What quantity is measured by a battery rating given in akailcnsl l.( ti0z,72 mpere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow ,iwan+ ..n xpw9xst9h away from the negative terminal in the circuit. But within the cell, electrons flow to t.9 i 9nhwxa ,xpsnw+.the negative terminal. Explain.

When a flashlight is operated, what is being used up: batter, 7fqpcr,x;;d5b6ta fn dr+di y current, battery voltage, battery energy, battery ,cidd6f , fa;q+xrptrb7n ;d5power, or battery resistance? Explain.

One terminal of a car battery is said to be con7npbp am 580tqnected to “ground.” Since it is not really connected to the ground, what is meant by this ex5nm80atq7bp p pression?

When you turn on a water faucet, the 0vqeb;tkxc t;.htkd:d6u(1n. 8 cor gwater usually flows immediately. You don’t have to wait for water to flow fred.vccghqn k:ko8bt. ;r(;ut6dt x01om 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 wire of the same length have the same 2s07600oyfb c vlnafl resistance? a0fly2focns67bv l 00 Explain.

If the resistance of a small immersionc6 n 9:j002qbn+onf uqqyylx ;h)ok(k heater (to heat water for tea or soup, Fig. 18–32) was increasnyqqfuq9 +k0:2(x0yj;b coolk)h6n n ed, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of leng j n6:-vp-p dmwnve5ns0n91 uaths a, 2a, and 3a, how would y5av vwj16pe0 -npud nnnm9:-sou connect the wires from 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 burns ou7 kdtaqp;w;c5mdg ,:ar4:ql69ecu mmt?

Explain why lightbulbs almost always burn out just as they are turned on amy9eico g(f* )nd not after they have been on for some tii *o )ce9(gymfme.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which hryd c(o5/q6fpx h.i6mas the higher resistancodx (h5.f6m6pyq rc/i e?

Electric power is transferg 8plws3+e7a:iy 2v vvred over large distances at very high voltages. Explain h 8v iv:apvw2ye3gl+s7ow the high voltage reduces power losses in the transmission lines.

A 15-A fuse blows repeat1kxa:k5-oi+izlic 3o edly. Why is it dangerous to replace this fuse with a 25- lkz5ax+:ciooi-1 ki 3A fuse?

When electric lights are operated on low-frequency ac (say, 5 Hz) n 24r7mashig0, they flicker nsm07n4 2higr aoticeably. Why?

Driven by ac power, the same electrons pass back and fo sp514mijjo v,rth through your reading lamp over a1sj5 ojipmv,4nd over again. Explain why the light stays lit instead of going out after the first pass of electrons.

The heating element in 1:e n,cq6pldda toaster is made of Nichrome wire. Immediately after the toaster is : ,nd qed1cp6lturned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? 7b, ar3o(tb2g woky ;zExplain.

Different lamps might have batteries connectj)vgx2o* +a1/irgsl. qfks 4led in either of the two arrangements shown il/qlgv x4 g1jor2)sski.+ *af n
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 2pblicf*)lnbgwv6z1.+u j h4 flowing past any point in the l.h1 jzfbubw4 ngv+)p62 l*icwire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A for 5.0 h. How muwfs gb7ew13z1h *)fb3nw 7 iuzf0ejp:ch charge passes fgbpw *w1if3n7h3b eeuzs:w 7 1fj )0zthrough the battery?    $ \times10^{ 5}\;C$

  What is the current in +v.z6u )::h z44pvy ekylxmdjamperes 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 to90s;;mz gn/3hpdc es yaster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.258 9 4sctg1dglx A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A whenn72+bcep t8ol plugged 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 a resistance of u :jzko n67pw41g ftblb09l x5$9.6-\Omega$.
(a) What is the current in the element when it is connected to 240 V?    A
(b) How much charge passes through the element in 50 min?    $ \times10^{ 4}\;C$

