What quantity is measured by a battery rating given in amp.)ij( e gvr popty8-oe23pi6 yl/;y mcere-hours $(A\cdot H)$ ?

When an electric cell is connected sa1a n2g2wpe4aaq.drc, jg0* to a circuit, electrons flow away from the negative terminal in the circuit. But within the cell, electr*c2r sa a,aegpdan21wj4 .0 qgons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battery current,x)o- umkr5 gi- battery voltage, battery energy, batgmi uxo- )r-5ktery power, or battery resistance? Explain.

One terminal of a car battery is said to be connected to “grozlrm-xg5;3/spdisj56p sz (6why h 3n und.” Since it is not really connected to the ground, what is meant by this expresl (-r p h zyhjz65/gswnd3m3xs5;6sip sion?

When you turn on a water faucet, the water usualljhg :i9uv/xj7s(f 9x fy flows immediately. You don’t have to wa / j9iv7h uxf9j(:sfxgit 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 terminals of a battery?

Can a copper wire and an aluminum wire of t; fempg sb7d8,rn fo7*he same length have the same resistance? Ex,end7r8 7fm* gfo;bsp plain.

If the resistance of a small immersiok ybtb14oe:g (n heater (to heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the 1t4(k geoy:bbheating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, and 3a, how ful .osn()a, p :(ziaewould you connect the wires from a bat() ia zaonsl, ef(:p.utery so 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 w: 0xpa7aq, vw2moed+out?

Explain why lightbulbs almost always burn out just asjt gnjwx,4ex ir92unmyp8 a3 92 1r3lu they are turned on and not after they have been on for some 3i249la j rx8tujx3ue,n wm9 rn2pg1ytime.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which ha sc:iv1y5 q83s0oqnv ms the highervs 3msvcoy iq1q085n: resistance?

Electric power is transferred over large distances at very h5orgo noogtlu9c)m -,hvd: -iyp)- l2igh voltages. Explain how the high voltage reduces power losses in uopg,-l-ri59 m dy2chonlovt)go)-: the transmission lines.

A 15-A fuse blows repeatet9ib77rvi r(zi re5r74o2hq edly. Why is it dangerous to replace this fuse with a 25-A fie4 rb(75 r7i etr vq9ih2zor7use?

When electric lights are operated on low-frequency ac (say, 5 uw:-alor+g2h,v jv: i Hz), they flicker noticeably. orlg :v:2-h w,ua+jiv Why?

Driven by ac power, thdcx:z vcu- 3kdm -91 tq9hae0pl*l)fhe same electrons pass back and forth through your reading lamp over and over again. Exxq -:v1a )zl0 edc -hd thk9lupf9c*3mplain why the light stays lit instead of going out after the first pass of electrons.

The heating element in -+lc g0wrkt2 .va) jyda toaster is made of Nichrome wire. Immediately after the t-v02k.tg j+l )wycadroaster is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Explain..1b,neq bdx4hqe( t *o

Different lamps might havecdr4 n;/nx9nj* mqn;t bs.s9f batteries connected in either of the two arrangements shown in jnxm9c4;/;*f snsq tn 9ndbr.
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 fmzz6jmc 7rdf+y lm-; 8lowing past any point in the wi8lm- y7rdmzj6cz fm +;re per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A for euts/ib bxuc3jv)p, qf 47*7k5.0 h. How much charge pass,vp7*be3fb s )t7uc 4iq j/uxkes through the battery?    $ \times10^{ 5}\;C$

  What is the current in amperepg695mjp- l v ouop0d8s 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 4aco-.4b xvo1 m.2 A?    $\Omega$

  What voltage will produce 0.25 A of current through .rkm*d3byfs) a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plut3,.hv4nzim w c4b9ld gged 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 heg g,bt3x-.yow ating 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 whose resistz x3jt)8 m0vqyance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transmission line carrying 2800 A (Fig. 1v-s g9ai05w6yw,rwa m 8–34). The line wa -gs,yaw i56wmr9v0has $2.5\times10^{ -5}\;\Omega$ 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 at 240 V. zp*p9mqnd 8 6jr2 ljo5
(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 :j.l/1xn,yc..ygn ds agles* 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 e*ts* /e9tpgpmvk 5 v7of 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 copper wire 1.5 mm in z d4ey-05dyvltf r.r+diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire 2.0 mm in diajl)1 z irlt.c,n+ih5dme)zjic+ln1.dtrlh i, 5ter, to 20.0 m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resista+640zm kov lt;tcxq 6ince as a tungsten wire of txc4kmizl66 tv 0+q;o the same length? Give numerical details.    mm

