What quantity is measured by a battery rating given in ampere-hourd,dn 0e+we3 -7ai*cc4 a;r+ nsiuvxfrs $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow 3xfzoc 2ei4d*o:.8 a s6mnbe baway from the negative tea4i e em.z f28n3bcb6o:sxd *orminal in the circuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being lk3.la67bgej9 :b md hused up: battery current, battery voltage, battery ener bd.37b69ka:ge j llhmgy, battery power, or battery resistance? Explain.

One terminal of a car battery i0aj+ neg5x; zus said to be connected to “ground.” Since it is not really connected to the ground, what is meant by this expre+ 0geuax 5;njzssion?

When you turn on a water faucet, the water usually flows immediately. qsne7j6iws6m)9 :fv fYou don’t have to wait for water to flow from the faucet valve to the spout. Why n )e swvm:9fij6n7 qfs6ot? Is the same thing true when you connect a wire to the terminals of a battery?

Can a copper wire and an aluminum wire of the same lengeqp,b pz ,3h+gth have the same resistance? Expzgb+3,qe pp,h lain.

If the resistance of a small immersion heater - sp/ v 367vsdnh1*dt1hjgd*mcftcrd 8*z7ry(to heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow v dn3t*1-7gtz/*1cmjy d dc6vs*pr fd87rhhs down the heating process? Explain.

If a rectangular solid mad)uuq bgmet0l:tf0.) ye of carbon has sides of lengths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resistance, (b) the greatest ru0qy )fle g:.mut)bt0 esistance?

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 bur d5o(lu 8dp;(lx;uaypx dzet5.b dxf v; k62r4ns out?

Explain why lightbulbs almost always burn out just as they a4oaltg jjd 3m) 6w-(kare turned on and not after they have been on for6(m tw-jkg4laj do)a3 some time.

Which draws more curre,veenfj+.gme.9 , hkr12r gcrnt, a 100-W lightbulb or a 75-W bulb? Which has the higher resist,.9rk2em njr+g rgevf e.1hc,ance?

Electric power is transferred over large distances at very high voltagsunpq+1-zv: . iefez)k) awg *es. Explain how the high voltage reduces power )z)u.-ksfz w1pe+*v i:nqaeg losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace thi/:pzk mb mg39qs fuse with a 25-A fusm/g zbkqp m39:e?

When electric lights are operated on los.g3sve7cw) j/x) thyfha 1g1w-frequency ac (say, 5 Hz), they flicker no) t.sxhygg 73esa h )f1j/1vcwticeably. Why?

Driven by ac power, the same electrons pass back and forth through /muul fyk:4 3dyour reading lamp over and over again. Explain why the light stays lit instead of going out after the first pass of eley4ulf um/d3k :ctrons.

The heating element in a toaster is made of Nichrome. op:a* +8tack7bb;hsk k(biy wire. Immediately after the toasta .7kaskho+cb;:bby( *kp 8t ier is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a o-pbl6+ikbt*mi0.wu resistor? Explain.

Different lamps might have batteries c-xc *hr-8+so u,oikiponnected in either of the two arrangements shownkpc,h-u srio-o*8 i +x in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many electr bndv .s(byk3j9 5u4ai q7t)hyons are flowing past any point in the w jaqni by(h)9vk.5d4y 3u st7bire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A for 5.pz (p7/ynlxa40 h. How much charge passes through the battery?ppz n7xl/4y(a    $ \times10^{ 5}\;C$

  What is the current in r+t*-m1 gc mfpamperes 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 bws 6f wh9iii8a ba((, v.lu/ipqx5f: a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of curre6m g azz,la 9rw,e:x* trkrs+:nt through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120:zbizry)a (--flii g e- iew)7-V line.
(a) What is its resistance?    $\Omega$
(b) How much charge passes through it in 15 min? (Assume direct current.)    $ \times10^{ 3}\;C$

  An electric clothes dryer has a heating element with a resistance of /v93spt o tyrjn i3(g4t:a,fh $9.6-\Omega$.
(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 conq/r e; enw+1hlnected to 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 tranyqmuu 4xu*8v-d )/uiusmission line carrying 2800 A (Fig. 18–34). The line h-u /divuy uq)uxu48* mas $2.5\times10^{ -5}\;\Omega$ 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 dra:ui.pl 8uf- vfws 6.50 A at 240 V.
(a) If the voltage drops by 15%, what will be the current, assuming nothing else changes? $\approx$    A (retain one decimal places)
(b) If the resistance of the device were reduced by 15%, what current would be drawn at 240 V? $\approx$    A (retain one decimal places)

  A 12-V battery causes a vc t4fe3r:qgeeh)8 y-h-ij q 0current 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 length of tungsten wire whose resist yb25nacws u367y: xgxance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wi7a9n cm.wqk1xre 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 d;p0h l4vag4vp iameter, to 20.0 m of copper l;ha p4 vg04pvwire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tungsten 3b hxp)jfqwm .a+t7pg 9a6g1a wire of the same lenfg13)p.xp7tq bjwagah+ ma 96gth? Give numerical details.    mm

