What quantity is measu 4r+rvk 7hayv;red by a battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a .c8of e) h9i*i-wtjcm lzagp cwm 7i0:-0b8pr circuit, electrons flow away from the negative terminal in the circuit. But within the cell, el8bfli).i*pawjc9i7rmc 8h0c:pm0 geot --w z ectrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battery c 4xio4r+hd0m7 8low urpfz9 ya sb12q4urrent, battery voltage, batteryupr balfd7z y +4oi14rqw8s9h m40xo2 energy, battery power, or battery resistance? Explain.

One terminal of a car battery is said to be connected to “groundcd0qc9uqs8la+1 nf-i p8 cfuvf *:u(c .” Since it is not really connected to the ground, what is meant by this e a1q v8fdcicf+s f9: u-u0c l(q8ucpn*xpression?

When you turn on a water faucet, the water usually flows immediately. You don’t+, +cthkq9ha x have to wait for water to flow from the faucet t9,q cahh++xk 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*9wfb46odi czuminum wire of the same length have the same resistancew6o 9bzid4f*c ? Explain.

If the resistance of a small immersion heater (to heat wateral7-r j .i6uwt for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the heating process? Explain.j67r .liu twa-

If a rectangular solid made of carbon has sides of lengths a, 2a,y0)ibr+ y3 s uqnzy3:f and 3a, how would you connect the wires from a battery so as to obtain (a) the nqs u)by +zfy3y3 0ri: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 burnbt8f:7jv re*+ -qoqems out?

Explain why lightbulbs almost always burn out just as they are turugxudpiz- :+7)e)krfned on and not after they have been on for so+)zgxd r-k :uie )7ufpme time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which has to)7p)0 maeqe1ir aniveoepn u8x*/2 7 he higher rie2* aoaq7n 0 8rmp /pne)vxoi7ue)e1esistance?

Electric power is transferred over :dp)8 cthuuyd 1ge)z-ci(qvny6h: / slarge distances at very high voltages. Explain how the high voltage reduces power losses in thh ( evh:z6)8)gq u-s/pd tyucic n:dy1e transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to re3bqk 3q 9 n)lxpznj4xjoixt.xq/a55/ place this fuse with a 25-A fuse b q4k/3tna)p9.izq5 j/lxoxq xnx3 j5?

When electric lights are operated ofjq2)zwf581wjkh*+ x a tfz;s n low-frequency ac (say, 5 Hz), they flicker not 1qx;2wfk* 85)jw+hst fjzf zaiceably. Why?

Driven by ac power, the same electrons pass back and forth thtw5vr4 1mfl 8bye ha2h*xg1s9rough your reading lamp over and over again. t2f495 1 *hlh rgvwsm8aeybx1Explain 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 a3i:rzuqvzkg*txm69 . fter the toaster is turned on, is g:utmzk3 *xqi r 9.v6zthe current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? E1yw3 m.i mv34wpevk /sxplain.

Different lamps might have batteries connectedyv(x h irk-q)i4ptr79 in either of the two arrangements kviip) 4h qt-xy7(r9rshown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A fl30; mr h w9+b2z1xtvuamgucu(ows in a wire. How many electrons are flowing past any point in the wirtva9 3rm2b1uwhmx0u;z (u+cge per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a cu eivu7*v x8v ;.6hvg+sm6fjourrent of 6.7 A for 5.0 h. How muchg8uesu6ohm ;jv i+76x vv*fv. charge passes through the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes2qo17 2 asqjfag0-sxj 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-3 ;;qnv keped toaster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current throud4ru q/pw(h0.plel6z 2te6ljgh a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A (i9:cz6snlo15u ajb xwhen 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/tefqri h: *a9 heating element with 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 c)xthyoogu rl, 3b;np t16 )7pbonnected 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 vfrvyw 4;p (r f7-x tfw.0g.obline carrying 2800 A (Fig. 18–34). Thf- wrto.g;fxv pvwry.4(b0f 7 e 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 hho.e;zb3kj9y l4 .nvpsgx1 3 ijm)u.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 o )jdyj66 +1x td)xccejf 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 length2s4tx: e r5cmr;s yyrykyz.41 of tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m lengt7w wxt2 z(0yiyh of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wireyc h9:cn+xto :m)nb)5c.vfxz 2.0 mm in diameter, to 20.0 x:h nc)bt 5myzc:)c x+ovnf9. m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same re3qd ,gu6 xvn(wsistance as a tungsten wire of the same length? Give numerical detail n (vgdwu,3x6qs.    mm

