What quantity is measured by a battery rating given ing6 ( *ia9st4sgl8pbi s ampere-hours $(A\cdot H)$ ?

When an electric cell g3x g4 5da9jv6q 5so1vg5am dmis connected to a circuit, electrons flow away from the negative terminal in the circuit. Buv 4xo35q asvggg9 5mmjdd5a61 t within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, whatf*a*ubscm;zvf k-4b gwu;90 x is being used up: battery current, battery voltage, battery energy, battery power, or battery resista vb*4f f0czask;wu-x*b ;umg9nce? Explain.

One terminal of a car battery is said to be connected to “grougt(c-k h yf)9ynd.” Since it is not really connected to the ground, what is mf h)yc( k-g9tyeant by this expression?

When you turn on a water faucet, the water usually flows immediately. Youh 6bdo-:q ,o2ujfd2uu 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 o dfhdqo2uju 6ub:,-2terminals of a battery?

Can a copper wire and an aluminum wire of the same l3w /lj m2pzv ugg d2tm9,)tfk4ctj6q:ength have the same resistance? Explait)g:,/6 mcwt3v luz9j 2gmdtp fqk 42jn.

If the resistance of a small immersion heate3uqoeqh0ql;5y p iy+/ r (to heat water for tea or soup, Fig. 18–32) was incr+yei3; q/qlpqhy0 5ou eased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides 8 bt7kx;ze ft21s in zbf5l6*inbf;3fof lengths a, 2a, and 3a, how would you connect the wires*btn f31f n6f;iitlkzfbxb8;5z27 e s 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 li ii,7st+d*4mmu 17bcujpa ;w zghtbulb burns out?

Explain why lightbulbs almost always burn out just as they are turned on anl;mgld u.s efu 02ye qp2t9 znz)h7.m0d not after theytqs nu9m.)e 2dz0f. 2mg7ezllup 0; hy have been on for some time.

Which draws more current, a owq9d;,v3 kag100-W lightbulb or a 75-W bulb? Which has the higher resistancdkq,9a 3w vg;oe?

Electric power is transferred over large distances agi):a+;vk dzy.t/n y 2dio se*t very high voltages. Explain how the high voltage reducesa vt ei;ks):z.g/d di+*2yo ny power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it danger-chiuyl a( 2m0ous to replace this fuse with a 25-A fuse?liu- 2ya0hc (m

When electric lights are operated on low-frequenh-9m*+5 nn k t*nqmqqjcy ac (say, 5 Hz), they flicker noticea + *n-nmqj tq5qmkhn*9bly. Why?

Driven by ac power, the same electrons pass back and0 jw6.qk( trbwdhs .uh j6(yz8 forth through your reading lamp over and over again. Explain why the light stays lit insb qu.k (yjh8hs. w(0dtr6wj6ztead of going out after the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. Immediately aa0gb 92qrs3 s4p1aodl fter the toaa143s sa9q0gl2rd bp oster is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a d zq0uzh:opnxg4uo+7y -9 /md resistor? Explain.

Different lamps might have batteries connected in either of the tyco8 6)b z)i ahtnl/mg7(o/ d j,uc,aiwo arrangements sho/ic, uyobj(g76h l8cat aozdi /m) ,n)wn in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many elel0u*wic i/b2gz y c4s1r)wku. ctrons are flowing past any point in the wire per se u.0bi4z kyci1rlg) *2/scw uwcond?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current n+vp4m1yh/cedto( / x of 6.7 A for 5.0 h. How much charge passes through the b/pe/hv + tdy(4 nxmco1attery?    $ \times10^{ 5}\;C$

  What is the current in amwovji d.*y mzci,9 16lperes 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 cur. y mw;3zhhe:crent of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current t91jm 0f1ns btvhrough a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-Vgwfx/v4ee h8 ( 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 dryx5uo n )whf);w0 h*oazer 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 to;t, -zf aowhuw2s,5ag 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 transmission line carrying 28 1mijnd04l,4ah1ieidllz74c, ed ec+ 00 A (Fig. 18–34). The lje didml01 dzn, 1ih4 74a,c4cel+ei 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 A at 2fb .cb/an-19+q vlez zf/ndt /40 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 l w0y4pgyj5hybs1e:59c; dtud ),sxe0.60 A through a resistor.
(a) What is its resistance, $\approx$    $\Omega$
(b) how many joules of energy does the battery lose in a minute?    J

