If two points are at the saa1/h kqmc. lc) bhmd9(me potential, does this mean that no work is done in moving a test charge from one point to the other? Does this imply that no force need be exert9.mq1m/cacbhk) l (dhed? Explain.

If a negative charge is initially at rest in an ele41)0sj+nfcde / ngxmpxht;3 s ctric field, will it move toward a region of higher potential or lower xhnfjxc4n 3s g0psm1)ed+t / ;potential? What about a positive charge? How does the potential energy of the charge change in each instance?

State clearly the difference (a) between electric pot opj+on7hs(w3 ential and electric field, (b) between electric potential and electric potential eo 7phso(+wjn3 nergy.

An electron is accelerated by a potential difference of, say, 0u.ypt w-0:qjrzc6l ,u.10 V. How much greater would its final speed be if it -jzptuu6,: rcyw.l 0 qis accelerated with four times as much voltage? Explain.

Is there a point along the line joining two ev:ir2izi p vz468;s ylqual positive charges where the elec; ivzrl ipz6is 2:v84ytric field is zero? Where the electric potential is zero? Explain.

Can a particle ever lemvku/*f8c/ axtas5 hg9 krq7-3nn/ move from a region of low electric potential to one of high potential and yet have its electric potential energy decrease? Ensc*7ea-r9x5 avh knguq8 l/m kt3/f/xplain.

Compare the kinetic ener/)ejndnh: 8ld gy gained by a proton $(q=+e)$ to the energy gained by an alpha particle $(q=+2e)$ accelerated by the same voltage $V$.

If $V\,=\,0$ at a point in space, must $\vec{E}\,=0$ there? If $\vec{E}\,=0$ at some point, must $V\,=\,0$ at that point? Explain. Give examples for each.

Can two equipotential lines cross? uu7;knn74p iamfukh jw y08. a9tmc(45 b4xhgExplain.

Draw in a few equipotential lin dsu.wpf7z)0jes in Fig. 16 – 31b.

What can you say about the electric field in a region o d4 mo,ed7j5mof space that has the same potentiald 54ejo7omm,d throughout?

A satellite orbits the Earth along a gravitational equipotential line. What shhskf0hs 2 fu+ls/( s(mape m/ 0fkss2sl(u+sh hf( must the orbit be?

When dealing with practical hvf*ezq5pn:2hhs 569 k-nrbs devices, we often take the ground (the Earth) to be 0 V. If, instead, we said the ground was how would this affect (a) the potential V, and (ehhsqh2655b9p n sz k:rvf-n*b) the electric field E, at other points?

When a battery is connected to a capacitor, why do thef5cih- mgt,+m-zjc njwoc88lp2 j3 7s two plates acquire charges of the same2 3jg+msj 7mfw-l o,cp8jh -zct85 cni magnitude? Will this be true if the two conductors are different sizes or shapes?

We have seen that the capacitance C depends on the size, shape, ey:l cm/a52ca t3af- rand position of the two conductors, as well as on the dielectric constant K. What then did we mean wh5ty:lcc eam aa-2fr/3en we said that C is a constant in Eq. 17 – 7?

  How much work does t:tmcb ozkisf04n.jv 3m /6ru,r ugh 45he electric field do in moving a $-7.7\mu C$ charge from ground to a point whose potential is $+55V$ higher?    $ \times10^{-4 }\,J$

  How much work does the electric field do in moving a proto(*kaw :w -oka27i,hhe:gra ezn from a point with a pok7k*h- , ewaa2rah(o:ewg:iztential of $+125V$ to a point where it is $-55V$ Express your answer both in joules and electron volts.
   $ \times10^{-17 }\,J$
   eV

  How much kinetic energy will an electron gain (in d4a9lz3u8rstn)mm cc c 4w24b joules and eV) if it accelerates through a potential difference of 23,000 V in a TV picture tub n42rt4ma8uz9c4 3c)md w csble?
   $ \times10^{-15 }\,J$
   eV

  An electron acquiresadogs7 3 xfci 06: g .1qotstfjh/41jwd3x/wo $7.45 \times10^{ -16}\,J$ of kinetic energy when it is accelerated by an electric field from plate A to plate B. What is the potential difference between the plates, and which plate is at the higher potential?
   V
plate ----待选择----AB 

