What quantity is measured by a battery rating given in ampere-+bvxl x0io3)amq 22abhours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, 4 hyzoe3-.nqs0u bf)kd7ytykp9. 8y nelectrons flow away from the negative terminal in the circuit. But within the cenk)7y4q 3o.yf z 9b8he yt.sk-yndp0u ll, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up:qf (cza s0f 3x3/dfr66 l,pepe battery current, battery voltage, battery enercd3fl e(p q6s,eff /a6 p0x3zrgy, battery power, or battery resistance? Explain.

One terminal of a car battery7l9/zu 2 ;dy5leo:ap8qr fhej is said to be connected to “ground.” Since it is not really connected to da2j;/78yfqe5l r ueh: pl o9zthe ground, what is meant by this expression?

When you turn on a water*w4tkyt((n z z-3 misr faucet, the water usually 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 true when you co(i ty(mszn4w 3tkz r-*nnect a wire to the terminals of a battery?

Can a copper wire and an aluminum wire of the sameq ( rrtbam)zk *f6b 3xwngk:6, length have the same resistance? Explaifxnt 6w6bk,rba)mg3k( * r zq:n.

If the resistance of a small immersion heater (to heat wate9d hur*; 2 mrmo.p/bqehb u;6wr for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the heatingwu r/bmo*;ph6m r.b2u;qhe d9 process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 9x0ml yh7un*p2a, and 3a, how would you connect the wires from9h7n 0lpyx m*u 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 lightbulb burnk .dq1xndh6)9 n2jcozs out?

Explain why lightbulbs almost always burn ou a0c0r(krs .blk)kjj8w xw3 4lt just as they are turned on and not after they have been on kwrr8sklblk w 0cj( 304jx) .afor some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Wheeg,l aemp : w8g/o7m2ich has the higher resista2 ao gge,lm /pm78:ewence?

Electric power is transferred over large distances at very high voltages.h *9jx mtv0(n++fww hsbsc+0j Explain how the high volta0n *s hx+sjm fh0tcwb( j+9vw+ge reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous towj 8qp 5(gh0jp replace this fuse with a 25-j5 8gpwh0(p qjA fuse?

When electric lights are operatedkbw. 4db8bys-9n by 1d on low-frequency ac (say, 5 Hz), they flicker . 4dyn8-1b9s wbdby kbnoticeably. Why?

Driven by ac power, the same electrons pass back and forth througto *7s yw;ojf.h your reading lamp over and over again. Explaio.; ysfwo*j 7tn why the light stays lit instead of going out after the first pass of electrons.

The heating element in a toaster is made of Nichromej8qq, ke46 gmvtc*z,as zt4g1 wire. Immediately after the toaster gce,,zs zt *8aq4gm6 41kjqvt is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? Explaindymx(o hh351p .

Different lamps might have batteries connected in eithr(,hchf(hlsog, l. x: er of the two arrangements shown ingr :l.o,f(x,h( hhcsl
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wybdf0, qup3k-yg0sw; ire. How many electrons are flowing past any point in the wirpk;w uy 003b,dy qgsf-e per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a batdy/i92hgi8:6whfv ptm(8c kh tery using a current of 6.7 A for 5.0 h. How much charge passes through the batdy2tvi :f6i 9h8ch(h pkmg/w8tery?    $ \times10^{ 5}\;C$

  What is the current in ampergve.z ms-r 4ksafvo9 c(qr) 99es 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 nxg:r-pli c0*mrek,, V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current k2. qse2v3kr2uqe c/y-sh :vythrough a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged into av.iq5yhgm b. 6ts l.x4 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 ha ed8js700rg uq uf5c7twgwn19s 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 rmw6t3x.w5 nfwhose resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transmissiony qmg z(0kf+a-d:yp,c l,okd; line carrying 2800 A (Fig. 18–34). The liol y(ay+,:pf md;dczq, g0k-kne has $2.5\times10^{ -5}\;\Omega$ resistance per meter, and the bird’s feet are 4.0 cm apart. What is the potential difference between the bird’s feet?    $ \times10^{-3 }\;V$

