What quantity is measured by a battery rating given in ampere-hours- jpo9:liwu yrq6sd-1 $(A\cdot H)$ ?

When an electric cell is connected to a cf4 8m14am nnrhqg:m (dircuit, electrons flow away from the nermn(q4h amn8 :df1mg4gative terminal in the circuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated,osm t6oemtx5 -xc33k5u9p on2 what is being used up: battery current, battery voltasto e3k2m6uxo mx953po -nc t5ge, battery energy, battery power, or battery resistance? Explain.

One terminal of a car battery is said to be connected to “gr+pibsv t0;pqe-wyg jbv5 5s*0ound.” Since it is not really connected to the g + vg0-bs*i5vsyw0jb ppe;qt5round, what is meant by this expression?

When you turn on a water faucet, the water usuatai7-w5 cafr b/b88yu7;atc2ev0 si llly flows immediately. You don’t have to wclifwsuta r - ea/b v88 c7ya7tib250;ait for water to 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 aluminum wire of *kibru0te g1za gn, 2j;6 g3gsthe same length have the same resistance? E2gi3a1egrtz0g;ksj 6, gn*ub xplain.

If the resistance of )is az6+o odhl9fsf59a small immersion heater (to heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the heating process? Explaoh9zdifs6a os+ 9 l5)fin.

If a rectangular solid made of carbon has si,zj4 zrxsnp4 kc2wx19v ,3wl zdes of lengths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resista kj44scz,z r3x2zw9vn1xpw l ,nce, (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 bux hxv 7dzx3bd b99)y1erns out?

Explain why lightbulbs almost always burn out just as they are turned on and nglcly dg,hlu* esmid*j2 z)1mt761 q+ ot aftt7mg +y16l g*2q*ehj zld lmc,s1 )duier they have been on for some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Whiytq9wx/c8 vprlt30g7hm c 7a*ch has the higher resistana8 g3ctq7/0rw cy97lx mvpth*ce?

Electric power is transferred over large distances at very high voltages. Exp,2rtdyv1alrlt xz:ms .-qn3 +lain how the high voltage reduces power lztym- d sq2l.a+, rl1 :rnxtv3osses in the transmission lines.

A 15-A fuse blows repeatedly. Ws8ljad2 :7mq shy is it dangerous to replace this fuse with a 25-A fuse:7q m sljds28a?

When electric lights are operated on low-fsi-mbk0 my4qe 1 sc4a.requency ac (say, 5 Hz), they flicker noticeably. W e4my mk 01bicq-ssa4.hy?

Driven by ac power, the same electrons pass back and forth th;q 5gh5xc0-vph h)fb prough your reading lamp over and over again. Explain why the light stays lit instead ohp 0h;-hqfvpx5b)g c5f going out after the first pass of electrons.

The heating element in a toaster is made of Nichrome wire./n6 , vmi zmhdab:((cm Immediately after the toaster is turned on, is the currec6 mi( m:h,amv z/n(dbnt $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor?;u7 qmr-idqh1q1 y y2i Explain.

Different lamps might have batteries connected in either of the two ;g*ubnqq s-e:t19 hyqpc n9q+sm ,7gcarrangements 7c b;1n:m qqs9qqu -+h*e9ygt ,sncg pshown 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 wd.7sss+by 0c(7yki e7*9mt6e5kd9 lw uusmhare flowing past any point .m ymsktd 5wis7cb7l0 9 ksuudy7ews(+h *96ein the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery us)y z+q,b2 d,2xd cfnyqing a current of 6.7 A for 5.0 h. How much charge 2 z qfd,,b+2) ndycqxypasses through the battery?    $ \times10^{ 5}\;C$

