What quantity is measured by a battery rating given in ampere- ,(z.9edudms yhours $(A\cdot H)$ ?

When an electric cell is connected to a circuit, electrons f ziat(n6 g)jn8low away from the negative terminal in the circuit. But within the cell, electrons flow to the negative jna8zt(i)gn6 terminal. Explain.

When a flashlight is operated, what is being used up: battercoh:jg78u 2 w9krc3mvc:f -qqy current, battery voltage, battery energy,38oc-2hug q kq7:w cc:rfvj9m battery power, or battery resistance? Explain.

One terminal of a car battery is said to be connected to “grou8v9t. o;ssbqc*5 brgond.” Since it is not really connected to the ground, what is meant by this expresbsr qcso*;gtob.v 589sion?

When you turn on a water faucet, the water usually flows immediately. Yo h;/z6ppi(q g hto+3nbu 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 to the terminals pb3n thp;(6qio/hgz + of a battery?

Can a copper wire and an aluminum wire of the same lengthsuqd 0 fu9 o:dv-0v(z au7 j+0ajyt(wg have the same resistance? Expl9 j aajy07uf0ov:g+wq(uv 0s dz tu-(dain.

If the resistance of a small immersion heater n w0:nocd *kh+(to heat water for tea or soup, Fig. 18–32) d0c nkno* wh:+was increased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, and 3a,d ypy1)x 9vy9g how would you connect the wires from a battery so as to obtain (a)y y)p9 1yxdvg9 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 burnts 2ksmf qgf8j 11d ll,(x4ee7s out?

Explain why lightbulbs almost always burn out juh.* u :zdeq ;b2j uhgk )z-6f:j3nzqqzst as they are turned on and not after they have been onje)d3 .z b zf :*z:6juq2q;-uzqhgnkh for some time.

Which draws more current, a 100-W ln9bc8s 94qv ffightbulb or a 75-W bulb? Which has the higher resistanc 99vnb4cff qs8e?

Electric power is transferred over large distances at very high v-u6rxy z d4j.0w1u mmroltages. Explain how the high voltage reduces power losses in .6rw1 4m-d0mr zu xjuythe transmission lines.

A 15-A fuse blows repeatedly. Why is t+ ocnn l f(v(u2oea9m44o mg,by1(pj it dangerous to replace this fuse with a 25-A mfp +e,o tc(ng4(o4y1b 2oamu9lnj(vfuse?

When electric lights are operated on lo av8eshw7wml8:1xf(l w-frequency ac (say, 5 Hz), they flicker nhx lf( 7ae:81w8lm wvsoticeably. Why?

Driven by ac power, the same electrons pamk z f(b8e 9vf49 9 ybw1ozfcqcj,2uu-ss back and forth through your reading lamp over and over again. Explain why the light stays lit instead of going out after the first pass of electrons94bf -k o z9 wjyu(z,m9e bf2cu1vfq8c.

The heating element in a toaster is mafl lk,j,36t8iav jzf t-xku/4de of Nichrome wire. Immediately after the toaster is turned on, is 6flx 8 ktfv3ki/,j u-jazl4t,the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistos kmlw:lv(jzh)*n 3l3r? Explain.

Different lamps might have batteries connesjxn/-l sseb8bbw 9tn /,xp ya.cb; 76cted in either of the two arrangements shown ,na86xy ntb.cpw/ sxs9e7- ;bbjlbs/in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows ,h od(jl;cx o-f fmhv92;o2ds in a wire. How many electrons are flowing past any point m ovsh(d jh ;fcf22xo, ol-;9din the wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a batiimw /s 5() vhkm7;dfetery using a current of 6.7 A for 5.0 h. How much charge passes through the battm 7)ihk(fi5swm/ed;v ery?    $ \times10^{ 5}\;C$

  What is the current in t/hs3;dtpk)v 2j5nrr-x :k ms amperes 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 producy*0 c4 abtu)gges a current of 4.2 A?    $\Omega$

