What quantity is measured bypf1d) ji-h+e3uwm) keq1 ka s4 a battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is co *rc fu. tt(*y)xfec7lnnected to a circuit, electrons flow away from the negative terminal in the circuit. But within the cell, el( clx uey*t.7)r tf*cfectrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battery cuu-ewtab-l guuslk..6-yo34arrent, battery voltage, battery energy, battery power, or battery resi3oeuwl bsaa.ut--y. 6l 4 kug-stance? Explain.

One terminal of a car battery is saislq* 3yqy7a2pj sp5,sait/u u8qly6;d to be connected to “ground.” Since it is not really connected to the ground, what is meant by this expres ,qu23a5spys8 *aqqilyt7sl6y;/ jup sion?

When you turn on a water faucet, the water usually: gyop-a)dd,ez u/od( flows immediately. You don’t have to wait for water to flow from the faucet valve to the spout. Why not? Is the same thing :)d o-ey,ddgp(/ua oz true when you connect a wire to the terminals of a battery?

Can a copper wire and an aluminum wire of the sayqtvq6 f k q)0gc,//qv 8hjx2cme length have the same resistance? Expla,q2/kfqg cvqvjxt 80chyq) 6/in.

If the resistance of a vmagd,a3ji2 1small immersion heater (to heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow down m djva2i13a,gthe heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, and 3xlx1r *usu01 va, how would you connect the wires from a battery so as to obtain (a) the least resistance, (b) the greatest resistance?ruul0xvs *1x 1

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 ligt(o9g 1uz vcsm/dl95ud+i ) lmhtbulb burns out?

Explain why lightbulbs almost always burn out just as *6 qv(;xqbneg they are turned on and not after they have been on for somv(*gxqn 6be;qe time.

Which draws more current, a 100-W lightbulb or cmb9 ;tgh8gz: a 75-W bulb? Which has the higher rgc8z :mh gtb;9esistance?

Electric power is tra u zwb94 y6wd9xu8xlt,nsferred over large distances at very high voltages. Explain how the high voltage reduces power losses i,x ux9 ty6wbuzwdl 948n the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace this fuse with a 2wkgg 5-u7n:c;l 8s qoz5og5kqu l-8;z :gc7 nsw-A fuse?

When electric lights are operated on low-frequency ac (say, 5 Hz), they fliu93 +ya)bx(nqr jukm( cker noticeably. Wx(q kjm)rabnu( 3u9 +yhy?

Driven by ac power, the same electrons pass back and f1 u i u ,gw6+bgs;+cs8srkk,gaorth through your reading lamp over and over again. Explain why the light stays isu;b gw6 1sr8+gu,k acg k+,slit instead of going out after the first pass of electrons.

The heating element in a toaster is made of Nichrrrdbf(+k) 0cdv tw d )mht/*x4ome wire. Immediately after the toaster is 4c*rfdkvh+x)wt)0rtbm dd (/turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resis:s rqa( ivqy,+tor? Explain.

Different lamps might have batteries connected in either of the two az m5q*qpck;um; rd .v6rrangements shown ipvqc6ud*; z5q;krm.m n
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many electrork42vw zeel p3 ).*zrr7fp )bzns are flowing past any point i7zkrelef)z43 )2. bvz*prr wp n the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery ucheo:+v:v r9sja c(x1 sing a current of 6.7 A for 5.0 h. How much cvh:(r+ :ecx o9sc1jv aharge passes through the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes ih1qde,c-t bl/tz p:+af $1200\,Na^+$ ions flow across a cell membrane in $3.5\mu s$? The charge on the sodium is the same as on an electron, but positive.    $ \times10^{-11 }\;A$

  What is the resistance of a toaster if 120 V produces a current of 4.2 A? a y95vd+6j)e(yyzk2ss jxw- k4mfb 14cmrvt8    $\Omega$

