What quantity is measured by a battery rating given in ampe4euq 6h )9v+uv rk-5ulwzeurz)a)13vb:j vv d re-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow away from gm+ qe64d2i5esx d oi2nc7y+pthe negative terminal in the circuit. But within the cell, electrons flow to the negative tere47xcd p52g+qoemiyi+nds6 2minal. Explain.

When a flashlight is operated, what is being used up: batk.rw83 y2rf g(przfepl*p5o30j:up z tery current, battery vz y2rop8:pulzr 3pew0.(j5k 3* gf fproltage, battery energy, battery power, or battery resistance? Explain.

One terminal of a car battery is said to be connected to 2 g fv7 1n:g)q2dn1m)vtehixd ;iqqd ;“ground.” Since it is not realq qvvm2q d d2;td7nie);1 nggi1f xh):ly connected to the ground, what is meant by this expression?

When you turn on a water faucet, the water usually flob9.ek r: 3mluhws immediately. You don’t have to wait for water to flow from the faucet valve to the spout. Why not? Is the .3klhmer : u9bsame 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 7hwosn/q +euf (5j.rh have the same resistance? Efn/.o7r jh+h u5ws(eqxplain.

If the resistance of a small immersion heater (to heat water for gn-l( r; 7xoqutea or soup, Fig. 18–32) was increased, would it speed up or slow dowx-ru(;n 7glo qn the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, and 3a, how woj 7 9 js )ygzxvhfl8);vtwp49ould you connect the wires from a battery so as to obtain (a) the least resistance, p97)tjo v9xslfj8 4zhw ;y)vg (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 pca5w;v 5z.abrv *k )tburns out?

Explain why lightbulbs almost always burn out just as they are tua*6y0 j e/zio3 -0db:xqsdlf drned on and not after they hav0ai: 0d-/yldox zbdj6qs3fe *e been on for some time.

Which draws more current, a 100-W lightbulb or a 75-W 2 s+rmmtxb 0q3bulb? Which has the higher resi+x mb032ts qmrstance?

Electric power is transferred over large/damn 1/3mkg wnt1s4uit gs-( distances at very high voltages. Explain how the high voltage reduces powergikw/un34/at 1 ms (-s gmd1nt losses in the transmission lines.

A 15-A fuse blows repeatedly. 47qaxmexc0; ty 3 3mwqcoi/d1Why is it dangerous to replace this fuse with a 25-A f te ia7/ox1433d0wqx cqc mym;use?

When electric lights are operated on low-frequency ac ( fzot* n(ler8xo ic,0sk22a 1fsay, 5 Hz), they flicker noticeioa ,tfo s r2exc8z(nlf12k0 *ably. Why?

Driven by ac power, the same electrons pass back and forth through 6ry3j ,vq5 pn3f ryls1your reading lamp over and over again. Explain why the light stays lit instead of going out after the first pass of electrqfr31njvry3 5y6,lspons.

The heating element in a toaster is made of Nichrome wire. Immediately afte ,ml0o-m0j3t jawvt2vr the t taj,m03vt 0 -2ojvwlmoaster is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistorjf- ;jvp3lvv7yh r 3ty2 wy1g.rfc9f4? Explain.

Different lamps might have batteries connected in either of the twr n5fkp 0hi-x)w(1g ito arrangementsx )51ipf n0rt k(gw-hi shown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a w:rv* 5k4al rkae t 2ol+guu:/vire. How many electrons are flowing past any point i a4ll5rv 2v:a*g+u rok:t eku/n 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. How m*82n +qvcaoqpu k:6mgkpb7k mg9w ,0juch charge passes throughk+:,w 6kkpmvpbq 0ga*9nj7cg2u qo m8 the battery?    $ \times10^{ 5}\;C$

  What is the current i5 k,axhgm.w9cn 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 o 8omc5an xukwz41l-)ne5n0 evf a toaster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce vvy)o-o 87zb,vzv 0l3sq el:m 0.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged int4xo;6/c2 npb n ,hfjkao 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/tkczj4d rg(t n*8ctf gnr 2 1wfu:,j6 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 whose resis(tt gdc:d;ht +tance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transmission l tcvse fmnldnsi(hvat;-dw 702 13y*,ine carrying 2800 A (Fig. 18–34). Thec3 atdy, 7s1efl02 n-wv*h;it v(ds mn 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 A at 240 V. euuhbg1br*i t3 -;)zr
(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.:kd )j ;+vb ge9nx0lbn60 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 tungste9nt gdxv4 9rf,:66zuvh t0oi hfb4.ren wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance kxm*y8,u w hxn2* vy7tof a 3.5-m length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10-ltwa 97ss10c;jvybn .0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in diamet ;lwv1j0n9ybsca -t7ser.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tungsten wiree om+yy(c9o/ y:ng+ru of the same( uycy +oe/gy n:9+omr length? Give numerical details.    mm

