What quantity is measured by a battery rating given in ampej*)a;k9m lmze u7c td(re-hours $(A\cdot H)$ ?

When an electric cellg ed. 0gg-3iti is connected to a circuit, electrons flow away from the negative terminal in the circuit. But withini0t3e.-ig ggd the cell, electrons flow to the negative terminal. Explain.

When a flashlight is operated, what is being used ups0lbx8 z j93ehj(l a7x: battery current, battery voltage, battery x(3j8leh9j 0sbz7axl energy, battery power, or battery resistance? Explain.

One terminal of a car battery is sai/za(9qt5 bb/ kr0t iurd to be connected to “ground.” Since it is not reall(/ q b5b0airt ktru9/zy connected to the ground, what is meant by this expression?

When you turn on a water faucet, the water usually fi g304n tcs5sw09/ .nw .6lkup/ hu:fpkz eozulows immediately. You don’t ha nt5kukhwze0fcn pz/i.slg.: 4p3w/9 6u0suove 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 battery?

Can a copper wire and an alumin;elckys 7f()f3aw d(3amm6d mt;j p4 num wire of the same length have the same resistance? Explainp anwldykfde(m73 m3stf)j (6a m4;c ;.

If the resistance of a small immersion heater (to heat water for0y57pp r: apmli5t (bi tea or soup, Fig. 18–32) l0iy 7 mtp b(pa:5rip5was increased, would it speed up or slow down the heating process? Explain.

If a rectangular solid made ofqybpu4uc7 *m/v6)g(ej has9c carbon has sides of lengths a, 2a, and 3a, how would you connect theu9gy)bh*c4/u msvqjc6(ep a 7 wires from a battery 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 bur009fxel cu/m;3 j6tcic4p* cbgymi. mns out?

Explain why lightbulbs almost always burn out jus.aj/s./ i2an-bla h 8yohfe.v t as they are turned on and not af8.-a v.hsf/2/j li nya.bo heater they have been on for some time.

Which draws more current, a 100-W lightbulb or a 75-W bulb? Which has the hi55be1yajgml 0n+r 0ptgher resistancebey p51tjm+5n lg0ar0?

Electric power is transferred over large distances atugq v b6ud+ )jr;tl;jacek:;d6 w3il+ very high voltages. Explain how the high;b)r i:twljlj;+q6 k3; g6u av+dduc e voltage reduces power losses in the transmission lines.

A 15-A fuse blows repeatedly. Why is it++81j+taq 5heutrb p luxc -o9 dangerous to replace this fuse with a 25-A t -1a 5+cuo 8q exhjr+b+tlp9ufuse?

When electric lights are operated on low-frequency ac (say, 5 n2go hm n +7g0mmcw3r4Hz), they flicker noticeably. Whnwngm 4hg3 rm 70o2+cmy?

Driven by ac power, the same elec m.gbwvwd u5w15m,zr) f,g ,btsj0m:ntrons pass back and forth through your reading lamp over and over againmww nfg smjv, )t,.u zwbbr5 d015m:g,. Explain why the light stays lit instead of going out after the first pass of electrons.

The heating element in a toaster is made of Nichr 0 +yx00yvnte pv,53.x vhk(of w;5j3ltecyt jome wire. Immediately after the toaster is turned on, is the currefn,00 vt+j5 xo th; yvxetv3yc350lp yek.wj (nt $(I_{rms})$ in the wire increasing, decreasing, or staying constant? Explain.

Is current used up in a resistor? wab3zn2 29h: hey o-xucb+e 1vExplain.

Different lamps might have batteries connected in either otb2b7hp3nlz. f the two arrangements shb 72p b3lzht.nown in
Fig. 18–33. What would be the advantages of each scheme?

  A current of 1.30 A flows in a wire. How many electro/kua8 e/r-xjx (a 1djins are flowing past any point in the wire per sarka1d/i-/ 8uej( xjxecond?    $ \times10^{18 }\;electrons/s$

  A service station charges a battery using a current of2 nl2rwt,,dplaz).l3 a9vmw j 6.7 A for 5.0 h. How much charge passel2t nd3p m9l,,2)la wajzrvw .s through the battery?    $ \times10^{ 5}\;C$

  What is the current in amperebenz hs6y9d(1 s 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 a current of 4.2 A? hc (;w8e wvvf(dd9wbljl) 6s0    $\Omega$

  What voltage will produce 0.25 A o :1tknh* t;7 ),pgx cw;mbk.zq lkp-rof current through a $3800-\Omega$ resistor?    V

  A hair dryer draws 7.5 A when po42n w qe: 6zglirt/2hlugged 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 rp:uxz y/ er.tnse42jem f-)h; esistance 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 :; oh( se.i*yh,.knuc ly,ru jis $1.6\Omega$. How many electrons leave the battery per minute?    $ \times10^{21 }\;electrons/min$

