What quantity is measured by a battery rating given in ampwjnp4zhs)h;9x. n wr9 ere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow awa cf:x a,p upigl23nn 9,z2met8y from the negatx ,z3a2pn,plmc 8:2 n tguf9ieive terminal in the circuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battery current, batterygjy0-7p4ccb 6/a+gg ma uu:kb voltage, battery energy, battery power, or batter ku g7a+jg/bp: gyc6-uc4ma0b y resistance? Explain.

One terminal of a car battery .tijdb/r)f 7 yis said to be connected to “ground.” Since it is not really connected to the ground, what is meant by this exdf /jt.y7bi)rpression?

When you turn on a water faucet, the water usuallyfxa0i 7u0 ajn 8*dk sjsw6xv2- flows 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 terminaw fdvj 7nu*0- x6ai0xa s2sk8jls of a battery?

Can a copper wire and an aluminum wire of the same9m6go83p6qwi*a,sw 2/eo tnhun f 0 fcsq,)ms length have the same resistance? Exps,fpo,0nq f86 36 *wog2q sm/semwi)utnac 9hlain.

If the resistance of a small immersion heater (to heat water for tea or soup, no k 7d.d jbcmv p:*cdn/lkz9 /vgv590Fig. 18–32) was incrl5d g 9ck*kv:j/dv9 cb./z0vndn7po meased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carxgx 8ac 32 :qtvs6-rvrbon has sides of lengths a, 2a, and 3a, how would you connect the wrc sxtrx32v8aqg-6 :vires from a battery 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 buztb*dm)wom dmv(v).,xq 9r) y rns out?

Explain why lightbulbs almost always burn out jomv4 sgoo; u)i.gi6t; ust as they are turned on and not after they have been on fog;)m sg4ovti i o6;uo.r some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Whaz 8buirl9l0v z0 g*p2ich has the higher resistanp r8z9 *0z ibullvga02ce?

Electric power is transferred vb pf oo. ovc0e0rsmpj7203h1over large distances at very high voltages. Explain how the high voltage 2bj000cvvopmf ho .e1o7rs 3p reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fuse wi8gm uq5 1pzg5 oahw- 2eazh*,dth a 25-A fus q82 gpzou5,a- waeh*zmdg51he?

When electric lights are operated on lo4* pd:dhnv lq05i:nsznxst39w-frequency ac (say, 5 Hz), they flicker no* zl q5sdnxv:dh :n4psni309tticeably. Why?

Driven by ac power, the same electrons pass baq+vdra h cjgqiw 1g v1qm9i6d*.-.7vxck and forth through your reading lamp over and over again. Explain why the light stays lit instead of going out aftera*1 -j vi9+q.ghvw q6cdv7grmxq. 1i d the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. Imm3+xcd k82gjg2rce p q.ediately after the toaster is turned on, is the dgckjxec +2.rg3q82 p current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up inls)0 7zvy 5oc1afjo7y a resistor? Explain.

Different lamps might have batteries connected in either of the two arrangemen 7)0qyhpsb.n utbg .u0ts shown inh bb0y0 )u.qtnpu 7sg.
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 5)k6bc o d ro9jao,nq(past any point in the 9ak jb d,(6ooqn) rc5owire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a cuirhrm*ck* oo05(dn 4i bs )y/srrent of 6.7 A for 5.0 h. How much charge passes through the battery? i b s *kr*yrhm/()sd4oci5on0   $ \times10^{ 5}\;C$

  What is the current in amperes ifb3iog.5bcqa,/ ee;bi $1200\,Na^+$ 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 tom q)/ jkoeil75y m,o+vaster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of curren * i,w*12nx7swacytxw+li ; 0lsg 69dx q;pggmt through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when 7cn dlm( w:m6-j ehili06fkm2plugged 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 drtk pn:lp x5y c4ha2 ,e9l9c5wxyer has a heating element with a resistance of $9.6-\Omega$.
(a) What is the current in the element when it is connected to 240 V?    A
(b) How much charge passes through the element in 50 min?    $ \times10^{ 4}\;C$

  A 9.0-V battery is connected tdaef;iz)o l7: o a bulb whose resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transmissio+apy em* 2e.kin line carrying 2800 A (Fig. 18–34). Tkem+.* ipyae2 he line has $2.5\times10^{ -5}\;\Omega$ resistance per meter, and the bird’s feet are 4.0 cm apart. What is the potential difference between the bird’s feet?    $ \times10^{-3 }\;V$

  An electric device draws 6.50 Absbyl:b fv3m h)ir+xq9,l *, h 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 thro2f1qf :aza 3)rkw:f ofugh 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 lengtjev p:m1sx p/i2v1mr 9h 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 diameter?hl;*8mms p 4i* pkn+zx    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of -uy4-il0oek gg2wm9 l the resistance of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copp2i wm l--yeg0lk 94ugoer wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance nk/-d1wyzn vex1bif(c 62 3rrf /u.unas a tungsten wire of the same length? Give numerical detail1kn/6vn- ru1/u2x3d efbcwz n.(yrfis.    mm