  How strong is the electric field between two bdje hs 7iuqdwh98 k-:)klp:( parallel plates 5.8 mm apart if the potential difference between ju 7p)es :k :dw8h9-bdkqlhi( them is 220 V?    $ \times10^{ 4}\,V/m$

  An electric field ofube7s *7r/nae $640V/m$ is desired between two parallel plates 11.0 mm apart. How large a voltage should be applied?    V

  The electric field between two parallel plates connected to a 45-V batter;g,v-f wfuw,a(j sw8g y is $1500V/m$ How far apart are the plates?    m

  The electric field between two parallel plates connr 8 dfy2fwrp5+hg3(skected to a 45-V battery is $1500V/m$ How far apart are the plates?    m

  What potential difference is neipthju,.gj( 5 eded to give a helium nucleus $(Q=2e)$ 65.0 keV of kinetic energy?    $ \times10^{4 }\,V$

  Two parallel plates, connected to at7r:2dc22wm-yh g (a z9iesxa 200-V power supply, are separated by an air gap. How small can the gap be if the air is not to become conducting by exceeding its breakdown valgdrxm2t7 e i-(yh9: 2sac2 zwaue of $E\,=3 \times10^{ 6}\,V/m$?   $ \times10^{-5 }\,m$

  The work done by an external force to moveii .fp;zl4 pm, a $-8.50\mu C$ charge from point a to point b is $15.0 \times10^{ -4}\;J$. If the charge was started from rest and had $ 4.82\times10^{ -4}\;J$ of kinetic energy when it reached point b, what must be the potential difference between a and b?    V

  What is the speed of ymih+)kf7s41cq .z luan electron with kinetic energy
(a) 750-eV,    $ \times10^{7 }\;m/s$
(b) 3.2-keV?    $ \times10^{7 }\;m/s$

  What is the speed of a proton whose kinrp7 n2s(eogn-3vl2)h fog,z vetic energy is 3.2 keV?    $ \times10^{5}\,m/s$

  An alpha particle (which is a helium nucleupt 9yfnw ln+h3yahbq4d* 2g0 ;s, $Q=+2e$, $m\,=\,6.64\times10^{-27 }\,kg$) is emitted in a radioactive decay with $_{KE}$ = $5.53MeV$ What is its speed?    $ \times10^{7}\,m/s$

  What is the electric potent95;f vxsey9dfial 15.0 cm from a $4.00\mu C$ point charge?    $ \times10^{ 5}\,V$

  A point charge Q creates an electricq j hyn2.oetbkv 9a09ya:x7 4-q ;uwgq potential of $+125V$ at a distance of 15 cm. What is Q?    $ \times10^{-9 }\,C$

  A $+35\mu C$ point charge is placed 32 cm from an identical $+35\mu C$ charge. How much work would be required to move a $+0.50\mu C$ test charge from a point midway between them to a point 12 cm closer to either of the charges?    J

Draw a conductor in +c nshe-ft76: fo+gfkthe shape of a football. This conductor carries a net negative charsnhgoce+f 7f:6f+t -kge, $-Q$. Draw in a dozen electric field lines and two equipotential lines.

  (a) What is the electric potential a dist4vqkbimw d0kj/6ne u;5u; -vtance of $ 2.5\times10^{-15 }\,m$ away from a proton?    $ \times10^{ 5}\,V$
(b) What is the electric potential energy of a system that consists of two protons $2.5 \times10^{-15 }\,m$ apart — as might occur inside a typical nucleus?    $ \times10^{ -14}\,J$

Three point charges ar(6p zke-ukg.6 c mh6o-kufn6ke arranged at the corners of a square of side L as shown in Fig. 17–25. What is mf6ok.en (-kkkuz-u6pc66hg the potential at the fourth corner (point A), taking $V\,=\,0$ at a great distance?

