If two points are at the same potential, does this meajv/caf qmt(j5w2, 8 fen that no work is done in moving a test charge from one point to the other? Does t/5 qem,fjtv( cwaf8 2jhis imply that no force need be exerted? Explain.

If a negative charge is initially at rest in an electric field, hsxn)v , ) vsktqj1rv0ds5.,qwill it move toward a region of higher potential or lower potential? What about a positive charge? How does the potentiqkr,j)tv ,n) q51 v.v s0sxsdhal energy of the charge change in each instance?

State clearly the diffz; qj8o qy,ja4g1d qteaws7 *7:zi5z ierence (a) between electric potential and electric field, (b) between electric potential and electric potenti; yozzet,8g*jd1zs q5ia7a wq :i7j 4qal energy.

An electron is accelerated by a potential difference of, lu 88 kt y** zls,vml*cb-w19sbr7zoi say, 0.10 V. How much greater r wklz98-ts*osz7yll1, mu *b i *bvc8would 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 positive charges where t nkj636nt9/l;j nkg2 qwmq:uthe electric field is zero? Where the electric potential is zek3jq 96u:njg26/tn tnwkqlm ;ro? Explain.

Can a particle ever move from a region of low electric potential to one40be8 m+a+cr lpf a i.ky-td(j of high potential and yet have its electric potential energy decrease? Explaitl0 cfa+d8m(j+ek ayr-p4b. in.

Compare the kinetic energyf k0ls.5a qpc9 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 linestzib29xn(t 9v cross? Explain.

Draw in a few equipotenob za3-e;/p n2m1 yeantial lines in Fig. 16 – 31b.

What can you say about the electric (g71 g28zr:l pkowxce field in a region of space that has the same potential throughout:7r2ecwgk (x8o lp1gz?

A satellite orbits the Earth along a gravitational equipotential linev;lzzp( jsfq - + sosv:e:0ad qzb*0t0. What shape m zz0qsjve0 bt:s0 *-+;a(pfzovq:sd lust the orbit be?

When dealing with practical devices, we often take themgzk246; huif ggc isk 91/;hv+ond* e ground (the Earth) to be 0 V. If, instead, we said the ground e;9*zhmikofnh;6gcug 4+ v2 1i/dksg was how would this affect (a) the potential V, and (b) the electric field E, at other points?

When a battery is connected to a capacitorl4iu)nlv3 9x psa2+vtp 1pd+ b, why do the two plates acquire charges of the same magnitude? Will this be true if the two conductorsivul9a l4+3 p +1sptd)nb 2vpx are different sizes or shapes?

We have seen that the capacitance C qf ;hc/kzw3k -depends on the size, shape, and position of the two conductors, as well as on the dielectri/- k w3kfchzq;c constant K. What then did we mean when we said that C is a constant in Eq. 17 – 7?

  How much work does th 3;e is30o4w cv afczm7x5mkh9/l7idk e electric field do in moving a $-7.7\mu C$ charge from ground to a point whose potential is $+55V$ higher?    $ \times10^{-4 }\,J$

  How much work does the electric om yu9 ive(,g,mjt*s -field do in moving a proton from a point with a potential of-gm9, t,em oju*( ivys $+125V$ 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 eV) if a:ganvb .0a/fit accelerates through a potential differeba na g/vf0.a:nce of 23,000 V in a TV picture tube?
   $ \times10^{-15 }\,J$
   eV

  An electron acquires l7q 3gq8sam iwj )72thsq;;bg)ty dq3$7.45 \times10^{ -16}\,J$ 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 plhs- x+ee 6pscn ay+-u4ates 5.8 mm apart if the potential differenccy6hu4xnses+ a-e-p + e between them is 220 V?    $ \times10^{ 4}\,V/m$

  An electric field of -/s s plhk3(uxagm-)w/ vc+4m lz;wka$640V/m$ 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 battery is j.0j/gy ;sjof$1500V/m$ How far apart are the plates?    m

