If two points are at tqowuapp8hy6 jl. :5b6 he same potential, does this mean that no work is done in moving a test charge from one point tjb:6hp86ly5 .o au pwqo the other? Does this imply that no force need be exerted? Explain.

If a negative charge is initially at rest i,rmk(x2zap 5u n an electric field, will it move toward a region of higher potential or lower potential? What about a positive charge? How does the potential enerp(2k,xu5mz argy of the charge change in each instance?

State clearly the difference (a) betw/nlxn;l83y8gyil-*7 oap rkceen electric potential and electric field, (b) between electric potential and electric pote gn/rclpyl- k88la3i n 7*;oyxntial energy.

An electron is accelerated tcbtcjd pklq5(s ; a:l064gy /by a potential difference of, say, 0.10 V. How much greater would its final speed be if it isq5clktdg6(/ps0cjl:t4b a y; accelerated with four times as much voltage? Explain.

Is there a point along the line joining two equagbvx9z;u-, :jep :fdpyc (lb 1l positive charges where the electric field is zero? Where the electric pote1:- y,dbzx:f; upv(9p cebjglntial is zero? Explain.

Can a particle ever movbc :ay: fp(1ose from a region of low electric potential to one of high potential and yet have its electricy :(f1 bosa:pc potential energy decrease? Explain.

Compare the kinetic energy gak1zf iz x.kfddz/6200 vgscw.ined 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? Explaixixu9emg w952/)1ximgraw + pn.

Draw in a few equipotential lines ya2 i7,y6fhsjycuhj,,.pu g0* ;tb iein Fig. 16 – 31b.

What can you say about the electric field in a re+g qhb mahn )6))a:xkrgion of space that has the same potential thma:)+rkh)gq 6xnhba)roughout?

A satellite orbits the Earth along a gravitawcl2et n05glt0iu b,y e1(r hrry,9z;tional equipotential line. What shape must 2eh 0z9,,w1 e;rgr5lt0 brlytyu(incthe orbit be?

When dealing with practical devices, we often take the ground (the Exwzj* :sov)iamyc y 97m2 5h(barth) to be 0 V. If, instead, we said the ground was how would this affect (a) the potential V, and (b) the electh2 ) (my:ajzcb5ximswv9y *7oric field E, at other points?

When a battery is connected to a capacitor, why doncm86ytyfp;1-f oe 4o the two plates acquire charges of the same magnitude? Will thisym 1coy of4n pe-;6tf8 be true if the two conductors are different sizes or shapes?

We have seen that the capacitance C depends on the size, shape, and r 2zflk +t,l5g6otn/iposition of the two conductors, as well as on the dielectric constant K. What then did w zlt , /ig5kn6or+2ltfe mean when we said that C is a constant in Eq. 17 – 7?

  How much work does the electric field do i n7p9 j 4dsaltrp:y7z/n 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 mobbb6*j w aj/m*ving a proton from a point with a potential of6jbw ba*mj/ *b $+125V$ 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 joula4)y7ovld rh6es and eV) if it accelerates through a potential difference of 23,000 y lvroa )674hdV in a TV picture tube?
   $ \times10^{-15 }\,J$
   eV

  An electron acquires frt*b hyfg63 ,x*cpb, a9 ncpak-j(u8$7.45 \times10^{ -16}\,J$ 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 tws/(dpfa.6d yb 9*symy )xiru/o parallel plates 5.8 mm apart if the potential difference between them is su9r(i.6p yas/ f*xddy)mb/ y 220 V?    $ \times10^{ 4}\,V/m$

  An electric field of aosw b/yb ea )9t 3sutcj.(2)f$640V/m$ 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 bat(a.q x t.ww j1x+jfgst9gp:9itery is $1500V/m$ How far apart are the plates?    m

  The electric field between two parallel plates coneer q6o0lmpsxyh9t p +2h72n) k lo1r4nected to a 45-V battery is $1500V/m$ How far apart are the plates?    m

  What potential difference is 7x0nzkn -ez fav277 grvhjk8s7)z 0aaneeded to give a helium nucleus $(Q=2e)$ 65.0 keV of kinetic energy?    $ \times10^{4 }\,V$

  Two parallel plates, connected to a 200-V powabx,ku. h opjkc6 1-9cer supply, are separated by an air gap. How small can the gap be if the air is not to become conducting by exceeding ob6 1 9 -hxcc,upakj.kits breakdown value of $E\,=3 \times10^{ 6}\,V/m$?   $ \times10^{-5 }\,m$

  The work done by an external force toz04yomga6/b5 aeqajsp3 xt,moq;/8f 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 kinetm f+)-cqztj)jz (4) ct wie2gxic energy
(a) 750-eV,    $ \times10^{7 }\;m/s$
(b) 3.2-keV?    $ \times10^{7 }\;m/s$

  What is the speed of a prg;x/up 7c5gyr oton whose kinetic energy is 3.2 keV?    $ \times10^{5}\,m/s$

  An alpha particle (which is a helium nuclelu wfo+wv*08fpza1 8 jus, $Q=+2e$, $m\,=\,6.64\times10^{-27 }\,kg$) is emitted in a radioactive decay with $_{KE}$ = $5.53MeV$ What is its speed?    $ \times10^{7}\,m/s$

  What is the electricm al t00un -dlm7wax7tg4rc-. potential 15.0 cm from a $4.00\mu C$ point charge?    $ \times10^{ 5}\,V$

  A point charge Q creates an electric potential of u *uez0t * *ngunq0mo)$+125V$ 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. Thiswz9)y* u-sa z f/thr6b conductor carries a net negative char ua-f*96rhts /byzz) wge, $-Q$. Draw in a dozen electric field lines and two equipotential lines.