  An electron starts from rest 32.5 cm from a fixed poin/ e.icjk,yt0fd2 ,yd fmo1k*ut charge with $Q\,=\,-0.125\mu C$. How fast will the electron be moving when it is very far away?    $ \times10^{7 }\,m/s$

  Two identical $+9.5\mu C$ point charges are initially 3.5 cm from each other. If they are released at the same instant from rest, how fast will each be moving when they are very far away from each other? Assume they have identical masses of 1.0 mg.    m/s

  Two point charges, $3.0\mu C$ and $-2.0\mu C$ are placed 5.0 cm apart on the x axis. At what points along the x axis is
(a) the electric field zero    cm leftof $q_2$
(b) the potential zero? Let $V\,=\,0$ at $r\,=\,\propto$.

  How much work must be don5jcybj 5bjc; j)ycj7i0st7.v h llg):e to bring three electrons from a great distance apart to cl jl5jb05)ybjvc):sjtjyg ; .7i 7 ch$1.0 \times10^{-10 }\,m$ from one another (at the corners of an equilateral triangle)?    $ \times10^{-18 }\,J$

  Consider point a which is 72 e 1pclmo o3;)hcm north of a $-3.8\mu C$ point charge, and point b which is 88 cm west of the charge (Fig. 17–26). Determine
(a) $V_{ba}=V_b-V_a$    V
(b) $\vec{E}_b-\vec{E}_a$ (magnitude and direction).
   V/m
   $^{\circ}\,$

  How much voltage must be us1bf dd)n 0ushwu:sv/:bj9l3 wz3 np7 med to accelerate a proton (radius $1.2 \times10^{-15 }\,m$) so that it has sufficient energy to just penetrate a silicon nucleus? A silicon nucleus has a charge of $+14e$, and its radius is about $ 3.6\times10^{-15 }\,m$. Assume the potential is that for point charges.    $ \times10^{6 }\,V$

Two equal but opposite charges are separated e bmw xd+a7x;0by a distance d, as shown in Fig. 17–27. Determine a formula for+ xmea 7;d0bxw $V_{BA}\,=\,V_B-V_A$ for points B and A on the line between the charges.

  In the Bohr model of the hydrogen atom, an electron orbits a protgqz8nt0y mh o wy/-()n2aoi 3non (the nucleus) in a circular orbit of radin0qnwy go2ozh)-3yiamt 8(/n us $ 0.53\times10^{-10 }\,m$.
(a) What is the electric potential at the electron’s orbit due to the proton?    V(Round to the nearest integer)
(b) What is the kinetic energy of the electron?
   $ \times10^{ -18}\,J$
   eV
(c) What is the total energy of the electron in its orbit?    $ \times10^{-18 }\,J$ $\approx$    eV(Round to the nearest integer)
(d) What is the ionization energy — that is, the energy required to remove the electron from the atom and take it to $r\,=\,\propto$, at rest? Express the results of parts b, c and d in joules and eV.   $ \times10^{-18 }\,J$    eV(Round to the nearest integer)

  An electron and a proton ar xe g:y5jm/7v*5ztfwhe $ 0.53\times10^{ -10}\,m$. apart. What is their dipole moment if they are at rest?    $ \times10^{-30 }\,C\cdot\,m$

  Calculate the electric potential duon ds(1-i 4z vs2vf;r6eunl( ne to a dipole whose dipole moment is $ 4.8\times10^{-30 }\,C\cdot m$ at a point $1.1 \times10^{ -9}\,m$ away if this point is
(a) along the axis of the dipole nearer the positive charge;    V
(b) 45° above the axis but nearer the positive charge;    V
(c) $45^{\circ}\,$ above the axis but nearer the negative charge.    V

  The dipole moment, considered as a vector, points from the umvy wt2 k6rd13s w/6pnegative to the positive charge. The water molecu3vs1wwdt m/26 ypruk6 le, Fig. 17–28, has a dipole moment which can be considered as the vector sum of the two dipole moments, $\vec{P}_1$ and $\vec{P}_2$as shown. The distance between each H and the O is about $ 0.96\times10^{ -10}\,m$. The lines joining the center of the O atom with each H atom make an angle of $104^{\circ}\,$, as shown, and the net dipole moment has been measured to be $p\,=\,6.1 \times10^{-30 }\,C\cdot m$ Determine the charge q on each H atom.    $ \times10^{ -20}\,C$

  The two plates of a capaciwu ouq;.c qk8.tor hold $+2500\mu C$ and $-2500\mu C$ of charge, respectively, when the potential difference is 850 V. What is the capacitance?    $ \times10^{-6 }\,F$

