What quantity is measured by a ba liapxs6p,-gb .rcg /7ttery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons p ye5x;3ytqs4.rj 4c ts*w1vlflow away from the negative terminal in the circuit. But within the cell, electrons flow to the negative3y.r j4y15cxwl p t*sts 4;qve terminal. Explain.

When a flashlight is operated, what i5 j14tynvhd) os being used up: battery current, battery voltage, battery energy, battery power, or battery resistance? Expla n5yj4hdo1 v)tin.

One terminal of a cary;a8 m*5 0,.a4-n r s5nxiguiyrjlpty battery is said to be connected to “ground.” Since it is not realn5.rgna 0tily5-jm4;u y8i sp, xr*a yly connected to the ground, what is meant by this expression?

When you turn on a watt6jmr,ku9 rz:*dw 3kw5z*fh oer faucet, the water usually 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 wwuk 6*z :kwr* ,h3o9dfjrmtz5ire to the terminals of a battery?

Can a copper wire and an aluminum wire o-le -3 d,:xddna/j go:mrp,tuf the same length have the same resistancne ,xr3 :,jtodg: l dap/u--mde? Explain.

If the resistance of a small immersion heater (to 0 6 vyr7 n/w,nxuj8 x;ubly2ncheat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow ru,x;x8 ny0w72cj /u6bynvl ndown the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, and 3a hw4hlgs2 m*;pv9jn- u, how would you connect the wires from a battery so as to obtain (a) the least resistap *w-;mu4 sljh2nvh9 gnce, (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 lightbulbzaadaq/m)+ y9a8cur) burns out?

Explain why lightbulbs almost always burn out just as they are turnedepsq q-) 2yxf+ jw2a8r on and not after they have been on for some axrefp2s 8w-jq )2+ qytime.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which has the)y y-acco, 6nu37vyx x higher r3cy ynx cux7),oav y-6esistance?

Electric power is transferred over large distances at vernn3-cmqsdi(/ a :t v7ry high voltages. Explain how the high voltage reduces power tvn/cn73-: adm qi(rs losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fuse2dnx+(kyph p. with a 25-A fux+2 yphkn dp.(se?

When electric lights are op/k -:i *r1jneo hk5km2k)1kwci- h uijerated on low-frequency ac (say, 5 Hz), they flicker notiu5*kkni1-:k1 )w i2oj /h-kkcj mihe rceably. Why?

Driven by ac power, the same electrons pass back al(ltgz6 zz,,5ykjc) lnd forth through your reading lamp over and over agai(z,l)z ly5gk ,z6ctljn. Explain why the light stays lit instead of going out after the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. Immedi67)8wnxco)v 7rcpzw/ jz ebfz/4m0esately after the toaster is / ej7) v)zofremnzpx480szb6 cc/ 7w wturned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? 1u essz j8+ li*y ry4bjgv22ty/z9dsb(,ng g* Explain.

Different lamps might have batteries connected in either of the two arrangemm,: di1gv,eceents shown in,1, ceevim: dg
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 pa bi/iwh4yb0z* ms c)ft3a3c/ ovv;o;b st any point in b;3viy ;cos3b vh)zcf/mti /a0 b 4*owthe wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A for 5.0 h. Ho *cfc6uqj 4 pxu9im35cw much charge passes through thu*94jc pcmc xq5uf6i3 e battery?    $ \times10^{ 5}\;C$

  What is the current in amperes if lb d.:2k:2 :sm vrmhhl$1200\,Na^+$ 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 currenty v/6yy5u,-d,t b0 chb5xfqq8-bwf dn of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of curren8zxwxkv-0b p18 9h +k-jq) plukk -igdt through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 1c) ijw c-taxa95v 2mk+20-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 ,/who.gpa(-*uyyoh di 5iw6a a resistance of $9.6-\Omega$.
(a) What is the current in the element when it is connected to 240 V?    A
(b) How much charge passes through the element in 50 min?    $ \times10^{ 4}\;C$

  A 9.0-V battery is connected to a bulb whose resisttnt4m(mcf/v :ance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transmis1k dsxsxn(:+ p5 au,qdurny :1sion line carrying 2800 A (Fig. 18–34). The line1:nsdds (p:x a,u y+qnxr15uk 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 6.5rard+:; d x;me0 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 causes ausb x .h- z11sc+e/rs5t zux7m 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 a 1.00-m vaxs ;f j/sig;hl 0nr010 j-xklength of tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m lenlr+e)t t ,w;rbo l+4x s(9uzcrgth of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistanf v18/vzi nbjbu c(b7ir+2:8.auar irce of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in diameter. vb njvz:iu(rb+cri 2af/rai .78b81u   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tungsten 0uctyewyvi8 7w2)7 z awire of the 7 iw0w7uvc a)yez8yt2same length? Give numerical details.    mm

  A certain copper wire has a resi x.9d 4jp*bjmlstance of $10.0\Omega$ At what point along its length must the wire be cut so that the resistance of one piece is 4.0 times the resistance of the other? What is the resistance of each piece?
$R_{short }$   $\Omega$
$R_{long }$    $\Omega$

