What quantity is measured by a battery rating given in ampere-hcgk 8 jcgj47 q4c7t *k5(pmtjbours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, el.t iz75 uj,qcxo ymrc,i;u+8 qectrons flow away from the negative te xyo5.rucu8j,i+ztm;7 ,qci qrminal in the circuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is beingp a.rw2q q +fbtsuz5d.17;-m)d( y inoyg ke*q used up: battery current, battery voltage, battery energy, battery power, or batt nzq aq 7b1etk5o.)dr gwpu(*+sf iyy-.;2d mqery resistance? Explain.

One terminal of a car battery is said to be conne n*faoj3-vajjmy;zkfr6g3* :a6mz9 d cted to “ground.” Since it is not really connected to the ground, what is meant by this ekzfoaanvz 9-a*6 ;yd*:6fgj3rjm m j3 xpression?

When you turn on a water faucet, the water usuall,cv) h36ecjkl);kd rfy flows immediately. You don’t have to wait for water to flow from the faucet valve t,el;kd 3 6rfch) )ckvjo 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 lekd3 hmu+fls/f. ;*u6oodgk b :ngth have the same resistance? Expl*md+ o 3o;6u/ u:slfbhg. dfkkain.

If the resistance of a small immersix9a30qf (nae +imj)w1/ yqjqoon heater (to heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the he jq(qio)j30 qy1efx9+awmn/ aating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, nz()uu 3sskgni yu9 :1o/cum:2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resistanc)k 3n/ 1s uz:gnumi(usc yuo:9e, (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 burns ou/n5eg ,fj3m fqt?

Explain why lightbulbs almost always burn out just as they are turned on and not /gm3g2yt3 mvf after they have/33 mfgg2tvym been on for some time.

Which draws more current, a 100-W li6.w qdt vt71ntghtbulb or a 75-W bulb? Which has the higher res tntw6d.17 vqtistance?

Electric power is transferred over uf( lbtq9kov e(1nt1cm/ )xu6large distances at very high voltages. Explain how the high voltage rmntbc6 (x)tl(1/ vuo1u kqfe9 educes power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fuse wm;7x(x noyh kp5ah6h(o2k s)e ith a 25-Axp khn5eoh k6)7(mah;y2(xo s fuse?

When electric lights are.;2sf nx7m vkf operated on low-frequency ac (say, 5 Hz), they flicker noticeably. Whyn;7ff .smvx2 k?

Driven by ac power, the samyre 3n x6mvi84bynk9 4e electrons pass back and forth through your reading ry4xk3i nm v8e4n 9b6ylamp over and over again. Explain why the light stays lit instead of going out after the first pass of electrons.

The heating element in a toaster is made of Nflu,nm+ (n:o;l ujm:k6a8e brichrome wire. Immediately after the toaster is nmkr8lo(6 abu :,elun:mf ;+j turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistsjsx ug9om3d;;je9s (or? Explain.

Different lamps might have batteries connec6v7h mk 9x:+tuvauqw0ted in either of the two arrangements a:ku+6u 09qvh7t wmvxshown in
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 b(2v 1d y w*b/wzti1yjol0v 1zflowing past any point in thwl i/ vob (yyj 1d2z0v11bztw*e wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of tdfr+y-/tu6ze+ me n7 6.7 A for 5.0 h. How much charge passes teu +d zrnf 7/e6tt-ym+hrough the battery?    $ \times10^{ 5}\;C$

  What is the current in ame0+yz2: w55p d u*cnaif,v ,jryb6 djhperes 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 toaster if 120 V produces a current of 4.2 A? m y*hhvc-0m5 pf xw+*05cqbpk    $\Omega$

  What voltage will pro v kjof;kg.va7c r+evyy6 :p*6duce 0.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A wvf +sr f ulb4l3-)6 kics6osc+hen 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 ooadw, cg6/ jkblewks o551-e:f $9.6-\Omega$.
(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 bul43 vbpve ox/-l:r2;zu mc5avib 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.70; z ehu1kc0bafy bt transmission line carrying 2800 A (Fig. 18–34). Tb 0a7; .tkbf 0zhcuy1ehe 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 3wt (m,xn7jn 8(26wgqag5 d4 awoyvg r jlhq6)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-bd),rw th4y g current of 0.60 A through a resistor.
(a) What is its resistance, $\approx$    $\Omega$
(b) how many joules of energy does the battery lose in a minute?    J

