What quantity is measured by a battery ratin1 a/pf)s 5kd sebrp3fxa:a8-mg given in ampere-hours $(A\cdot H)$ ?

When an electric cell is c wkq) ptlszy3fh+*a *:onnected to a circuit, electrons flow away from the negative terminal in the circuit. But within the cell, electrons flowsqaw+ kz f )*thp*l:3y to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battery current, q e d3;.d7uueubattery voltage, battery energy, battery power, ordde.euuu;73 q battery resistance? Explain.

One terminal of a car battery is said to be connce-hzn.)+ x pjj*y hh.ected to “ground.” Since it is not rz x*-)h.hynhj+.epj c eally connected to the ground, what is meant by this expression?

When you turn on a water faucet, the water usually flows immediatwj ute zme+6gc-ug5 (b ;3ny4fely. You don’t gmy bc3u4z;5 ewt+eu jnf -g6(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 wire to the terminals of a battery?

Can a copper wire and an al )xeij:t) w,krc4d yr0uminum wire of the same length have the same resistance? Exr4ke,xd)c)j:yiw tr 0plain.

If the resistance of a small immersion heater (to heat water for tea or soup, F 6+yngff bpt(:ig. 18–32) was increased, would it speed up or slow down the heating py tfp 6(nb:fg+rocess? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, and 3a, how ohu6pw c8zf+)xf q*7gnc, ( xswould you connect the wires from a battery so as to obtain (a) fu *)cgf8w,x (hn67 cpq+ xzsothe 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 bix - zvhwp(qw69jlv mt-. +vx5urns out?

Explain why lightbulbs almost always burn out just as they are turn*;ms2zoq -icna 5weg4 xm)gv/ed on and not after they have been on foeazwsmc/g42) -nq i;x* vgo5 mr some time.

Which draws more current, osq:8x5,w;1iky.z .lm a/ x ga1 ii)ye sobrj2a 100-W lightbulb or a 75-W bulb? Which has the higher resriwl:,q z. kax2e5.1si x1 siymo) by;ao8j/gistance?

Electric power is transferred over ,)qhmbpk n:5blarge distances at very high voltages. Explain how the high voltage reduces power losses in the tr ,mhbnbk:)5 qpansmission lines.

A 15-A fuse blows repeatedly. Why is it dangeera. :u vgn5 zuc;64gsn(7tberous to replace this fuse with a 25-Anv n 6u;4cgg7es5t u(a:r b.ze fuse?

When electric lights are operated ou p bky*vp;7h,n low-frequency ac (say, 5 Hz), they flicker nupvbk* p 7,;hyoticeably. Why?

Driven by ac power, the same electrons pass back an-2 6cvixa bgujrt) )q6d forth through your reading lamp over an6)tba2i- 6u jrx)gqc vd over again. 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. Immediately aft 24+h kygtt9e. 0ihhwh3oka8ger the toaster is turned onoa+9h2tg h khw3. 48ygikt0 he, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a repe .c 9gl,f4;jvz1z b:m4z ,6tw dhdifsistor? Explain.

Different lamps might have batteries connected in eita9 x-vb(rrg6s her of the two arrangements sgsxr 6r- ba9(vhown 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 lr9t53(k7rdqwa z;xsons are flowing past any point in d7z 9qrkls wt5x r;a3(the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using hhtw +(f(s4mzgw/c,l a current of 6.7 A for 5.0 h. How much charge passes /w(+s 4fczhh m(g ,wtlthrough the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes;;lwqk v+bg.ki7j9u .z (enfe 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 pz;z3 q(l1jyo if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will prl xayy-shzh7p81 -gy ;oduce 0.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugge 5il ud+ :y7f8vmr2qckd into a 120-V line.
(a) What is its resistance?    $\Omega$
(b) How much charge passes through it in 15 min? (Assume direct current.)    $ \times10^{ 3}\;C$

  An electric clothes dryer has a heating element with abf ezwri-k7i+e .cr.)-ce 2h m 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 connecte q-6i/h 7orxbgv h7fsm5yr3/od 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 transmission line carrying 2800 A :dv:o0 b;/y( ergmtss(Fig. 18–34). The line hv yb :;(0m/rt: dsgeosas $2.5\times10^{ -5}\;\Omega$ resistance per meter, and the bird’s feet are 4.0 cm apart. What is the potential difference between the bird’s feet?    $ \times10^{-3 }\;V$

  An electric device draws 6.50 A at 240 V. 1k sh.x9j)(q 0jlh.jjtto. z t
(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 through a re s-vcn0 5 9ahpntl3/)hb+jr ajsistor.
(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 resistance irpfeg0t),v + cs $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wuub, v;9 3syb46dxxjd ire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistancet/8kfdn sof250ay/f6a ao8uj of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copp8/tun/ffojf0oa ykad25s a68er wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tungsten wire o qp5u y cv/n*1o3u auu*5eqossvnnw nyf4(5 /1f the same length? Give numerical uuq n/1noewsc1f*sn q5u45pynu 35aovvy ( /* details.    mm