  How much would you have to raise the temperature of a copper wire (o +) qtd7bqh048dklsvjriginally at h4vq+d qd)t7k 8lj0bs$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will havd(1lhh l79ncyq - ac(le the same resistivity as tungsten does atl9-q1clhcld7h( (nay $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a if6mx;ebf-ac 7mh fbi yey/3x:u2/0d resistance 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 aloi v-qwnv - a*zabk.x. t,zj-8rng a 26-m length of household no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm and ctx8zaa -w nzi- .k bvq.-jr*v,arries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths 1.x mj+dfq+u l:(0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, resp+:ujmx +(fl dqectively (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. Igp(xbuan55)c w(wn 7i)y7m xj f one has twice the length of the other, what is the ratio of the diameter of the longer m7( b(xjwgu5 x) yc 7pia)nnw5wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wi;fjzq+d8j w+68i2g ewinq 5vjre is connected to a precision 10.00-V power supply, and a curreq+jd;vi6jfn8w 5+eji 2 g 8wqznt 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 wire98,tgsb - etk7iaz-ndgkd/;0 t;xyy:cam jq4 consists of 5.0 m of copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is placed acrosska/mxd-; 7tg;g0 8sb e4a ,ydjq-c zt ynk:it9 the composite wire.
(a) What is the total resistance (sum) of the two wires? $\approx$    $\Omega$(retain two decimal places)
(b) What is the current through the wire?    A(retain two decimal places)
(c) What are the voltages across the aluminum part and across the copper part?
$V_{Cu}$    V(retain three decimal places)
$V_{Al}$    V(retain three decimal places)

  For some applications, it is important that the value of a resistanc u5fkgn (bos//qs2 6 .0xxq*btbz3k uie not change tof/3b6gns2q b5*bkk (zxxiqs/ 0.uuwith 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 iyzjn 3c*7-v bis designed to produce 3.3 kW of heat when connected to a 240-V source. What mbzny7 v- i*jc3ust be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V port v7-;dr 7:,qw,-v gv onjtjr-uk: uzbgable CD player that draws a z;g-r,jvk rq:,jgvo7budw- tn7:uv - maximum of 320 mA of current?    W

  What is the maximum voltage thabcei r3w2 p6ufb.39 dit can be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current throughbsmgcoa)8)r y .w:bke;ts w 6:, a 75-W lightbulb connected to its proper sourkcg:)m; 8wy e)sa wtrbob. :s6ce voltage of 120 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heater is rakp sb:ny*4(sgted at 110 W. Calculate
(a) the current through the heater when it is operating,    A
(b) its resistance?    $\Omega$(Round to the nearest integer)

  A 120-V hair dryer has two settings: 850 W and 12 dsl.5ya(-tp9j/i trr50 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 is delivered to homes at 71g +77 w+aqhd5osjio aiq)t2h -qnlqa1dx c( 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: assuh 17 +jsxal(-d 7i)oaqd+aog21qhniqwt q 5c7me 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 is7d3)cc2odskqq,+hx.g - kye v in operatiod 3q.+y7d q)sovkx2, gcekh-cn 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 a 25-W porch light avcye,, vp/gg4( ,l gqon day and n/laqg (ve,gypv 4,g ,cight for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batter2sxsazw52 2n w:zo8kaies connected in series as in Fig. 18–4b (Fig.zzw oasxa2252s8 knw: 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 amodanq3 /7k qj)+.ok47ns xkhta2 t1rzwunt 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, connected to 120 V as i r3fzsk(jiq+vtm 376 4add b5zn Fig. 18–20, can be used without blowing a 15-A m 3d4fr3 sztj6vqd+(5b ia7 kzfuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 copp l1y3m ul0abymc cu)4c( ou7c-,ffklo,nq c,8er wire) and of length 2.7 m (9 ft) is connected to an electric heater which draws 15.0 A on a 120-)3 u, 4-8yacq lc7m,, 1 mocfcyluubclko0nf(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/3ka e3 .i-+2jzmyisuqqa:oo wires with total :me /zq i+uaq33.oo -kasyi2j 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 electrop2;vds3,( a gchtuq- umagnet connected to a 240-V line is 17.5 A. At what rate must cooling water pass over the coils if the water temperature is to rise by no more than 7.52t3vpq-suhc,ug ;(ad 0 $C^{\circ}\,$?    kg/s

  A small immersion hea8 ea/v z-rbbc(ter can be used in a car to heat a cup of water for coffee or tea. Ia(b-zvcr8 /bef the heater 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 cum:h1sm hj5o9wxh;t: frrent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180p/ ubs2sfx(g5 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 k-yaq;zm.d qdobv8b.6 2z(pw 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 alternatinrebb9/m8a,w 0 esar6ug current in a 1500-W device is 5.4 A. What is the rame b8 96b/a wrs,0uerms voltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected tymx 2 29/46aoa3aqt41ly nlc)cafiga .ptf0 d o 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 disr8c mns(m(0 dvsipated by a 3.0-hp pump connected to a(rm m80v dscn( $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected tq ong2:de,d7:rnu (wfo 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 cy:ez r2elrc s23w+k9 o dez3:tarries 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 c( ucjmw4/nb5qurrent when 22.0 mV is applied to its ends. If the drn(w u 5mbqj4/cift 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 atmosp g e,uc s;9s kmvccksys-j9,3. yt.zfr9e yu.(here, $He^{2+}$ 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 thw9yp. r jcxp/)c9t oe/e 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 electricp2.df;q4w b1nc oylq6 field across an axon membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated wyz* c 3rco,ay2g,5u mfith an electric pulse. The action potential is detected at a point 3.40 cm down the axoar,,co3g my2u*y 5 zfcn 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?)    m/s

