What quantity is measured by a battery raqp nn /zl;ys w ad+6,f9,n)kmpting given in ampere-hours $(A\cdot H)$ ?

When an electric cell is lk. vsp8mnb-83a (jemva8g 5bconnected to a circuit, electrons flow away from the negative terminal in the circuit. But within the cell, electrons flow to the negative termbm (. vs8gv m3paa5e-bj 8lnk8inal. Explain.

When a flashlight is operated, what is being used up: battery 5ma/rvm-o- fe current, battery voltage, bef-m-mv / oar5attery energy, battery power, or battery resistance? Explain.

One terminal of a car battery is said to be connected to,o8z kgx2pp(6i s6v sf “ground.” Since it is not really conneiss6op f,x v8p(z62 gkcted to the ground, what is meant by this expression?

When you turn on a water faucet, the water usually flows immediat5p .hhzi +4pfr:sgg0r/ps8m xely. 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 connect a wire t/pgx5h +0rrh fpg ssp4m 8:zi.o the terminals of a battery?

Can a copper wire and an aluminum wirew: b1yfpof 7iht;q)( u of the same length have the same resistance?p (iq1ht7o )wf;f:uyb Explain.

If the resistance of a small immersion heater (to heat way4e d.zp xcjc8h2)wypo-0*x w x qrm+5ter for tea or soup, Figjqmcxx oyc+y58w 4*2h .re -wpzx0p)d . 18–32) was increased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of8d7 uh -pxi;oc carbon has sides of lengths a, 2a, and 3a, how would you connect the wires from a battepuoh8dc7i -; xry 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 outm-5gpsaxx60 *6 a mnjv?

Explain why lightbulbs almost always burn oz vyczn*+1ly 1ut just as they are turned on and not after the lnc1*vzyz1 +yy have been on for some time.

Which draws more current, a 100-W lightbulyfi,2f/h5ood 7 asg)o b or a 75-W bulb? Which has the higher resistanceg)h o27oa5s yiff,od/?

Electric power is transferred over large t a8; z/njsp *aw9qjvi0 64qvrdpt.2xdistances at very high voltages. Explain how the 4.2q6jnv*;ap 80dt txsvrz9qw p/ia j high voltage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous r c;ly rpbc7jyct6/6 5i+rwqgxvs2*:to replace this fuse with a 25-A f;/ybr:*6c 27 tj 6c5xrv q+cyirwgpsluse?

When electric lights a*cux9zp8gt:h ef+; ig re operated on low-frequency ac (say, 5 Hz), they flicker noticeabie9x:p8f* g+;thzucg ly. Why?

Driven by ac power, the same electrons pass bac-wl 3s *iw,pq.o xc (yxe7hn)m+ael9u k and forth through your reading lamp over and over again. Explain why the light stays lit instead of going out after the first 7 ec.qpw+ lesw9nou3(iy hlxm)- a*x,pass of electrons.

The heating element in a toaster is made of Nichrome wire. Immediak;;ejbwkx* u8tely after the toastejekb;u*8x w ;kr is turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistozdkc; cjsv3n6qv 0/ )zr? Explain.

Different lamps might haf1u+t 4nhkpou/j-9 arve batteries connected in either of the two arrangements shown in 94f ntu1r+au/h pkj-o
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. H,fc ss pxg20 ssj7)7gkow many electrons are flowing past any point in the wire per ,0s7g ssk cf7x) gspj2second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A for 5.krj zt6bn a3*mbb5s;dd; h5/ q0 h. How much charge passezr*bm5jdh nbt s6;a d53;b k/qs through the battery?    $ \times10^{ 5}\;C$

  What is the current in amperes if ls93u .r;fvd1 ao7x+.c 9 ab8ufmmzkm9-fzi l$1200\,Na^+$ 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 torvc n4l5ml8 b.aster if 120 V produces a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current through a-hso+tllw 6xs5o 7ro/ $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when:2vz.xd7 w ewy plugged 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 heating elsy dw)g-x( x5pement 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 whose resistance is lgr of-912zsv $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transmission linebysg.g bdzz:n8a0 (w:kjl ;3 v carrying 2800 A (Fig. 18–34). The linzg:;b : ydzbvj8s(w g3n0ak l.e 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 249nx 3an*b cn2-hamxe (0 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 cu qs(qe;zvpn;hgk jo5v jho)0(0/d0mp rrent 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 osd o3 88vph9efk puak: sd 05vo beri;sx.y::7f a 1.00-m length of tungsten wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance o6xq) c;hkwz 17 ;39amuifla fcf 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 2.0 mm in diamwk 9)rd45vv wqeter, to 20.0 m of copper wire 4wvv59k rq wd)2.5 mm in diameter.   

