What quantity is measuredkvkq*(a-,( w1byoobg ci-;y a by a battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cel7 +6+boicbiwl w(3dpz l is connected to a circuit, electrons flow away from the negative terminal in the circ+p7b3d 6w+wi ib(zo cluit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is o 9/ysr(jb yqifj3j t8-k;jy4 t*5womfperated, what is being used up: battery current, battery voltage, battery energy, battery power, or 8*ky ;t-j(fmij/fj 5jy9orqbt 43syw battery resistance? Explain.

One terminal of a car battery is said to be connected to “ground.” Since it tpu q*wx)n 7s-60qeau is not really connected to the ground, what is meant by th-*qe su6 n p0)uwax7qtis expression?

When you turn on a water faucet, the water usually flows immediately. You doxds tuau a3.79mf2/we n’t have to wait for water to flow from the faucet valve to the spofwt/ 3s2au du.9mx 7aeut. 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 hihfe;( ztk-; have the same resistance? Explehh(-i ;t;fzkain.

If the resistance of a small immersion heater (to kdez3v kvl.w;fqcn .;5i-bi :heat water for tea or soup, Fig. 18–32) was increased, would it speed up or-zw fq3c;: v iie.nld.;v5kkb slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, and 3a, how wyobuyk 2(y+0 nould you connect the wires from a battery so as to obtain (a) the least resistance, (b) y(byy0 un+ko 2the 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 burnsj )8/y.zl:hdvqxi b/v out?

Explain why lightbulbs almost always burn out just as the657z-lj ,sts dkh; q,w yvv mc4fly-+zy are turned on and not after they have bew; yztzdvjy,56l,vkm-hfs 4 +s7- qlcen on for some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which0-mau2 z ilj.0zmu3y x has the higher ruxu.0 3az ly-jimm2z 0esistance?

Electric power is transferred over large distances at very.um z ;s b+.xxwvut*79rbdk/o high voltages. Explain how the high voltag9bku;.mszd*7 r+w ./xxvo ubte reduces power losses in the transmission lines.

A 15-A fuse blows repeat;v)cpuprz/ hy ck) 3y(zp:)ne e:ib 9redly. Why is it dangerous to replace this fuse with a 25-Abep krnz zv))ric3p9y:h: p u;y c()e/ fuse?

When electric lights are operated on low-frequency ac (say, 5 Hz), theuuy3us/d7apko p b)ft v1;/7s y flicker noti/bvt3oupk7fdp71; u a uy /s)sceably. Why?

Driven by ac power, the same electrons pass back and fwp e6 e2x8+w6-+n/enzphk xyhorth through your reading lamp over and over again. Exp y-nkhh 8x ww+p2 6/ee+n6zexplain why the light stays lit instead of going out after the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. Immediaukd;y6 2kuyc -.1 hihmtely after the toaster is tur.y2y6- hum;dukhk i1 cned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistolq 8 r;xyjyzjxfr5./2r? Explain.

Different lamps might have batteries connected ,s ;0iovy i(rxin either of the two arrangements shown in (r i x0yisv;,o
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows inc05 ccfmktd:b y3s)y, a wire. How many electrons are flowing past any point int3mbcs)0 5yc k, yfd:c the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A for 5.0 h.(1rp h a3hmp ek*v;;ab How much charge pashhar;3b(epm1v * pak ;ses through the battery?    $ \times10^{ 5}\;C$

  What is the current i+ ;ld./ke) jjhtb 5d/eeohz2n n 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 a toaster if 120 V produces a curre fva 6c/eye)4 t8we8fwnt of 4.2 A?    $\Omega$

  What voltage will produce 0.254*/n6u ,iaco4 u8s-k ,zwdlt dmy5ram A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120--vl.iwz k5r.m s-f8g nV 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 dry6/ 8- uuvcmx ssidxe/;er 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 bulb whosj ec(r)ivo /c8y4* iese resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electr ku )xity)b uw2)vwr24ic transmission line carrying 2800 A (Fig. 18–34). The 4ri2 xvty )bk))wwuu2 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 6.50 ifhp0dv mfvx9 0qtz3q 7:2tg-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 current of 0.6082 a *s3dqn5gwm)7f n1p(vdqkx7wt al 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 resistui :n3-ip*,p . tj4aqhe x*s nhf-0m-6bxczcp ance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1.5 pv(tt)y92:cb ln8o wl mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resr;rok mhe (hx4zme arb7k961 2istance of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wi ho rmrx7h4er1z e(abkk6 9m2;re 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copnlk,l3f+np 4qper wire have the same resistance as a tungsten wire of the same +,pklnl34f n qlength? Give numerical details.    mm

  A certain copper wire has a resistank3,hy *oe/dhee )w7m kr l33fvce of $10.0\Omega$ At what point along its length must the wire be cut so that the resistance of one piece is 4.0 times the resistance of the other? What is the resistance of each piece?
$R_{short }$   $\Omega$
$R_{long }$    $\Omega$

