What quantity is measured by a battery rating givew; 2 bblno1b.e(0hqlxi/ ;2o/ ywaszv n in ampere-hours $(A\cdot H)$ ?

When an electric cell is conne),53yc)njx+nokbq d0x)of zn cted to a circuit, electrons flow away from the negative terminal in the circuit. But within the cell, electrons flow to the negative terminal. Explain.) z)cnfxn) ,x+0nyo5bk q3doj

When a flashlight is operated, what is being used up: battery current, batte ipz57hh6 wajcd: s,h(ry vol,s5:6hc pidj(hwazh 7 tage, battery energy, battery power, or battery resistance? Explain.

One terminal of a car battery is ce*d duor fk0-o+jxf+-0 hpx1 said to be connected to “ground.” Since it is not really connected to the ground, what is meant by this expro od r +x0-c*+-fj0fu1dkxehpession?

When you turn on a water faucet, the water usually fygk m 2uqb+i+6lows immediately. You don’t have to wait for water to flow from the faucet valve to the spout. Why not? Is the same thing true when you connect a wire to the tebk2+qui6 m gy+rminals of a battery?

Can a copper wire and an1 x-u2lz0x c9zwin as1no;q6-vf g9 lf aluminum wire of the same length have the same resistance? alfx lxv 9n9 q-0ci;z n16z2ufs-gow1Explain.

If the resistance of a small immersion heater (toyh8 *d5l c -ntd;fr:9- snxh:xw el4gc heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the heating process? 4 sdxl5 h;: 8d-:*lctcgr n9e -hnfwxyExplain.

If a rectangular solid made of carbon has sides of lengths a, vg*r csm0sk;:ta ,7mh2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resistance, ( g,amt c7 sm:k0h;sv*rb) 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 t9s-*yy ;t0br-cxsf()o l ade-:prdiburns out?

Explain why lightbulbs almost always burn out just as thvb cp /h35mj1bc ,4wd .fa-vth4+h p9dvu6whiey are turned on and not after they have been on for some t6h,/3 4vbw wth9d1vd5a +mc.pu i fbh4jcpv-hime.

Which draws more current, a fevh*hq6w0j +q + i)se/rpnv- 100-W lightbulb or a 75-W bulb? Which has the higher resistancsn- )w++qq60vrphhiv /fe ej *e?

Electric power is transferred over large dia. 6upe)fwrz+ma2r r v k76y3nstances at very high voltages. Explain how the high voltage reduces power losses in the transmissio)m6 fw6 vpareka32zurr+ny 7. n lines.

A 15-A fuse blows repeatedly. Why is it dangerous to 0 m/1d ;d8tqay2phxx x0)zbl e2gth( grr;:wtreplace this fuse with a 25-xb wdlh mr ;p)/(z8exg0;a 2 dr2hy t0qtt:1xgA fuse?

When electric lights are operated on low-frequency ac (say, 5 Hz), thgu e)2gd0xe)zey flicker noticeably. Wh0e)u)degx2g z y?

Driven by ac power, the same electrons pass back and u48l+a*0y7gkp3v qr p i73gwf,l. 0cas nnbblforth through your reading lamp over and over again. E+slbnp a 3p04fg*b7.7u q3 lcln8vwr, iy0gk axplain why the light stays lit instead of going out after the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. Immediately after the4jf le ycscc7:d.d (:v to(.c jfel7:dc sv y:dc4aster is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a r+-ac3u gn qzae84mn gy+n crd285ys;d esistor? Explain.

Different lamps might have a9r50 yd hzrm ,p+u1aqbatteries connected in either of the two arrangements sh,q51aa y rmzrp0uhd+9 own in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many electrons are flowing past u*5wo6 wemm-u, rbl6g*ia7e sany point i, r* bmoui-667e ewmu*lw5ag sn the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current slhy:v5jwz)m x+; / neof 6.7 A for 5.0 h. How much charge passes through the bat:)sm j5nv/lh+w; yez xtery?    $ \times10^{ 5}\;C$

  What is the current inp;i6ks8xisc . 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 prodl lm1w*0aca6o. bl je;uces a current of 4.2 A?    $\Omega$

  What voltage will prodz b.m(sg fr q8kr51:ovuce 0.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 fq e1g2j/ - 5vno:e1kc0f hrkyA when plugged 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 cixxz ;p,n 1yd p8lv*9a 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 a bulb wfhtim7y )q-*w,k z,mwhose 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 carrx/r7b;em hd v,ying 2800 A (Fig. 18–34). Thhmxdvb ,7e /;re 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 drawsfcfhi92n*s0(* kr jyn 6.50 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 A throulb ) kzt(y.7ib7(iubn gh 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 tungs e0cvb9gd;75neqv e,q ten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length 4r ageego14acq33ev; bm /t 6fof copper wire 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 sv-v2qc(rua1vy 6;tddiameter, to 20.0 m of copper wire 2.5 mm in diams6c;aqt yrdv1u-v v2( eter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tungs4n( 8i0echs ctten wire of the same length? Givns8eh4cc it( 0e numerical details.    mm

