What quantity is measpdjll*m/9;ipl .l (9fhbe 0 keured by a battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow awa/ sq5ndxt :+6a2tw bqay from the negative terminal in a /q t:b5ndwqxs6t+a2the circuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being usq 8 t2ovwv8h.*eyfq:y8d;)zy* xj x dred up: battery current, battery voltage, battery energy, battery power, or battery resistanyrvt2yqj8dy.* ;8o:*w8 x hv)qfdezxce? Explain.

One terminal of a car battery isyi:v+3l zopxn us)t+- said to be connected to “ground.” Since it is not really connected to the grvsn +oilu+3ypz)xt :-ound, what is meant by this expression?

When you turn on a water faucet, the water usuk8 nq:q7 8anbgally flows immediately. You don’t have to wait for water to flow from the faucet valve to the spout. Why not? Is 8n q7 nabkq:8gthe same thing true when you connect a wire to the terminals of a battery?

Can a copper wire and an ar0ovf(,, zmnwai bhqo-0:sg:luminum wire of the same length have the same resistance? Explmzohqo-s,:a0i,gnr (v:f 0 b wain.

If the resistance of a small immer7a)0;v.l a: ugmm mwrgsion heater (to heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow amumr:m0 7w.) ;laggvdown the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2e+ x/qk elt;h4ua 7,dca, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resistance, (b) the gc e/7lh+e, a4dxt;qukreatest 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 ligh v06xu2nig6 eftbulb burns out?

Explain why lightbulbs almost always jz/,+t.oud7 czoouo 1-- vpbkburn out just as they are turned on and not after they have beu,zo. -d+jouzo 1o7-bp / vkcten on for some time.

Which draws more current, a 100-W lightbulb o4nhbpi8./tlsmfm ;(q r a 75-W bulb? Which has the higher refpqmm8t(/ .n s;4ilhbsistance?

Electric power is transferred over large distances at very high voltages. Expla- 5uff :k1jqoyin hyuk-:5fjof1 q ow the high voltage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous tzcd5:gx tb+ 4vo replace this fuse with a 25-A futc zx+5gb4:vd se?

When electric lights are operated on low-f lbuosa7r4s 33 u9q:.xok9gwu requency ac (say, 5 Hz), they flicker noti9.3g bqwku:x oas74ul9uo3 srceably. Why?

Driven by ac power, the same electrons pass baa5a (nuy* .vkvck and forth through your reading lamp over and ov.v yk*a(nva 5uer 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; 3sofv-gv0yo wire. Immediately after the go 3vo;0 syv-ftoaster is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a,n3g)vl2l+ fqiyv xr) resistor? Explain.

Different lamps might have batteries connected in either of .tr(7r0f)p pa mm26bu2v+hvka2 4 nk q)lgxnethe two arrangements shown in mlvf74 g0mr n.rt)2e)2bkanapkh62v +up (xq
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How mwfc3ldjkno m7*1.qd,l 0 v;dekii: *j any electrons are flowing past any point in the ,kdq0 icf ld*7j3 ;.k* l:wo1djenimvwire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A for 5.0 hwn7yw p:m (oo+2o/ko*4 nsjra. How much charge passes throuwoonpyk wo*74r:ajms2/ o (n+gh the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes ivl a ;/ryn8g8s0wl+jef $1200\,Na^+$ ions flow across a cell membrane in $3.5\mu s$? The charge on the sodium is the same as on an electron, but positive.    $ \times10^{-11 }\;A$

  What is the resistance of a toaster if 120 V produces a current okij s)18s1 vm j:1pfxtf 4.2 A?    $\Omega$

  What voltage will produce 0.25 A r 4eu8c2 ),o,4mfzfegpy j,tm of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A6p1 /pjzomtr7 when 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 resim92c+mo/):cm 8yug amkjahn +stance 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 whose resistaq2n:n2yqey ,ance 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 b bp5 b5/uqka+1eg)it A (Fig. 18–34). T1qk5 ub)peab 5/+gtbihe 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 240 V. qh m,.cy/++ (bgup47 z dkioqo5uu+ xw
(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 y )hql;mvq*n7 rgbh6 .of 0.60 A through a resistor.
(a) What is its resistance, $\approx$    $\Omega$
(b) how many joules of energy does the battery lose in a minute?    J

  What is the diameter of a 1.00-m length of tungsten ae 3z41kqffquef. -x ksc13;hwire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of coppefy1y-;gpcisg + .n 4d4oybi(er wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resi(m*y:- z wxjaeifg;0vstance of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in j(-i:vxz0a*; fewygm diameter.   

