What quantity is measured byq/rb))fc ljld2ur6 ya 2-hwq; a battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell isjv 5er3 jfufhzhl 6)/. connected to a circuit, electrons flow away from the negative terminal in the circuit. But withi/h.j3ue) r flv jfh5z6n the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, -z i+drm23ilqwhat is being used up: battery current, battery voltage, battery ene -lr3zq2d+i mirgy, battery power, or battery resistance? Explain.

One terminal of a car battery is said to be connected to “ground.” 9(w s)pseyvmm4bp0z 98s2timSince it is not r4v ey8s0 w 9mmspstp2 )ib(m9zeally connected to the ground, what is meant by this expression?

When you turn on a water faucet, the wate: dnic(s9 or lm+/xf3lr usually flows immediately. You don’t halmrndxl(f +o s:/9ci3 ve 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 terminals of a battery?

Can a copper wire and an aluminum wia;;gto l12u(w(r 8 yq;vgyytc re of the same length have the same resistance? Exp wlyucay;; 81(oy( v;tr2gtqg lain.

If the resistance of a small immersion heater (to heat water for tea or vt +vfo*x 6no2rmf5:n soup, Fig. 18–32) was increased, would inf mxt2v*+: o65fnorvt speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, and 3a, how.i-t5 y/ j0uk (rhjkcr would you connect the wires .5jyjkrh(u i -k0tc /rfrom a battery so as to obtain (a) the least resistance, (b) the greatest resistance?

The equation $P\,=\,V^2/R$ indicates that the power dissipated in a resistor decreases if the resistance is increased, whereas the equation $P\,=\,I^2/R$ implies the opposite. Is there a contradiction here? Explain.

What happens when a lightbulb bu vzriao h)dwf9yb890*pr7 d3erns out?

Explain why lightbulbs almost always burn out just as they are turned obc7h/8cy6sooip2qv0jj( r8 v vmk 4.nn and not afteoch4 qoj2vynbvs6pic.j 0 88v(km /r7r they have been on for some time.

Which draws more current, a 100-W lightbulb or a 7n0+)s vqh1elbhq cyhs*d 0a3,5-W bulb? Which has the higher) y,hhsvs3a*0n+1 cqdq ehl 0b resistance?

Electric power is transferred over large distances at very high voltag af*pts3ox; :9kwv id:es. Explain how the high voltage rev; 9:ai3top wdxf*k:sduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why isp cssjrxr7)52n5:ngmt1( ) rcu1k buh it dangerous to replace this fuse with a 25-A5:mhrr (bn7urcs1c1 )pts k) 52xunjg fuse?

When electric lights are operated on low-ho1sxlhh7 8 w3frequency ac (say, 5 Hz), they flicker noticeabl81x o7hl3shw hy. Why?

Driven by ac power, tizxumz, p8g3vorbcyl42 2 2/z he same electrons pass back and forth through your reading lamp over and over again. Explain why the light stays lit instead of going out after 83c, px/ul2om2zi24g bzyz vrthe first pass of electrons.

The heating element in a toaster is made of Nichrome wire. Immediately ee/4sauy,* ) ( ri4 gsjzpbzqwjs,9m+after the toaster is turz 9*ge4q(mb,j4eups rza)js,i ws/y+ned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resisz* sg 1a60rktfwoa(y),w r7yotor? Explain.

Different lamps migh g/ qt(;tqqhzpw1/b1 et have batteries connected in either of the two arrangements ;ewbz 1t q qqt/1/h(gpshown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many electrons a9-rnd5bhp wg5( -wywure flowing past any point in the wire per sec-nu 9 (ydrgwpw5b5h -wond?    $ \times10^{18 }\;electrons/s$

  A service station charges yq)qf s-n+qm/a battery using a current of 6.7 A for 5.0 h. How much charge passesq/ y+n-qfmq )s through the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes w*j+qj5vhk a, 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 resistanccwd l6kt2 bj,.e of a toaster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current thre*y*2: eeint rough a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged io9iyog 68pstpn a3t j)kq.) b6nto 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 heaz2 f pehe9d);qting 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 a bulb whos/ztr/5ow0ffc+1t w cte 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 2800 A y; ejvv9(iv2 0q ri3ye(Fig. 18–34). The line hyj(evy iv3qe 2r9i 0v;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 dah:g 9 2sofu+oraws 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 cause3g-iru,n e r*ds a 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 length of tun1nn:qc1 u mnz1.0on(qwh nc 35eptqz8gsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistanc4au un5/* fss,x/ v l-hkfgg4we of a 3.5-m length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the ref2oglvh/lm 62u1r v8dsistance of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 1rmv8/22ulvfg 6ohl d2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tunl,ba58o6s ;txpn/b a p0q +ogtgsten wire of the sameag;68 qt/o tabns,+ pxo 0bp5l length? Give numerical details.    mm

