What quantity is measured by a battery rating given in ampere-z;xa 3fphgpd+ xf2/o*evt9 .vl 1f,cchours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons flox+x x6)-xq:gpvz d5 b kfy ayp1(rs*k1w away from the negative terminal in the circuit. But within the cell, electrok : xpx+1brqag- sv1kp(zy5dxy*x f6)ns flow to the negative terminal. Explain.

When a flashlight is operated, what is being used up: tip +xv3(zp7 2is pq,obattery current, battery voltage, battery energy, battery power, or battersi2p,x(q vp7 + zitp3oy resistance? Explain.

One terminal of a car kb1hmi +-3slbpkuokv-sd(9.4 r ;dgj battery is said to be connected to “ground.” Since it is not really c31kdrdkgov- 9.ulb ( spmh+i k-jb4s; onnected to the ground, what is meant by this expression?

When you turn on a water faucet, the water usually flows immediat)2q zxyzlu 1ro(2vwu3+uy: ui ely. You don’t have to wait for water to flowz y32+1zyi ) u:vux(r2luqw uo from the faucet valve to the 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 ha j,( dw*jdna vq;u4ar +vxl0f:ve the same resistancx q*duaa;vw+:0 jdf4 ljr n(,ve? Explain.

If the resistance of a small immersion hea29asp n6mc*jo n5-7j1b xheleter (to heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow down the heans2o9-j lec 6h7m5an*xbjpe 1ting process? Explain.

If a rectangular soli+j 9zv* chj1rr*s1 ysad made of carbon 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 gre* yr1 9ascsjh*1 +jvzratest 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+ 5bf* )tl/4(uit u jhnf2slue out?

Explain why lightbulbs almost always burn out just as they are tur9w uqw+l3 c8pwned on and not after they have been on for some 93c uwlp8qw +wtime.

Which draws more current, a 100-W lightbtvxy-v -b-fz qzn;56 wulb or a 75-W bulb? Which has the higher resistn-z6q-tz;bw fx v-vy 5ance?

Electric power is transferred over lxg.tn5b:05 8c uqhgtif 3,m hsarge distances at very high voltages. Explain hou5 .gb t 0:chstq3mxg,fin 5h8w the high voltage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replace thisjfeahlhuz9y***lg8 rj;s /q d *:u1ir fuse with a 25-A fusl**1l d:rq isfrg yj/huj u9;a*eh*8z e?

When electric lights are operatedtfe;gkr+ e6p 1*hq(ns on low-frequency ac (say, 5 Hz), they flicker noticeabs rqf gen61+hkt;ep(* ly. Why?

Driven by ac power, the same electrons pass back and forth through your rea ,t;x.juh)cebding lamp over and over again. Explaijch )eutx .;,bn why the light stays lit instead of going out after the first pass of electrons.

The heating element in a toaq3u 3b58w ja-bzrz d3. 8td(obsn+duester is made of Nichrome wire. Immediately after the toaster is turned onjq. adsud+nzo38bd3 r38t( wu5ez b b-, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a r l-,h/-6di owi,hbyfu esistor? Explain.

Different lamps might have batteries connected in either of83nbb *;kxu wn the two arrangements shown in b*b3xwunnk 8;
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many electrons af/dl;nzkc 0 -qre flowing past any point in the wire0/nz flkdqc ;- per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A for 5.0q(/ 4ukafl o2 c+:io i68ks-aw3uckr d h. How much chok-oq sd(wua /48rfu3 :cac6+ik2i klarge passes through the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes 9 x4rao52glkfif $1200\,Na^+$ 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 12neil;h tvrsn0( 0w ,zda+pmi k(0v0ye(gz8s(0 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of cur3 draqly j,i70rent through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when plugged inspr6:k z ,js;2li4rdw to a 120-V line.
(a) What is its resistance?    $\Omega$
(b) How much charge passes through it in 15 min? (Assume direct current.)    $ \times10^{ 3}\;C$