  A certain copper wire has a 1bou9hs 6,jkh; f6 lnkresistance 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 (originalli + 5qk /x12gndmdf5chy at 5+c1kfxnhqi/ d2mgd5 $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature 3cxljeo4n6c ; 5h:ftfcopper will have the same resistivity as tungsten doee5cfc:;lf 6 h3 4nxtjos at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistanh,-ghii+*j d7g)k g czce 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 lenav ip5tx-q,3n3 x(j rdgth of household no. 14 copper wire (used in 15-A circuits). The wire has di(3t3dxxp5qv rjn,i-aameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carb ohq(-ez-; rrbon 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). zh(-;o erqr-b 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 r 6tui spvcei8jt3.3 2c*6 rzwgesistance. If one has twice the length of the other, what is the ratio of the diameter of the.ip u 8vrizg2ct3 c3swtj6*6e longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V power supply, kak5dk-dn q xbvx);/; and a curre5d/x v-qnk)x;bk kad; nt 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 wire consists of 5.: zt:. avfgn:;opml9 dadbz2- 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 across the composite wire. mdn: va::ogl bzz; 9a-.2 pftd
(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 applicationyk727(qxsziozno)+( 1 kd f3sjppo h5 s, it is important that the value of a resistance not change with temperatzk3 pnkh(1zo(ps7oyi)xo q7d5sj 2+fure. 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 electu,mwm yr49; xxric oven is designed to produce 3.3 kW of heat when connected to a 240-V source. What must be ywm 94;ux,rmxthe resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player that draws hi9lqycz6 0j9 vey02t a maximum ofz09ly 2y q60tiej9 cvh 320 mA of current?    W

  What is the maximum voltage that can be applied acrol29m,8 fpsxay tx09 qx*2bxeyss 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 connecp4 3fu qcrl6hv).)l duted to its proper source voltageu)vl6cl h3qr)f .d 4up of 120 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank hee:pk:.i; g qvhc(pc,fxe9b ) tater is 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: 850 W ;au 9-1b4ss:mohlz.dve9j wrand 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 i8a kuk6c4-3tuhj: 2/yyur 9lga, r qies delivered to homes at 240 V. If yra8k6l3 a j:yy2kqru4 uu-/, g9i ethcou 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: assume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use in the morniwp4df18o dc,b2f q y)ker63 qe x0x9dlng if it is in operation for a total of 15 min? At a cost of )xw42cl,yk red x98d6 1dq0qobp ef3f $9.0\,cents/kWh$, 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 co12ix. vwybk. kst to leave a 25-W porch light on day and night for a 1yxi.kvkb. 2wyear? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected in series 4( d0xy s-g h81w9xrvpz*sbcras in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when turnedry0-dhb s(*rwzsxpx149v c8g 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 st)em+ .1 yhn2hmw* rjefored 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 in Fig. 18–20, can be used wc( ee).z/pj*j5phuq26ttf/1smr drsithout blowing a 15-A fmptpz( .2e s1h/t*6s cq5e/ru drjf)juse?    bulbs

  An extension cord made of two wires of dio5a/ pibk 9kin ze2315 l5udniameter 0.129 cm (no. 16 copper wire) andp93 d5nk1i 25l zeaukbo5n ii/ 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 is dissipated in the cord?    W

  A power station delivers 620 kW of poweqk:g (k k1-kwwbj(6nw29dsnkhz9 wh/r at 12,000 V to a factory through wires with total resistanc kk1nwh -j6hg/ :b29wzwks d( (qwkn9ke $3.0\Omega$ 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 wha0 0jmkompzerbx o9uk/,.f 1e) t rate must cooling water pass over the coils if theze0erbu1m)x mk o,fj/po. k09 water temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car *n. k6- wh2jba)y zflp;nkt+vto heat a cup of water for coffee a)n y.lv+h;n6zpb f2kj*ktw- or tea. If 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 curm 5je3,hpdm/ grent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value i+d+7uifqy1gvfvsr mv v(ufyr3 k,/85 s 180 V, is across a $330-\Omega$ resistor. What are the rms and peak currents in the resistor?
$I_{peak}$$\approx$    A(retain two decimal places)
$I_{rms}$ =    A

  Estimate the resista5vh rsq2omo/wc, 4( usnce 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 alternating current in a 1500-W device is 5.4 A).xwmt. ridd do,x4j;. What is the rms voltage acr.,xi dt;dwox d4m. )rjoss it?    V (Round to the nearest integer)

  An 1800-W arc welder i1oe7. x)f4qggzfnvmz ,( xl i8s connected to a $660-V_{rms}$ ac line. Calculate
(a) the peak voltage$\approx$    V(retain one decimal places)
(b) the peak current.    A