  A certain copper wire has a resistance of dw2 v7lwjj7v16aquw4c h a(o.$10.0\Omega$ 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 (originalmd-j y+4r w;mm+4 re5ew,ruslly at sme+4yrweuw m4,j; -mlr+r 5d$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature coppebhhm m:: 47tusbrs:2 a psua:+r will have the same resistivity as tungsten does at ::2r b pbhstah+:msuu4m as:7 $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance on/u..1jz neq jf 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.l* d-a b(t,ptm 14 copper wire (used in 15-A circuits). The wire has didtt -pl(,*amb ameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengthdv6s/tz9gbsod1t edl 83pn,/s 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 current that pas1zdbs,t9d v/d teo/ pn3ls68 gses 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 hr 3us* 6tnzg .p/o1cer;fb/:yux; jnlkev0.eave the same resistance. If one has twice the length of the other, what is the ratio of the diameter of the longer wire to the diameter of ek6cnuu.z;erny l; v:o3j/ s/bf1ep 0x.t*rgthe shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V power supply, and /y /j3a,sm ek.bnc 9n4ufz;u ka cur3.nz 49e ;//umkn f,csjukbayrent 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 followe 2nq xrxgv,e:w-7tlh/d by 5.0 m of aluminum, both of diameter 1.0 mm. A volta/,2nxq7lh v r-tegw x:ge 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 n o4i;bumiag/2sy w -;the value of a resistance not change with temperature. For example, suppose you mab-4;an/yso i 2; mgiwude 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 2-vtmbc- yew03.3 kW of heat when connected to a 240-V source. What must y -cwbtm-02v ebe the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable Cok2f9/8mb4 gb* ggtzt D player that draws a maximum of 320 4t gbg8b2m/k9 * fgtzomA of current?    W

  What is the maximum voltage that can be applied across a .mkl .w k*p-0qo) lvmg$2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and cu- 0ev*b0j qvsl1h*g vtrrent through, a 75-W lightbulb connected to its proper source voltage ofs- jv0q0 *te1l*hvg bv 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/x4jtpzh .,h9igt :asjz l8x: 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 1-8 7 cxu,)oa-r ynl( brcntb+f250 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 electrilnxn:vwett (.qh/4fs7 jcv+7 city is delivered to homes at 240 V. If you use the lightbulb in the United Stat+7nvs ftx/q:4(cwth7 l.jnv ees 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 is inah2s*3w icm-y0bda +w operation for a total of 15 min? At+dha b i-s*ymw32w ca0 a cost of $9.0\,cents/kWh$, estimate how much this would add to your monthly electric energy bill if you made toast four mornings per week.
energy $\approx$    kWh
cost $\approx$    cents/mouth

  At 0.095 dollars per kWh, what does it cost to leave a 25-W porch li yr2cn/sjrt/5)1 fi l4 rkm-flght on day and night for r 4)trckflifjym/s- r/51l 2na year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V bawg;,:sqmse k)tteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when turned ;m)e,kq: ss gwon.
(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 7* sisimc:jngs1q16vv j ns.7 of energy stored in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, conneciq8zy ygiq + c(5y4k,jtw *x3tted to 120 V as in Fig. 18–20, can be used without blowing a 15-A fuse? yzjkc ti*58g+y4yw q(,3 xiq t   bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 copper wiri)tumq lj h pg2+cs50,e) 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 dissipateup2 gc+ h)ij5,ml0stq d in the cord?    W

  A power station delivers 620 kW of powkv+i 2vb (vh/iw)fsu1er at 12,000 V to a factory through wires with total resiish2( fv+)v1 uwvb i/kstance $3.0\Omega$ 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 17.4k vaur, pjyybvw, :/85 A. At what rate mujvv,yrbu/a4wp8yk: , st cooling water pass over the coils 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 to heat ad ,+8 xtchd/ca cup of water for coffee or tea. If the heater can heat 120 mL of wattdd +c8 axhc,/er 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* 0d+zfc.q04d eeexx6rbo wpo:ie. w5nt in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak valuelucdc n9l79g* zjdclo6 6v/.l is 180 V, is across a $330-\Omega$ resistor. What are the rms and peak currents in the resistor?
$I_{peak}$$\approx$    A(retain two decimal places)
$I_{rms}$ =    A

