What quantity is measured by a battery ratr6v 0oc 4xhu0fing given in ampere-hours $(A\cdot H)$ ?

When an electric cell i0 gf dh6b*/)p zqdvuhf*6g (vks connected to a circuit, electrons flow away from the negative terminal in the circuit. But within the cell, electrons flow to the negative terminpg)df( */vfkhvgz6qbhu d *06al. Explain.

When a flashlight is operated, what is being used n h/(jyw.xb+b up: battery current, battery voltage, battery energy, battery power, or battery resis bj+ yhb/nx(w.tance? Explain.

One terminal of a car battery is said to be connected to “ground.” Since it i qg1xwth gb7no9,a)uyj3n*5 is not really connected to the ground, what is meant by this eqo)t7n3g b niy xhwg,5u1ja9 *xpression?

When you turn on a water faucet, the water usually flows immediate;u jjubf1f3 51ayy b m:n 3l(jpqy-nb(ly. 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 connja jyn ff y1lb3mq-py5(;b(31 bjn: uuect a wire to the terminals of a battery?

Can a copper wire and an aluminum wire of the same length have the same resmi6gm d91 cpj.istance9g1j. c mpmi6d? Explain.

If the resistance of a small immersion heater (toe2cagmh q8.qfv0c2 k ( heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the heating process? Ex0kqc2 (f v8amqgh. e2cplain.

If a rectangular solid made of carbon haslzck5a d(vp)f4yi; q)a 5kgw 6jxyk,9 sides of lengths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resistance, (b) the greatest resistanciz,xl 6kyj yf5;kpa 5)dakgw9(4)qvc e?

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 out?*)*lpt vu 9knv

Explain why lightbulbs almost always burn out just as they are turned on and no )8uji: oxrikcg: 1/dtt after they have been on for some timitdxgrc8o1i j):k/ u: e.

Which draws more current,q5ax9c/jdv -wg7m: 3d uhf pii*/sy4e a 100-W lightbulb or a 75-W bulb? Which has the higher resi5 fcv/s d*-q:4i uiey39a/md7pghwxj stance?

Electric power is transferwsab7-n)q6 k w3 qfkw(vj1r9tred over large distances at very high voltages. Explain how the high voltage reduces power losses in the transa6 s3(tjqbf7w ) wk9w-vnk rq1mission lines.

A 15-A fuse blows repeatedly. Why is it dangerous th3w0re+iuog r 43 j7+k*ilw lzn z/aw.o replace this fuse with a 25-A fuseiwn*o.zri437ura/w+ lez0g j h3+ wkl?

When electric lights are operated on low-qs5rss k 8 ,2bk14zxotfrequency ac (say, 5 Hz), they flicker not8rs2os z 1k,s4txb5kqiceably. Why?

Driven by ac power, the same electrons pass back and forth through yoiq+lyzp+ 8;fqaq mr 7/ur reading lamp over and over again. Explain why the light stays lit instead of going out afz 7 iaqlryfqm /pq;++8ter the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. Immediatel-6 io/dnkdyn* bk7s-yy after the toaster is tur*bid nk/kos--n6 dy y7ned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? . j-7hpha b1 fk)3lcrxExplain.

Different lamps might have batteries connected in either of the1v kccmjk/cx1(am4 k) two arrangements shown ik4 1/k(1jmca)vc mkx cn
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many electrons apbl.;l)v 2vg-if ,n untk15rl re flowing past any point in the wire pe nvl.p1)nu k;l5t- 2rilg,vfbr second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current ofo7qkjvog );f0/los 5d 6.7 A for 5.0 h. How much charge passes thrsl o;gvq5k f 0/oo)jd7ough the battery?    $ \times10^{ 5}\;C$

  What is the current in amy+3 xa58tat83yh hf*q abdt e7peres if $1200\,Na^+$ ions flow across a cell membrane in $3.5\mu s$? The charge on the sodium is the same as on an electron, but positive.    $ \times10^{-11 }\;A$

  What is the resistance of a toaster if 120 V produces a current oniua4r3k+ km88/g gsf f 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of curre xx)()g i*ls gcn1 /vg/amie6n78damv(zh5 glnt through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged, 29d( x,byr7 eqp-mcs/a suyf 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 res :1 ph2fmf)lexistance 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 whose ,pw:t 6tifd .gresistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electrhw5 8k+d1yn xjic transmission line carrying 2800 A (Fig. 18–34). The line hxk+nh 1wd85jyas $2.5\times10^{ -5}\;\Omega$ 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 k v39qx1oz)ri9lt x gt;+ 4wjd6.50 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 0.60 A through a resistnyd 2ii2ci)5 k;w+4gw hiv;wror.
(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 wi denp fbk.w1m r)x.- 3+hp2odhre whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.y8ba 2x+rxfze 3(dcy95-m length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of ad.+tjdj fos(2n 0t6aq ,wp9nsjbk8n1v t g-/kluminum wire 2.0 mm in diameter, to 20.0 m of cod 0kj,.t ftsq1(dnonn89 -v taj+6skj/w2gpbpper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wir k ns-b*fzczkt g6.4idb 8qz*7e have the same resistance as a tungsten wire of the same length? G7z*q6z kkcnbif bztd.* g8-4 sive numerical details.    mm