  A 9.0-V battery is connected to a bulb whose resis 4s-zcqaz.2 ncfpf,b4tance 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 7:nut.a(0of sr1gj/w. d lm yhA (Fig. 18–34). Tr.t0sdw gj: l/ 17yufm(on. ahhe 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 A at 240s4cg9 h/08 t(fp4qlumkp6 s qs 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 avt7iz*0xk8or3 ek,gvi 6uo q2 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 n8 e d ( ,srjr+ohyk-o0y6bdy3of tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance ozyoy v0-d buppb28 w kvf-o,4p:h +z9zf a 3.5-m length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of th h0e4zhvcqt-xp / /+txe resistance of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of ptzc -xq/+th4h/ vex0copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the svk glp99ea(; tkvr+g9h2a io 8ame resistance as a tungsten wire of the same length? Give numerv2;9pa h lt9gaoreg8k9k iv(+ ical details.    mm

  A certain copper wire has autnf -w4u i.4a 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 wire (originally ax w lun*0e(((/7xgiwgq+ efkctflqge0enx c(+(w /gu7 xik*(w $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivity 8q omieb qam x*y4)0+cas tungsten doesme)*4coqiy x+ m8 qb0a at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of a(,((u gwjp2/ngjbqr w bout $12\Omega$ 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 household no. 14 copper wir 5s db5 e/vboq1xps0,t0h bf3de (used in 15-A circuits). The wire has diameter 1.628 mm and carries b5f3/d1dp5sboqv txe,0 h0bsa 12-A current.    V

  A rectangular solid made of carbon has sides osy( v /gh+n)nfoahj .3f lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, re/yg nns3 j(ah. fv)+ohspectively (Fig. 18–35). Determine the resistance for current that passes through the solid in
(a) the x direction,    $ \times10^{ -4}\;\Omega$
(b) the y direction,    $ \times10^{ -3}\;\Omega$
(c) the z direction. Assume the resistivity is $\rho\,=\,3.0\times10^{ -5}\;\Omega\cdot m$.
   $ \times10^{ -3}\;\Omega$

  Two aluminum wires have() jjddiqyolsl6pax)0h 4.( f the same resistance. If one has twice the length of the other, what is the ratio of the diameter of the longer yo))( 0ji4p6xh( lljfd .qadswire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a wv j/q +9nlf/kprecision 10.00-V power supply, and a current of 0.4212 A is precisely measured lw/nfk+9qv /jat 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 followed by 5.0 m of aluminux bi3g6i3wp+9 v)x, c;alj apem, both of diameter 1.0 mm. A voltage difference of 85 mV is placed across the compa,6ep3+pajxwigv c;l)x3b i9osite 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 importgtnv1 hfs- *;vant that the value of a resistance not change with temperature. For example, suppose youvv1;t* nsg- hf 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 kW3.hd* uwwnf3 k of heat when connected to a 240-V source. What must be the resistance of the element?d*uf wnwh 33k.    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player g)r a,g.zml4a that draws a maximum of 320 mA of cu.amag4)g l z,rrrent?    W

  What is the maximum voltage that can iv p0g1y p;+j3a 0q omuvrtte-tz.:5mbe applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current througe;ko-k h(5k d8wz ae7dh, a 75-W lightbulb connected to its prwh7d;zkk-o ( ke85adeoper 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 racdydt)2la8q 3ted 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 pgb5 j5.ce2*jvu gsr y4wo:t 8two settings: 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 homes at 2icwahqjic9:,b s k7w f l83r6940 V. If you use the lightbulb in the United States at 120 V (assume its resistance does not change), how bright will it be relative to 75-W 120-V bulbs? [Hint: assume roughly that brightness is prowcs:r6lj c3i9b 89qkfw7h ai ,portional to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use in the morning if it is in ,k2cfo /4 mseemkq0 2uoperation for a total of 15 min? Ats4q202u/co,meke k f m a cost of $9.0\,cents/kWh$, estimate how much this would add to your monthly electric energy bill if you made toast four mornings per week.
energy $\approx$    kWh
cost $\approx$    cents/mouth