  What is the diameter of a 1.00-m length of tungtf 2:9lr jda+s6n0a busten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length ozr45 +9r.e t/x6f wxtucxkq.vf 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 diplqa+59k i hq* lt+wq6ameter, to 20.0 m of copper qiw*+ q5atph l 6kql9+wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the sc tz6w6ue0 k0a kth;4came resistance as a tungsten wire of the s0tehz6w6c;kut a0 4 kcame length? Give numerical details.    mm

  A certain copper wire hvkggi-jf9 iqkg5 d )+hq* ,x2eas a resistance of $10.0\Omega$ At what point along its length must the wire be cut so that the resistance of one piece is 4.0 times the resistance of the other? What is the resistance of each piece?
$R_{short }$   $\Omega$
$R_{long }$    $\Omega$

  How much would you have to raise the temperat 6zc /4) t7ds)we,s k0pxrjah6+j ueedure of a copper wire (originally ate)4) hr,te6z jxja6 +suceps0 /k7 dwd $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the samer8 + pfw s9t.n1.g,kaxstf 5yr resistivity as tungsten does 1.g. r+x,t wkpfyss rt9fa8n 5at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a rw8ch/n i78q28.ol*o7fa j+ yo exa qpsesistance of about $12\Omega$ when cold ($20^{\circ}\,C$) and $140\Omega$ when on (hot). Estimate the temperature of the filament when hot assuming an average temperature coefficient of resistivity $\alpha\,=\,0.0060(C?)^{-1}$ .    $^{\circ}\,C$

  Compute the voltage drop along a 26whoo6p 3h/3xsmz)*,al um,vw-m length of household no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 m 3/mux*3 hh w)z6lsp aovm,,wom and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of3sxptof r;os6ct;0r * lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respe; ;xtfcp r6*orots30sctively (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 twiji js*0 ly7,nsl++mwq ce the length of the other, what is the ratio of the diameter of the longer wire7s* +0l yqsi jwjnm+l, to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a prff2uc1 bejnmc.4h (q5 ecision 10.00-V power supply, and a current of 0.4212 A i ff(b24cj5 q.1hume ncs 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 5.0 m of alumcsc5o ;1v1m otr9dsnnul rr /,h 4p6,tinum, both of diameter 1.0 mm. A voltage difference of 85 mV is pla 1o 6n;po5, 9msvc/r4 r uh,lrstntd1cced 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 th36ybg5cd4 , pogo-orx e value of a resistance not change with temperature. For example, sup rdg5b-oc6gxop y3o,4pose 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 dejkiik3+c6i6 s signed to produce 3.3 kW of heat when connected to a 240-V source. W+ic3jk sii 66khat must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V po7h;hptce 0bv2;(hi tnrtable CD player that draws a maximum of 320 mA o0ih7n;e chp t2bvh (t;f current?    W

  What is the maximum voltage that can be applied acrosst0rxk /kzpls -d. )ow4 c n1cq+kqlc-* a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the redh,5u ivhw;ea8)ah;gsistance of, and current through, a 75-W lightbulb connected to its proper source voltage of 15h hdi;ev gua8),h aw;20 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 110 W. Csbe+ -ugyv)7lq0smd2 5o c)d malculate
(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: 850pv:9p .xc wj5dcd2(md 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 iuwl ave;)lytx*z2.+h n Europe, where electricity is delivered to homes at 24w *xl)y h. vl2aet+;zu0 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: 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 2(emow2kycy b 6zn /ka;8hg,gin operatioc( yoa/k h8kb;g y ,2gwz6n2emn 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 it cost to leave t6c(3x,nnhav a 25-W porch light on day and nigh,v(thnaxn 63c t for a year? $\approx$    dollars

