What quantity is measured by a b p2 xxh:q-0ar rng,qe1attery rating given in ampere-hours $(A\cdot H)$ ?

When an electric cell is conneg/ r;r 0gjxzp1cted to a circuit, electrons flow away from the negative terminal in the circuit. But within the cell, electrons flow to the 0rrg/zgpx j1;negative terminal. Explain.

When a flashlight is operated, what is being user sgsmr * ew9.7bx5sb2d up: battery current, battery voltage, battery ens9rms* rbw7.b x 2s5egergy, battery power, or battery resistance? Explain.

One terminal of a car battery is said to be connected to “grou: ;dtqhjzc ;otu 0m/ er104cuind.” Since it is not really connectedro: ;u4tc/ ec1tz idum;0qh0 j to the ground, what is meant by this expression?

When you turn on a water faucet,vhr/6kbsw b rw/v68.n the water usually flows immediately. 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 to the terminals of a batterb vb8wvw kr6//hsn.6ry?

Can a copper wire and an aluminum wi es -/qhw/7si*mnl8v:g ds gb:re of the same length have the same resistance? Explailghs/m 7bd sv ::qe*n8 /-giswn.

If the resistance of a small immersion heater (tod/m ,76eccwe-m 1cf zd heat water for tea or soup, Fig. 18–32) was increased, would it speed up or slow me,z /c7 ce-6fd1mdwcdown the heating process? Explain.

If a rectangular solid made of carbon has sides of lengths a, 2a, al;w30r h/hfpie sv 3*(o ;lhiknd 3a, how would you connect the wires from a battery so as twe;v o f hh(kp0/ ;3rl*si3hilo 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 o;,k-t,h c(iasen zp3rmvmw+, ut?

Explain why lightbulbs almost always burn out jua sv in uf74m4j8qi1eqzexhe4 + l-2fwa.-5q hst as they are turned on and not after they have been on for some es8 5hj- 4i7ix zef uq4-ma leq2+v1.qanw4hftime.

Which draws more current, a 100-W lightbulb or a 75-Wqglc2;b 5 j gs3f(ks+g bulb? Which has the higher resc ss5lgkbg f(;2q3jg+ istance?

Electric power is transferred over large distances at very high voltax.qobfdwwr e6:m00s ,ges. Explain how the high voltage reduces power loss.ws 60 xwfoqb,m0:rd ees in the transmission lines.

A 15-A fuse blows repeatedly. Why is it dangerous to replqf-kls 83h6 hoeoq/o17lx) n nace this fuse with a 25-A o1lh7o6q l-nxheq8)nso 3k/f fuse?

When electric lights are operated on low-frequency ac (say, 5 Hz)( s djwlz8e .fiz eb,2huip615, they flicker no., izz2hf w6u5sel pd iej(1b8ticeably. Why?

Driven by ac power, thnyvqibf: 3b ;z -6:jmo:ltp/de same electrons pass back and forth through your reading lamp over and over again. Explain why the light stays lit instead of going oupb-ion df::jmz 3/btl:q; vy6t after the first pass of electrons.

The heating element in a toaster is made of Nichrome wires++1dqan4051n vttkn g bl em7. Immediately after the toaster i+gb e+tsnan k1qt40n5 d1vml 7s turned on, is the current $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor?/efw9 vzebu6s u1kz7 : Explain.

Different lamps might have batteries cf p-u fivdbp04m*kj8 ,onnected in either of the two arrangements shown imkp4j p*bfv ,d-0u8if n
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 sj+h.(hd fppk3+) m1 n: 4 qlnj0ssailflowing past any point in the l s ij0+a dfk1 (p.smh+: jlnsn3h4pq)wire per second?    $ \times10^{18 }\;electrons/s$

  A service station charges a batt; jm2jxkbr6uhu-q.9ov1 0jea9u + *xqqll 3 ijery using a current of 6.7 A for 5.0 h. How muchv1jaib* 9hukuuqj+ 6re3x-j q2 m;q ljxol.09 charge passes through the battery?    $ \times10^{ 5}\;C$

  What is the current in aqm:fv -).xlqbj r+ zwn9aqi6 2mperes 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 produce,ar 2vz12k cbps a current of 4.2 A?    $\Omega$

