What quantity is measured by a battery r48nbob 8iw/ccating given in ampere-hours $(A\cdot H)$ ?

When an electric cel5l 5rg5u2afyo l is connected to a circuit, electrons flow away from the negative terminal in the circuit. But within the cell, electrons flow to the negatialogr u55f2y 5ve terminal. Explain.

When a flashlight is operated, what i pytu9f6s4xr0 s being used up: battery current, battery voltage, battery energy, battery po x46s tryp9u0fwer, or battery resistance? Explain.

One terminal of a car battery itf :) afc+ pjn0 +ros)idyg,cp0)k b:zs said to be connected to “ground.” Since it is not really :0 oigztp) ark ,0 +ns:c)j) fydbc+fpconnected to the ground, what is meant by this expression?

When you turn on a water faucet, the s wq)3/vv3ykp:wvl1 a7m hp ;pwater usually flows immediately. You don’t have to wait for water to flow from the faucet valve to the ;7)ps vk 3ywl:h v/vqwm3pap 1spout. Why not? Is the same thing true when you connect a wire to the terminals of a battery?

Can a copper wire and an 3*vu ts ;i)mycaluminum wire of the same length have the same resistance? Explain.uy )3vscm;i*t

If the resistance of a small poqs.z s/ur4*immersion heater (to heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the heating psuq /prz s4*.orocess? Explain.

If a rectangular solid made of carbon qal(f f(g8c(lhas sides of lengths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain ((8cfa( lg flq(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 lightbckfz .k.ce- 2lulb burns out?

Explain why lightbulbs almost always burn out just a4e 720 a hwfvqi )cj7u5ruhjm4s they are turned on and not after they have been on for some time.f7umch5i0rv )uajje 2hq 47 w4

Which draws more current, a 100-W lightbulb or a 75-W bun(gvnrb yc2h/dc9 u,6lb? Which has the higher resistan(cnyu2ghv6nb /cd9 , rce?

Electric power is transferred over large distances at very high voltbe v*xn8 d 0,zway21wkages. Explain how the high voltage reduces power losses in the trve0* 8bzw 21,dk wnyxaansmission lines.

A 15-A fuse blows repeatedly. Why is it4kk5hgcm ,g*f dangerous to replace this fuse with a 25- fc5g,*k4hkgmA fuse?

When electric lights are operated on low-frequency ac (t8k:yu(ysstk pc7u lr. xd:fxwq / 4+,say, 5 Hz), they flicker noticeaty,fsu7d/.c4pxsr8 l:w+t (k kxqu:ybly. Why?

Driven by ac power, the same electrons pas suvmc3*d )+ccs back and forth through your reading lamp over and over again. Explain why the light stays lit instead of going out after the first p)c 3scvuc+*dmass of electrons.

The heating element in a toaster is made of Nichrome wire. Ib- oqueh;+ i:7 wm/wdommediately after the toaster is turned on, is h;wm+e7:bqo/ d-o wuithe current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in(c9wz t evs5yj)n x 5nod.l4;qk-7kou a resistor? Explain.

Different lamps might have batteries connected in eith 1tks0ho56 oardxxl4 *er of the two arrangements 054sh*6a 1 loodt xkxrshown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flowp84vl0ia b9tq (uv pf/s in a wire. How many electrons are flowing past any point in the wire per second?vv /(a9pbu0lp8qit f4    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A for 5.0 h. e f8d8z+kdivqhu ufo-0p5 58tHow much charge z8e5h d-+8 uu iqkdovt0pf5 8fpasses through the battery?    $ \times10^{ 5}\;C$

  What is the current in amp9dn* wus j1xn0 /x 20iw;*enbibtsf w5eres 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 b m1g1yeni/t, c lj; u((v1zcrci:d3na toaster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.29rs1g b9i*r:cozw7 fb 5 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7/efizo3z7aupkuy - op)3u (7y.5 A when plugged into a 120-V line.
(a) What is its resistance?    $\Omega$
(b) How much charge passes through it in 15 min? (Assume direct current.)    $ \times10^{ 3}\;C$

  An electric clothes dryer has a heating element 4xn huc;y9 nag:p2)bhwith 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 bulzwt,e79 5b,o( bmwctb b whose resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a d/ql eq l;u710) flg*lj 1wcxtoc electric transmission line carrying 2800 A (Fig. 18–34). The line h*w0qlcg jut l/le11xl;) 7foq as $2.5\times10^{ -5}\;\Omega$ 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. 16 i u2zc;k3vpyp9 iuy
(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 throutf n(og js)w782gvjeg jt7 t.1gh 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 tungsten wire whose resznr a 9fpe:mkyha8s9idf4 58i dog). -istance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1.5 mma1rdv s4cokgxxm: .h1)so0v3 in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire 2.0 zmt ))2z2gycmu8r(l x mm in diameterzyx28rl tucm)g )(2m z, to 20.0 m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resista amihss4t,l-4u iti4-a4add0z. xa r2nce as a tungsten wire of tha.i-0dul4 s i4hazxams4-r4 iat dt, 2e same length? Give numerical details.    mm