  How much would you have to raise the temperature of a copper wire (1zsjg 8w vwtitsu8i wt6i 70):originally atw8: v7z6 18s iti )0tgjstwwui $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature coppe oui :bzgzv xoy3- f;o8xs*);ur will have the same resistivity as tungsten does at gzo:8 )ixozsv b3*yuf x;-;u o$20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistanf: lts; r:i1pn dj)p,ice 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 househ tll6r vbm*l;9soh k:0old no. 14 copper wire (used in 15-v;sr6ol90k lm: *lb thA circuits). The wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carb4 a k6(y6myqwbl,:fbago ( xr4on has sides of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 184 fl6r(am(b qk: wy4xyg6ba,o –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 tw pcrnubzy 8q5g35r hh gv)(29pice the length of the other, what is the ratio of the diameter of the longer wire to the diameter of the shorte5n5ybgr9uqhp c )vp3g(r28 zhr wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V power z blnt4c;m2) fsupply, and z m;l)n2f4tcb a current of 0.4212 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 wire consists of 5.0 ,./u3cf; )hht khcig 96rnypnm of copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage diffe 6ghk9h/irtu )nh,.f ;pcncy3rence 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 imporb xqi1xh1-+p9q9iljib i 33v ztant that the value of a resistance not change with pj19+qi9lbq-h1 i izx3 vibx3temperature. 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 is designed to pro/)ylw,b2 ffrfc++uqkn2 jn1 a duce 3.3 kW of heat when connected to a 240-V source. What must be the resi nqlw)+ r j1fb2y2nk+c,fuaf/stance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-h zqbr*82o,. /pzlkpyV portable CD player that draws a maximuh, z*qz2br8poy./l kp m of 320 mA of current?    W

  What is the maximum voltage that can be appli1g(apqvl .g1 w;vtd +hed across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current th,+qti b(bpu2hhzsg pq)-h55a /dz 7hxrough, a 75-W lightbulb connected to its proper source voltage o5/ s)zhbhz5 dp xqph7(ha + g,utb2q-if 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. Cay cwz ;jz)od5 xa,q(l.lculate
(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 t9 bw5*bin 4dwsx((zv sal)5u: 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 isg4iv -awa/tsv75h(5dwr b3 3fl udwe0 delivered to homes at 240 V. If you use the lightbulb in the United States at 120 V (assume its resistance does not change), how bright will it -i ww/a0f4tw 7vr5 (edh3s5lbdguv a3be 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 morne,7 h)3zvwrl cing if it is in operation for a total of 15 min? At a cost o)cl e7,hw3vrzf $9.0\,cents/kWh$, 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 cohjk8 azzx8jtai3) 7 4wdcrw0nt9)16jre mhe2 st to leave a 25-W porch light on day and night foh 2axjzk8jnr7z3j) wedrac e h14w)96 it0t8mr a year? $\approx$    dollars

  An ordinary flashlight uses two D-cmya-0fi7ic k ctz1 3w5ell 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–cmwkay 1-f3tzic0i75 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 amount of energy stored in a 12-khvxhb* 2 :cn8mp0u a,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 Fig. 185 9el q3vosk8qu3 a5uo–20, can be used without blowi9 vku5s3 q8q3eooalu 5ng a 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no.fv4j jl :s9l qvly31v+ 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric heater which draws 15.0 A on a 120-V line.vvv j:4yl39q +lf lj1s How much power is dissipated in the cord?    W

  A power station delirtcpb:z nq*eo2 :5 d8xvers 620 kW of power at 12,000 V to a factory through wires with total rec*r e x:z:q8odn2 tpb5sistance $3.0\Omega$ 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 connectedz0 .,ic)zznb5vktytu 6kh4*u s -rtw5 to a 240-V line is 17.5 A. At what rate must cooling water pass over the coi zkru0t-b,y6snci4t. kzv5w) 5 htzu*ls if the water temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heateuf1;1emwmo/w r can be used in a car to heat a cup of water for coffee or tea. If the hm 1 of;/uw1emweater 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 curreno8o ouq kb- +ua,+:ih9g dvz*tt in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak qjp+ajx cx9z7 3h:9t jvalue 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 resistance of pw/ hg5j),w/7oxn+qh ivu6 egthe $120-V_{rms}$ 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 5.4u;h/79ssk1sf jzv1b k p2r*un)c4tfs A. What is the r4 / scrtvfp 9 uzk)*ksf2bssnhj7 1u;1ms voltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connec6sgu4c /;d vydted 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 instantaneokiw7bf)sehr83bfz)yp1 k 0x) us power dissipated by a 3.0-hp pump connectedrw 7bebfz1)8s0i 3 pkxfkhy)) to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to a /m wa88f;6tfhqh/bq f s: qz5e$240-V_{rms}$ 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 of35 1newluccc: $2.3\mu A$. 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-bhs.v0 x4 o/kkmA current when 22.0 mV is applied to its ends0h.b/ 4kxvs ok. 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’s atmosph0l vdo; s4 3vgos6y*nrere, $He^{2+}$ 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 xf 8fndr*8k*q)ubu)k 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 magnitud)tyan: w-k+ tj1h)lpie of the electric 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 pun*utjr;3)x qglse. 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. What is*u3nj;q r xgt) the speed of the electric pulse along the axon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much enearci;:kte cro51w 34i rgy is required 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 a tkwieai r1c oc;35r4:xon 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 potejwfo hde h 08b zpj3r cv-0x9;t2-,hznntial, $Na^+$ 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 amp)yp(i zrb /n7pere-hour?    C