  Can a 2.5-mm-diameter copa4vlbeb4i2esv h9 ,f9my,i9vnk 05 owper wire have the same resistance as a tungsten wire of the same binefm k vs0wa4 ,l,59 hbvv2iy994eo length? Give numerical details.    mm

  A certain copper wire has a resispd)v ;1c w.g2kquvmsuq az714j:j : iktance 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 (ov op0cv kqh8)wt 06qi9riginally at00pqv96oiv khqwt c8) $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same reu3 s73 udfqlzjn2j ;6zt(x 2elsistivity as tungsten doesq3 nust ;f32z2 djl 6jelxu(z7 at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a re8 gllv 68k *z0abkrujtbn:1b7sistance 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 hosv )e8djbx ci)(fz75wusehold no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm and carries a 12-A currejv87x) i sbewc(5fz d)nt.    V

  A rectangular solid made of carbon has sides of lengths 1.z0ei ztd;039pzj u+b i: hylw00 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectivelyy03;il:zzje u0tdh b zw+p09 i (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 the same resistance. If one has tz2kthb 4oo;m 2wice the length of the other, what is the ratio of the diameter of the longer 2t4kmz2bh ; oowire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision vwst60p3.mal 10.00-V power supply, and a cs.a6mltwv 3p0urrent 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 u.a rul(8h0k f5.0 m of aluminum, both of diameter 1.0 mm. A voltag(fr0.k a 8hulue 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 re,.9y,db / lrkr .h8pxenz2gm bsistance not change with temperature. For exa,82xglmn/ p br hy,e.z rk9db.mple, 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 hgv/ftnaw: m3x-al1c+t.j+ ,r ol6 zbto produce 3.3 kW of heat whwf6alcmgbj -+,to v3 xt/:hnar.1 zl+en connected to a 240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player that d33f//o i m87j3jv7qsdq fe brvraws a maximum of 320 8qvd mrjvj7 qo3ef 73s/ /3bifmA of current?    W

  What is the maximum voltage thatujws58oe 0 .4u zww;xi can be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, andmo8(p/-eluu ldn 2u 2b current through, a 75-W lightbulb connected to its propelul8upn2bm-(2e od u/r 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 ratef)8c7d od/vdau m(lzm+m cu29ikw2 *aw3kx5 pd at 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 settings: 850 W dx8 se*kys:3land 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 h0h6gqq r5:mby omes 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 proportional to power con0rmq:5qb gy 6hsumed.]    as bright

  How many kWh of energy does a 550-W toaster u/ccnq: 7 pi1ljj/gk/ f/g9 :lk8cgluose in the morning if it is in operation igccl9 8okc7/ /j1: /qgk/ j:glufp lnfor 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 ts3kyr+m3dh 1 does it cost to leave a 25-W porch light on day and3t1+m3yd ks rh night for a year? $\approx$    dollars

  An ordinary flashlight uses ug0eyc/tv .t keer;1j5 12 ccetwo D-cell 1.5-V batteries connected in series as in2 ru/ec etkje5v gce 1c;.t0y1 Fig. 18–4b (Fig. 18–36). 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 amount of energy storeda-wo qjfq5bm p9)35 (au pmd+b 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 5uxop4 5 *mrphin Fig. 18–20, can be used without b5mr*o p4u5h pxlowing a 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. zcgl3kk.5m0m qu w3my 7c-)nu16 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 mu)wlc.ym gcz3 knk-u 0mu537qmch power is dissipated in the cord?    W

  A power station delivers 620 kW of power at 12,000 V to a factory througcgcx;;v1* +.jqjwvikyq7)e bh wires with total resistj eq) jv7. ;;*yxw1bvqgcki +cance $3.0\Omega$ 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 conne( )(i5dx/n1weh9t qnel ys(4y;opgdwcted to a 240-V line is 17.5 A. At what rate must cooling water pass oqno g/( en ;)i5wxpw(e4 ytydlsh(9d1ver 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 c;,co0+8 jte/* xx ,k yrtphh 0k-rmnfkup of water for coffee or tea. If the heat,jt/+y0e hkk to n -p;rf,x*c8 rkm0xher 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 current ink:qsc 13-o- fc*aggjb a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V,61t5,evzfjw. vw3 4m)mkfcp78ivbv w is 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 thew(,6r qgc*r g0asita qp9- ub 49uz0fm $120-V_{rms}$ 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 15 mhncvc4e:81c 00-W device is 5.4 A. What is thc:ehnc14 mcv 8e rms voltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connecte 4n k)f vm:(7mei.zuayd 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 dissipated by a 3.0-hp pump 51 x3 8g6;+6bbebtvkkqml p mkconnected to ek1bb3gbm;6tpk5 6m k8ql v x+a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to afq,t9 )p ;9 vs2x6ijwzqia;za $240-V_{rms}$ 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+i pbx-*jy jv8 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-ts9 60.bevybw 9a lb3umm-diameter wire carries a 750-mA current when 22.0 mV is applied to its enu9b3s.ba9w 6 vtbye0lds. 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) kpldjw gvj3f; 4n4b1’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 zw r k7ag:;(t1oraa(fbe+ mzc .x.(rxus+;ks 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 magnitude of the electric field across an axon memfvv8d2iza. y )brane $ 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 potentialcf94ednq l 6vk5 8opa)37g pnx 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. Wh9n foak)nq85p4 e dgc73p vl6xat 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 alox6xa/d joon;) ng the axon of Example 18–15. ; jxa x/nod)o6[Hint: the energy to transmit one pulse is equivalent to the energy stored by charging the axon capacitance; see Section 17–9]. What minimum average power is required for $10^4$ neurons each transmitting 100 pulses per second?
E =    $ \times10^{-11 }\;J$
P =    $ \times10^{-5 }\;W$