  Estimate the resistance of thej*+ 8sah3n ejo $120-V_{rms}$ 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.2owrc0ys4r1x e ( bph device is 5.4 A. What is the rms voltage acro.es24 (y rcorhx 10bpwss it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected to a8vy1 4 rsqkd*p $660-V_{rms}$ 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 dimhos -lfx1;qxbh1 *)(dd/og mssipated by a 3.0-hp pump connected to hh(m-xs 1;fb1m oqdgxd/o)*la $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connectedj1z7ir/g(h 7osh fbg+ 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 w gcor2rq78 odd21ya +n)ku0iwire carries 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 mV o;l 9p h2myqx0hm*acn)o u l1rp3(gt2qm(5kois applied to its ends. If the drift speed i*l; 5 t(nk(2mpc guom )3q01xhqo hyamo2r p9ls $ 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 thot;z kmww 3b2 r-w3yuwf0-oj6e Earth’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 xfq26j- ;u cerEarth’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 av;mvoii,7uv :7 c mm)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 elecbd6nde- ft) 1e6j me*ztric pulse. The action potential 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 instead of only one?)bfm1edzd -6 tnj*)e6e    m/s

  Estimate how much energy is required to transmit one action potential along the1f9co;pn3 t , kcjsb(v axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalkcfo;t p1b 3,v(scnj9ent 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 potential5 f,jkn4) ;0gzluaxup, $Na^+$ 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 2nh,fl,ym;yrcdhaw cd 8/t6 2 there in 1.00 ampere-hour?    C

  What is the average current drawn by a 1.:8 x f-syr)rpb0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. afjpwq,y+:zx*84nw bIf each of the two headlights uses 40 W and each of the two taillights 6 W, for a total of 92 W, how long will a fresh 12-V bat +wb4w ,f yajpq8x*z:ntery 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. If it isp.d1j* 6q gimca,shj;t ;1npu made of iron, what mustq ; j,c16*madhtj; ipu1 .gspn its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of a yat 43izqh0z:n object is defined as the reciprocal of the resistance R;:i hq0t43azzy that 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. Suppi xc9/wkp+qjem 1fngb;d0r hv80i,q 7ose that instead of using high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a81iqmk7 hv ,idq9;c0x0rw/fb+n jp ge 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 usew8j krq n-.(3 evnntmu uwcw4(+cvg78s 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 z;55xczrs,ujk s/ t3 w gbv( 0pqa3uz2half and the two lengths are wrapped together side by side to make a thicker wire. How doerwcj,gb v35/uq; pa3 (tzkzusx52s0zs the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 117 V. qg/c esjr-ays/86+ cf
(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 u3olklq6, uu,v.d d:bit does not become so hot as to start a fire.u.3 :v bld,k,oduuql6 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 length?    $ \times10^{ -3}\;m$

  Suppose a current is given by t bybsb .+,2ueshe 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 runn9xy/nddrekj: 3g**g zing at 65% efficiency delivers 950 W of energy per second to the interior. Fine*dr/ zy9 xgjd3gk:n*d
(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 9-f vf.ba5 jvsx f5i7dthe same material. One conductor is twice as long and twice the diameter of the second. What is the ratio of th9f x bs.vi-j 5fafd5v7e power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used t; 4pody xi/q)oola,boj2r ha03 (:jzqo 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 a 240-V sou-7vdzeqv,jk 3 rce.
(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 storagey7e;5u ct bkxx2h *f5t batteries as its source of energy. Its mass is 1560 kg and itk *t;x5che 275fxuybt 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 lightbulb03e dwy, ln8rm h5gr8g 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 accelera5)8jqt pav w4ptor at Fermilab (Illinois) is designed to carry an 11-mA beam of protons traveling at very nearly the speedv) 5w pjpqt8a4 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. Theursqd65 fq:k( connecting cord is copper wire with a dia 6q:rdkf5qus( meter 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 ratedn *0o;-obk4t7 xel 8wvh(hvw c at 95 W when connected to 120 V. The heating element is a coil of Nil-wbw* evt(0 4ho7 onkvc8 ;xhchrome 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 v-vet 0b -i1gpiaries 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 tg 1-iiet- 0bvphe 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 household applications. Light8-ht, v bz4ypxbulb B is rated at 12 V and 40 W for automotive applicavtx p zb-h8,y4tions.
(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 connec asbuv+ 0z9yhak+2 k(bt a set of appliances at 120 V, which draw 2250 W of power tota2zvs0bb hk( y9k+ua+a l.
(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 ins rbyt5,-0lfqrp/ )wfw ide diameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). Wfpr,/w ywtbfr0l -)5qhat is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance Rlm9 +i rx/o.xlg4lwc* is stretched uniformly so that its length doubles, by what factor does the power dissipated in the wire change, assuming it remai9rx i omcwxg/4ll.+l *ns hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operatej(s m+sk6 ,fs3i*ybs ms at 0.20 A and 3.2 V. If is f ,*ssm6kb(mjs iy+3ts resistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$