  An electric device draws 6.50 A at 240r b3msq 1-.1twky)ci /dnnd(s 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 curr fw2sj8fcv(k 3gosa1xe49 d )pent 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 wihlwa 60zl9 f)yk v8r(ere whose 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 diamet0d qli)3e2c ad av07e/*o ;kx lcuflt7er?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire 20 3zx c7v8 ffmaq+arm +uc+g5n.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in diameter.qmnc+r zf0u3vxc87f + +gm5aa   

  Can a 2.5-mm-diameter copper wire have the same rex kf(eioxvx-f+(7gh *sistance as a tungsten wire of the same length? Give numerical detaif7 h(x (f-xvo gi*+xkels.    mm

  A certain copper wire ha w c0bo7h8oph+j2gp8e- c9cqjs 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 3 1rg.c vmlfk,raise the temperature of a copper wire (originally at, .k1v3rcglf m $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will hpy dx ify:)o-,;4zh isave the same resistivity as tungsten do o;diy), f-:yxh4sizp es at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of about da jrf99 ;n u-foe,e shl)k2:d$12\Omega$ 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 wi 4c5ulshum0fl6f gp, ,re (used in 15-A circuit0 flh, 5l,muscfg6u 4ps). The wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of l l5qh*d)wjh. (v+orb qengths 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 (jo5lhdq hw. *q+b)vrthe 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 uy/b 07b+ .cw/xy(bo byns2ih the same resistance. If one has twice the length of the other, what is the ratio of the diameter of the longer wib7 y b.0xh2iy b+(/ c/ouwsynbre to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is j llr-09wkg1hconnected to a precision 10.00-V power supply, and arj9lwgklh 1 0- current of 0.4212 A is precisely measured at 20.0$^{\circ}\,C$. The wire is placed in a new environment of unknown temperature where the measured current is 0.3618 A. What is the unknown temperature?    $^{\circ}\,C$

  A 10.0-m length of wire consists of 5.0 m of copper followed by 5.0 m of alumin8n gvqc,g t.n(um, both of diameter 1.0 mm. A voltage difference of 85 mV is placed a( n,ct.g vngq8cross 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 t*b5 mj zmz:3qm zl/mo1hat the value of a resistance not change with temperatu :mj*1zzz3bmmq o5/m lre. 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 desiotd)ige;.4 -+darpp x v w8c-mgned to produce 3.3 kW of heat when connected vdm)-aw ;ge rpxi+4o.-c 8 tdpto a 240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power u9eh;br zc,(5;0dtno9e wuyh consumption of a 3.0-V portable CD player that draws a maximum of 320 mA of current0 ;zwuue9d5 ;,ne c9yrob( hht?    W

  What is the maximum voltage that can be appliez ,6lpz 8q4hzp 6sxtp.d across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistanc +am z8am*58th 1fs:x-zmwe sqe of, and current through, a 75-W lightbulb connected to its proper source vol:hz8mwsamsef* 1 x8z mt-a+ q5tage 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 110ib2 t lz.k1ox,m ru+u, W. Calculate
(a) the current through the heater when it is operating,    A
(b) its resistance?    $\Omega$(Round to the nearest integer)

  A 120-V hair dryer has two settings: 850 W and 1250 W is8p97r k z+m(va+35lizs s ;qqflw*b.
(a) At which setting do you expect the resistance to be higher? After making a guess, determine the resistance at
(b) the lower setting;    $\Omega$
(c) the higher setting.    $\Omega$

  You buy a 75-W lightbulb in Europe, where electricity is delivered to homes 3xzhefyoxswf+b)4u7f;idn,+0w1jn at 240 V. If you use the lightbulb in the United States at 120 V (assume 0xb,wd 4 +)x1u;+ ni f7f3y onfewzhjsits 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 use in the morning if it icfx.v lx(8t r*s in operatic8tlf(x rv*. xon for a total 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 9cmoezgn36p;ha+8s e to leave a 25-W porch light on day and night for a 9pc8em6;az3e no+hsg year? $\approx$    dollars

