If two points are at the same3v nbh1 y5pobwm 88ee7 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 n38b w1hbo vnp85 y7eemeed be exerted? Explain.

If a negative charge is initially at rest in an electric fibcon, irzrh 5r n+7 h)po2;d(keld, will it move toward a region of higher potential or lower potential? What about a positive charge? How does the potential energy of the oroir;( 5)hc+zb2 ,r h7npdk ncharge change in each instance?

State clearly the difference (a) between electric potentialacp5gd1cfaa .9g)n i ) and electric field, (b) between electri )9d5f.iacg) ag1ncapc potential and electric potential energy.

An electron is accelerated by a potential difference of, say8o5uu(3ijtlp tsm4zg ..p1g u, 0.10 V. How much greater would its final speed be if it is acceler354lpu sg. zop ug1i.(mt8tujated with four times as much voltage? Explain.

Is there a point along the line joining two equal positive +yp(csygf*q 9p ve9a -charges where the electric field a(s-*yeq v+gcp99y fp is zero? Where the electric potential is zero? Explain.

Can a particle ever move from a reg tsu w2d**obc(uk c.1rion of low electric potential to one of high potential and yet have its electric potential energy decrease? Expla*cb.dw(u 2ocr*k tsu1in.

Compare the kinetic energy gained by a pjt.2uhlu6r h +roton $(q=+e)$ 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 cr/f ,tqlc p0uk1 u+bh1loss? Explain.

Draw in a few equipotential lines in Fig. 16 – box 1 mj4w 6txnc-ic;-31b.

What can you say about the electv te/g.mzo ,(ury+ j9s/b s(jfa2z1wc ric field in a region of space that has the same potezcy2 .1,br/om+9( a usf tjv/zsg j(wential throughout?

A satellite orbits the Earth alon,s2bw e,kka9wmv)g + qa.c/ bwg a gravitational equipotential line. What shape must the orbit bes,bbk92vc w, /.+ww aak)m eqg?

When dealing with practical devices, we often take tlt a1-pe2zhz06o cg) ehe ground (the Earth) to be 0 V. If, instead, we said the ground was how would this affect (a) the potential V, and (b) the electt 6hg)1oz l-zce2pa0e ric field E, at other points?

When a battery is con+ ),qb5q9 fgduhqm/ kinected to a capacitor, why do the two plates acquire charges of the same magnitude? Will this be true if the two conductors are different sizes or shabdqfg/hiqku 9 5 ,)q+mpes?

We have seen that the capacitance C depends on the size, shzlbw9l* 2i6cj z9r 2atape, and position of the two conductors, as well as on the dielectric constant K. What then di92 act*i629 jwbrllz zd we mean when we said that C is a constant in Eq. 17 – 7?

  How much work does the electric field doy:4ke un95w gtw* )pcgnno* *a 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 elec 3rldcxwk24f)mxs zcn5t-kt+/m 2 - ndtric field do in moving a proton from a point with a ponl4 xn/d)t5w+c tmc-m2 2xfkz3s r-dktential 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 joules and e5 b,jjcho 70j 1m3opamoj/.irV) if it accelerates through a potential difference of 23,000 V in a TV picture tubrh o .3jmpjb,j1a750omcji / oe?
   $ \times10^{-15 }\,J$
   eV

  An electron acquires :teu)o1xb n-d/ ynu qhizi02sh; k09g$7.45 \times10^{ -16}\,J$ 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 parallel plates 5.8 mmhl qphnf;.-uj f*pdu 7hz/+ e* apart if the pop7/p * qe-jdf.zulf n; +*huhhtential difference between them is 220 V?    $ \times10^{ 4}\,V/m$

  An electric field of uy( ownsxl31j,z62t l$640V/m$ 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 battet)fphyah +m-/v, )yzp w+ 3cmxry is $1500V/m$ How far apart are the plates?    m

  The electric field between two parallel plsuvz1 (3za4p xoxt1g e n27:wpates connected to a 45-V battery is $1500V/m$ How far apart are the plates?    m

