What quantity is measured by a battery rkfiu7w1ih w1z 0p9z+9 9vdrhefqk7 u5ating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow away from fh9/ifpkxhd:85 py0an0s*tq the negative terminal in the circuit.f/p0is 8*a9nk5:p qhxh f0ydt But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is u*yx-ipx8kg- tjhq 6y;pr ;9b being used up: battery current, battery voltage, battery energy, batxy;bu-ij8pqk6 -x9ht gy pr*;tery power, or battery resistance? Explain.

One terminal of a car battery is said to be connected to “gro.( q-enl dvb(nund.” Since it is not really connected to the ground((n qlvn-e. bd, what is meant by this expression?

When you turn on a water faucet, the water usually flows immediarwhzkp-(j)v*xwi m 39tely. You don’t have to wait for water to flow from the faucet valvm)v-irp3( *w x9kzwjhe 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 af m:kj0o,k; pfo l*ha)luminum wire of the same length have the same resistanceako m*l0 ,;hpk o:)ffj? Explain.

If the resistance of a small immersion heater (to heat evsd3.x+qz u(l i i*1owater for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the heating proc(ue3dx1szi .q* ol +ivess? Explain.

If a rectangular solwy8p*gfkx y3gg0)y n*id made of carbon has sides of lengths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the l wnk3yy**8x 0gggpyf)east 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 b5f fx.g1vr( axt w;nqe;2 .aqllw;hg(urns out?

Explain why lightbulbs almost always burn out just as they a6 wyu5eal4e6o3jhhnmbxl n 14/0nt6yre turned on and not after they tmlohx/uh1y0 n65w43jnane e4 6by6 l have been on for some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which has the hj eqv*h ubnx4 t;;uo5.igher rq*5b ;o uj4u .ev;thxnesistance?

Electric power is transferred over large distances at very high voltage3o 5dqqwa8;hys3ktuagkh 13-+/6wp c zorq a;s. Explain how the c q 1t w3awq/ksoo8khzh5ap3 ; q+gar6udy;3-high voltage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to repl*)pe: wbqco-lg.gs . ajbrn9;ace this fuse with a 25-s q.nw .gg)p 9jrlabco:b;-e*A fuse?

When electric lights are operated on low-frequency ac (say, 5 Hz), thxqn9oxlprk) t a13x98fyqp1x o5u f- (ey flicker noticea5a1o8 -o f)qrxpuqtylxnk fx1p9( x3 9bly. Why?

Driven by ac power, the same electrons pass back and forth through yo3*q4eljy.kb pc/ keb2ur reading lamp over and over again. Explain why the ligh32ype4 c/lbbq*k .ejkt stays lit instead of going out after the first pass of electrons.

The heating element in a toaster is made of N3424nh ipez wqichrome wire. Immediately after the toaster is turned on, is the cwp24 4qie3hnzurrent $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Explainc tu3(kc58ghisk :x5d .

Different lamps might have batteries connected in either of the two arff2n54* y*usm tntve;6v, aivrangements shown6t2ytvv5f n mse, f*uvi*;4an in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a 530d /wo 4qpfegv(cynwire. How many electrons are flowing past any point in the wire per sen( o/vydp5cgw q4fe30 cond?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A for 5.0 h. How much-f3oy4zy w2e z charge passesywzoy4f3ez 2- through the battery?    $ \times10^{ 5}\;C$

  What is the current in ampe* ma x nte*+e41l4vjfyres 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 cure nmibi7 tp 7f3 5u itk4r6s;nbz,a2r1rent of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A oky*b+fr(f ,s oxob;i,f current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plug4 wzo3(d 3uc *)zmjl/kvlx/.jd ubq w8ged 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 resistance m sxg8jz6 jxi*xy- ij8b+9 l+uof $9.6-\Omega$.
(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 whos;-zpw2f. a7e+z cjtkqe resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc elec kj.cw) :l4qtcn shv7t, 9r8prtric transmission line carrying 2800 A (Fig. 18–34). The lin4srlqv,t9rw 7.jktc ): p hc8ne 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 dra5k4 d4k;xmm ) )cttulwws 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 cause845 bhm;3f4 abgbx;wktdi:z q s a 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 a06b)qrn4e o gb 1.00-m length of tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a7, d7egy:l bqo 3.5-m length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of 9y: wm wkgrp8zvj6c8 7gqn *z3aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in diamg*qjnmrk96vyw8 z:zc7 8wg 3peter.   