  The two plates of a capacitor hol ir4s lfhr 5*w5/++taw wst.ltm7:o evd $+2500\mu C$ and $-2500\mu C$ of charge, respectively, when the potential difference is 850 V. What is the capacitance?    $ \times10^{-6 }\,F$

  A 9500-pF capacitor holds plus andn3krjq4sktz- qmwy*zuzj 4+ i/ 0)ke ) minus charges of $ 16.5\times10^{-8 }\,C$. What is the voltage across the capacitor?    V

  The potential difference between two short sections of para 9;, )o.odim6 zdqikbillel wire in air is 120 V. They carry equal and opposite charge of magnitude 95 pC. What is the capacitance of theb odo.)d, z;iikqm i96 two wires?    $ \times10^{13 }\,F$

  How much charge flows from each terminal of a 12.b:rvn*g+7: wuwv vw88kp:pp ka(arq1 0-V battery when it is connected tn8r qvw+avwg barw7:ku*p8:(v:k1pp o a $7.00-\mu F$ capacitor?    $ \times10^{-5 }\,C$

  A 0.20-F capacitor is desired. What area must the plates havrjxj3x1ex :e*z3wg )we if they are to be sepae ww*gejx:) x31jxrz3rated by a 2.2-mm air gap?    $ \times10^{ 7}\,m^2$

  The charge on a capal5 ,f-wge pbd(citor increases by $18\mu C$ when the voltage across it increases from 97 V to 121 V. What is the capacitance of the capacitor?    $ \times10^{ -7}\,F$

  An electric field of:umperyr3 )cj-w dqa 3nvq2h-y- 3:a h $8.5 \times10^{ 5}\,V/m$ is desired between two parallel plates, each of area $35\,cm^2$ and separated by 2.45 mm of air. What charge must be on each plate?    $ \times10^{ -8}\,C$

  If a capacitor has opod)9bj zn6*/ t*nco cuposite $5.2\mu C$ charges on the plates, and an electric field of 2.0 $2.0\,kV/mm$ is desired between the plates, what must each plate’s area be?   $m^2$

  How strong is the electric field between the plates of ad)xudht2x a23)+ pqfw $0.80-\mu F$ air-gap capacitor if they are 2.0 mm apart and each has a charge of $72\mu C$ ?    $ \times10^{4 }\,V/m$

  A capacitor is charged by a 125-V battery -aq0 +uo*bycw8tf/h/e gw3e x (Fig. 17–29a) and then is disconnected from the battery. When thi+bu3 f0-//wce *8oah xqtgey ws capacitor $(C_1)$ is then connected (Fig. 17–29b) to a second (initially uncharged) capacitor, $C_2$, the final voltage on each capacitor is 15 V. What is the value of $C_2$? [Hint: charge is conserved.]    $ \times10^{ -5}\,F$

  A $2.50-\mu F$ capacitor is charged to 857 V and a $6.8-\mu F$ capacitor is charged to 652 V. These capacitors are then disconnected from their batteries. Next the positive plates are connected to each other and the negative plates are connected to each other. What will be the potential difference across each and the charge on each? [Hint: charge is conserved.]
$V_{final}$ $\approx$   V(Round to the nearest integer)
$\begin{array}{l}
Q_{1}\\
\text { initial }
\end{array}$   $ \times10^{-3 }\,C$
$\begin{array}{l}
Q_{2}\\
\text { initial }
\end{array}$   $ \times10^{-3 }\,C$

  What is the capacitance of two square parall -j;zuc6bc2 ppel plates 5.5 cm on a side that are separated b6u 2p;ccz-jpby 1.8 mm of paraffin?    $ \times10^{-11 }\,F$

  What is the capacitance of a pair of circular plates with a radiia 9uqqi w; mhga3 fc8a,39fl(us of 5.0 cm sepaaai;f cwil( m qu3gq,3f899 harated by 3.2 mm of mica?    $ \times10^{-10 }\,F$

  A 3500-pF air-gap capacitor is connected to a 22-V battery. If a piece of miz43ah 3 ld-f ,r1c1/m:i+5mtdd ov7khyzkttxca is placed between the plates, how mmotdhil x3 az1 mr14fhy/vczttd-:d5k7 3 +,kuch charge will flow from the battery?    $ \times10^{ -7}\,C$