  What is the current in ampe 3nj;i ew399/gydkpj *k(vjhzres 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 ae7 s-oeu+ lnasq4g e 71k i4n261hhovi current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current throu)jw8249c,wpn mb mhzj gh a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plug bvwq5 *v48kdcged 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 rt/w d05x g:t;cn1v69xpq raxv-z cvr) esistance 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 r/bqov*x81d eqa y( bl8esistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric tr z7tkr1z - saybiqfse7a(a rjyw887 m,;f8qd5ansmission line carrying 2800 A (Fig. 18–34). The line has fya7myf87,jz 1ds-tea58b k(rqsqz;ari w78$2.5\times10^{ -5}\;\Omega$ 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 Agj6r*r h/ n) ztc(,pznc* (fxd 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 ru(4zxwrr m/ lt12xk pzgptr zp7y.-+/ esistor.
(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 leng* a,rl:fx)o wzay/,cv:ku yb /th of tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of .i/ wi(jd2zj53stzqra 3.5-m length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m ao7 rzp12yg(4 ic 0mccof aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire z0 c2m ciy(1gao rc74p2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resis k:y3p8ex7pai;f3k1k6br kfztance as a tungsten wire of th3xpfyzk8fk3 prkkai 61; b :7ee same length? Give numerical details.    mm

  A certain copper wire has a39e/0s3a8uib f aomait y sc)* 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 (orb2hd w q2x5no4xva )n5iginally at ox)hdbvw q42nna5 25x$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the skjmj9mk d u s7t;fk+;;ame resistivity as tungsten doek;js kmku ;dm9 +7jt;fs at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a r ig:( nkl-7nogl kvo-+esistance 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 2r-j 3w7gn:fzf6-m length of household no. 14 copper wire (used in 15-A circuits). The wire has diamwgj-f zr7n3f :eter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths 1.,p4wl1 fm vwe ,,l:skj0 cm, 2.0 cm, and 4.0 cm, lyingkp:e,l wf4wj1 v m,l,s 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 t;rgjjq y c(.-c:jj.gs he same 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 shgj( csgj;yjrj .qc. -:orter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10u)yepnl 09 i0j4rfo- p+wxg8g .00-V power supply, and a current of 0.4212 A is precisey4igjf9e -n0p)ug+8o0lx prw ly 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 consistt jc6:as-ijh+ i9u/hns of 5.0 m of copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is placed across the composia6h-uj sj 9h: ii+tnc/te 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 a. rnn0zq5,4o p/ )m:hzjidjt is important that the value of a resistance not change with temperature. For example, suppq 0tznho4: d. ,azj)pmnir/5jose 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 fu.,213v7 r5 xy tqcqi3*mtrm mo+hhu electric oven is designed to produce 3.3 kW of heat when connected to a 240-V source. What must be the resistance of q2vi u3,uy+ f3o.tmxt5mcrr1h q7*mh the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable Cqut fy1/rw3c 5)xa:jw D player that draws a max3 :a w)/tjuxwqcr yf51imum of 320 mA of current?    W

  What is the maximum voltage that can be appli74 ec)kl 5mhhced across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, a 75o wfvp-ncb;(0 m3 j7cv-W lightbulb connected to its proper source volt(-fbvn;w3 j vmpc0oc7 age 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 rated at 1iutj(f.n b7i0 10 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 W and 1250 W. bxtqm4c/44n bc4xgri(x .5s25k c qgo
(a) At which setting do you expect the resistance to be higher? After making a guess, determine the resistance at
(b) the lower setting;    $\Omega$
(c) the higher setting.    $\Omega$

  You buy a 75-W lightbulb in Europe, where electricity is delifkj1 *ul sa3j0vered to homes at 240 V. If you use the lightbulb in the United States at 120 V (assume its resistance does not change)jalu 3j*1 0fsk, 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 energyaa4ci)6 quzpk* k97 eg does a 550-W toaster use in the morning if it is in operation for a total 6 a9ecg) k7qua*k z4ipof 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 izfdhcw/k2y;p)f jwgx*/-k ( porch light on day and kf/wxi(kh)wfp2zg ; j*-/c ydnight for a year? $\approx$    dollars

