,d.:jqed c ast if it is rated at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of a 110-V, 1500-W heater is 5.4 mwd1 a1qn: rpf8gfs8 6jk6c)be long. If it is made of iron, what must its diameter bdbafg8q1c n j668)1k:wprfs e e?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal b) qj*c0:wlco w zsm r8+cff;7of the resistance R; that is, 87b0scowrz c qcj )+;*:mlw ff$G\,=\,1/R$. 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 po2ng m1l(jg+b(qa; gobwer. 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-diamgqj1 b;omg a+(bl(ng2eter 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 usess/cfz 6- uzhf5pnt+ g+s+a kb1 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 lengths are wrapped together si.iv)tcg qw0l )q5efinb 7/v5 ede by side to maki)eq fi5)7lb.wn0c5e v/ tq vge 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 115+l;aracr-w0 o ixdj/7 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 thi f 7c*gp, )nvxstk*6kvck enough so it does not become so hot as to start a fire. What diameter must a copper wire be if it is to carry a maximum current of 35 A and produce no mt7kkp*s)vxfg6nv c*, ore than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by the equatihq7y* xa 4;yumon $I\,=\,1.80sin210t$, 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 deliver.xoq9 q (olb 0zf7yl2; hxjz;rs 950 W of energy per second to the interior. Fi(h2;r9qlzzfx ; by0.qo j7lxond
(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 material. One ca 7xph cyb(2*iknwa 1-onductor is twice as long and twice the diameter of the second. What is the ratio of the pxw*aic7 kp( 1-h2bnayower transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room of vn ,uz0kg w6soq 9xd9qt)kct:)olume $62\,m^3$ 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 240ub kdb;* s);fx-V source.
(a) What is the resistance of the oven?    $\Omega$
(b) How long will it take to bring 120 mL of 15$^{\circ}\,C$ water to 100$^{\circ}\,C$ assuming 75% efficiency?    s
(c) How much will this cost at $11 cents/kWh?$    cents

  A projected electric vehicle makes use of storage batteries as izc1h fcg ,)qa2 6h/heuts source of energy. Its mass is 1560 kg and it is powhgch ,6c e/fq)a2u1 hzered 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 2v7ht h2tzhggj) r+y- yh; o0pa resistance of $12\Omega$ when cold (20$^{\circ}\,C$) and $140\Omega$ when on (hot). Calculate its power consumption at
(a) the instant it is turned on,    W
(b) after a few moments when it is hot.    W

  The Tevatron accelerator at Fem*qz6s. j.ej;k +bqlc rmilab (Illinois) is designed to carry an 11-mA beam of protons tcmzs e.6q+ .;jbjql *kraveling 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 rcj2, x3 t9l3z*wz dgmcord is copper wire with a di3cl r3gdj2 t,xzm*zw9ameter 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 ratp+z1frz b9i* er9bmyo54wf6 oed at 95 W when 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 is the diame oo*r4b5z 96zf y1rebp im+9fwter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltag *ghlkubb;9;v e 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 from 12 V to 13.8 V? Assume the headlight resistance rg*;hbvb l9u;k emains constant.    % increase

  Lightbulb A is rated at sw ls12.5npf f* av (c7skrth8d t6em8120 V and 40 W for household applications. Lightbulb B is rated at 12 V and 40 W for automotive applications. vsk561e(7sm pnd 8t hlf .8w2tarfc* s
(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 co m;:dmnrp8 ;osnnect a set of appliances at 120 V, which draw 2250 W of power total.mspn8;;m:r do
(a) What power is wasted in 25.0 m of this wire?    W
(b) What is your answer if wire of diameter 0.412 cm is used?    W

  A copper pipe has an inside diameter of 3.00 cm and an outside diametzaprm 20r t;v:er of 5.00 cm (Fig. 18–37). What is the resistance of 10.0 m omvrt p:a0z ;r2f this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretchesx 5fo 0zfx+1l xgdd+/d uniformly so that its length doubles, by what factor does the power dissipated in the wire change, assumi+d5dx1 g0xxlof / +fzsng it remains hooked up to the same voltage source?

  A tungsten filament usedo8n7i3 af(w3i ( gxlfi :y)w1u;vcfxy in a flashlight bulb operates at 0.20 A and 3.2 V. If its resistance at 20if7 33;nc f 1yi w)((a:ywovuflg8i xx$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$