  A certain copper wire has a resistance of ifzjl1us/.mq jke /8 9$10.0\Omega$ 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 rf)a1lzn qd +t6aise the temperature of a copper wire (originally at 6d)zaq 1 tl+fn$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivityx dh1 *bf6p8db as tungsten does fb1xhb6* dd8pat $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of aba3d y 5 3kzx,/kktssm,out $12\Omega$ 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 rag f3;a+ i(fwlength of household no. 14 copper wire (used in 15-A circuits). The wire has diameter (;+3awafi grf1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm, 2.0 cm, and 41p/a qw.g kth:fbw n;8yxdca;b; z,o6 .0 cm, lyx g/;;abpdao; z1 bnhtk f6,c:w.q8wying along the x, y, and z axes, respectively (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 resist;e -nq z3vxw b7cuff28ance. If one has twice the length of the other, what is the ratio of the diameter of the longer wire to the diameter of the shorter e78znxfbw c; 3-fvq2u wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is cjchez5;,2t,ww3z7ixyl a3n hge f5- e onnected to a precision 10.00-V power supply, and a current of 0.4212 A ieh-izwfh y tl,5ce3e z; a 3x2jg,5nw7s 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 5.0 m of cowm,+g/ )g5 hgh :kkv4ogqw5 gtpper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A vovh4tg,wk:gwo 5)g+kq/ hgg5m ltage 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 not ch*l1hzl*i6 v iwl(,/ieegfy n6ange with temperature. For example, suppose *el, i/e6 i1y(zfgh6 nlvl*iw 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 designed to produce 3.3 kW of-b legj v(23mu heat when connect j2mulb-vg(e3 ed to a 240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of qu 2-gv79x od,x1 zcrie,xx +uzqd//c a 3.0-V portable CD player that draws a maximum of 320 mA of curu 1e+-v /qqrxud9z xx,2/g,ix7cczo drent?    W

  What is the maximum voltage that can be ap(z fql)h7j;bxt4:n s*p4pccmplied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, a 75-W ,puiabomv36v 5b5 an:lightbulb connected to its proper source voltage ofu ina 35b,p6aov:b 5vm 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 110 W. Calculate uqk ccyuo)28 2,alz1n
(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 /*f1+we ogc jib i9pjxj);)th/px6 ey two 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 lightbulbev ( gcxv8 8z7ap/arfq+0em w9 in Europe, where electricity is delivered to homes at 240 V. If you use the ligpwc8qmzx/ v e9 a 8ge+(vr70afhtbulb 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 k q(3p bft zc45tcl4r(zl64mavm-g /c the morning if it is in operation for a total of 15 min3tp( rclm6 q-g/4z blz 5tm(4f4ck cva? At a cost of $9.0\,cents/kWh$, estimate how much this would add to your monthly electric energy bill if you made toast four mornings per week.
energy $\approx$    kWh
cost $\approx$    cents/mouth

  At 0.095 dollars per kWh, what does it cost to lxr/g.j q v3-yveave a 25-W porch light on day and nigh qyvrv./g-3 xjt for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.pmanxcot8 kc,8 y( 5-a5-V batteries connected in series as inakm ncy,(8-8o ax5 tcp Fig. 18–4b (Fig. 18–36). 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 energyhok.q65:vr1 ng.rgl-btw5s g stored 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 vv1b2l y( j( +bglps9bused without blowiv+l91sv p2l yb(gb(jbng a 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.12-.tepi* r:jn v9 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric heater which draws 15.0 A on a 120-V line. How much power is disr: pnti jev.-*sipated in the cord?    W

  A power station delivers 620 kW of power at 12,000 V to a factory through wi5rh, q g30vnq*zrrmr/uva2 g*res with total resistan mgr5nq, /ahur2q0vzv rg*r*3ce $3.0\Omega$ 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 ldyj fje,miqo/c b(h21; ypc.(hc h1e)ine is 17.5 A. At what rate must cooling water pass over the coils if the watjehjm i hc/; .hcp2d( by(f,1o)1yqce er 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 wajvz( )yv.b1c4tama76 r ym (oyter for coffee or tea. If the heater can heat 120 mL yvt)orma47(vz.y(y6 jc1b am 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 a3p0 h4/ysur.bomf 2 ej $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peakmg-.f 7qh5pvw 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 of thepr 5yegr) 5tf o,igu3* $120-V_{rms}$ 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 1500-2)ladj )xroo.jz e:t (W device is 5.4 A. What is the rms voltagale: )xojrjzd)t2( .oe across it?    V (Round to the nearest integer)