  An ordinary flashlight uses two ag7-onnbrc (y 09wt*aD-cell 1.5-V batteries connected in series as in Fig. t a0-*wc7yn(abog9n r 18–4b (Fig. 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 en * y 1beg4vreg l3b ry0x5/,riuc-oz4aergy stored in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connected to 120ft +) (*q+t bvt nlibkczg*s72 V as in Fig. 18–20, can be used withofsbc2*+*ik+zvt l t)(bt 7 gnqut blowing a 15-A fuse?    bulbs

  An extension cord made of two wires of d5w3 kst w6m:driameter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric heater whichw3r5:6wdk m st 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 wireh hf 8hgn*)a.r.okqgsd: g8c2s wi.nfg)cdgh q*82 g8 hk. r:hsoath 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 connectp*4yn4tj, mj9uk*g ocwb w(b85n hj0ged to a 240-V line is 17.5 A. At what rate must cooling water pass over the coils49o8h*4w*jjntyw,mg( 0k c jn5bug pb 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 a cup of water for coffekp/ef :bv7v)qe or tea. If the heate7)/: evqb pkvfr can heat 120 mL of water from 25$^{\circ}\,C$ to 95$^{\circ}\,C$ in 8.0 min,
(a) approximately how much current does it draw from the car’s 12-V battery, $\approx$    A(Round to the nearest integer)
(b) what is its resistance? Assume the manufacturer’s claim of 60% efficiency.    $\Omega$

  Calculate the peak current in ahpmt9sm 3)ht) $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is eo;*fupkuow(0sy tam j 9 :b70180 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 e)u v)77ce+ uj5u p8jys*go adof 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 device zd.si x.u:1q8 kcpha7 is 5.4 A. What is the rms voltage across1z. ixq h7u.ck:8 adsp it?    V (Round to the nearest integer)

  An 1800-W arc welder is connectfzs;kpx3 2l q-)b *squw ,lhk2ed 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 pusan,8h0/wi o xraii -w0pan /*mp connected to aa-s rwahio* 0/8pix/ n awi0n, $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected tok.dtuwzc q4c( n57 mbc aq;*r f ehkuv5,5;e8p 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 currentthnxsyckg,w70 quxs p662 o77 jl +zszq(0g(l 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 currentf bo9yb 1 gj4,ecxs+c( when 22.0 mV is applied to its ends. ccb j4,9y 1(g+b ofsexIf the drift speed is $ 1.7\times10^{-5 }\;m/s$, determine
(a) the resistance R of the wire, $\approx$    $\Omega$(retain three decimal places)
(b) the resistivity $\rho$.    $ \times10^{-8 }\;\Omega\cdot m$
(c) the number n of free electrons per unit volume.    $ \times10^{28 }\;e^-/m^3$

  At a point high in the Earth’s ea ,s wse..ti,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 Earth’s ;dq5 poq ha,x,atmosphere, $He^{2+}$ ions in a concentration of $ 2.8\times10^{12 }\;/m^3$ are moving due north at a speed of $ 2.0\times10^{6 }\;m/s$. Also, a $ 7.0\times10^{11 }\;/m^3$ concentration of ${O_2}^-$ ions is moving due south at a speed of $ 7.2\times10^{6 }\;m/s$. Determine the magnitude and direction of the net current passing through unit area $(A/m^2)$.    $A/m^2$  ----待选择----NorthSouth 

  What is the magnitude of the electric field across an axon membrd1 fw/sk9p abk9mc .y-ane $ 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 potential is7kxx k xkz*6k8 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 th*x z6 8kxkxk7ke 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 potential alongkd zxq 5)82a vgr.jv8w the axon of Example 18–15. [Hint: the energy to transmit one pudvr8kwq.ax28 ) g5vzjlse 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 potential,jz qcysn*whc (m6si,ogsc a1/q -;33 y $Na^+$ 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 ampeay;bhce wk9(.y+r:wn 9 qdtk 6re-hour?    C