  An ordinary flashlight ttlvmj4* nqsk *47+yo yc)bd *uses two D-cell 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulbyoj* v+*4nts7ck dbq)4lmt*y 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 en3xd1 9pen wad+b j-d,vergy 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. 18–20, can be used witou t*1;pajm,x0wczwjxkw 8e6, st:3b hout blowin6x jmetzx1j ;wt8op3bc , wa,k0u* :swg a 15-A fuse?    bulbs

  An extension cord made of two wires oi 8uc,08sdywf0u :paef diameter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connect:afw iup8yus80 , edc0ed 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 of power at 12,000 V toq8s 9flxkwwhzo3599ybb0 t4h a factory through wires wiobws 9q hwfb9yz0l94k x3t 8h5th total resistance $3.0\Omega$ How much less power is wasted if the electricity is delivered at 50,000 V rather than 12,000 V?    $ \times10^{ 3}\;W$

  The current in an electromagnet connected to a 240-V line is 17 xqy :*bpy9o/o.5 A. At what rate must cooling water pass over the coils if the water tp*q /xo:obyy9 emperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a p r f3f(g 83fsnzbkm:9s-:0- wjckr cdcar to heat a cup of water for coffee or tea. If the h wfrj ds (09:pkfsn3z- 8cc3:mrg- bfkeater 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 curren,* a7zyz scm-ht in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak valuokuv;rhz+-:cm :2pz6 -q g(lcyon yd8e 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:5gi trv9his. 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 alterntg.mga s+y, x0j6(do vating current in a 1500-W device is 5.4 A. What is the rms voltage acdm (,ja vgosx gt+60y.ross it?    V (Round to the nearest integer)

  An 1800-W arc welder is conne8 sv nw(/2 dbu)3cvis5sxo:stcted 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 disem32 r n0d3fyq qx2l:lu30tcwsipated by a 3.0-hp pump connected toq lyf3wn2eqdu3 2 ctm3:0lrx0 a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connectc3+j; eb :yzrbed 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 copper wire carries a tiny curr+ ww;ab 6rl6 91fwi;0wqit+xgv5 kqibent of $2.3\mu A$. What is the electron drift speed in the wire?    $ \times10^{-10 }\;m/s$

  A 5.80-m length of 2.0-mm-diameter wire carries a 750-mA current when as fj2zz+g/nin 4+/m iar+)tg.a7guy22.0 mV is applied to inaag ++z4m 7 af . z/igyjnt)isu+g2/rts ends. If the drift speed is $ 1.7\times10^{-5 }\;m/s$, determine
(a) the resistance R of the wire, $\approx$    $\Omega$(retain three decimal places)
(b) the resistivity $\rho$.    $ \times10^{-8 }\;\Omega\cdot m$
(c) the number n of free electrons per unit volume.    $ \times10^{28 }\;e^-/m^3$

  At a point high in the Earth’s atmosphere,4crvq. a:m (hx $He^{2+}$ 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 atmospherulnrx+2zis i- m0r54ja r9,yve, $He^{2+}$ 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 theptwhdrg (:q72 l5i9vl 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 pulse. The aixh+. fx.e/ ftction 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 ish +/xe tf.ixf. 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 actiongs66us7vb po uyc9 v0 u*)ozlo m,1np; potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energ z 69c106*yuo;vu vmso,lbgus ppo) n7y stored by charging the axon capacitance; see Section 17–9]. What minimum average power is required for $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action potentd 8h ) * *lkbv90mbm-(o-.sozdlafqbi ial, $Na^+$ 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 1.00v: falr2 u 2,xlm5 5)w-hawfiy ampere-hour?    C

