What quantity is meascje3if e..10xm d, j(yhly g9dured by a battery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a cir .z(riljue18ncuit, electrons flow away from the negative termizr1.u l( en8ijnal in the circuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: battscm+1dglu, n7 ery current, battery voltage, battery energy, battery power, or battery resistancln+gs1cu d,m7 e? Explain.

One terminal of a car battery is said6c; 4q (1fzmfd2w svpwhq4.fn to be connected to “ground.” Since it is not really connected to the ground, what is meant by this 4 m 1pq wqz2sfnc6f;h.4wvd(fexpression?

When you turn on a water faucet, the water usually flows immedigvkvr5;1c0pyxf t- b4ately. You don’t have to wait for water to flow from the faucet valve to th cyvgrx b1v54t-p0;k fe spout. Why not? Is the same thing true when you connect a wire to the terminals of a battery?

Can a copper wire and an aluminum wire of the same length have the same resistaq x-p 2k9 i1wus2fc *1achrb)rnce? Ex*pr wsk) hq ci12a2ru9cxb 1-fplain.

If the resistance of a small immersion heater (to heat water for tea or soup,fncmg 6,h8z;k Fig. 18–32) was increased, would it speed up or slow dowzn68f;mh,gc kn the heating process? Explain.

If a rectangular solid made of carbon has sides ofzhie x;3 4y2eq lengths a, 2a, and 3a, how would you connect te y4zq32;hxiehe 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 lightbulb burns oyz6h t2ip r7i o+dem: *vjc+(out?

Explain why lightbulbs almost always burn out axe;.b;:pyjeh 5*xhe just as they are turned on and not after they have been on for so ;ahbx; eyh 5px*:j.eeme time.

Which draws more cur;i/5cq iis1vhrent, a 100-W lightbulb or a 75-W bulb? Which has the higher resistance?/i;hcv5qs ii 1

Electric power is transferremzg3u;fhf9 t 3 e34 5gz) ;nsscrqjy,ed over large distances at very high voltages. Explaif9nr e gu3c y;sm3 stzjzghf;qe5)43,n how the high voltage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it danr)vy7x cb1h,pgerous to replace this fuse with a 25-A f,7p1vrc ) xbyhuse?

When electric lights are operated on low-frequency ac (say, 5 Hze.lj8m;dygzy g(/9zb ), they flicker noticeably. Whyb8/j(ygzdlgmz ye9 .; ?

Driven by ac power, the same electrons pass back and forth through your reading u /lbm;:n ppaup1n/w+lamp over and over again. Explain why the light stays lit instead of going out after the first pass ow;u n+bua/l/1pmp:p nf electrons.

The heating element in a toaster is m-cjt0zacnv0cb/z- g; b o:l5oade of Nichrome wire. Immediately after the toaster is turned5g- 0;j:obzan/voc 0c c-zltb on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a re t( 67 96i 9tklhgnzm..fkaobfsistor? Explain.

Different lamps might have batteries connected in either of f6n: /gq+z 1:ofxc9;o rmojpmthe two arrangements showo:cx1p6o;/9 q+f jfn go:zmmrn 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 pa5i 4,0 vyixgwost any point 0voy54,wix ig in the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery usiz .*qrc xdge,+ng a current of 6.7 A for 5.0 h. How much charge passes through the batte.ez d rc+,qgx*ry?    $ \times10^{ 5}\;C$

  What is the current in amperes ifllt.7v16 tva h $1200\,Na^+$ 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)v avi )xt hk(;v79m6kdi-c tr?    $\Omega$

  What voltage will prodc:wixr39 ft:dd2zv0u8qv q 6q uce 0.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged2b:d)ve2 rh sgwu.muf e3a;ec.-m n+y 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 h/aj x dxk8gy9f+u:dw99 km/mleating 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 al twoghy19b1i sy i(*8 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 transmission line carrying 2800 A (Fig. 1d dcm4. s8mfs4hm+v: d8–34). The line .c4mshsvd+f: dd 4m m8has $2.5\times10^{ -5}\;\Omega$ 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 d u0uer;up) u3braws 6.50 A at 240 V.
(a) If the voltage drops by 15%, what will be the current, assuming nothing else changes? $\approx$    A (retain one decimal places)
(b) If the resistance of the device were reduced by 15%, what current would be drawn at 240 V? $\approx$    A (retain one decimal places)

