What quantity is measured bye4fv4kfo dodnrf+ q 707k,ho a 0:(scm a battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, eb8*mv6: y42q6bj pj9zbgs(hcif (su klectrons flow away from the negative terminal in the circuit. Butuigh( 2bb 86sfj b(q4y:9cs6*vp jkz m within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up:s, x)c,sx-ae z battery current, battery voltage, battery energyescszx ,),-xa , battery power, or battery resistance? Explain.

One terminal of a car batvekbkz5 apf 8(e5rp -(nr/ f5rssw1+wtery is said to be connected to “ground.” Since it is not really connected to the ground, what is meant by thi ws1rv b (5p-55kw ps(a +ff8r/zrnkees expression?

When you turn on a water faucet)bywi6v,nb9(e1 (vcamm0 cj s, the water usually flows immediately. You don’t have to wait for water to flow from the f(c6(svmw abj9 )c0 ye,1binmvaucet 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 pro 6smxi 1c .y/85 -za+fb oq2gmo8lzhave the same resistance? Explb-18/o6o85pscg +a2oy zqfr xmilzm. ain.

If the resistance of a small immersion heafb+eo ixi8,kf1r nn8b e+gc7 d9a(u0pter (to heat water for tea or soup, Fi,f9+go78f8ne d(br1k+enxpbi ua ic0 g. 18–32) was increased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has,k; f,d q4cn;qv vh6rj sides of lengths a, 2a, and 3a, how would you connect the wires from a batte qr6n v4kjd;c,q;hvf,ry 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 lightbulb burns o;0*l7 .hvvmwuzrzmd3,sz/+liw 4 npsut?

Explain why lightbulbs almost always burn out just as they are turneio)iwzz,s+ f 1d on and not aftosziz)+w f1, ier they have been on for some time.

Which draws more current, a 100-Wwrm5yg* e )-.j ,;vmsh6s okyn lightbulb or a 75-W bulb? Which has the higher ren5,kswgr .)yseovj*m h;6my- sistance?

Electric power is transferred over large distances at very high voltages. Explrg;yx7y bv6hza (:wr 7ain how the high voltage reduces power losse7 ;rza:6xwv( rbhygy7s in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fuse wi:dopqf r-:2clvzp:2 lth a 25-A fop-cq l2 fzrl:v::d2 puse?

When electric lights are operated on low-frequency ac (say, 5 Hu*gs/(qb t9 cyz), they flicker stuc/ gb9y*(q noticeably. Why?

Driven by ac power, the same electrons a mi6xn5+,tu)-ybhv z pass back and forth through your reading lamp over and over againhxn-,yt + )uvmib56za . Explain why the light stays lit instead of going out after the first pass of electrons.

The heating element in a toaster is made ofpd;39rigl a p. Nichrome wire. Immediately after the toaster i l;da93.g iprps turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in aoyibtohhp0r imd2 27x6b w-; ubbv:-5 resistor? Explain.

Different lamps might have badfb yxy.f hyy vh6a6 27.;qlc+tteries connected in either of the two arrangements shown 2yxchy+f6 l7q;yh.vb.f 6ady 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 are8vov0ldslhxk jf 4a:)( ap44 zlk15dr flowing past any point i(lpo4 k4jhfxkl8d4sa0v :d5 1vaz)rln the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A foaguwr pk+:(t7r 5.0 h. How much charge passes through the battery? u:k(gtpwra +7    $ \times10^{ 5}\;C$

  What is the current in ampere4do8hhu g 7 ioznd(j)nl03j,cs 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 ifmsp/ jbhb 78cu 3ru:2o 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current throughpi2j-bz y*. dm (g5 3sixe+zzr a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-V l.(i:8mz mu jpaine.
(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 nt+ oo2 ;a*1vqijy+p i42d zzgresistance 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 co 9mi4y)1dmb5c i0u1rd,dl zj5i gz.nynnected 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 line carrying 2800 A (Fig. 1 66e hyf. /avhlrf.-lb8–34). The line has re/ l6 .y-ha 6vfbl.fh$2.5\times10^{ -5}\;\Omega$ 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 At(srav +8ypy , 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 currenx)7te:+bk+ 6xs9e rv 2:o jpo5qzki pdt 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 t ,dn1c, ix chb*3tjq*lungsten 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 mmp0nuc1 yj6q) k in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire 2+ hz75c jt/jr7;hh kee.0 mm in diameter, tore;he/ c+k7j7z5 j thh 20.0 m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resist7 3p. /peug6wjkg rsvuu v0*g7ance as a tungsten wire of the 0g .puk6 sv*pj7g 3 g7ewru/uvsame length? Give numerical details.    mm

