If two points are at the same potential, doe+5y os bvfrv51s 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 bof+ 5vv1 sryb5e exerted? Explain.

If a negative charge is initially at rest in an electric field, will icq gj8k)9l9p cb2aiko zxtv 39g f5)b86bzc)at move toward a region of higher potential or lower potential? What ab5afcib k 8) 6p3cog 8kb99j q)vcla)xtg2z9bzout a positive charge? How does the potential energy of the charge change in each instance?

State clearly the difference (a) between electric ps93w jq8lh)gw .oy/dpotential and electric field, (b) between electric potential and electric potendwgq w jls839o)yh/p. tial energy.

An electron is accelerated by a potential differencfo u:8 gk jcajs4j2r-5r fhd59e of, say, 0.10 V. How much g9g jsfj kfc 5u:dj- 4hoa28rr5reater would its final speed be if it is accelerated with four times as much voltage? Explain.

Is there a point along the line joining two equal positiveci+2 dfp0 80 3uc4(ob kqoy1b8mrimkl charges where the electric field is zero? Where the electric potential is zero? Eo3+(2if ui8qk8 lbrm1dccy0 bpmko 04xplain.

Can a particle ever move from 6 c 3k/5mtz,9 tisgfgd;.vfwoa region of low electric potential to one of high potential and yet have its electric potential energ3 s6gf.g/;z9tdcofki, vwt 5my decrease? Explain.

Compare the kinetic )+vztjkmbw5tnow + +4energy 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? Explap:/*vo-f1(1mqqw,3 3aiee ugucwk5m okn .f h in.

Draw in a few equipotential likko4w;pvh.(3p p s0d9p2 vyk tnes in Fig. 16 – 31b.

What can you say about the electric field in a region of ee )st+k , ye2asnpnwxy.,1- hspace that has the same posee1x) kneyn t+ ph,.w-2 sya,tential throughout?

A satellite orbits the Earth 3cn9ox jm 2i+y6nmhj/ v1c)lyalong a gravitational equipotential line. What shape must theinn91clj o xhv3c6 )y/jy+2mm orbit be?

When dealing with practical devices, we often take the grockign-:l+s idn7xq-l , 5qw*iund (the Earth) to be 0 V. If, instead, we said the ground was how would this affectiq 57n igsdwli*xlnk c-+:,q- (a) the potential V, and (b) the electric field E, at other points?

When a battery is connected to a capacitor, why do the two plates acquire chargw(9c9c,5f uftdx djozw /b1x7es ofduf9x x,ojft5/c(b7z 1wd 9 wc the same 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, and position *izrfy:.n ouydzgr2 xuk:-/1of the two conductors, as well as on the die/*g:yf- uzn .1ruo yikxr:zd 2lectric 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 fieldfe7t-/;3hu4 vrdkw4byqfps ) 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 a point with a niuw/,jv655pbzy1 hcxg5 5 ynio rb+).wwjr- poten1bi 5 v.5r wcuwnyhni j 6/g-xro)b5z,wpj+5 ytial 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 jqc 1p,p fzl(j*x/h(i uoules and eV) if it accelerates t*l(x 1hpzf, (uc /iqpjhrough a potential difference of 23,000 V in a TV picture tube?
   $ \times10^{-15 }\,J$
   eV

  An electron acquires ul24m--yu ,8i o2y htkvnp6yf $7.45 \times10^{ -16}\,J$ 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 para uo:w a;hmv9y(l;t,p yllel plates 5.8 mm apart if the potential difference betlp:;ty,wvho ya mu;9(ween them is 220 V?    $ \times10^{ 4}\,V/m$

  An electric field of vdjxt: m 2ln68$640V/m$ 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 zbq 7jrn;xm:kad(.V battery is $1500V/m$ How far apart are the plates?    m

  The electric field between two pak0d gh+ iwibot w+0tih ;e0b(4rallel plates connected to a 45-V battery is $1500V/m$ How far apart are the plates?    m

  What potential difference is needed to give ah .mcdc 8-c2 sb/oc2i9o.spet helium nucleus $(Q=2e)$ 65.0 keV of kinetic energy?    $ \times10^{4 }\,V$

  Two parallel plates, connected to a 200-V tbn zj;*1+ha1hw7nzk power supply, are separated by an air gap. How small can the gap be if the air is not to become conducting by exceedin zn*hw7k n;bh+t1az1jg its breakdown value of $E\,=3 \times10^{ 6}\,V/m$?   $ \times10^{-5 }\,m$

  The work done by an ex;2no2 e.bbfv4tlvhdib a i9cv)54 xb/ternal force to 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 oftg ka*axff h70pnr9) . an 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 kinetic enufdbtaj,;r8s w :(x7 vergy is 3.2 keV?    $ \times10^{5}\,m/s$

  An alpha particle (which is a h*hs z(cxwc2(hw 9zq+kelium 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 poteege9qf lpn0 kmp + +88t6vaf2rntial 15.0 cm from a $4.00\mu C$ point charge?    $ \times10^{ 5}\,V$

  A point charge Q creat*idzyl;x0:4,1dydac 3si/hekw xo (b es 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 conductor carries a na1(54ex / d;se2w8l7fvxpa xrub .uol et negative cha2(./vx fbla wlu7u4;pa8x5 xed o1se rrge, $-Q$. Draw in a dozen electric field lines and two equipotential lines.