  Can a 2.5-mm-diameterd(+raw( zox7 n copper wire have the same resistance as a tungsten wire of the same length? Give numerica zn(7xr +dow(al details.    mm

  A certain copper wire has a resistant5upt hbhqv2c; .dn(0 ce 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 tem;9zmsjuf/ i.qoz7dcb gv8+8eperature of a copper wire (originally at c+dgqvumz9o8 7/8.jsib;fze $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature coppe mk2 3e6:daotir will have the same resistivity as tungsten doestoa :d3k2e6m i at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistankg i (go vphr+ccq11,4ce 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 ;cds/sj,+p-bpep1 - q 0jgzou household no. 14 copper wire (used in 15-A circuits). The wire h/qb-pps;u1 j zsj,ope- 0cdg+ as diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of le-.3zwg y, fs/0l of7a8jnszxjngths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respecti. -yfj fjwsz8g,7/0aln x3zos vely (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 the same resistance. If onhx1dl) s utc+g5l/)dmqj ew,-g3h) one has twice the length of the other, what mlwhg/hg )35+-ux)jls) ddetnqc,o 1is the ratio of the diameter of the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.0i dx8/s rq/-ff0-V power supply, and a current of 0.4212 A is precisely m/8rq /- xdsfifeasured at 20.0$^{\circ}\,C$. The wire is placed in a new environment of unknown temperature where the measured current is 0.3618 A. What is the unknown temperature?    $^{\circ}\,C$

  A 10.0-m length of wire consists of 5.0 m of copper f:p7rg*+d kv waw0ik7j ollowed by 5.0 m of aluminum, both of diameter a7k0vrk jdg *wp:i+7w 1.0 mm. A voltage difference 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 resistance nli z4zj n4v;m9ot change with ;nv4j 4l 9zizmtemperature. 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 designed0 / jzpbi: ya tg7om03truo:l9 to produce 3.3 kW of heat when connec0m :i9o 3/ 7lgutbryt: apo0jzted to a 240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player that draws -hrtno vsw.k+d6 t 4iur0,j*qv2wfi 4a maximum of 320t rvnd tv+sjk2wiq- r6h fwu 0i*.o,44 mA of current?    W

  What is the maximum voltage that can be applied a()nz-j im:6j dc1ndsm cross a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and currentstyk9a d-n:,itn:4ef -rc8x r through, a 75-W lightbulb connected to its proper source voltage ofa8er:xrt- 9s nt4fyc- nkd :i, 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 11o)d /l o0n(m4v,akv; 7ovb,u whv3mwg0 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 s0xy ickqyz (5+ettings: 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 2qf,./+gru ) pd3njept40 V. If you use +.u3eg)/qftr n, jd ppthe 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 morning if g jgs uyer75y*12dj6bo3xex 5it is in operation for a total xud6xb27j y5gs 1e 5g*oj 3yerof 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 a(+t99n sek kwkWh, what does it cost to leave a 25-W porch light on day and night for a yearks n+(t9a9e kw? $\approx$    dollars

