What quantity is measured by a battery rating given in amperef+h 9drj w)7mw-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow away from kd3v-q)0t h0grhsd c/ the negative terminal in the circuit. But within the cell, elect0rkvd chgd-0 )/sht3q rons flow to the negative terminal. Explain.

When a flashlight is operated, what is bein-ev bg:8wxt3f g used up: battery current, battery voltag gf xebvt:-w83e, battery energy, battery power, or battery resistance? Explain.

One terminal of a car battery is said to be connected to “ground.” Since it is voiol/84/lik sf:0 + nkm4ex8 knjo+bnot really connected to the ground, what is meant by +l//+m8 n jve:i4oksibx84fon0ok kl this expression?

When you turn on a water faucet, the watbi6f *.9eg0en;r cn duer usually flows immediately. You don’t have to wait er9*.ndc;nbf ieu 60g 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 oxbdfharn stl w d956w3// x3 zqb; uodc):.)qcf the same length have the same resistance? Explain.;bcz)x w/d qucq5hod6fw3) 9.xs:d/3ban rlt

If the resistance of a small immersion heater (to heat wa ron.yav (emajy4-o gu7/ i4b8ter for tea or soup, Fig. 18–32) was incr uo 4m ovjgyi4n8ay(r -a/e7b.eased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, and 3a, hv -/h; i64a a1sexavn ;s)yw qene)(ynow would you connect the wires from a bv6a;e-sxw/ n avn1ei(y;en)a4h qs)yattery so as to obtain (a) the least resistance, (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 lig)vr4lc trf,pdkvl*2;htbulb burns out?

Explain why lightbulbs almost always burn out just as they are turned on and noor 91 h*hyz n/7lfe g8t(ls.rdt after they have been on for somynr sfg*helr(/1o9 t7d8.hlze time.

Which draws more current, a 100-W lightbulb or a wwh5,:dgm. y-j)nsn q 75-W bulb? Which has the higher resistan5s:,-q d) jyhwg.nnmwce?

Electric power is transf l y81 tovlbyb14vjdx4 cl84g:erred over large distances at very high voltages. Explain how the high voltage redu4 t18lgdylbb jx:yv4 c8v o41lces power losses in the transmission lines.

A 15-A fuse blows repeatedly 853rglf6yv tc. Why is it dangerous to replace this fuse with a 25-A fusrlt3 y6f8v5 gce?

When electric lights are operated on low-frequency ac (say, 5 Hz), they flickeioh llt.w)8hd .m2rs*r nos. rilo. t8whlhd *m2)ticeably. Why?

Driven by ac power, the same electrons pass back and forth thtxso k0d /)e5:0 fev ru6ejq.qrough your reading lamp over and over again. Explain why the light stays lit instead of going out after the first pass of elect :k)qq6jrev50oex. /etsufd 0 rons.

The heating element in a toaster is made of Nichrome wire.:8wdiavcu8/ n x czpl91na./y Immediately after the toaster8:w/1 dlcc i n p8zy9ax./navu is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Explai5y;u kh5w93 )lnczy yruvt8-, oqrd n:n.

Different lamps might have batteries connecem7w-39 vxnq go0bmf,ted in either of the two arrangements shown ifmg73 be, nqoxv-90 mwn
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How ma,d,hb5 govihijnd .-op 7u/(ony electrons are flowing past any point in the wig5i/ddn,( o,-ub. joph 7vhoi re per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A for 5.0 h. Ht 4u,7:a-hyqc87v/xfmb w amvow much charge pa/ tam,yf:m bavv-w c4x7qh87 usses through the battery?    $ \times10^{ 5}\;C$

  What is the current *kk7s/olasjj1 * *- xm2fmzo6cjdno. in amperes if $1200\,Na^+$ ions flow across a cell membrane in $3.5\mu s$? The charge on the sodium is the same as on an electron, but positive.    $ \times10^{-11 }\;A$

  What is the resistance of a 9a mn-izd/ x- pgv5(fn7x.uerd;3iu qtoaster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of currea9aqw l1bk+m z+.ln1 vnt through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into :c1hq 6e ynj76rmf s,ga 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 drqt04p6ajki t5yer has a heating element with a resistance of $9.6-\Omega$.
(a) What is the current in the element when it is connected to 240 V?    A
(b) How much charge passes through the element in 50 min?    $ \times10^{ 4}\;C$