  What voltage will produce 0.25 A of current 4nicnt(qo5o 1through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-V lins) , 32ad-dkcwzwsee- fyn0b 8e.
(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 dr0ee7j o t.*fyzyer 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 ce/ uc*6pzrrr;r/ t)(j o l2dqdonnected to a bulb whose resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric tranvk , q+0.mfcj .sn- /zt,r5psuffg7qhsmission line carrying 2800 A (Fig. 18–34). The lineu,k 5svsr t,nffh7/p z-qf.gc. qjm+0 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 mnwum;2 3me cn1mn5)m 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 0-5wni908l xv1evfjy t.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 u ee akh,t w35sh0 x1;sgj/4eywhose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1.5 mm in diametetm7pr3j+w7iih;bq1 sh) e a-ur?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of alu hvf0f6e h2ncms5/z a *a9a1axminum wire 2.0 mm in diameteae/*m6 92ashhafx zf 5a1v0ncr, to 20.0 m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tungsqtvga /.jqo7ii91* ci ten wire of the same lengti .* o17iv i/9qatgcjqh? Give numerical details.    mm

  A certain copper wire has a er.zbb7/jt yq9zy; ng 8z1 3rcresistance 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 6 q 3exowjpqj /h:-ii6ouoc *7of a copper wire (originally at/p6 cqiew 6*x7 q3 jui-ohooj: $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature coppvsgnx4fl* /1 tr hc5m5er will have the same resistivity as tungsten dxn 1mf 5hs45tclvr g*/oes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of aboutzj:*ghnv drw9f ( t12xw1yoo5 $12\Omega$ 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 househxk yd8m(ob a50h2vz5ehz tl )i kr)z8.old no. 14 copper wire (used in 15-A circuits). The e)hzkk habiy)v 2(5t58xz0 z.o m8drlwire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths 1.0w8l-0o akpix3 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine alpkox-i083w 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 ha0;r/wgwf4xq wj r;uj,oql:3sve the same resistance. If one has twice the length of the other, what is the ratio of the diameter of the longer wire to the diameter0or lqj,4u;srfj/wq wx3g:;w of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V power supply, a5lkgx e2,) gxtnd a current of 0.4212 A is precisely 2 k g5x,e)txlgmeasured 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.ux/0bizq:sra.k) v pp9nn k410 m of aluminum, both of diameter 1.0 mm. A 40k.:p/n sknbui 1)avz9xpqrvoltage difference of 85 mV is placed across the composite wire.
(a) What is the total resistance (sum) of the two wires? $\approx$    $\Omega$(retain two decimal places)
(b) What is the current through the wire?    A(retain two decimal places)
(c) What are the voltages across the aluminum part and across the copper part?
$V_{Cu}$    V(retain three decimal places)
$V_{Al}$    V(retain three decimal places)

  For some applications, it is important that the valu5d 1ro2n3ud -ujws3we4dk 6 ere of a resistance not change with temperature.wk-2dw33e oju resd 1nur54d 6 For 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 0 bq 6hzqs0sc)8y/oio.3 kW of heat when connected to a 240-V source.o scqz00is6y/hoqb8) What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player that6g 1d8xl2qcvp draws a maximum of 320 mA of currenlx8dcg pv 261qt?    W

  What is the maximum voltage that can be applied across a s ok-cyg4 yw*;/y6tyw $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance o7y/x4lfz* yb fag/qy1 f, and current through, a 75-W lightbulb connected to its proper source voltageglfq*yzfy7x a 4y1/b/ 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 110 r7pb7q : v k8nw4ra i-+q6 hq/g,fmhmat2j9he 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 an ; tjx,q5 vt,c t.kr9ivuw*v(cd 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 caaj;h9dfyuu n(/7 ud8 +qg- rdelivered 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 bright ; j7-uuqa9uadfg (+ rhy/dc8nness is proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use inmi04s n5kluc 3 vl,yq7 the morning if it is in operation for a total of 0nslvyic k 537mlq 4,u15 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 lg0a- .xnvz:1o5l f h+dungpe hlq7+q,+bnus.ight on day and night fnbgnxe+-:+fodzll7p. 5 + vsq unh g0 h,qu.1aor a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V y5m/k)ato0l2.onlune2r5 -zbfk .b f batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bum5).fn0oe2o.l kbnr b2 -l/ua t5zkfylb 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 ene +nlqhe3 fo d+e(w2v)srgy 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 bybx ml ;b5co1e; 22yghe used without blowih1b; xym5y c;2 leogb2ng a 15-A fuse?    bulbs

