What quantity is measuredk oq7 ah3ut/n8i+sm .h by a battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected t1nqo65fo*ljr f5va7s o a circuit, electrons flow away from the negative terminal in the circuit. But within the cell, electq jv7f1o*fsona 5 6l5rrons flow to the negative terminal. Explain.

When a flashlight is operated, what is )k sn 8ysm,q7gbeing used up: battery current, battery voltage, battery energy, )nq,m8k 7 gsysbattery power, or battery resistance? Explain.

One terminal of a car battery is said to be connected to “gr j u:i 3fygndl30ew/zg ofj7) qmw//l* a1wv0jound.” Since it is not really connected to the ground, what is meant by this 7jeao mg nwwq: wv 0yifg3*/zj0f/1u l)l/3d jexpression?

When you turn on a water fauctz:krw4w63n det, the water usually flows immediately. You don’t have to wait for water to flow from the faucet valve to the spout. Why not? Is the same thing true when you connect a wiredw4nkz wtr6:3 to the terminals of a battery?

Can a copper wire and st3jx),p-1e c ( uphwsan aluminum wire of the same length have the same resistancepsws3x-phu(1)jtc ,e? Explain.

If the resistance of a small immersion heater (to heat water for tea or souwb0ua;pp3v0+ 2zy yuk p, Fig. 18–32) z y 0pbp3;va0 2yk+uwuwas increased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2 . x /h;o/opr*yy(gjqpa, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resistance, (b) the great hr.x//y;*py go jqop(est 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 lc,6jp) lo4om4 bf9dw m4sc0 nq) /z/ 6zbhglebightbulb burns out?

Explain why lightbulbs almost always burn out just mioq0j * 4 q(8kqwv0ybas they are turned on and not after they have been on(i qyoqm0qb*k0 8wvj 4 for some time.

Which draws more current, a 100-W lightbulb or a 7er fr,syfq* dt7 g3/d xc*-q9i5-W bulb? Which has the higher res*, -yff q3 c 9dgitx7qdrer*/sistance?

Electric power is transferred over large distances at very high b *c.5y.ziemp*5x i wdvoltages. Explain how the high voltage reduces power losses in the transmi*ei xwbpm 55yczd* ..ission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to rai q(/tti6a3 f-gz;uve(v c r3eplace this fuse with a 25-ufeq;/iv3 (z3r(vi- 6 c tgaatA fuse?

When electric lights are operated on pjg - .+wkom/:oey/l k;qc0wzlow-frequency ac (say, 5 Hz), they flicker noticeakw p-:jy0zo.e +w;oqc/kmg l/bly. Why?

Driven by ac power, the same electrons pass back and forth thrns3 wxauwl73/ ough your reading lamp over an uls7an w33/wxd 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 v.;2asbfh2 isgf) cyf qt z70t 0sk;hv)+rc1cof Nichrome wire. Immediately after the toaster is turned on, is the cb0vci ; scsgk qfs1ht a0 tzrfc2;h)y2)+7v.furrent $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Explaum-k9;fqb0qe a o 5(1 bnx6rimin.

Different lamps might have batteries connected in eidk-fl -y/(3d.o zwk oq 1o rw(5 +m:x9coluzvlther of the two arrangementsoy+fz5o(-9xw1 /ol: d luokqwr.dc (z-k 3mvl shown 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 arrv.x* 7crrv 1g glbm(5e flowing past any point in the wire1c g7lr mv5. *gxbrr(v per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a ba v,x9 o y2zs.8uaxfoj/ttery using a current of 6.7 A for 5.0 h. How much charge passes through the ,/zj8xox auos2.f9 vy battery?    $ \times10^{ 5}\;C$

  What is the current in amperes i xsxp 9 r pjl; :/tt2qz743x9d-dspgqkf $1200\,Na^+$ 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 4j53mh,z 8 jr9af wt +mmqa2;,dxu bt mq730wxx.2 A?    $\Omega$

