What quantity is measured by a battery rating given in ampere-4uhtg- eutp 61hours $(A\cdot H)$ ?

When an electric cell is con ;arkwngsoz.s w k 68(0qq6vn4nected to a circuit, electrons flow away from the negative terminal in the circuit. But within the cell, electrons flow to the negatisqn;8owkzgs6nk( 6 rv a q40w.ve terminal. Explain.

When a flashlight is operated, what is beinzc; n04s)gtdx 36sswlg used up: battery current, battery voltage, battery energy, battery power, ornd swt6 zssxc)0 ;gl43 battery resistance? Explain.

One terminal of a car battery is said to be connected to “3 uwdcm1n 98nvuu9l 6pjpe8 j6ground.” Since it is not really connected to the ground, what is meant by this expressioj 6u8 e8nmpvc u 1j639pduwn9ln?

When you turn on a water faucet, the water usually flows immediately. You uwv46j hl wcjph* 1j:.don’t have to wait for water to flow from the faucet valve to the spout. Why not? Is the same thing true when you connect a wire to c hh.jlp6wjju*wv:41 the terminals of a battery?

Can a copper wire and an aluminum wire of the same length have the sambbt e+ ey90 f ehe,zfk-1o-ar8e resistance? Exp r+akye8et f b0bohfz ,9e--e1lain.

If the resistance of a small imkq(: 9y9of u.hwgd r)pmersion heater (to heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the heating proces(yw 9guro.) qp9:dfhks? Explain.

If a rectangular solid made of cakwtk 4-u7z4dz3o8xu .-)zw coxwiw a :rbon has sides of lengths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resistance, (b) the greatest resi8k-ud- za4w xcwziut.ox:3w)zow k7 4 stance?

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 burns o1neqomgj. r1) p7/c ns0u/ oxkut?

Explain why lightbulbs almost always burn out just aksyd+3 ,9g1tz 6feswa k6aow:s they are turned on and not g19a3swwk:aty6kdo 6e fs ,z+after they have been on for some time.

Which draws more current, a 100-W lightbuwf 0:-xr7brcdlb or a 75-W bulb? Which has the higher resibrrx7f:-0wcd stance?

Electric power is transferred over large distancege +nvj;.4/d1ms0inzfw er:v s at very high voltages. Explain how the higvzief rn1:dn.gj+e w m;0/4svh voltage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangero+a3mjf 2op j2aus to replace this fuse with a 25-A fus3pf a 2+mjj2oae?

When electric lights are operated on low-freq96bs r + 2+hzpjeydue*uency ac (say, 5 Hz), they flicker noticeably. 9z b*yh +p6sj2ud ree+Why?

Driven by ac power, the same electrons 68z0g3ifih v n;pwlpw/g, .akla- u9 kpass back and forth through your reading lamp over and over again. Explain why the light staysw,/6ik0 knlpau38gg9 lv. p wahz;fi- lit instead of going out after the first pass of electrons.

The heating element in a toaster c vcp+;ktt,p.dx )r) tsd.qh4is made of Nichrome wire. Immediately after the toaster ip dh.spkvq)xd4cr,tt ;.) +cts turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Explainknni 2 g99ww,(lpy3o g.

Different lamps might have batteriqkr my1w sxj-*( bjsy -8nu9h7i6tz-zes connected in either of the two arrangements shown in hrysij1by 6k n u *-q8 xz9w-m7(jz-ts
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a w76 pdpm kth;qss(h 7h1ire. How many electrons are flowing past any point in theqdt(h1 mp 6 s;7khp7hs wire per second?    $ \times10^{18 }\;electrons/s$

  A service station ch mip hdcy f( /pmi464)1jotms5arges a battery using a current of 6.7 A for 5.0 h. How much charge passes through( ysoidh )6m cij4/1 fptp45mm the battery?    $ \times10^{ 5}\;C$

  What is the current in ampv1e gov609z gby )wvworwvib avtm(( so80; 56eres if $1200\,Na^+$ ions flow across a cell membrane in $3.5\mu s$? The charge on the sodium is the same as on an electron, but positive.    $ \times10^{-11 }\;A$

  What is the resistance of a toaster if 120 V produces a current of 4.2 A? + yr5dnsg): fg1dpo2r    $\Omega$

  What voltage will produce 0.25 l+2+t owbvpi;A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into a 120-y+qphq7 cih3 4V line.
(a) What is its resistance?    $\Omega$
(b) How much charge passes through it in 15 min? (Assume direct current.)    $ \times10^{ 3}\;C$

  An electric clothes dryer has a heating element with a n.q ysb96v ltdnb5dl*oi18 s9resistance 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 b9:32lbweox; y4(g- lbj sid8pl3 fi cqulb 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 tranvld 8xhl0))*pjpkx 3 nsmission line carrying 2800 A (Fig. 18–34). The line hndl)x xpplh)380*jk vas $2.5\times10^{ -5}\;\Omega$ 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 2f; 2dxb ymrsl48:/j xn40 V.
(a) If the voltage drops by 15%, what will be the current, assuming nothing else changes? $\approx$    A (retain one decimal places)
(b) If the resistance of the device were reduced by 15%, what current would be drawn at 240 V? $\approx$    A (retain one decimal places)

