What quantity is measured by a battery rating gi,z.s 2gh xx+zqven in ampere-hours $(A\cdot H)$ ?

When an electric cell is connectedneh2b2mb*/*1 da yr ka to a circuit, electrons flow away from the negative terminal in the circuit. But within the cell, electrons flow to tha1 a*nr /y22bm*hkdebe negative terminal. Explain.

When a flashlight is operated, what is being used up: battery j jjidq 3+v4+ uq/vm-bcurrent, battery voltage, battery energy, battery power, or battery reqi4 vj +qb/-j+dum3j vsistance? Explain.

One terminal of a car battery is said to be connected to “grh2w *l6kje.zn ound.” Since it is not really conneej hk6wl .nz*2cted to the ground, what is meant by this expression?

When you turn on a water faucet, the water usually flowpqp x0h s0 4a01u+dfx xg7nw*gs immediately. You don’t ha0xw0hu n gdf a1xq0*p7+spg4x ve to wait for water to flow from the faucet valve to the spout. Why not? Is the same thing true when you connect a wire to the terminals of a battery?

Can a copper wire and an aluminum wire of the same length have the same res c7m9 2d1axwuaistance? Expl9w1d2aumxc a7 ain.

If the resistance of a small immersion heatejdjj r9( :zphqpnv5,/r (to heat water for tea or soup, Fig. 18–32) was jvp/rn9j (jdh,z5 q p:increased, would it speed up or slow down the heating process? Explain.

If a rectangular solirxm9ydb io +9cg8 sw6/d made of carbon has sides of lengths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resistance,i rwcg9/ ys6+9 m8dxob (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 buaw,p)f 8+f exfr- upp9-ux 7ln(w v9ayrns out?

Explain why lightbulbs almoskuwec(o0i it(q tn,a xa8*gltt7c/ .1t always burn out just as they are turned on and not after they ht c,ko t/.8 0geittx*nuc1 iwa (a(7qlave been on for some time.

Which draws more current, j-q7+bvt: ei) :llwbpa 100-W lightbulb or a 75-W bulb? Which has the higher resis:)lbq p:vwb7e-+itjl tance?

Electric power is transferred over large distances at very high vo ma7sdaf,-9dt 7r 2zb2oer1zd ltages. Explain how the high voltage rrde ,- a9o7fm7bzz d1r22adsteduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fu) dgt1ozk .r;nse with a 25-. dor1zk)ng t;A fuse?

When electric lights are operated on low-frequency ac (say, 5 Hz), they flicker a g9dai sg4k*8noticeasidggaa* 8 k94bly. Why?

Driven by ac power, the same electrons pass back and forth through your readingwxp ctc/t*2:5p )7 p2l0-tzzpdoh sx; uut y/p lamp over and over-x:xp5u*hz )p dttltp/ c 2z/o0wspupty7;2 c again. Explain why the light stays lit instead of going out after the first pass of electrons.

The heating element in a to. nv kdt10/cgtaster is made of Nichrome wire. Immediately after the toaster is turned on, is thtg/ .dnvc0tk1 e current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a rebkf 38fadm*t,sistor? Explain.

Different lamps might have batteries connecp 6iu9aj ,vo(mted in either of the two arrangements shown in j muv6(i,pa9 o
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How m.2nuws8 mgwunwu/+kp q pt1/0any electrons are flowing past any point in the wire per +qp8n1kt.wgm2 u 0suw /n/wu psecond?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A fobyy p 1fabuq1p;hh, .;r 5.0 h. How much charge passes throu;p,b ahqhy f11.;y pubgh the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes if is 5y wvrs,:rxd(2 xnsqe :e(2$1200\,Na^+$ 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 toi, czw ik(p-+nsp1 io/zwv*1taster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of curvdso ok.) 6j2rrent through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when 29;hwjxh1 vry 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 ew cycdn5as*g4* p.f, 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 bu2z 0anyr9ls,n lb whose resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transmission line carryindr did8)frcb l pn9100lr-m2dg 2800 A (Fig. 18–34). The line hasl rfd01 2pbd)mi-0c8d9lrdrn $2.5\times10^{ -5}\;\Omega$ 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. b7kb0f(fh 1hx
(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 resistyw0k,n;b x6*z8rrn rtor.
(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 whosl8 l2 nfixip-)-fu trxr.az.*e resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance-d) yr k2/ido3wvc (be of a 3.5-m length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the rdzr6h16 - +wev caaa6zesistance of 10.0 m of aluminum wire 2.0 mm in diameter, twr6zzd 6h+eacv16a -ao 20.0 m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same dxe. b-05diu xdz:r0lresistance as a tungsten wire of the same length? Give numericalx-0 uebd0r5.x:id zld details.    mm