  A certain copper wire has a resistancb +nk/yy16i y(t wrdp4e 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 copper wire (originally knpy)s 4oq2v erqy1iax622ha- * y.br at 6)qraq2 yv *a2 nx-bsy1yhre4o.ip 2k$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperye2 )e6f3 9pfxpoym /lse n(k2ature copper will have the same resistivity as tungsten doop y/f 6f(k2s29nyxpeeeml3) es at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resisk--1oxmt2. qo6qkwy)wr4h1 ep kd twxw-7se2 tance 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 alonufr 8n 7/7qiwq ( x6s2f1bgzkrg a 26-m length of household no. 14 copper wire (used in 15-A circuits). The wire has diameterkr 7xq birgwuf6(f7qz 8s1n2/ 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 cmw-kh 8ygjr5tnbp v 7**, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for current that passes through the soliw 5kgth*r-njp * 7b8yvd 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 resodbvk g hgp8wrhkeiw14 zj)4t ;s7061istance. If one has twice the length of the other, whewkow0jthz4k 4b gh 7s6r8p)i1 vgd;1at is the 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 connected to a precision 10.00b4u r6 )/dm --qglvige-V power supply, and a current of 0.4212 A is precisr4li) m6 u/gd-egq bv-ely 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 copper followed by 5.0 m tt.sk5xa d v*s7*hdg( of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is 5tkth*7(ssdv *g xd.aplaced 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 vaa-;/pehoreh+cygw tn 1d,2;x lue of a resistance not change with temperatured+t2engh1a wh;o/yrp-cx;, e. 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 produce 3.3 kW of ( kxdxf1bio: 3h 6vmawb43c1hheat when connected to a 3xm43(hikboxfhd :6w1 b 1vac240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3-ic bx.s3sgw wg;y3b/.0-V portable CD player that draws a maximum o ssx ;bw3g b.ig-w3/ycf 320 mA of current?    W

  What is the maximum voltage that can be ,(ajhf 83brgo.uvu 0q 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 lightbulbco .0g6rk1vc a connected to its proper source voltage 1c.ar 6g0kcov 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 11cp.njy xja e)/;)f1ym0 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 settio)5p1dt 4yj cbngs: 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 Euronka- 6qagni+ *m *dzv8pe, 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 za6+8i*kv-*nnmdqga 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 thfi8;z3 rup5xve morning if it is in operation for a total of 15 min? At a cf ;pvr5x83uziost 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 perzkx/ioidw6m7 rxd: sm)h6s ua2 r/u*: kWh, what does it cost to leave a 25-W porch light on day and night fok/u rr67wsdhd6 *zmxiai/ s xomu2: ):r a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connectebubc br3r8/8vd in series as in Fig. 18–4b (Fig. 18–36). The bulb u vr88/rbbb3c 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 energy stored in a 12-V, gz*8io, m8o91ydjejh n4 y2x- vucwu0 $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulby, k/eksc2d7+ l 8ugwep-j-ths, connected to 120 V as in Fig. 18–20, can be used without blowing a 15-A k2/7,ul yg k-h8-te swdjpec+ fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (ncgzs, lwbcg s,u3 *gvxk3sg/,-se2c*o. 16 copper 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. How much wg*2g ,g gsel/ucs,k -3z3s c,xcsbv*power is dissipated in the cord?    W

  A power station delivers 620 kW of m 4pc8bwdj. b5c7p* zkpower at 12,000 V to a factory through wires with total resist587b bcm*p zwkcdjp4.ance $3.0\Omega$ 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 electroma; cgc ospjl1,hm* c k:zuq/8e3gnet connected to a 240-V line is 17.5 A. At what rate must cooling water pass over the coils1cu,/: sc; kge8mj*hoc3zq pl if the water temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car t 5mr bmj9 1-fz;+yxnkf;+jh 4 xgm.ckbo heat a cup of water for coffee or tea. If the heater can he-r.m jkb++zx 5mm;fkc; g19j4hbnfyxat 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 cur7bww+n+tc8 e,uik8twrent 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, y z+5bmlie h0- 4uf)clis 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 p .+b)8o e+a9axty/c*nd onpsof 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 78vm3rkuqm e :alternating current in a 1500-W device is 5.4 A. What is the r37umrqkv e:m8ms voltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connectrjm3bza 7q; 7ged 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 dissew/ n9q3m9qx(0kru v dipated by a 3.0-hp pump connected to/vk 3 (rqu0dq w9e9mxn a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to ace,fl5bfo:5 gc)ozd1j vy6; n $240-V_{rms}$ 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 cakv 79bzgb 7dwn(he8a8 rries 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-diameter5d -mfenvy lnbc h5w2460y jjl-( dhz, wire carries a 750-mA current when 22.0 mV is applied to its ends. If the drift speed is l bj-2v0nh556 ynwj(efld - dhcy4 m,z$ 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 atmbs tq20cy4mpc9nu i* 4ecyc+oe6 6tx (osphere, $He^{2+}$ 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 atmosphereh57k8wgv pm t*, $He^{2+}$ 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 o so vbrra94,6of the electric 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 potentd i2;e eaqx81oa 4-iohial is detected di48heoax;12- i qoaeat 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 only one?)    m/s