  What voltage will produce 0.25 A of current thr)o m;:q)y*adll(jb.5hbw5wqqmd a*/ du 8wy uough a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when pl )l4fgkej d2z17/weq z9pfq1 hugged 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 heatinir )0nbi7m 2qtg element with a resistance of $9.6-\Omega$.
(a) What is the current in the element when it is connected to 240 V?    A
(b) How much charge passes through the element in 50 min?    $ \times10^{ 4}\;C$

  A 9.0-V battery is connected to a bbwp7 cvl*9k 36rn8gpy /qvui1qmh(-xulb whose resistance is $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc 27rmx2-n m vk6,fs-bmfeu1j uelectric transmission line carrying 2800 A (Fig. 18–34). Th2eurv bm26m -7xs1j,f fuk-mn e 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 drhoq-;wh+ gsc *aws 6.50 A at 240 V.
(a) If the voltage drops by 15%, what will be the current, assuming nothing else changes? $\approx$    A (retain one decimal places)
(b) If the resistance of the device were reduced by 15%, what current would be drawn at 240 V? $\approx$    A (retain one decimal places)

  A 12-V battery causes iph + gltn( -z/a8w azm) 6cv+az(+ jr.jogsj7a 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 res-+;lsg4y;bbuan m; cfistance is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of coppe:kh-6f3 gkhv 5n2gx hjr 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 diavrlt7/pv9 rgj8 m*9afmeter, to 20.0vj / g r98l9f7rta*pvm m of copper wire 2.5 mm in diameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tungstevshm6)d;u8c l4quw *l3 fre 6b7x:awdn wire of the same length? Give um 6h ;l8qw)6v*xa :dl s7r34fuwbec dnumerical details.    mm

  A certain copper wire hou4; za ogb9n3as a resistance 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 ravmuu 5 ai5:y0fise the temperature of a copper wire (originally atuai5 v:5fmu 0y $20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what tempen9y/rd :-t9 qe3xveth rature copper will have the same resistivity as tungsten do/ et9e n3- q:rx9vthydes at $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a re5 c(bv+rhq 9nn8c bep)sistance 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 26f,obegai/y v. 8/nubx; m 0b9v-m length of household no. 14 copper wire (used in 15-A circuits). The wire has dm/ .a y/0fbo8vbbn x,gvie9; uiameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid made of carbonyt.3q+3 zly hoj/rq 0m has sides of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 18–35). Determine the resistance for current that passes tj0l+y3qzo/myth. 3 rqhrough 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 twice the length of t6c g(b3o l.)ahlh-thv,b,d oo he other, what is the ral3lh(cbb avh ohg,-,oto. d)6tio 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 connected to a precision 10.0g3s06ja5h9vp i kbfa e3vwdr- d7;f9q0-V power supply, and a cu f 7- wp93sdj9dr fq 3ikvh5abg;6ea0vrrent 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 o37pg ..6nf5oc: rmkw vu2 *yv5 xssdvuf copper followed by 5.0 m of aluminum, both of di7cgkuds oxn5.:y 56r.smv3*vv uw2fp ameter 1.0 mm. A voltage difference of 85 mV is placed across the composite wire.
(a) What is the total resistance (sum) of the two wires? $\approx$    $\Omega$(retain two decimal places)
(b) What is the current through the wire?    A(retain two decimal places)
(c) What are the voltages across the aluminum part and across the copper part?
$V_{Cu}$    V(retain three decimal places)
$V_{Al}$    V(retain three decimal places)

  For some applications, it is important that the vadi);q l1)dsz5tx u.j5z.pkwalue of a resistance not change with temperature. For examipjzqdwa)ltks du1.;) .55z xple, 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; w 0w,v;iw/0pc;ib f(ntdm5x bw, lxw to produce 3.3 kW of heat when connected to m ;ip;d0vb n5i fwx;ww 0wbx,/ltw,(c a 240-V source. What must be the resistance of the element?    $\Omega$

  What is the maximum power co94 2 ukr 6dq/huqru5y :dn6inbnsumption of a 3.0-V portable CD player that draws a maximum of 32du5 d49yirk6 uhnq bq/62nru:0 mA of current?    W