  A certain copper wire has xk k (;pm-kl01s:6e leupbvh*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 w 1 qyahcz,pp: q/:euqyy )*hi;ire (originally at qq)chqup,e ypa *;z:h: i/yy1$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resi5cb9q6 v 1k;qvvbwuc2stivity as tungsten does atq1v; ubqvc5ckv9 w 6b2 $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance o+,v m7wew8* rz+u.1jnm syzywh h52ecf 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 wire (e2wdn .jrq1e1uc. 0eg.s uq a,useena ec,1g2j10w uuqrq. s.d .ed in 15-A circuits). The wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths l(g4rct t 1m;dwgnb+91.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respective(d+twc4gtg l rmn;9 1bly (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 resista peudhit,0 4vcrg.*9g nce. If one has twice the length of the other, what is the ratio of the diamh9d u,t.iprg 0 vg*4ceeter of the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected toha g90vr+*:vumr 3c *lr)g uzi a precision 10.00-V power supply, and a current o39v:gmr irvgrzu *+c0*) luhaf 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 of alk *g/1g,w y-3crf,ufe+a bdmauminum, both of diameter 1.0 mm. A voltage aukwc1+a 3gr,fd*,g yf /e-mbdifference 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 clxq0i 6ri/e8xhange with temperature. Foe ixl80rx /iq6r 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 produce 3.3 kW oxi +hq 8vt1npbs f *)c)k(ii:lf heat when connected to a 240-V source. What must be the resistance *xhl pqvi )8ib (:ci+sfk1)tn of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portableggm 26gyh ,+bm CD player that draws a maxhbm2 gg,+ gym6imum of 320 mA of current?    W

  What is the maximum voltage that can be applied acro+a3qchx(ji9f ph gz55 ss a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current )ky 1qa9 mf0pothrough, a 75-W lightbulb connected to its proper source vokmf0) o1 q9yapltage 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 ra8 6q)5im dze - jvr/cjfntqo8;ted 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 W and 1250 W. co1l(p:.rzm4 / jrc ey
(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 delivered to homes avjd;xdyyyv2yty 62 iu. 20fcm+1dmq5t 240 V. If you use the lightbulb in the United States at 120 Vi . 5c6y 2m20 myuytjv+dyqx2 ;df1dyv (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 does a 550-W toastv6 cb* ,as2tclws-.pp er use in the morning if it is in operation for a total of 15 mi-tpa cc*bsw2,s. l6vp n? 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 leavw,*3prze m df4e a 25-W porch light on day and night for a year?rwef dm *4p3z, $\approx$    dollars

  An ordinary flashlight uses two D-celw8jy3 m)buxcjkmt mx,1huq ,(*1 0i bcl 1.5-V batteries connected in series as in Fig. x1(,,wbmt*ubq kyj cm1 8)xm0uc3ihj 18–4b (Fig. 18–36). 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-V x df*fpufvrc2 +4ja43, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connected to 120 V as in Fim: e,(d3 (u( yde ftyozzix)(ag. 18–20, can be used without blowing a d3(,:(ue ixd(e fzmy)y(z o at15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 copper wa7d/ k )c5syx+0lkr2g p2ktz aire) 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 much power is dissipated in the cord? ka25 )kd0/7yacpsz 2+gr lx kt   W

  A power station delivers 620 kW of power at 12,000 V to a factory through w8ls-owv- jpvr8lr.5rires with total8- 5ojpr rs l-wlv.r8v 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 line04dvt,. e zr/r,b stmy is 17.5 A. At what rate must cooling water pass over the co0,m.,d s r4 zyr/tevtbils 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 gim:-:mc+ +pl/lxu x cto heat a cup of water for coffee o-mlmp/u l+ :x xcc:+gir tea. If the heater can heat 120 mL of water from 25$^{\circ}\,C$ to 95$^{\circ}\,C$ in 8.0 min,
(a) approximately how much current does it draw from the car’s 12-V battery, $\approx$    A(Round to the nearest integer)
(b) what is its resistance? Assume the manufacturer’s claim of 60% efficiency.    $\Omega$

  Calculate the peak cu9p vs8 j2bvgh0rrent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, is across a 1jo254 ijbk t dd1y8uo$330-\Omega$ resistor. What are the rms and peak currents in the resistor?
$I_{peak}$$\approx$    A(retain two decimal places)
$I_{rms}$ =    A

