What quantity is measured by a battery rating given iy2c z2xq8cn 0pn ampere-hours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, yt5qhmd8 a- 8celectrons flow away from the negative tem8ah tqc58d y-rminal in the circuit. But within the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated; e)bs*:;lhdfjnb17n 4ta ay 0a(pbdx, what is being used up: battery current, battery voltage, battery energy, battery power, or battery resistance )ld( hb1 j4de b0n:tspaxb7f;n;y*aa? Explain.

One terminal of a car battery is said to be connected to “ground.” Sinu/w 2w(cn3kfkce it is not really connected to the ground, whw3(u cknwkf2 /at is meant by this expression?

When you turn on a water faucet, the water usually flows immk5dtkbw0w7 i ;ediately. 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 conneitkdb0;5wk w7 ct a wire to the terminals of a battery?

Can a copper wire and 3-xedp2k1)oxs( wm/b du7n; *pzqyi dan aluminum wire of the same length have the same resistance? Explsw- qn)1 d k(*/eo27xpy;m3xdpi budzain.

If the resistance of a small immersion heater (to heat waterj.isco v o/1yd 3m* v:qz20lfy for tea or soup, Fig. 18–32) was increased, would it speed up or slow downfm.coqz:odj20sv l y* /yv1i3 the heating process? Explain.

If a rectangular solid made of carbon has sides of lsx t fnhhq/78nh,w .)xqve ;a:engths a, 2a, and 3a, how would you connect the wires from a battery so as to obtain (a) the least resistanxnn8htw ) e: ;ah,fsv.7x/qqhce, (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 burnie eoad*i *:+v can,w+s out?

Explain why lightbulbs almost always burn okxk8hi jjd)06f w)3 zbut just as they are turned on and not)086zd3 jhfb jixk) kw after they have been on for some time.

Which draws more current, a 100-W lightbulb or a5 s67n*rqjmaze7 5dzy 75-W bulb? Which has the higher resistancer zsed j65yqam7n57* z?

Electric power is transferred over larx1a:1p3srf ktge distances at very high voltages. Explaink:atpsrf31x 1 how the high voltage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it da oq w15 5:brd86hwwlsxngerous to replace this fuse with a 25-A fuxq 6bl h 1sdwo5:5wwr8se?

When electric lights are operated mip-8mcf7vmi s+x..e on low-frequency ac (say, 5 Hz), they flicker noticeam..smev i xm7f+c-i 8pbly. Why?

Driven by ac power, the same electrons pass back and forth throught )*py )pjnuo. your reading lamp over and over again. Explain why the light stays lit instead of going out after the yu nt*op).jp)first pass of electrons.

The heating element in a toaster is madeu5ai- w9taqw 9 of Nichrome wire. Immediately after the toaster is turned on, is the current aq-w9iwa tu95 $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resi f0n+fbx,g(ce y9q7+4 t,lax0tql tzjstor? Explain.

Different lamps might have batteries connected in either of theyt gl7 ugf sa q+) jr*b-7xx9.w7qp2vm two arrangementsrqapl2jb7-q*7) tx s.uy g+ f7wm9gvx shown 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 f6ay)c7f v )zmtr5k ml9lowing past any point in the wire 59z7v)) t lykf6ammcr per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of 6.7 A for 5.0 h. How mmj5mav8j k5l;hjm)b r) o:j(buch charge passes through ;vr8a :mml( jjj)bkho j5bm)5the battery?    $ \times10^{ 5}\;C$

  What is the current in wxd) 1mkmvwn0a:f5 h,b 7 nkx3;wuu3kamperes if $1200\,Na^+$ ions flow across a cell membrane in $3.5\mu s$? The charge on the sodium is the same as on an electron, but positive.    $ \times10^{-11 }\;A$