  A certain copper wire has a resist;9bfs6hsurv yf630v2c a zc(bance 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 mqvbz55ppz hwc1y 1-* to raise the temperature of a copper wire (originally atzq m1b5zpy 1pv -c5wh* $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same u6w; ;r.46ysj3dm 7igacsi he )ok)rs resistivity as tungsten doi.;)c s7 )s 6jhdkrr6ao4u; esmw3ygies at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a rx hica*/9o/c0p2bpi-6 jrtz sesistance 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 26-m length of household no. 14 copper wire)a 5j buekw*-s (used in 15-A circuit- eu)s 5kwbaj*s). The wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm, 2/* c,o* f,gaj cpt4nvm p4ybi3.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resi,atm p/ y4*ncj bcgo,*if4v3 pstance 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 twice the ej2p-hv 8bja0 length of the other, what is the ratio of the diameter of the longer wire toeabp02 h jj8v- the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V power sjn z:f r+aa(8d1on99;muso yrupply, and a current of 0.4212 A is paso n aunfm ry1;r9 d8:z+j(o9recisely 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 o ) dp2ep8ybcp0f copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage differencep)8c2yd 0ep pb 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,;extju.ae- d8 it is important that the value of a resistance not change wxejt.8- e;da uith temperature. For example, suppose you made a $4.70-k\Omega$ resistor from a carbon resistor and a Nichrome wire-wound resistor connected together so the total resistance is the sum of their separate resistances. What value should each of these resistors have (at 0$^{\circ}\,C$) so that the combination is temperature independent?
$R_{0C}$   $\Omega$
$R_{0N}$   $\Omega$

  The heating element of an electric oven is designed to6aqkw,+x9-hgjmh v54ac hk yuil 65l 0 produce 3.3 kW of heat when connected to a 240-V source. What must be the resistance-5cl6m4y0hvq6 5 a xk hiwjgk u+h,a9l of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player thatmb ,45 qzkq5i,y5fj(qo vz;vk draws a maximum of 320 mA of current? qq5bf, zqok55 i(vj z;kym4v,    W

  What is the maximum voltage that can bfl +zq3jl ms sgx5+p45e applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistaluej:bt*ju77n4mzv :p,k y2qnce of, and current through, a 75-W lightbulb connected to its proper source voltage of 120 V. n*l v:k2zmj p uje7,:qut4 b7y
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heater is rjlupov (3p x8,k:b /moated 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: e):sdu4 g+ cfadxf:y ;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 Europe, where electricity a(ey5lz6xsz7qvw p4fa* x(9f 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 buzvf(q(z 9apfyw l 46sex*a x75lbs? [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 morniqqrsz,5 .6ngf ng if it is in operation nq q 6sr.z,fg5for 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:(: 9ngo-f.ruba g* fp+smzre leave a 25-W porch light on day and night for a year?oa:bfen s 9furr- gp:zm.*+(g $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected in series o16qtuu:se ed: eo3.l as in Fig. 18–4b (Fig. 18–36). The :.olud6:t ees uqe31o 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 energy s2:q,f chu osg4tored 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 120 V as 3tenxb4gdap* 6q/5b n in Fig. 18–20, can be used without blowing a 15-A fuse? *n xa5egn4bqbp6/td3   bulbs

  An extension cord made of two wires of diamettlnd uca*a3:d(s2 z(ser 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric heater which draws 15.0 A(dc2dn tzs*as 3al:(u 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 throug km*q4+hrwa+ y sj;:ckh wires with total + k+j;m :c4r kyswqah*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 rvw.5(b(t unrqwkf,5 pate must cooling wate(v5qw. 5tu , brwp(fnkr 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 cad5ekl j,pjmnm28b5:l : z;chyr to heat a cup of water for coffee or tea. If the heater can heat 120 mL of watl ybp je5jm,5n: c:z2dmlhk8 ;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 current in m0uw.0u26my55ii(h1em1kkvf5 ulo pp:bn zba $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak va .616mozj fi wptp4(wflue 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 onx+78*zub w-ps4nr4zmr:pf ef 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 is 5.4 A. Wwa3 s qv,.vdv2./nuq bhat is the rms v , adv..uq3swn 2qv/bvoltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder8dh*q.hw7ninz5+ ecyb 4ay3o is 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 pun:zpqyt wz*+) ctp h r1c,.n,zmp connected to zr*c,h t)n+p1pzc t:y,.zwnq a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connectgcutkjma/ vzc4gr7y +7kv c*i (*x76 red 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 wirtc pp zua7v*eml9p4 3*e 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 aw s-6xzg1 to8q 750-mA current when 22.0 mV is applied to its ends. If the drif-w6tos8z g1qx t 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 atvfij g t*89bt)w ) hye035omqfmosphere, $He^{2+}$ 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 thepx/ ipqu u++y* 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 