  What voltage will produce 0.25 A of current c a2pt.:99 zk7 cidqugthrough a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A wh3 nk ik5)e 0qr+prakx+j)l +bqen 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 res86jqczd y- hqp n1w5-y8v+dwyggvlqm6/; zg 4istance 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 oudxms- ny3w;u:5 a0s whose resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electr/8ft g ym- gxdd gj9p+r25n6a2+x rgx/ lyqch(ic transmission line carrying 2800 A (Fig. 18–34). The line has/a(x +hfq-ymg6 8lgrd d2r52/xp9xycgtg n j+ $2.5\times10^{ -5}\;\Omega$ 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 draw m)l y(j2++lob;) hj;xejgxsqs 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 current of c *b m iubbvh28t ,le9fcrtn) 28ld:3m0.60 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 ed8p 4.wtl; fltungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.q1)4 sauj 4,8mnacmhv5-m length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminumku ii * pj rkz,pkn):e7*.:mzg wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in dik*)ig*rezmk j7 :unk,z pp:.iameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tu+h079o ra8qdq *wls esngsten wire of the same length? Give numer+7odlhwe 08s9s*qa qrical details.    mm

  A certain copper wire has a resistance ccd9k3gam zo /:zbj;7of $10.0\Omega$ 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 u 6mm xe-8 2b0xh4xinyqrz*,w of a copper wire (originally atnxz y*qx r wm-h,x84u6m0 ibe2 $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivity as 9gi+u;c vkbkdod 6ul 7.l.x2 itungsten does at uk6doc kd7;u92bi+.l v.igxl $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a rm)tnp(d jg56 1e1 g1 xrfvolxr: 0)faoesistance 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. 14 copper wfqr grg,g at*(4wxp, 0ire (used in 15-A circuits)., q04fx(g,* gga rwtrp The wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm, 2.pm/- )dbbwii /twxo4ovj7e 1;0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for current that passes throughbd bw;) 1tvw-i 7pi/oem/oj4x 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 samhzpf;u+;o2 if e resistance. 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 shorteop;f;+ i2 zhufr wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V power supply, anuxsv0nhktt3 .y)hg ;bp8l+k(d a current of 0.4212 A is precisel).y8xlh( k;vgb kpus 0t3n+hty 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 follocz bquh;fv u7co(6-*a wed by 5.0 m of aluminum, both -vcu6c ;(qfbuoh a7 z*of diameter 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 orxi boex)f- ql98f3 :important that the value of a resistance not change wixq-)elfroo : 3xb89if th temperature. For example, suppose you made a $4.70-k\Omega$ resistor from a carbon resistor and a Nichrome wire-wound resistor connected together so the total resistance is the sum of their separate resistances. What value should each of these resistors have (at 0$^{\circ}\,C$) so that the combination is temperature independent?
$R_{0C}$   $\Omega$
$R_{0N}$   $\Omega$

  The heating element of an electric oven is designed to produd3 x b+x3v0iggce 3.3 kW of heat when connected to a 240-V source. What musd+vxbxi03 3gg t be the resistance of the element?    $\Omega$

  What is the maximum power consumption of,mnaz 2ifhq5 - a 3.0-V portable CD player that draws a maximum of 320 mA n, m ia-5zfq2hof current?    W

  What is the maximum ,m(5vg5vyq kenyl2 )ovoltage that can be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current throug. s8 pfwmo; zbp(e/cs;h, a 75-W lightbulb connected to its proper source voltage o ; (ss/p ebf;ocmpz.8wf 120 V.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heaqcb )crqpmt1q2- )yrnt bx*) +ter 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: 85+:vkzn nb6jz)0*etg yskz lzi6 /p06 i0 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 Euro*drm.b , z luj:hm)t-uqb0e*ppe, where electricity is delivered to homes at 240 V. If you use the lightbulb in the United States at 120 V (assume its resimbubd*tj.q, l*:0 upmez h-r )stance 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 doesoi.n lmbi7ki2z k (q5/ a 550-W toaster use in the morning if it is in operation for a total ofiib2 oki 5zl(nqm7 .k/ 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 l f.whr-z3lf(e xb+/yit cost to leave a 25-W porch light on day andyfbl.zr (3+ he/lwf- x night for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries c27amliqdge 4oviyig2)kdj 1 , io3 45connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 4qikyc )ge53 i aj4v2d i,7om g2oi41ld50 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 energy9j 2i6wipz0 mi0 azlj q13x8djgc4u6 l 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 Fig. 18gsd;j-q9b5tkkc xcp +la3 9 5j–20, can be used withouxc3c kl+5tsj bq 9gpd5; jk-a9t blowing a 15-A fuse?    bulbs