  What is the diameter of a 1.00-m length of tungsten wire whose resistance is i cu5xiof*br- +yl4za:6jp+y$0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1.5 mm cys-pcqb /1hpc/km 70in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m ofd,y8o-h. 3y hp9wayb8-s tyzt aluminum wire 2.0 mm in diameter, to 20.0 hs8y-ypo.ta3ybhywtz, 8 9 -d m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the j-amd( esj.k2v/oc)t same resistance as a tungsten wire of kc2j da(vte/s om-.j)the same length? Give numerical details.    mm

  A certain copper wire has a resist7 ps6 e2ew tih)88znqoance 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 coppe1:6 re0+ku;b4rg ynunsza 8q mr wire (originally at gzn6: rs nbq 08u+k; emu1ar4y$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivity as tungs n0+tm 6fe9ck66 roafrten do+rma60cf6rnto f ek69es at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb hai 007f4x/awif n0ycrcs 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 of household no./njtqzm,v9 to e8 p,1 y1axrp+ 14 copper wire (used in 15-A circuits). The wire has diameter 1/ nr,exajvp tm+,9optyz81q1.628 mm and carries a 12-A current.    V

  A rectangular solid made 3: ;0bb0 /uhcvrvacq sof 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). Determine the resistance for current thatu3r qa/bc v ;c0bh0:sv 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 hcc gk:ft:q()2lsmth -1 e*hxz as twice the length of the other, what is the ratio oem l)zctt1 2hkc*hs gx::q( f-f the diameter of the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.0 +/8vq1lb)5+ zgs2gs bt 6jtxvkgnp4q0-V power supply, and a current of 0.4212 gqbsn k5v g2g6tlsxv1+ qj+b)p/z t48A 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 consists of 5.0 m of copper followed by 5 +sz:1ezimz 59 zab,es.0 m of aluminum, both of diameter 1.0 mm. mza bsse:ze,zz +i195A voltage difference of 85 mV is placed across the composite wire.
(a) What is the total resistance (sum) of the two wires? $\approx$    $\Omega$(retain two decimal places)
(b) What is the current through the wire?    A(retain two decimal places)
(c) What are the voltages across the aluminum part and across the copper part?
$V_{Cu}$    V(retain three decimal places)
$V_{Al}$    V(retain three decimal places)

  For some applications, it is important that the valu8pv(4.mn oguu y3m6lke of a resistance not change with temperature. For examplemo g3nu(.v6lmy4 8kpu, suppose you made a $4.70-k\Omega$ resistor from a carbon resistor and a Nichrome wire-wound resistor connected together so the total resistance is the sum of their separate resistances. What value should each of these resistors have (at 0$^{\circ}\,C$) so that the combination is temperature independent?
$R_{0C}$   $\Omega$
$R_{0N}$   $\Omega$

  The heating element of an electric oven is cc+9f0 acyv x7designed to produce 3.3 kW of heat when connected to a 240-Vvc09c axy7 cf+ source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player ldz9 ux z( 84nwoisew*1qqz2 3that draws a(le*4wz1dwx39 qoiz zsn8 u q2 maximum of 320 mA of current?    W

  What is the maximum voltage that can be 7m s 1vkb uw05hvq6tnsnbetr +2b(:)s applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, a a ggq7yxcy:8.mq xzr7 v: i6,v75-W lightbulb connected to its proper source v7g ,crz8gv xqay6ix.q:mvy :7oltage 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. C-+h j kyi0va0ccrpod4*6jaubz 1y i7f*f1o;e alculate
(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 ha:switq0,x /j ds 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 lightbulb in Europe(1 /rxdwsx mz,a8-j ld, where electricity is delivered to homes at 240 V. If you use the lig/1l wj s-da rx8mz(x,dhtbulb 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 doesjavlg zdah6 w: 8ievp7 xx:ko 29am(e9:h:i7 f a 550-W toaster use in the morning if it is in operation for a total of 15 min? At a cg2ihh:7: 7: :lzwxv(kama6 pdvexj89 oea 9ifost 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 c2zl u+ yvny 7 qyh p 2ms/hxg3/k+rnz4a3;yn8yost to leave a 25-W porch light on day and night for a year? y nm 7lz8v2zqp;g/2 khry/y4yuyx3+ n3h+san $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batc* b ;q7 boe3jk(ap03sx-ogrx teries connected in series as in Fig. 18–4b (Fig. 183 -xo sec x(prb;jb0 7kag*oq3–36). 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 amytx+ 8 o g9guit,t9jj/ount of energy 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 Fir7 tah 9*un-l ggv7v,-1jgiubg. 18–20, can be used without blowing a 15-A ihu g j9vtl,-7 7-1 gnuar*vgbfuse?    bulbs