  A bird stands on a dc electric transmission line carrying3(ibb (*pmn0 cp-xkll 2800 A (Fig. 18–34). The-(p(l bc lnx0 b3pk*mi line has $2.5\times10^{ -5}\;\Omega$ resistance per meter, and the bird’s feet are 4.0 cm apart. What is the potential difference between the bird’s feet?    $ \times10^{-3 }\;V$

  An electric device draws 6.50 A at 24fo 10oivmt2h dj+j-d) 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 current o -dhz c.1i(m;yo;c 6 ,+uxiue umdqao/f 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 resistancylv sk9d gkx qy490ph798 +kyce is $0.32\Omega$?    $ \times10^{-4 }\;m$

  What is the resistance of a 3.5-m length of copper wire 1.5 mm c4/,psu 4td(h6r5y)uwsvc bzin diameter?    $ \times10^{ -2}\;\Omega$

  Calculate the ratio of the resisquo-u3d 4sch::d bho)n ghb01tance of 10.0 m of aluminum wire 2.0 mm in diameter, to 20.0 m of copper wire 2.5 mm in dih nbc -4q b)u1u:ddho0h:g s3oameter.   

  Can a 2.5-mm-diameter copper wire have the same resistance as a tungsten wire n6ztimr3l) pc6shqdm (( w22 lof the same length? Give numerical details s() 22ihcmztdprw n 3q6m6ll(.    mm

  A certain copper wire has a rxs* j28zm1s6 suw .pyb vgs:p4esistance 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 1nuk 5js(img .of a copper wire (originally at .(imsun15 kgj$20^{\circ}\,C$) to increase its resistance by 15%?    $C^{\circ}\,$

  Estimate at what temperature copper will have the same resistivity as tunmsy /z0chhk/yywm j)r r022c-gsten does at2hc cy) mr-y/mw/zs2r h00 ykj $20^{\circ}\,C$.$\approx$    $^{\circ}\,C$ (Round to the nearest integer)

  A 100-W lightbulb has a resistance of about7x/j)uxvhq7i9 hs ez 1 $12\Omega$ 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 h9: *aw/7nfvyzt)9fou 3invr2 f( s wa q(d.xsbousehold no. 14 copper wire (used in 15-A circuits). Tva)fi(s9xonf 3 nww97/t.:bva ysf*zd q (u2rhe wire has diameter 1.628 mm and carries a 12-A current.    V

  A rectangular solid madb w)7 s8nrkjj22o31jbsy* wupe of carbon has sides of lengths 1.0 cm, 2.0 cm, and 4.0 cm, lying along the x, y, and z axes, respectively (Fig. 187* s) sw3pj 2bjo 128yknwurbj–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 hac e ri:0xp(b4ys twice the length of the other, what is the ratio of the diameter of the longer wire to the diameter (xb y4e:rpi0cof the shorter wire? $\approx$    (retain three decimal places)

  A length of aluminum wire is u 3oj:cr58octf ad4k 9connected to a precision 10.00-V power supply, and a current of 0.4212 A is pkcc4:ja8 5fuo3 dtr9orecisely 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 follovn 0)9ca(covun0:l l,j r ezg7wed by 5.0 m of aluminum, both of diameter 1.0 mm. A voltage difference of 85 mV is pvc(l0aro nvun ze,0):cj9 gl7 laced 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 importalj z7qmy y9wospxs:*a0.k ;+cnt that the value of a resistance not change with temperature. For example,qcymsapx k l;w+ o.0z* 9y:js7 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 des; 0phf0tv+ h/u dnj4eyigned to produce 3.3 kW of heat when connected to a 240-V source. What must be the resistance of e tn f0yjp4+hdu/0v;hthe element?    $\Omega$

  What is the maximum power consumption of a 3.0-V portable CD player that dr womm*y4n*+8ol 7lew:ab8 nuv aws a maximum of 38ybnv 4+7aowmmu8wnl :** elo20 mA of current?    W

  What is the maximum voltage that can be applied acrc 10laxrgled( 15gf.r oss a $2.70-k\Omega$ resistor rated at $\frac{1}{4}$ watt?    V

  (a) Determine the resistance of, and current throuiq4a- sq:uc bx c;).jzgh, a 75-W lightbulb connected to its )qq:;4izcx s ujc b-a.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. Calculw; be5b3jbpp;iqr ;s3ate
(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 x5(-g2k1aqzeudk/ ut W and 1250 W.
(a) At which setting do you expect the resistance to be higher? After making a guess, determine the resistance at
(b) the lower setting;    $\Omega$
(c) the higher setting.    $\Omega$