  A certain copper wire hheny 6s yq1ep.q4u1ry;du0tn6 9y/x zas 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 to raise the temperature of a copper wire (origina,kfmbphxgo( x 1(*bh5lly at pk ghox*mb5 xf b(h(1,$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivity a z(imwjv fn94n( n;yk u2vh;)ms tungsten doe v4n9)nn(jk; 2um;zfhm i(wyvs at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance o.9y rcqjpl( i(f 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 cokol.u:l- wd( gpv2 8kbpper wire (used in 15-A circuits). The wire has diameter 1.628-klkw82.dvl( o b pu:g mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm, 2.0 cm, anr+nre-w l1uk kvcz(3.a; e7k/aty v8bd 4.0 cm, lying along u7;va zev k1ta/(.ry k+ew-cr lb38knthe 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 bi w3 rh2)9 pwb.ly96ijbn+aaone has twice the length of the other, what is the ratio of the diameter of the longerb3j w ar9yp. n962+i)wlhibab wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precisin5wg;8z syp( aon 10.00-V power supply, and a curreg;panw y 5s8(znt 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 m of copper followed by 5.0 m go x 9f(eiu2 nb4qz47gof aluminum, both of diameter 1.2i z9f xnoqe4 g(gub740 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 ch7aefv-) dkv4+ r3xsx f9g.xjbange with temperature. For4vsrx.-+ f3xe fxb9 jd)a7kgv 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 eleck5o6 rx3 rlfc6n 0wobzeo:8u(tric oven is designed to produce 3.3 kW of heat when connect6 :uo85e zfw 6lrboo3 (0nxkcred 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 CDrrp3x (4pddxrr ,j.z k(u,z ib0cmm34 player that draws a,(ix,mzdpp3x rdrmk c4b0rzju(3r . 4 maximum of 320 mA of current?    W

  What is the maximum voltage that can be appl 1d 6i.or krloll0:gp1ied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistackk05hcu -wn o/sz-1wnce of, and current through, a 75-W lightbulb connectedo - k-uckz5 swc1h/0wn 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 her shkz5 ymd, ka+ :.vr5lhywv )+rvwq((p7t+ vater 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: 850 80yu*rmj- qqfsj*d)t 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 Europei0q s; mvbno5+ pymh9/, where electricity is delivered to homes at 240 V. If you use the lightbulb in the Unitep +mnb5/;io0hyqs 9vm d 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 d-b vnvr nje6z2 m 2u5mp.s2eqxi,16in oes a 550-W toaster use in the morning if it is in operation for a total of 15 min? n,2jmnv q- r12vx e2up5i6 nbzsie 6m.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 kWcst or61:t.ys h, what does it cost to leave a 25-W porch light on day and night y6sr.t t:c 1sofor a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V battz. 1t)k (ns5mazcbh / vc(pjq9eries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when turned on. z9/ p(nkjv5zsq( t)cc a.hb1m
(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 e,/b *wlxh nw2*ddy 7wswy99i jnergy 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 yde0kb6y6+pk3 lh7v fas in Fig. 18–20, can be used without blowing a h +3v0yfy7d66 ebkkpl15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 ci ;d7t69zjaf2 ibt4gdl 1+i anm (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 120-V line. How m+9 dfdal7 tg;1initz6bij a 24uch power is dissipated in the cord?    W

  A power station delivers 620 kW of power at 12,000 V to a f,4cjupw9p 5q iactory through wires with total c9wj5uqi4p ,p 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;4ac jj .d: llsyd75.flfcr/z0-V line is 17.5 A. At what rate must cooling water pass over th4c5lc./;ar ldysf:zdj.jf7 le coils if the water temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater +d4 z40woweif can be used in a car to heat a cup of water for coffee or tea. If the heater can heat 124+efd zw4 wio00 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 curr ()*fh0o 33 eyxzwtm ks8yv+;b9y vjulent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak vv)i-r;cn,m*a6du n8 jreq,flalue 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 resistancaor9 4v3y jh0de 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 alternag-z x3acvv)u/ ting current in a 1500-W device is 5.4 A. What is the rms voltage acro -xv/3zc)gav uss it?    V (Round to the nearest integer)

  An 1800-W arc welder isq dzxgq7jeq a 1p-gs-ph1/xzh,s( c(2 connected to a $660-V_{rms}$ ac line. Calculate
(a) the peak voltage$\approx$    V(retain one decimal places)
(b) the peak current.    A