  The electric field between the pl cl u3z2g2dg)mates of a paper-separated $(K=3.75)$ capacitor is $ 8.24\times10^{4 }\,V/m$. The plates are 1.95 mm apart, and the charge on each plate is $0.775\mu C$. Determine the capacitance of this capacitor and the area of each plate.
   $ \times10^{--9 }\,F$
   $m^2$

  650 V is applied to a 2200-pF capacitor. How much energy is stored?94a -ims0)c/ pgy+p;uvfxm s; ofga)6yz od5 c    $ \times10^{-4 }\,J$

  A cardiac defibrillator isvgeob jg3zuy v(126 j/nu9p3y used to shock a heart that is beating erratically. A capacitor in this device is charged /913v pezgynyj u vbgo6 3u(2jto 5.0 kV and stores 1200 J of energy. What is its capacitance?    $ \times10^{-5 }\,F$

  How much energy is stored by the jf4a-la mpp:ht/e d0* electric field between two square plates, 8.0 cm on a side, separated by a 1.5-mm air gap? The charges on the plates are equal a la0tp- jad/ 4*hfem:pnd opposite and of magnitude $420\mu C$.    J

  A homemade capacitor is assembled by placing two 9-in. pie pans 5 cm apart 8lc3g h2c 94aac-ubocand connectingu 8 ah9a c243boclcc-g them to the opposite terminals of a 9-V battery. Estimate
(a) the capacitance,    $ \times10^{-12 }\,F$
(b) the charge on each plate,    $ \times10^{-11 }\,C$
(c) the electric field halfway between the plates,    V/m
(d) the work done by the battery to charge the plates.    $ \times10^{ -10}\,J$
(e) Which of the above values change if a dielectric is inserted?

A parallel-plate capacitor has fixed c m2l4cyrm w)56nlf-yf uvitt14 z/6u jharges $+Q$ and $-Q$ The separation of the plates is then doubled.
(a) By what factor does the energy stored in the electric field change?
(b) How much work must be done in doubling the plate separation from d to 2d? The area of each plate is A.

How does the energy stored in a k:ns2ss k, 5f0diqc0 ex/kh0.q ,euticapacitor change if (a) the potential difference is doubled, and (b) the charge ose,kxec/0, 0q:ku2k .dhtns f5iis0 qn each plate is doubled, as the capacitor remains connected to a battery?

  A $2.70-\mu F$ capacitor is charged by a 12.0-V battery. It is disconnected from the battery and then connected to an uncharged $4.00-\mu F$ capacitor (Fig. 17–29). Determine the total stored energy
(a) before the two capacitors are connected,    $ \times10^{-4 }\,J$
(b) after they are connected.    $ \times10^{-5 }\,J$
(c) What is the change in energy?    $ \times10^{-4 }\,J$

  In a given CRT, electrons are accelerated horizontally by 7.0 kV. They,nys udc9q6z.f qwzsxns,wg u;0.g;7 then pass through a uniform electric field E for a distance of 2.8 cm, which deflects them upward so they reach the screen top 22 cm away, 11 cm above the ;6qgsgz s ,.9u dfn;uy wcwz7xn. 0s,qcenter. Estimate the value of E.    $ \times10^{5 }\,V/m$

  Electrons are accelerated by 6.0 kV in a CRT. The screen is 308lae,g .q t 1zx5+nj1 1vywikp cm wide and is 34 cm from the 2.6-cm-long deflection plates. Over what range must the horizontally deflecting elel.wnq 8ipz 1xat1v+5kej y,g 1ctric field vary to sweep the beam fully across the screen?    $ \times10^{5 }\,V/m$ to    $ \times10^{5 }\,V/m$

  An electron starting frmxyrky6lq/ .+re*i -pom rest acquires 6.3 keV of KE in moving from point A to r .le+m*-qi/ypx6k yrpoint B.
(a) How much KE would a proton acquire, starting from rest at B and moving to point A?    keV
(b) Determine the ratio of their speeds at the end of their respective trajectories.   