  A certain copper wire has a res l)kx :)p;kwucistance 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 jbavsbel(/0/ at0sj(l /a b/bve $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have thec:) w9rzxfr :l onbqjx; q2/d; same resistivity as tungsten d/xw:rn2 cdoqb9 ; xjzrq);l:foes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance0gg+2udf9 vel 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 length4v 8mv-)puf)gk mmm x9 of household no. 14 copper wire (used in 15-A circuits). The fm)vk 4 v8)u mpxg9m-mwire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lenv+kn .gf3c5o bgths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the xv gcf+ 3ko5n.b, 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 resistb3,,*gs cmj.ccz )1 mjttaz 7zance. If one has twice the length of the other, what is the ratio of the diameter of the ac,tjm 1c7.)gb,3zc zs m*ztj longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V poweeo:45yurpqn l mq79q0 r supply, and a current of 0.4212 A is precisely measure 47n:qqylermqo9pu 05d 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 followes *baxu1s6/wvd by 5.0 m of aluminum, both of diameter 1.0 mm. A voltag*b s61avsw ux/e 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 r1ba 1qatp2qp -esistance not change with temperature. For example, suppospq1a-q2b t1 pae 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 ele vpfqd,rh-cflg p77+ 6ctric oven is designed to produce 3.3 kW of heat when connectp7cl,fh q7gp6+-rvd fed to a 240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumpta f q3acr-a;c 1h* vd+t7gox7rion of a 3.0-V portable CD player that draws a maximum of 320 mA ot1cg+v*7 af;dqa3 hcrar7o - xf current?    W

  What is the maximum voltage4(,pgq5qj2cf7x ud h l that can be applied 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 lightbulb 52j1.;5txxq2r3 yn w xmwodj uconnected to its proper source voltage of 13j wxy 1r ;umtxwqn5jxo25.d 220 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 l )bcgt8x,6 izxap48s
(a) the current through the heater when it is operating,    A
(b) its resistance?    $\Omega$(Round to the nearest integer)

  A 120-V hair dryer has two settings: 850 W and 1250 Wzyi3 voycw7 - sd;(.r8xjov d3.
(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 electr+js -vk5yvx f7icity is delivered to homes at 240 V. If you use the light+7-5jy v vxfskbulb 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 m4w c9w7 uq7so550-W toaster use in the morning if it is in operats797wmo 4ucqwion for a total of 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 kWh, what does it cost to leave a 25-+.0)m) 2gqbtdp aqym dW porch light on day and night foa+d qqpd).0) ymbt gm2r a year? $\approx$    dollars

  An ordinary flashlight uses two D-celllzpxis+p 916-mmtqr- 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb9pmq -s1mrzlx6ip +-t 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 storedl. (lvw (2tw v 7y(wtpmvynm61 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 1yt +vqhe.t5) + sgi*tdgg0o8r20 V as in Fig. 18–20, can be used without blog8t+t+oi t)g 0sqdgyh*.re5vwing a 15-A fuse?    bulbs

  An extension cord made of two wires ,8yw*thwklw9e. 1mtd -8 v wp67huq zkof diameter 0.129 cm (no. 16 copper wire) and of lengqkyk81 we lvhzu -wwt. *mdp,w68t9h7 th 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 g em,-gqcnt v 5h+slfnav.um7w 9*r sv)5a:0 zV to a factory through wires with total resiag 5m,:mvh wnt+esvrsvg0cz97 -nlqf a)5 .*ustance $3.0\Omega$ 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 electcqu( q kv,h- mp9(7bn 8ozn1ybromagnet connected to a 240-V line is 17.5 A. At what rate must cooling water pass over the coils if the water temperaturepcbo,k nvnbzq78(-(q m1h u 9y is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heavvx5tnnxl ) 4 .gwnq(0ter can be used in a car to heat a cup of water for coffee or tea. If the heater can heat 120 mL )4n.xtvx nn05lvw(gq 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 axemqcs. ;/m. r $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, is vcohb6p5 :( n ):i-(f irrnwc o)f oxw;r0x3jpacross 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 resistanc;rbv9yz-nd j,bnuux o/ kgw0 8iv11:je of the $120-V_{rms}$ circuits in your house as seen by the power company, when
(a) everything electrical is unplugged,
(b) there is a lone 75-W lightbulb burning.    $\Omega$

  The peak value of an alternating curren 1 sacb2z: i)p/jbx)vft in a 1500-W device is 5.4 A. What is the rms vo/vbf) iaxz:j)sp2b c 1ltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is w3;-jwzgf z-jm e,1hm 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 instantanw -8o443coc iu0vrl kieous power dissipated by a 3.0-hp pump connected toio03l44ccwuv ok r i8- a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected 59 xmgqd11t-jycfir 99upube4yf ;. pto 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 curren cid (y;a0mr-pt 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 wir,5 9x jykbna5re carries a 750-mA current when 22.0 mV is applied to its ends. If the drift speed nry xba59k,j5 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;lfs2b ieqnft f:2+q .’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 atmosphere, bj gorubol-jg rg;/3b8d6+e* $He^{2+}$ 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 me(w x0w wge0p,ymbrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with an electric pulse. The action potential is detectej7 ym 2e.(:hczi7a ,dattnr( ud 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 ti7d ei r .atnu zch2(t:y7aj(,mme 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 r,- /cspk9vs qvequired to transmit one action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the k v,9scvs-/qp 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 potentiac ms8 yhc1;;kzl, $Na^+$ 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 amaf9 6i e3z*8di.wwwhc pere-hour?    C