  Estimate the resistan.cz- cjfbzcp*m 7n);rce 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 alternating current in a 1500-W deviqaxeq(+ t: 2;m:e gbr05jctr rce is 5.4 A. What is the rms vo0 rt+;5a:eje gxtrr2cqb:q( mltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is co+.1 tf i 7x 3lvtirrcl8(:tbpnnnected 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 (kp 6ns0bwq0x j 9jyn+power dissipated by a 3.0-hp pump connected to a 90s nx 60pbwq+kj yn(j$240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to q52rltf v/j4 uldh 17ka $240-V_{rms}$ 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 coppepu-q)bl)e 1p gr 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-dv31 )dr6z ekmqxq )wy8iameter wire carries a 750-mA current when 22.0 mV is applied to irwdqqez )1 m683y vk)xts 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 atmosphru +1m (7ja n ax/cr8qalln7;jere, $He^{2+}$ 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;h9swsrdd4 tz o/3 ;y-rvj b*j.zutc 9 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 the electric fielqh3 xcfq:q)f;+g -qj td 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 elect. 2b x7jjno+szric pulse. 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 ox.7jsj n2bz+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 ty oux27hr+nf7 4 ucwq/ransmit 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 axon capacitance; see Section 17–9]. What minimum average power is requiy72n+ uxr7 /uqfch ow4red for $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action potentz( 2ty3;)y i5fcfs )rxrok;qhial, $Na^+$ 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 7r7 ides3hcwb lyo-r5.l,x t-ampere-hour?    C

  What is the average current drawn b qzfdc-wx v9w+r. h2z-y 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 the two *.cp:cx - iv xyrq.lom(gi ,5bheadlights 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 m rp*( vq. -.lcxiboicxg,y5: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 m long.n 7tiqz a.(2q1pe;lc: ngs;zqs8qy +a If it is made of iron7zc eaq8(i+;q;2l ga1qn tq.nsps :z y, what must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of the resistance R;v;2ww;wfqmm+ )y be vo1h0a7w2vwyhb)wmmve0owf ; wq17 +a ; 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 tck*gxw0 g, hfdam o g44c;944xscl/tbhat instead of using high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a two-wire line ofwbg4 4 /xc,xats*d;4gcchgmk0l4 9 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 a 1.8z5i6,r oq 1gui-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 the5 *1o k4d/w*fe/rhsx 7elr xcr two lengths are wrapped together side by side c7 /lko5 r4 r*ed*rxh/fxe sw1to make a thicker wire. How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for v: 18tz,cfso27k tx bj117 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 soyb,w6n0-g ppl*xms s6t8 m -ao it 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 more than 1.8 W of heat per meter ofmoa-t0,x6wp ygn8 ms 6 -lpsb* length?    $ \times10^{ -3}\;m$

  Suppose a current is *d k67c28ws g(i tninf3x:eqqgiven by 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 of env*m b)jw 1c.iy/l2;hex3j iknergy per second to the intex2kb j1hm* iy.cv/)wej i3ln; rior. 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 sameb8- /5 ,-bsktlqgqajs qc88tg material. One conductor is twice-tg qbq 8 cs-g,bqk8jt85sla/ 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 is used to heat a rp3i u ;eux5g7kz*eje )oom 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 hook2k+v. cihdz:2+vem)a+t i esxed 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 its sojk wuxud,t4 vgc1f he5k;m-8,fi79yjurce of energy. Its mass is 1560 kg and it is powered by 24 batteries, each 12 V,k1w 7,5uv9h;- mctiue ,yjxjgf8kd f 4 $95A\cdot h$. 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 resistanceemxhro- 2sgyhx*. - oz/6nw8j 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) itljw u5 jdowl-pfr+-e -*h::fs designed to carry an 11-mA beam of protons traveling at very nearly the speed of l*jewwo- :5r- :fjuh-dt+ plflight ($ 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.okpv v)c9t3 l7n+o 9bq The connecting cord is copper wire with a diamet 9q v)oo9bv7k+nc lp3ter 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 4el)xx- vv2ypjp 2 del42hp)p95 W when connected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, th -px xpl j22pl2p vd)y44hev)ee wire has a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system v dbxe ;bw*10h3)k4 h/cfi5rbpzzl0ev oltage varies from about 12 V when the car is off to about 13.8 V whekl)wbfzhvexd3 0/5 c ibhbz4 epr1*0;n 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 headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V an6yjx,rkf.ay g0 t+-pyd 40 W for household applications. Lightbulb B is rated at 12 V and 4ga-y +y0.6 jrk ,fpytx0 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 connxf + 7kjxt*zopvl60 +aect a set of appliances at 120 V, whl tp *kax7 ++vfx6jo0zich draw 2250 W of power total.
(a) What power is wasted in 25.0 m of this wire?    W
(b) What is your answer if wire of diameter 0.412 cm is used?    W

  A copper pipe has an inside diameter of 3.00 cm and an ougj2v3t77 sqe btside diameter of 5.00 cm (vj7 es 7t2gb3qFig. 18–37). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so thcte k7 m: +*dc- rx;ib.wk6,.uvh sqnxat its length doubles, by what factor does the power dissipatsbmv7,ui -t.nrh;xdc.:ckqke * 6x +wed in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb oper-.t (im,.k0x.y dlt/fsmy mnwates at 0.20 A and 3.2 V. If its resistance mwitnmf(.0ylym, d . t s-.xk/at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$