  An electric clothes dryer has a heating element with a z,a6dl wzes +mv2ii* 6resistance of $9.6-\Omega$.
(a) What is the current in the element when it is connected to 240 V?    A
(b) How much charge passes through the element in 50 min?    $ \times10^{ 4}\;C$

  A 9.0-V battery is connected to a bulb whose resistancm9 /cse+p/8pnw6 cg)b3wcui je is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc elnnm,xz m ycn +192wa wm(0p:ujectric transmission line carrying 2800 A (Fig. 18–34). Thczuw0xp(m9 ny1j2aw+nm,:m ne line 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 ar 7wum7an58dut 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 amd.tfnui:lh ob;b 95 6u5m9ia current 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 wire whose resistance isa.ts un788js/bgymu b: 6l ctzh1h:5y $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1.5 mn x0kza:;loz i1zy3*tm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m i, vjoroyv 2sq 3*d9n/o 9+o2tkzgm9vof aluminum wire 2.0 mm in diameter, to 20.0 v9 32z*/i,oqd ynvo+gs2 9ok9 jtovrmm of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter cop wjo.p3c -euu-per wire have the same resistance as a tungsten wire of the same length? Give numerical details- c 3.-eujpuow.    mm

  A certain copper wire has a resicizv)+/ )2rj8xs snac;7 jbldstance 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 rai+231tvm ajq cd1 3tsu9ql*yj mse the temperature of a copper wire (originally atyu +jjq31tml3m*scaqd29 t v1 $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper wih2vlrq (uiv56g 6h tk* h4jmj:ll have the same resistivity as tungsten does at 45gvu6l( 2v h h*:qtmk6jhijr$20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has am;c tmaja7 76xb7vt+ q resistance 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 a0s)2z:0o ygu zmmmm s5long a 26-m length of household no. 14 copper wire (used in 15-A circuits). The wire has diameterm5s g00:mymz2 su)moz 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm, 2.0 fay(- wrvmoxu.4 h u*nta-*u *cm, and 4.0 cm, lying along the x, y, and z axes, respecvn*u-o(*w4ayt * urfa. ux-hmtively (Fig. 18–35). Determine 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 have th/ c,*awh 2nzave same resistance. If one has twice the length of the other, what is the ratio of the diameter of the longer wire to the diameter owzhn, /2 a*cavf the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V po d0 p6 sjm2/*umk ghbh4bdps./reyv 6/wer supply, and a currentb2s gpj0h/dbhvd* syre.4/6p/m u6km 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 alm5rttb 8a6rf; uminum, both of diameter 1.0 mm. A volta btar8fmrt6;5ge 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 ome ivv9mxz7w12))e iqf a resistance not change w2vx97 mi)zmv eqe i1)with temperature. 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 electrsg7 2 -17nidbcuwb mf6q, rza6ic oven is designed to produce 3.3 kW of heat when connected to a 24r 7i 6,26b1-7zdqb wscgumfan0-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consrp ihtqf9 35a0umption of a 3.0-V portable CD player that draws a maximum of 320t 35qahr9ifp0 mA of current?    W

  What is the maximum voltage that ca/*v gs yov-uk5ii tr6(n 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*yg t lwq0jpc-r19 r3i-W lightbulb connected rg i0*twryp -q391lcjto its proper 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 at 110 W. Calcul9muhooa5bn*4)z.b1abmv :o i l1h w8pate
(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 setting;b.,rfd cz6tl p1r7iapv5m9 e s: 850 W and 1250 W.
(a) At which setting do you expect the resistance to be higher? After making a guess, determine the resistance at
(b) the lower setting;    $\Omega$
(c) the higher setting.    $\Omega$

  You buy a 75-W lightbulb in Europe, where electricity is delivered to kmdp:m 9fm-k 9homes at 240 V. If you use the lightbulb in the United States at 120 V (assume its resistance does not change), how bright will9mm mp-9:kd fk 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 is in us798sle+ 9q5 tdo 1 ix9culocoperation for a tlu 8 17 s9sqoot5e9 ux+ci9dlcotal of 15 min? At a cost of $9.0\,cents/kWh$, estimate how much this would add to your monthly electric energy bill if you made toast four mornings per week.
energy $\approx$    kWh
cost $\approx$    cents/mouth