  A 9.0-V battery is connected to a bulb whose re r5boz1 xnei53sistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transmission line carrying 2800 lmgzl n z1u(prj1p8 .-A (Fig. 18–34). The li (-1zml 8u rgnpz.jlp1ne 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 drawsl3 pwwgi pj2,3..,v7yvncru z 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 currentjkh y*go *b-ck9*(sz z of 0.60 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 tungsten wire whose resistance ihis /6f)a3kcr7jk 7ams $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m lenk2byh :th9t)p4 tqg vggv ks60o ,6fe2gth of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of alumn2f2; v)az 9jxkvpm f+inum wire 2.0 mm in diameter, tfn)mfx +2z2kpjav 9v;o 20.0 m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance0d)-egs f87cjzf7dl2bzr f i ; as a tungsten wire of the same length? Givc)ds7bd-8er;lffigjf 72 z 0ze numerical details.    mm

  A certain copper wire jf3o.sfn.sce1/, neu,9v cxq has 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 teli 71aq)xs q. ,;mac,mro/wg lmperature of a copper wire (originally at ;al1 .s7imcog qx)alwm,r,q/$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivity as tungsten dnm ; 4fiblgz,pzs54*s oes4n,5m sz4lbgps*f i ;z at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb haxq sf8lc-++c6 d hjt1.biv9noguq 2d9s a resistance 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 coppeiv vjwq*5e ys.bv98h+apq *f 7r wire (used in 15-A circuits). The wire +f 8aiq sv hv7jew*5p9v*.bqyhas diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made ofo)n- oy +wm,hk carbon has sides of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, an hw)nkm-o,oy+d 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 sairj41had6w9kcz b b2 )me 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 shorter wirzi9 )b4rdc6jw2 h1akbe? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V power suppi f *r10t:fdyxly, and a current of 0.4212 A is preci*ir1:tfdy0x f sely 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 copp. *ajsyr b9wv5er followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85s .br*9avyj w5 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 v 7xvoh x*f 7) lvdml 8m6p3ezx5:nfdd0l5ptd,alue of a resistance not change with temperature. For exampleo7) vvfnp z:x d3,m6x5l dxet*ll7fd pd0m 8h5, 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 ove )a1omsk8mijkkuo .3b15jt0 qn is designed to produce 3.3 kW of heat when connected to a 240-V source. What must be the resistance of kmj 5jt.u3kmsa )08oqb1o ik1the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player that dftf8 cn /r :pzpf.p: 7z/.uh( wq,sdzxraws acp:htz8zfn 7, .wuf.p/pd f/ zxsq:(r maximum of 320 mA of current?    W

  What is the maximum voltage that can be appli/uojoj -(bf , 7itz(mzed across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, andma/z 3pvqe /k6hs/mclx1fk3( current through, a 75-W lightbulb connected to its proper source voltage of 1 /3pvf 1sm q/z/3eck xhla6(mk20 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 a:l 5cj5xz*mmt t 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 ande1/(;adddd sn 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 ink/m p (mqsyy8fff4(-o7 : mb46qqkyqb Europe, where electricity is delivered to homes at 240 V. If you use the lightbulb in the United States at 120 V (assume its resistance does not change), how bright will it be relative to 75-W 120-V bulbs? [Hint: assume roughly that brightness is prop7q8 ypf kfy(soqy/mm(-4 :6b 4bfmq kqortional to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use in the morning if it is in pgqkol:yw1+s4z) iwau0 m(h3 operation for a total of 15 min? At ui:g 1q3 4 0sylwozpmh(kwa )+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 anmr : tg)4o4hu 25-W porch light on day and nighu :ngh)4mr4 tot for a year? $\approx$    dollars

  An ordinary flashlight d+gr s0f6 u u(ym1l3iouses two D-cell 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–3 ugy0molsur(+if d61 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 enerw 6b*pa :g: wxvl6lqv:gy stored in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connecqz 54p o5g d ,xde.umuz9fv1olu :f+;zted to 120 V as in Fig. 18–20, can be used without blowing a 15-A ge f dlum:9v. 4u5dqz,f51o;po zx+u zfuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm q4p 07 vz0lfn30 drzo9pfzj,qp* uig* (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 12jl**fzi90r0u pgd f30 7 zqpz, ovq4np0-V line. How much power is dissipated in the cord?    W

  A power station delivers 620 kW of por p 4sea078lquwer at 12,000 V to a factory through wires with tot40e7ql as r8upal 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 17.5 A. At v g205hsk7lg ) 3+cdcpnlr2jswhat rate must cooling wavl0p3c2+gr5)s k7j2sn hdlcgter pass over the coils 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 a cup6ce t:mpok2o - of water for coffee or tea. If6t:oe2om - pkc 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 current inbu +)tuk8h cy9 a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak va.sxl g x7c,1l e (uh-z9volt:mlue 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 resistancesl 7gdu+-ir8c 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 alt1v xi3wqb ce)+ernating current in a 1500-W device is 5.4 A. What is the rms volt +ibq x31)vewcage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connectxrx f;r3e: cymnv pguf/4 *d*)2ul,nzkp)tz(ed 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 maxim6oc uaa6:( 4q u wgtd*owaj cj51rkb1(um instantaneous power dissipated by a 3.0-hp pump connected to(ajka(a11j ou ub4 *6gtc:d5qcwo6r w 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 )3qllnpx w55ddxm:j( $240-V_{rms}$ 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 curren/f eahs4lb1w g)e(1nxt 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-diametx0n pcrqzlcf bsx.057*8v,bf*7 mt vtp 9yl w/er wire carries a 750-mA current when 22.0 mV is applied to its ends. If thepl l/ tf05bmy7fct sxbpvcq0 vr7nz *w,*.89x 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 Earqcq a2um(;z/jth’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 