  The electric field between two parallel plates connected to a 45-V jou j.b n/ff s)7+u)tkxx;y;qbattery is $1500V/m$ How far apart are the plates?    m

  What potential difference is needed to givee 8fgufh-4z rq+ g wa+92ua3hf a helium nucleus $(Q=2e)$ 65.0 keV of kinetic energy?    $ \times10^{4 }\,V$

  Two parallel plates, connected to a 200-Vww8rbm64fg1 w5/ gn appqh09oebyl hmse779- power supply, are separated by an air gap. How small can the gapb nqy pwsp0w7m m47r51 -o / 6h8lea9g9wgbhfe 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 to move ahs1 +vod nh49c $-8.50\mu C$ 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 eh1 w f+s(4g;qt;pre6 lc jra3olectron 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/,1kl d*vcore j1bx,t energy is 3.2 keV?    $ \times10^{5}\,m/s$

  An alpha particle (which is a helium nucd1p22a lld1z zleus, $Q=+2e$, $m\,=\,6.64\times10^{-27 }\,kg$) is emitted in a radioactive decay with $_{KE}$ = $5.53MeV$ What is its speed?    $ \times10^{7}\,m/s$

  What is the electric potential 15.0 cm from a vnbm fu626:* 3o/*3di 9ovij srhkbb u$4.00\mu C$ point charge?    $ \times10^{ 5}\,V$

  A point charge Q creates an electric potentb0ox-; hiu oh/ial 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 4accry+a-8*u ,fxyqr a net negative charge, f cux4- ay,q*8car+ry$-Q$. Draw in a dozen electric field lines and two equipotential lines.

  (a) What is the electric potential a distance ofk e-s*8(i gcgm $ 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 ts56+sk ke9xrd he corners of a square of side L as shown in k+xd95k6ser sFig. 17–25. What is the potential at the fourth corner (point A), taking $V\,=\,0$ at a great distance?

  An electron starts from rest 32.5 cm from a fixej5 u50sz *qz hyadmd 4s auw7hmtj9fn8j*7,y2 d 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 t :gwp5jsmxl q jt0*y9t7rtb 5.o bring three electrons from a great distance apart to7q x5j 9tgt0r5:stw jybp*l .m $1.0 \times10^{-10 }\,m$ from one another (at the corners of an equilateral triangle)?    $ \times10^{-18 }\,J$

  Consider point a which is 72 c*ley ydko *g,4pph4, tm 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 us rt.otl4qn):f ed 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 sepwey9 q;hx(ruhwtjg*,8e y-9g b zp6;qarated by a distance d, as shown in Fig. 17–27. Determi(bq 9;jyw,ee;6g9xwyuh8r-tpz gq h* ne 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 proton (the 4 .ctd)uphx 4g v8t/ve:j1xhp nucleus) cvt.:/phxu1v 8ep4j gthd4)x in 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.9gb *2a+s+(h otd 1egsgg agh $ 0.53\times10^{ -10}\,m$. apart. What is their dipole moment if they are at rest?    $ \times10^{-30 }\,C\cdot\,m$

  Calculate the electric potential4:u uqreui nwn( 7 jzzpo-9gzfak+9 24 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, consq 7guaq2w,/pu idered as a vector, points from the negative to the positive charge. The7q g2paq,uw/u water 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 capa opc-sn 7x,nb92minno.6tl;fcitor 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 capacit 0)cit a3dxqv:or 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 md)bx:s 20+ongmc1usvux6bp7inus charges of $ 16.5\times10^{-8 }\,C$. What is the voltage across the capacitor?    V

  The potential difference between two short sectisp nd1 iegf)53 2k3c ;ufukyxsoi07d:lmf7e 5ons of parallel wire in air is 120 V. They carry equal and opposite charge of magnitude 95 pC. What is t5uf)nlmx7k efkf:ey p10 5 o;3gii7ud2ss3cd he capacitance of the two wires?    $ \times10^{13 }\,F$