  An 1800-W arc welder q64k,ancci(. : t5 uqb b,yvutis 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 dissipateuc,v8o+at 2az yg:n j+d by a 3.0-hp pump connected 8j a+tuv c,:zan+ oyg2to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connec0k w;3wp8nl1 6fempgeted 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 car)xxft32k7j m rm1v: wzu/(q ;js/vpttries 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-diameter wire cabvfbfv2 r mrk;kv7)o-e r/3+ arries a 750-mA current when 22.0 mV is applierb2frr;m+-7 abf )3/ vv koevkd 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 atmosphermba7s t:++ cdie, $He^{2+}$ 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 at-x gssls12l -lmosphere, $He^{2+}$ 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 an8,v6ct 2yp or-nx9o wo axon membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with a2 b+/ ipg3adup).vfnvn 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 7.2ua ipfv +b3vnp/)gd.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 action potential along n0i3 go ojhl 8+tbg-t5the axon of Example 18–15. [Hint:-+tbtig oo0ghj8 3l5 n 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 potential, bic+ v dl5z5xttlg+7 (qg 8r4w$Na^+$ 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 arev in8sh8a rk+oz mos0sa:m909 there in 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0-hp 120-V emg1 .3tzi wox;n. :womotor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally3sau, 4wd /2wwvc mk3 )ug/+:zhdymaj leaves a car with the lights on. If each of the two headlights uses 40 W and each of the two taillights 6 W, for a total of 92 W, how long will a fresh 12-V bat :w asuv h/wy,dd/mujcmwa3gk+42 z)3tery 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 l/ *-tn)i0ewo 1 n)iw fuze.lszong. If it is made of iron, what m * 1nliw zitz/e)fe n0os.u-w)ust its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the recip+y1zf)g3j(b e9kj hiarocal of the resistance R;agkj1h+yf3 e) z9b(ij that 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 pnl1oe /5ud97jxh 1od3x rcxyif:w2 x2ower. Suppose that instead of using 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 p o2njxd ei 3/:fy51od1rlu9xx7 hwc2 xer kWh.    dollars per hour per meter

  (a) A particular household uses a 1.8-kW heater rwo3iu+:- 6i a0zaha(ozpk 6r$3.0 h/day$ (“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 i)e kkz*2svvfbm(b4p7 n half and the two lengths are wrapped together side by side to make a thicker wire. How does thpbm* 7 sze(v42 kb)vkfe resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 1hqu)rtz 1:3cno:,beg 17 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 a)oq- p1prdfd,a;xi 8 e:bnb2os to start a fire. What diameter must a copper wire be if it is to carry a maximum current of 35 A and prb1bq8ad 2x-f re:o)i,op dn; poduce no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by yn vb29ea +ol2the 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 eneo5z /9y(lbi .mcgr;v irgy per second to the interiorg.v 9iym(rzc ;o/b i5l. 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 madeapx8ogc +vo t1)w8i0s of the same material. One conductor is twiiv +go a w)8oc8sp01xtce as long and twice the diameter of the second. What is the ratio of the power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a roomcxx 7,uq(sq(9b ji et9:er qtv:j/8q fq6fr2h 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 sour n45. 8 r7;q;lvkvqylrvfy x/rce.
(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 u yyxz-qq8y4g c.8kn2its source of energy. Its mass is 1560 kg and it i8 .nuy8-g4yq qxyckz2s 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 of ;*nkbovb xp zc6,;3ao$12\Omega$ 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) isbdc ;vd e5c2+d+:yf8 w9jgfgr designed to carry an 11-mA beam of protons traveling at very nearly the spe+de +bfj9 w ;dcy2 vf8gr:5gcded 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 2glyauo/o3b dod00: 7c20-V ac. The connecting cord is copper wire with a diameter of 1.6augo/30old :oy0bdc 728 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 connected to 120 V. The heating el g* jox3:.odmgivz,d7 s/m o;lement is a coil of Nichrome wire. When uncoiled, thvgojz :do, m*x;mi7d 3s.l /oge 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 abtu.snlfjtze 0)- z2*jout 12 V when the car is off to about 13.8 V when the car is on and the charging system is in operatio zfts*0je2).t-nzj ul n, 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. Lightbudwm;gu: . b.n8to e/me8s6bsz lb B is rate .stued: m;w8z smonbg/68b.ed 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 diameter 0.259 cm is used to connect a set of appliances at 12; g5xf66e(9umgyu3 iemhy d 4p0 V, which draw 2250 W of e95m um(feg3yu6h6x; dipg4y 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 diame0pa h(:or9.mln6 bfu lter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the resistanca:6hrpu0f(lm 9.ob ln e of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its length ge2m8 8)v2cckv rmgcj v0f4ro4 m/(bqdoubles, by what factor does the power dissipated in the wire change, assuming it remains 8f4r vg m(vvom8r bjc02k4cqgcm)e/2 hooked up to the same voltage source?

  A tungsten filament used in a flashligwrwz7r:jfb )ka : 3u2ght bulb operates at 0.20 A and 3.2 V. If itkbw)2z7:gwj3u: f ra rs resistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$