  A certain copper wire has a resumfn -7( huxkvs:4(o p9n8f wfistance 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 pof*g- gq9w+uthe temperature of a copper wire (originally at u-gf wpq+og9 *$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivity as d)vunw/zi 3c75*ku s ktungsten does at 7 cs/5*)3ivdnu uzw kk$20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resist)y sq3sjt y4w3 k6tqo.ance 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 no6ax p ef u;- 4b2odxq)v-p4d/ow *znzh. 14 copper wire (used in 15-A circuits). T euv zp/-;db aowoq6zx pxh )n44f*2-dhe wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides ofer ba/r/ /*2g p8wxymu lengths 1.0 cm, 2.0 cm, and 4.0 cm, wr /2bxr/ga eyu p8/*mlying 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 has twice the lgd gpsu8t q,:(aq- l+0wprz8zength of the other, what is the ratio of the diametpq pzgd8 +gu, -wz0sltq8ra:(er 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 10.00-V power supply, :k(3v msd cfkk,q +u:qand a current of 0.4212 A is precisel k f:dsum+3qkq:k, (cvy 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 consy kducy8p. 6;-,jto rk.uak(xists of 5.0 m of copper followed by 5.0 m of aluminum, both of diameter 1. p.cakj;rdytouk8u-.6 y k(x ,0 mm. A 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 value of a resistance not changet.aep (o: fgiks5d(w0 with temperature. For example, suppose you mak. depiwf:(5 asgo(0tde 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 q-gn f ra vqdn +1kr0yw0k9up(h/7f1r4m1ii e3.3 kW of heat when connecte0riiy41pmd gr 9f- (v f/ka0nkq+e hw 7u1n1qrd to a 240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player thwu 87hjims4wob-/0 b ln- i0anat draws a maximum of 320 70 hja8wmlb-nowib0nu-s/4 i mA of current?    W

  What is the maximum voltage that can be applied acrhahe yl8d /g51oss a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, a 75f7 z .thtqj(o)-W lightbulb connected .t)q fo7(hjzt to its proper 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 heaterui:b(dvy( j)d cg/2ls is rated at 110 W. Calculate
(a) the current through the heater when it is operating,    A
(b) its resistance?    $\Omega$(Round to the nearest integer)

  A 120-V hair dryer has two settings: (h.kap /w:wxpbl/4zoideu); 850 W and 1250 W.
(a) At which setting do you expect the resistance to be higher? After making a guess, determine the resistance at
(b) the lower setting;    $\Omega$
(c) the higher setting.    $\Omega$

  You buy a 75-W lightbulb in Europe, where electricity is delivered to homes a1p dk.5yp vabvp k 4.8t/cth1xt 240 V. If you use the lightbuvavdby h1t1cp5p 8kxk. p .4/tlb 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 dox qldbz(g a-uh,e9 ; zyb9(67p; fqmtnes a 550-W toaster use in the morning if it is in operation for a txn9 ( muzfpz9h 6e ,t;a-y; bqlqgd(7botal 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-k- nff4:tp rwnhu.z) :W porch light on day and night for uw .-pnzrf :4kn:h f)ta year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected qdh;rvosw; w(a38 .oh in series as in Fig. 18–4b (Fig. 18–36). Thevao;o.q hsd 8whw3(r; 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 stored in ztwun* mp-m4y3d q37p a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connected to 1; cy/dcn p s4kxp,cja8k ek;;-20 V as in Fig. 18–20, can be used without blc-8; p 4 xpcd /ke;j,caksykn;owing a 15-A fuse?    bulbs

  An extension cord made of two 9af ;icv8v9m( ad mj2kwires of diameter 0.129 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 1dmmkf8 9ac ; (ijavv2920-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 factory thro ebjdwa9h d)2n9 2zd.nb e33lough wires with.zd dh)3 bje2lew3badn no9 29 total resistance $3.0\Omega$ 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 24 ubn)+w5v.r orcl (s3q0-V line is 17.5 A. At what rate m )qobs3c(+5w nvr.ulrust cooling water pass over the coils if the water 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 heatk0p9l1jjm+ yf h.bj 0l a cup of water for coffee or tea. If the heater can heat 120 mL of w+m0 1h l9jp. flykjb0jater 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 curream ygqdi8wn8,50dos);gg 3s pf*2 .uq fdtq.ent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peaki i0n )pn+6:haycn6 68cm+fr apbpz8 n 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 resistanczgd 7+)e;aldlxbp.h)m.eo5se 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 cue-1vmxh4s91wla t;(ol8ke edrrent in a 1500-W device is 5.4 A. What is the rms voltl xw (1eee l4 1m9adtsvko-;h8age across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected to a sb,p-i brp9::go5 a )tr(,id jw rqi8m(mbj-o$660-V_{rms}$ ac line. Calculate
(a) the peak voltage$\approx$    V(retain one decimal places)
(b) the peak current.    A