  How much charge flows frox m6vxz9)gg gdq*k 0f1m each terminal of a 12.0-V battery when it is connected tod01v6xg9k *g z )xmqfg a $7.00-\mu F$ capacitor?    $ \times10^{-5 }\,C$

  A 0.20-F capacitor iqr-,c zw2t5y cs desired. What area must the plates have if they are to be separated byzwcy2c - ,5tqr a 2.2-mm air gap?    $ \times10^{ 7}\,m^2$

  The charge on a capacitor increase(l3s:yxj5lj) sp,tov s 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 jayg2dw76 * ih$8.5 \times10^{ 5}\,V/m$ 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 ohdn6)p; , zqwrf13+w chdqx w5pposite $5.2\mu C$ 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 platpeyj1l,;-si res 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 baty3/ qp yya.8gho2m c6gtery (Fig. 17–29a) and then is disconnected frp/a. m26c3yq8gyy o ghom 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 square parallel plates 5.5 cm on a side thatzudj 4w3s q bz4.4yt.k are separated by 1.8 mm.y4 qk 4t4.jw3d bzuzs of paraffin?    $ \times10^{-11 }\,F$

  What is the capacitance of a pa-j m-tx+. qpfgir of circular plates with a radius of 5.0 cm sep. qj--tpxm +gfarated by 3.2 mm of mica?    $ \times10^{-10 }\,F$

  A 3500-pF air-gap capacitor is connected to a 22-V battery. If a pi )y 7uxif fyogjpzb2f-,eqp cz8+6;j/ece of mica is placed between the plates,oyczp; ),6bfz-+ f8e2ypjuqj7 f/ ixg how much charge will flow from the battery?    $ \times10^{ -7}\,C$

  The electric field between the plates of a paper-separa /fynx48 x2t*lch c 2:h.vpwgpted $(K=3.75)$ 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 muchy,39fqtu h k4ls4(y ftv-vnp2 energy is stored?    $ \times10^{-4 }\,J$

  A cardiac defibrillator is used to shock a heart twnpf c 415cqz6a+48bsx k *(cltog ae(hat is beating erratically. A capacitor in this device is char8pkc4zl( gta1fs64+baqc(* xe5n cw o ged to 5.0 kV and stores 1200 J of energy. What is its capacitance?    $ \times10^{-5 }\,F$

  How much energy is stored by the electric field between two square plates, 8.0 c jkgkz:f3t0ef+vyy2 . m on a side, separated by a 1.5-mm air gap? The charges on the plates are equal and opp:jzve+3 . k2yffty0 kgosite and of magnitude $420\mu C$.    J

  A homemade capacitor is assembled by placing two 9 2 )1yntzdvir7-in. pie pans 5 cm apart and connecting them to the op2 )vty1nzdi7r posite 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 capa7g a 3;idldy7ocitor 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 h7lr38fxyq 0z 1n9v 6v9gzewjchange if (a) the potential difference is doublwf6g9ez hzq01n9 xlrv8 7jv3yed, and (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 are accelerated horizontally by 7.0 kV; a wmsumgp)20wkswvjlq46hf) p a l4j*0m.)x. They then pass through a uniform electric field E for a distance of 2.8 cm, which deflects them upward so they reach the screen top 22 cm away, 11 cm above the center)0xmv2lphsf4j.a p uqs ))wgm0;wk l m*aw64j. Estimate the value of E.    $ \times10^{5 }\,V/m$

  Electrons are accelerated au h8rnqn ,p1fat. /o;by 6.0 kV in a CRT. The screen is 30 cm wide and is 34 cm from the 2.6-cm-long deflection plates. Over what range1ua nrf/8,o;ahptq n . 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 point A to9etb.gna2s891r 57dm u,r db0 v ermlo 7 n ur.99br ddsol, mt2agm05 br8ve1epoint B.
(a) How much KE would a proton acquire, starting from rest at B and moving to point A?    keV
(b) Determine the ratio of their speeds at the end of their respective trajectories.   