  An extension cord made0* nxksv7:,i ymkp f*/luag vw30xg5o of two wires of diameter 0.129 cm (no. 16 copper wire) and of length * fu5xgvkamwyl 7o:x/3kgv*p ,0is n0 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?    W

  A power station delivers 620 kW of power at 12,000 V to a factory throuyc,xb;k 7+ zap5y-cyq gh wires with qy-y+ ;7kp5ca xyzcb,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 connec(2 p bw zmadc*1m8h+meted to a 240-V line is 17.5 A. At what rate must cooling water p w*8+e1zhmcd (b am2pmass 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 usejn d:xe6x7xf3/u3emgd in a car to heat a cup of water for coffee or tea. If the heater can heat 120 mL of water from 25 ndx7g3:e x3/eux f6jm$^{\circ}\,C$ 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 current3 wif5l2gxwzu 983fdc5npdu ) 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)3h s kzis8; z33(e:s crguarq 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 resistancs0z/shv4 .zq bxpr;d1e 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 h .kl;io:i x428u9t+m0 hpyj.5 ioppx3zyer sdevice is 5.4 A. What is the rms voltage3ph.yijomieyx0; s4ik 59 8r:2pxzt +po lh .u across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected to a8wb yznwz,;qyy p bcg )7gd6nf1deew6;,22 lm $660-V_{rms}$ ac line. Calculate
(a) the peak voltage$\approx$    V(retain one decimal places)
(b) the peak current.    A

  (a) What is the maximum instantaneous power dissipated by a 3.0-hp puyt7ig6 +) amoump connected tgtmoi+7 )au6y o a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connectf eqcd 5cee)*t6 jwh+9ed 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 o6 +hp s: d9dfewjwc2-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 i2) w5 l v*yafk9;ihoj;9vrzy ps applied to its ends. I lkowy9z ry9 2avj hf;p;*5v)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 Ea8hh ip -82bc:z) 3x( qqvm fk/+clflqvrth’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 Eartfe 7dcw sphz (,-.;dzxh’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*;f f smvft(;w 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 actddbsjf(-g h ,w.d2iy) ion potential is detected at a point 3.40 cm down the axon 0.0052 s later. When the action potential is detected 7.2-bd2,sj f)h ( idwgy.d0 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 energy is required to tr9,h m i)rpd/egansmit one action potential along the axon of Example 18–15. [Hint: t/ pd ,)mgre9hihe 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 required for $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action poten :9c(k. ypugbqtial, $Na^+$ 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 m2rfc buox- q2pc-yapeu6g.o 3j8 1k.fa .eh:ampere-hour?    C

  What is the average current drawn by a 1.0-hp 1m63 u*md9vafruw9gr 320-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the 40ykl+ nj*qtxn+ yjr* lights on. If each of the two headlights uses 40 W and each of the two taillights 6 W, for a total of 92 W, how long will a fresh 12-V battery ljxnyyrq k4* *lt+ n+0jast 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 kb+qh obr0 p;+6i*i z1azc4 5dir3rfl is made of iron, what must i*+3 zfh0 k+4rrbar1lpidbc 6qoi5;z its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of the resistance R;r b2xr2:q0f eoei6 *kj tha:erjo fr6ex2*2ki0 qb 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 abo9y1 7wvikr.cl-8vuri vu)x u, ut 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-wire line of 0.50-cm-diameter copper wire, estimate the cost of the energy lost to heat per hour per meter. vrk luic8 x).vrv -y i19w,u7uAssume the cost of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular household uses a 1.8-kW heate6db pg htek719r $3.0 h/day$ (“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 a4-vtrld h fv gs:96wx7*jo8c 6ai5yo gre wrapped together side by side to make a thicker wire. How does the resistance of this new combination comph9tdjro8og6c7vi:v s5g6a x 4l*-w fyare to the resistance of the original wire?