  What is the average current drawn by a 1 7rpgat(4sium/a 7xyusf1. 3 s.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each of the two85lv /rjg7 ybk headlights uses 40 W and each of the two taillights 6 W, f/ 8kbvy57l gjror 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 110-V, 1500-W heater is 5.4 eert 6zw a6374o(apql m long. If it is made of iron, what must i ( a3alrqw o7tz6pe64ets diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined4cz x:j4i (f*4cwp48 mzu cbje as the reciprocal of the resistance R;c44 bue:(4m*jz xc4i c pfwzj8 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. Suppose4l k(/z6jnbt+fog)c0zf / mn u 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 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 ktz // l 6)mzbck n4fng(fjou0+Wh.    dollars per hour per meter

  (a) A particular household uses a7qq -ylcgl +hz1+ 1;mqug d7la 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 wrapped togethujbdkt2+cbx/a ( 2h x7er side by side to make a thicker wire. How dkbt jub 2a/2x(hx7+dc oes the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 117 6t; 1jolfxbm9s bo1qs : fk8c0V.
(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 a4)9drqblfr y mx v6ha/ +cul,7wl/a6e vlw ;8ps to start a fire. What di/xcwrd6v l8 a,6fv e)7 bplwuay9ql;rh /l4+mameter 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 the e,9fua;er gpm;quation $I\,=\,1.80sin210t$, 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 delivi6d l2zhvy z+yk0u;3 hd:f7zf ers 950 W of energy per second to the interior. Fdfly2y60z 7z dv;fu3:hikh+ zind
(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 0 z s/pkyspgm4s9b 0fy; zx6e3different conductors made of the same material. One conductor is twice as long and twice the diameter of the second. What is the p 4exks;pzyyzs b90s3/ 0g6f mratio of the power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room of volewn+h9r */s mqume $62\,m^3$ Air is brought into the room at 5$^{\circ}\,C$ and is completely replaced twice per hour. Heat loss through the walls amounts to approximately $850 kcal/h$. If the air is to be maintained at 20$^{\circ}\,C$, what minimum wattage must the heater have? (The specific heat of air is about $0.17 kcal/kg\cdot C?$)    W

  A 2200-W oven is hooked to a 240-V sour.n7, rlz+qsxcvrb3) rce.
(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 its source:td-gwol ,dcj1xz) 4a of energy. Its mass g o,:tzjd)c-axl 14dwis 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 has a8j00krk+5c-gn (s bfl (oc 7vhehsia 4 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 designed r8ux-ma: 9zejto carry an 11-mA beam of protons traveling at very nearl:ezuj-ar8x 9 my 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 cordifiaqp pm89p p8-po// w6yj:t is copper wire with a djip - 8 p9w ay/m6t8/pqip:fopiameter 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. The heating element t:wxk,gwwv .) is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What is the diam ),vwwkt .gx:weter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, thny4(qgyd ;s 1k :bdow;q:c;xu e system 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 innb1 u;gx4yqd:; dw:ck ;oq sy( 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 headlight resistance remains constant.    % increase

  Lightbulb A is rated at osbs 72zu2xk 80wvf7y g.obl-120 V and 40 W for household applications. Lightbulb B is rated at 12 Voyg2su7s 2o0wblz- x f7.8vk b 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 diamety,)mg k0-m/owz r vt+yer 0.259 cm is used to connect a set of appliances at 120 V, which draw 22 mwtgvym -ko+)y0,r/z50 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 outsidie80 ny,itbi1ls 9zm8e diameter of 5.00 cm (Fig. 18–37). What is the resistance of 10.mzylt1i8 0n9i i8e, sb0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched unifovv:;upb+t4r5(f upj bbe )v+n;cf d2nrmly so that its length doubles, by whcb2(r + bfne;d)4v v; t+ :u5pfbjnupvat factor does the power dissipated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament usedy:801i3flo0fzcyoqb riyi9) g-bj 0a in a flashlight bulb operates at 0.20 A and 3.2 V. If its) q jyoi r9y0ilbcfba og 0-f3i8y1:z0 resistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$