  Can a 2.5-mm-diameter copper wire have the st64ux) 2fgvx( lxjxk7ame resistance as a tungsten wire of the same len2f xx g(l4x6u)jkxvt 7gth? Give numerical details.    mm

  A certain copper wire has a7oq6gd 0 h1h.zke5fsy2td9 jn;hd 9mj 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 raisego7c7wt kqhxux5p: 4vdt hy h8;mt:; , the temperature of a copper wire (originally at v:d7 7c;qtk oymx54hw, xuh8t ph:tg;$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what tem)b,jvde,* o cr ;o2wmmperature copper will have the same resistivity as tungsten doem;vr* o),ew jc ,o2bmds at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of qsgg)mzl l+pm(3xv6 x* :vz1-i1xzpiabout $12\Omega$ 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 alon cl:6iv3ohhxtb) 30fwl.bzy,g a 26-m length of household no. 14 copper wire (used in 15-A circuits). The wire has diameter 6iochl3.yb)t,xflv:z3 w0h b1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of len3n6i-s ekdibs n7w w-:gths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for n:wn 6s3i7kew -ib s-dcurrent 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. fmtn:kcs::g+ r d0i7 eIf one has twice the length of the other, what is the ratio of the diamsgdmftk ne0ic +7:: :reter 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 precis(peyhp3 d59arion 10.00-V power supply, and a currente59prh a3y(dp of 0.4212 A is precisely measured at 20.0$^{\circ}\,C$. The wire is placed in a new environment of unknown temperature where the measured current is 0.3618 A. What is the unknown temperature?    $^{\circ}\,C$

  A 10.0-m length of wire consists of 5.0 m of copper followed by 5gy v9/7mqytbf6) 9u vj.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is placed across thejb6tyuf99/g7mvqyv) 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 ofz,q:gm 9. 0rjy:tvcbxhv z u4: a resistance not change with temperature. For example, suppose yhgmcv4u.:v r:yt0z :bx 9q,j zou 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 produnjn qs4i(u e 3ibxh6y(h1 /en6ce 3.3 kW of heat when conneebhxi1(i4ejn n/u y 6qhn3(s 6cted to a 240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD plc sz6wu81m7s*x 3e0p9rti bz s7hoi.sayer that draws a maximum of 320 mA of c7iis 1t73zhr seo*px6 uss mzcb80w.9urrent?    W

  What is the maximum 1)w/9+mgbf l/ 5tjiv+brj; jq ubbxo5voltage 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-W lightbulb conpb7d -ew3 x**6 ptdo, oxn.wxvnected to its proper source voltage of 120 V.-nd*doxv*tww 3pp xb. o,7ex6
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heater is rated at 110 W. Calculate jjf2mpoo5 r3jpyd(5o8n 0 c. p
(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 settinonk w -6+lgle/ea9/i ol8jf*rgs: 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 i2(e *duilou95f 8ehzEurope, where electricity is delivered to homes at 240 V. If you use the lightbulb in the United States at 120 V (assume its resistance does not change), how bright will it be relative to 75-W 120-V bulbs? [Hint: assl ho*z fe(i89d5uu ei2ume 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 is imn *l4f5koysn /3.c jrn operation for a total of 15 min? At ac3 45jnols fkrmy .*n/ 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 cost to le;rr5 p xcd*r rt3ei7m(ave a 25-W porch light on day and night for ad;(rerix53m*7rr ctp year? $\approx$    dollars

  An ordinary flashlight uses th. mnq:s4 (7z7 oknflnwo D-cell 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA n7 f.o4msqlnn(kh7: zwhen 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-f7 8yvo2wp 2wlV, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connected to 120 V amhrzsgl2pq) (cwk j:-:/6ir cs in Fig. 18–20, can be used without blowing a 15pm: zs -j)r2kgircq(hcl/:w6 -A fuse?    bulbs

  An extension cord ma 2 nb ex+nwvv3pl4qf*4de of two wires of diameter 0.129 cm (no. 16 copper wire) and o2xqb v+* pvnwl4e3n4ff 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 in the cord?    W

  A power station delivers 620 kW of power at 12,000 V to a factory through wires vj)xv5k;c lev 6 zx.h;w xjh)evv6z;vkl;c5x. ith 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 17.5 A. At what+yoa.j9x ocl avm0c-( rate must cooling water po0-la+oajm(yvc9. x cass over the coils if the water temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater c l 05xr yv)30ivxx6xxwan be used in a car to heat a cup of water for coffee or tea. If the heater can heat 120 mL of water from xx 0605xv 3wl vxiyx)r25$^{\circ}\,C$ 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 in a 1btq) ::z ,+udrn,qs5slhi yf$2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value-o - gymh4zma zt+qlc z2+ ttx9v,,1xf 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 resistand 0bpek6k(ae:6oyb w3 ce 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 de5dxcw*hh z4ub/ lc/ o.vice is 5.4 A. What is the rms volta .ohuwdx/b h*54l zc/cge across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connecte(t fziq.:va u1d 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 a q)bmg0 50prgpump connected to a mr0)bg 0ag p5q$240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connectedh b3tfea) a97 w+/dnwz 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 a tiny curre/4ih -+7 :ebrdiy;tdo smjdj9 nt 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 mV is1o7gw u8eqqxmsx+bk1 .q*xa* applied to its ends. If the drift speed ae qsw*+bxxku* 1q8.1xgqo m7is $ 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 atmosphere, pq*dz,wai)kl j3yi.) 4ifj.x$He^{2+}$ ions in a concentration of $ 2.8\times10^{12 }\;/m^3$ are moving due north at a speed of $ 2.0\times10^{6 }\;m/s$. Also, a $ 7.0\times10^{11 }\;/m^3$ concentration of ${O_2}^-$ ions is moving due south at a speed of $ 7.2\times10^{6 }\;m/s$. Determine the magnitude and direction of the net current passing through unit area $(A/m^2)$.    $A/m^2$  ----待选择----NorthSouth 