  What potential differe ztclqx (05ais2yv(m6nce is needed to give a helium nucleus $(Q=2e)$ 65.0 keV of kinetic energy?    $ \times10^{4 }\,V$

  Two parallel plates, connected to a 200-V power sup1umf8. wvl5k*r d 4tteply, are separated by an air gap. How small can thu mw .vftr*led5k8t 41e gap be if the air is not to become conducting by exceeding its breakdown value of $E\,=3 \times10^{ 6}\,V/m$?   $ \times10^{-5 }\,m$

  The work done by an external force 7 vx+9e8 juej1enfr9lto move 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 an electro 2gj+ jqbzzea ,6n/hi/n with kinetic energy
(a) 750-eV,    $ \times10^{7 }\;m/s$
(b) 3.2-keV?    $ \times10^{7 }\;m/s$

  What is the speed of akzshx,,y fe*6 proton whose kinetic energy is 3.2 keV?    $ \times10^{5}\,m/s$

  An alpha particle (which is : ;+sc qsiqer/j63thya helium nucleus, $Q=+2e$, $m\,=\,6.64\times10^{-27 }\,kg$) is emitted in a radioactive decay with $_{KE}$ = $5.53MeV$ What is its speed?    $ \times10^{7}\,m/s$

  What is the electric potenti28wc 558wzbfbv9 nar xal 15.0 cm from a $4.00\mu C$ point charge?    $ \times10^{ 5}\,V$

  A point charge Q creates anm4 yz3pw.k uv+ electric 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 the shape of a football. This conductor carrie lo ksh43w6tcprr4d +6s a net negative chargk rcpdhwst6 46or4l+ 3e, $-Q$. Draw in a dozen electric field lines and two equipotential lines.

  (a) What is the electric potential a distaved7hr xa9ta129d y:m-) hbjezee9 68a. odoxnce 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 are arranged )ru/qr14k hqaat the corners of a square of side L as shown in Fig. 17–25. What is the potential at the fourthk ah/rr)1u4qq corner (point A), taking $V\,=\,0$ at a great distance?

  An electron starts from rest 32.5 cm t3;-zx pbj;rc9gy ;q* dyeih1 from a fixed point 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 done to bring three electrons from a grea-2u(lunw/34- z udakvvn tu.5kynw x /t distance apart tolx/ku5wz -un2nn uyuk.v 4aw/-d(vt 3 $1.0 \times10^{-10 }\,m$ from one another (at the corners of an equilateral triangle)?    $ \times10^{-18 }\,J$

  Consider point a which is 72 cm north oj: gmzr /()3yshki +fnf 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 uff8b l,/p-c wmsed 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 bvjdem1fo 01 h)xrb8m:)u zcn9y a distance d, as shown in Fig. 17–27. Determine a formula foe1c)j9f1 bh8 :vu)0m drxzno mr $V_{BA}\,=\,V_B-V_A$ for points B and A on the line between the charges.

  In the Bohr model of the hydrogen atom, ann4 26jou.zjpyh. ni (8h cwm *yh,l.uo electron orbits a proton (the nucleus) in a circular orbit of radius p.o( 86hw yjmjhc4 oynni2.uuh,*lz .$ 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 are vtq-2 .9 hrmyd6t 0nnx$ 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 due to a dipole whose dipy762dp i8vkn jole 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 ne2za,g-gsu4 gh gative to the positive charge. The water molecule, Fig. 17–28, has a dipol haz g4sugg2,-e 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 cap)h 3nl5e0pu fe+y+tor rzb g/ (lpr.9zacitor 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 capack;xg7l6/v+qods6 x -1zehcv mitor 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$

  A 9500-pF capacitor holds plus and minul80j6ay(d. e:cd rl3 znrl dn0s charges of $ 16.5\times10^{-8 }\,C$. What is the voltage across the capacitor?    V