  You buy a 75-W lightbulb in Europe, where electricity is delivered to homes at 1.x9fa6sb4unz*f y vlk5af)b 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- )ua6fzyxf.sal f*4b5v91bknV bulbs? [Hint: assume roughly that brightness is proportional to power consumed.]    as bright

  How many kWh of energy does a 550-azod-o+h86 /*r)ri gg+zsw 9dpkf: rbW toaster use in the morning if it is in operation for a total of idpgrfbz*:o++k rdrw89ahz / -sog6 )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 por2i0 xh v09uqx o,wl: igif;ug7ch light on day and night for a yex 79 i0gfuo,ug:iw0l;h qivx 2ar? $\approx$    dollars

  An ordinary flashlig2 iy/ gt8iled6ht uses two D-cell 1.5-V batteries connected in series as in Fig. 18–4b (Fiit /di2 yg8el6g. 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 amouzmk zo +)v5a(y8*3h ( azsvlkvnt 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, cly-/to:1; :+mgw ixyc(ctk enan be used without blowing a 15- t(1 ex;:l/:i-ct+ky ym wogncA fuse?    bulbs

  An extension cord made of zk0snur 4s0ave ,b:*a szq*nivr2y0/ two wires of diameter 0.129 cm (no. 16 copper wire) and of length 2.r40ve2n/yz ain s,zb*k0uvs sq*0r : a7 m (9 ft) is connected to an electric heater which draws 15.0 A on a 120-V line. How much power is dissipated in the cord?    W

  A power station delivers 620 kW of power at 12,000 V to a fm-ah48 q(kzu 3be hhl.actory through wires 8kzul4hh3bamq. (h -ewith 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 electromagb,sga;)x3 u g5 xmb hyc;s 0+hxl4alr-net connected to a 240-V line is 17.5 A. At what rate must cooling water pass over the coils if the watehs4yc b5lh ) +xs 30;rbgxax,-la mg;ur 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 cup of water for coffeymw/ .tvxwar (d7/cl;e or tea. I xa7;yl.dv wmtc(w //rf 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 curxr6p:ze s g6 ;u1vme-+vkeze q+n-y8 vrent in a $2.2-k\Omega$ resistor connected to a 220-V rms ac source.    A

  An ac voltage, whose peak k:qcy 55dbpqt.b,sj+ value 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 libj-d dry9 ++.haiw .$120-V_{rms}$ 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 k2m;va*dx. tp A. What is the rms*k;2tda m vxp. voltage across it?    V (Round to the nearest integer)

  An 1800-W arc welder is connected to jwwp367m3h-aq:9pc byldgw /p /fn3s 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 ins(k y8q5.9s hm)udzfw ctantaneous power dissipated by a 3.0-hp pump connected tosm) whdfz(uk 9cy.q85 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 ,6pq::np;d;dd kvlhe$240-V_{rms}$ 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 cninla ),o*3)( *w slfawzo :nxurrent 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-diame0ln0h1an9 pc v)zx5m 2 7bpggyter wire carries a 750-mA current when 22.0 mV is applied to its ends. If the drift specz0 2pxhn0a lp97v 5ng bm1)yged 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 idyo4iva 9lkxy-:6-+k u gwe. 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 

  At a point high in the Earth’s atmospherexo j.y0;zw. te, $He^{2+}$ 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 meldee* x - hm/4+zhk8uambrane $ 1.0\times10^{ -8}\;$. thick if the resting potential is $-70 Mv$   $ \times10^{6 }\;V/m$

  A neuron is stimulated with an electric pva 6mpqhl-8iat 1gmm51 u )oj4ulse. 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 two measurements needed instead p)qgv6i- aum 84at5lmo1jm h1 of only one?)    m/s

  Estimate how much energy is required to transmit one action potential along the ,kcxqnu0x)k,axon of Example 18–15. [Hint: the energy to transmit one pulse is equivalent to the energn0 )x ck,,kuqxy 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 potenti+ak -gg;n2 )ku9-j+fgtyx obsal, $Na^+$ 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-hourl2-b*m d 0trw cvlhw.: d d4/bfrto)a)?    C

  What is the average curnw1l//o3+jj pufex -zrent drawn by a 1.0-hp 120-V motor? $(1 hp\,=\,746\,W.)$    A

  A person accidentally leaves a car with the lights,q6hp6 zxj/sl2g6 m1ps2px xr 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 baz6 2x,hgrxsl1xm6/psp q2jp6ttery last if it is rated at $95A\cdot h$? Assume the full 12 V appears across each bulb.    h

  The heating element of a 110jeoc/8.g2)v ww0e iko1ek4:viqmq8 7uc 1hus-V, 1500-W heater is 5.4 m long. If it is made of iron, w 4o/ v8jq711 w0euv2e 8uh)siwcgcoi :kkm.eqhat must its diameter be?    $ \times10^{ -4}\;m$