  (a) What is the maximum instantaneous power dissipated by a 3.0 v 3*vbh*gjcan ;;8wualxh/ 0o-hp pump connected to aha*;0c; w/g hv8jv*lo bun3a x $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected t,+nq fxhh cx:,o 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 cugv6oz,kjv c+ q4;eav6,gfi e twh3 6j8- o(gdurrent 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 *lb49 jxwzu(6yp wpr (bf/y )h2hmoq2 22.0 mV is applied to m h wuj(/2 ly xfo(42qbw)6hr9* pyzpbits 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:ysjyf-oikcxk m(6;5)ek3 zl ’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 thv ho6fl bh-.z64 zyj/ce 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 e yn2/6-jk.c -kmusvj llectric 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 potzckt v g9.wu m.w*mj k3.5khf42)ucnfential is detected at a point 3.40 cm down the axon 0.0052 s later. When the action potential is detected 7.20 cm from the point of stimulation, the time required is 0.0063 s. What is the speed of the elecz.5)cwc92.uu* mkf g4mhv ktk. 3jfnwtric pulse along the axon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much energy is required to tlmii1y ui yk)y :x-s-o;8vmc*ransmit one action potential along the axon of Example 18–15. [Hint: the energy u* )8kms oi ivyy:xm1yl;i--c 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,x 5 rr bz.)g-oea;t;sw $Na^+$ 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 ee8 n )jsajk)0qm q*t,there in 1.00 ampere-hour?    C

  What is the average current d1m6n a.dfeo:b.c e:rkrawn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of ph+k vuxq+n0k2gqt jk* vh(,tw+ 7or/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-Vgr/ (kp+ot x +kkvuw, 2h7qqj0h* +ntv battery last if it is rated at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of a 110-V, 1500-W heater is 5.4 z9xtyq1(d qy*kx+sn6 m long. If it is made of iroyz y x(qt+*16nqk9 dsxn, what must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defin 4aad. 0/zsa*4hjetgq6r jse1 wuav*8ed as the reciprocal of the resistance R; thata4u4qj t .z *6ses1da*we/8 vrj0aah g 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. Supposej hx)o+knry+e 78i8p5z ydzr-w.xp /x 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 k wp/x8i +n-.d y5e+ zzr)87yxroxhpj copper wire, estimate the cost of the energy lost to heat per hour per meter. Assume the cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular houjg i 4prvg 2p;8rxa4l3sehold 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 atci:j wmn+c-i-i+;o cv2 +zah re wrapped together side by side to make a thicker wire. How does the resistance of this new combinatioc ;-hcazt++i-imn wv: ic+ oj2n compare to the resistance of the original wire?

  A 1200-W hair dryer is, nd(uih z/ ,9mlt+bea 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 ejf4)4kb6 dt0mt a f-kwnough so it does not become so hot as to start 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)44-dj ft6kfakm b0wt of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is g0 )yv233v pwfxvs :vbdiven by 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 deliox +xygip82r) vers 950 W of energy per second to the interio8xi2xo)rp yg+ r. 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 qd dszl2 :-e2 9i3vsfjof the same material. One conductor is twice as long and twice the diameter o-3zfd9:eliq2sv s2d jf 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 ; kq2 .fsd,gofheat 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 sour-r a 5rpgf3a0gce.
(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 itsnhbb an)pnr.f i+5 3.l source of energy. Its mass is 1560 kg and it is powered by 24 batteries, each 1n+bhnlfn5.bpa i) 3r.2 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 resis)j m6teu9.lm wtance 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 (Illinois) is designed to carryamaqlz:n s evap,7 s o:*8)6jy an 11-mA beam6,la*yssvjp 8a)oq7:nm a: ez of protons 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 2208v hnjr:fg0- f-V ac. The connecting cord is copper wire with a diameter oj08r -:hnfvgf f 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 Vso, m6)m.k0cgnc9byh . The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. W.y9)c6m okghcsbm n,0hat is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies fro9zo 2*cgw 4hgjok+3*a0;i kntri1 qdut 7o 7ism 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 the voltage changes from 12 V to idi9ko4jru+o0c*7g nq3 i 7oatw; 2* h1zgtks13.8 V? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for household applications.*,q ft o6er90r*f2 g/zf jsdko Lightbulb B is rated at 12 V and 40 W for automotivftr/ jd9e o0krq*f6,sgf* 2zoe 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 diamete9n ohpkyq)e h+ cgu/*ucx y+.2r 0.259 cm is used to connect a set of appliances at 120 V, whipyy.u 2hn*9q/e ch okg)c+u+x ch 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 cb 46 xionyl.,(nl fzpe2w2 s2zm and an outside diameter of 5.00 cm (Fig. 18–37). What is theoxbe,wi2(lf2 z26s .y nnl4zp resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched tfb tw8x+8l te n()s krrgghn r5; 3;4/jn-zjiuniformly so that its length doubles, by what factor does the power dissipated in the wire change, assuming it remains hooked up to the same voltt+g;wf4x (sni/ h rn;r8ljtz)kgnj85b-etr3 age source?

  A tungsten filament used ivme*-d upr 4r1n a flashlight bulb operates at 0.20 A and 3.2 V. If its -u 1m*v4prderresistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$