  The potential differencek2(dsmwf: l 6bdw,;md between two short sections of parallel wire in air is 120 V. They carry equal and opposite charge of ma2s ; ,6dbmflmk:dw(dwgnitude 95 pC. What is the capacitance of the two wires?    $ \times10^{13 }\,F$

  How much charge flowsi92vc5mnu0 c v from each terminal of a 12.0-V battery when it is connectedvc59vm c02 iun to a $7.00-\mu F$ capacitor?    $ \times10^{-5 }\,C$

  A 0.20-F capacitor is desired. What area m5w t u6:; v.(7qwhpqzqkvpa5wust the plates have if they are to be ut.5v;(5p aq hpwzvwk76 w:qq separated by a 2.2-mm air gap?    $ \times10^{ 7}\,m^2$

  The charge on a capacitb,p0 q5gdm a0 9kdi:qzor 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 u,kct4h;m+qd vx:cj,. km cpc g z*9*t$8.5 \times10^{ 5}\,V/m$ 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 opposizw9+)zisfa ) lte $5.2\mu C$ 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 tgj43qr(vgbf9;ba kn 7he plates of a $0.80-\mu F$ 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 (Fig. 17–k nk+ z,1 5doc0gogyrk5 ;uq,m29a) and then is disconnected from the battery. When tzk1o q5dgo kc 5m,kuyn;g+r0,his 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 parallel plates 5.5 cm i p/o4vh++ng. msfyr ,y:xs2pu+ s8b yi/ji d8on a side that are separated by 1.8 mm ofo,ydb+ss.8+umi/i/srxg+in2:hf j8vyppy 4 paraffin?    $ \times10^{-11 }\,F$

  What is the capacitance of a pair of circular plates with a radius of 5.0);d6u2wr )2arua sea,ezex r0 cm separated by 3.2 mmars,e6au0) er)u2exwzr 2ad; of mica?    $ \times10^{-10 }\,F$

  A 3500-pF air-gap capacitor is connected to a 22-V battery. If a piece lg (qb no 46zbi yod;);54znqgz+u2oxof mica is placed between the 54z4b)ybozi;xg(26n; lo qnuqzdo +g plates, how much charge will flow from the battery?    $ \times10^{ -7}\,C$

  The electric field between the plates of a paper-separatpnzon 3pgxkj054-n8 s ed $(K=3.75)$ 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 storwlp, kmk9g47avb(ym0 ed?    $ \times10^{-4 }\,J$

  A cardiac defibrillator is used to shock a heart that is beating er6r(.phff e8 zq1v e+qzratically. A capacitor in this device is charged to 5.0 kV and stores 1200 J of energy. What ie8qf.h1+qzr(6 f vzeps its capacitance?    $ \times10^{-5 }\,F$

  How much energy is stored by the eleat)1cuto.ln 9 ctric 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 and opposite and of ut.loc91atn) magnitude $420\mu C$.    J

  A homemade capacitor is assembled by placing two 9-in. pie pans 5 cm apart and ipzd- *)n:ino ruk4fyd8;six6 3 1uduconnecting them to the opposite terminals of a 9-V ip*uxr)uukdsz no-i3:n 8yd; i6d 4 1fbattery. 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 capacitorzi: q usms.p(0 has fixed charges $+Q$ 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 storeiubd8rc +x x;l- i ,z1 ikrd3x/j/chl7d in a capacitor change if (a) the potential difference is doubled, and (b) the charge on each plate is doubled, as the capacitor remains conneci-i8xr ih3l7drlkj ,+bcx/x u c/;1zdted 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 accexy c)(7b+m oi,xjn:s elerated horizontally by 7.0 kV. They then pass through a uniform electric field E for a distance of 2.8 cm, whj, em (y7)bcxxi:s+noich deflects them upward so they reach the screen top 22 cm away, 11 cm above the center. Estimate the value of E.    $ \times10^{5 }\,V/m$