  A 12-V battery causes a current of 0.60 A through a reypa nl15b3d(-q1t r6hs3obcqsistor.
(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 tungsten7 ch3+: gaugqsdu q,*g wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance ofj*mg-zsm2v .c a 3.5-m length of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire) rd3fy bppax-8bi3d yh8 37vr 2.0 mm in diameter, to 20.3x)d7rv rdp8a 3 -fbhby8i3p y0 m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copp+( y8ir8bc tvter wire have the same resistance as a tungsten wire of the sam+y(8vtibt 8c re length? Give numerical details.    mm

  A certain copper wire has a resistanco-7s yb;*sx l3 ll7vfte 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 coppen+co1xo3 z07yja h2dvr wire (originally at j371+a xhzdc vyo0o2n $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivity as tungsten 2 yf5yn ykq5*dm, g5)vm;iyii does at iyn g5qm5yym*dkf,y5i; 2)iv$20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resw0u1jss-*jpxn36a izz-) -6 ww ot ljqistance 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 copper wire (usb2. )rxyy 7fdeed in 15-A circuits). The wire has diameter 1.628 mm and carfyy. x)7ed2rbries a 12-A current.    V

  A rectangular solid made of carbcp 7lc2k3) mrbon 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 current that passes through the solid p3 mrc)7c2 lbkin
(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 resi:-- qhn6l sln f(pmy6pstance. If one has twice the length of the other, what is the ratio of the diameter of the longer wire to the-qy-hpp:l(f nm 6sn6l diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected toafl/mkle19* 2 7ygoh 2nbgfr9 a precision 10.00-V power supply, and a current of 0.4212yfgab1 9 7o2e 9h glm*lfknr2/ 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 x /p(6b -6hxjae,s g,q:a/rolo8rnz h 9y2zroof copper followed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage differenc6- ro:oy2//ph bzj,zg enrqaxl96hrx, osa( 8e 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 cy7 q :8et wcgp0.,wfgn5 t0anyhange with temperaturgegq w5:0ync.fyw 0npa t87,te. 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 3m9s; shbe -sa;3ct+:4zq f iq6 kanx)d.3 kW of heat when connected to a 249s b4ak;+ms3s6hz-)fne: q c;iadtxq0-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V po*cd9jn; m wu x:rv-a*zrtable CD player that draws a maximum of 3-* wczv*n;aj m9x rdu:20 mA of current?    W

  What is the maximum voltage towpn 5wb,:n 6xhat can be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, a 75-W (po kgadd hh14u0 .4otrf u8gh;6 dqb7lightbulb connected to its proper source voltage of 120 g4(dq 8p;g h1ahuo0u6b4t 7dfordh.kV.
   $\Omega$
   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 W. Calculate./ 0r+ brsb rsy9a;a .:nsflcf
(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 tanm1/9ii d ;ybwo settings: 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 elec 2ml6r6(dxwl ytricity 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 proporti2xw6ry ( lmd6lonal to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use in the morniftu7j4pv( m535j3etub lke /s ng if it is in operation for a total of 15 min? At a p3lm 7(5b/e3e5sfutk u j4tjvcost 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 o bwc4x-z 7ifj-e7pjuc 3 a;w5bn day andz;bxui4-j7-bfc jca5wp7e 3 w night for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected in ssy2 ,xcou 0ta3z sow7+ equ+d.eries as in Fig. 18–4b (Fig. 18–36)oz+t0axus.2q 7e3c+ swo yu d,. 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 amoa/ vs)8wkfi+hyva *+xunt of energy 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, ca3gq6xwz0 o*pp+8tsz9y 9;. - iusz hezksae2qn be used without blowing a 15-+; *ias9zpzw3hzex 6 98 otz.k2yq eugps0q-sA fuse?    bulbs

  An extension cord mad zib uw2n1 rs2zd2a(j0g :/ggte of two wires of diameter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ftzw1gdb:s(22aj0 t gr 2gn/ziu) 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 facte0 xlqcnj3 )*um r/+qtory through wires with totarqt3c)l0 e*xuq n/j+ml 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 electroma hb t -rqr7u(;rhkvqe08ang// gnet connected to a 240-V line is 17.5 A. At what rate must cooling water pass over the coils if the water temperature is to rise by no more tvrh 8 /rr e7hu/-nt0gqk;a(qbhan 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to heat a cup of water fhyf4a(- (yg-6 bhrlr,1zoo zsor coffee or tea. If the heater can heat 120 mL4ayhz-r( g s6yof(h l1 zb-ro, 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 curmjbdccjxbx ,8k:wc6 s 5y, :5srent 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)8+vy8n pk ihk4c w1hyzv47ux across a $330-\Omega$ resistor. What are the rms and peak currents in the resistor?
$I_{peak}$$\approx$    A(retain two decimal places)
$I_{rms}$ =    A