  What is the maximum voltage that can be applied acm 82rs(9t vty hqyo7oj3 9nqk+ross a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current through, a 75e)7l* :khb-aigtc/ almqn e:1-W lightbulb connected to heae 1nmiqcll)gk* ::a7 b/t-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. 0lh/rxmpf o;la)da 7: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 1aax a1k( zh9gms0*8tf250 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, wherucd p+r-v3s67p dgy2je electricity is delivered to homes at 240 V. If you use the lightbulb in the United States at 120 V (assume its resistance does not change), how bright will it be relative to 75-W 120-V bulbs? [Hint: d+y36rppv2cuj 7-dg sassume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy does a 550-W toaster use in 60eozn.r,kx wthe morning if it is in operation for a total of 15 min? At a xkwn.0zr6o ,e 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 7;dhw wnoj w71porch light on day and night for a yj h71; 7wdwonwear? $\approx$    dollars

  An ordinary flashlight uses two zt4 rg0im03yb1g+xu fD-cell 1.5-V batteries connected in series as in Figm 0z4fx gt0+ig1br3yu. 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 opy,v,o m-d su7f 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, conn p 0*ey-dlbm9zks a2a-ected to 120 V as in Fig. 18–20, can be used without blowing a 15-p*edsy-29lb-a kz0m a A fuse?    bulbs

  An extension cord made of two wires of diameter d i ffrc(x p3:h0k+ w:vme4gn5kdo -+l0.129 cm (no. 16 copper wire) and of length 2.7 m (9 ft) is connected vf : -+x+oimdndk3rhf0 glw(e:4kpc 5to an electric heater which draws 15.0 A on a 120-V line. How much power is dissipated in the cord?    W

  A power station delivers 620 kW of power at 12,00wg.1/v hl3 tvk*t4zd cp*fh* w0 V to a factory through wires with to*k dt3 hfw*c*vphzl.wt4 v/g1tal 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 +pw ognko5n 6/a 240-V line is 17.5 A. At what rate must coolingpno6n/+ okg 5w water pass 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 h.owx)hi 9pw d9,7 nk*1ai2yiqwvi1mv eat a cup of water for coffee or tea. If the heater can hvhmi9i ,w d1v79 w)x2iwp*. qikyona1eat 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 )/lpititf ,q vo-l-i/in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak valk7* kgjsa 1fh3ue is 180 V, 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 the , qoy63)-qhmmnt +cmb $120-V_{rms}$ 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 cur1tprr l7rft 3 /cur)/krent in a 1500-W device is 5.4 A. What is the rms voltage acros7ttrr kc/r)f lu3r1p/s it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected0k0ch-oqypr (e0 wh o gd-3(jj 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 (dx*:y/9qw*c/gwqns 8z uo ep3.0-hp pump connectedcsz* /(dn q *ogxe/8ypwq9:u w 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 a rb j4;e q(wht4q mbc ,hycd4dg3)mh8 2$240-V_{rms}$ 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 tiny 6 v l3 9axvv5b8 dqt:8pty40bv/hdbfwcurrent 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 :gm*z tsd dii6a *v5-gcurrent when 22.0 mV is appligm:ia*-6 vtd*dz 5gsied 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 Earth’sadds sm+ 22ue5l1l e;v 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 Ea-eot rks7.l-j l6: sxhvllcw7 9.dh9 frth’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 93b :nfpxvlok*u/ nf8yvtg)( electric field across an axon membrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated)ffx:j0ks8 rq 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 potentk)qf:f xr08sjial 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 only one?)    m/s

  Estimate how much energy is reqetspa4t 8za;c1sh-3 mk a-qh0uired to transmit one action potential along the axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energy stored by km a ;a3shcp1e8s0 at-t4-hqzcharging 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 pot ny./;jal lgg.ential, $Na^+$ 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 am46yg8 qgn6yibid z48 jpere-hour?    C