  At 0.095 dollars per kWh, what does it cost to leave a 25-W porch light on day aev-pbo:f dw+ n6(r1q wnd night:-n (fwervb16p qow +d for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connected in series as igm54-8geqrfm n Fig. 18–4b (Fig. 18–36). The bulb draws 450 m48mr fm5g-eqgA 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 energ+yd2wkkm+9mcqvtmf(,ec4 xwsg ,) u3y 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,lbkrn2w +c 1qwdv* :y–20, can be used without blowing a 15-A fu 1vw bd2lk,qcr*+n y:wse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 copper w ujiisv ,l+bn1)7mr;1 e, kt2jxpv*ha o9vu k5ire) 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 xtu 2,ip,i*j a;os 7kub v51mnjk1lv9vr+h)e the cord?    W

  A power station delivers 620 kW of power at 12,0mq.t/z omn;:l0z ef9b00 V to a factory through wires with toebftzm9l q/z :0;.nmotal 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 5q4vn+k5su pxted to a 240-V line is 17.5 A. At what rate must cooling water pass over the coil s4+5vnxu5 qkps if the water temperature is to rise by no more than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can im4xv8 lrhi 9 n0r(p1fbe used in a car to heat a cup of water for coffee or tea. If the heater capv4h01n 9 xr8(imrlifn 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 current injc/q: k l71nim 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 acros5/o(s ds.l 6d7eyvvw cs 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 resistand/:rsz*wm 5c :njci( b7we7 qrce 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 device0(p w0ie+x *bcbx4wu y is 5.4 A. What is the rms voltage across it? bucw0 4(eyp wx*0+bx i    V (Round to the nearest integer)

  An 1800-W arc welder is connectedx;c 1;c p*lgj67mezj5 ys3orn/j q4rn 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 dissieljt /6j;m(c , vj,(s nkq5b4/ lfarzepated by a 3.0-hp pump connecte4ks;elvl ( r (jn5,zj j m6f/qtea,c/bd to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connect.s h;zps0os,65 dsy paed 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 tini73n-qan -q y ai49tsxy 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 c)knwu 3 s9ssfrg2/x p r7max9:arries a 750-mA current when 22.0 mV isr:r9swu 3 p9 sf kx/27a)smngx applied to its ends. If the drift speed is $ 1.7\times10^{-5 }\;m/s$, determine
(a) the resistance R of the wire, $\approx$    $\Omega$(retain three decimal places)
(b) the resistivity $\rho$.    $ \times10^{-8 }\;\Omega\cdot m$
(c) the number n of free electrons per unit volume.    $ \times10^{28 }\;e^-/m^3$

  At a point high in the Earthp .dl7;qry t3mzw )3ns’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 Ear up6a.qnxizhnyp(1,2 th’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 field across an axon membrcxka6o002 l/o cui, zc;jqq; wane $ 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 potentialsp z4 -uvl4s2l 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 measurements needed instead of o4 zslpl u-v42snly one?)    m/s