  What is the resistance of a toaster if 120 V produces ay,q exs; h 8g80hxhhum5x h78s current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current throug3zc4)m;lf. al pnt*ay h a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when pluggev6(v. ygjks;7gryk z)t89lm kcn.1 vgd 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 element with aqkcsky2 6vau*hiyqq)tc np;;( wbi+2(2 5 fng 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 connectp:9g o 0rwa b(bej7cxu 5w-w;hed to a 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 carr0 qk3o;9 bclomying 2800 A (Fig. 18–34). The line hasql3m b90 kcoo; $2.5\times10^{ -5}\;\Omega$ 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 240 Va8q+mu 7w(ib r.
(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 resinio/ym x /1p.7bbo*tvo-oh;yyf s 6b6 stor.
(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 tungstetv.zv.3m t5pao8lk q5n wire whose resistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistancej-cbs- v/ x9 pm7h xb oxiqrch)5m/*c5 of 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 alumin qcw) 7 047atxi2uoc*/ hwuhqoum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in diameter. hi u wq 7xq) h2ac/074t*cowuo   

  Can a 2.5-mm-diameter copmsu q2 d4rt0.tper wire have the same resistance as a tungsten wire of the same length? Give numerical details. sdt2t.rm qu04   mm

  A certain copper wire has a resistance of pn+q8-xys3lin 6ah /0w ukpj*$10.0\Omega$ 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 horst (w9hg29wave to raise the temperature of a copper wire (originally at2t9row9h wg( s $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivity as tun(3x4 7mcq zvb1ic)f:dp z*ua ugsten does vp:q d i(ubz*4zc )au3f17m xcat $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistav3ws)trbz;xm8yz1 rgp, a . 0q ;s(usynce 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 alor)l.k:8 u ckaj2b:zmzng a 26-m length of household no. 14 copper wire (used in 15-A circuits). The wire has diameter 1.628 mm and carries a 12-A :kjcazkz :ur2b). m8 lcurrent.    V

  A rectangular solid made of carbon has sides of lengths 1.0 cm, 2.0 ca/( 5 vfkrno0wm, and 4.0 cm, lying along the x, y, and z axes, respe0(/kfnw r5ao vctively (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 restks)kaiy*s )-/wk nj:b+fh w/ istance. If one has twice the length of the other, what is the ratio of the diameter of the longer wire to the diameter of the shorter wire?i/bs +/kh kw)*:f jt)sank-y w $\approx$    (retain three decimal places)

  A length of aluminum wire is connected to a precision 10.00-V powegt s2j/fy /yyo+ju+w 4r supply, and a current of 0.4212 A is precisely measure4jyw fy+/t/+2jugyo s d 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 follow. u hz7r3k+p-6k y)ybezsxe5ked by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is plsx 6re)+ euk-y k3bz.hp7k5 zyaced 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 rmq5*y0z oglfc+xr5 cqqejk: -)z8p9besistance not change with temperature. For example, suppose58*q) 0m zc+z q:eyq5g oc-rlbxpk9jf you made a $4.70-k\Omega$ resistor from a carbon resistor and a Nichrome wire-wound resistor connected together so the total resistance is the sum of their separate resistances. What value should each of these resistors have (at 0$^{\circ}\,C$) so that the combination is temperature independent?
$R_{0C}$   $\Omega$
$R_{0N}$   $\Omega$

  The heating element of an electric oven is designed to produhpr .jm;jp.:-hu(zaetd*7io ce 3.3 kW of heat when connected to a 240-V source. What must be theurh;io. d p.j-htz j*7e(pa:m resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player tgx(t 9vg h9i2hhat draws a maximt9h(9h vgix2 gum of 320 mA of current?    W

  What is the maximum voltage that cankeb*l9w.ij r9 be applied across a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, a 75-W l+h92boxo*ym5ll(ul 6kap(6 jg.bqxcightbulb connected to its proper sb9uljx+x6 ph(* goa.oy2 ql cmb56 kl(ource 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 - 9pvsi49iqjq 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 am06f0 *ncg u;cj7jn hvnd 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 homes ixoj7b .8k65rc/ r ymx;t y6jwat 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 r r yr6wx8j7jybmt 5k/cx6. ;oielative 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 vtn z.(av;/di operation for a total . tvz(;/nav diof 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 lixjkuxjrw 1; m4,a4p1f ght on day and nigux aj44 k;xmrf1 w1p,jht for a year? $\approx$    dollars