  Estimate how much energy is requibc2f1y;) m0 7s ywqvlered to transmit one action potential along the axon of Example 18–15. [Hint: the ef) sb1y2vl;ec0w7qym nergy 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 potentr3pdu 7m zunwr .i57buxc7 *5dial, $Na^+$ 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 ; ytww+2*v kbf1.00 ampere-hour?    C

  What is the average current drawn by a 1.0vb:8 :6e m- ws qdxbe fq);n40gi,rzdm-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of the two h0 f 1;y fprw/nhehi2p*j o07xgeadlights uses 40 W and each of the two taillights 6 W, for a txjfyh r i f*02p0e;7ho1pngw/ otal 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 long. If it is made of ipgenjfl ;1b .:wo xl(ur*wb.5ron, what mus5 ;w: bnx*.(j1g w rl.uopelfbt its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the bmwmy9wuz zw8 6h )d(6reciprocal of the resistance R; that is, w6bh6zw9)u 8ymw zdm ($G\,=\,1/R$. 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 of uas-yn+.t c fg0sing high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a two-wire line of 0.50-cm-diameter copper wire, estimate the cost of the energy lost to heat per hour per meter. Assume the cost of electricity is aboya-0gn f+cs .tut 10 cents per kWh.    dollars per hour per meter

  (a) A particular household uses a 1.8-kW heater br 7 l:y59bli-hs akwk(dr03w$3.0 h/day$ (“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 length:h80i)4ir) rn 2u0 jlup atxams are wrapped together side by side to make a thicker wirx mpta)rn0jhal: ui ) 4r820uie. How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 117 V. k.sru v u 9x (p1tb.;0ncny5ck
(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 vfbp-j82(v ckto start a fire. What diameter must a copper wire be if it is to carry a maximum cuv(2f kjcp8v-brrent 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 the equatio 6iucusy),mp8p b;9svods(/zn $I\,=\,1.80sin210t$, 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 delivers 950 W of energy ph2+ 21eaeojy+kt0vnd ih+ vz9 er second to the interior. F ke 0otv++2d +1 hzanhv2yei9jind
(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 mae 4. 8j,.gbm jg/kfwrcterial. One conductor is twice as long and twice the diameter of the second. What is the ratio of the power transformed in the fir/jbc.e j , f.8kgw4rmgst relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heap6+4o)iky ovoc: qo;dznlw- +t 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 x34dtm na (7bjto 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 vehi4kjo* rhru;*g) i/cyzcle makes use of storage batteries as its source of energy. Its mass is 1560 kg and it is powered by 24 batterhc gyuz*) jk*/4o;rir ies, 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 lightbuf2s29 waewp-j a/obe1lb 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 accelerator at Fermilab (Illinois) is designedcnm1z/ 7n)xh4tqk 40 aip lk*u to carry an 11-mA beam of protp ik4l/70qhc4 kxmu)n1ta*znons 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 coppe s6 cqjus-7 ej8fwlq;6r wire with a diameter of 1.s u7- q6 j8wcfel;j6qs628 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 o .ewkg4)lvltnmuu08+4i( 0ceps7gz 95 W when connected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What is the diameter og0 vl )i4084(uwm e sn7+otkcgzpl.uef the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from about 12 V when the car is off aj e.kqsne +(;2l1wpd to about 13.8 V when the car is on and the charging system is in operation, a difference of 15%. By+ jesq;2pd1w (.elkan 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 for household applicm.ub.xid bs9g q)sie 4 8jmfs8e ,)cl8ations. Lightbulb B is rated at 12 V and 40 W for automotive apx8. ) 8.s4qmb)cb f jseu ii,eslgmd89plications.
(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 diamedpp n8qgi0)9( gtj we,ter 0.259 cm is used to connect a set of appliances at 120 V, q ()890ngpei,d wjgptwhich 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 an khvf.imlg7c6b6n /v 6 outside diameter of 5.00 cm (Fig. 18–37). What is the resista 6l/m66v vcbh .kgif7nnce of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched unfu2bgaq +bwaz1dfw5 (1f58e ciformly so that its length doubles, by what factor does the power dissipated in the wire change, assuming it remains hooked up to b aa8bf1 ufdw512cfze(q 5w+gthe same voltage source?

  A tungsten filament used in a fld.z uhex 6x8)retnz 7 uf:25teashlight bulb operates at 0.20 A and 3.2 V. If its resistzx5e6f8d.euu r2tez: )7 txnhance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$