  (a) What is the maximum instantaneous power dissipated k( rzo2qsp 6f;ffq-,6 :fv zz4ie(xvaby a 3.0-hp pump connected to af 6(vf z4-x ifozf ,qzqv6(rkae:s;p2 $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected d oiy6c-a50p4cyg zl n)7 z0q)lbsv 2kto 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 ot;clat o 4xu m6n7p k4;u**doa 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 carrie-jgg 0di,c us 8qc9(ikn s)vd1s a 750-mA current when 22.0 mV is),(n9c i c8 s0quvgij-sdkdg1 applied to 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 Earth’s a-xx wnl 4ber yyr12/g/tmosphere, $He^{2+}$ 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 atmosphes,l6fq4t/ .hptdt 6pwre, $He^{2+}$ 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 thhb7l (1 cywr(he 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 with k b1zp o/-vma v .(ew5x3bfyo8an 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 pe 3 x5 bzoyvo.bwv18ma(f/-kthe 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 one action potentiu(epsvd h48*c al along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy ssuc peh(dv* 48tored 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 potentia cme-iw1rcj7 1wj-; dxl, $Na^+$ 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-hoqbf5 exp9imw cmq3ra5r/5jt095 or jl 7w,dq 2ur?    C

  What is the average current drawn by a 1.0-hp zulz(tjkn 55d :8 lzy*120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. Ix qi 5zd/6p7wwshsx19f each of the two headlights uses 40 W and ws ph/i17x 59wzsd6qx 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, 15fx3wlj2 ws)rp +zt1* k00-W heater is 5.4 m long. If it is made of iron, what must its *xp 2 )3sw+j l1kfrzwtdiameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the renuc5 f5/u* l jylxq3pegox .78lslf:9ciprocal of the resistance R; that n:lqo u355j.x9uc8/7ff py*elxl gsl 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. Su5k ) 4kqlb:yqnppose that instead of using high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a two-wire line ofky)4qqlk:5 nb 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 usescj ;./h 6gp.pybqr3 zu 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 the two lengths are wrapped together side bpjg1v 8o(-z /o-et wbay side to make a thicker wir gtjep b/-zov18a w-(oe. How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is d 9)yu*(/c ,q-hp z:jz0pbuhw iun,fjkesigned 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 house must be thick enough so it does not become so hot as ln/o ac0x/ 3spt vc2s8to start a fire. What diameter must a copper wire be if it is to carry a maxivac t82sx/o/lnc30ps mum 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 givep; pfn6ci1+ yhn 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 ewy6ylm,by h6v x4 e-d83;lw oonergy per second to the inte6 mwo 3b8yo4d xy ,evy6;lh-lwrior. 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 kaxc*t23qy c*n5 af6itwo different conductors made of the same material. One conductor is twice as long and twice the diameter of the second. What is the ratio of the power transformed in the first relative to the second? i* t6nk*qayc5 32cafx$P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a ro (rsn hvci5rwz2s/pm g e(35p)om 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 24d ogd07b;u (ccfv(p4 7s0oxo6 ks+rvs0-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 o u.oiv65dxrd l5l/w5m)gut- hx, szx+f storage batteries as its source of energy. Its mass is 1560 kg and orx6) lgd +,l m xh55.zutvwdx-5usi/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 a resistance 3f+suan *v(g sof $12\Omega$ 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 acceleratwqsb*c8 2kp/ g9mv4)hmbbdm : or at Fermilab (Illinois) is designed to carry an 11-mA beam of protons traveling)kqg2bm:h s8m mpv /w9b4 d*cb 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 wire wi8:k*iyvqeh:t w. m4ryb;;ynr th a diameter of 1.628 mm. bv4 *:nk r; m :;tyyeryi.hw8q
(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 ik rzx5)h+07uu dru*rw s rated at 95 W when connected to 120 V. The heating element is a coil of Nichrome wire. When unco r0d)*w+hux 7 rrkzu5uiled, the wire has a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from about 12 V when the car is 1crg m d42jqi s-1pg9boff to about 13.8 V when the car is on and the charging system i1g9gdrc p j4b1qms i-2s 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? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for household applications. Lightbulb nw7je)+ 4zsrmB is rated at 12 V and 40 W for automotiwm s+n rj7)e4zve 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 connc1bhwdhtv:; m* z)9kdect a set of appliances at 120 V, which dv1dh )z:mbhd9ktcw *; raw 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 outside diametea/)nk.;9 xc rziter g:y0)rl3ve3ioe r of 5.00 cm (Fig. 18–37). What is t)kr) cxivyez .l 0tgr3;n ie9:/3oe arhe resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its levqim1) 74 abhrngth doubles, by what 4)i avm bqh7r1factor 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 at 0.20 A and 3.2 V. Ifrcw 3qt+41am+,l yu -yhz gdo) its resistance atwg +1,m 3+u)y-lrzh yo q4tdca 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$