  An ordinary flashlight uses two D-cell 1.5-V batteries connef,l 4 x-1dpknqcted in series as in Fig. 18–4b (Fig. 1dfx-1 4knqpl,8–36). 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 amoun0vlzdhn9z* sw3 ni33,fob u/qx9w( xot of energy stored in a 12-V, $85-A\cdot h$ car battery when it is fully charged?    $ \times10^{6 }\;J$

  How many 100-W lightbulbs, connected to 120 V as in Fig. 18–20, can07tbv ,rw;b6f9 w:i8z imt sjr be used without blowing a 15-A fus, b i wi6bft8sm7w0;vrj9z:tr e?    bulbs

  An extension cord made o/cq-lbml7xg 0vftrv.c26z 3ff 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.b .c32xv ff7t lz0l/-rmgcq6 v0 A on a 120-V line. How much power is dissipated in the cord?    W

  A power station delivers 620 kW of power at 12,000 V tfzx*pa -3(: sdmlo g)y-1tzhdo a factory through wires witfa- 3d:* xyml s-t )1hzog(pdzh total 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 2t 21,tpwsqdb+ 40-V line is 17.5 A. At what rate must cooling water pab2+dttpsq ,1 wss 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 rzir.*3y gn;e a cup of water for coffee or tea. If the heater can heat 120 mL of i3;r .gry*nezwater 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 invl : hy-t8.ly,rpal+i 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 across2d9wf d vanaca,v. jb0x zr*-; 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 the; y:07vv7+qo *vxxz *rtp c3vg(jq9 rqmtg:oj $120-V_{rms}$ circuits in your house as seen by the power company, when
(a) everything electrical is unplugged,
(b) there is a lone 75-W lightbulb burning.    $\Omega$

  The peak value of an alternating current in a 1500-W device is 5.4 A. Wh 12mh )4oz o,g.m sdmt*;fkpavs y52adat is the rms volts*; hsyd akv4o a 2)1go2.tmfp,dmz 5mage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connf, -- lu1yivmq 292/l;jdd ftfa(zc nkected 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 instantaneo3h1 /tcv)+ugxylgfzl+c v 7)kus power dissipated by a 3.0-hp pump connected hgu/x ktlg+c z))c1v +yfl7v 3to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connectqo;pif lda ;.4ed 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 co yj 3i5.*j1+sqn vl t;hm8mb1o9ebd*yja6dm lpper wire carries a tiny current of $2.3\mu A$. What is the electron drift speed in the wire?    $ \times10^{-10 }\;m/s$

  A 5.80-m length of 2.0er 7-6bc wft*p-mm-diameter wire carries a 750-mA current when 22.0 mV is applied to its ends. If r-7t6f* ebpw cthe 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’s atmospher,7,y 33pfgwfjd* yxbbyw, s;ye, $He^{2+}$ 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 atmosphere, j0br-7 vxto 1q$He^{2+}$ 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 +n3h:xhg cx9jfw(sumr 81 n(t an axon membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulatedbmvqgh2 .rt urbdx:9jab7,) * with an electric pulse. The action potential is detected at a point 3.40 cm down the axon 0.0052 s later. When the action potential is detected 7.20 cm from the point of stimulation, the time required is 0.0063 s. What is the speed of the electric pulse along the axon? (Why are t) uvbh,q g7rrbjba.x*:t9m 2dwo measurements needed instead of only one?)    m/s

  Estimate how much energy is required to transmit one action t)am.tml ; 627y i*vmbqr7ivkpotential along the axon of Example 18–15. [Hint: the energ.m* )ikry v v6i72b7qamlmt;ty 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,+hiq d7u. pt.p $Na^+$ 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 i5kyxqmxn2n dwed9od* 965avz(g/)re n 1.00 ampere-hour?    C

  What is the average current drawn by a 1.0-hp 120-V mqica4 d*ztx2+otor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leavj*81 orf; +ll-reulak z9j4mt1* vsoges a car with the lights on. If each of the two headlights uses 40 W and each of the two taillights 6 W, for a lo la+jovjrl48sf9;k-m1 1urg**tez 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-Vk vycynblb3z+z9u,0gf e 2w04, 1500-W heater is 5.4 m long. If it is made of iron, what must its diam ngc3fuzbb9k,0w4zv y+2yl0eeter be?    $ \times10^{ -4}\;m$

