What quantity is measured by a battery rating given in ampere-hourra cgbxq6 m2 1r(w.q-ds $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flow away from tzlb;5, qeej2 ihe negative terminal in the circuit. But within the cell, electrons flow to the negative ter;i zl,bjq 2ee5minal. Explain.

When a flashlight is operated, what is being used up: batterv zci7e45r k1ry current, battery voltage, battery energy rck7 4veir5z1, battery power, or battery resistance? Explain.

One terminal of a car battery is said to be connected pbj44*lq3z w kvkj(c.aq*f:yto “ground.” Since it is not really connected to the ground, what is meant by this ez4.*jf3 wpk aqj (v*qbl 4k:cyxpression?

When you turn on a water faucet, the water usually flows immediately. Yocwdg1xvpk rq+1k,+ , yu don’t have to wait for water to flow from the faucet valve to the spg, ,rd1 cx1qp+vk+ ykwout. 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 the say3lthcqv8swq+ v ui, b.,b x-4me length have the same resistance? Explain..ytqx wqb s b8-v3+hi 4clv,,u

If the resistance of a smalla2c v;6-sqzb;- lvfnk immersion heater (to heat water for tea or soup, Fig. 18–32) wkfz; b-v-v6q2al cn s;as increased, would it speed up or slow down the heating process? Explain.

If a rectangular solidw+jwf,ck9x5ux k+316 m u igtv made of carbon has sides of lengths a, 2a, and 3a, how wouldjfucx 3vk,+u 5x9kwg 6w+1im t you connect the wires from a battery 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 ligqdj9f k(tm 5z94bv lu*htbulb burns out?

Explain why lightbulbs alm vw81er)b-zqm8succd65h)) p xl/vl cost always burn out just as they are turned on and not after they have been on for some timel s56 xv)pc1rd8clce m wbz ))v/qhu-8.

Which draws more current, a 100-W lightbulb oaj+fp az 7k1n/r a 75-W bulb? Which has the higherp7a+jfk za1n/ resistance?

Electric power is transfe1ut2ujnzwco wi2 (l5 0xa tq8*rred over large distances at very high voltages. Explain how the high voltage reduces power losses in the transmission linest1 j lxu*o (z2cn2i uawwqt508.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fuse with ( j6nya/x 3eup (rtr.la 25-A fusl 6utjnp(a 3r( .ye/rxe?

When electric lights are operated on low-freqhcuq+ y,5v rrl7xu4p8 9 ama04pfcx+l uency ac (say, 5 Hz), they flicker noticeably. p+qrm7+l89 40c,u lxy4cpvufxha r a5Why?

Driven by ac power, ojr1z.h+p 3v(ji, mxnthe same electrons pass back and forth through your reading lzrpo, xm.njvj3 +( i1hamp over and over again. Explain why the light stays lit instead of going out after the first pass of electrons.

The heating element in a toaster is made of Nichrome wire. Immediately arnw p 8b2fm5ihg6ibwiy -x r2jdr:( -;fter the toaster is turned 5r;mi2di b2w-ypb- g6jn(8h f:wrirxon, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up ine 5zhegv-2tka gw.k7 - a resistor? Explain.

Different lamps might have batteries connected in either of the two arrangemev,*ehkic4:0kzr , srlnts showik, rlsc,:z04ehkv r* n 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 are flowing pf7ngt*l 5(jbay 2xych2i3 - jtvpzg7e j/x8q.ast any point ic/3g vjt2aqitbnyj 7xy(pe 2.gl8x- *5fjhz7n the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a currentpmwi5i;hgiu *24vyq , of 6.7 A for 5.0 h. How much charge passes through the batter;u2yvgiqi h*w5,p i4m y?    $ \times10^{ 5}\;C$

  What is the current in amperes if ftu.pn 0yp 1w*1j2 foy$1200\,Na^+$ 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),gy 281bdjzl9dd:r.ioaa h hso4o 6s V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.c; kw6e5 i:7oszff7 io25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A whe 8sg5rw8 3 dpuy7ar0evn plugged into a 120-V line.
(a) What is its resistance?    $\Omega$
(b) How much charge passes through it in 15 min? (Assume direct current.)    $ \times10^{ 3}\;C$

  An electric clothes dryer has a heating elemenkhuew :xl3 bsj.w 1;6;yn zk:*rl7brz t 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 ree6nkio ,w wuh 9vip(q9 twa(,1sistance 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 A (Fig. 18–36,p 5ilg1uev,0yipao4). The l pg1aipu50, v6l,o yieine 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 bj6j xkd85/h fu8ks-rat 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 oe7f qr m1pgg13f 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 resistancer3nffh8ve g6 r+wjrq/ f6k40x is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of m/ ezid1+5nq0 u5cyng copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminuf9 xtq /whm+1pr,ppkgo *bg)i,, .oicm wire 2.0 mm in diameter, to 20.0 m of cop g,h*xqm.cp,f opwb 1r/+g) p 9k,tiioper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a t: zrlkhd* c296 tcvth7ungsten wire of the same length? Give numerical 2c:zl96r hh*7tdk cvt details.    mm