  What is the average current drawn by a 1.0-hp 120-V mh)c6ccfvn10rxb3 e3iotor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves az4i91 gc7y;qq nejm(-8yz jbi car with the lights on. If each of the two headlights uses 40 W and each of the two taillights 6 W, for a total of 92 W, how long will a fresh 12-V batter 8j q71gn yei( q;4czmz-bji9yy 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 z cdd i/cl z()jue +97u+vdb6cmade of iron, what must its diameter be? 9+ z)uce/dd76(zvjcd u cbi+l    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocali*gy /pme 3yw95) ztk5wu1qoj of the resistance R; that is, 5w) mqyw 3jet*g5 z1u9yp/oki$G\,=\,1/R$. 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 power. Sueob g-+jl0w 3c(pr4ce*tx+cj m6dx2 a ppose 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 -c43 p*6 2gxdcjeoxmew+ abl0j (r+ct of electricity is about 10 cents per kWh.    dollars per hour per meter

  (a) A particular household uses a 1.8-kW heater+ czio ad79s0c $3.0 h/day$ (“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 lengilawj,e+xqjw/5q 4s.)/rzeo ths are wrapped together side by side tew. //4+ ji j5eqos lxwzr,qa)o make a thicker wire. How does the resistance of this new combination compare to the resistance of the original wire?

  A 1200-W hair dryer is designed fgx,bez *a85 b,azt* xror 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 bebo/qckwa/0l * come so hot as to start a fire. What diameter must a copper wire be if it is to carry a maximum curro0qb /lwck/a *ent of 35 A and produce no more than 1.8 W of heat per meter of length?    $ \times10^{ -3}\;m$

  Suppose a current is givoj/1;gnr :,svz0ilpben by the equation $I\,=\,1.80sin210t$, where I is in amperes and t in seconds.
(a) What is the frequency?    Hz
(b) What is the rms value of the current?    A
(c) If this is the current through a $42-\Omega$ resistor, write the equation that describes the voltage as a function of time. (  sin 210 t)V

  A microwave oven running at 65% efficiency delivers 950 W of energy pejoi+jt9v9zcz2n *i b2ezax9m + ltk:.r second to tvi9b++ ct jm92xzkzanlto2 ie:*9j. zhe 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 conductors matnf/hf6+q5 r5* m /kg4gv bujwde 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 the first relativgbn 54m/qkv/fgtj+ r6 5u* hfwe to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a rnpc7y:.3rc0yw cg25 0beqm/ e e(acogoom 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 siy ua7ge -s02g1gd z8aource.
(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 batteriesri3v gf+wex0jovs(- ; as its source of energy. I-ofs+3 vg iwr0;x ejv(ts 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 a resistance of a lxahkywf 7(3ad4*xw7:v7h i$12\Omega$ 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 d/-f m75c sm7hx -jm xq3efri8 -lxl/cxesigned to carry an 11-mA beam of protons traveling at very nearly the speed of lighxi3mj-ex8m-5 xlcsfm 77rqlhcx/-/ft ($ 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 copp:qrfdb mh e;o7hwn* d*)*svc5o9qq;ner wire with a diameter of 1.628 mmq **:bq csq*5 mrnfno;d7 wohe;vd9) h.
(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 n*2ke6i9e hmbV. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.8 m. What is the diametn *mihe9b6e2k er of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the systeqppwu99m;x c 09iy 2k 8.xz3zeubobv7m voltage varies from about 12 V when the car is off to about 13.8 V when thpxvk o29bp9miyzu;b z30 uew 7c9.q8xe 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 headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and yv ie5tk./h3qj dg-or6 95dze40 W for household applications. Lightbulb B is rated at 12 V and 4kqo/ ej5t.v9g5dhr -i6 z d3ye0 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 appliances at 120 prr w/,hxd3fnr -cj+f3k2 )xp V, which draw 2250 W ofn, wp 3rd+kx3)2rc hrfx-pf/j 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 an outside diwa1z*(hj i js5: gfqf1ameter of 5.00 cm (Fig. 18–37). Wf 1:jsq(15 hfiwzgja*hat 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 length doud npj ).*nc :)*;xls.nvb ewocbles, by what factor does the power dissipat d ) pc*xlco.we):bnjvs n*.;ned in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlid*pxlvx0a6960s ,ux-stn dx y dbs0,jght bulb operates at 0.20 A and 3.2 V. If its resistancpd0xl x0u ns0d xs 9b6-jvxdats* y6,,e at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$