  An ordinary flashlight uses two D-celb7u2*zx fc)n) mbz e4vl 1.5-V batteries connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draw vcf)m7*2 x4z) ubzbnes 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 store*p dxtmhjn6 gc0(8, btwv )heb6qt- q/d 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.e bu/nn..s 3xr 18–20, can be used without blowing a 15-A fu3 .xreusn/n .bse?    bulbs

  An extension cord mad( h ha/hq+u3bne of two wires of diameter 0.129 cm (no. 16 copper wire) and of l h/h3u(qbha+n ength 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 k5vql 85k1 hrkeW of power at 12,000 V to a factory through wires with total reqhr85v ek 1l5ksistance $3.0\Omega$ 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 connectr)awr/8 x+ngh ed to a 240-V line is 17.5 A. At what rate must cooling water pass over the coi/h)gx n+ar8w rls 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 cup of wat6i kyfd/x7p7t)/iesf er for coffee or tea. 7/i6syfdfe)it 7k x p/If the heater can heat 120 mL of water from 25$^{\circ}\,C$ to 95$^{\circ}\,C$ in 8.0 min,
(a) approximately how much current does it draw from the car’s 12-V battery, $\approx$    A(Round to the nearest integer)
(b) what is its resistance? Assume the manufacturer’s claim of 60% efficiency.    $\Omega$

  Calculate the peak c.: ,m.iqbzotdurrent 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 9hbkpvwkf73 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 resistancus-g t2glbc+b2 lg1i/ x21lv ye 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 altybtth9lr1g zvvr0 , oe0 3.jl3ernating current in a 1500-W device is 5.4 A. What is the rms vor .3rlt vzbg3t,ej90y1 hl0v oltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder +jpouogruy;v /p8x( 9 is connected 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 instantanen/mrrljoc:1- ksylc7h j4-c2ous power dissipated by a 3.0-hp pump connected 2l r:cyjc o/m jksc-ln14hr-7 to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connecteq3)c n) mhjmi0d 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 carries a tingup e1 ;c;mqno9rw9m0tu;ipt; n2/opc4b :cv y 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 xj+ :ut t *qlwihuc5.4is applied to its ends w4tuhutj.c+qli5 :x *. 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 3j- d9jh5 kyr-z wy.;axt prg,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 

  At a point high in the Earth’s atm+xubarv9/pd)b7j sf5g o 7;yjosphere, $He^{2+}$ 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 across an axon memi o4/fa8c4kembrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with an electric pulse. Thev1.bnx :u b km2b vtld1n/0:vo.x:tv) dki)ii action potential is detected at a point 3.40 cm down the axon 0.0052 s later. When the action potential is detected 7.20 cm from the point of stimulation, the time required is 0.0063 s. What is the speed of the electric pulse along the axon? (Why are two men1v x x:d/ontv..u bmi:iv0ti)b1l:k v2)db kasurements needed instead of only one?)    m/s

  Estimate how much energy is required to transmit one action potentialuj3o jqpsf;4 vsfc v )h)k)o.2 along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored by charginv fs;j q 3f4j2suvp))k c.o)ohg 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 potentia8 vx(rc1w 0pn/cat)r,l y j)hwl, $Na^+$ 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-hour? gt :y7u/xx rl0;b4odi   C

