What quantity is measured by a batteyylh ar m1v:f58oe)g jllwk(d6 c1e)(ry rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow awa: 9feygi/co-z y from the nega9f/e gc:z-yoi tive terminal in the circuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: bana up7bg,q;o5ttery current, battery voltage, battery energy, baa uo5gq7 ,n;bpttery power, or battery resistance? Explain.

One terminal of a car battery is said to be connected to “ground.”:ivv f8i/6znv Since it is not 8/ zi vnv:ifv6really connected to the ground, what is meant by this expression?

When you turn on a water faucet, the water us4 u zmetz4gm88ually flows immediately. You don’t have to wait for water to flow from the f44zeu 88t mzmgaucet 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 sam on+m l:ol+x/ae resistance :mn+ /oall+xo? Explain.

If the resistance of a small immersion heater (to heat water for teyau.ooa+t 1,za or soup, Fig. 18–3a+o.u1a t ,zyo2) was increased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, and 3a, how h8ure8kte.n3d e(kq4kw 3x6jwou3nhrkxk3qj8 k8euw4d( e.6 teld you connect the wires from a battery so as to obtain (a) the least resistance, (b) the greatest resistance?

The equation $P\,=\,V^2/R$ indicates that the power dissipated in a resistor decreases if the resistance is increased, whereas the equation $P\,=\,I^2/R$ implies the opposite. Is there a contradiction here? Explain.

What happens when a h2t /y jpkhewl7+ 4noh a+lu+hb 2bl8)lightbulb burns out?

Explain why lightbulbs almost always burn out just as they are turned on and noca*h( 3 fxnkb5t after they have beennkhca 5(b*xf3 on for some time.

Which draws more current, a 100-W lis:s2eccox ,s80l aprv)3 rsryf5r ,o*ghtbulb or a 75-W bulb? Which has the higher cs ,re vly3,2cfr5s paoo xr0s*)8r:s resistance?

Electric power is transferred over large distances at very high v fs ngrclv(p sx4cl47/l-1+a r+l7 hvroltages. Explain how the high voltage reduces power losses in the tr4lnxhac +4s(+grs7l/rl v 7cpf -vl1ransmission lines.

A 15-A fuse blows repeatedly. Whyn z:bn( ml,7us-pon0s, riy q4 is it dangerous to replace this fuse with a 25-rnyn 0:b ,(ns4ls,p-7mqu zioA fuse?

When electric lights are operat-j0i0 *g tnzloed on low-frequency ac (say, 5 Hz), they flicker noticea - nltziog*0j0bly. Why?

Driven by ac power, the same electrons pass back andrf;+jt /w/wozd 4yzn qk2pl;. p5nxe3 forth through your reading lamp over and over again. Explain why the light stays lit instead of going out a/nn/ .lqj o5k w4yf ;rd2epxz+;twpz3fter the first pass of electrons.

The heating element in axau/lt: rt5sr-mt: g s4w,8 nl toaster is made of Nichrome wire. Immediately after the toaster isr5n rsl /lsxtt:u: w4-8g,atm turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Explain.+z nfn*v(; sfx

Different lamps mightzy2qeyh n0p)c6(om )h. tf4uk have batteries connected in either of the two arrangements shown . 4h(f2uoh)6mcnytep) y0z kqin
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 fl wfh(s:,/l.pxf fdr,qh8s;scowing past any poinh ,/8scfdxf qwpr.sl,:s h(f;t in the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a currento0o hya( :mrqjnf5/m 2 of 6.7 A for 5.0 h. How much ch2h(5jy om:q/morn0a farge passes through the battery?    $ \times10^{ 5}\;C$