  What voltage will producee,l yn3 r5yh*r2l-f lu 0.25 A of current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when pl;z d3 m+0lfhpibdf 9,kugged 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 a rb *n4vr8mh-u,i a3fh cesistance 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 coigo+i w589ch2jd)p2mz. j.zf 6c 67p iztdyjvnnected 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 carrying 2800 A (Fig. 18–34).q9j /*). qiwj rimy;gw The li*;rwmj 9. jq/g)yiqiw ne 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 240 p/r/1 //,swreja bvmlV.
(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 resist 4smey) r,alx+or.
(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 ofu :nmp+wksj i*vs.d/w .*n, fc 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 lengayuyf n ;kjvwz2.:0 h1xp e*)xth of copper wire 1.5 mm in diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resistance of 10.0 m of aluminum n1 2*6cbxqih bw ydh1;kn7 -stwire 2.0 mm in diameter, to 20.0 m of copper wire;txs7kbwi1b2* nh6-1hnc yq d 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tungsten witb*au8qv)5 arut ak:f9 trq8)re of :)rt ubt*k 5v8qa)q9 r af8uatthe same length? Give numerical details.    mm

  A certain copper wire has a ryv q9y0bq ,q/gesistance 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 /c8 jsmj-l7p .8vjjysx8c2 jwthe temperature of a copper wire (originally at s /c8.scljpx 8vwjjy287j -mj $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temc56w), ,)fjpu depq.be5rd kaperature copper will have the same resistivity as tungsten does ,df)d q a 5 e,c6bpujk5.w)rpeat $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a 0dwu94 j. mm8d8ntzi aresistance 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 household no. c slv+lj1 m36 rt f5zi.l0u0bk14 copper wire (used in 15-A circuits). The wirel6fvck3m s0 .u5+bzrjilt0 l1 has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbon has sides of lengths.t1npmcx;fz3 i+bu l3 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z tl 3.i1nu;fx3cmbz+p axes, respectively (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 ha 3661l1pg4tn yichdjeg vh1(yve the same resistance. If one has twice the length of the ot16td l13 y (4jpch vhen6ggi1yher, what is the ratio of the diameter of the longer wire to the diameter of the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is connefx )6 najt3 xm)h*b3tccted to a precision 10.00-V power supply, and a current of 0.4212 A is)m nbx*h at6cx) 3jt3f 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 alum(k(p3v v5t ) lntsld(8fkj4cuinum, both of diameter 1.0 mm. A voltage difference of 85 mV is placed across the compljdck83sp ) vtk (lnf(5tu4(vosite 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 thgejafz1k5y 69 e value of a resistance not change witzaj61g5yk e9 fh 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 electric oven is designed to produce 3.3 kW o o0(y.js8qjgef heat when connected to a 240-V source. What must be tho.y8qj sgj0e (e resistance of the element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portablvk--r3o:5 wgqx gad j*e CD player that draws a maximum of 320 mA of curre- j:vod3gxwrg a k-5*qnt?    W

  What is the maximum voltage that can be applied acrm :xh)nhvt nc;,r f)(uoss a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, axwq qndlh3iza3 . ,1c* 75-W lightbulb connected to its proper source voltage of 120 V3caz nw. hi*x1 3,qdql.
   $\Omega$
   A
(b) Repeat for a 440-W bulb.
   $\Omega$
$\approx$    A(retain one decimal places)

  A 115-V fish-tank heater c4gxh m- ft.2eis rated 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 and 1svkfkbm+f,: r*x vx4 8250 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 w c p +)j.fgj;/qnqw(khn4in 7s9v )51ekygzmEurope, 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 jkkgpw4hn.;/z q+5njimg) w 7 nfes) v (c1y9qbe 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 toasx f(3qvpd-y+ wter use in the morning if it is in operation for a total of 15 mi +q3vfwx -(ydpn? 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 kWhct: *amp:gz/ o b12bo(utta zv) q15jn, what does it cost to leave a 25-W porch light on day andj2z z1 u)*vgn 5:q:(op1/t at obabtcm night for a year? $\approx$    dollars