  An ordinary flashlight usessq5q e b.3b7xt two D-cell 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18– 7stbb eq3q5x.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 of energy stored in a w55p :e pmh(t1u8xooj 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. 18il yddnrxr h;10 (wy:3–20, can be used without blowinrl;y0dy :xih3rw (d1ng a 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.1v f5dujh-.wj4lwuoefen :4* 924yvje29 cm (no. 16 copper wire) and of lvwfu244 fo *j :.h eue5wdnj vyel49-jength 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 l/ncbx4+yc 0on+yk7q kW of power at 12,000 V to a factory through wires with total resil+oy4y7b/nx+ kcqn 0cstance $3.0\Omega$ 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 2 95xqxvv-ms on 7lxvqpnss9* m3 l+;g-40-V line is 17.5 A. At what rate must cooling water pass over the coils if the water temperature is to rise by no more thansp+;q 7sx9g5slqlo n*3v xn-m mx 9-vv 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car t(gw;tszq ,lba f9ob45 o heat a cup of water for coffee or tea. If the heater can heat g l9 ,f4bw;s5qtbo(za 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/:u1 8w3 vqy d1 it;qc(qf;2tubndtgn a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose5k8 x,x+w fx-p wzsigxd6+o +u peak value is 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 resistance 9xj3 hb r+s. r0mzkx*dof 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 curre-q6cns zw6 v;ent in a 1500-W device is 5.4 A. What is the re cqwvns 6;z6-ms voltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected to w1 )msggh 81 bi+*utb-x +bmzwa $660-V_{rms}$ ac line. Calculate
(a) the peak voltage$\approx$    V(retain one decimal places)
(b) the peak current.    A

  (a) What is the maximum instantane n ao;dc)/qjg.t04ahious power dissipated by a 3.0-hp pump connectec.4)a/a hn;gt0dijq o 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 t43/ 2 t zcvpw31woxkih 9zmb0go 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 curr jau-*d cr:3krent 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 a 750-mA current whe. yg9ua wh/bi1n 22.0 mV is applied to its ends. If the drift spe9a /ygi.wub 1hed 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 atmosphere 7uztt*n 8q9;// lh/yu7 4zklzkgfwbj , $He^{2+}$ 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 th 1f;jv3 yhq*nee Earth’s atmosphere, $He^{2+}$ ions in a concentration of $ 2.8\times10^{12 }\;/m^3$ are moving due north at a speed of $ 2.0\times10^{6 }\;m/s$. Also, a $ 7.0\times10^{11 }\;/m^3$ concentration of ${O_2}^-$ ions is moving due south at a speed of $ 7.2\times10^{6 }\;m/s$. Determine the magnitude and direction of the net current passing through unit area $(A/m^2)$.    $A/m^2$  ----待选择----NorthSouth 

  What is the magnitude of the electric field across an axon membrane fkb1f 7st00sj/f f7,y elp4v n$ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated wi/sz9 *mem 2tggoyv-.pth an electric pulse. The action potential is detected at a point 3.40 cm down the axon 0.0052 s later. Whez.mm*g /ept 9voy2-sgn 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 to transmit one actilxx.25th 1xu-j rd 5tpon potential along the axop5rt2hux 1 tdj-x.l5xn of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored by charging the axon capacitance; see Section 17–9]. What minimum average power is required for $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action potentia,xp f1-mq;uc nl, $Na^+$ 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-h6 fvbehp37;ai our?    C

  What is the average currrtw2b i d+ts94ent drawn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with t r1,2yh nt.imwhe lights on. If each of the two headli,1 wimyn2r.th ghts uses 40 W and each of the two taillights 6 W, for a total of 92 W, how long will a fresh 12-V battery last if it is rated at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of a 110-V, 1500-5dblyo xqi6ng9 o5,t2d 2)tlqW heater is 5.4 m long. If it is made of iron, what must its diameter l d2o9tyi5b5)q,6x ogtq2dnlbe?    $ \times10^{ -4}\;m$

  The conductance G of xa+hi)fpugk *a :1l .man object is defined as the reciprocal of the resistance R; that is,kgaul:* mxph1+.f)a i $G\,=\,1/R$. 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. Suppodlhz9gm,xhv-avz+o5f4 5 9tcse that instead of using high-voltage lines to supply the power, the powelh tdm vaox,zgh94c 5f9+-v 5zr 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.b.hg btey ,3o 8j4x4 it)ybyy98-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 and3fesw .jww19zoacju(n5+ sa- the two lengths are wrapped together side by side to make a thicker wire. How does the resistance of this new combination compare to the resistance of the original wirewa +wj(scnu5wa9 j-13f es.zo ?