  What is the current in amperer/ bv+m, fvahbz l.upz6 9bo2rm;/o2qs 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 toasmw(n) x3qf4abb 1n4hr;vv e9ster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of /(r0 aerujm97 *cw; q 2 jjuxcwxzgo/)current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when a1i -eg75pcy kqxpte5(lz+h) 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 cdbxu2 .3j.z )t)pxu nhas a 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 connected to a bulb whose resistance mw -e,d, 5ibzv/(dwbmis $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transmission line carryr6 tpc5(6 ize9(ywrpb, uuid-ing 2800 A (Fig. 18–34). The 6 5idib-yr wu6u eppr(,9 zt(cline 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 9nnp6mghcubt9e 6 25i4 k,rsx 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 0.60ar*,ut1q+nh( vqn 2i c 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 tungste (ebkqg; y ifau.ye75 7th5m* fckge g;m:+x.fn wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1.5 mm in diamzdu20fs4)an t2eiv h+7b uxs0 ljw8, oeter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire 2.0 mm in diabwf :. n kj;3avl(+ 5l+,qmohletp6rzmeter, to 20.0 m of copperp( +la+ hn6: mw.bf5lqe,orkvjltz; 3 wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resisq0e s(b.ppxm5tance as a tungsten wire of the same length? Give numerical(sq pb.0me5p x details.    mm

  A certain copper wire hasc+s: n4nt4ri7(fkxc( u4s pauh8 v6vs 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 coppe+xbv bt p7;8lbr wire (originally at p;bb+ bxlvt8 7$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature , h /1,aqtze44r4nlxwge8xxrg ma)+ qcopper will have the same resistivity as tungsten doe4qlrg x,n 1aqg8)azhx/,x+me 44re wts at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistancekolhl p za9-z;u 1d53e 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 householdv p+wqvdas4 r655 qdg9 no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm and carries a 12-A currvarqpq4 s9wv5dd 6+5 gent.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm, 2.0 cm, andz// sh3 mnzk5q+vapmcat t9frwz, 4rv-x 9.4 c 4.0 c.z4ctm / 59x-4 /wm 9a +trafhpzszr,vnv3qkcm, lying 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 resistance. If one haszc b ouc n1 )35v4svet::wys;/hftbc9 twice the length of the other, what is the ratio of the diameter ofshzs4bvt:wu 1c)v/y:b f 3 c9otc5 e;n the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wirav dji ;lw ha7b738+gbe is connected to a precision 10.00-V power supply, and a current of 0.4212 A is precisely measuredgbjlh8 dv7aw3ba7+i ; 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 followed by 5.0 m of aluminu5ul( 8 t2x p5nufbiva7m, both of diameter 1.0 mm. A voltage difference of 85 a5n5i 7(xul2 ptbu f8vmV 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 : pbff/ng8e:his important that the value of a resistance not change wi:/ gn :8effphbth temperature. 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 isy.ox0tksu7g+ 6rtnfeu mkfy( 54o 2. b designed to produce 3.3 kW of heat when connected to a 240-V source. What must be the resistance of tkyfrokg u2 5t(+f0x6bu oyem7.4st .nhe element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player that drawst.v + f(y3cou0c 3vuxh a maximum of 320 mvuovu.c03f3ct( +xh yA of current?    W