  A certain copper wire i 5g(e n cpxz8qnz :a:o3:hln,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 temperatxhi ,oxgj (7b q-yt-q*ure of a copper wire (originally atg qxqt-*-7x b(johi,y $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivity as tungs2n k2lf nq7d p*3lhd*cten d2qd2 c3* p*d hn7flnkloes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of abo;hv6bb63ye b nut $12\Omega$ 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 cop )m 1(x-ppa4 mw :hz ki7rkh1e3bfko9hper wire (used in 15-A circuits). The wire has diameter 1.628 mm and carries a eh9p4ahw ro mp3kzxh:(f1k i-k)71bm12-A current.    V

  A rectangular solid made of c:f(mq0bcb )xsl,b l,myu2 i5barbon has sides of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for curren m(lbxb2ybi:,f0l b,mq) u sc5t 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 one has twice the length of the gk.;h z) j8so1wvtg/eother, what is the ratio of the diameter.h )kg1to es 8gjw;z/v of the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a pr+yt:( / eyvkloecision 10.00-V power supply, and a current of 0.4212 A is precisely measuy/vy+ o:(etklred 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;lilxej42+ hm ag*d6 k.0 m of copper followed by 5.0 m of aluminum,l2 gk6e;mha *xl+d ij4 both of diameter 1.0 mm. A voltage difference of 85 mV is placed across the composite wire.
(a) What is the total resistance (sum) of the two wires? $\approx$    $\Omega$(retain two decimal places)
(b) What is the current through the wire?    A(retain two decimal places)
(c) What are the voltages across the aluminum part and across the copper part?
$V_{Cu}$    V(retain three decimal places)
$V_{Al}$    V(retain three decimal places)

  For some applications, it is i r)gsg7iq op9eob*)9ymportant that the value of a resistance not change with temperature. For exampybor i))qegg 99 so*7ple, 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 odt- 4 *qzchix74 3j)cslbgs,,qvo 5i bf an electric oven is designed to produce 3.3 kW of heat when connected tocb,qsgs q7 4j,*4xl5cbvo3tdzh- i)i a 240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V porta2 wci ddh3,vh9ble CD player that draws a maximum of 320 mA of current? i c3wdv9,hh2d    W

  What is the maximum voltage that can be applied acrx 3o7fp n l6ezeuz .xro-q2e4*oss a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and currenthma; i -kh3 84p9ncr.scixcb; through, a 75-W lightbulb connected to its proper source voltag.c8 nbp ir i-4hcksm9xc3;ah;e 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 a.kjsxts +frel w , v8i;8wj1v3t 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 sett yy;;u7 r bqqa/ r:yih.:cojd6ings: 850 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 Europe, where electricity is delivered to dg f;p+w+)ij zh w,zv0homes at 240 V. If you usef+)vpjgzizw ;+ w,h0d 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 proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster umia f;8ff3 j1ose in the morning if it is in operation for a iom 3f af;j81ftotal of 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 porch light on day a;9+foh tuja udu l.r.7nd night fou7;fa tl+.hu rj 9u.dor a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connesu lybooin:kqw3l*e q+g5tr) 4;(c8octed in series as in Fig. 18–4b (Fig. 18–36). The bulbklnwr53 g*q:ito+bquel8) y o( 4o;sc 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-u7hp.o cxjj(g x+7 b4g(o,xt nV, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connected tzg-9.r5 q ryyzo 120 V as in Fig. 18–20, can be used without blowing a 15-A fzyr y9 r5z.q-guse?    bulbs

  An extension cord made of two wires of diam9ymmv by4t. 6teter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric heater which draws 15.0mym9y.t64v bt 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 to5adn7t 4je(vno+j(iv xd /y, nli2. gr a factory through wires with total resis2d 7r(d, n+yx5 v l/igj4vnijn(oe.tatance $3.0\Omega$ 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 1xev-3as nrsq( r;53ug7.5 A. At what rate must cooling water pass over the coils if t;vqssu5rer- n( 3agx3he 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 cup of water for cozm5k3 v9 s3zohn389ktnyzh g: ffee or tea. If the heater can heat v33hz8y9gm 3z9t ks kn5o hz:n120 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 is0j ua2n)lm, zn a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, ihw,v+g rfd. fxe4 g,mh2r( ve6s 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 resistal7 tptxp1;3 5(pueu itnce 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 device is 5.4 zl6 jr16 2 ib87 fv(5soytk8 adqtbpd)A. What is the rms v b kqfstdtly68b6z 782dvpj(ar )15i ooltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected to a 0krm3 ab,5;fk 1q iqpn.xixr8$660-V_{rms}$ ac line. Calculate
(a) the peak voltage$\approx$    V(retain one decimal places)
(b) the peak current.    A