  At 0.095 dollars per kWh, what does it cost to leave a 25-W porch lwhb8c+ i( at3oight on day and night for a yeabtow8(c +ah 3ir? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected in series x s1ggt20 n8lqas in Fig. 18–4b (Fig. 18–36). Thexl 1 80n2qtgsg 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 of energy stored i7o2cjl6 d ;qmpn 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. 18qk fw6pl8pepc*75b .l–20, can be used withofbpl6pcp5kelw * q7.8 ut blowing a 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 copper z -* iwne8)q/ ub+zef-sm 6cqzwire) and of length 2.7 m (9 ft) is connected to an electric heater which draws 15.0 A on a 120-Vbe8ew zzmqzi6n fuq+)-s* -/c line. How much power is dissipated in the cord?    W

  A power station delivers 620 kW of poweposfmub8iy633b 5 , jur at 12,000 V to a factory through wires witjb,mopu3s 863buf yi5 h total resistance $3.0\Omega$ How much less power is wasted if the electricity is delivered at 50,000 V rather than 12,000 V?    $ \times10^{ 3}\;W$

  The current in an electromagnet coux-4q (igwoq e0cti )g46 dp.d9rvl:k4ghi5fnnected to a 240-V line is 17.5 A. At what rate must cooling water pass over the c0r9 l4v4d dqig tgi: (ufw46p. 5qek-xgicoh)oils if the 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 to heat a cup of water fory) d7e;yyfx* )*feo w.v*vh+yrjeq l2 coffee or tea. If the heater can r)eyow *yq y+eh * dej )yf*;vlv.xf27heat 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 in a jw-:w2ljt4 yx$2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, is acrosk5n ea5l 5n8xkqlj 8r3s 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*cwr7wf6vt sc0 tf6( h 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 ansgj.nq i t -og3ycs3.)s6ej;d alternating current in a 1500-W device is 5.4 A. What is the rms voltage ay;-oc3g3snts .dq)6.sige jj cross it?    V (Round to the nearest integer)

  An 1800-W arc welder is6 p*sqgy+ gn7i 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 inaj;oonla kr:6qf 0 5p)stantaneous power dissipated by a 3.0-hp pump connected to lj:; apa05fq onk) r6oa $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connectecvca- l1,f nrmuzkg1t-) 8 0 vh;1fawkd 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 coplw yay+hca .p77zmq4/per wire carries a tiny current of $2.3\mu A$. What is the electron drift speed in the wire?    $ \times10^{-10 }\;m/s$

  A 5.80-m length of 2.0-mm(asr6d9pg*e*,jpp+in ;fw3m woaov 9d9)z kk-diameter wire carries a 750-mA current when 22.0 mV is applied to its ends. If the drift speed ig6is+ro* opkn 9e3zd 9kawv p*; (j,w)9afdmps $ 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 Eartie;t/o +jzrlu3; ir5hh’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’fhg hd+uz2; psn*hshzj :73)bs 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;x96rnkm4csii t0 i1 t of the 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 an b 6niuwd9i1 t56xj8p celectric pulse. The action potential is detected 5idu18i x6wptc9 jb6nat 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 needed instead of only one?)    m/s

  Estimate how much energy is required toe -qvsn 0+gh+m transmit one action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored by g+0qs -e +nvmhcharging 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 potentir/ji*r;f zo2 3zka b6aal, $Na^+$ 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 anl84lx.fus3sw19i 3t4l gkyzfu7z o; uie c- 8mpere-hour?    C

  What is the average current drawn by a 1.0-hp 12gw r kt6jp:*88q oy5 znleo*6x0-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on.d5w7pu 8p0xbi- aw+vh u0 uuw4 If each of the two headlights uses 40 W an+d0u u50vhbwp8uiwxpua-4 w7d 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-x7 vgj3,6ei ohg59nx4r h+j kxV, 1500-W heater is 5.4 m long. If it is made of iron, what must its diameter be? v5xh 4n7+ x9o, kjrhij63ge gx    $ \times10^{ -4}\;m$