  (a) What is the elect2k5agw qegy if2i,j67/ qvrx5 ric potential 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 as z* 1lxd0x/ydxshown in Fig. 17–25. What is the potential at the fourth corner (point A), takin z*xd0/1dlxyx g $V\,=\,0$ at a great distance?

  An electron starts from rest 32.5 cm from a fixed point charge with + q0xl2kn,bjaf n gq:7$Q\,=\,-0.125\mu C$. 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 great distance a mzu4b6qn)u1srpi/ y /d96*rh pro e,px74 mtxpart to n7xrd 1so9emuzmh/rtr * ppp /xy6,4u) 6qi4b $1.0 \times10^{-10 }\,m$ from one another (at the corners of an equilateral triangle)?    $ \times10^{-18 }\,J$

  Consider point a whic1r5m m*tarv t2epcukyuy +).;h is 72 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 accey n2x1i kpc9*klerate 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+ l youlcy)t/f vd;-xm5(fc9w charges are separated by a distance d, as shown in Fig. 17–27. Determine a formulaf lytv(ux/ m;-cyo d5l9w)c+f 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 elo ;kr1-g+yg kcr3 7qq0bq ;,8eyhktxkectron orbits a proton (the nucleus) in a cir ok3 +1 ehrqg;y;gxyk8qr0tbq7k- c,kcular 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 arodgg/i;kqi aux l3 .: ymg:;ksa. (dz2e $ 0.53\times10^{ -10}\,m$. apart. What is their dipole moment if they are at rest?    $ \times10^{-30 }\,C\cdot\,m$

  Calculate the electric potentdz6 2 ie t9e07vjqgvkcjx804dial 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 as a vector, points e b/d*8o0(jpan.j po 0 ttkj0hfrom the negative to the positive charge. The water molecule, Fig. 17–28, has a dipole moment which can behpb8p0j jak/00(et* oot nj. d 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 ca pgb v7 e419i n( tijlhcr6uqm/d1-sp0pacitor 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 capacipod8xpqn3x+f,vaz9l 67 nt*vtor 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 charges;4tb9 .s f4enp 1wfkm)yqz0tt of $ 16.5\times10^{-8 }\,C$. What is the voltage across the capacitor?    V

  The potential difference between two short sections of parallel wire in air is lo8ldld4c (f4xx ;+nnn+s yzf.f+4mq 120 V. They carry equal and opposite charge of magnitude 95 pC. What is the capacitance of the two wi(sq o 4 lzn;.n d4+fxyfx8nc mdf+4ll+res?    $ \times10^{13 }\,F$

  How much charge flows from each terminc3up ,*hp1;/qvfl iba al of a 12.0-V battery when it is connected to a /fq3ipulv1ch *;ab, p $7.00-\mu F$ capacitor?    $ \times10^{-5 }\,C$

  A 0.20-F capacitor is dk sxua2qx7 audr3y3g74n yc+3esired. What area must the plates have if they are to be separat3r37q ayn4ygad2ux sxc + 73uked by a 2.2-mm air gap?    $ \times10^{ 7}\,m^2$

  The charge on a capacitor increases bwpedx1,2b.vfo um wz.vy*oru d6s. -.y $18\mu C$ 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 de xlb(-l+c r 81wqu8lgf9 qx3$8.5 \times10^{ 5}\,V/m$ 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 oppde.6u i2 9j8ibquame 5osite $5.2\mu C$ 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 elech+w 6 s aqf4-:b1 sjdadgjzf+:tric field 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 (Fig. 17–29a) and then is adfv3 * 0uqnz4disconnected from the battery. When this cap dq 3zfau0*n4vacitor $(C_1)$ 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(/aed) oobh ep (ef spl,z(2(r square parallel plates 5.5 cm on a side that are separ hre,)zdse(2o p(lba (ep f(/oated by 1.8 mm of paraffin?    $ \times10^{-11 }\,F$

  What is the capacita5qvl /nt*vvz mf u8,hyj6:w 4ince of a pair of circular plates with a radius of 5.0 cm separated by 3.2 mm of mj4u /t*vy,wil5vh:mz 8fn6q vica?    $ \times10^{-10 }\,F$

  A 3500-pF air-gap capacitor is connected to a 22-V battery. If a pi ./azla2dx-dibzo 9z0 r+ 4xswdw3m4bece of mica is placed between the plates, how much charge will flow from the batteryaz .i 4wow zd/3d0d49albsb2 + -zrxxm?    $ \times10^{ -7}\,C$

