What quantity is measured by a battery rating given 9)j52gjtpw :h 0r rlwqin ampere-hours $(A\cdot H)$ ?

When an electric cell is conn,+oy 0-ndzlklected to a circuit, electrons flow away from the negative terminal in the circuit. But within the cell, electrons flow to the negative terminal. nk yz-d,+l0l oExplain.

When a flashlight is operated, what is being used up: battery cuyk7 lxvvc g,(cy 2s3w,m:jnq-rrent, battery voltage, battery energy, battery power, or battery :xj(kqsn ,l 2-wccy,7gy vmv3resistance? Explain.

One terminal of a car battery is said to be connected to “ground.” Since .8 m2lel(m+atn a. wjfwx2q: mit is not really connected to the ground, what is meant b amlf tqn8+w2.(xem:m. alwj2y this expression?

When you turn on a water faucet, the water usually flows immediately. You doa8x76 2 d)ogeu zybbdd39iqb5n’t have to wait for water to flow from the faucet valve to the spout. W qze8y57dbu 9d)2oiab3dxg 6b hy 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 l/ 2ys6ep;k:h 4pykdy dength have the same resistancp sp /hd:keykyyd 4;62e? Explain.

If the resistance of a small immersion heater (to heat waterhr6ou:7 tii o( *oqr (l0gfb2n for tea or soup, Fig. 18–32) was increased, would ( h iq fgu72o(*:tnb0oi6orrlit speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, zngbq9 5sg5 md gcd2(,and 3a, how would you connect the wires from a battery so as to obtain (a) the least resistance, (b) the gregg5c,b z( s2dn9dgm q5atest 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 out.pqib2dp 6h w8?

Explain why lightbulbs almost always yfuf(3de cv;ioaez, (-kx( ( wburn out just as they are turned on and not after they have been on for somf(yee(; zwuxfi-dv3ok, c (a (e time.

Which draws more current, a 100-W lightbulb ory,u:zxbm9yi 0 (cmhdq:,cd/ f a 75-W bulb? Which has the higher resisum:z:(xcq,m, df ihd/90yy cbtance?

Electric power is transferred over large distances at very high voltaga,dvi- ;.b: ktt+ah+q, usoyx es. Explain how the high voltage reduces power loss;t-:abk qtu,ox,vd s+a i .hy+es in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fuse with u+ 7ml7vqnvecv3 w ,c,5qn;cb9h8 jcwa 25, cu3c9 7wv;qeh8cmwv,nv5 j c+qlb7n -A fuse?

When electric lights are operate zzu;;zw1g2omj9 i n*a(gi*fud on low-frequency ac (say, 5 Hz), they flicker ;zj2u inu1aif 9**;z wom(gzgnoticeably. Why?

Driven by ac power, the same electrons pass back and forth through your ojq1 sy0nq(0(jkq zp) reading lamp over and over again. Ex( s)n0qo0qj pkjz(qy1 plain 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 after 2.swqj- cp vc-the toaster is turned- q.2cjcpvw-s on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a- y d8,osi4m7shm7wcj resistor? Explain.

Different lamps might have bbkzbiucm 5-(wmdh:,; ks01wb x 6(fiyatteries connected in either of the two arrangements shown iwh- (x0:mw6buzdi(; i 1,bkc fm5kybs 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 flowing past anhjis :gy+ x4l8y point in8s:ljhg4ix y+ the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a bz)j x0g h/wms+bf+8bhik8*mwattery using a current of 6.7 A for 5.0 h. How much charge passes through the battery?0xmg h*bfh k/w+ z)bs8m+w8ji    $ \times10^{ 5}\;C$

  What is the current in amperes if l635hcyo 7 lfh)0i y6a(tz jdo$1200\,Na^+$ 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 of 4.2+xx/ -jzokl7(s/zq cv A?    $\Omega$

  What voltage will proy tv h5 hoyxy9fq2r:c 76m39bgduce 0.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 cukl5b7a / 7fd2gtz pw j7.ba2A 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 with95 xok1s vffn0 a resistance of $9.6-\Omega$.
(a) What is the current in the element when it is connected to 240 V?    A
(b) How much charge passes through the element in 50 min?    $ \times10^{ 4}\;C$

  A 9.0-V battery is connected to a bulb whose resistance iv i5p8ylnmr;h(ww9+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 (Fig. 18–34);-eeyw o-33 qs3ldys i. The line ha e 3;o-ye33wdys-iqsls $2.5\times10^{ -5}\;\Omega$ 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 draw;fq(q- 3j zjeks 6.50 A at 240 V.
(a) If the voltage drops by 15%, what will be the current, assuming nothing else changes? $\approx$    A (retain one decimal places)
(b) If the resistance of the device were reduced by 15%, what current would be drawn at 240 V? $\approx$    A (retain one decimal places)