  A lightning flash transfers 4.0 C of charge and 4.2 MJ rf/jje92c;jfl lm ;d0of energy to the Earth.
(a) Across what potential difference did it travel?    $ \times10^{ 6}\,V$
(b) How much water could this boil and vaporize, starting from room temperature?    kg

  There is an electric field near the Earth’s surface whose *ipi gpl,8q j anqtyj73g*q+ 7magnitude is about $150\,V/m$ How much energy is stored per cubic meter in this field?    $ \times10^{-7 }\,J/m^3$

  In a television picture tube, electrons are accelerated bo 1 ft8cj6cxw5y thousands of volts through a vacuum. If a television set were laid on its back, would electrons be able to move upward against the force of gravity? What potential difference, acting over a distance of 3.0 cm, would be needed to balance the downward force of gravity so that an electron would remain stationary? Assume that o5w6 8c1jtxfcthe electric field is uniform.    $ \times10^{ -12}\,V$

  A huge 4.0-F capacitor has enough stored energy to heat 2.5 kg of water from*pkl50q:a lo4 trb(f s 21$^{\circ}\,C$ to 95$^{\circ}\,C$. What is the potential difference across the plates?    V

  An uncharged capacitor is connected to a 24.0-V battery until it is fully ch j8us-v eimcl wmu/t (- xoe-v),ixi55arged, after which it is disconnected from the battery. A slab of paraffin is then inserted bel,w(suj- c8x)e5-/mm vv i -xoi eitu5tween the plates. What will now be the voltage between the plates?    V

  Dry air will break down if the electp5h g6b x;nnd:ric field exceeds $3.0 \times10^{6 }\,V/m$. What amount of charge can be placed on a parallel-plate capacitor if the area of each plate is $56cm^2$?    $ \times10^{-7 }\,C$

Three charges are at the corners of an equilateral triangle (side L)xi(t p /37)pnb: :wsr k7iqsab as shown in Fig. 17–30. Determine the pbsxrq7 sa: (i3pkn7:ip)b /wtotential at the midpoint of each of the sides.

  A $3.4\mu C$ and a $-2.6\mu C$ charge are placed 1.6 cm apart. At what points along the line joining them is
(a) the electric field zero,    cm left of $q_2$
(b) the electric potential zero?

  A 2600-pF air-gap capacitor is connected to 4 lp2l w:4rb12hikh;y o6nseg a 9.0-V battery. If a piece of Pyrex glass is placed between the plates, how much charge will thenoehlkp4iy:gw61 h 2rs2b;l 4n flow from the battery?    $ \times10^{-8 }\,C$

  An electron is accelerated horidh- 2uzu+ iozdwp1 ;r0us ;;mhzontally from rest in a television picture tube by a potential difference of 5500 V. It then passes between two horizontal plates 6.1u;-dh0; zw;zimrup 2 o udh+s5 cm long and 1.3 cm apart that have a potential difference of 250 V (Fig. 17–31). At what angle $\theta$ will the electron be traveling after it passes between the plates?    $^{\circ}\,$

A capacitor of capacitanc-z(gfr3rj dx5 e $C_1$ carries a charge $Q_0$. It is then connected directly to a second, uncharged, capacitor of capacitance $C_2$, as shown in Fig. 17–32. What charge will each carry now? What will be the potential difference across each?

  To get an idea how big a farad is, suppose you want tzbvg99), ggt dn3 1bds:y-rbjo make a 1-F air-filled parallel-plate capacitor for a circuit you are building. To make it a reasonable size, suppose you limit the plate area to What would the gap have to be between the plates? Is this practically achi3ty1:gvb srg d)bngzb9 -9dj,evable?    $ \times10^{-16 }\,m$  ----待选择----YesNo 

  Near the surface of the Earth there is an electric field of ab 2 *rsqtuco.0;mw8driz h0uo. out $150\,V/m$ which points downward. Two identical balls with mass $m\,=\,0.540kg$ are dropped from a height of 2.00 m, but one of the balls is positively charged with $q_1$ = $650\mu C$ ,and the second is negatively charged with $q_2$ = $-650\mu C$. Use conservation of energy to determine the difference in the speed of the two balls when they hit the ground. (Neglect air resistance.)    m/s

