If two points are at the same potential, does thq -s:p8s9e5s iprww vqt/ 9x4eis mean that no work is done in moving a test charge from x seevt rq4s9sw:-/ i8wpp9q 5one point to the other? Does this imply that no force need be exerted? Explain.

If a negative charge ivbt6v*di ete5l((6 u ps initially at rest in an electric field, will it move toward a region of higher potential or lower potential? What about a pp* tlu dbit56e( v(ve6ositive charge? How does the potential energy of the charge change in each instance?

State clearly the difference (a) between electric potential and electrp- 7nj-hp 1rwc12o dzsic field, (b) between electric potential 1sp7wr2h o j-p n1dz-cand electric potential energy.

An electron is accelerated by a potential difference of, ub(348tp5izu it6 fc ssay, 0.10 V. How much greater would its final speed be if it is accelerated with four times as m t( z3p4u8iu6fcts 5ibuch voltage? Explain.

Is there a point along -wbu czb 9nbh 5cl4rsn1-;w 6zthe line joining two equal positive charges where the electric field is zero? Whhlbzwb-nc;sz9 n wu-r c154b 6ere the electric potential is zero? Explain.

Can a particle ever move from a region of low electric pote rzjiwvt 0/k5ci;:yze2 o(s9 tntial to one of high potential and yet have its electric potential energy decrease? :z0e iwi(jy 5z92; octk/ tsvrExplain.

Compare the kinetic energy gained by f7ztw3f9c(4jj r9dn f 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 cx4lyfoeti2 key -5;1h ross? Explain.

Draw in a few equipotential line.1cox8t o- l:3ut sx x,vxbw1k;qmf s6s in Fig. 16 – 31b.

What can you say about the electric field in a region of space ti 55kc2yyaeel*n :lr-hat has the same potentice-2rl:yn5 5* aykl eial throughout?

A satellite orbits the Earth along a gravitational equipotential line. Wf c pb an+8q(6rh1jqfml yv072hat shape m lfc0(r+17 q8avm2 pj 6nyfbhqust the orbit be?

When dealing with practical devices, we often take the ground (the Earth) to benufbk .9: 0vno 0 V. If, instead, we said the ground was how would this affect (a) the potential V, and 0 .k9:onnvfub(b) the electric field E, at other points?

When a battery is connected to a capacitor, why do the two plaigbh ugopd4k n:h/t(5sf xn-87on: l/tes acquire charges of the same magnitude? Will this be tru:tdob5x7n(ins8/hp4 nkl -hu fg: og/e if the two conductors are different sizes or shapes?

We have seen that the capacitance C depends on the size, f7gifh3u fsz.jxezx - ;np+k-,k31n rshape, and position of the two conductors, as well as on thx+ 1;gikk3z rjnxfuepzfs-,3.7f -hn e dielectric constant K. What then did we mean when we said that C is a constant in Eq. 17 – 7?

  How much work does the electric field +(/3v/ .jupaolumd if 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 proton from smz zfv) 3m rl/e,yz6*a point with a potential of e)yvz/m3z,*zm srf l 6$+125V$ to a point where it is $-55V$ Express your answer both in joules and electron volts.
   $ \times10^{-17 }\,J$
   eV

  How much kinetic energh b0jpn7ghj+f1yl+ p 6y will an electron gain (in joules and eV) if it accelerates through a potential difference of 23,000 V in a TV pjl h+p jbpg+ h6y7f0n1icture tube?
   $ \times10^{-15 }\,J$
   eV

  An electron acquires lul/v v rk0yxia) a(3xp)) 2vl$7.45 \times10^{ -16}\,J$ 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 kc5x: x2n3w,yi jr) cmp;4hgv.8 mm apart if the potential difference bwi5;mx)vx p jkcy:32hg,cn 4retween them is 220 V?    $ \times10^{ 4}\,V/m$

  An electric field ofiny:xll/j 4lkkf)a (+ $640V/m$ is desired between two parallel plates 11.0 mm apart. How large a voltage should be applied?    V

  The electric field between two p1 xq nvi3+jdi;arallel plates connected to a 45-V battery is $1500V/m$ How far apart are the plates?    m

  The electric field between two parallel plates connected to* q.b*7y rdpt sl1xgj- a 45-V battery is $1500V/m$ How far apart are the plates?    m

  What potential difference is needed to0ayv ,t3q;c.egh 3iif *m 3ejd give a helium nucleus $(Q=2e)$ 65.0 keV of kinetic energy?    $ \times10^{4 }\,V$

  Two parallel plates, connects4:q qulaa*p 1ed to a 200-V power supply, are separated by an air gap. How small can the gap be if the : l*qs1a4uqap 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 to6oglyg3o/ktgv0g 73dx 4/ xl e 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 electron with kinetic nqm7w85lb 5dz energy
(a) 750-eV,    $ \times10^{7 }\;m/s$
(b) 3.2-keV?    $ \times10^{7 }\;m/s$

  What is the speed of a proton whose kinetic energy is 3.2 kdag s ie(0):xeeV?    $ \times10^{5}\,m/s$

  An alpha particle (which is a n1 v(*svq3qp 3,fqnlghelium 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 poxnwe :g+ 62bw1ny)0 ni:t silnj/bg7 wtential 15.0 cm from a $4.00\mu C$ point charge?    $ \times10^{ 5}\,V$

  A point charge Q cre(3cy rlh+g:x wkwnu7 5ates an 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 conductolu1ekaj+ : y)lrj qemi8-.9h0 9jni tgr carries a net negative 8e ai j) yimt -9hujgl.:1lqjkn+0er9 charge, $-Q$. Draw in a dozen electric field lines and two equipotential lines.