  During an action potential, gn(h q*e0ebc9$Na^+$ 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-hour7 b0nmqi fa0 :y+zwm4p?    C

  What is the average current drawn:tj v,;9w .nqwion 3sj by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights mric4tmcbp2d-ey* 1*on. If each of the two headligh2p mmt yc1*d4*ec-ribts uses 40 W and each of the two taillights 6 W, for a total of 92 W, how long will a fresh 12-V battery 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. If it 9a6a-5 mu(4mmj9gupel usv4w is made of iron, what must its diamete4 ga -uw9je(4v5a6smpmu lu9m r be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of the resista1vcvc rzzg5ey4 -bq.6nce R; that r5b4q yzv-zv gc.ec16 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 s-*:(yftje,ougfsp/ about 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 enerje(s*s y/:,-utof gpfgy 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-kWpr1j 16l8 jb,6vhfui h 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 in half and the two lengths are wrapped together side by*ijfl/6;0 ju3l+eufa )i qv nn side to make a thicker wire. How does the relj;) *failf niqu/06jenv u+3sistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for 117 V. 5 qw(-e2ut c+8xr buxz
(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 hoi5om g59ormk .t as to start a fire. What diameter must a co9 5k o5mm.ogirpper 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 given by the equat ,moqm bbz7us6).ae )aion $I\,=\,1.80sin210t$, 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 detlgh w ju/)s9a-b.vv3 livers 950 W of energy per second to b)sv/ut g3 -hl ajv9.wthe 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 cukh.( n gk 6qglcg3 ;y,3khsw3onductors made of the same material. One conductor is twice as long and twice the diameter of the second. What is the ratio of the pown3y kh glkgsu.,336 qk cgw;(her transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to hea,tu *nm c8-7 hek7 bjolmru*u0t 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 1unon tz(b ucx qbzga1/u00 6.240-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 ofnss6);0ygqs c+wm 7g m storage batteries as its source of energy. Its mass isnq c07smg; +sy6gm)w s 1560 kg 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 lightbulb has a resisv(kn*wgthqws29kctyib6jy 6 )-- y 6 utance 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 accelerah-(5jbo - sblsbm+o 5gtor at Fermilab (Illinois) is designed to carry an 11-mA beam of protons traveling at very nearly the speed mbhbg 5-(o-sl +sbo5jof 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 witr9 l/kqhkyw )9q.wp(re with a diat y.hkqw9k(w/rl9q) pmeter 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. * 9nwbj5 pbvy0r+x uspc(z p74The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What is the dia9p rzw5j pv7p bcbnus0 (*4x+ymeter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from aboubyf+qvdx5+9i,v; cgw t 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%. By what percentage does the power delivered to fxqv+yvi9w;5+, gdcb 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 ;(6e (jcmogz oayct 2zc1j0q n:s/fp4for household applications. Lightbulb B is rated at 12 V and 40 W for auo6acen z12ojz:0c j/ f(qtc(s;m gp4ytomotive 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 ofi -bt;c/ snc(l appliances at 120 V, which draw -tslcc; /b(ni2250 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 diameterp e*:-6l)cw ;vn cbrnw of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37). What is the resistance of 10. wc v;b)pe*c-:nlrwn60 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that ipo(2y4-k( trnnavoj.9nw,ck li z +3ots length doubles, by what factor does the power dissipated in the wire change, assuming it rcn(4(yi ltpo9 jo 3zv2n,kakro -+ wn.emains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operateszr;hs ++zguoq5 6n -kg at 0.20 A and 3.2 V. If its resistance a g+n;5qrzoku 6sz+ h-gt 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$