  Estimate the resistance of z m0vuk54 c0itthe $120-V_{rms}$ 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 A. nr t ,k988be 6plrsa/d) 6dkicWhat is the rms voltage across it? 96p r enl/d6t d)8br ,sa8ckki    V (Round to the nearest integer)

  An 1800-W arc welder is cus3zjh2 ,g:yq q,i9y uonnected to a $660-V_{rms}$ ac line. Calculate
(a) the peak voltage$\approx$    V(retain one decimal places)
(b) the peak current.    A

  (a) What is the maximum instantaneous power ds s- qnuvfod.i2,v3w3issipated by a 3.0-hp pump connected ui-3vs f3, dnsqvw.o2to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected c 7ogy5g 0,2cf:pc eteto 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 copg 37ak3n 3ez idyaz27xvnd95nper 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 carrie.( iql crc,xk1s a 750-mA current when 22.0 mV is applied to its ends. If the drift speed lr cx1(,cik.qis $ 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 Eart(dkyvn +hy6 ,qh’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 Ezyog b9;3 ey4earth’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 elh5 k(fdl7-wggectric field across an axon membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulate v8nwm-sn6g+a/ c3eomb7 ro*td with an electric 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 stimu t-n7e nm m*a68ocgb3vs/wro+lation, 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 transmit one action potential along th6bv8z; ia. on 3ddp7lse axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored by3 slv.z7dio6;nb 8a dp 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, )/v elh*t7snz $Na^+$ 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 zi).z;av mabvm 3o11q there in 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0-hp 120-V motor c(d e5ww1m+kn? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the biw+aj8tpt4q m/ckz-0,f9jv4 q jhn(lights on. If each of the two headlights uses 40 W and each of the two taillights 6 Wtq/q+-4v0j,i8nb (m jh ja9 tkc4p fzw, 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, 1500-W heater is 5.4 m lonvtxl95 a8 qd5cg. If it is made of iron, d tx5q 9v5lca8what must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the )eu (yx(mf, xxw:5rnireciprocal of the resistance R; that isxe uixf,:m5xwn )r(y(, $G\,=\,1/R$. 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 higq+08fvln4/t1 zs+uqum qw g8eh-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 e0+tuq w qlfg4u+ /vqns1e88 mznergy 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 hi5 :zil yjob39eater $3.0 h/day$ (“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 cc qqty)6b(h3 wrapped together side by side to make a thicker wire. How does the resistance of this new combination compare (hqcqcb 3)6ytto the resistance of the original wire?

  A 1200-W hair dryer is designed z ; x7 )a6u0t+lhq/hdp1lm bzafor 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 become s4xp5b24 *ejmoaypf x9o 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 thp5 4 * b29ye4fmoxajpxan 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is gy;a7mp.xa ezw4sj . +uiven 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 energ0x)ey9mcy .ar y per second toaycry ).mex9 0 the interior. 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 same material. bseqivw )rh2o31gk+2One conductor r3b1+ow kge)2vsi qh2 is twice 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 room of - 4 6t z xeimhz( sitgsc+7q9p0m-fhu)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 b 8i ma m;w;49lcz wi8-sclz8oto 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 n,v pc1cu6d7 nstorage batteries as its source of energy. Its mass is 1560 kg cncv6n,p7d1 u 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 lightbulgwpa;wum*e 09z ) sgvddzsza/p(.,e /;vgg +w b has 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 designed to cak jg.ku wt08/drry an 11-mA beam of protons tt.w8 kg dk/0ujraveling at very nearly 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 afwm+s5d )k0 bdt 220-V ac. The connecting cord is copper wire wi) 5 fdm+w0dsbkth 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. T5wf*8+amrmvu vd1 u bn)f, qkw;m4e -hhe heating element is a coil of Nichrome uv4v8a nu ffbhmd e q-;ww*r,m) +mk15wire. 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 voltaomv(3v(+j gt50;dlrc w 5ula qi 3uxe6mnl-w3ge 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%. (tm5e5l3wi+r c w6j-gv n o0umlxu(q;a3 v3ld 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 household asb b2 pqt)q -mj24ko-rpplications. Lightbulb B is rated at 12 V and 40 W for --tj2sq bq)rombk4p2 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 connect a set of applky08cnzuwv f8:2. f46q unetmnzx1a 2iances at 120 V, which drae0 fn8 : ykwxc26f.2vm quzn41za8tnu w 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 diapqe ;h+*m z-zm 52nt hhl)fp,gmeter of 3.00 cm and an outside diameter of 5.00 ce)q; *h5 mpp mzn+hltz-g2,hfm (Fig. 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 so6ei 0cm(7:mvi qmf3y- oq:wqi m 8si/f that its length doubles, by what factor does the power dissipated in the wire ch/c6qqemif i0w8m3ofyq m( 7: -ivm :isange, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a m0r bg.b1kpes55 9gbvflashlight bulb operates at 0.20 A and 3.2 V. If its resistance b 1.5e05p9bkgmv bgsrat 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$