  A 12-V battery causes a current of 0.60 A through a resiskiasw2sf3 q+ ( g/z7j2te +mmltor.
(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 is9-yt ma/-(kw*cpnxld $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance ofs q)-dfe rwz.0cy8f1 c a 3.5-m length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.1m6k:zv mtk7y0 m of aluminum wire 2.0 mm in diametervtkz m76y1 m:k, to 20.0 m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire hav ozilcl;v610r)e 9mvu e the same resistance as a tungsten wire of c); le9io vz1m0l6ruvthe same length? Give numerical details.    mm

  A certain copper wir, sm xh0 (y;xs+cp)ya -u wu8tlpe83yoe has a 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/(p 9l+s z jtsp.;dvfo (originally at d;/+ v9p (j.optszf sl$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivity as tung5 1z-jwvz;g,xgq z; oesten do ev zqzx,15g-g; zw;joes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb ha2 ;9jkk2qluw8 4byhm rs 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 along a 26-m length jhcxrhi- +rld,vq)/ 3,ml s0eof household no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm and carries a 12-A c-ishhlr 0,vx j/d+,cmqlre)3 urrent.    V

  A rectangular solid mado ssoy1jf74zsx *d /e7ukg 2y1by9k8he of carbon has sides of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Dedy kf /7sk1ju2yoyb8 1e4oxs9*7 hgsztermine 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 hm +:.qbkd if2have the same resistance. If one has twice the length of the oti b+2 hf.:qkdmher, what is 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 connect0 ei (aa1 jmxmxe -ny2+dx/*jped to a precision 10.00-V power supply, and a current of 0.4212 Aiaxej1 xp(0m/m-dae * jnxy+2 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 cp2 6wvc g)1obponsists of 5.0 m of copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is placed across g vwb2opp6 c)1the 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 nrhe ;ita1u57 whyn s z7fqm51*ot change with temperature. For example, w;enr 5 qmh 7syh11t 7iu5*fazsuppose 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 ove h3nnx5b7 lllp;*0od e 7ssln9n is designed to produce 3.3 kW of heat when connected to a 240-Vse0nld5* 73bl7l;so hnln9x p 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 drawfw7 )pqrs0il2:bovv .yhi1- ws a maximum of 320 mA of0 o.if1phqb7-l ) v2: rvswyiw current?    W

  What is the maximum voltage t ;khwxpy8 7y4ue; 5/rata(bhh+l2ufo hat can be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resista7sru rtl2 2r21ni7y5pweb13 h.xpmg nnce of, and current through, a 75-W lightbulb connected to its proper source voltagew yp5s r7 hgut 12 3.lrxmn172irbpne2 of 120 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heatergox* qv5f6:1tztrm0sp/o1vo-g5p l w 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 ienael tk v+3 .u::3w:/hrhfg: 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 elecawed,ip( +9t qx0;v6 tw+ jkeptricity is delivered to homes at 240 V. If you use the lightbulb in the United States at 120 V (assume its resistance does not change), how bright wilx ;p ,0p e+vjw9 kiat+(6qdewtl 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 the4-.rb :7rob0ccpge ee morning if it is in operation for a total of 15 min? At a cost pere cr:e.b7g4 0-cbo 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 kWhnqr:ci*7 j7;ui8yhd)9 ,ft r. w i*hqyqa:vke, what does it cost to leave a 25-W porch light on day and,ii n e)th.w u8rq7k cj;qvy *9yia:hrq7df*: night for a year? $\approx$    dollars

  An ordinary flashlight usex7.,zcuy dynyf1e6sy-3 rhw 1s two D-cell 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when 16e3-yh fu y,7 .d1synxzy cwrturned 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 s.l c;apss:ui8f eb2)g tored 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 amnju l)(rb*s8 s in Fig. 18–20, can be used without blowing a8(brujn*) sml 15-A fuse?    bulbs

  An extension cord made of two wires of diamet*mz etdxx0,7+fdnip;er 0.129 cm (no. 16 copper wire) and ozn;+x 7 xf,pdim et*d0f 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 power at 12,000 (q))qjuysyg- V to a factory through wires with total r( )g qyus-jqy)esistance $3.0\Omega$ 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 whagk,sy)r fl43yl mp .1;n(uj b48j uyykt rate must cooling water pass over the coils if the waterjsr) 8 3n1j4py,;ygul4yu yb(kfk. lm 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 for conle d.d;y0wj als05xvw: 3 -ovffee or tea. If the heater can heaton ;x w0a5 3jw.sy-:vllve d0d 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 ymqm 7.mj)n,h:pd+te$2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, is ta/zlfd+c3 8 dacross 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 th xy ko s*ww(4ify5m,u/e $120-V_{rms}$ 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 vurof+c qt2* hg(ycy40/7bhb A. What is the rms voltagvot+q0fy( b c4h* 2uch/ryb7ge across it?    V (Round to the nearest integer)