  A 1200-W hair dryer is designed forn)gpi0n 5jba4(0 g k7hxggg ko4bcu82 117 V.
(a) What will be the percentage change in power output if the voltage drops to 105 V? Assume no change in resistance.    % decrease
(b) How would the actual change in resistivity with temperature affect your answer?

  The wiring in a house must be thick enough so it does not be(h 8r,u0a wwhecome so hot as to start a fire. What diameter must a copper wire be if it is to carry aw whuh 8,e(r0a 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 equatidczcw+d9d8np a3 20gyon $I\,=\,1.80sin210t$, 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 a1.e /e ,ey f8kj8u)0tdbjvzokt 65% efficiency delivers 950 W of energy per second to the interioreekv0etzj.)u d1,fko8j y b/8 . 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 differ 9hgnhws /ae ui8p61m3ent conductors made of the same material. One conductor is twice as long and twice the diameter of the second. What is the ratio of the power wmig uaes386p9nh1/h transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to xeu(;of(- s1qv(c-w yttwy m)mb4 x5cheat a room of volume $62\,m^3$ Air is brought into the room at 5$^{\circ}\,C$ and is completely replaced twice per hour. Heat loss through the walls amounts to approximately $850 kcal/h$. If the air is to be maintained at 20$^{\circ}\,C$, what minimum wattage must the heater have? (The specific heat of air is about $0.17 kcal/kg\cdot C?$)    W

  A 2200-W oven is hooked to a 5chxt.v: n2zgpx2 ux* xj +b*e240-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 source of enod56*rpjy8 wywk nm 4q++s y8pergy. Its mass is 1560 kg and it is powered by 24 batteries, ea4yw jd8q+*5+8p6w rkmpn ys yoch 12 V, $95A\cdot h$. Assume that the car is driven on level roads at an average speed of $45 km/h$ and the average friction force is 240 N. Assume 100% efficiency and neglect energy used for acceleration. No energy is consumed when the vehicle is stopped, since the engine doesn’t need to idle.
(a) Determine the horsepower required.    hp
(b) After approximately how many kilometers must the batteries be recharged?    km

  A $12.5-\Omega$ resistor is made from a coil of copper wire whose total mass is 18.0 g. What is the diameter of the wire, and how long is it?
L =    m
A =    $ \times10^{-4 }\;m$

  A 100-W, 120-V lightbulb has a resistance zd*v2gjgb 3 l1ku6-i : gjmr-oof $12\Omega$ 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 accelera1dn:qi-l5+5 w wf( h ytoqka6etor at Fermilab (Illinois) is designed to carry an 11-mA beam of protons traveling at very a kt wn+6- (e1:yfh5wqoiqdl5nearly 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 k4k u1qqpt o5(ks +(zlcord is copper wire with a diameter of 1lkp((+qkq k4z5uost1 .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 kixs*:f,3/h ezrjwr 9fq n-d1at 95 W when connected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.e *krjhi3rfs,zq: 1d-nxf/ w98 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from about 12 m,q g votc9mi)-:nj8d )req4worg j1oc-*kj- V when the car is off to about 13.8 Vd -k 9)nvr)j1q*jcqgo8g mr,i t4-wmjo:-oe c 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 13.8 V? Assume the headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V an85c4fw jtwal .d 40 W for household applications. Lightbulb B is rated at 12 awlw 8ft4 jc.5V 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 diameter 0.259 cm is used to connec/ugo71 ciuh;xt a set of appliances at 120 V, which draw 22 g huoiu;cx1/750 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 diam/x9v d6: (iuq poxg)rreter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the)ox6d9 vr/ :gruqx i(p resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uncw6,2trn/vuwlyh*(ii6b0 nsiformly so that its length doubles, by what factor does the power dissipa(*0vwyniub6 6wn 2/l,t ri schted in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a fly4x zylb5; w8zashlight bulb operates at 0.20 A and 3.2 V. If its resisb5 l4 yyxz8;wztance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$