What quantity is measure;7) h8 okuqrsgh 61wykk 5.hwbd by a battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is covi,r ve2b3 x+;, hhaardv/ca /nnected to a circuit, electrons flow away from the negative terminal in the circuit. But within the cell, electrons flow to the negative ter/2 h bac,e,3ivdr +;ar/xvhv aminal. Explain.

When a flashlight is operated, what is being used up: battery n. e6 sse5n6qx91rdcy current, battery voltage, battery energy, battery power, or battery resistance? Exs9yn . 6nc5qre6exs1d plain.

One terminal of a car battery is sj5mm.zmv eih/wurs 5z 4l-23maid to be connected to “ground.” Since it is not really connected to the groh2m3i mj 5swz -ve4lmz5r/.umund, what is meant by this expression?

When you turn on a water faucet, the water usually flows immediately. You dx +p81q9yrpu40cw ef *5sv,k b0oqpsj on’t have to wait for water to flow from the faucet valve to the spout. Why not? Is the same thing truekx q1,r*pqcufb9 8o0ys4jv+p 0p5esw when you connect a wire to the terminals of a battery?

Can a copper wire and an aluminum wire of the same length have ttg86n. 7iz xtczqi+v ;he same resistanc;6z7+cn zititvq.8gx e? Explain.

If the resistance of aopvz zri(/j71 small immersion heater (to heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the heatingvr(z1 jp 7i/oz process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, and 3afy x d-4ohg0+qg+ 3xeah 4r0av, how would you connect the wires from a battery s+xyeah+030 fh agqrvd x4g -o4o as 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 lightbulb burns oi 5p7(gk cd(qjut?

Explain why lightbulbs almo .+l .e9wxa wrki::hopst always burn out just as they are turned on and not after they have been on for some the9aw.il:+. prwxk:oime.

Which draws more current, a 100-W 1 nb w:q /fo sg*bw7j6qjb:wtli)1+jdlightbulb or a 75-W bulb? Which has the higher res wb17wq/owqbsn16tdf +g j)j ::* ibljistance?

Electric power is transferred over large distances at very high spl gjw wn37ry8488kjvoltages. Explain how the high voltage reducelk3 yw r8pj s478g8njws power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fusazy;a2t .zsy 2e with a 25-A fusy azt22yz .;ase?

When electric lights are operated on low-frequency ac (sa+k7za c mzlqq43j;vu)c oo 0*my, 5 Hz), they flicker noticek qa7v 4 u*ql jom30;z+cz)ocmably. Why?

Driven by ac power, the iqeb2d-q ),83aw iuspsame 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-ae,dwq)3bu2 8i psqi first pass of electrons.

The heating element in a toaster is made of Nic5b 2*lrtin 7bfhrome wire. Immediately after the toaster is turned on, infr57l* btb2 is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up ixoayw +v6-0 (umm2wpl (yc uf*n a resistor? Explain.

Different lamps might have batte1 n*vo.jkp qdlf)6w/c ries connected in either of the two arrangements s w*fqd1cj/vo)kn. p6lhown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How manyt p(e5jcl4,ky electrons are flowing past any pointe4pcjt5yl k, ( in the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A )m1iox85 8h8lby4rcm pkks-f for 5.0 h. How much or8l mc ih85- fm14 kx8b)skypcharge passes through the battery?    $ \times10^{ 5}\;C$

  What is the current in b08p3g: ja/ikuixeb;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 A?v(m7 +kg(hvz k    $\Omega$

  What voltage will produce 0.25 A of currenex+q u:h dq4w+t through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugge5 ey7;,an whc r:)miwed into a 120-V line.
(a) What is its resistance?    $\Omega$
(b) How much charge passes through it in 15 min? (Assume direct current.)    $ \times10^{ 3}\;C$

  An electric clothes dryer has a heating element with a xfzi4+alh.7zis u t68resistance of $9.6-\Omega$.
(a) What is the current in the element when it is connected to 240 V?    A
(b) How much charge passes through the element in 50 min?    $ \times10^{ 4}\;C$

  A 9.0-V battery is connected to a bulb whose ciurrxuq 5:-szi7))j 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 c rc5u y mtz2aujl:;a um;wu92/arrying 2800 A (Fig. 18–34). The liu;y9:al2 mt52/mcuuaz;ruj w ne 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 6.50rpq6jurhxr c.6 ,(9ya 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 ao1 1ly 1f.qs i6p *u:4y co6jkaygq4wm current of 0.60 A through a resistor.
(a) What is its resistance, $\approx$    $\Omega$
(b) how many joules of energy does the battery lose in a minute?    J

  What is the diameter of a 1.00-m l+07ii qxgu4d q6,bhfxz5 fn :p2q7 pgcength of tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-momdz;cmjt hgg9.ew.u7 yp, g-v+e ,y+ length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistanlbj6 k,c4saz 6ce of 10.0 m of aluminum wire 2.0 mm in diameter, 4 j6scl,kabz6 to 20.0 m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wir0-wh tmx8v5 ese have the same resistance as a tungsten wire of m-80hesw 5xvt the same length? Give numerical details.    mm