  An 1800-W arc welder is conn8o yx3yvr0ap;ected 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 3.0-hp pump con9xju v6q 5 gp9yq) plj+wah)p8nected to l)wq5x 8g pavpu6q+)y9p9 jh ja $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connect:d 9* vlst7ogrghu ri iv-4s:(ed 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 ar8i g6swfm*+ x 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 carries a 750-mA 4kjs2 pz9;mqvpgx55 )o4lr xs x*zjj6current when 22.0 mV is applied to its ends. If the drift speep9oss*z;px55 4xkrj4j l 2v)xj6q zmgd 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 tz-:s**qqm thphe 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 

  At a point high in the Earth’s atm*w uq+1tr5zn oosphere, $He^{2+}$ 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 acros si(gz-xinyel 8kql1le: ks*+k9g s0 .s an axon membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated witbp9og2x vzi6( h 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 obgi6 px(z29vthe 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 tdx 6db is :r,g.z44hbc(m (vvpransmit one action potential along the axon of Example 18–15. [Hint: the energy to transmit o(gmd 6b v d,:rx.(4vpsz4icbhne 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 potential 3rdys*8ldgw6, $Na^+$ 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 k 91;ki. zsx,t snh6lso0m9 nn1.00 ampere-hour?    C

  What is the average current drawn by -iu.4.s6afxly6 sv2jikk;x e a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leavese e;f1oa-/tsc a car with the lights on. If each of the two headlights uses 40 W and each of the two taillt-f soc; /eae1ights 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 5.4 m,abxet07va1*d0 kn ox long. If it is made of iron, what must its0b d tekxxaa1n ov*,07 diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciproca+hz6fr zlys6w lb/v9 :d66 )vbwi os00ww hlv7l of the resistance R; thab/ld0v w9 wiyz+z wl6w6h6 s:v r706fvhob)sl t 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 p r0ddwh tw76v4;l;yl 10 MW of power. Suppose that instead of using high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a two-wire line l7hdrplt;w;6 0vdy w4of 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 1.842+ oso h 4yoxqedr9kg;/rz7m -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 toaooz x y:7xw *i8,/4tn9dxzec gether side by side to make a thicker wire. How does the resistance of this /oxztdnw7,ex8oac x94*yiz: new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 1 - ./ym;ghh/vudws6 xu17 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 hotxayly 50qgbzc7-vj e :wt2q 0- as to start a fire. What diameter must a copper wire be if it is to carry a maximum current of 35 A and prqb7 y5 c0 ta0vg x2qeyl-:wj-zoduce no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by pb2i:zdsp,nd ku2/3i ng. xs 0the 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 ejv5ykvlv u i,/mf:c23nergy per second to the interior.vjmlfk/u3v , :v25 icy 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 :p ckw-+ ft:f-zayj:qay8,j gthe same material. One conductor is twice as long and twice the diameter of the second. What is the ratio of the powerj:yfga, -j pqz c: -kfa+tyw8: transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater iqnsc l4l;s4/g5 69nghmamt j5 ysd-z* s used 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 24h;y83l7bz swx 0-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 vehdoxbt y9g, mk8 ,f.oplt sr3,5icle makes use of storage batteries as its source of energy. Its mass is 1560 kg and it is poweredmy,5,s8 oorb9 t gp x.t,k3dfl 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 resuh t2 x)f;i7n /9j ooewl1a0gtistance 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 Fermijb*r 11asymy3lab (Illinois) is designed to carry an 11-mA beam of protons traveling at v yjrsy31 mb1*aery 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-Vbr aq/pxa hmo, ,px-f4d3w0e2 ac. The connecting cord is copper wire with a diameter of 1.628 m ax/qb,p 2wohfe3xa -4p0md,r m.
(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 connected to 120 V. The hea2 wi3gn ls,7rn2ump tkx*6 6ifting element is a coil of Nichrome wire. W62m,3ts iuw6*ir 2pnnl gf kx7hen 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 about 12 V when the car is ofc65 p kk(lr nwxvq*a98 s gt5ta2oslb08rxc6 (f to about 13.8 V when the car is on and the charging system is in operation, a difference of 15%. By wcnas s6vt*8 ktl qkogr6(09a5w5(b8 cpxrx2l hat 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 B da7u syavzkr7;/pc9*is rated at 12* 7 dc;7au/rvazsp9ky 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 diameter 0.259 cm is use*jkgb unoppg( +i;;7od to connect a set of appliances at 120 V, which draw 2250 W of power to g;p(nbu o*o7kj+gi;ptal.
(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 insaclz8dhl ybu5 m6/e(w 5g y* x+3jw1ukide diameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18( *luj 6l5 ywah15+exw km/cbud y38zg–37). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched unifor 5t avo.0mam0zkt;of *n o43z21sbllpmly so that its length doubles, by what factor does the power dissipated in the wire change, assuming it remaina05t znot*34.pv m0szl;oo 2mlk 1bafs hooked up to the same voltage source?

  A tungsten filament used in a flashligzimeize-/ ** ghdj(lz) r0peefa6 ,r9ht bulb operates at 0.20 A and 3.2 V. If its resistancer/ha 9e)r *d zeeg-,fjipei (m 60*lzz at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$