What quantity is measut*r ,e9t s3;xzrox 8zered by a battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is mx 1wl, r ,bzok2lr(1yq *jzuho83zeu327i ny connected to a circuit, electrons flow away from the negative terminal in the circuit. But within the cell, electrons flow to the negatr w7,mob(i13lz2 qz zyyur1xu*jn o8he,kl2 3ive terminal. Explain.

When a flashlight is operated, what is being nlt)*bdn4ycss* y r5 c6j9mz5used up: battery current, battery voltage, battery energy, battery power, or battery resistance? Expsmn*j b5*y 6s9y5lzc tnr)d4 clain.

One terminal of a car battery is said to be connected to “ground.” Sism c wr37z/w1znce it is not really connected to the ground, what is meant by z/17ww 3crs mzthis expression?

When you turn on a water faucet, the water usually flop rua a7amkte(e (k alrdh 33+2;c el0w*w2l.uws immediately. You don’t have to wait for water to .k w2ua( 7a3ca0;p l( d*leultherra+kw3e2m 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 alums3j9e.e7m3hxz5g 9n h 0lfeqq inum wire of the same length have the same resistance.7n3 q9z5jfh30e eq 9eghmlsx ? Explain.

If the resistance of a small immersion heater 9 +j zd-qtq1op dhqk7 26fk1m;gdiyb* (to heat water for tea or soup, Fig. 18–32) was increased, would it speed up or s6dd2dk; 9q +ptizmbfh7oj -*ykq1g1qlow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a,)y pn jm*r9:s)ul4ssc 2a, and 3a, how would you connepus)*msrl n9j) 4c:ysct 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 lightbulb 9d:xwf k gzkw-08gxv +burns out?

Explain why lightbulbs almost always burn out just as they are ture6bjxnjh* -x,1jp(h wned on and not after they have been onj1xhn(p6 -b* xehj jw, for some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Whicevac : fykvp3 c9 6;00z*thjtgh has the higher resista3c:0vj9*thv6p cz; f0 tayg eknce?

Electric power is transferred over large distancesjg4ju0;;m) pnzs +m ((quhces at very high voltages. Explain how the ucpz0qhjugsme;4+ms n j (;()high voltage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why :pk n((;qtd sais it dangerous to replace this fuse with a 25-A fuq(k asd:;npt (se?

When electric lights are operated on low-frequency ac (say, 5 Hz), they feoo * d0wqmcaq7/p;( flicker noticeably. Wh; (doa0ew o*p7 qfcm/qy?

Driven by ac power, the same eo4x g23rk 3ube+wuco9f b+ e5mlectrons pass back and forth through your reading lamp over and over again. Expl+goerx 5bw 39umfc4ou bk3e+2ain why the light stays lit instead of going out after the first pass of electrons.

The heating element in a toaster */cdtf;eqc: mf2 2axq is made of Nichrome wire. Immediately after the toaster is turned on, is thmfc t2dexq:;q2fac*/e current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resisttfpga l3q6i8-fker7 *or? Explain.

Different lamps might have batteries connected in either of ta:gs898ch)idr gr1 b ehe two arrangements shown i8 98aggs bi): 1crrhden
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 flowing 2+qbiuyshtzy a+7a56;y k5)nzbz9ua past any point in the wire per sz57u +6a5q +t9;bkyh ny2zbz) uyiaasecond?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A fa(dy0fi 9k9rell87 z for 5.0 h. How much chargf9fke7d a lr0y zli89(e passes through the battery?    $ \times10^{ 5}\;C$

  What is the current c(j+2lg3gsf z9yu,o 4 bao*tcin amperes 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 4gdln3d 7d3l3vq) fmba toaster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0dl /,j t-w r:/ ww)q 8ltuxv1uhid9ap(.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-V, b,tofvl3s 3q 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 d:wxke4ugx wied.9dt8 2-is3 bryer has 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 bu2pr 2- u.y t4v ujg86wtv3htn,s+orxolb 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. 18–34). Tvcoh9 cw ly.61hec 9 1o6.wvcyhl 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 drawy :y0mhka3 n vtykas- rw;fs4m885f(os 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 )ex.d6 ml,oq2 2 damgdcv x9i9current 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 tu6 /mjo lvt*we5z6. bzqugx3t2ngsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire/ 1mokr wptwyd ifygm*h46 34i(gu f;: 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire 2.0 mm in t1, wg,e:7qljucfe1g diameter, to 20.0 m of copper wiw7,e1 cfe, lj:gt1uq gre 2.5 mm in diameter.   