  A certain copper wire har;ap4c /aqoz1tmpq j :v( z;*ms 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 temper)fm ,h 5(l(4iddquqt klhl:+uature of a copper wire (originally at hhtull: q(d+5kluf (i m,4qd) $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same dm) +za;3prhv resistivity as tungsten doeshza; +p)v3 dmr at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has ate8/d+x+ nif l resistance of about $12\Omega$ when cold ($20^{\circ}\,C$) and $140\Omega$ when on (hot). Estimate the temperature of the filament when hot assuming an average temperature coefficient of resistivity $\alpha\,=\,0.0060(C?)^{-1}$ .    $^{\circ}\,C$

  Compute the voltage drop along a 26-m length of household no. 14 copp8*ks(a,e odwmer wire (used in 15-A circuia *ow(,kd8sem ts). 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, and 4.g7em-o)qvo(;cp ;s ,w4oihkb g) 8 hth0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for current that pa m; cp)hw,v) gb 4sthgki;(o7qoe8-ohsses 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 resist n o;*;pmv htftm4c0e+ance. If one has twice the length of the other, what is the ratio of the diameter of the longer wire to *c+0mpm4vht f;t;enothe diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V power 7apuge)c) eq yj6c0w;supply, and a current of 0.4212 A is precisely qc;7yp ejc6 geuwa0 ))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 q py()cf(lrb75f0/ac kq *h tq5.0 m of copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage a)yqcf/ql7cft( b q*r5 k0(hpdifference 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 qm z+mzg71 (jh6akyky (*gna*the value of a resistance not changeqm1zm*( y+jzgh a6kak(7 gy*n with temperature. 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 bp ( na:c54jjuoven is designed to produce 3.3 kW of heat when connected to a 240-V source. What must ja 4(bc5j :pnube the resistance of the element?    $\Omega$

  What is the maximum power consumption ofocf9lob+9ff 0/uf v g+ a 3.0-V portable CD player that draws a maximum of 320 mvf ufl+ o0b/9cfg+f o9A of current?    W

  What is the maximum voltage that can be j nmy4 -6shw(d 6vas5tapplied 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 lig t0plw q :,jdap*f 5t)gkbf8s(htbulb connected to its proper source(gpp ks8)*:0wtdfl,afj qt b5 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 atle1)+ zg:q iad 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 hak0 2jj dim*4erzd54vto1 v 1wfs two 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, where electricif+ve;wk co4/jc lg 6x5saa8,vty is delivered to homes at 240 V. If you use the lo6lwe vga +8cfxc s;/j,v 45kaightbulb 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 power consumed.]    as bright

  How many kWh of energy does a 5k)() hmv0uz gr50-W toaster use in the morning if it is in operatik) )umrgz(0vhon for 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 do6ffv tl 9hn9;des it cost to leave a 25-W porch light on day and nig9v9f6dlh t ;nfht for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V ba* zkxn9;j, 9b5s*huzo6b mudmtteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when turned on.jx,sb6nzk; *uu5b9o 9m dz*mh
(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 stored 3dq1flekg)m:z d.pje r2,7w qin 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 wipx 9 t:b)eb: h:n:a:igg ovn(jtzeg -4thout blowing ax-t pebjz gvigbt) n:n:9:4oa g( e:h: 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0 kt/ qi (17yfk-c(uxab.129 cm (no. 16 copper wire) and of lengthtc -kuqy7ikb(x( 1/af 2.7 m (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 deliversj4epw98it) uf gl)f+dcn ,nr0 620 kW of power at 12,000 V to a factory through wires with total resis4d0ft, )gl f)p9+ n8iujw nrcetance $3.0\Omega$ 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 17.5 A. At whag o + gf2 7ku9me*-1udond kbirq6)v0lt rate must cooling water pass over the coils if the water temperature is to rise by no more than 7.50 96uubvq7od o*e2mr- ) g in0d +1kklfg$C^{\circ}\,$?    kg/s

  A small immersion heater can be used in sr0w :3weei)i a car to heat a cup of water for coffee or teawi ei re03s:w). 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 curre* ,uy e34(f2+r 4xuhamtorfi2u1tsx w nt in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, is acros;y6 sdl9lku3 bs 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 th 743lfiyxcfq+lu rw wdt300: be $120-V_{rms}$ 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 1500-2d7q 0soqesrn+fj +0sha5a 5hk,rm7 l W device is 5.4 A. What is the rms voltage across it? qjas+h ko rrq2+s7h0efn05a mds 7,5 l   V (Round to the nearest integer)

  An 1800-W arc welder is connected to 8j)fh*n n* c2yw0g ji(+gkv5 bfbrl5 ha $660-V_{rms}$ 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 ; n8ot) gxtnxt w,7e1ydissipated by a 3.0-hp pump connectedo )x1t;tt8n,xwe7yn g to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected t6l m;fvksz j54o 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 current hy g.gc(8ujgky e)n k m05n3k*of $2.3\mu A$. What is the electron drift speed in the wire?    $ \times10^{-10 }\;m/s$