  The electric field between te xy4xj1t0c90y 0 cpprhe plates 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 capaci c0v4(dllfa1 gp77mg ifnm8y( hl +3rnvo14netor. How much energy is stored?    $ \times10^{-4 }\,J$

  A cardiac defibrillatoiid(8 42u oafs*.ib3nyq* iypr is used 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. What is its capacitay8anqio*i fy 42s dib(p3 u.*ince?    $ \times10^{-5 }\,F$

  How much energy is stored by the electrici6r tmch9-o b5;zk+rp field between two square plates, 8.0 cm on a sipi6+r5 oz;chmrt9- k bde, separated by a 1.5-mm air gap? The charges on the plates are equal and opposite and of magnitude $420\mu C$.    J

  A homemade capacitor is assembled by placingfq9 chb tv),sfq3f7f6 two 9-in. pie pans 5 cm apart and connecting them to the opposite terminals of a 9-V ff,h379qqvstfc6b ) fbattery. 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 fixedq:epv +:c) 6e/prxsb (han ;tm 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/ds 2 (nfup,z(l+ w6gikwcm7 a capacitor change if (a) the potential difference is doubled, and (b) t6kn 2mz7i fw( agl+ uc,dsw/(phe 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 are acceleratedokhnc5uu3jo2k39 +j q -n-4bo9hwgp m horizontally by 7.0 kV. They then pass through a uniform electric field E for a distance ok-mhk3 +gb op w o3jo49 nhq-92cuuj5nf 2.8 cm, which 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 cm wide anfttdd*i 1r4dkz;s+m.,ihm 3 bm9jm( kd is 34 cm from the 2.6-cm-long deflection plates. Over what range must the horizontally deflecting electric field vary to sweep the beam fully across the screen?,mdihk3( mt1 ;d.+ jk9bisrdmf*t mz4    $ \times10^{5 }\,V/m$ to    $ \times10^{5 }\,V/m$

  An electron starting from rest acquires 6.3 keV of KE inyg 76nxu uln e:7jple277/qet moving from point A to point Bp76u:/q 7exul2 eljten 7n y7g.
(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 tra gw9(haolkxzgw86uc(s av84 (nsfers 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 sur.uvzp; (l2w grface 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 tube, ele63jukpzd rm,8ctrons are accelerated by thousands of volts through a vacuum. If a television set were laid on its back, would electrons be able to move rdupjz 3,6m8k 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 the electric field is uniform.    $ \times10^{ -12}\,V$

  A huge 4.0-F capacit109 8mxffj twmtmi7 ;ne2k(b por has enough stored energy to heat 2.5 kg of water from 21$^{\circ}\,C$ to 95$^{\circ}\,C$. What is the potential difference across the plates?    V

  An uncharged capacitor is0sm/zw j,5bna connected to a 24.0-V battery until it is fully charged, after which it is disconnected from the battery. A slab of paraffin is thjanb05/ms ,zw en inserted between the plates. What will now be the voltage between the plates?    V

  Dry air will break down if the electric fie;* /h;7gpqzulzi4ee lld 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 cor)agu+ua jbjzv4p p r6-oc-+q0ners of an equilateral triangle (side L) as shown in Fig. 17–30. Determine the potential at the midpoint of ea4pqz+ c gr6 -bpvjao0ua+)-uj ch 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 piex0hq;d2m9iwh5 a +tujce of Pyrex glass is placed behdm tj+awx;2h05qu9i tween the plates, how much charge will then flow from the battery?    $ \times10^{-8 }\,C$

  An electron is accelerated horizontally from rest in a televisiol 3/iknwo7( ynn picture tube by a potential difference of 5500 V. It then 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 ay/inonk3( lw7 ngle $\theta$ will the electron be traveling after it passes between the plates?    $^{\circ}\,$

A capacitor of capacitanc4: k xcma6)oqve $C_1$ 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, supposk2ius f4nh:j7(slhzi9+ovo; c9g wg4e you want to make a 1-F air-filled parallel-plate capacitor for a circuit you are building. To make it a reasonable size, suppose you limwks:4;gg sclo4oj+2ih7uz (vn9 9i hfit 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 the5s .ffma)kch r:q.fo*e1(lr v Earth there 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 laser hasjyk7k9j;qys o9/,eon y 7/atk 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 differenqqu25vbpi h3 nj wb3,:ce between the Earth and the bottom of the thunderclouds can be as high as 35,000,000 V. The bottoms of the thunderclouds are typic2pbnq ju3:q 5v3bhwi ,ally 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+ su e3gjvv7pis+ri5054 oxpz (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, another plate above the bariv0u+45 rj s3 xpoiep+vz i5gs7um 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 identi-p1qno9yqjm y0 i/,i :blg0udqb 9 k/ncal $+33\mu C$ 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-+uzl k/fq0n q+diameter coins separated by a 0.15-mm-thick pi/lq+ 0fkzu+nq ece of 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 plate arer5 l n.iepdm24h)hk*2 6md suya $2.0cm^2$ 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.)c7d x 8ud*ond0 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. 173 lxg(uhyel)rg6ej ;/8 w 3;np hwv7pt–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$