  What is the maximum voltage that can be applml):6jh: omo5gg 8rbpied 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 g5)ypgl49zz9r./xea i tq (1gx w j+f8wqlt:gconnected to its propee ltgw5g 9 ixxzy 8pgaw :. tq4(/jq1)rzfl+9gr source voltage of 120 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heater is rated at 110 W. Calculate oe/klqygg3 5ib1:;h i
(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 125c. t;*nvb5. 0oqo.9vtv trqda0 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 eleccnb9vltk(fdn3 4x-ym s u9-dnq /34dotricity is delivered to homes at 240 V.nx bv odud- 34 y43 m9(-ldfntqsnc/9k If you use the lightbulb in the United States at 120 V (assume its resistance does not change), how bright will it be relative to 75-W 120-V bulbs? [Hint: assume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use in th-(fez a(oinh3e morning if it is in operation for a total of 1i( en ofz3a-h(5 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 0q 9li u6fyt3 v ipfi5oq:b+h7a 25-W porch light on day an:i0qyiv7olhfb u9 ft5qi63p+ d night for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V ;ir, jgpm -dd)batteries connected in series as in Fig. 18–4b (Fig. 18–36).jd;, rpm) g-di 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 21od .0 -vdw *c m51kzwcqwxqystored 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 asd,w annf95 )wg in Fig. 18–20, can be used without blowing a 15-A ffwan ,w 5g9nd)use?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 copp6 6nd5 a-wsq*v0 ogpkoer wire) and of length 2.7 m (9 ft) is connected to an electric hea6d0o a qv-s6o g*5pknwter 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 V to a factor3g*c p daiaf5 w 0i if9vid7+0tqud:s:y through wires with total resistan: 7i*fs 5f gc aupd+tq03da9wd :0iiivce $3.0\Omega$ 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 2403m(s n-*ppxl9r lvzk ,.q 5nks-V line is 17.5 A. At what rate must cooling water pass over the coils if the water tempe p,s.-(nxs 9n vlkz3l*pqrkm5 rature 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 cofq*cm ic ,8,o fzert vb5:rjy/y1t45grfee or tea. If the heater can heat 120 mL of wm j yv,/t,bzfr4 y1:c5ri gqer*toc85ater 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 t* og 1zaj5yhi /yg5u4in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 , xvs*pcbm 5ga-b-wi: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 thea .d1z9;i2kf(q ;qula8oerbf f+cc. c $120-V_{rms}$ 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 A. W/a mt(od9ox i+lrx;y1hat is the rms v(r txdm9a;l+o/xiyo 1 oltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder -n 9/yuqo57s lhk k9 pmro6n-kis 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 instantanetx : .y. z-hbu9l9gzyn(f7lr1i eswe6ous power dissipated by a 3.0-hp pump connected tl 6nfwr 7(hyz 9yie 1ls..9zb :-tegxuo a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to 1qv 0oi9l5u c*ds)zub 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 :;ubh3tk ezz -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 current when 22.0 mV iqqm 6cgu4k 6t8 by1z3zs applied to its ends. If t6 z4ym31ck6qb zg8qt uhe 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 atmospherzxo* scr 37.lu6b2ms ve, $He^{2+}$ 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 atmok lu0muypml+z 6e3+ 5 llxe*8csphere, $He^{2+}$ 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 fdmaucg -p, 6m e n0kow)2f)k,qield across an axon membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with an electric pulse. The action potengc9 b9terl:ro9i4jp-tm uw1yga3. x )tial 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 timeg4m tu3ey9:la9w gc9i -trr.ojx 1bp) 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 requiredwm2x 5bu qkd;v:yq0+s to transmit one action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored by charging the axon capacitance; see Suy 2+0;v:w sxbkd5q mqection 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 potent6:tqx1r+li2 w* s + dkd0mepklial, $Na^+$ 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 am r/pw--8l2; qyfwvyv8c w2 7r m5uidespere-hour?    C

  What is the average curre4atde jim +,:lt1/w5n:: pm g2rtplf fnt drawn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. c6auc 5k4c.kpcx ;x.fIf each of the two headlights uses 40 W and each of the two taillights 6 W, for a total of 92 W, how loka .cxfuc5 ;ck p.cx64ng 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 a4og6m us(ly l/69t),vc fq rhx 110-V, 1500-W heater is 5.4 m long. If it is made of iron, what mustyc oh,t6urxsgm4v qlfl/)9 6( its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of+fw j;cw)a.0tvz0r bl an object is defined as the reciprocal of the resistance R; that is, ;vr0 )zwa 0j+bw c.tfl$G\,=\,1/R$. 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;by/)2(- yllnxj pfen 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 enel)f/2(y l;e bpy j-xnnrgy 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 1.8by;dprza7tl-w (3 . oi-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 wr,k( r 2;.g mjf8+qyo6. nbq7ntxsvhy lapped together side by side to make a thic.jhy.7r 2ytv+qobn8g(6 q;ksnmlxf,ker wire. How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is5mn:cpmdg (g77pvxw; designed for 117 V.
(a) What will be the percentage change in power output if the voltage drops to 105 V? Assume no change in resistance.    % decrease
(b) How would the actual change in resistivity with temperature affect your answer?

