What quantity is measured by a battery ratin5-1wyw1et nog rn/fl)hvli, /g given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connectj k( cda3/kt+z(3wm r lvv b/)xp7v7pned to a circuit, electrons flow away from the negative terminal /vw( / cdpr7v k+k z v7n3(ap)ml3tbxjin the circuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is opera(vrv1,;g:p kxvmk. aa ted, what is being used up: battery current, battery voltage, battery energy, battery power, or battery resip,1am.v:kv(;ra kxv g stance? Explain.

One terminal of a car battery gipa:p) pt+o7 is said to be connected to “ground.” Since it is not really connected to the ground, a tpi:gp+ o)7pwhat is meant by this expression?

When you turn on a water faucet, the water usually flows immediatels0 o(n9kz mqszn28at-vs.ow 3y. You don’t have to wait for water to flow from the faucet valve to the spout. Why not? Is the same thizsmvoosz 9qnn0 823 .kw(s -atng true when you connect a wire to the terminals of a battery?

Can a copper wire and an mg4-.io7rb m-0uqukd aluminum wire of the same length have the same resistance? Explain7- o-.bmik4gd0urq um.

If the resistance of a small immersion b() dm:qp0 :gkbe9rrs:t pl6 mheater (to heat water for tea or soup, Fig. 18–32) was increased, would itrslk:)b q:rgd0b :6pmtm(p 9e speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths *8rzi 7( nunqca*cpz 8(cs7bia, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the leap*ir c((* c8 78nabn zis7uzcqst 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 burns ogwcdt+1 : i (od)gy(mxut?

Explain why lightbulbs almost always burn out just as they are t1zd 7jem9* 1hh6kyem vurned on and not after they have been on for sm y7k*6h1 m eedh91zvjome time.

Which draws more current, a 100-W lightbulb or a 7 me2yugi*42oi 5-W bulb? Which has the higher resistan 2gu*m2ei oi4yce?

Electric power is transferred over large distances at very high voltagesb7o cp5u;mmidhd, 7c znj/-s 1 )lhx-j. Explai7bi5xmz hd d;/jhlcm) cj-np7,-ou 1 sn how the high voltage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why isjlhb9 f4s3gcd ,b)4fu it dangerous to replace this fuse with a 25-cs,hdgf ) l4 4f3b9bjuA fuse?

When electric lights are operated on low-frequency ac (say, 5 Hz), thez,/4 eiuizvz4a yu7;ry flicker noticeab44zyu/ ; uiva,zi r7zely. Why?

Driven by ac power, the same electrons pas5jx re4 xit (0 ghs14k,tgo;g h+7iryns back and forth through your reading lamp over and over again. Explain why the light stays lit,gt4r0hj(;og g rhxyi5te nik+s147 x instead of going out after the first pass of electrons.

The heating element in 4kqoa m).;gzra toaster is made of Nichrome wire. Immediately after thezom.q);4ka rg toaster is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resish o g5x5dtyew2:u6mt :tor? Explain.

Different lamps might have batteries connected in either of the two arrj s i(x-pd+(jwkt7 n1mangements sh nj1kdws+mt j-p(i(x7 own 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 are flo, 4g ng)dhw58fp toe.bwing past any point in the wire pdw4on 5tfh8.gbpg) e,er second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a rmc :i /dcep54current of 6.7 A for 5.0 h. How much/i:cmerp c5d4 charge passes through the battery?    $ \times10^{ 5}\;C$

  What is the current qk3e kxli/kt3x18 (aug* 7mzoin amperes 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 toasn6npr g.a2c *kjyi mr4/0a)g lter if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of curry*m h1h-mvadv; )t+g34juwrb -dis 6 ment through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into az ,a;386wpq (tqz;r zzc;qoq i 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 with a resistancect ;pmfg7,xi ) 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 conkzf8ln;( n1;jfcg8l hvh d2*z* o3i bqnected 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 electr.20ftg1 x i8dq+oeoc iic transmission line carrying 2800 A (Fig. 18–34). Th1 8+ce t02xgidifo.o qe line has $2.5\times10^{ -5}\;\Omega$ resistance per meter, and the bird’s feet are 4.0 cm apart. What is the potential difference between the bird’s feet?    $ \times10^{-3 }\;V$