  What is the average current drawn by a 1.0-hp 120-V mo bp7t06n atg-mttjl0 (tor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of th:yxzxzrg( ql6 8m9-mne two headlights uses 40 W and each of the two taillights 6 W, for:r gxm-l9x 8 q6nmy(zz a total of 92 W, how long will a fresh 12-V battery last if it is rated at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of a 110-V, 1500-W heater is 5.4 m lofx,. nsxo wktgw*31wn. hp;1 qe4ish;ng. If it is made of irooi;*hk4.13.thf sgewpq1n; xw , nxs wn, what must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an oz3tsufs;yw 1q5ab+ p/bject is defined as the reciprocal of the resistance R; that i/3;z w5yt bsq+1upfass, $G\,=\,1/R$. 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 (w2+dq:hvnd rxt9gtntl *g) 0instead 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 *hn0nw tg2:t xtvgq) ld+9(dr 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 househ;w mkoz3w4 k)enaob6/ old 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 are0ohu 1)rs r;zl xofq:0 wrapped together side by side to make a thicker wire. o) z q1fshlr:ou0x r0;How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 8g .czqx/u7.v4h edte 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 betfdhvi 3 2lt:iwx,h ) nz2+)db k3v7xkcome so hot as to start a fire. What diameter must a copper wire be if it is to carry a maximum current of 35 A anl x73i +dx)tz: )hfvtw2b2h3ivnd ,kkd produce no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by foa sg0y),8r37ac p jbthe equation $I\,=\,1.80sin210t$, where I is in amperes and t in seconds.
(a) What is the frequency?    Hz
(b) What is the rms value of the current?    A
(c) If this is the current through a $42-\Omega$ resistor, write the equation that describes the voltage as a function of time. (  sin 210 t)V

  A microwave oven running at 65% efficiency dq4dqcnm:g0 d.h/rrx z-bw/ x5elivers 950 W of energy per second to the inqbz :m 0-dr5wxg rhq//d .nx4cterior. 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 samv;4d6q n5fkma e material. One conductor is twice as long avakf4; d5 qm6nnd 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 used to heat a room of volumecp*5 ) adhw9yrn8(yje $62\,m^3$ 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 sour 6vc;m((ta6hueq8 xitce.
(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 veojg-rt q 3cl9b9ryw-* hicle makes use of storage batteries as its source of energy. Its mass is 1560 kg r3qlyc*- og rt9-wj 9band 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 q- 9yb z e*oark3b7tl+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 acceleratwi*n,7v 2k 8 4klcbgipor at Fermilab (Illinois) is designed to carry an 11-mA beam4k iw g7nkc2l*8b ipv, of protons traveling at very nearly the speed of light ($ 3.0\times10^{8 }\;m/s$) around a ring 6300 m in circumference. How many protons are stored in the beam?    $ \times10^{12 }\;protons$

  An air conditioner draws 12 A at 220-V ac. The connecting cord is copper e 5d5qtjgpd(q)v)57i wema* c5uqns.wire with ag)a q(jd5 tdqpu)n5q5 7e viewm*.sc5 diameter 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 iskf9 d(t3 g:xj5o* (rqkwtv1vw rated at 95 W when connected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a tota f(:q1(3dojw wg9 t5vkxrt*vkl length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies fro7v.ltbun 8 d9n-.lbv hm 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.9u l7 bvnb-vn.lth8d 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 ,8 kk6ukfr+kp40 W for household applications. Lightbulb B is rated at 12 V an6k8kp,kr+ uk fd 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 o/)fv))i/ubsuz8u3al; w +b)hk qqbc p f appliances at 120 V, /w+ suvi8 bla)bb )q ckq ))3uzh/f;puwhich draw 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 and jy- vts t g4hj--j*y*can outside diameter of 5.00 cm (Fig. 18–3 h--vy* -tcst gjj4*yj7). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R i9y9sx mo:r3 mq8) 9eba ilzp, tex/j5zs stretched uniformly so that its length doubles, by what factor does the power dissipated in the wire change, assuming it remains hooked up to the same voltqmyei /r99smazx,5o ezjt :3 8blx9)page source?

  A tungsten filament used in a flasrj7 3eh+tu9 )i8c 8krrfg 4xjohlight bulb operates at 0.20 A and 3.2 V. If its resistance at 20h)o79g fir84r8 x j+cteuk r3j$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$