  A certain copper wire has a resistance of vn dup/4ar 75afy )dtu4yv)4g$10.0\Omega$ 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 haf9q f2xmklc, ik2 ;kf.ve to raise the temperature of a copper wire (originally at; m .x9c2kif2fqklk,f $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will havedm(d zsnb fgo9 -*o*,q the same resistivity as tungsten does 9b- m(do,q* sodnfz *gat $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a rb ;uqro1d+t;t esistance 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 :qzj+g6ob pn4 household no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm and carries a 12-A gznbo6: p+jq4current.    V

  A rectangular solid n sl. 8h4e th88:snbcimade of carbon has sides of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–3: 8ns 8hhsb 4ne8itcl.5). 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. 4y;ajnah(b-bn *t:(*peq b uwIf one has twice the length of the other, what is the ratio of the diameter of the longer wire to the diameter of the shorter wire4ajw a:b( t*h(en* q ybp-;bnu? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V power supply, o/dw) 5+ i0 yk c-eiv2/izifbfwx zu5.and a current of 0.4212 A is precisely measured at 20. 5+0v/b-k fy5ixdwzif/iw2 c )u zioe.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 consistsmmc zh.p0ly5 *2tp8ad2 /th9/hudzjb 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 .d8uj*hat/d m 52py h29tpc hbml/0zz 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 the value of a resistance no. (u*e xgiom3 ltig5+vt change og +i(e*m5 l3uivtx.gwith 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 to produce 3.3 kW ofi4wv wrb)i9c, heat when connected to a 240-V source. What must be the resistance of the cwi),9vwrib4 element?    $\Omega$

  What is the maximum powerqi23 tyxjw/cxl(r4j 3.ful2 d consumption of a 3.0-V portable CD player that draws a maximum of 32qrj2jl3dx x f3.iw2tc/l 4 yu(0 mA of current?    W

  What is the maximum voltage that can be apporlztv+j;xkrzx + z7((fj 5p3lied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, a 75-W lightbn( rp1c)z(ab8:wrve + fx,,n p ctotj0ulb connected to its prope t a8n (r1rfjc0vo+x,ze,pcb:wt(pn )r 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. Calc.pxnhw2 87f nifa e1d6ulate
(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 settinelw s7cjcsbk2zpy,*r 4) s+j9gs: 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 is delivered to homescg d)5ce; bs+82i irw.u7otnl at 240 V. If you use the lightbulb in the United States at 120 V (assume its resistance does not chc) ii 7 +dros;g 52etn.bul8cwange), 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 mom(ihgmnd0u/nt ,g jf e78f, 3o:8 hwlorning if it is in operation for a7mjl, / 3hg:gi8efnud t0hm,(n ow8fo 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 p/ v*+ 1zyeh5wtftyb5d,yw c6 it cost to leave a 25-W porch light on day andf6t51t/*bewydzpy+c,y w 5 vh night for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected in s2cnjg8 j;p2lleries as in Fig. 18–4b (Fig. 18gl2 n;j c82jlp–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 wf* *0src4-txeho:fm4 x0 chc 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, ,cz z g;4f(0dkryvw.lconnected to 120 V as in Fig. 18–20, can be used witho,c dv ( .;fz4ygwlk0rzut blowing a 15-A fuse?    bulbs

  An extension cord made of two wires of diah 71n5afjzk jc;,k*k00q(0ka axj bir.f9 wph meter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electr pnri0f0 jhk;cx(a*7h f wjqz0b.j1 9 kka,ak5ic 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 12,000 V to a fxy./elgir: - u f1wux,actory through wires with total resistancuu r ,wx:ly/1gf-ex.i e $3.0\Omega$ 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 rat8/z+ a3nh2ls.jdzdj s e must cooling water pass over the coils if the water temperature is to rise by no more than 7.5n8s+zl .asdz 23hj/j d0 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to heat a cup of watep /*wx 6fpqj3o3( qey0fcq d:mr for coffee or tea. If the heater can heat 1j6:e/cfp(0fd q m poqx3*3 yqw20 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 c-p5ng9 tmoe.(9tv-l a:snu r burrent in 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 acrl 3u) rz.so0 sv8d cf(2;d-zy+td xn8bxow4wa oss a $330-\Omega$ resistor. What are the rms and peak currents in the resistor?
$I_{peak}$$\approx$    A(retain two decimal places)
$I_{rms}$ =    A

  Estimate the resistance of thetf :q2 )mlfo,i $120-V_{rms}$ 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 8s+*c-ipwf , sjvi 7 5mteuadz(f84qx1500-W device is 5.4 A. What is the rms vol4ft8+ (,vpim-du csf*5siqa8jwz xe7tage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected tg:v2afwvif tn 40l (cg )9d ;2uogh1lio 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 instantanesb/yo;7 vgvapn8z8u 7 ous power dissipated by a 3.0-hp pump connecteous8;yanb8v7p/ g 7vz d to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to mb4x*y bdnrsdjtp+-impn*2 9s f*5t0a $240-V_{rms}$ 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 tdp*m:n1hk i x/m)du1b iny 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 e y3h9h*ut( zfa 750-mA current when 22.0 mV is applied to its en9 (h3tz y*ufheds. 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 Earth’s atm* s+y)gmg9v0we0dpg n 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 