  What is the average current drawn by rmx3,eh 2(1( l(6m2 jdm pfyh.vbyzoxa 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights on. If ead 8)0zjgch)3t tm/ hccch of the two headlights uses 40cc0/)md8t)3h gc zh jt 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 mm u(3v2rq0y5jnt .s t,k.wqiof a 110-V, 1500-W heater is 5.4 m long. If it is made of iron, what m.53qmsi0 2kvqr( tnw,uy.t jmust its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of the , iiy/k*1 m:cz6rcb t-n ip, iaz33nvhresistance R; that is,nc6i3vyiz 3 kmr1ihbzp/ n,ci-:*ta, $G\,=\,1/R$. 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 tkwk3(tdaw z/br q 4 b.6jh8-m10 MW of power. Suppose that instead of using high-voltage lines to supply the power, the power is delivered at 120 V. Assuming a tw .6k/4wzw bt (bdt8jk-3hmqrao-wire 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 /o**a3euuw.6fvnt s muses a 1.8-kW heater $3.0 h/day$ (“on” time), four 100-W lightbulbs $6.0 h/day$, a 3.0-kW electric stove element for a total of $1.4 h/day$ and miscellaneous power amounting to $2.0 kWh/day$. If electricity costs $0.105 per kWh, what will be their monthly bill (30 d)?    dollars per month
(b) How much coal (which produces $7000 kcal/kg$) must be burned by a 35%-efficient power plant to provide the yearly needs of this household?    kg of coal

A length of wire is cut 67vukywa */qdin half and the two lengths are wrapped together side by side to make a thicker wire. How does the resistance of this new combination compare to the resistance of the original w/6ya*kuqdv7 w ire?

  A 1200-W hair dryer is designed fi 7*lh7l8hhpva0zmynfska ux h+/5q)4z 1d g1or 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 so hotfwc 3h5i,j d-d as to start a fire. What diameter must a copper wire be if it is to carry a maximum current of 35 A and produce no more than 1.8 W of heat per meter of len3j,5fd wih cd-gth?    $ \times10^{ -3}\;m$

  Suppose a current is gi(bu5 :bbiyw/bsa02n xven 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 ;0w:y65cf tt obbat5o950 W of energy per second to the interior. Find ta6y0of 5 c;tt5 bobw:
(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 m9 mus( lyj0aolz,i/t: ade of the same material. One conductor is twice as long and twice the d 0ja( 9ostz/iml:l,y uiameter 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 ii:x*h)/s wrnii hi0g1s used to heat 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 240-V souri,ie4 sw0bsjv ,j8z7l4an.x sqcy 7*bce.
(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 stor+. hv(2 vew wixj 5d0rhf+u .qrca)4o.s qkj:iage batteries as its source of energy. Its mass is 1560 kg and it is powere)wi ar4u rd.k(c2qw+ jqhix50:s v ..j+efho vd 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 lightbulbyou9h u; l0zq5,g,jir 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 carry an 11-m*odo;d*s *vtb /-z g6oz+ayw rA beam of protons traveling a+ z6yo ; rdbg*d vtsoa-/w*o*zt 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 at 220-V ac. The connecting cord is copper: nxodcqw8r m,e0u l+/ wire with a diame8 r+ w/,l0nd x:oeumcqter 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 connectezh 60t2y:syeje) g/f:nj xb- ed to 120 V. The heating element is a coil of Nichrome wire. When uncee6z ) b:x:2 gyte0yh-s/fjjn oiled, 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 voltbgk+ij2 fc ;7 3om6taxage varies from about 12 V when the car is off to about 13.8 V when the car is on and the chargingbjkci x3gaom ;t762+f 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 and 40 W for houw/xc9 ajo.d*dq.up :msehold applications. Lightbulb B is rated at 12 V and 40 W for automotive appli/9w.dd:cpuxj .*aq o mcations.
(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 appliances at 120 uu3i2m4t)dy09/nj mrysjt,mV, which draw 2250 W of power totalr s34t/0mit 2nm,)djuy9y umj.
(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 ins eeq/z*8d m;looi1l,s ide diameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the resistance of 10.0 m of this pis ei1q;l*le/doom8 ,zpe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that f h2se7n1v(vo6z11pn -im eulits length doubles, by what factor does the power dissipated in the wire change, assuming it remainzlf61 no2uh(i 1 vveens -m1p7s hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb ws oe0 (qrvzd()0 t1hb jig:2soperates at 0.20 A and 3.2 V. If itesh2z )jvt g( (:bwrq010od sis resistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$