  An extension cord made of two wi6 kbdffh ;:fz:l+2pshres of diameter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an el slk+ h:df62fhz :f;pbectric heater which draws 15.0 A on a 120-V line. How much power is dissipated in the cord?    W

  A power station delivers 62iu/12iz)i8 ccf8 jof+ epwk3v0 kW of power at 12,000 V to a factory through wires with total resistaw2zic ic)v f8/ou+fi 3k1jp 8ence $3.0\Omega$ 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 wh*g w2c7qh8ls i3a;ho hat rate must cooling water pass over the coils if the water temperature is to rise by no more t2 wh*h ;7sliahg8qco3han 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to heat a cup of water for coff,j jtun-omjxl9pq+ ,6 ee or tea. If thjm+9xn-jtoq l j,6,upe heater can heat 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 ioklm1gpml:b m6kuu85( x.z,m n a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, is acr y lab.,uri*8tyezl/z+7m4g:shu cs1oss 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 resistan2wt6yj ljrmmpd3 +.k;ce 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 current in a 1500-vy sm/q de)yr)d 33*dtW device is 5.4 A. What is the rms voltage)/3ym)dy dest* v3qrd across it?    V (Round to the nearest integer)

  An 1800-W arc welderoo1c/2 wwvojy.e/m z 1 is 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 dissi r(m3dti6+le5p)kd(kpi0 pi hpated by a 3.0-hp pump connected to ae0likkp5pt h m(i+3)dipd ( r6 $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connecv.p /t8 /9s v7t bd5 lqmhd7agljzos-1ks;5r dted 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 a tiny current b(. a7f*s,uyua4j ac hof $2.3\mu A$. What is the electron drift speed in the wire?    $ \times10^{-10 }\;m/s$

  A 5.80-m length of 2.09i3vrua9.3lv zb x-qojv ,x ll;xpd9--mm-diameter wire carries a 750-mA current when 22.0 mV is applied to its ends. If the drift speed.vxq9x l-9dv9p l z ;3ijarb,u3lxo-v 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 theo5vaa t:itukk(e .,i, 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 theq:s-9 2n mzep fl 0mc;m0dcim2 Earth’s atmosphere, $He^{2+}$ ions in a concentration of $ 2.8\times10^{12 }\;/m^3$ are moving due north at a speed of $ 2.0\times10^{6 }\;m/s$. Also, a $ 7.0\times10^{11 }\;/m^3$ concentration of ${O_2}^-$ ions is moving due south at a speed of $ 7.2\times10^{6 }\;m/s$. Determine the magnitude and direction of the net current passing through unit area $(A/m^2)$.    $A/m^2$  ----待选择----NorthSouth 

  What is the magnitude of the elj7s(+4sh pn caectric field 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 potential is znup4 haoqk* .ma /-l7b5 ra+kdetected 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 the speed of the electric pulse along the.kp a+ma krqnlu4o*/ b-ha57z axon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much energy is required t)u4kn ubhr:5 co 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 u rk5:hnb4c)uSection 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 pot85 da6 ui,uidfential, $Na^+$ 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 1.6wg( -:/)o cvdl hvoqz00 ampere-hour?    C