  Can a 2.5-mm-diameter cqe0;t)tvv 2v bjh zmzzt*7 dmv5)o 6o/opper wire have the same resistance as a tungsten wire of t7)hv*60d52z)jb;zovozqe v/t tmmtvhe same length? Give numerical details.    mm

  A certain copper wire x)bs 1apj3q*lh 8o* a5qpg;0e:t yk)csz.zf thas 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 *zh(q )0imefgto raise the temperature of a copper wire (originally ath (zm*gf)ieq 0 $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper bif qblzrid8rye6t (dz 23983will have the same resistivity as tungsten doefqlb3(r2d8 e3y btzr iz68i 9ds at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resista wui2zf 4 k+oe)re/3djnce 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.:/:,wzoed cau s a+/uy3qia-w 14 copper wire (used in 15-A circuits). The wire has diameter 1 :o-:/uc uaisew,w/yqada3 +z.628 mm and carries a 12-A current.    V

  A rectangular solid made of c fh ;kb1(ls6bsk a:ergqz*oi1u 7.a1 warbon has sides of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lyis1k. 1b*z1ea l:7bos gh( k w6iruf;aqng 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 resistanctg dznny g fnp* u.zs;0z-i3(yt8hf/7 e. If one has twice the length of the other, what is the ratio of the diameter of the longer wire to the diameter of the shorte ntz3z-gh( 80idf/z *7ynfts;u.yg n pr wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connectl : q8yf24,yo5mzvptw ed to a precision 10.00-V power supply, and a current of 0.4tz lwo8yy:4f,mp q25v212 A 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 wirez:25 d k)sfh/hyqc-sf consists of 5.0 m of copper followed by 5.0 m of aluminum, both of diame qz:h5s-2ff)sk/hcd yter 1.0 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-44c2e) n .vfe.2( zr, jstws 8wb3hfkgfwgab the value of a resistance not change with temperatur)r bwz g4wgctn(h3vj-k..f,2e ewbfs4s 8f2ae. 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 o-o-6 z zo.tqjsven is designed to produce 3.3 kW of heat when connected to a 240-V source. What must be the r6toqzz- j s-o.esistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player that c (kr*pkww8n sk+0t2g draws a mgp c0(8t+ nkrkws w2k*aximum of 320 mA of current?    W

  What is the maximum voltage that can be applied acr f)bf*uk6m j (bcjqd7nai+13koss a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current thr2 3sfgwn 6blk)l-,jdn ough, a 75-W lightbulb connected to its proper so3), glj6fwsnd-kl nb 2urce 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 raths+mn) b.roxv k8 2u ec2v2fk2ed 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 settic.cjf/-sk k 6i7kd:gpngs: 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 lightbul/xc0qks3jb k*- zmca:b in Europe, where electricity is delivered to homes at 240 V. If you use the lightbulb in the United States at 120 V (assume its resistancex cqczm-3 sk0k/a *b:j 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 the morning if is;50 5uhw wcife /yyw6t is in operation for a tycuhewws/ 6y5f 0i;5 wotal 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-W porch light ohpcmo)mb0iun,n. :z vz,el*3o6 ez9 un day and night for a yee9ic,on:,)zv hplz0un. m* u6 zom3bear? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected inp/jk ;gnz(a q7 series as in Fig. 18–4b (Fig. 18–36). Tz;ak(g7/ qj nphe 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 amou3-gxccezd 64osima 4 :nt 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, cs)5gjb 8xb5 ox)lg1a9ton .hwonnected to 120 V as in Fig. 18–20, can be used with bnt5j.5lasogbgw8h) 1)9 x oxout blowing a 15-A fuse?    bulbs

  An extension cord made of two wires 9q;5al,xnezjuqz jlmm17d e, gk; -.tof diameter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electk9jm tz;-e5,j.ze1gmlnx d ;ql u7a,qric 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 12,000e x8w x j4l4)lox9w:,whr1n wy V to a factory through wires with totaly wwh1:wn wl8xeo9l4xx,4 j r) 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 240-V li8xd)kc(j6 /otx hr.t9xtho ez9f:qyy o68r 0tne is 17.5 A. At what rate must cooldt6: z06kyo 8tjh.9/x)8ot (xexhrf oqct9y r ing 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 t3f w( nwxafb,/o heat a cup of water for coffee or tea. If t nxf f,bww/3a(he 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 ih)m;lud2 ;nbz n a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 Vk8meajf v)d0q4q3i.)lxk +lra57 or e , 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 r1aw*dt6a p i7*uv1x5 4yub aspddq61the $120-V_{rms}$ 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 alte+0o vatthv2+ if;aw4k rnating current in a 1500-W device is 5.4 A. What is the rms volt;0vawtvtof2 k ++a i4hage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected ton0w9,bg,kfo0m sl7h e 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 dissipated by x6mytm50a k/u2yjqp-a 3.0-hp pump connected y- qm2j0y5/uak6pxmtto a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to abm he1fj/61c zydl kjk q2zf1/ g,1g/e $240-V_{rms}$ 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 of wza6r3q asuxp/imkr (0342jdcca) 7u $2.3\mu A$. 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 22.8xwaj k.g k4(j0 mV is applied to its ends. a k k.4xgj(w8jIf the drift speed is $ 1.7\times10^{-5 }\;m/s$, determine
(a) the resistance R of the wire, $\approx$    $\Omega$(retain three decimal places)
(b) the resistivity $\rho$.    $ \times10^{-8 }\;\Omega\cdot m$
(c) the number n of free electrons per unit volume.    $ \times10^{28 }\;e^-/m^3$