  An ordinary flashlightp4 tyft 81ava-r wvyjs6/i r22 uses two D-cell 1.5-V batteries connected in series as in Fig. 18–42 wvti1yrtyr/-as6j 2 p f84avb (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 amou-txn x-w;u:e3: gzl we9sq2cjnt 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, can be used withp7pc urp*p)5( l,9h; pjq xwuzout blowinhq(pp5 ucw ur7p) z*9;,xpljpg a 15-A fuse?    bulbs

  An extension cord made of two wires of diameter 0.129 cm (no. 16 copper wire) apq:4 krm rnro+m/: pf4nd of length 2.7 m (9 ft) is connected to an electric heater which draws 15.0 A on a 120r+no4qpr:p m k4f:rm/ -V line. How much power is dissipated in the cord?    W

  A power station delivers 620 kW of power at 12,000 V to a factory throk. s/ u3wp0qgo+5miygugh wires with total resistanc+smug3. op/ qkgyw 5i0e $3.0\Omega$ 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 ac p 1c9gdk3h,t 240-V line is 17.5 A. At what rate must cooling water pass over the coils if the water temperature is to rise by no mortp1cchk,3 d g9e than 7.50 $C^{\circ}\,$?    kg/s

  A small immersion heater can be used in a car tgfnh.y0i /yr (o heat a cup of water for coffee or tea.yn.fih(0y/ r g If the heater can heat 120 mL of water from 25$^{\circ}\,C$ to 95$^{\circ}\,C$ in 8.0 min,
(a) approximately how much current does it draw from the car’s 12-V battery, $\approx$    A(Round to the nearest integer)
(b) what is its resistance? Assume the manufacturer’s claim of 60% efficiency.    $\Omega$

  Calculate the peak curreot6 : khmaex:.nt in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak value is 180 V, is acrs;5 w(n6dvqxg 9v5ugjoss 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 thfit 6 s6-jsng)o(ff4owom 5;x e $120-V_{rms}$ 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 alter;ccw,ge+qzb dht;i7s/ e. 0g jnating current in a 1500-W device is 5.4 A. What is the rms volbc qdwz c,;i 0 e.egsht+;7/jgtage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected tohyo;1fdr oggymp 7:81p v ;7bv 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 connecom.o 5-q1 t+eydxkee2roa +y: te:qa- 1kx+y5+ o ee dtr2mo.eoyd to a $240-V_{rms}$ ac power source?    W
(b) What is the maximum current passing through the pump?    A

  A heater coil connected to ad5kinub itf (onj00s4d) y 9k+;jhz hqen4l*. $240-V_{rms}$ 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 carr+- *) g.fa)uwt qw78 fafgxftnies 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-diameter wire carries a 750-mA current when 22.0 mV q/rxkycbogpqo : jp6.tdtfz,m4 03-1is applied to its ends. If the drixbtc dqzpg . o6:fy3,tq-j/o1r40 mkpft 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 c;3w1o1ej qu qatmosphere, $He^{2+}$ 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 thee1lsc, .psrche l0 564y b*ols 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 acr 1dmiaf nc-+4detwm6-,qb9 h yoss 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. il n0* dgwz,q-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 o-d*lqgw,z0 n if 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 t 6*q7p 9zpzro*o.jnlaction potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to *l6 o*p jrntqz7p.oz9the 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,qem 8x(wu4/m +oiq(fo $Na^+$ 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 an59t b69 eewjompere-hour?    C