  Estimate how much energy is required to transmit one action potential aloqz(1z4fh 2lhi-ei:va ng the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the enerzf(- ih:21iqvzh l ae4gy 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 potentia )p1,px obu30 ;a sanl1, idpw6cdqum(l, $Na^+$ 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 arvm4w5qu0ge-f6 -xw6 sasl:p-w1dndv e there in 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0-hp 120-V m5p4 ,qg3) qvoegl-v-w9uuo alotor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally lee16yio)x 2w(w,g0xy+d o wpllaves a car with the lights on. If each of the two headlights uses 40 W and each of the two tail o y2e xwlpi d01w(wlx)+6gy,olights 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 of a 110-V, 1500-W heater is 5nr8) mk0n+zv 9q0h 8dmf jut/h.4 m long. If it is made of iron, what must its diameter bez0)8 u+m0 qmrnk j/v9ndhf8t h?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the 9g3ekk g 2vd;qreciprocal of the resistance R; the2 gvq9 kgkd;3at 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 dgril,q*a( ssasqm s u+kr.y n/* ;n;,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. Assume the cos q n+asl.r (g,dui ns;y;,mq*k/*assrt of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular household uses a 1.8jt9d7o .z3pz;pq1 k /s hks +dibtje)+-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 q x 8ppuiyenh0v(:;pw sot ke:) /4w5qin half and the two lengths are wrapped together side by side to make a thicker wire. How does the resistance of (;w0k:yipxtoq5hqwv/4 )enp 8 s:pe uthis new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is deqp+4ej.bw2u dsigned for 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 hot as, f-zbt : 1nc/nw5o/ntwyg.x b to start a fire. What diameter must a copper wire be if it is to carry a maximum current of 35 A a nx,t:zf-b y.ng/wnc1ob5tw/ nd produce no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given b+w rzy.8n-sogzly1 k *y 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 d2g+ /mdpl+ dy1 ehn)hbw (6njay7p)zyelivers 950 W of energy per second to the i +p6+z21ny() hdndplmaye/7h) b ygjwnterior. 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 of5t)8bk ho3 ;gx bxjr;f-jn dv+ the same material. One conductor is twice as long and twice the diameter of the second. What is the ratio of the power transd8t r );bxv+3gb5fjoh ;xj-nk formed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a room .h -yrluvvz) ;, ggi ea06r/ldof 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 hooj-z7s: :racn zu*als:e5vs6 hked to a 240-V source.
(a) What is the resistance of the oven?    $\Omega$
(b) How long will it take to bring 120 mL of 15$^{\circ}\,C$ water to 100$^{\circ}\,C$ assuming 75% efficiency?    s
(c) How much will this cost at $11 cents/kWh?$    cents

  A projected electric vehicle makes use of storage batteries as its sourceit lur3pax 0/wno00y1.i vxs; of energy. Its mass is 1560 kg and it is powerw.0xtx1 ilu /isrv y 3n0;aop0ed 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 has a resistance of ia6f lp7b xp-o1)ffip3j9a* f $12\Omega$ 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 y cnq;scle7 (b(9j z)xto carry an 11-mA beam of protons l sxj c; (zn7(b9e)yqctraveling 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 at 220-V ac. The connecting corbaj5p5) 6gyfrvg, +ywd is copper wire with a diameter of 1.628 w5vfayypjb5+gg, )6 r 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 g-op0cl*cq(p connected to 120 V. The heating element is a coil of Nichrome gq pcl(*p 0-ocwire. 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 voltage varies from about 12 V when the car is oq:s7l 0jb:b*,e xn zisy:kc9v6 j/zg vff to about 13.8 V when the car is on and the charging system is in operation, a differeksy:cnlb::sx j9*j6 i/7,0geq zb vzvnce 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 household applications. Lightbul:7p 6nw:fx;i ffduy8q 7s l9lgb B is rate:pqfl xfuil97 y f867w ngds:;d at 12 V 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 crea (hn*5c.t) hv+y laonnect a set of appliances at 120 V, which draw 2250 W of power total)aa(yhh .ec5r *+nvtl.
(a) What power is wasted in 25.0 m of this wire?    W
(b) What is your answer if wire of diameter 0.412 cm is used?    W

  A copper pipe has an inside diameter of 3.00pb lnv, rzl v,eh*+s4; cm and an outside diameter of 5.00 cm (Fig. 1*+ v zpl,; ,v4hlnerbs8–37). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its lengthuu. s 05m( vh oqvb)bacowu14y645 heb doubles, by what factor does the power dissipated in the wire ch5 4bvb(1bh h.u6a)ysq4w0m ueco uov5ange, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operates at 0.20 pdb3s e +o(p +hh7m zt5:9tcrmA and 3.2 V. If its resistance actd pem+ t p+7mb9hr:(oz3h5st 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$