  What is the average currenta .*gr 396rsifsr) pca drawn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the le/g 9qr 5 mha5 + r.i9xyvqhhwz2f)6rgights 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 batte 9)iyhxa/ rh. 6mz2h wv5egrqg59fr+q ry 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, 1e+861:+omm r wrxiktn500-W heater is 5.4 m long. If it is made of iron, what mu8 erxw i+mmo+k1r:n6tst its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of the resip:kpkt1 qb t(+stance R; tp (kb+qtt1p: khat is, $G\,=\,1/R$. The unit of conductance is a mho $(=ohm^{-1})$, which is also called the siemens (S). What is the conductance (in siemens) of an object that draws 730 mA of current at 3.0 V?    S

  A small city requires about 10 MW of power. Suppose that in -o4 xkfv55g-hwj q9nhstead 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 loswj5n-45hgh 9 xfv-oqk t 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 1.8-kW hx8izo dkf/+ l-eater $3.0 h/day$ (“on” time), four 100-W lightbulbs $6.0 h/day$, a 3.0-kW electric stove element for a total of $1.4 h/day$ and miscellaneous power amounting to $2.0 kWh/day$. If electricity costs $0.105 per kWh, what will be their monthly bill (30 d)?    dollars per month
(b) How much coal (which produces $7000 kcal/kg$) must be burned by a 35%-efficient power plant to provide the yearly needs of this household?    kg of coal

A length of wire is cut in half and the two lengths are wrapped together side by3w,8 8ecwetmjfk4mgc0qy9 r+ side to make a thicker wit,c34mk +ywj8 9c0w gm er8efqre. How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 117 V. dol 5ok43e+1ms* xe6kcbvdm1
(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 s 2:l*+anu1busv ms ,ibo it does not become so hot as to start n muvai1 s2 ,sbb+*u:la fire. What diameter must a 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 equat oh+m vp;rf61xion $I\,=\,1.80sin210t$, 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 energy per second8cak(snh b7rcqu9::u to the interior. Findqn8c h 7ub: cu9(sa:kr
(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 madedcvw4pn-1:r ac*wxk(fa k0 a0 of the same material. One conductor is twice as long and twice the diametd0f(v: kp0n*acac 1a- rk 4wxwer 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 room of volum 82jy(w3 gel8h comet0e $62\,m^3$ 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.di3s3lyb :xdn 9sh5s,
(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 ma:f/x6tnnpfgl ej4mk.; x8: u mkes use of storage batteries as its source of energy. Its mass is 1560 kg and l :/fpu 8.tk6n;mjg:nxmxef4 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 rlsc/84 yy8e phas 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 Fermilab (Illlc)ko lr*n2-z/b9+e gpi*yjhinois) is designed to carry an 11-mA beam of protonsg2 i p o*c-b+rly9el)njk*z/ h 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. The connecting cord is copper wire y3po6+.n eg)/hjbsg mwith a diametbj/6moe y sn+ph 3g.g)er 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 connected to 120 V. Thu ua;vy ,-sj1+xym1aae heating element is a coil of Nichrome wire. When uncoiled, the wire has a t1mua, ;yvjuaxa+sy1-otal length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system volts f 948rk,w.srz+zc skage 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 thws zr+. ,fr k8c4zss9ke voltage changes from 12 V to 13.8 V? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V a yps.cvx9 ib o.k/n3i9nd 40 W for household applications. Lightbulb B is rated at 12 V and 40 W for automotiv.py /s 9nxc 39b.iikove 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 v8e vd3me:(yr cm is used to connect a set of appliances at 120 V, which draw 2250 W ofdymr ee:(v3v8 power total.
(a) What power is wasted in 25.0 m of this wire?    W
(b) What is your answer if wire of diameter 0.412 cm is used?    W

  A copper pipe has an inside diameter of 3.00 cm atrc mmt *sr2dj/v) 8x/nd an outside diameter of 5.00 cm (Fig. 18–37). What is the resistance of 10.0 m of this pipc2 jvsx/t *t8mdrm/ r)e?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched unilh 5 z1 e805mjf fopjq5+ykn2rformly so that its length doubles, by what rq5 m0+efn5zjoky h jl8f152pfactor does the power dissipated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb o0st,hq,e/n y zperates at 0.20 A and 3.2 V. If its reqnzy e,,/h s0tsistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$