  An electric device draws 6.50 qz47l*-xw*zmct* ch v t2 pc,o1jw p4jA 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 current of 0.60 A thkr+z,1z 9dekh8o.p oq rough 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 lk3ao 6)gixk0:+d elxq1 eu 9ykength of tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of cobck(.avxxz 1(6z :q edpper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum x24 +ufqnx3siwire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in3n+xuqf2is4 x diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tungsten 7p0zjzt:9 uob wire of up :o0jtz79bz the same length? Give numerical details.    mm

  A certain copper wire has - myqd nt,0so4a resistance of $10.0\Omega$ At what point along its length must the wire be cut so that the resistance of one piece is 4.0 times the resistance of the other? What is the resistance of each piece?
$R_{short }$   $\Omega$
$R_{long }$    $\Omega$

  How much would you have to raise the temperature of a copper wu0 qzdr/ t0-wv) d.ut wbih63eire (originally at qd.ut6)0 t-bze3w/0drhu v wi $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature cm:2+kbh oh1phdl,s* dopper will have the same resistivity as tungsten does ats ,:1b+2phdmhdo* hkl $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb hasaaub:1 2m*wxi8 : 2zg9rbx-l; mz48e dkdhpzg a 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 alo)v 0 uco9sr1ksng a 26-m length of household no. 14 copper wire (used in 15-A circuits). The wire has1r9 0cok s)suv diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengt ka5 m*i8ecf/shs 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (e /ic* mkfas85Fig. 18–35). Determine the resistance for current that passes through the solid in
(a) the x direction,    $ \times10^{ -4}\;\Omega$
(b) the y direction,    $ \times10^{ -3}\;\Omega$
(c) the z direction. Assume the resistivity is $\rho\,=\,3.0\times10^{ -5}\;\Omega\cdot m$.
   $ \times10^{ -3}\;\Omega$

  Two aluminum wires have the same resistance. If /kwjetnfy/j6k* puj;ws,1 ,vone has twice the length of the other, what is the ratio of the diameter of the longer wire to the diameter of the shorter wire61ntuvfjkwyjsw *k;p/ ,,/e j? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V power supply, an loqycf*17v v5(jsyh ,d a current of 0.4212 A is preciseh v15* yql fvoyj7(,csly 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 coppema7/ q/qgw.aeh9is n8p9ex 1: w8d lv2iy.df sr followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage differeied8em8vq1hny. ds7f/a ls9xi92 g p/a: wq.wnce 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, it is important that the value of a resistanceqt kzi 7s +;cr-/y(muo not change with temperature. For example, suppose you madeo;t(q7/symuk ri+ - zc 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 lh :wm1s *,t 7pui/jhzj 7m7 rjb0ksc03.3 kW of heat when connected to a 240-V source. What must be the resistancec jjri p7wtj7mz0 1hu:lmskb7,* 0s/h of the element?    $\Omega$

  What is the maximum power consd n(rt)cwg*nr4 9iai -umption of a 3.0-V portable CD player that draws a maximum cni9 r)ig w-dn(a4*trof 320 mA of current?    W

  What is the maximum voltage that can be applied a1;gjp6-whfil)j9zz a cross 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 co87 /n4b 5pqubn7dlbakd84n rbnnected to itrnp48bdqba n8dlu5nk74/b 7b s 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 i33u b*o5s w)ywonrez7s rated 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: rk hlq+ knjki7ms*326850 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 Europ.:t3uwzkq ml bb(2s .ue, where electricity is delivered to homes at 240 V. If you use the lightbulb in tublm:qb uk32 z.t( .wshe United States at 120 V (assume its resistance does not change), how bright will it be relative to 75-W 120-V bulbs? [Hint: assume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use in the morning if it is 1i6uif1wh2.tr b adm1 in operat1hw rufa1.tbi62d im1ion 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 j4)-t.e)xthr ckl drm* k7n)W porch light on day and night for a year.tw kek))-) dmrl n*7jth4cx r? $\approx$    dollars