  A 12-V battery causes a current of 0.60 A through a resistor.otmkhel7k grc630 - vq+b+e-i
(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 kpq flm,m x 7 t5;cu8ldo/0:af05xpyeof a 1.00-m length of tungsten wire 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 0r+89 nl(h seqbaz ch;diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum wire 2.0 mm in d j av0 pjf*lx5k,4a0jeiameter, to 20.0 m of copper wire 2.5 mm ina*jja 4pe 05kvx,0 ljf diameter.   

  Can a 2.5-mm-diameter copper wire have the sameii bfwd/2dc 0z7t06 ml resistance as a tungsten wire of thd 0276t0 ibizwd/lcf me same length? Give numerical details.    mm

  A certain copper wire has a resisrqu9tmpy-b+ :o pv 7yb5ece48tance 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 copper wire (originally a d)txfo0qqlr t a.t9+bl7 w7u9t a.+rf)97xltq od l q0 u79wtbt$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what tempeitfo m ):g rn9 a) xb-3dhaj9r:(ssp6erature copper will have the same resistivity as tungsten does at )xt9j9goes b-3fmd( :hnrr i)ps6aa:$20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance ofq6ht 9n (;qtbm3j7n j -fyfbv, 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 2 8w/wsaa,+ /zm puk 0wrjk8qu96-m length of household no. 14 copper wire (used in 15-A circuitsuw/u8w z 9sjrqk 8a/k,m pa+0w). The wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm, iau4arxg)eish1o+ (v j s0/a,2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance a j/h +ae gi,o1s)uaxiv(r40 sfor current that passes through the solid in
(a) the x direction,    $ \times10^{ -4}\;\Omega$
(b) the y direction,    $ \times10^{ -3}\;\Omega$
(c) the z direction. Assume the resistivity is $\rho\,=\,3.0\times10^{ -5}\;\Omega\cdot m$.
   $ \times10^{ -3}\;\Omega$

  Two aluminum wires have theoq(v ju-szn ), same resistance. If one has twice the length of the other, what is the ratio of the diameter of the longer wire to (j n)sozqu v-,the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V power sl0 xe obd)pb tna(j:41upply, and a current of 0.:j) dnx (1 belota4bp04212 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 consist ug d8w6vu n:+)8,om. iqrpehks of 5.0 m of copper followed by 5.0 m of aluminum, both of du+ r. dh68wmp 8guqnevk,i:)o iameter 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 important that the value of a resistanc;g kp4htud*t 5uje8 o(e not change with temperature. For example, suppose you made a;* ug(keth84po5udj t $4.70-k\Omega$ 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-h8( rwan hp0l to produce 3.3 kW of heat when connected to a 240-V source. What must be the resistann (rhp0-h8alw ce of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable d wjw4bam*cre3nyo.n:d:i,8 CD player that draws a maximum ofownne :jwayi m4bd. *,d:3r c8 320 mA of current?    W