  The power supply for a pug b gtv) ;,l/sirn*vz7lsed nitrogen laser has a $0.050\mu F$ capacitor with a maximum voltage rating of 30 kV.
(a) Estimate how much energy could be stored in this capacitor.    J
(b) If 12% of this stored electrical energy is converted to light energy in a pulse that is 8.0 microseconds long, what is the power of the laser pulse?    $ \times10^{5 }\,W$

  In lightning storms, the potential difference between the Earth ajz mw/5slseqgat y /reb8i0oo- m066:nd the bottom of the thunderclouds can be as aqz 0o58y6ms mt:e0o/iwe-/sgb 6 rlj high as 35,000,000 V. The bottoms of the thunderclouds are typically 1500 m above the Earth, and can have an area of $110km^2$ Modeling the Earth–cloud system as a huge capacitor, calculate
(a) the capacitance of the Earth–cloud system,    $ \times10^{-7 }\,F$
(b) the charge stored in the “capacitor,”    C(Round to the nearest integer)
(c) the energy stored in the “capacitor.”    $ \times10^{8 }\,J$

  In a photocell, ultravioleasjj0iw25ph n l8,i7y t (UV) light provides enough energy to some electrons in barium metal to eject them from a surface at high speed. See Fig. pwan257ijiy s 0l hj,817–33. To measure the maximum energy of the electrons, another plate above the barium surface is kept at a negative enough potential that the emitted electrons are slowed down and stopped, and return to the barium surface. If the plate voltage is $-3.02V$ (compared to the barium) when the fastest electrons are stopped, what was the speed of these electrons when they were emitted?    $ \times10^{6 }\,m/s$

  A point charge is placed 36 cm from an .xsjrko 8ci,/f-5iw cidentical $+33\mu C$ charge. A $-1.5\mu C$ charge is moved from point a to point b in Fig. 17–34. What is the change in potential energy? $\approx$    J (round to one decimal place)

  A capacitor is made from tz/z. u8s ybjw j+w:bj2*btw,1:nt fdewo 1.1-cm-diameter coins separated by a 0.15-mm-thick piece of pzb b ej:.s ,t1d*zy/jwf2 wu:8t+bn jwaper $(K=3.7)$ A 12-V battery is connected to the capacitor. How much charge is on each coin?    $ \times10^{-10 }\,C$

  A $+4.5\mu C$ charge is 23 cm to the right of a $-8.2\mu C$ charge. At the midpoint between the two charges,
(a) what are the potential    $ \times10^{ 5}\,V$
(b) the electric field?    $ \times10^{6 }\,V/m$  ----待选择----leftright 

  A parallel-plate capacitor12ewd6 zm hqqo+;)b7xifv)i c with plate area $2.0cm^2$ and air-gap separation 0.50 mm is connected to a 12-V battery, and fully charged. The battery is then disconnected.
(a) What is the charge on the capacitor?    $ \times10^{ -11}\,C$
(b) The plates are now pulled to a separation of 0.75 mm. What is the charge on the capacitor now?    $ \times10^{ -11}\,C$
(c) What is the potential difference across the plates now?    V
(d) How much work was required to pull the plates to their new separation?    $ \times10^{-10 }\,J$

  A $2.5-\mu F$ capacitor is fully charged by a 6.0-V battery. The battery is then disconnected. The capacitor is not ideal and the charge slowly leaks out from the plates. The next day, the capacitor has lost half its stored energy. Calculate the amount of charge lost.    $ \times10^{-6 }\,C$

  Two point charges are fixed 4.0 cm apart from each other. Thc, o1;hmi oz92 m vcy6vit74d: nbxta5eir charges are $Q_1$=$Q_2$=$5.0\mu C$, and their masses are $m_1=1.5mg$ and $m_2=2.5mg$
(a) If $Q_1$ is released from rest, what will be its speed after a very long time?    m/s
(b) If both charges are released from rest at the same time, what will be the speed of $Q_1$ after a very long time?    m/s

  Two charges are placed as shown in Fig. 17–35 wix: ccurb7, )fbth $q_1$=$1.5\mu C$ and $q_2$=$-3.3\mu C$ Find the potential difference between points A and B.    $ \times10^{ 5}\,V$