  At a point high in the Earths: 60ad8 h0u:en hdekn’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 au;z z9.6aaoqq,vf yt9r dhw-3jo+ju7 cross 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 action po)hqie8 cg 65 tsasxkyo18ew- (tential is detected at a point 3.40 cm down the axon 0.0052 s later. When the action potent gwiya5h so8xs(q8et ce1k-6)ial 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 enf55h y(wl;eow ergy is required to transmit one action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulselo5ehwwy ; (f5 is equivalent to the energy 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 potential 7f r.4d tkc7zem1ben6, $Na^+$ 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 t3 k )sd n-s2-u smjhpax4whp73here in 1.00 ampere-hour?    C

  What is the average current drawn by a 1ki *3x9 j)hknk.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If each s 9,ry q xsak-ym,np6)of the two headlights uses 40y x9 rmps,aq,) -snky6 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 rated at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of a 110-V, /t5cmj f 7l j *o(p/i wq)9ma5qbtuy:a1500-W heater is 5.4 m long. If it is made of iron, what musuq95 clt/p bt:oai)a(fw7jm q5 */jymt its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal -ivfeu-q a(w ge-;*9 y tf)rodof the resistance R; thagqeo w iday -;utfr)f9*-(ve-t 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 that instead of using high-. a oge0f.yfy;voltage lines to supply the power, the power is delivered at 120 V. Assuming a two-wire line of 0.50-cm-diamga0yo f fey;..eter 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 1.8-kWt kg 7(f4vq(lwrigwx7ds. + ts1yx ;w1 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 together side ke0xdk,gb( ;z yfq)kpg0* h3e by side to make a thicker wire. How does the resistance of this new combination compare to thzhbpk*)ke ;qy 0g ,e(gdk0x3 fe resistance of the original wire?

  A 1200-W hair dryer is designed for 117 V-muh)kmhhb (g3rws ,/x; d3hm .
(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 odn/)r-c hfx- )m b/uohot as to start a fire. What diameter must a copper wire be if it is ofn bu//)m-)ho-drcx 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 giveej7o zg 68krt.n 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)jtv:t rzh svyo w34/5% efficiency delivers 950 W of energy per second to the interrv3 t wz4s/t5jhyvo:)ior. 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.uvix6fv 5 acd0 1e0je76qsml the same material. One conductor is twice as long and twice the diameter of the second. What is the ratio of the power transformed in the first relative to th0axe6vi5 d 6cvesfm 170jl qu.e second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room of volumeihd/p-pbb,oq r pvts8wt7/ (9uap:elldb +82 $62\,m^3$ 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 b 8,r9oe2ytyobhz ai th):c8.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 7b ;2lp e;0uxag;k vvpas its source of energy. Its u agv;e p;7kp lx20b;vmass 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 has 0*62 ,zverwoo(xm xsfd48arc 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 desig fi2b*b,k8eig vn4xm2 ned to carry an 11-mA beam of protons traveling at very nearly the speed of light (x ivmg*ibek84b,22n f$ 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 2vl/ *kg0tbiA at 220-V ac. The connecting cord is copper wire withgklit 0v/ a2*b a diameter 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 elem ay97;4 qgienment is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What is the diameter n qay7;4gim9eof the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies fr7.ukqc3 yc2 stqoy+mz:iij (5om 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 osq 7 k+mi ycj: iut32zq.5yc(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 and 40 W for housel ke2gz or,/u5hold applications. Lightbulb B is rated at 12 V and 40 W for automoti,l/gurez52k o ve 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 o/+yqaw;l2qpk(b 59 1maptoi0i id 6 ubf appliances at 120 V, which dr5ii(+abwk 0m6d2obpp /19uq; taqliyaw 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 outs5b n2v l:b6kpeide diameter of 5.00 cm (Fig. 18–37).e6lb5pk :b 2nv What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformmrps8oz.45jkzae qh thmect7u9 /eh9 o014d5ly so that its length doubles, by what factor does the power dissipated in the et kmc m /ezzr8 1eu0o4ot9a. hd7h5sh p9qj45wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bn/q: jlxyr1280 pfhdifw z/ 8aulb operates at 0.20 A and 3.2 V. If its repirj281fz:n// 8qawl xf0dhysistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$