  A 1200-W hair dryer islld8,yo jts(b+k.9 b a 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 irm iloyzpj6,s kn;b)dym r:t h2 d7,9:t does not become so hot as to start a fire. What diameter must a copper wire be if it is to carry a maximum current of 35 A and produce no mor:bp;ddhmo9y ,rty, r :i)sl z j2kn7m6e than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is gigs :p3*3c :u*fqdaez:ak 8zpfa;x*jgven 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 delivjtz:)(8tdxx ;0jtyf vers 950 W of energy per second to the interi(x:tvz f;tj) y t8x0jdor. 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 oi0o+u*qckud m+gfy7b w 8+c 8kf the same material. One conductor is twice as long and twice th8c wbq g++fm0 u8i+yok*7kduce 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 z6g2;e8n-f fmab qnj.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- 17nfp:t;fwyf V source.
(a) What is the resistance of the oven?    $\Omega$
(b) How long will it take to bring 120 mL of 15$^{\circ}\,C$ water to 100$^{\circ}\,C$ assuming 75% efficiency?    s
(c) How much will this cost at $11 cents/kWh?$    cents

  A projected electric vehicle makes use of storage batteries as it9mau*n3:qk0/m thwh u s source of energy. Itska*/w q09umtmu h:hn 3 mass is 1560 kg and it is powered by 24 batteries, each 12 V, $95A\cdot h$. Assume that the car is driven on level roads at an average speed of $45 km/h$ and the average friction force is 240 N. Assume 100% efficiency and neglect energy used for acceleration. No energy is consumed when the vehicle is stopped, since the engine doesn’t need to idle.
(a) Determine the horsepower required.    hp
(b) After approximately how many kilometers must the batteries be recharged?    km

  A $12.5-\Omega$ resistor is made from a coil of copper wire whose total mass is 18.0 g. What is the diameter of the wire, and how long is it?
L =    m
A =    $ \times10^{-4 }\;m$

  A 100-W, 120-V lightbulb has*/0 q:bbby aczx )j72rufs5 ms 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,bk we+3pbeolzy:05 i Fermilab (Illinois) is designed to carry an 11-mA beam of 3:e ,+ebbli5zkwyo 0pprotons 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. 6sk,w a -utbjbn;x(t9 The connecting cord is copper wire with a bxtjbsn ; 9,(wtu-a 6kdiameter of 1.628 mm.
(a) How much power does the air conditioner draw?    W
(b) If the total length of wire is 15 m, how much power is dissipated in the wiring? $\approx$   W(Round to the nearest integer)
(c) If no. 12 wire, with a diameter of 2.053 mm, was used instead, how much power would be dissipated? $\approx$   W(Round to the nearest integer)
(d) Assuming that the air conditioner is run 12 h per day, how much money per month (30 days) would be saved by using no. 12 wire? Assume that the cost of electricity is 12 cents per kWh. $\approx$   cents per month (Round to the nearest integer)

  A fish-tank heater is rated at 95 W when connectewm:l md z.e4i(5no;r ,u ep3 xzs9ja4fd to 120 V. The heating element is a coil of Nichrome wire. 9re5w3xm j 4u4ezifn:apms;. ,dlz(o 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 voltage varies from ozipo;x++s r g shj4q ;wy;-j,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.,gpxsi; -jh; ows++qz;oryj4 8 V? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for household apqx5o fi1hc.ivjz7guk y3lk-2hk8z-*ustr . 5plications. Lightbulb B is qz- 7rhv* k 8hus5 y1lj 35gi.f.uoct2zkix-krated at 12 V and 40 W for 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 diametec/3gp. uh2dpe r 0.259 cm is used to connect a set of appliances at 120 V, which draw 2250 W of powegu. p2p ec/dh3r 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 diame0 ka2oz:kwa3qu,4 vs te2fo2g :7in qvter of 5.00 cm (Fig. 1 kv4 :qqovnziek,2gw27:0 2 tas3fuao8–37). 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 d,z-3ooy0ps 8tv uz (5)pwop:s/kcy ymoubles, by what factor does the power dissipated wyyc,: po-( v pkpms03 s uo)8ytoz5/zin the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bys 03x9d)8zj d;h y +qmjupt-h y98dzkulb operates at 0.20 A and 3.2 V. If its resistancedp m 980uzq xyd 3-jh zy8k9j;)+tdyhs at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$