  What is the maximum voltage that can be applied across a si.3mbkt) (zw $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, a 75-W lightbulb : . 4s j,gizjpi(ak8bo l3vjh2connected to its 4z:l(3hk2jbp.j, s a o 8gijviproper source voltage 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 acm//djj :od i.n gkg7r(, ;lcl,g6 :lapbt z.it 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 setti ;p gvg-0fu a1cwei(uqoj e 9ej.9ok++ngs: 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 lightu*v xs5x9v5azu /r 3;v-ytsfu bulb in Europe, where electricity is delivered to homes at 240 V. If you use the lightbulb in the United States at 120 V (assume its resistance does not change), how bright will it be relative to 75-Wxxf3vs u-5v;y9v szr/ ta5u*u 120-V bulbs? [Hint: assume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy doe*lx(. kbosa z 3janc*0s a 550-W toaster use in the morning if it is in operation for a total of 15 m 3(ozb0alncx*skaj *.in? 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 doesua6d mm1:9rc 3ylk(u ,hqhn6w it cost to leave a 25-W porch light on day auhmch6n y9d,r a(3 16qkmwl:und night for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batterieh re-ia rv20+ zdg-r3zs connected in series as in Fig. 18–4b (Fig. 18–36). The bulb draws 450 mA when turned r+0d-rre i- v32aghzzon.
(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 /aiaj89f/dn5h5vypqrgy stored in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, cof(30lwt r,rk sxor jh 40zo3*p8+eeus( stdv)nnected to 120 V as in Fig. 18–20, can be used without blowing a 15-Aj 8(tzx30 vw*+ oep0dt3ek )h,4(sus rrfrlos fuse?    bulbs

  An extension cord made of.f 3x5nx+y 6a,d aqndmg0q18lrf q6ry two wires of diameter 0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected to an electric heater which draws 15.0 A on a 120-V line. How much power is dissipated in the cord? q6m+n q6f.yd31q0rfg dxrna x l,8y5a    W

  A power station delivers 62003mqsqy c-/6,bn bm us kW of power at 12,000 V to a factory through wires with total3u 0 ym-cqb6b/ qnssm, resistance $3.0\Omega$ How much less power is wasted if the electricity is delivered at 50,000 V rather than 12,000 V?    $ \times10^{ 3}\;W$

  The current in an electromagnet connected to a r: r +;vifwm 7:5pqsuw240-V line is 17.5 A. At what rate must cooling water pasw ru:swm q ;7p5v:fri+s over the coils if the water temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car to heat a cup7jy/dag : 2ehz68:j pp-uxjhy of water for coffee or tea. If the heater can heat 120 mL odyyh7h2xu/ jg:ejzja:p -p68f 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 in ag0x qkr7f*;kkv31n g/ vjqvj4 $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, is xwwl;4tib02 facross 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 6obt )g/fzjwvw4x:5 j8t ,0edd ws t,b7krak3the $120-V_{rms}$ 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 devicectkr6dcyy: vgn*;0s6 is 5.4 A. What is the rms 6k:6yv dg;* ryc tscn0voltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected to a 2jpfnf)k 6 (qkbp*c2u$660-V_{rms}$ 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 3a,1,n5 yd+s. )hfrqu ,/ gsyicqq5uxb .0-hp pump connected to a q,h /cdssi )y5f5qx u1.y,ba gq,un+r$240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected t jh tr9i:lz0*no 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 hpudp ccp/17biv- u3a*h1u 1 ywire 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-dir1d9vdh 3 nz- 6vrai;yameter wire carries a 750-mA current when 22.0 mV is applied td-3h;id1rzv nv6r9ay o 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 jiju d-4h./lj’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 thewmdzv+cv q x/ e)33quh21 gd3j 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 magnitud cyl(93wkl 2ysqic/ 6qe of the electric 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 action potential is detectou g-cxr77yv 0e0 mlw*ed 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 xo7 yrlm-7*guw0c0ve axon? (Why are two measurements needed instead of only one?)    m/s

  Estimate how much energy is required to transmit one act .+4gujbexjh rjlyc m/+g88-dion potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored by h jm48ub-xjj/.dge8l+y g +rc 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 potenti;f*mg-kr hzg5al, $Na^+$ 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.hsx prx+::l p 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0-hp 12d,m4vr+.z s3le 9iamd0-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lightjd x-lwd(- :xoy 1dsqcz:n2 kb603jlts on. If each of the two headlights uses 40 W and each of the two taillights 6 W, for a totax wbz- c:l(d2 t06qon djk x3jd1ly-:sl 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 long. Iij.6ty s7 une*f it is made of iron, what must its diameter be? 7ys t.juie*6 n   $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of the resbae,0 yhg 4u4aistance R; ,b 4eahya g4u0that is, $G\,=\,1/R$. The unit of conductance is a mho $(=ohm^{-1})$, which is also called the siemens (S). What is the conductance (in siemens) of an object that draws 730 mA of current at 3.0 V?    S