  At a point high in the Earth’s+-8gk w)awl0wuwwhqlnes5/ . 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 f7cp)zg4b 1 nneield across an axon membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated w7;rankt,zrwt w1wy71 ith an electric pulse. The action potential is detected at a point 3.40 cm down the axon 0.0052 s later. When the action pw 1wa; rtt7zw n7ky1r,otential 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 required to transmit onegb r(z)md 34ob action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored by ch4ob3mb()z gdr arging 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 pot00i)kv,a8td de3b oncw x4r e0ential, $Na^+$ 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 ar8by m*2pv x,obe there in 1.00 ampere-hour?    C

  What is the average current6xz*n7q8x. o t(xqo fd drawn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with ta n;eo p+-kl)bhe lights on. If each of the two headlights uses 40 W and each of the two taillights 6 W, for a total of 92 W, how long will a fresh 12-V ;n-bkaeo +l)pbattery 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-coi e 13tqms+,0h.kximts1*h9 1:i ab+cg eiaV, 1500-W heater is 5.4 m long. If it is made of iron, what must it sih0 ,i ce.:magie c m91xt11a+h*b3qskito+s diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of the mg.ss2 uq3j8u(h- tuslwv3 c +resistance R; t3wl2s um8. u3vqsu+-(hs jc gthat 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 usi,- q)unnx*w,xro og;ulg+6gkng high-voltage lines to supply thq n,g*u6)g;ou-+ r xln,k xogwe 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 hh1);nboiael0wo nk(9-b b v (jeater $3.0 h/day$ (“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 wr) 0lg dfn6ct6uo 4h idjt,uz1)apped together side by side to make a thicker wire. Holfud1,h)c tjz u6 tin6)g40dow 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.tmg2krp jm+( l(n. ekuzpya :+x .)4pr
(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 9 x(sdycgwn2swy oo2))f9me .become so hot as to start a fire. What diam2 )sf2s nyxodwgec.wy9)( 9ometer must a copper wire be if it is to carry a maximum current of 35 A and produce no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is gips 9j54)lk llxven by 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% efficiency delivers 950 W of energy per sek kzn9iz;8*qxukc4xlc+ t(n6ypj / *zcond to the interiorkjncic/ 6u z*z+xkzx49l 8(tp;k qn*y. 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 same material. One cond zt: .xj+26.rbweuw xructor is twice as long and twice the diameter of the second. What is the ratio of the .x reutr zw2: bx6wj.+power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room of volumdlg4u *) +ophqe $62\,m^3$ 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 sourcgm 5fh4e *+hw u,vdf3ke.
(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 sto wcwzid; 3n2/id,oo ppe4u;1p *j xnb:rage batteries as its source of energy. Its mass is 1560 kg and it is powered by 24 batteries, eachi2/o e;pp 1,4jw :doxnpu3 nwdcb;z*i 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*/fo8sq o p.tt 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 (Illijiz -cimm1di t o;+djr;lk1g nrwe50w 249j x0nois) is designed to carry an 11-mA beamor;gdjnm52jc4 mz iwr;109-l 1de ki0xjt+ iw 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 u( 9u0iahxeuu8ssxh - -t4pw5wire with a diameter of 1.628 m0ph8-usuw u x x 5at4(ihu9-esm.
(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 whee c, rv+ x7rhk *4vur8tn5oex/n 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 57ruxh /rveo cn*k +t4e,rx8vdiameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the sysrgft/( rtv*o su)rpzsrl4p+ky 71 /g(tem 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 power delivered to the headlights vary as the voltage changes from 12 V to 13.8 V?orl k7rrs *//)4zpp( +(tggtsuy 1r fv Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated n,2,f 4i ngon-7 glnn8hqlbb-at 120 V and 40 W for household applications. Lightbulb B is rated at 12 V and 40 W fogi,,gn l lo- nb2fh847-n nnqbr 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 un7o14-ogt ev0/ ky 0j cbf1+c8wcg3 z1wxpsklsed to connect a set of appliances at 120 V, which draw 2250 W 3eslcc4nk1w +y 7k10x-wz /cg1v gt8oj b0fpoof 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 ol b5rwvc1 eqam97ot )1s,lt;u utside diameter of 5.00 cmtq vs7u e;,rwlc 5obt1l)1ma9 (Fig. 18–37). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniforml /bw, m lsq2(l3iaip)yy so that its length doubles, by what factqys l3b/pmaii) l,w2(or 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 operates f, z8 1bv*lmkaat 0.20 A and 3.2 V. If its vmk bl8*,1z afresistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$