  What is the average current drawn by a 1.0-hp 120-e4vr8r3w+13p axz 1 l si1ahnfV motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. n1yd;p.bp btrpy5u86c/- ymd If each of the two headlights uses 40 W and each of the two tailligh mt y1c5u.dnypp8ry6/b-pd b;ts 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 ofj1s wn0 qx2hpp jf523r a 110-V, 1500-W heater is 5.4 m long. If it is made of iron, what must its diameter j32frq2 xppjn5hw1 s0 be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal4z y nne55s8cmrg*g+s of the resistance R; tharz 5cssn *n+ 4m8g5gyet 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. S svc+ )0x1rj +9r1ubwioiv m/ouppose 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 loi vxb)ro+1w cumi vrj os/19+0st 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 householr4t32qbj 8 mvyd uses a 1.8-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 wrappek*nxguj jzoct6 kl 73p e-l8spc de2yw;x 96:)d together side by side to make a thicker wire. How does the resistance of this new combination compare to the resistance of the orig67u*93cped;t8:y x-)2jp selkl ocnwx 6kgj zinal wire?

  A 1200-W hair dryer is designed for 117 V. u);p( l f5u+ m)u/pqwzukh v9j
(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 nj6ume n1y (6a8tcfzg 8ot become so hot as to stcum68jn1e 6fz at(yg8art a 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 h:n (cq+ cgxz0by the equation $I\,=\,1.80sin210t$, where I is in amperes and t in seconds.
(a) What is the frequency?    Hz
(b) What is the rms value of the current?    A
(c) If this is the current through a $42-\Omega$ resistor, write the equation that describes the voltage as a function of time. (  sin 210 t)V

  A microwave oven running at 65% efficiency delivers 950 W of energy per seco;cw3ap/vo1tzdb 1 :av nd to the intead w1: pv/a bvctoz;13rior. 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 differen ;-qcdwq; j9k+ p1p vv+hoxkz+t conductors made of the same material. One conductor is twice as long and twice the diameter of the second. What is the ratio of the power transformed in the first relative to the seconckv+;px +zpqq1wh 9jvk-;do+d? $P_1$ : $P_2$ =    : 1

  An electric heater is used+v9fp jd37 qqae3et2k 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 63s*,e2xpj hdhlks-y to a 240-V source.
(a) What is the resistance of the oven?    $\Omega$
(b) How long will it take to bring 120 mL of 15$^{\circ}\,C$ water to 100$^{\circ}\,C$ assuming 75% efficiency?    s
(c) How much will this cost at $11 cents/kWh?$    cents

  A projected electric vehicle makes use of storage battpuop+8;gwh+6 zl0r mieries as its source of energy. Its mass is 1560 kg and it is powered ;pozm+gi+ u hpr6w8 0lby 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 hastm 4 5id9r fl+9fkzj ic77c/9ucakcscb3; 2tl 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 accelerator02xiwtkc0. lx, ; epbe at Fermilab (Illinois) is designed to carry an 11-mA beam of protons traveling at very nearly the speed ox0;bekc0ix el,2 .p twf 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.7 bu+vq uvqe:-l)6usn The connecting cord is copper wire with a diameter of 1.628 mm. +u:lb uqvnqe-)su6v7
(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 rat gc3gc +hav,y(ed at 95 W when connected to 120 V. The heating element is a coil of Nichrome ,c(c3h g+yag vwire. When uncoiled, the wire has a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from abalnsbgc2 6hd e0+d9/zout 12 V when the car is off to about 13.8 V when the car is on and the charging system is in operation, a difference of 15%. By what percentage does the power delivered to the headlights vary as the voltage changes from 12 V to 13.8 V? Assume the headlight resistance remains +cdg0hab n69 2z/s delconstant.    % increase

  Lightbulb A is rated at 120 V and 40 /f jzn40lou*4s9b cel W for household applications. Lightbulb B is rated at 12 V and 40 W for automotive applicati /o04fz4elc nubj ls*9ons.
(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 applian/i mpl-wp9 nyu+ /kim2ces at 120 V, which draw 2250 W +-i yku/mpniwm9 lp /2of 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 a j c**z5lj:wxvn outside diameter of 5.00 cm (Fij v5zlj*cx:*w g. 18–37). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretchedlw7 yv h/*3kn7qdri* g uniformly so that its length doubles, by what factor does t3y drqhwk7in*gv l*/ 7he power dissipated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operates at 0.20 A and,y khbo f8z r0se*,q/7zzm9vw 3.2 V. If its res8, fhk,vw0z/ * yrbzmo79qzesistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$