  What is the magnitude of the electric field across+dmvrk .7yj 5a 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 fx1: e kp39u)pc2z pwoelectric 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 measuremen)p9p:1cx3f2ou ke pzwts needed instead of only one?)    m/s

  Estimate how much energy;nzdo wgp-(gtt9t l52 s1i4b q is required to transmit one action potential along the axon of Example 18–15. nd;5to9-lqw4pbg 2gitz (1st[Hint: the energy 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 potential,wye7 i)e0kd,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 ampere-houru6 srf(3 do/4chg8e k(xk po:ij/ yx8r?    C

  What is the average current drawn+t+tb 1-ncur(w1 7 ,;iz2crqi bfzyvl by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the u(i4l.ku 6c)lrqi q4jlights on. If each of the two headlights uses 40 W and each of the two tailj4cqui ( 6)k4i. lurlqlights 6 W, for a total of 92 W, how long will a fresh 12-V battery last if it is rated at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of 8ukgfo,+856d fo zqxg a 110-V, 1500-W heater is 5.4 m long. If it is made of iroko,fgx6o+5f gdq8z8u n, what must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is dtizti )(btq lntc00-1 efined as the reciprocal of the resistance R; that ist01bi zt ic0qnl(t )t-, $G\,=\,1/R$. 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 instead oflkqu qjj*o/ u-x:e :z5 using high-voltage lines:kz:/jlqe5-uo*xq j u 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 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 heat nuk;k1iz;0rml. r-g cer $3.0 h/day$ (“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 side bgl)5zm x7cvku; +6yx qc 4s(qvy side to make a thicker wire. How does tc4v7s g;5z)uvy6+mxk qxc(l q he resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for a2.v-m(st4l w-fs tjb117 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 become so hot as toi0d*-o fswgymk9*ws lj(;b1d start a fire. What diameter must a copper wire be wdm90s*-sj o(*w kfy1bli;d g 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 /8-onx+o *kkals0xn r 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% effy8qiw )h juw5ewm2 .65l cjy1miciency delivers 950 W of energy per second to thl m jqyi5muwwj1w5 26e ).y8che interior. 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;gm 6tvk 5q7 pv*e msode7u/p; 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 relativo ;pqm5e v/ 7stuv7p*d6ke;mg e to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a romy+w5wm4c i e;ykr3 e3om 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 sourcekyw2 :)egrz2 +de9 rcm.
(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 vehrug(+6o:tffz* 37k7gd dozeaicle makes use of storage batteries as its source of energy. Its mass is 1560 kg and it is powered by 24 batadkeof7g7:+o u t 6rz(z*3gdfteries, 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 re 2nbx(l:pn, vft7v6/t0swtuosistance 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 1 mv-m1k) ryzg+1-mA beam of y-m +gr)1kzvmprotons 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 2*iteo ey18lrconnecting cord is copper wire with a diameter1yi2ro *et8 le 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 connected to 120 V.x(yspqu) 58ksw :z *io The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. (p)8ko* zyx5:uqsi sw What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from about 12 V when the car is ofukc/1u; twi0 e,ch w+lf to about 13.8 V when the car is on and the charging system is in operation, a dik c,0uweil1/ ;c twhu+fference of 15%. By what percentage does the power delivered to the headlights vary as the voltage changes from 12 V to 13.8 V? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W fo mog9p+ fnaa;e918r f b0(zhmfg ei);er household applications. Lightbulb B is rated at 12 V and 409 f)e(0gbf z;gpe haiar8m no+f1m9e; 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 diameter1s0dxzamvj -3)j f;p rx7:mmw 0.259 cm is used to connect a set of appliances at 120 V, which draw 2250 W of power tjr-mjmmx a7 zxf30v1p)dw ; :sotal.
(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 5.0tph 9bj ;k4h+hao2v-u 0 cm (Fig. 18–37). What is theut +9bo-kj ;hh2avh4p resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its le759j-pls ga)9fyh01 7bdhgev u a0f hj*h cq(hngth doubles, by what faybd*00 q sha79fljhg7fve()hph 5 cg-9aju1hctor does the power dissipated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb opera9ti +16 +evtj r:d30izwvgz1f z o(nfotes at 0.20 A and 3.2 V. If its resistance vi:tz+ovojnt196z3w i(0 z1f grfd e+ at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$