  (a) What is the maximum instantaneous power dissipated by a 3.0-hp pui0cd tsjui -0q t+0cq0mp connecte ti+sc0dqtci-u00 jq 0d 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 wi1px(/ vwvfu t ,/zksd /2nz+$240-V_{rms}$ 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 rh/j.ku zwyi3j/b;8dym 9 dxd h-06qqwire 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-diameter wire carries 21 cyib3jng0 6*h j6xyzc 7ltda 750-mA current when 22.0 mV is applied to its ends. Icnbhdty3 z 6j cl1y62 i*x0gj7f 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’sz6s r0gsi2i/p 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 tudmru)6 -azya:i,fb;7 56jgtma(kyghe 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 thlu:u gzbf f c9.uz4 .pwx---nue 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 pulsx ok)t;dw+fr gj6zd.-e. 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 the speed of the electric pulse along the axon? (Why are two measurements needed in-;xw6dr)f zdjkt og .+stead of only one?)    m/s

  Estimate how much energy is required to transmit ob z2mzgu- wo srr;5/6yne action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored by5z;gr6rm2o yz-w/u bs 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 potm ( up5md+j*seential, $Na^+$ 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 ampe(nr/fx;/x+ uqg meh e8re-hour?    C

  What is the average current drawn by ai p65fb u sgay:++lrd6 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the,jew +yaovd 9su(;+pm 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 a fresh 12-V battery last if it is jpm,;(y+9e +wvuaso drated at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element o2/l ilhf :7awqf a 110-V, 1500-W heater is 5.4 m long. If it is made of iron, what must its di:a/q7f 2wlihlameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object isknba chp*b;9r 3l9 3tt defined as the reciprocal of the resistance R; that 9tbp 9; h33 *bcntlrakis, $G\,=\,1/R$. 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 lpbdl0mm8 pr y74 *bi/cg4th;that instead of using high-voltage lines to supply the power, the power is delivered pdlgb h /mi;r7 tm*4ly8c4bp0 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 hour per meter. Assume the cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular household uses ad 1ixw1 n2 ;hcxcv ywjg,r38x* 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 th(.)kaf:uhzfarz gnl a m4v;7,e two lengths are wrapped together side by side to make a thicker wire. How does the resistance of this new combination compare to the resistance of the4zk) ah.l,7n vf(gu ;ma:fazr original wire?

  A 1200-W hair dryer is 2sevtrk6ve93 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 enough so it does not becomtty608nldiq h-hhp+s l ,k/z0 e so hot as to start a fire. Wha/ 0nth ,dt8s6q-+ ikpzhl 0lhyt diameter must a copper wire be if it is to carry a maximum current of 35 A and produce no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by ths5 )w xic jc)5ox6dd2e zdx3tz4uw,3w e equation $I\,=\,1.80sin210t$, where I is in amperes and t in seconds.
(a) What is the frequency?    Hz
(b) What is the rms value of the current?    A
(c) If this is the current through a $42-\Omega$ resistor, write the equation that describes the voltage as a function of time. (  sin 210 t)V

  A microwave oven running at 65% efficiency delivers 950 W of energy per sexg r4 sby+-8pgsc g-8s+ trlr7cond to r8 tgl-gp-4gs+b +rxsyr 8c7sthe 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 conductors made of the) t+mcsp dvs4, same material. One conductor is twice as long and twice the diameter of the sec s+ s,v)t4cpdmond. 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 hea89 u 4wms 6x4s3z*u: tfqvanbit 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 hoo5qurl8 g.jry-ked to a 240-V source.
(a) What is the resistance of the oven?    $\Omega$
(b) How long will it take to bring 120 mL of 15$^{\circ}\,C$ water to 100$^{\circ}\,C$ assuming 75% efficiency?    s
(c) How much will this cost at $11 cents/kWh?$    cents

  A projected electric vehicle makes use of storage batteries as itn::uii h6f+ fjs source of energy. Its mass is 1560 kg and it is uh6: f:i+n ifjpowered 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 has a resistan.grqqp*n /8i8tbck3tce 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) +3**+ x vlshd.hfdpx ois designed to carry an 11-mA beam of protons traveling at very nearly the speedx+lf.+h*o v d*sh3px d 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 220-2;wlyobzl*4 y -amgm 3V ac. The connecting cord is copper wire with a diameter of 1.628 mm-a ywyz*; l 3obmlmg42.
(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 pu0f+u2-esa m. /yqduv*d qv/ 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 the wiudps*/a0 uu/ev. fmq y- +2vqdre?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from about 12 V when s)g4zyo;q1k8b69q edliifp ;vuf.9uthe 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 fr qd;6zi ou.v4 fl qipy;bk99eug) 1f8som 12 V to 13.8 V? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 y38 ekb nbsu6)n*rh )hW for household applications. Lightbulb B is rated at 12 V and 40 W fo)uky)8he3r6 * bnhs nbr 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 c7p(oh :0rk cnhonnect a set of appliances at 120 V, or(nhpc:0k h7 which 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 *(p.lv 8(rxcha zoii3 inside diameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is thex* ho((z8li3p.vrc a i resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched unifor) ufscn;:be8 hcq:)(mt;i b1.emjt jfiece,3mly so that its length doubles, by what factor doej .m1(eiqti:b jec8cfbt ,ch; 3ns;)mfu ee :)s 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 operates at 0.20 A and 3.2 V+ymbl w84w 1;/c0wzaq,mh us u. If its resi0lm,/yubq 14 whz; wcma+8wusstance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$