  A small city requires about 10 MW of powj+- +i ,wx3ngic1jk :u ln-xhper. 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+i :x3cgh1,u wk+-j xnpijl-n 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 heatj ;5flw1y(jq ber $3.0 h/day$ (“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 wrap guz ( v8b,y6,5hya wed 0h9anuordh1;ped together side by side to may(herb,n0w9hyu86 az ,h;o ad1d5u vgke a thicker wire. How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 1u gw.af2.e;6bhd. m.qgb / igo17 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 lf(aeg, 1ec5pbecome so hot as to start a fire. What diameter mu p ceea(,g15lfst 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 giv16ryv ; k7nnok6xlmd5en 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 ofsqq 2 v:nqhdg(lt((cv:l6,f y energy per second to thn,l sc(2(6: vqvyq gfld hq(:te 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 coec ) mz:x r+(fg 90yuolfk1o/bnductors made of the same material. One conductor is twice as long and twice the diameter of the second. What is theyfc 0o+r:mk1u(xf l z o/e)9gb ratio of the power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used 9 pyh -p1 rtffjnx/*6mto 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 hoo n9 w4 yq44aans-3qhbtked 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 vehic4b cjr,4d-*d(fx;e7uckbmi ale makes use of storage batteries as its source of energy. Its mass is 1560 kg and it is powexmdf-,ea4bjuk(*ri 74 c c;bdred by 24 batteries, each 12 V, $95A\cdot h$. Assume that the car is driven on level roads at an average speed of $45 km/h$ and the average friction force is 240 N. Assume 100% efficiency and neglect energy used for acceleration. No energy is consumed when the vehicle is stopped, since the engine doesn’t need to idle.
(a) Determine the horsepower required.    hp
(b) After approximately how many kilometers must the batteries be recharged?    km

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

  A 100-W, 120-V lightbulb han:y,)atuus lgevd91hma .1 d8 7j ve3ts 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 Fermilazs,/e( q4 k+ ycfklzj.b (Illinois) is designed to carry an 11-mA beam of protons traveling at very nearly the speed of lic(y.q fz,jkl4k /ezs+ ght ($ 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 is h0y r38n*jn220-V ac. The connecting cord is copper wire with a diameter of 0nr*n38hi yjs 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 ratedzjumj :.)qr 7rq+kg;b(u1ycx at 95 W when connected to 120 V. The heating element is a coil of Nichrome wire. When uncoiled, trb:7q)myu1 uc . q;r kzgxj+j(he wire has a total length of 3.8 m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system volb x-lnu h--cdy9zn3* atage varies from about 12 V when the car is off to about 13.8 V when the car is on and the charging system9n-bxl* cdn -u3yh z-a 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 120tnl-2hkwx9 vnidye2o 5j u2 -2 V and 40 W for household applications. Lightbulb B is rated at 12 V 2l-tidxh2vkw 5y2 e2oujn n9-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 1oy-*zo rc6 ( ntn:or:qd8g crcm is used to connect a set of appliances at 120 V, which draw 2250 n r* :z(c1 8crogtor6dqyo- :nW 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 /q9dl+4seg0j)( z ztwxo (tjs 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 thiw/g(osdqxt )tjl 94 s+je0z(zs pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stret; e3aiy:/ 6euoodcn 2yched uniformly so that its length doubles, by what factor does the power dissipated in the wire change, assuming it remains hooked up to the same voltagee3ca/ ou6oy;dni 2y:e source?

  A tungsten filament us 3+jyr d-obhte(xr/cdq8/4 raed in a flashlight bulb operates at 0.20 A and 3.2 V. If its resistancerc /3ytejhd dxb4/ -rq(a8ro + at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$