  Electrons are accelerated by 6.0 kV in a CRT. The screen is 30 c:n *q pr:ee)zcm wide and is 34 cm from the 2.6-cm-long deflection zc r:pq)e *ne:plates. Over what range must the horizontally deflecting electric field vary to sweep the beam fully across the screen?    $ \times10^{5 }\,V/m$ to    $ \times10^{5 }\,V/m$

  An electron starting from rest ac1- aq7g 8yihfhdw6 z2xquires 6.3 keV of KE in moving from point A to point B.d-x7wzih q gaf126hy 8
(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 transf(1ofs :m2t7d;yljxuz;feco ;w4ob 7 zers 4.0 C of charge and 4.2 MJ of 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 whoshs3aty,tlsyui/)a ,tisv, 80e magnitude is about $150\,V/m$ How much energy is stored per cubic meter in this field?    $ \times10^{-7 }\,J/m^3$

  In a television pictur*; *wneu+(cf ;/k7v5xv -kt ufsdlmfs e tube, electrons are accelerated by 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 stationa lc-fe5k;v*7 ;mx*kfftv+ /(usnwusd ry? Assume that the electric field is uniform.    $ \times10^{ -12}\,V$

  A huge 4.0-F capacitor has enough stored energy to heat 2.5 *5jd yypg0 ls*kg of water from 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 b6eg8 ceu5xr 3bw ;n4bwattery until it is fully charged, after which it is disconnected from the battery. A slab of paraffin is then inserted between the plates. What will now be the voltage5reun; egww 34xbcb6 8 between the plates?    V

  Dry air will break down if the electr( bcl4r1bh-ad,e7h y tic 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 Ln2 7rt ;lavk+i) as shown in Fig. 17–30. Determine the potential at the midpoi;vkr2il+7 tna nt 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 a 9.0-V battery. If aeh61r 5le1-u ;b qy*1mlm bhcw piece of Pyrex glass is placed between the plates, how much charge will then flow from the battery? e-1w*bl5 crmyq;eh1l6m1buh   $ \times10^{-8 }\,C$

  An electron is accelerated horizontally from rest 6y;quxdq gm3z k9 15gjin a television picture tube by a potential difference of 5500 V. It then qyg3um1z6jd5kq9 ; xg passes between two horizontal plates 6.5 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 capacitanso t54wz e,wkt (p;v++wbd5 ilce $C_1$ 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 to make a 1-F air-v8 vzild gksri;b1//cp4k/h3 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 rch1bvk/;4gl3d z iv/p8ski/ practically achievable?    $ \times10^{-16 }\,m$  ----待选择----YesNo 

  Near the surface of the Earth there is an electric field8y dt- mvr 8s yfe/e6kq(s bp2uut/3d7 of about $150\,V/m$ 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 pulsed nitrogen laser hvpf4ymkbg-xgp:o6k+: 0 xlg3-a b*yuas 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 Earthq 3del2bnjix,4yyu4 - and the bottom of the thunderclouds can beni2y3 qu4d,4x-ybejl as 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, ultravib zlfe wtu38/ l-axx7-olet (UV) light provides enough energy to some electrons in barium metal to eject them from a surface at high speed. See Fig. 17–33. To measure the maximum energy of the electrons,-lb fa7u/3xt e8 -xlzw 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 iden1 2a8osbsz+xt1n3czq b( n qy2tical $+33\mu C$ 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 two 1.1-cm-diameter coins separated;aagk7i )c w;ox*zsc3g(o tk / by a 0.15-mm-thick piece of pap cca7 )xg;ooki3(*zs kt wa;/ger $(K=3.7)$ 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 capacitor with plate are2 4qe+:,3zuvohh-0gk . m/ t;djea zpbvg8nlva $2.0cm^2$ 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. Their charg*w)nvxkie)f 6v/, w daes 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. d (e9:zsuy 7xk17–35 with $q_1$=$1.5\mu C$ and $q_2$=$-3.3\mu C$ Find the potential difference between points A and B.    $ \times10^{ 5}\,V$