  The conductance G of an objec(az mz,gudui/-13 l no+t0uzci8ez 5r t is defined as the reciprocal of the resistance R; th1ziz+5u0ei ,/l mu3(u raz-dcnto 8z gat 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 (* iv c;slx5ki q9tj5zpower. 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 cost of electricity is aboisxq; tl* 5k(z5ci9vjut 10 cents per kWh.    dollars per hour per meter

  (a) A particular household uses a bh 87z ed(:x e;koo ls0hj4:mr1.8-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 ielm1z (yg vxq9m03k0 ew2wh ;in 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 resist lmq20(x9v1myg;h0eik3 ez wwance of the original wire?

  A 1200-W hair dryer is o8wz-/uu abglr+( t/ adesigned 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 c8.o aja+9q6 1jo ad9cam.qepnba*)e not become so hot as to start a fire. What diameter must a copper wire be if it is to carry a maximum current of 35 A and produce no more than 1.8 W of heat pdbo9aaa a oecnq +m*p1.9qc.6jj)8 aeer meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is given by the equt(h q.ouhw(hfc/ ox8, *x +i+y+bssj nation $I\,=\,1.80sin210t$, 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 run; 9g7 +bpue;x9msi0dk a o3fekning at 65% efficiency delivers 950 W of energy per second to the interior. Find e; og i7pukaf;xeb+s39 dk09m
(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 diffe9gk r;/*sdwre n5 hyn+rent conductors made of the same material. One condwg;d5+rerns/ nk y9h *uctor is twice as long and twice the diameter of the second. What is the ratio of the power transformed in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used b:rwyi 1sx;f 4to 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 qab) a2nf1sjv1 (jb3 1r4x fjhsource.
(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 itmp*8eu qrv 3fuj;)vdg 1*zotz8c 65yjs source of energy. Its mass is 1560 kg and it is powered by 24 batteries, each 8f5z3muj)68*t gve zury q;o1vpcd j*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 resist(y1 xse1 l-uztf/*4ntse 3s gmance 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)0mvqfak9p*on xjf8, -5cgw 4.w 9irdo is designed to carry an 11-mA beam.g5-wv cr0 jf fpdo 9kw,nmioaxq8*94 of protons traveling 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 cord is copper wires rj,1: z:x .db:xphb ohaul;+ with a diameter of 1.628 mmx.a:,hrsz: +lj uph1xd;b o:b.
(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 12ydjo jn d11j/oy t:zl-)m,w0gazz*6 d 0 V. The heating element is a coil of Njdna*:jy - dg06l,zot1 zyj z/wo )md1ichrome wire. 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 f6nci +f:3k3fpjlctv1 rom about 12 V when the car is off to about 13.8 V when the car is on and the charging system is in operation, a difference of 15%. By what percentage does the power delivered to the headlights vary as the voltage changes from 12 V to 13.8 V? Assume the v3ltjcfki fnc :p6 3+1headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for household applicatim)t3)(osaao kwqb68+d o d1l kons. Lightbulb B is rated at 12 V and 40 W for automotive applications6d1 s)o aq 8)b(ta+mlkod w3ko.
(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 ap:rlq:l g/ndp, pliances at 120 V, whi:,d/llp g:r nqch draw 2250 W of power total.
(a) What power is wasted in 25.0 m of this wire?    W
(b) What is your answer if wire of diameter 0.412 cm is used?    W

  A copper pipe has an inside diameter of 3.00 cm and (n oyh84)vher, i:knw -ri9rran outside diameter of 5.00 cm (Fyr4hkr)( hn9w-o:ivr e8nri ,ig. 18–37). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformly so that its l0ciavu 2up/io( )4 lk5lniem jn4)m/ cength doubles, by what factor does the pocni pi/)evnk40 jmo24i l)mc/luu a5(wer dissipated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operates atsh:fdup8 e6:)+.-ilv yyaa/cay .n pk 0.20 A and 3.2 V. If its resistance at 2 apld6-p :ivcea8n yayf/ y:+uh.sk .)0$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$