  A 5.80-m length of 2.0-mm-diameter wire carries a 750-mA current when 22uh rkn+08z60ce ,lzpn.0 mV is apn8+n0r 6h c,u 0klzezpplied 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 Eao j(j3mh-6gyu8sg6 7evh*pgzrth’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 Eartzf06m2dv. qnytyj:w 3h’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 axoq/qtv*tdd+/zdfe )- q k)he+c n 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 potentialwrmq j;;1fzqb1 : b7sm 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 inste7sqfbjm rw ; mz:1;1qbad of only one?)    m/s

  Estimate how much energy is required to tra3-m8 no h7xsybnsmit one action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored by chargingomys n hx73b8- 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 pot*w1na93a8e5c rfd sdnz thx(1ential, $Na^+$ 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 therxu7skdf:9: cnx +: pyie in 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0v cnjy)o80 zb(-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with thi/1gf xa62yyxxw rr 7pk rb7jpt25*0m e lights on. If each of the two headlights uses 407mtx7x65a ri*ywbj kp fr/ g120pyxr2 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 $95A\cdot h$? 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.wtlpzb.qm,zs;)-( ei6 iucv- If it is made of iron, what must its diameter be? i e6q)s ibuv(mzz t,.w-lpc-;   $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of t :ni2x )wysm7yhe resistance R; xm n7w 2yy:i)sthat 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. Supp sv u)a7akpo:*ose that instead of using high-voltage ova :kpua7*s) 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.    dollars per hour per meter

  (a) A particular household uses a 1.8-3 bgtl,0gylm 3kW 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 a anbep f/m./p 9+eqoi3re wrapped together side by side to make a thicker wire. How does the resistance of this new combinatiomfo+i.nbee /q/ pp 93an compare to the resistance of the original wire?

  A 1200-W hair dryer is/7z 4. ovufaoe*0 u;kyc s;ijl designed 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 szw9y)v,v y0 k k7pl;8x.thvvb o it does not become so hot as to start a fire. What diameter must a copper wir8;.97, byvw 0t)hypxvvl kvzke 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*j46b 56.li,u etlu zpydg ocxclbzo7a -+c;6 by the equation $I\,=\,1.80sin210t$, where I is in amperes and t in seconds.
(a) What is the frequency?    Hz
(b) What is the rms value of the current?    A
(c) If this is the current through a $42-\Omega$ resistor, write the equation that describes the voltage as a function of time. (  sin 210 t)V

  A microwave oven running at 65% efficiency delivers 950 W of enhf 6zu 6nlm+kkb6y9w cll4u86 f8 c)mhergy per second to the interior. Find zb68h9y+uhukncm8lmclf 6 6lkw 46)f
(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 :.q/ ;2s pwcswgvz;rlconductors made of the same material. One conduct p/w2 lqg;;wzv:c rss.or 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? $P_1$ : $P_2$ =    : 1

  An electric heater i/8mu 2bexm .krm zdv3*s used to heat 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 hoohd)r1d p(um+ oked to a 240-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 batteriesaenatkg7/m:u7 mb i57 as its source of energy. Its mass is 1560 kg and7:7ait7/men kbgu am 5 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 h w- j9qgo4j,na 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 Fermilab (Illinois) is designed to carry an 1evc0gx07p6 r uy2) v 0dx,rrdr1-mA beam of protons trx)7rxgr vr2d 0p60uy 0evd,rcaveling 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. Tv,0adu/ 3j*eamu*l,h gel hu:he connecting cord is copper wire with a diametl3 / *hla*u,hmve,u0dgaje :uer 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 attxshgz4:e 5 zrh (/ri4 95 W when connected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has zh:rtxi(rhzs4 e 4/5 ga total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voxwr1c1v .(rqj ltage 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 remains q( 1xcj r.r1wvconstant.    % increase

  Lightbulb A is rated at 120 V and 40 W for household appl .2jjhcmk6u,dications. Lightbulb B is rated at 12 V and 40 W for automotive app. u,kjdj mch62lications.
(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 i ucqif5lqe, my7l-.5zjw jo:j8+jgq. s used to connect a set of appliances at 120 V, which draw 2250 W ,+qqf:wo y5 lu g.jej7 5mil.q-jzj8 cof 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 3.00 cm and an outside diadq3.i* ohcmh3vb v7zowg-i7:meter of 5.00 cm (Fig. 18–37). What is tvidbm3:7oc.- v z ih3q7 hogw*he resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretchedx;f(z :mod4vqsu,q -c uniformly so that its length doubles, by what factor does the power dissipated in the wire change, assuming it remains hooked up to the same voltage sourqf,q mdsxc-:o; u(vz 4ce?

  A tungsten filament used in a flashlight bulb operates at 0.20 A and 3g j* z2t8ufmv7.2 V. If ivj78g*z t2ufmts resistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$