  Estimate how much energy is required to transmit one action potentialgxr ku*jx 0x5b);rn *h along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored by charging the axon0 x;hgr*xr x 5)knub*j capacitance; see Section 17–9]. What minimum average power is required for $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action potential,s 3ewvqtl 3s9/ $Na^+$ ions move into the cell at a rate of about $3 \times10^{-7 }\;mol/m^2\cdot s$. How much power must be produced by the “active $Na^+$ pumping” system to produce this flow against a $+30-Mv$ potential difference? Assume that the axon is 10 cm long and $20\mu m$ in diameter.    $ \times10^{-9 }\;W$

  How many coulombs are there in 1.00 ampere-hqamcss; 7 )g:3ov1ryij;p4gmour?    C

  What is the average current drawn by a 1.0-hphorout( rt,n e9phoq 6627c a: 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of the i+)r m de(mucbq1, g((fm(domh t m5c.two headlights uses 40 W and each of the two taillights 6 r,dm qo tde5 mm (cifmm1)u(gh .+((bcW, 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 11 u1um lrdzxq0y. olg;i);+zp+0-V, 1500-W heater is 5.4 m long. If it is made of iron, what x0)lgoiy u rq;+;zm d+.plz1 umust its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as t,x e* 6cea0pbxhe reciprocal of the resistance R; that x6ap*,bee0x cis, $G\,=\,1/R$. 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 (jlu .e iy;ta-p4lp7s of power. Suppose that instead of using high-voltage lines to sut-4e; upi.y p(sallj7pply 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-kWj h8zjy2th9+u 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(*7nec 1r8 c5 *qd rdbx:oczri two lengths are wrapped together side by side to make a thicker wire. How does the resistance ofzxn*r8 (:crdq*1bdc75ceior this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for (w,oi;vabq/ 6 ygf7: ctxybq9 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 not7o7vhd x a r+.u5u3k9a znuq3l become so hot as to start a fire. What diameter must a copper wire be if it is to carry a maximum c37.7rn la+x u ovud3kzq 59hauurrent 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 ,zp5 0 9sjnjblby 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 run rufwu0*uhz3 d/:fc a6ning at 65% efficiency delivers 950 W of energy per second to the interior. Find u6fr 3c:wa *fdzh0u/u
(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 8u i3.bqs3ba. b)euttp81 k 4s)uethkmade of the same material. One conduct)u8epkb3a tt 8et4q subs).3k1buih.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 is us* s304z2hifeowoar -ved 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 hooked to h d1x xk4g+f ;x f0iqdf0n/mr: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 vehic qvus3mv61fiw 8brj ;8le makes use of storage batteries as its source of energy. It86us3 rvim q1j8fb wv;s mass 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 lightbuw3.zy6wm.8wio:v-n:v-x 7 vk dmqol r lb has a 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 ( 9yas. lxd7 guwd)j*s 2jdbmu y9p5c;an 11-mA beam of protons traveling at verp2adsb 7yddu ).(m; 5uj*9scgwl9yxjy 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 drawspbxaaeg1-+ xh2 9e/ow 12 A at 220-V ac. The connecting cord is copper wire with a diamet/gx2 +bhp9oaeew 1ax-er 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 coj-9 7qtkyxn2v ; c sqy vmd1)vi6q(qk11 +ouqfnnected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.(27q q)nvivy11 djsq q q f9+;vckxmoyt6k1-u8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from abo0z tyui(qi4(e ut 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 die utiq((0 yiz4fference 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 constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for househol 9m5.;*0e+ipbqmml vw v zdds0d applications. Lightbulb B is rated at 12 p+ebs i0 l0vq9 . vmwddm*;z5mV 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 tc z+za8j/lva6 o connect a set of appliances at 120 V, which draw 2250 W of powcz+aj86 /azv ler 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 insinq fdj,2fcer6bb6wi x6u8 e.* de diameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the resistance ,wrjf6ueef6. n dx*6bq 2ic8bof 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that )o6zm y*ok ,tb7n uso8its length doubles, by what factor does the po u o,t m7ksoynb*)o68zwer dissipated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used insa; ak se92i*k a flashlight bulb operates at 0.20 A and 3.2 V. If its re*ka2sia9 sk;e sistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$