  What is the average current drawn by ac3nu6ba*r qbdq kbuz7 :n:0z , 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves nx( ls*hk 8*zna car with the lights on. If each of the two headlights sl*hkn 8* xz(nuses 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 is c1azyji,;-kj v*( 9qm8v9nzbiehf; o made of iron, what must its diqa;-*kybc1vf ji,mh 9;vzi(enz9 o8jameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is define; 8l+pf,r (icuk +yhqdd as the reciprocal of the resistance R; that is8rdqcu h;+l i+f p(ky,, $G\,=\,1/R$. 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 afmtx3c)g 6v3cnk/izh*4,kq 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 energy lost to heat per hour per meter. Assume the cost of electricitckmt 3,q)vk3n*xgc4a zfih/6 y is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular household uses a 1. *b(xlb,xa:ko8-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 in half and the two lengths are wrapped togerh qw(r) j*cf i2*vei:ther side by side to make a thicker wire. How does the res*2 :*we)ivqrrhjc(f iistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed for hpr - 5lejwygikbv2c61xt ;j 9e 08a8d117 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 becomq 38x0 u2r4owb x c-krh-o;cxje so hot as to start a fire. What diameter must a copper wire be if b2xo8rq-roxw0-4x3c uhk jc; 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 eykys h93tba 7tjs *-t9 l4s*2js;prfk quation $I\,=\,1.80sin210t$, 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 of energy per seconaecayvc yf; -ewz 8:l*a 1tgc46.w,a wd to theaa6cg*y ya afwcv,-e18;wl4:e zt.cw 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 eune 4xl7tm2xh,g5z9h qlf 5, two different conductors made of the same material. One conductor is twice as long and twice the diameter of the second. What is the ratio of the power transformed in the7e,q 9,m4u l52hxx5 flzgt ehn first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heatlh07y2so d0vg echc63 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 hooke5 )vkig)x p0fo:e.vded 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 aly ,:xj( db-opncz)4smn (4ustorage batteries as its source of energy4p)dc z- s ,ou:((n nb4yxmlaj. Its mass is 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 s)ey3,r zzwb0 a resistance of $12\Omega$ when cold (20$^{\circ}\,C$) and $140\Omega$ when on (hot). Calculate its power consumption at
(a) the instant it is turned on,    W
(b) after a few moments when it is hot.    W

  The Tevatron accelerator at Fermilab (Illinois) is designed to xr * xuwloxy30*2ibp0carry an 11-mA beam of protons traveling at very ne0**rpi0lyx 3x2uxobw arly 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 cor:nbgde 8ynodki7 v32 mg17 :wgd is copper wire with73ov:b kd:2nygd1 8gegm7 iwn a diameter 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 tok2 jvk87rb(,rbry /jy 120 V. The heating element is a coil of Nichrome wire. When u rb,8v2jkbyr/( 7jyrk ncoiled, 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 w 81 (zbpfss0k:q;no/ wa0h lhqhen the car is off to about 13.8 V when the car is on and the charging system is in operation, a difference of 1 q(80khh1w : zl/ qpsosba;f0n5%. 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 syb i q6 +8t6/ol46qzpt ykgl1W for household applications. Lightbulb B is rated at 12 V l 8qtt6 6lykpq gi+o4 y/bz61sand 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 connect a set of /7a 0) rykuagx:xl nnror3y (6appliances at 120 V, which dr6 aon (u3y7:)l rrnxga/kyx r0aw 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 diamete a2sdiggf3(hnh: (0kyp dil(;r of 3.00 cm and an outside diameter of 5.00 cmisyh3dki:glan ;f(( 0gdp 2h ( (Fig. 18–37). What is the resistance of 10.0 m of this pipe?    $ \times10^{-4 }\;\Omega$

If a wire of resistance R is stretched uniformgf-l) kucr/dv.s2s+e ly so that its length doubles, by what factor does the power dissipaterse dc/- lsfv)g.u k+2d in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight ed , z)2/fkeotbulb operates at 0.20 A and 3.2 V. If its resistance at ,e/ ) okd2zfet20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$