  (a) What is the electric potential a distance of eugnz h hr0kqpa(07 8.$ 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 squjt0y k x2o5xqu48*hph are of side L as shown in Fig. 17–25. What is the potential at the fourth cornerjpot05huyk 84h *2x qx (point A), taking $V\,=\,0$ at a great distance?

  An electron starts fromn .ux5:k3k vpl rest 32.5 cm 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 p, *wga:owmni/z0qg 9 three electrons from a great distance apart q /m9n:gg,opiw wa*0zto $1.0 \times10^{-10 }\,m$ from one another (at the corners of an equilateral triangle)?    $ \times10^{-18 }\,J$

  Consider point a which is uc5/1n lzw/oz72 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 accelerate a prod8t3n5 qq0rpjbw9vs)ton (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 by a distamc8w8 :n6xx lynce d, as shown in Fig. 17–27. 8ymxwn:l8x c6Determine 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 hydr7eta;, (drkjk ogen atom, an electron orbits a proton (the nucleus) in a circukekr,(da7 t; jlar 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 proton93/ ap -u0it * b(jkbgwk1nsdt are $ 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 1wa2gti : ax0nto 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, d g 9.e05fnir3zr 4ewtljs:2bpoints from the negative to the positive charge. The water molecule, Fig. 17–28, has a dipole moment which can be considered as the vector sum of the two dipolz.4 tb dw5n0e2lf:rr9i3se gje 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 capacit:x w xg-biev+-9l3snlor 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 hb0gi- k2mb fa(old $+2500\mu C$ 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 pluscxect9iy.19q4q1,i0h r*e za n*gg xm and minus charges of $ 16.5\times10^{-8 }\,C$. What is the voltage across the capacitor?    V

  The potential difference between two short secz 1t,;aycxknlaxy(x( 9/m y 8ctions of parallel wire in air is 120 V. They carry equal and opposite charge of magnitude 95 pC. What is thx,/m ln (a ykxc zy1(a9c8;yxte capacitance of the two wires?    $ \times10^{13 }\,F$

  How much charge flows from each terminal of a 12.0-V batq1l 06 yuoz408loopb ptery when it is connected to a6q0 o o80oy1lplp4zbu $7.00-\mu F$ capacitor?    $ \times10^{-5 }\,C$

  A 0.20-F capacitor is desired. What area must the plates have if they are:7laefx 1 1jjq of:9 lvyryh;( to be separated by a 2.2-mm air lfey ::1yf 7qvlj 9( rh;jxa1ogap?    $ \times10^{ 7}\,m^2$

  The charge on a capacitor gpn*dp 2 :j k02q(qqqtincreases 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 oouk8m(1p9(v7esty(je j6,c vvv fl5g y,u1z$8.5 \times10^{ 5}\,V/m$ 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 opposit6if4v kll .dj8h3fpj3go v4/ ,/hl rxbe $5.2\mu C$ 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 plf4h*n3k2nzz :6fda kb ates 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–f yi49 7j tw 4e(lomvhoj2qe1)29a) and then is disconnected from the battery. When this capaci jfehy4t(1v 792)io4 mqjow eltor $(C_1)$ 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 kau(3-: 0ul fj:csqyiplates 5.5 cm on a side that are separated by 1.8 mm of paraffin? 3asu(fc::l0-ykq iuj    $ \times10^{-11 }\,F$

  What is the capacitance of a pair of circular plates with a radius of 5.0 cm sep 8b :d wxzfm9d.9 -a4ewrj3sizarated by 3.2rfbj 3i9 x4-.wmzz sdw ade:89 mm of mica?    $ \times10^{-10 }\,F$

  A 3500-pF air-gap capacitor is connected to a 22-V battery. If a pieb3cn: jwqu/u;icf 5 b4haa.o1ce of mica is placed between the plates, how much chargeafbiuj;41. oha/b cwncqu3: 5 will flow from the battery?    $ \times10^{ -7}\,C$

  The electric field between the ,z w( 5t7ioizr19czt 0af jkl2plates 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-puq7/ (xb2ailbhq1 9m rF capacitor. How much energy is stored?    $ \times10^{-4 }\,J$