  The wiring in a house must be thick enough so it does not become so ho2n)a5 f9. (xe wvo9c 7fpbe yf8vzzg4dt as to start a fire. What diameter must a copper wire be if vfxdfzo89 vac4ne e)fw.z7(by5pg 29 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 equa k/ek)z el3qse((-cmnuzd *:6e0ndf dtion $I\,=\,1.80sin210t$, 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%s/m9vekab7 +1vi+cx. dxzp 0rmo7)oz efficiency delivers 950 W of energy per second to/7pxei ak.07vsxz)vor+doc 1mm9b z+ the interior. Find
(a) the power drawn from the source,    W
(b) the current drawn. Assume a source voltage of 120 V.    A

  A $1.00-\Omega$ wire is stretched uniformly to 3.00 times its original length. What is its resistance now?    $\Omega$

  220 V is applied to two different conductors made of the same materiaexb :lq,4:uw4j*l61da lpu twl. One conductor is twice as long and twice the diameter of the second. What is the ratio of the power tra4ud lu6 wwtbl4a*l1pe qj,::xnsformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is usnk:s*9eaazu. lb 6*x wed to heat a room of volume $62\,m^3$ Air is brought into the room at 5$^{\circ}\,C$ and is completely replaced twice per hour. Heat loss through the walls amounts to approximately $850 kcal/h$. If the air is to be maintained at 20$^{\circ}\,C$, what minimum wattage must the heater have? (The specific heat of air is about $0.17 kcal/kg\cdot C?$)    W

  A 2200-W oven is hooked to a 240-V source3 2 du4xq duc-,vdyaf*.
(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 9f4av 3bn4h(ymsx3xu15 nknuas its source of energy. Its mass is 1560 kg and it im3 4bn9 sxfvn5 (hxa3uuk4n1 ys 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(s3j ogt:bu7;i3 cwylo/ i1in 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 accelerajl )64 .rdcub-mkq* nbtor at Fermilab (Illinois) is designed to carry an 11-mA beam of prruk- b*6)jn. dlc4qmb otons 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 iljkb2att03k+9nu 3ta j-ncl 1s copper wire witu+3a30btl2ja clkn-nt19kj th a diameter 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 x7d5z2z xj77xyk q z *pcwsui6w.a)f/at 95 W when connected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What is the kyx z)s7 /w c2qwi6j57px7 zx *zf.adudiameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from about 12 V when fzjgd2id gnf;/+ e21p 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 percenejnf2z;dp1g+fdig / 2tage 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 n+zap,bojh2/1cz:k* c nj) c mB i/kc ,chcop2zbn j jm)n:a*1z+s rated 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 connecdowij f4 d:x p2fyy-v981 *hmzt a set of appliances at 120 V, wh f1-pi 4wo9vhy f 8ymdx*zj2d:ich draw 2250 W of power total.
(a) What power is wasted in 25.0 m of this wire?    W
(b) What is your answer if wire of diameter 0.412 cm is used?    W

  A copper pipe has an inside diameter of 3.00 cm and an outside diamn.hrdj si3s1r.c9u+g eter of 5.00 cm (Fig. 18–3.r9+hi ruj.d1 gs scn37). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R ib9c qyp (o :)er2m0xf;a1e raxs stretched uniformly so that its length doubles, by what fa)a:mexe 0coaf( p 9r;1xq2ryb ctor does the power dissipated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlid w r* ;zazd98 cs7g7kx+qkxis40ndq7ght bulb operates at 0.20 A and 3.2 V. If iq4sad09s kxr idnz qz+*;gwcdkx77 87 ts resistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$