  What is the average currwy 5 8 03q9*a,jmxrhbn. inhylent drawn 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 tht e;qn28wy8i4b/qzgx / 6(f f niz:h4fj*jx dme two headlights uses 40 W and 24ih4 b jq/qi 8fzmg6xxzd; yf(n8n/*we tf:jeach of the two taillights 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 of a 1)i+//z;s s9sh,oot ij*d q1bpw tbc,u10-V, 1500-W heater is 5.4 m long. If it is made of iron, what must its db/;sho,1co tdwbz/s9 ut,i *ij)+psq iameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object f3ma (-obcdjohv+25) ywcf q6is defined as the reciprocal of the resistance R; that isqo-f+6mvc3b a2ydcf5)j w(oh, $G\,=\,1/R$. 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 instead of using higv/ dia97we .,ndnai 4dh-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 lost to heat per hou9dn a/ ndv4 7ediwa.i,r per meter. Assume the cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular household uses a 1.8-kW heater :tuj y3 vk54dh$3.0 h/day$ (“on” time), four 100-W lightbulbs $6.0 h/day$, a 3.0-kW electric stove element for a total of $1.4 h/day$ and miscellaneous power amounting to $2.0 kWh/day$. If electricity costs $0.105 per kWh, what will be their monthly bill (30 d)?    dollars per month
(b) How much coal (which produces $7000 kcal/kg$) must be burned by a 35%-efficient power plant to provide the yearly needs of this household?    kg of coal

A length of wire is cut in half and the two lengths are wrapped t2n tce hxwqs *2q,)wl,*:vngwogether side by side to make a thicker wire. How does t ),,wexlh qcgwt*ns*2 v qn2w:he resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is dsc rr3p8lc;; 8 ka8ip7rbsum4esigned 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 ot.7o+*76k/op1ht ji o ltkltnot become so hot as to start a fire. What diameter must a copper wire be if it i1+*7.o / p klotltt7t6khioo js 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 bgc: ez1xx 6o ybe(*4wxy 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 off+q9;wtl q x/w energy per second to the interiow+twxl9q/ ;fqr. 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 differentv**ap -koxqft3 c88fd conductors made of the same material. One conductor is twice as long and twice the diameter of the second. c v8*8opd3xfq-fka t *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 *i/y13jxxwgcit wfl/qtzo z.7-l ) tg ,2g u.mto 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 souro2,ks1 /zk qlpce.
(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 makey .u3t goeatp97r/7fds use of storage batteries as its source of energy. Its mass is 1560 kg and it is poweredt.orugfy et97 pd7/3 a 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 ha x q0afcro5wz +9/ shgn2b7d.d44fpgas 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 acceleratdafl4w8kyml9i6j.p+u * +dl uor at Fermilab (Illinois) is designed to carry an 11-mA beam8*uajdw+9i4+k6mpf llld . uy 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 connecting cord is copper w(zx-ui eb 6a-: ol.ncpb;9i ,okkre/ vire with a diameter of 1.628 mm. ul. azp bn-krvk9c-e, : /eiox(b6oi;
(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. The heating elemenewn wqxzc0 wsvv8 1)r5zc *z 5fut*j**t is a w 0jzs8wcxt5fnq ev wvz*c *z5ru1)** coil of Nichrome wire. 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 about 12 V when the car is offfj:c1usznc7, 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 headlightf c7n,usj:1 zc resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for household applim03gfy y;c. fecations. Lightbulb B is rg;30yc . mffeyated 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 0.2tz3o0ffr7- v -uqpav+59 cm is used to connect a set of appliances at 120 V, which draw 2250 W of po0p+u-qf vtzo ar-vf37wer 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 om 6 .-xp ccq*skw9 qyqco)2/binside diameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is t6c- 9kq/c2o mx)qcqwspo by*.he resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniforuaa1n+tk1zwlwu)u+zmk76 8 0bna2dhmly so that its length doubles, by what factor does the power dissipated in the wire change, assumh1z0n)b 6ku k z1awa+wa+dm u2 nut8l7ing it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb opn,iwsv2q .r 5rerates at 0.20 A and 3.2 V. If its resistance 5vrq r,.w si2nat 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$