  The conductance G of an objg54m ,su1bbq5g;skr(v eix /gect is defined as the reciprocal of the resistance R; that is 4,5/skm(i1e5r gv g q;xubbsg, $G\,=\,1/R$. 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 ggn jo1n7s+)js;lmk + high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a two-wire line of 0.50-cm-diameter copper wire, estimate the cost of the energy lost to heat per hour per meter. Assume the cost of electricity is about 10 cents per kWhn++m);o kgsj1l g7 sjn.    dollars per hour per meter

  (a) A particular household uses a 1.8-kW h n .;0p.8xs.bvy wzduveater $3.0 h/day$ (“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 twsxcg*8n w 8ai,q8s 9s/x :ig r m9otq7m3ovlf4o lengths are wrapped together side by si*l8/osmv8 f83 rt q9gii 4owxgnm7sx q:9,ascde to make a thicker wire. How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is n brr(qv4s5e) 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 house must be thick enough so it does ey-ue,k5ohu (not become so hot as to start a fire. What diameter must u,u e-kh5 oy(ea 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 given by the equatiovy jju5 bp:hi7+ a.tt(neo44an $I\,=\,1.80sin210t$, 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 rd w/ 3i8nzvv365% efficiency delivers 950 W of energy per second to thi /8dw3nvv r3ze 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 made of the same m rlav 17+s s1b/ugl5ynaterial. One conductor is twice as long and twice trlbsy1 sl a/vu5n7 1+ghe 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/d5zpp 4z0-r2 djm lbo to heat 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 240-V source cilc7pknt -2 h/eo7:*gz7v ow.
(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 storage ba8m-m0f 0 +xsosznfoc1tteries as its source of energy. Its mass is 1560 kg and it is powered by 24 ba08ox-mfs mc+n0f1s zo tteries, 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 aae(5jx wk z+t1 resistance of $12\Omega$ when cold (20$^{\circ}\,C$) and $140\Omega$ when on (hot). Calculate its power consumption at
(a) the instant it is turned on,    W
(b) after a few moments when it is hot.    W

  The Tevatron accelerator at Fermilab (Illinois) is designed to carry an 11.a o 82hywf4; t( aeu-i4oytjn-mA beam of protons traveling at veri 8anu-y.(at ofeoj ;yth2w 44y 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 connecti/,ohqku rjq7ny6aq,apc)*6mng cord is copper wire with a diameter of 1.6qpqq 6uykraa,,6ojc*mh7 n )/28 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 a o l9uwv02jxqti;n,*wt 95 W when connected to 120 V. The heating element is a coil iv 90xt*un,2;oqwjwl of Nichrome wire. When uncoiled, 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 vojhm 1.m ov*x+st ./ir3k( mdjhltage 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 v( dhxs .roj+jm*v3/m.ih 1mktoltage 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 applicebzp ;wkled:t od w4x3we/jt 25 u4r33ations. Lightbulb B is rated at 12 V and 40 W for automotw z pdtb2wd4 el5;e3 x3:/eo3rtwkj4u ive 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 connect a set of appliances at 12z n0b/b h 93-bzktmrg)0 V, which draw 2250 Wn/-zh3krbzb9b g )0mt 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 diwq+3l1e,ht t); yxgr3fc j3efameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the resistance of 10.0qt13h fe,ct) f jwlrx 3gy+3e; m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so thatv4ffi1 8ei2ok4j,k e l its length doubles, by what factor does the power dissipated in the wire change, assuming it remains hooked8k,vif 42e4fk1l i jeo up to the same voltage source?

  A tungsten filament used in a flashlight bulb operates at 0.20 A and 3.2;cu4x- mbygzfc.l,f 2 V. If its resiucx ;gfzclbmy-f4 ,.2stance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$