  An extension cord made of two wires of diameter k8:*1a1kje*vu psq ohg1cogx- -v n9w0.129 cm (no. 16 copper wire) and :*g8gpwj9e vv-qna11ok*x k h1u-osc of length 2.7 m (9 ft) is connected to an electric 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 qf xz: vmwut6.zg w148of power at 12,000 V to a factory through wires fmw 1wt6 8vz.:x4uqzgwith 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 cono;tbs 6hz/ b gc73 s mmj(g 9x;ozs)u*4frr7hfnected to a 240-V line is 17.5 A. At what rate must cooling water pass over the coil4fu(f7gs6r sx;9mhrt; g7zs)hjb/ mbz3oc o *s 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 heat x4j(ge1a pk a 1wovc*qvb5r.3a cup of water for coffee or tea. If the heater can heat 120 mL of q 3ar (ejv1gpcov1k*w54b .xa 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 inv+ ;swn5ca6( k1 ioujs a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is z7 + 3+clgz-aa vhh0ld,*gncq180 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 th6d+l7 z vrp2; n :5qhdhr+wiege $120-V_{rms}$ 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 alteoa:r e e7l1v 2d2bl6bo/2tl svrnating current in a 1500-W device is 5.4 A. What is the rms vo6 /l asr:lebvte2b oovd27l12ltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connectec a4,xdkd ( d-g3)qvnmd 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 maxim crz2js:p ))rmum instantaneous power dissipated by a 3.0-hp pump connected t cjspr2m)r):zo a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connectedq w7 zf43/l.gkek*fr y 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 copp3dv )qjv* fej+q;pp n9er wire carries a tiny current of $2.3\mu A$. What is the electron drift speed in the wire?    $ \times10^{-10 }\;m/s$

  A 5.80-m length of 2.0-mm-dhua. arc, **;j cmm1k sc3n eq1pnw);jiameter wire carries a 750-mA current when 22.0 mV is applied to its ends*1)qaj; *nn kmps,1u;whremc.ccja 3. 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 atmosphntg; ob8x-4: +yu gcbhere, $He^{2+}$ 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 Ecxm 6bvj2p:yq0h85 m garth’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 electric field across an axon membrane e8znch/7m3pyi,pn-a /4 fzf v $ 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 q5q-kjj(tbe(potential is detected at a point 3.40 -qb(k(t q5ejjcm 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 axon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much energy is required to transmit one action potential alon8m syvub 2mf9 h8-6w;dtozri( g 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 Section 17–9]. What minimum average power is requiredw-; ts6drmfyi89bvz8hmo ( 2 u for $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action potential).sb6 yjn v2gx, $Na^+$ 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 n,t 1v +emlr x:ljx82d1.00 ampere-hour?    C

  What is the average currenldeuezo 39d rfj:/y8+t drawn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lightsqc0 pjf2sc6w 3 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 a fresh 12-V battery last if it is ras32 j fcwpqc06ted at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of a 110-V, 1500y1lu+ss;f ny(-W heater is 5.4 m long. If it is made of iron, what ;u s1lf+yyn(s must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defdu i*ewg+e h++ined as the reciprocal of the resistance R;e+w d*+egu+hi that 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. Suppose vjxfck/ 8ktwnr3v9 .,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 c9cj8/xr ,wv vtkknf.3opper 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 household uses a 1.8-kW heater x/ yp u01mpgig ;.*bjr$3.0 h/day$ (“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 arqe; tf h961i o m h+6nsx1awjbceb2q*4e wrapped together side by side to make a thicker wire. How does the resistance of this new com1nwq aohj6 hbifeqse6*x 9c12;+t 4bmbination compare to the resistance of the original wire?