  An ordinary flashlight uses two4tj /af(2 ,iyb wp ks:iqu xr1i0qt2;a D-cell 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when turnet4if 12 / rqp;y ,:aqkti(w 2xjasi0bud 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 s8ai)x.vn (prptored in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbu9uhqs9c hs 8jfkg qj9.) acj-o8pvv1*lbs, connected to 120 V as in Fig. 18–20, can be used without blowing a 15-A fuse?-uv 9 g.q8scc)f9q 1*hsapj 8v 9jokhj    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 copper wiromtq8j x-*x eey 9k5w/e) and of 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 ixew5 / myx8j-qo9k e*ts dissipated in the cord?    W

  A power station delivers 620 kW of power at 12,000 0b7i4eakiu1h rt+9n;uz)o g he8fsr /V to a factory through wires with total reshat0ue4r87fz ieo;+ 9rb1n)s khg iu/istance $3.0\Omega$ 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 electromah lkj2/lh.)l3izcnc *n0rt s6 gnet connected to a 240-V line is 17.5 A. At what rate must cooling water pass over the coils if the watez n3rjhnll2l) /c s0 *hi.tkc6r temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater canx 4wv(6x p:jzf fmtlow 7m47m+ be used in a car to heat a cup of water for coffee or tea. If the heater can h+4pf fm6 7v4xo7jl:z xmwt( wmeat 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 cuz9 ;ngjgq m(5kw o+mp.rrent 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 acrosksrv za()i3dlf +ln4 /s 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 th2* q;gmua+ uye l+9kk dv0jo9s /p*psbe $120-V_{rms}$ 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 150kd0gm 6q)6)la vw1cl y0-W device is 5.4 A. What is the rms voltage across it? 60kvagdq1l c) myw)6l    V (Round to the nearest integer)

  An 1800-W arc welder is cw8 skg v1a2/jtk1o,- 0 or;c ixn 8otzfksfi7)onnected 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.z 51jubzzhd3pw/ xon17 2ebr* 0-hp pump connected to zhz115jb/zbpn73* rdo 2w xuea $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connec,:/eglapm9 p xted 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 wire carries a tiny currenx8hhme3ai94x(u/)cbsu pz2 ot 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 wy e gc;l3x:x,pire carries a 750-mA current when 22.0 mV is applied to its ends. If lg pxc:xey3,;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 Eart*bnxdqj+ : :xxh’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 atmosj nkrae, y1i)y+ qwli knv3vwn:4(,(cm0v(xkphere, $He^{2+}$ 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 e vn.m y 2o1)ge:xfkc*3rcb3 ethe electric 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 witqzq + bw)ld wsmig+) ,znk1m15h an electric 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 awq+)l) k+gmwnbq1z ,zsi d5m 1re two measurements needed instead of only one?)    m/s

  Estimate how much ene foutj:+ww)yc+8 a;mmopr7c3rgy is required to transmit one action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is eo87+cm 3yuw jo+wfmpact:;)rquivalent 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 potentialiqd d ot21fm zgh*0iz4p2.bx+zk,e z7, $Na^+$ 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 aa0 ebdbvb; 8 pi(2tm/there in 1.00 ampere-hour?    C