  (a) What is the electric potent4ig 5ipypt.03cizv h:zsakm+r1x c:3 ial a distance 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 at the corners of a square of side L zvs) zi7qf6,d as shown in Fig. 17–25. What is the potential at thez,7 zv qf)6dsi fourth corner (point A), taking $V\,=\,0$ at a great distance?

  An electron starts from rest 32.5 cm frkqqs f 8/tsp 7v;m;au (x/y5cvom 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 don qais 43lxj3u+e to bring three electrons from a great distance apart to sx+iua43j lq3$1.0 \times10^{-10 }\,m$ from one another (at the corners of an equilateral triangle)?    $ \times10^{-18 }\,J$

  Consider point a which is 72 f0(*tb7rqdq rsofa)(fobd7 u x2 t*9m cm 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 used to zsn87 )fm:poyd5tl w5-ln0rx2k)j s faccelerate 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 sepnrz( :uyd72i.uwjx z3 arated by a distance d, as shown in Fig. 17–27. Dejw 27:3udnurz y( xiz.termine a formula for $V_{BA}\,=\,V_B-V_A$ for points B and A on the line between the charges.

  In the Bohr model of the hydrogen atom, an electron orbits a proton2qwag-*d/f1z i ec ,7ii e0v4ggcag/hayb7 s6 (the nucleus) ia/0w 7i*geg7/1a42h cez -ic agdgsfi6 qyvb,n a circular orbit of radius $ 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 p 36basah0) ; vulejz,:l yw -tj29pec$ 0.53\times10^{ -10}\,m$. apart. What is their dipole moment if they are at rest?    $ \times10^{-30 }\,C\cdot\,m$

  Calculate the electric )*a3dlh aqs9ih( sc,xpotential due 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 an/ahwt;+1vaxgs ti +)s a vector, points from the negative to the positive charge. The xh;wanv gat)+t+ /is1water molecule, 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 ca6 78,a n m.ilkojn4jtlpacitor 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 c6g pllzr5mcpj;xpk6, j0 7q+9ak m)mpapacitor 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 minus caoqho 3lp, 35mharges of $ 16.5\times10^{-8 }\,C$. What is the voltage across the capacitor?    V

  The potential difference between two short sections of pwqqf fqnn;i9*a b -/fy*16l0afsz3iuarallel wire in air is 120 V. They carry equal and opposite charge of magnitude 95 pC. What is the capacitance of the twonw*z 0f9n s/lyufqaibf36q;*fi1- aq wires?    $ \times10^{13 }\,F$

  How much charge flows from each terminal of a 12.0-ms vzfdjl ch2;rkn-n;b ;99v;V battery when it is connected to a fbhs;jc lndz9r-vm;; nv9k; 2$7.00-\mu F$ capacitor?    $ \times10^{-5 }\,C$

  A 0.20-F capacitor is desired. What area must the plates have if they are to9mt9 y iml7(yy ,w,xtf be separated by a 2 yty7 mitm,(,9w ly9xf.2-mm air gap?    $ \times10^{ 7}\,m^2$

  The charge on a capacitor increases bygftna 22jy o/rx729pgs)b r3f $18\mu C$ 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 vunqkmdef8fz8* iaa: ev310 9$8.5 \times10^{ 5}\,V/m$ 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 oppositelv nv6b*o0znf jk+9- e $5.2\mu C$ 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 fieb h.m * oxr-z9f.5nqx+p ah) +9awjkjxld between the 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 (Flxu7vziqvx5m4 nvq )67okz16 ig. 17–29a) and then is disconnected fvqnxliv mk 46q6) xuzz571v7orom the battery. When this 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 squareivk* y t:q2mify4v ;4d6sp)yy parallel plates 5.5 cm on a side that are sfdv*4m s 6i yi2yqky)v4t; y:peparated by 1.8 mm of paraffin?    $ \times10^{-11 }\,F$

  What is the capacitance of a pair of circular plates with a radius of 5.5 ugmyrpn .)h.0 cm separated by 3.2 mm oprynu5. .m )ghf mica?    $ \times10^{-10 }\,F$

  A 3500-pF air-gap capacitor is connej mr) e3(8he5h(skejd5kta 1p cted to a 22-V battery. If a piece of mica is placed between the plates, how much charge will)dsmr 1h(3j eah58jp5( kte ek flow from the battery?    $ \times10^{ -7}\,C$