  A 1200-W hair dryer is di:x2ha428nf -qet ipaesigned 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 it32soci2;dprthx( q 9i 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 moc(iq2r;h9ox2tp 3isd re than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by c.flxai0c j4 0the 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% efficiencyz+ tt g5l.u6gl delivers 950 W of energy per second to the lt5gz 6u.t lg+interior. Find
(a) the power drawn from the source,    W
(b) the current drawn. Assume a source voltage of 120 V.    A

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

  220 V is applied to two different conductorsyfo 44yr az,,g made of the same material. One conductor is twicega,4rzf oy4y , as long and twice the diameter of 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 is4r (t mglf52nc;mt- zg used to heat a room of volume $62\,m^3$ Air is brought into the room at 5$^{\circ}\,C$ and is completely replaced twice per hour. Heat loss through the walls amounts to approximately $850 kcal/h$. If the air is to be maintained at 20$^{\circ}\,C$, what minimum wattage must the heater have? (The specific heat of air is about $0.17 kcal/kg\cdot C?$)    W

  A 2200-W oven is hooked to /, rb r;lxc4vca 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 up6 m,.rvnel* sse of storage batteries as its source of energy. Itl*mprv ens 6.,s mass is 1560 kg and it is powered by 24 batteries, each 12 V, $95A\cdot h$. Assume that the car is driven on level roads at an average speed of $45 km/h$ and the average friction force is 240 N. Assume 100% efficiency and neglect energy used for acceleration. No energy is consumed when the vehicle is stopped, since the engine doesn’t need to idle.
(a) Determine the horsepower required.    hp
(b) After approximately how many kilometers must the batteries be recharged?    km

  A $12.5-\Omega$ resistor is made from a coil of copper wire whose total mass is 18.0 g. What is the diameter of the wire, and how long is it?
L =    m
A =    $ \times10^{-4 }\;m$

  A 100-W, 120-V lightbulb huo+epmb91d-mqj *kh : as 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 (Illinois) is desie1p+khhb qejz pie0 ;wf;) 3u.iu((fpgned to carry an 11-mA beam of proi(jehp1;bew.fqp puik0; z )e 3h(u+ftons 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 o)6b-h:nb2c 78i vejxluof v;12 A at 220-V ac. The connecting cord is copper wire with a diameter of 1.628 mmx :8b76n-o f2lchv ou) ivbej;.
(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 0uw d eerpzs*;/fwm5xpu/ +ag* m94cy95 W when connected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What is the diameter of tawr p zs5 /9d;0/x*p euumyfw eg4+mc*he wire?    $ \times10^{ -4}\;m$

  In an automobile, the systud6bqnmxc49v 4;0f b* a7apz kk5bz8jem voltage varies from 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 vo k4 8p xamb97z5k4bzqnfdjbu; ca0v6 *ltage 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 fon lg0 48exkr( hd(ri(lr household applications. Lightbulb B is rated at 12 V and 4 d4e0nhkrr(il8( gxl(0 W for automotive applications.
(a) What is the current through each bulb? $I_A$ =    A $I_B$ =    A
(b) What is the resistance of each bulb? $R_A$ =  $\Omega$ $R_B$ =  $\Omega$
(c) In one hour, how much charge passes through each bulb? $Q_A$ =    C$Q_B$ =    C
(d) In one hour, how much energy does each bulb use?    $ \times10^{5 }\;J$
(e) Which bulb requires larger diameter wires to connect its power source and the bulb?  ----待选择----Bulb BBulb A 

  Copper wire of diameter 0.259 cm is used to connect a set of applianceech78 heb jjom84f-c12 xne/cs at 120 V, which jhx-b7/eccm2 41oce88fj hnedraw 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 i z wplz;8m1+r ap pzdi91r:v)cnside diameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the resistance of 10.0 m of thi zicz;pwzv+l) ar119r p:dpm8s pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched u muv0pc0oh4f:5 ul9goniformly so that its length doubles, by whatm:fl0o cu9p0g45 hou v factor does the power dissipated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operaz+ *h;vx-2ojwknc lt8 tes at 0.20 A and 3.2 V. If its re-c*82j+;wo hktxlzvn sistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$