  A certain copper wireu4d dw/eino. f (ka.7 5uc-vdz has 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 t v4re6 rxsm8hm u6jo.3o raise the temperature of a copper wire (originally ath8rv 4.jrmuex so36m 6 $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will havewg3l+h1a*rqt mr 8oz w32t *br the same resistivity as tungsten doe qwm1rtwab t3+ 83zh grlro**2s at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistanc 3do6dm 2vs6ct--x ozte 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 ho umedds66 3v*xi 4dy6yj/up )cusehold no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm and carries a 12-A curren)ded3yuyu*p6ms / 46c idv x6jt.    V

  A rectangular solid made of car2 n2xnfkb fawg*8+we +bon has sides of lengths 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 2f *2fn+bena w 8xkgw+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 uq f.:)i mmry:gb,v8w has twice the length of the other, what is the ratio of the diq,r yimbf:g )muw.:8v ameter of the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precisi8iago.u sx2m3*pc 0ke on 10.00-V power supply, and a current of 0.42m cs3x2 *o0 i.paueg8k12 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 folb, 88 fgj-jph*k zmjy1lowed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is pj1jhmy *f-kz8g8bpj ,laced 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 on1,gl3cicr 9important that the value of a resistance not change with tem,gc 3o cn1lri9perature. 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 to m8) rnzqm6 dfp pzjdu70(jn56produce 3.3 kW of heat when connected to a 240-V source. What must be the resistance0n6j6 p mf(m7z)urzj8 nqddp5 of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portam h91sc v-a2qnble CD player that draws a maximum of 320 mA c- 2an9sm1vh qof current?    W

  What is the maximum voltage that can be applied a8ip9*e 1k*vr w dnz.rs.,cu pocross a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, a 75-W lightbulb connectem +qpqx --ob.idbo-qxi p m.+q- to its proper source 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 rated at 110 W. Calcul*g33 mqgoyw kvl1 +,ke .wmya3ate
(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: 85p pa2r*r8ci/dt -5h rbpt)di20 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 electr ypt rvccl8ds: r0d y;wtf/;72icity 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 blv/w d 0r:y ;7 28sfdtryct;cpe 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 gz)1;ml/ o+fxz(d/u 6a h oyoj550-W toaster use in the morning if it is in opera (o 6)maf/ud/gl+1yo j zoh;xztion 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 leah5 .lx , (x lgc+hup/fi-2* ublkgr/ylve a 25-W porch light on day and (r.lxb /l5cg,hu i k-g+*2u xyfll/ phnight for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected in serietru gf 0s *(6kn2gup,fs as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mAf g2tfu nspu6g*k, (r0 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 stored in a c4qa9 98o cyb y4.v8-dvm,qgdoqul4y12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connected to 120lsiajb, -v y:0 V as in Fig. 18–20, can be used without:b0l- jv,a syi blowing a 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 copper wire)dfy99s9o s g*t u,co+r and +y osr 9*f99gctu,d osof length 2.7 m (9 ft) is connected to an electric heater which draws 15.0 A on a 120-V line. How much power is dissipated in the cord?    W

  A power station delivers 620 kW of power at tk8c5m0 i2t: f34oghf p9m ex o/a5pte12,000 V to a factory through wires with total a e5t9em2 4 3pi 5o/ft g:h8xmfokp0ctresistance $3.0\Omega$ 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 1apes0.g/hjezu a(9u 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 7.50 h9a g/z0 .ep eu(ua1js$C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to heat a *cxsfap0pf p*s5c;)u cup of water for coffee or tea. If the heatec 0;upf*p)p *cfaxss5 r 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 ia/w.v .zmxr ;wbg 2uh;n a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, is 9jeoru n .jc;0across 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 *zro *ygm qc j(u8n cnsgb/376of 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 1 fr/n-r;wjhk4hnp, b(500-W device is 5.4 A. What is the rms vol, nbpjwhf r;4rn /-(khtage across it?    V (Round to the nearest integer)

  An 1800-W arc welderbl l qtz6:8;e 1 n,g4o bqdx/uzb5rc9t 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)kzrzm tby8hb-01 n r66nce,-zy n*dg instantaneous power dissipated by a 3.0-hp pump connected to d6n-zy6ny1)n tmr-c8 ebk0zb*rg ,zh a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected t.dpd6.p mz732jedt gmo 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 tinyq c: ;tt63-z pk/qt3:4gw sbkhvg9phu 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 wirf;:qwp p *i+d8dx0x 6puk7 ifwe carries a 750-mA current when 22.0 mV is applied to iq;xdp0k pwwff:d i78u*+x6p its ends. If 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 )zc up)z yy)k)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 Earth’s atm p zjs;f.jt(sq6ot/o /osphere, $He^{2+}$ 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 anji *bhr2*nm5 1gm 1f65v07fyllbfta xij9k w * axon membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with an electric pulse. The action potential is detectjv3zlf6dhh fs7g7:* qed 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 neededjlhfgfzh736 sq*dv7 : instead of only one?)    m/s