  A lightning flash transfers 4.0 C of charge and 4.2 MJ of energy to th(o,*ga 6cudei e 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 suucw wogjhf6(: *i9x p,rface 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, electrons are accelerated by thousands otdfi aw h8r8k-cy4 54lf volts through a vacuum. If a television set were laid on its back, woul5h f i8w acrdl48k-t4yd electrons be able to move upward against the force of gravity? What potential difference, acting over a distance of 3.0 cm, would be needed to balance the downward force of gravity so that an electron would remain stationary? Assume that the electric field is uniform.    $ \times10^{ -12}\,V$

  A huge 4.0-F capacitor has enough stored -m 7;whs9ug x 7ub1xjgenergy 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 is connected to a 24.0-V battery until it is fully chage y8rnp-3 hw5rged, after which it is disconnected from the battery. A slab of paraffin is then inserted between the pl8y gwrneh-p 35ates. What will now be the voltage between the plates?    V

  Dry air will break down if the ewvkyy ee5o* i9;j4p*glectric 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 (s3k3 ahg(c utw-kiu7. 8xg8f4dkj hqr.ide L) as shown in Fig. 17–30. Determine the pot th igj hdwa.8ku34r7ck g(. xkf3-8quential 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 pju8izvh:0d-0c8btk lww 4kp/ iece of Pyrex glass is placed between the plates, hcp /hj0iub0tk 8l8-:k4dvzwwow much charge will then flow from the battery?    $ \times10^{-8 }\,C$

  An electron is accelerated horizontally from rest in a televis.m,nf m j5/;w: cv:alw 9hbaypion picture tube by a potential difference of 5500 V. It then passes between two horizontal plates 6.5 cm long and 1.35mcwvnafa .m/p:hw9 b;,jl :y 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 capacitanbk0n+8rbus3 c ce $C_1$ 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, shyxkh8 ezqk7t4u /c mqea03)zjz(o*r0ku /r .uppose 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 yhm7)4(czu / /e*uhjoz.erq8 aqr0zy3 xk ktk0ou 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 thers0m cn +t-e(jke 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 :*9,puhk w uwhhas 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 and the 4udwm )a:lb*6sixk yy:7pz;hbottom of the thunderclouds can be as high as 35,000,000 V. The bottoms of the thunderclouds are typically 1500 m above the Earth, and c): k :m ;4iplayzx* y6d7bsuhwan 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, ultravioul6svy-0) m8slpe nc;let (UV) light provides enough energy to some electrons in barium metal to eject e)sm l0vl; -su86 cypnthem 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 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 place986 mn5jtrh(awo3hn qd 36 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 separated by a 0.15-mm-t .srnc*cwj :- :uapz)dhick p *rjc)pu ncdw-z.:a:s iece 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 wit9odke+vjz cc)+cazzsn+dl1m /tb3 (6 h plate area $2.0cm^2$ and air-gap separation 0.50 mm is connected to a 12-V battery, and fully charged. The battery is then disconnected.
(a) What is the charge on the capacitor?    $ \times10^{ -11}\,C$
(b) The plates are now pulled to a separation of 0.75 mm. What is the charge on the capacitor now?    $ \times10^{ -11}\,C$
(c) What is the potential difference across the plates now?    V
(d) How much work was required to pull the plates to their new separation?    $ \times10^{-10 }\,J$

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

  Two point charges are fixed 4.0 cm apart from each other. Their charges are wmhkgka1 1 dk-ijqg-;cf) 3minu2 ;1 m$Q_1$=$Q_2$=$5.0\mu C$, 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 c-at cxjan2+.k(ko 8ein Fig. 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$