  What is the average current dra ylqhw10:m pqyzz-- 5vql .vv/wn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a cz/ de-gxxym)-2*ib- gk-me ewar with the lights on. If each of the two headlights uses 40 W and each of b-dm-gx*ie z-kxmewy2/ e)g-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 fzxo b*. *d)gklb;9v*h dw8zg2)vmpu5.4 m long. If it is made of ironkg9)v;d*ob. v)zzg2xh fl*8bu*m dwp, what must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an5wm+ pyb18 oeebb3( jt object is defined as the reciprocal of the resistance R; that isbopty m( 5 bj18w+bee3, $G\,=\,1/R$. 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 using hm8 aaii-( izd0 ,jma -x2ufls4igh-voltage lines to supply the power, the power is delivered aam 0 u-,fisiz 4l 2jai8max-d(t 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 1.8i90 g,saikua gve;85u -kW heater $3.0 h/day$ (“on” time), four 100-W lightbulbs $6.0 h/day$, a 3.0-kW electric stove element for a total of $1.4 h/day$ and miscellaneous power amounting to $2.0 kWh/day$. If electricity costs $0.105 per kWh, what will be their monthly bill (30 d)?    dollars per month
(b) How much coal (which produces $7000 kcal/kg$) must be burned by a 35%-efficient power plant to provide the yearly needs of this household?    kg of coal

A length of wire is cut in half and the two lengths are wrapped tog4mf lsbgy;( yx/beb**ether side by side to make a thicker wire. How sxgmbb(l y/* e;b *yf4does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 117 V.qx1k r8vqozrr ei t +82:yks--
(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 doesaq6)pwal2qg07 * 0jo zia+zo n3aw lp5 not become so hot as to start a fire. What diameter must a copper wir6lw5paw)a0oj *0qg7 32 lzzo+ apa iqne 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 given b4e w-q2x q1qxxb6tk ,ny 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 ofa ,0 qimu1v 9k,ecf+4nylc0rw energy per second to the interior.4unwcikq10fe +yar0 , vl9 c,m 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. On.fz jzal- fk8:lvdi90e conductor is twice as long and twice the lj.i0-l8 z:9fazvfdk diameter of the second. What is the ratio of the power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat30cq5hk jglqev f ;d(hhg/)ds. ey;l( 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 to a ylfrt -rbg+*l4 oy3k*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;tnn/q pfmppzf)+(y / use of storage batteries as its source of energy. Its mass is 1560 kgfyf (n+m/p;ntz/p)p q 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 light2:k kv(ato 1m()rqho5ekp: vybulb 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 accelerr4jiavqkj, :d8ui1 6hator at Fermilab (Illinois) is designed to carry an 11-mA beam of protons traveling ah,av q ii j4618ur:djkt 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.u v tmg+e/(nj pq.c*gr wire with a diameter of 1.628 mm./njq( tvucg.ep gm *+.
(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 950wo)m5pp pe 65 hddho5 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 tdph 5mwpe 0o56o5dp h)he diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from about 12 Vk( 6wq 0kekaz:wb(t 8t 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 aek:ttba k k8q((wz0w6s 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 hous 5* vgx:vugqc,ehold applications. Lightbulb B is rated at 12 V and 40 W for automotive applications. xgvgq,v: c*5 u
(a) What is the current through each bulb? $I_A$ =    A $I_B$ =    A
(b) What is the resistance of each bulb? $R_A$ =  $\Omega$ $R_B$ =  $\Omega$
(c) In one hour, how much charge passes through each bulb? $Q_A$ =    C$Q_B$ =    C
(d) In one hour, how much energy does each bulb use?    $ \times10^{5 }\;J$
(e) Which bulb requires larger diameter wires to connect its power source and the bulb?  ----待选择----Bulb BBulb A 

  Copper wire of diameter 0.259 cm is used to connect a set of appliances atraayjf3.hf2v3 :zf 1 w 120 V, which draw 2250 W of power tota1 h.:w3 jf2a3fy rvfzal.
(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+q 30wcr/smagqvv sai6+o 5y, diameter of 3.00 cm and an outside diameter of 5.00 cm 56gr q cwvi +s mvosy03q,a+/a(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 uniformly so that its length doubles0fg5(1 tdwfl p, by what factor does the power dissipated in the wire change, assuming it remains hooked up totg l(f50 fp1dw the same voltage source?

  A tungsten filament used in a flashlight bulb operates at 0.20 o)pa6d,wp2q*/m p+vw dc:l pcA and 3.2 V. If its resistancwl/2 c 6q,ap) w+*d:v dopcmppe at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$