  (a) What is the maximum insta-*fm 2wffa) /5b/7nbq0ed,err vlgivntaneous power dissipated by a 3.0-hp pump connected trw/fv gqben7 2bv 5f0r,-i)*afe/ld mo a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connect8ha 7/o6 xrds8ermot3ed 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 coppm,9:iudcuq: ;+y4gcyjb 2nt eer 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-diameter wire carries a 750-mA current when 22.0 mV ix,5mx w,1quxm; wpc h*s, ;cm ,xhw*xqwx1um5p applied to its 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 atmo6w fkd2.m ,jgusphere, $He^{2+}$ 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 tha*0n-pg7pe gua /bu:ie 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 fiel3adr;os tq.nguby *ancx65 tk t6;:,zd 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.wj* trg03y)f ru:h( r0,x m a(uye6sdj 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 jmjh(3 gy)*s0u ray 0td6(w,fu r:exris the speed of the electric pulse along the axon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much energy is required to transmit one action potential along ; 0t3+;x *dqth hbxc5lt1b:pca* d okythe axon of Example 18–15. [Hint: the energy to transmit one q0;xpddh *kcbxa+t:lhb5 yc1;t 3 o*t pulse 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 potex e4n +gkra gr)b-7/ :b+bcbko zk0cj+ntial, $Na^+$ 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 ampere-ih+2)e+y a5;lv e2 yfygjaf v+hour?    C

  What is the average curren 7k4.kyk4ofnn, pzfa 1t drawn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights onm5a:q+kc.n cko hi(v 7. If each of the two headlights uses 40 W and each of the two taillights 6 W, for a total of 92 W, hocihcn (+ka 5.k m7qov:w 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 m long. If it is made n4i(0;gt h0zhixbrv8 of iron, what muh00b nzv(ixt gi;h84rst its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the recij )8 h2fwm2j6+xdqv- uz qeue)procal of the resistance R; that is) +x8u6)hmq eej 2v-wjqzfd2 u, $G\,=\,1/R$. 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 abo 8yk :e(u:idnuut 10 MW of power. Suppose that instead of using high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a two-wir:n8(id ek: uuye 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 a 1.8-kW ay s1mr g 0+ucma8+lbc1qi t52hzax+8heater $3.0 h/day$ (“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 ny k/6q.,dyw0 eq*nxwtogether side by side to make a thicker wire. How does the resistance of this new combination compare to the resistance of the o6xw0.ykqe/n* dnw ,qyriginal wire?

  A 1200-W hair dryer is designed for 11hp. a+v-,e5 smtncv3 b7 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 en s4 x9drl frx(oc7(fv/ough so it does not become so hot as to start o rld7vf /cx4f( (sr9xa 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 of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by th n;lgd5b-za 7he 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 second jg-yk+r- yar 3to the interior. rr3+ - jak-gyyFind
(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 same material. Opw a kdj;rvl 5l4cvub47a2f 24ne conductor is twice as long and twice the diameter of the second. What is the ratio of th2p;744jvlucwlbark2 fd54 av e power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room of j7*tx;gks2mz8 .m dpx volume $62\,m^3$ Air is brought into the room at 5$^{\circ}\,C$ and is completely replaced twice per hour. Heat loss through the walls amounts to approximately $850 kcal/h$. If the air is to be maintained at 20$^{\circ}\,C$, what minimum wattage must the heater have? (The specific heat of air is about $0.17 kcal/kg\cdot C?$)    W

  A 2200-W oven is hooked++) oc(cyrxbm 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 us*1n.cg4m d9;i tonpcxe of storage batteries as its source of energy. Its mass is 1560 kg and it is powered by 24 batteries, each 1 c in.x;dtp*mc o1n94g2 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 resistance -/-fsj0m-hj 0euzl.2cf opaf 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 to c g(cqh2sa7ov f(*gzt1 arry an 11-mA beam of protons traveling at very nearva2(gf ch * (zqtso71gly 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 cord is cpr+7ov1 p5eqzc61q b aopper wire with a diameter o7+56eb avr ppzq11 coqf 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 heatxvxem 5ui:25o0wt 5zf5 4b,3sy;mn kjrerc 1fing element is a coil of Nichromezvnf12kry u05 xc555r4tsmx,;m:i ofwe jbe 3 wire. When uncoiled, the wire has a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system vo*9 g x/hcgod(wltage varies from about 12 V when the car is off to about 13.8 V when the car is on and the charging system is in operation, a difference of 15%. By what percentage does the power delivered to the headlights vary as the voltage changes from 12 V to c*gd9 hxo (/gw13.8 V? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for household applications. Light*,pvizrfw;n evfw8 8w5jrd.4b 3m rg.bulb B is rated at 12 V and 40 W for automotive applicatiwf;jwi5 8p *rr3vm.b. e rnzvwdf,4 g8ons.
(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.d+y- s9fg c9xa259 cm is used to connect a set of appliances at 120 V, which draw csdfyxg9a9 -+ 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-x-.xyyu ulo+ 3.00 cm and an outside diameter of 5.00 cm (Fig. xo-.yyu-xl+u 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 that itjj c:jhks3h1 w*tf /e .slq-/gs length doubles, by what factor does the powertqjs3lfjs-1 h/ew./kgj : c* h 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 vt)40(s)vft )t fvbnr3.2 V. If iv vrn0 f()tst4)vbt)fts resistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$