  At a point high in the Earth’s atmosphere, u8 w*mhy/zw 0coi t1u8$He^{2+}$ 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 acrovnqc.enw* q)snxs6g;6o js -)ss 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. T2 pi5k6m nybo0he action potential is detected at a point 3.40 cm down the axon 0.0052 s later. When the action potentibny2m 6kpoi50 al 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 to59(o +ziip-0tpca bz wm :ku1b transmit one action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored by charging the axon capacitance; see Section 17–9]. Whazpuc 9wk i5bo1bia t+ (:p0zm-t 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 potenti0;p o9f,ncplval, $Na^+$ 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 inzk* s7+9 daqpd 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0-hp 12ff;u 7 qaumc/)cp v-hdvo;s+:0-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of the two y ylsfewli +5g9)))nn)s al4 rheadlights uses 40 W and each of the two taillights 6 W, for a total of 92 W, how long will a fresh 12-Vf+lyn 4 ae5 nsr)g)yl)s9 lw)i 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, 150srw- ) r;tp3/aqsm3qa0-W heater is 5.4 m long. If it is made of iron, what must its3a-;aprmwqt/) r 3sq s diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of exbq .guzh *kxca 68z/.q +wu4the resistance R; that i*. xw6 q+uba/e8zq khg .zx4cus, $G\,=\,1/R$. 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 ab1lg, w (7jflkkout 10 MW of power. Suppose that instead of using high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a gl7 k, w1lfk(jtwo-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-kW heajv lm7:u57p gata)o9hter $3.0 h/day$ (“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 an)9z;jph t*y rhcswm3;d the two lengths are wrapped together side by side to make a thicker wire. How does the resistance of pw ;jh rt9my)hc ;3s*zthis new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 117 V. k7mc a, , aq.d,nk( dkiih:+rb
(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 become so hot as t/*9 o jsjzxoe32utmei((3n roo start a fire. What diameter must a copper wire 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 lengn u*oire9ojmt3j2xsz o((e/ 3th?    $ \times10^{ -3}\;m$

  Suppose a current is given elk2j dyv*g ao)1pk) 3by 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% eff6iady9)y 5 zxbiciency delivers 950 W of energy per second to the iaz5ib)9yx6d y nterior. 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 conductors made of the same materijd g wwul;3k9(opw 5g+06 woioal. 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 second3k;w (g0wu+d liwo9gjpo56ow? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat asl b)g/hb*kmwh/ e+bxx7 59o2 kh.d jj 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 + deokpx5s,:1f-t dl.,i:n6o lpuco j 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 batteries as its source of gj ) zw jecq8j(qbu7nr/tgual1:43:w es lp9,energy. Its mass is 1560 kg and it zl)ujwtbje4sp c:g eq wj3ru:/l7(91q ,ag8n 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 r1u ,zd64 kpbipesistance 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 11-mA bnt cn kf3k3(g-ar+gsss* jm3 5jjdo7m) a4;z beam of protons traveling at very nearly the speed of la n nmsgr+*5kgb4fj zo3kss(; a d3-7jcmj)3tight ($ 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 dra7dhjc 1ryt9pgy e7 1i7ws 12 A at 220-V ac. The connecting cord is copper wire with a diac77jry 1 ht7de 91gypimeter 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 conn :ev2a) t arodz5:zta8ected to 120 V. The heating element is a coil of Nichrome wire. When unczt5t a:va2or z:)ea8doiled, 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 voltagdf -oatd-n;y x w4l+ s.e)b5gte 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 headld nx-d f t;t.wobel+-y 5sag)4ight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V a.md 9szemmu/y;jc* 9e, cnog3r) z wf)nd 40 W for household applications. Lightbulb B is rated at 12 V a3zw* dce m.m9s,ymnzu/r) o;cf9)e gjnd 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 t(b+8 1-m tmradkq-yz 9ew o5v0.259 cm is used to connect a set of appliances at 120 V, which draw 2250 W of power total.yv- t8mq ramte d-owz91 k(+5b
(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 diameter of 5bi,hgq*9z 2q v.00 cm (Fig. 18–37). What is the resistance of 10.0 m of this pip *zqb ,29gihqve?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is7jq 92ztmre gpho t4*xs e.0ao41d a)f/q.ucl stretched uniformly so that its length doubles, by what factor does the power dissipate17pso0hfq e.*jzg rud x/ t2ea4qm oclta.4)9 d in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bug umrlz;t, 02l9g2xqblb operates at 0.20 A and 3.2 V. If its resistance at qbtllg 2,90uzr; 2gx m20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$