  Estimate how much enerlxaqy61 0mt8j a-6c6lp t7a lbgy is required to transmit one action potential along the axon of 6tmla qxa-j8 16ptyclal06 b 7Example 18–15. [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 potene: nk.1 ordt5jc2ax 9qtial, $Na^+$ 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-houyg6vnf rkkuq905)(0 fz 0nzsrr?    C

  What is the average currenhah mibjg*dh *,4ermjkpi; v.9 k48 y,t drawn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves x;9vwl)ibi )7ketbxmyxed g *(;+ is+a car with the lights on. If each of the two headlights uses 40l+;w *9xey+ibt(xsde;km vgx) iib 7) W and each of the two taillights 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 a 110-V, 1500-W heater is 5.4 m long. If it is made o w iw (iq7-;omc0q3g2tm 7qknmf iron, what must its diam mc wqi-77q3tn q;i2mk0mwg(o eter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is definew)8ydc g wl)d0d as the reciprocal of the resistance R; tha8cl gwd)y )d0wt 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. Suppose that instead of ,sgr2lk4f)bwhtx(m,mv , z4 k using high-voltage lines to supply the power, the power is delmvhgs),,xlkmwzb r4 2,ft(4kivered 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 hou)aj r;ks0 v2vkhdd)t:sehold 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 uevb w*r y;w:+gm0 3xbthe two lengths are wrapped together side by side to make a thicker wire. How does the resistance of this new combination compare to the resistance of the original wire?3yueb+g:w0 w*rv ;mbx

  A 1200-W hair dryer is en .fftrp(shjjc j+z9+ sn*;;designed for 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 hous *azj3 iuc*dr*e must be thick enough so it does not become so hot as to start a fire. What diameter must a copper wire be if it is to carry a maximum current of 3cr*a *zijdu* 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 e -rfuadd6*o(gws,twdxf *c3;quation $I\,=\,1.80sin210t$, 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 o8k.u wgoa/u, tjzpl,rdc w.33f energy per second to thewp.clud . urokj8 g/t33w ,az, 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 mple mu ;q0l e3vcedl4o1k98-lade of the same material. One conductor is twice as long and twice the diameter of the second. Whlqm4vkc -8p;e9e 0 llle 3udo1at 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 rim 6o)rt5yk0n.tfthu a 4 .+rdoom 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 au p/tc . c9mah0d8upm..a zu(s 240-V source.
(a) What is the resistance of the oven?    $\Omega$
(b) How long will it take to bring 120 mL of 15$^{\circ}\,C$ water to 100$^{\circ}\,C$ assuming 75% efficiency?    s
(c) How much will this cost at $11 cents/kWh?$    cents

  A projected electric vehicle makes use of zdlex5dt39kobe* kb;/bq3 7 fae+c g2storage batteries as its source of energy. Its mass itge c7zeb3xdk5q/*k3bf dl;ob2e+a 9 s 1560 kg and 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,ei, e 7v3ef7j(.hbj*h y edhk 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 (Illino;f1lq c gwu,/ wvv/qc (- 5oatwgxj7h:is) is designed to carry an 11-mA beam of protons traveling at very ch (vtql u;q1w:c75 -ojww af/ggv/x, 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 connechg:hk 3l z:q7o,c vj0ating cord is copper wire with a diameta7h,lg z qk0c3oh:vj: er 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 wfbdnr f h1u*;2coy/r0hen 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 di; brf2uy01 /r*dhco fnameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system vw9 gjkv6skld d*h 5*/voltage varies from about 12 V when the car is off to about 13.8 V when the car is on and the charging system is in operation, a difference of 15%. By what percentage does the powek6l9k*vj hsw5/g *dv dr 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 ant5a 3ukp:j -whd 40 W for household applications. Lightbulb B is rated at 12 V and 40 W fwu-h: k53patj or 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 caut01fgx p .*xonnect a set of appliances at 120 V, which draw 2250 W of poweruf p1axgx *t.0 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 outside diameter of 5.0dvg9zvxd7vb8;hw)o + 6 wu(hg 0 cm (Fig. 18–37). What is the resistw; odv 6b+(vuxvhdgz97wg)8 hance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its length douu6nv7q6 szo d33ybvao()l e- sbles, by what factor does the power dissipated in the wire changulv6 7o3a(y)bqde- sz3n6vo se, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operates at 0.20 A and 3.2 V.7h9f0/ uf t:wb tj; +gcqn-kmh If itmt+ 9/ 7wh;tf-0cqbjuhnkf g: s resistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$