  A certain copper wire has r m+u+d- sp(*i t5hzxoa 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 temperature-2-kw2stay cl5 5 uiw+gxkp7w of a copper wire (originally atwykt5apw- 7sk+cug wi x2l-25 $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivity as tc b7gp- outl (1plou 6.jniu9;ungsten doesjlpcnbo9p.u- 1 ; u( 7ui6tglo at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of abou uj is;x9(oq 0j,ppr0db49kji-iobe 2t $12\Omega$ 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 copp9d l; yuzh l9+fkdmi+(er wire (used in 15-A cirf;y9+ dzlikmd + (hul9cuits). 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.b060ssnqusr o3 : v +;tvar1tc0 cm, 2.0 cm, and 4.0 cm, lying alqt; 3s+1rn0s s tau6b:v 0ocvrong 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 twi(3( sz2q,noh tjn 8/faf gq2euce the length of the other, what is the ratio of the diameter of the longer wire to the diameter of the shorteotu/q, g f j( h(as8nen22qz3fr wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connecovril6t(cs/m4. c:w6 erm / iyted to a precision 10.00-V power supply, and a current of 0.4212 A is precisely measuredy/src 4t v/cwmimo6i6(le:. r 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 p.0a,jdeuqn+ke 2o;)kj 7zy frp+z, r m of copper followed by 5.0 m of aluminum, both of di ; reazj j+fq 7nr.k2pp) zuod,,+key0ameter 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 va .l3zi9q qh jjki6)q6blue of a resistance not change with temperature.il6h3.qibqj z j)k9q6 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 c2b+8(o yxp rhan electric oven is designed to produce 3.3 kW of heat when connected to a 240-V source. What must be thp x8ro b2+yhc(e resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player th92 lxmj:wo+ iv7a+/.tw vst ytat draws a maximum of 320 mA oalo+j 7w+svt.yi tt :9v2/wmxf current?    W

  What is the maximum voltage that cal -pnl1-ip up+12 *tv iaitec-n be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance owi/-v t. *wzhkf, and current through, a 75-W lightbulb connected to its proper *.kzh-wti/wvsource 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 -h+ k,kzu*uj 5p1ubz wrated 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 two settings: 850 W and 1250 W. sgwh+xs:m/8)ce :hqwut0 : we
(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 electricity is delivered to homes at 0,87x s ou65e2mjlspzd0pv-oxv*b pi240 V. If you use the lightbulb in the Un6pd8s xbl,0j e*2mvoxpi sv-u5zo p70ited 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 it isbk-w1.(kmo)ik;fvsk 3g) kpy in operatio pkvok (sym )w)-3g ki;fkk.b1n 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 does )ip;6g9wp lr g h t3g4ugfgf97it cost to leave a 25-W porch light on day and night for a yeag7u g 9pgr f4)w3 6it;glp9fghr? $\approx$    dollars

  An ordinary flashlight uses two .e2hmpn5w x7pD-cell 1.5-V batteries connected in series as in Fig. 18–4b (Fig7wxp5.m2 phn e. 18–36). 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 jl y44 vezi79eenergy stored in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbsea k5 ;7z9weab, connected to 120 V as in Fig. 18–20, can be used without blowinz5wb7; a9kaeeg a 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 copper wire) jy yi i2ewnt1k5 7cd6.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 power is dissipated 2 7y1j wdyci5te.nki6in the cord?    W

  A power station delivers 620 kW of power at 12,000 V to a l z ,-j,as9 wxkwn9/vgfactory through wires with total resaj v ww9k,,l ns-/zg9xistance $3.0\Omega$ 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 d 14e1 dytgl.,f9hvora 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 7.50gl 1ryote.fh1dd,49v $C^{\circ}\,$?    kg/s

  A small immersion heater c - ,j.ym dw 1b,ir:nuxejg;bs7an be used in a car to heat a cup of water for coffee or tea. If the heater can heat 120 m r w i,s1u:7bj-.xjb dmne,gy;L 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 currenjtzlm2 k (+ pw0f.+3z0jllqnr:dt/jz t 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 qvy.paxv1)gmeh6(s +m c7mz;c6 keku fh*(:j, 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 resistani:u s4xq6g *-qtz 0vdr35ku hnce of 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 dev+kf 0oy7rv dgcj06 9qrice is 5.4 A. What is the rms voltage across+ydr0q 0 j69fgvro7ck it?    V (Round to the nearest integer)

  An 1800-W arc welder isynihyj-5 :( -s jf r,ne7)f6xvfz wpv) connected 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 dissipated by a 3.0-hp pump connlp+q( vk4 lgsla;r.32,o tb dmcf 7d.vected7+ lbdkg 4v(pa q2ltsfd, m;..rvl co3 to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to a /gi ein,jc.v 11es4chzn6 b5j $240-V_{rms}$ 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 kyy1wgene q6y 35h zak(3t (8 9:tb3ayf/ljihcarries a tiny current of $2.3\mu A$. What is the electron drift speed in the wire?    $ \times10^{-10 }\;m/s$

  A 5.80-m length of 2.0-mm-diameter wire carries a 750-mA current when 22.0 mVu69v -v;gzuwfv 1s6-wyp - kdw is applied to its ends. If the 6 9v-w1kupfw6; dvv -gws-yuzdrift 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 Earti q-t e:boqc:3tmwpr+pl9;g n7.w1j eh’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 Efxdz,7+we* 3l i3 sghbarth’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 acrossouzl*i i.7/2 kqrk g(q 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. Theh tj5wyb4/ dd+ action potential is detected at a point 3.40 cm down the axon 0.0052 s later. When the action potential is detected d5+thd4wb j/ y7.20 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 potentiadhm4 2e3zz5 8tkkg u-al along the axon of Example 18–15. [Hint: the en2u54mk tze gkz d-ah83ergy 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 potem mgct+.f 3j7ivp *gk.ntial, $Na^+$ 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-houwc7t g.sm xq77g4iv: or?    C