  At a point high in the Earth’s atmosphkg -3qn/iomd5 ere, $He^{2+}$ 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 atmoje /h /lmr 92ebb2rt/zsphere, $He^{2+}$ 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 emen6 b tqv8ho0kb1)c 7lectric 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 pult7sqba z cgwr4-4-) ks0fr h) 6g6ohyjse. The action potential is detected at a point 3.40 cm down the axon 0.0052 s later. When the action potential is detected 7.20 cm from the point of stimulation, the time required is 0.0063 s. Whj-s6wqfgr0b h hc7s4 -a)g) 4rtzyo6kat is the speed of the electric pulse along the axon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much energy is required to transmit one action potential along thcst3r 7o/y r9jg2a,v be axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored by charginj3v/s aort 2c,b7 gy9rg 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 potent ql/ 8a8uk2d4fez f9diial, $Na^+$ 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 therrzq 5 4iw7rh r.6hbg/fe in 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0-hp 120-wb+xhnox *u- aw6p q/y-np-k; V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leimh 76o7irw4:hfs ( v9i+uzo yaves a car with the lights on. If each of the two headlights uses 40 W and each of the two taillights 6 W, for a total of 92 W, how long will af i7izrmohs w y :(vih6o4u9+7 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 a 110-V, 1500-W heater is 5.t45 ivuj u;/v c-zlds)4 m long. If it is made of iron, wh45 j/v;zl-)t uiv ucdsat must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined a y7sft g.glzb.vk. s-olu8(6ms the reciprocal of the resistance R; that is, suv.g6t.ykm.o7 l( fb sl8z-g $G\,=\,1/R$. 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 iv 1-jlzay aj04 6nrku/; )kve4iezv6 pnstead of using high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a two-wire line of ;0zk)e-n6p/va j44 y1rviuj al6e zvk 0.50-cm-diameter copper wire, estimate the cost of the energy lost to heat per hour per meter. Assume the cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular householm:- qjas;ga ( 5o)0 y, zobss-eew5cfld 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 wrappedv h+ 5wzqj( -gctzfb m9rtt9/( together side by side to make a thicker wi9 9mwz tvfztch(bjgr5q/-(t+ re. How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed+/ k8j 5ltjeduqs2yqrs 9vn9jmhbl/h( :6 6 mr 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 hot xyc3h /h sk:i/as to start a fire. What diameter must a copper wire be if it is to car sx:k/3hyc i/hry 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 equn1(dmmcv7 (.v t r1zlpation $I\,=\,1.80sin210t$, 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 deliu .7f kwnn2:thvers 950 W of energy per second tf.:w 7t2un nhko 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 i+n 2p2nuo /wytwo different 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 transforme2un pwoin2/+yd in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat avyfj)t. y0 zf .1e4lqf 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-m 97fma :h i4czx /y:l9wnkhv*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 uk *c/nxflc 9+vse of storage batteries as its source of energy. Its mass is 1560 kg and it is powered by 24 bat9k*c/n+flc v xteries, 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 lightbkpdm3 jmqg fn4qe(*f :ly6 /t(ulb has 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 (Illi .hdzvxj1mx( 5nois) is designed to carry an 11-mA beam vhmxjx.d 51z(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 220-V ac. The connect;qr0.q pnv f- v8mzz0ks2gh c3ing cord is copper wire with a diametv2kgz0 nrc pzv.;f0m8-sq q3her 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. Tmw(mo: 6pyyezwswu;)h y*3/ z he heating element is a coil of Nichrome wire. When 6w/my:;ywyzsp ) me3 wzoh*u(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 abo d(za i2ic /yh-wf(qs.ut 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 po z c(/2ysh(-di wiqfa.wer 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 forl,2qyec )m1on household applications. Lightbulb B is rated at 12 V and 40 W for automot ol1qm2,ne) cyive applications.
(a) What is the current through each bulb? $I_A$ =    A $I_B$ =    A
(b) What is the resistance of each bulb? $R_A$ =  $\Omega$ $R_B$ =  $\Omega$
(c) In one hour, how much charge passes through each bulb? $Q_A$ =    C$Q_B$ =    C
(d) In one hour, how much energy does each bulb use?    $ \times10^{5 }\;J$
(e) Which bulb requires larger diameter wires to connect its power source and the bulb?  ----待选择----Bulb BBulb A 

  Copper wire of diameter 0.259 cm is used to connect a set of appliances at 120-fmk28e;/ le*t apezp vow n8* V, whicmop- /ealk8 n8 pefz 2;we*vt*h 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 outs f4(az)kbl 0eside diameter of 5.00 cm (Fig. 18–37). What is the resistance of 10.0 m of this pip0bsfae (l)k 4ze?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformltt0 aie e yb0tc29p*bi)lyc*a0a1 e w,y so that its length doubles, by what factor does the power dissipated in the wire c0ib20ea aa0cw) t9 *bie, ce tt*ylp1yhange, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashligh7 ni2i3si7cqgf k:- encuw(4et bulb operates at 0.20 A and 3.2 V. If its ekeg-:2scq3iwcu7ifn (4 7niresistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$