  The conductance G of an object is defined as the reciprocal of +b 8tybz5ltms+uq6y9the resistance R; tmstbq++9l5 6y uzt8ybhat 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 power. Suppose that instead .v dx3vo y (6egsd.oj1ofu9jep56ig1of 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 (e6os 1gyd9f egoj61o. 3v5xd.uj vpi the energy 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-k6 ortfp a.qba:4 0rcb3W 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 a yqzbkb8g,o9.re wrapped together side by side to makbb qkygz9,o.8e 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 7a5(llsgck 5x for 117 V.
(a) What will be the percentage change in power output if the voltage drops to 105 V? Assume no change in resistance.    % decrease
(b) How would the actual change in resistivity with temperature affect your answer?

  The wiring in a house must be thick enough so it does not become so hot asw,la5(b5;ydgoo)o kwr54 k f v to start a fire. What diameter must a copper wire be if it is to carry a maxigrok w(fdv4y,bak) l; oo5w55mum 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 equatio/l sz9t*bcjlz7df l.( n $I\,=\,1.80sin210t$, 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 ta/e-w4ayz aw(0:16 raaer 7z*hym m tof energy per second to the interiotze rmw(azw/ eara1t:67ah4 my*-ya0r. Find
(a) the power drawn from the source,    W
(b) the current drawn. Assume a source voltage of 120 V.    A

  A $1.00-\Omega$ wire is stretched uniformly to 3.00 times its original length. What is its resistance now?    $\Omega$

  220 V is applied to two different conductors made of the d2j/sc)log l* same material. One conductor is twice as long and twice the diameter of the second. What is the ratio of the power transformes cd/lj* gol)2d in the first relative to the second? $P_1$ : $P_2$ =    : 1

  An electric heater is used to heat a roox9 0eqihg :k:rx;:xn u e9q5ggm 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 t(a8 wk )oajk; v2gj+vwo 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 o1 ux*-ib0ja wsf storage batteries as its source of energy-i1xaswuj b*0 . 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 lightbulqh-9ffrtgx ;i b/t)zix;3c : tb has 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) i rer72hezdy5xv6m sx9v/ vl/ 4s designed to carry an 11-mA beam y72e/r vxrde4z6sxmv /lhv59 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* (l;r e z ukw-5vjuifq1g5:u,;snwwv cord is copper wire withf: (;nuw5- qegv;rw1j5kuswuv izl ,* 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 to 120-)2z8clai mftr w;(f v V. The heating element is a coil of Nichrome wire. When uncoiled, the wire has a total length of 3.882t(rvmicfw -; fl) az m. What is the diameter of the wire?    $ \times10^{ -4}\;m$

  In an automobile, the system voltage varies from about 12 V when the car itrgmx(0 .rgj25owy2j, ew ie9s off to about 13.8 V whwij02yw5m r ,erxg(j te2o9g .en 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 headlight resistance remains constant.    % increase

  Lightbulb A is rated at 120 V and 40 W for household applications. Lightbulb B o w(5 .l; reanm+:,+ttouyjcvis rated atv +l5jrwuye+o m c;o:n ta,(t. 12 V and 40 W for automotive applications.
(a) What is the current through each bulb? $I_A$ =    A $I_B$ =    A
(b) What is the resistance of each bulb? $R_A$ =  $\Omega$ $R_B$ =  $\Omega$
(c) In one hour, how much charge passes through each bulb? $Q_A$ =    C$Q_B$ =    C
(d) In one hour, how much energy does each bulb use?    $ \times10^{5 }\;J$
(e) Which bulb requires larger diameter wires to connect its power source and the bulb?  ----待选择----Bulb BBulb A 

  Copper wire of diameter 0.259 cmdjue ql5b .3.v3hx/l h is used to connect a set of appliances at 120 V, which draw 2250 W of power total. v bj u.x/h35ll3q.ehd
(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 insid vepn:.0giaj w 4pulh4;ohr2*9zssl)e diameter of 3.00 cm and an outside diameter of 5.00 cm (Fig. 18–37swp0ve p u:;a4jhlh) *4r2sn.lz9io g). 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 length doubd 3mjy:z9+ak jles, by what fy3+ zma 9:kjjdactor does the power dissipated in the wire change, assuming it remains hooked up to the same voltage source?

  A tungsten filament used in a flashlight bulb operalzcqf2 t zq pq -y+-rsb:2hm1cwi z6,o.i*ln7tes at 0.20 A and 3.2 V. If its r ,c672 mqhn-pcq1*wirl+li 2 ftzz.y:zbqo-s esistance at 20$^{\circ}\,C$ is $1.5\Omega$ what is the temperature of the filament when the flashlight is on?    $^{\circ}\,C$