  The electric field between the plate ./(q s.chztu8ackx-w s 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 stor 8)og fzh+a ze spfl;4i.;fio(ed?    $ \times10^{-4 }\,J$

  A cardiac defibrillator is used to shock a heart th(;ivz*tzppg i:p3s qao9i)n5 n/3vr mat is beating erratically. A capacitor in this device is charged to 5.0 kV and stores 1200 J of energy.zp)p9iqv: t3;nz(3 pgv/nrsm oi5ia* What is its capacitance?    $ \times10^{-5 }\,F$

  How much energy is stored by the ele:8d:2xgox(5: zpdk.o ufihw p ctric field between two square plates, 8.0 cm on a side, separated by a 1.5-mmkoxf.u:xh82(::o p5 z dgpdwi air gap? The charges on the plates are equal and opposite and of magnitude $420\mu C$.    J

  A homemade capacitor isg4w ezdjsjo/w8kfqyy eri-g./ 24 78y assembled by placing two 9-in. pie pans 5 cm apart and connecting them to twr4k. jfw 8yq 7oegze/d/g-8s2yj y4ihe 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 hno,.jh q ww 8i-(7*tk0 wx+o9 bycippvas 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 stored in a capacitor change if (a) the potential ditb6x7mk8s a i)fference is doubled, and (b) the charge on each plate is 7imk8 xst6a b)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 horizo: awh-x 9i7:rqqha* mbqr lc.4ntally by 7.0 kV. They then pass through a uniform electric field E for a distance of 2.8 cm, which deflects them upward so they reach the iha4h7 q:wc.r*9qax ml:br q- 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.7fo,9mpa.d */pr d sov The screen is 30 cm wide and is 34 cm from the 2.6-cm-long deflection plates. Over vo/.7pa*o p ,d rmfds9what 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 asgn8m a2;8a;uuc bed(cquires 6.3 keV of KE in moving from point A to pon2agsbcdam 8(eu ; u;8int 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 c lyk;y)*-utbm.pc-.k lb7mfsharge 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 t:y-k mi93xwbz z6i 4cipbv:t7 he Earth’s surface whose 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 picture tubeq (5z9, l e2ddfo5zsgx, 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 go,elxs9dz2 (5zq5fdof gravity so that an electron would remain stationary? Assume that the electric field is uniform.    $ \times10^{ -12}\,V$

  A huge 4.0-F capacitor has enough stored energy to heat 2.5 (d*78iljzppq8r9: rm r5tq iykg 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 7k(nb 6g whx,8p7m )s6vibg;8i arbgebattery until it is fully charged, after which it is disconnected from the battery. A slab of paraffin is then inserted between the plates. Whatkhb7isi(,7gpb8 ) 6exgrma;v bg86wn will now be the voltage between the plates?    V

  Dry air will break down if th5 tbev- tz.;(rjyzf:x e electric 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 c1j q7.tpqzvvv-r: uo9orners of an equilateral triangle (side L) as shown in Fig. 17–30. Determine the potential at the mqp.9v-zvo 7j:vq1rutidpoint 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 a pie*sthe85lj u e;3gl 0bece of Pyrex glass is placed between the plates, how much charge wi85 b jlueeg*tl e30sh;ll then flow from the battery?    $ \times10^{-8 }\,C$

  An electron is accelerated horizontally from rest in a television picture tubeh xs+56/)vz e ,*bkmwczsvyr7 by a potential difference of 5500 V. It then passes between two horizontal plates 6.5 cm long and 1.3 cm rmv)/zbvehz*wcs7 y5x6 ,ks+ 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 capaciv,1/mdaue -7wgrq.e n0ajz5ttance $C_1$ 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 ais ajq me)z-j)3 td);v 1-F air-filled parallel-plate capacitor for a circuit you are building. To make it ajqt )-)sdzai3m; )ej v reasonable size, suppose you limit the plate area to What would the gap have to be between the plates? Is this practically achievable?    $ \times10^{-16 }\,m$  ----待选择----YesNo 

  Near the surface of the Earth ther l-p26vik0o ele is an electric field 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 l;r(hbu c;ooc 4aser 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 pot9uoxkmi8d3 *oiw gmx:n42ag 1ential difference between the Earth and the bottom of the t1xn9 m do3*ko8g ui g2mai4w:xhunderclouds can be 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, ultraviolet (UV) light provides enough energygm0:11 hysydy 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, another plate above the barium surface is kept at a negatismyh gd1:0 1yyve 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 id ;3ogz:kop(nnm(o kg6,xl + . a:whfrrentical $+33\mu C$ 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 by am y.d6-qn()k- f yenf fn(ksj- 0.15-mm-thick piece 6dkf( (en k.- fn-)yfynm-sq jof paper $(K=3.7)$ 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 plat29pxolzii b/ t(4-dfve 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 4.0ia7em l+lrf.9 cm apart from each other. Their 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. jolqw :v+:z* cko,fo- 17–35 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$