  A cardiac defibrillator is used +dw i48v(tpk wgrj1lxe; plr c ro22+;to shock a heart that is beating erratically. A capacitor in this device is charged to 5.0 kV and stores 1200 J of energy.rd 2wworpiktrg+; lj+p 4x1l 8ev;c 2( What is its capacitance?    $ \times10^{-5 }\,F$

  How much energy is stored by the electric field between two sqxo /avadhu w8o7p(5lc*-o1lbuare plates, 8.0 cm on a side, separated by a 1.5-mm air g-oa w(vbo d8l5 uc/o7lpah1* xap? The charges on the plates are equal and opposite and of magnitude $420\mu C$.    J

  A homemade capacitor is assembled by placing two 9-in. pifvked:-+b 2aec uw34vqb; h5ue pans 5 cm apart and connecting them 43wbfq bke ucuv e:v-;ha +2d5to 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 capaci05b9v)i)u r7j pwlr citor 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 stored in a capacitor change if (a) the potential dtb4 xz v aaag93q+sab1; j:k:*2jchuh ifference is doubled, aj2:g:uabbxh tz1q 3a4jk; v9+acsah* nd (b) the charge on 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 ab n1w2b qygu*.lzmkr43,9t gx re accelerated horizontally by 7.0 kV. They then pass through a uniform electric field E for a distance of 2.8 cm, which deflects tt4u*,2n3gb lqrgzw 1m kbx 9.yhem 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 scpf9 jef6cad; d (+e(flreen is 30 cm wide and is 34 cm from the 2.6-cm69efjld dafpf +((c e;-long deflection 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 acquires 6.3 keV of KE in moving from gy)n 2i8tpz; npoint A to poi)p 8gny 2nt;zint 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 chargy)1o ye 8lrillxp*i/0 xt3koq wevmad)) 5 k70e 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 whose magnitude4b p0br fdgyw /-n8gy 7fs*9pz 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 tubqyvd. k68- btqe, 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 u qt bq.yvk8-d6pward 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 the electric field is uniform.    $ \times10^{ -12}\,V$

  A huge 4.0-F capacitor has enough stored energy to heat 2.5 kg of wah3d8uc; 1jlgoter 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 battery until it ih7tkht ff7 86wxoh 39ts fully charged, after which it is disconnected from the battery. A slab of paraffin is then inserted between the plates. What will now be fth3 xh96twt7 7hfo8kthe voltage between the plates?    V

  Dry air will break down if the electric field p*/m /e7 go+qfn;xry rexceeds $3.0 \times10^{6 }\,V/m$. 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) as s) 63w lxxymhyd05eye5hown in Fig. 17–30. Determine the d5x)y3 05 weh 6yemxlypotential 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 a 9.0-V battery. If a pzb 61 y*jso3rmiece of Pyrex glass is placed betweeby *61mo3 rjzsn the plates, how much charge will then flow from the battery?    $ \times10^{-8 }\,C$

  An electron is accelerated horizontally from rest inhdf(k.a g0y5)(:z xdx*akspf a television picture tube by a potential difference of 5500 V. It then passes between two horizontal platg* p(kkya:xa0 s(d x.h5 fz)fdes 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 capaci/uh 4 0:btady 68bqz;q djhm0vtance $C_1$ 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,g/hqang7a/ scn y t 44;b1b 5zi4j;lcx suppose you want to make a 1-F air-filled parallel-plate capaci4 qz acgbh 4/7tg;c;4bnnyl j5x/is1ator 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 achievable?    $ \times10^{-16 }\,m$  ----待选择----YesNo 

  Near the surface of the Earth ther g ib.. t04mpziv.ofp)e 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 )qg gzet/ m0x p ctm a65zy,apnh)3546-edarupulsed 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 bb,0ll1 cz4fv d6 wtm:and the bottom of the thunderclouds can be as high as 35,000,000 V. The bottoms of the thunderclouds are typicalb6 fl4 bw lm,ct1:zd0vly 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 (pqy(d: b rkx19k/lk w db8r)r.UV) light provides enough energy to some electrons in barium metal to eject them from a surface at high speed/ldd8k1br prbr9q) (.w:kxk y . See Fig. 17–33. 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 3( t1 iwat 5oq0zl-eu2u6 cm from an identical $+33\mu C$ 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 u/;n5;y*yghhd3hb6 l)mv2 lvtjg 1ya jz(p6vseparated by a 0.15-mm-thick piece of paper6j*n 2)yajpvub3h ( tmvly;5;vhg 6/hyd zgl1 $(K=3.7)$ 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 w)jlmbspk w 8(x*h,2ijith 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 fromt(-mxdt*vys o3 ae8z / 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. 1xy5dh-fpt -p .7–35 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$