  What is the average current 56s ucfi ,ax i58javh.drawn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lig 5b9pbx:(s+vq *ffn:0 hge.grir-am phts on. If each of the two headlights uses 40 W and each of the two taillights 6 W, for a total -r: p xv(p0+r fgb*eg5 9ba sqh.:infmof 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 ks* mpe2 jb- 2ymto,+ y6mrs,k110-V, 1500-W heater is 5.4 m long. If it is made of iron, what must its diameter bee,-yssp26mj yt k* m2mr ,kb+o?    $ \times10^{ -4}\;m$

  The conductance G of an object is fx mle0,j5b1m d+kr z6qz( i1udefined as the reciprocal of the resistance R; rkmqj i1ul f 6150,exz(mb+zdthat is, $G\,=\,1/R$. The unit of conductance is a mho $(=ohm^{-1})$, which is also called the siemens (S). What is the conductance (in siemens) of an object that draws 730 mA of current at 3.0 V?    S

  A small city requires about 10 MW of power. Suppose that infl, /gmo.wh -tstead 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 ,o/ht- w.mgflhour per meter. Assume the cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular house yp8. k91uk-edak5:yzw h0rqj:fyl o1hold uses 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 sidx*s:krg,s q uy(l/3vhv :o pp9e by side to make a thicker wire. How does the resistance o3::uk(vlh,xvy/p *prsq9 og sf this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is g5y6rl wot+rue 0l9m3 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 so it does not :s6,/chpz8kj lchi 8uyr6 e*a kl47qpbecome so hot as to start a fire. What diameter must a copper wire be if it iy7rusz6k eh,4l8 6p8*kq/l : ai phccjs to carry a maximum current of 35 A and produce no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by the8:kiv sm2 )fsz 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% efficqv;(t ei8atg2 l2p0qcfk adi 3il(-l (iency delivers 950 W of energy per second to the intea0l ct(e28a l3qtl2p(f d;i(q-i gkvirior. 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 conducto 1o255i+ yk9ujan 1gp5cguqlnrs 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 go 2l9cukj5 pgn+a55 11y uqnisecond? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room of volum) lit 7iur,kf pm;agt7w2)k6z e $62\,m^3$ 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 240egu6:9qzgf/l9s3 iwp -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 ict3 0ic/mlqs3vpqf 9 ,ts source of energy. Its mass is 1560 kflcq0,93 vc3t pi sm/qg 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 resi:cuv7.c wks (astance 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 acceleratzu c+.t ;z)ehg7fb 4buor at Fermilab (Illinois) is designed to carry an 11-mA beam of protons traveling at verytb);4zufb.uzg+ he c7 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 at4p rczdiw bo+) t pp6f:).p3av 220-V ac. The connecting cord is copper wire with a diameter of 1.6dp b )3ip 6wv:z)ar.4octf+pp 28 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 12 -b 057kr/d v1k;gtibv4pr yny0 V. The heating element is a coil of Nik 4rb/v7iykpt; r1 n5yb vdg0-chrome wire. When uncoiled, the wire has a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from )fb.bz( qb5igwdjd:o8p8*m mabout 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? As ji5bdw o 8dpb.b) (z8m*gq:fmsume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for household applications. Ligh:n wt/dqai6c6i40vx dtbulb B is rated at 12 Vi0wq d/:v 646an xtcdi and 40 W for automotive applications.
(a) What is the current through each bulb? $I_A$ =    A $I_B$ =    A
(b) What is the resistance of each bulb? $R_A$ =  $\Omega$ $R_B$ =  $\Omega$
(c) In one hour, how much charge passes through each bulb? $Q_A$ =    C$Q_B$ =    C
(d) In one hour, how much energy does each bulb use?    $ \times10^{5 }\;J$
(e) Which bulb requires larger diameter wires to connect its power source and the bulb?  ----待选择----Bulb BBulb A 

  Copper wire of diameter 0.259 cm is used to connect a set of appliances at 120 V9) bvkx3nib r*n/8s,9rqhhuf, which dr k, nsh8*v3nrqbfihxru /)9b9aw 2250 W of power total.
(a) What power is wasted in 25.0 m of this wire?    W
(b) What is your answer if wire of diameter 0.412 cm is used?    W

  A copper pipe has an inside diameter of 3.00 cm an+y:o a2gqi0/ch n4 rsfilf)8zd an outside diameter of 5.00 cm (Fig. 18–37). What is the resistance of 10.0 m of thiai/2 nz8:cs 4i0lyf hoq)gf+ rs pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance t vfn) 6(wd+biR is stretched uniformly so that its length doubles, by what factor does the power dissipated in the wire change, assuming it re6db+w (t)nvf imains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operates at 0.20 A and)h xh75xlf1c p 3.2 V. If its resiscp175)xh xh fltance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$