If two points are at the same potential, does this mean that no q7bu(+ 6i voucln l99pwork is done in moving a test charge from one point to the other? Does this imply that no force need be exerq9l 7b+p9n i6cl uuv(oted? Explain.

If a negative charge is initially at rekg1 d g8awwm 9-bx9zly, 4wtp*st in an electric field, will it move tow*8 1 aw9 wt9- ymd4xgwglk,zbpard a region of higher potential or lower potential? What about a positive charge? How does the potential energy of the charge change in each instance?

State clearly the difference (a) between electric potential and electric f4fi46 nibr 0ayyg4jnf.7 tcy2ield, (b) between electric potyj agy.fy44r 0726 fiibn c4ntential and electric potential energy.

An electron is accelerated by a potential diff uou; 0-cg3jsference of, say, 0.10 V. How much greater would its finalcfs0; gouu-3 j speed be if it is accelerated with four times as much voltage? Explain.

Is there a point along the line joining two equal positivepo.z x r.-wotxi,w6v0 charges where the electric field is zero? Where the electric potential is zero? Explain.x,itwv. 6 x.w oorz-0p

Can a particle ever move froma;4xwwht3u z + a region of low electric potential to one of high potential and yet have its electric potw4+xu 3wt zh;aential energy decrease? Explain.

Compare the kinetic energy gained by a protoqw9 q(w3lskk0;)t4l qfs6(a a8nty kn n $(q=+e)$ 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? Exp-f f,l boz9+g)ixpun+ lain.

Draw in a few equipotential l ae5g qpd2vwr22 c(,rlines in Fig. 16 – 31b.

What can you say about the electric field id a) pkslm(+x5n a region of space that has the same potential thask)plm(x d 5+roughout?

A satellite orbits the Earth along a gravitational equipotential line. What shadybpe9b 5eyxtefk (c9w +0n, 2pe fxen t2ceb+9kywy ,0bde(9 p5must the orbit be?

When dealing with practical devices, xii i8h/ zja)5vpzw(2we often take the ground (the Earth) to be 0 V. If, instead, we said the ground was how would this affect (a) the potential V, and (b) the electric field E, at othervj(z x/8phiwzi2a5 )i points?

When a battery is connected to a capacitor, why do the two plat9wu7oi;g s4nyes acquire charges of the same magnitude? Will n47ywo;9si guthis be true if the two conductors are different sizes or shapes?

We have seen that the capacitance C depends on the tne;w0 p *5maq mbh8jir; ,c* yasbp02vldv,/ size, shape, and position of the two conductors, as well as onqnyhc5r* v,d, l 0aje ;/s p;a8wbm 2t0vpmb*i the 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 do in moqul gmi5v*8/xc 2e7wd ving 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 po9:8-- iownll jo3ron9n9cnsqpu ;kb.int with a solbqn;o:n cwor9l.9p8n3u9ik - nj-potential 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 wiagm(w u5,.oppy wz4 tx 14lr-xll an electron gain (in joules and eV) if it accelerates through a potential difference of 23,000 V in a TV pictuto(wyx5w p. z -,gl4mxu4a1 rpre tube?
   $ \times10^{-15 }\,J$
   eV

  An electron acquires 3tw ymdie9mqg;8s*a hhru 0- d,:ult5 $7.45 \times10^{ -16}\,J$ 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 planz1(h(q*0ua;rllh nates 5.8 mm apart if the potential difference between them is 220 V? llan (uh(raqz;1hn* 0   $ \times10^{ 4}\,V/m$

  An electric field of4lvpsofajv0z/r5b v 9+ r2 v5k $640V/m$ 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 syw6e). zid ;wwd,x) wis $1500V/m$ How far apart are the plates?    m

  The electric field between two parallel plates connected - kd+jgp0 edxnc* t;n9vuf: :rto a 45-V battery is $1500V/m$ How far apart are the plates?    m

  What potential difference is need4bn )wkxxlb -f3eq/*ued to give a helium nucleus $(Q=2e)$ 65.0 keV of kinetic energy?    $ \times10^{4 }\,V$

  Two parallel plates, connected to a 20o6jya /l bwvpety)g,//mza0- q(* r.qv.qpbk0-V power supply, are separated by an air gap. How small can the gap be if the air is not to become conducting by exceed(,b.ypy/tj0/ km -q vbzlo6q*)a/pqwvg.r eaing its breakdown value of $E\,=3 \times10^{ 6}\,V/m$?   $ \times10^{-5 }\,m$

  The work done by an external force to move af)3qexrd7qjlhu942yc ol29;gt ot :g $-8.50\mu C$ 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 withrgk +( prit(sy3h5v 6w 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 energy is 3.2 ke9;xl y1:j 0+bx x*mvfuof3vyxV?    $ \times10^{5}\,m/s$

  An alpha particle (whf7mzf bwj/m -oj-o/c;ich is a helium nucleus, $Q=+2e$, $m\,=\,6.64\times10^{-27 }\,kg$) is emitted in a radioactive decay with $_{KE}$ = $5.53MeV$ What is its speed?    $ \times10^{7}\,m/s$

  What is the electric potential 15.0 ck zd.s gm3lkc zzv,:(.m from a $4.00\mu C$ point charge?    $ \times10^{ 5}\,V$

  A point charge Q creates an eh6,e0vsvuq ,14qh a7gqtule .lectric 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 fwpf3of );h(qr5v r2 qnet negative chargfohqv) wfp(r; f52r q3e, $-Q$. Draw in a dozen electric field lines and two equipotential lines.

  (a) What is the electric poten0mad3u7hwcnqx y3cu; fa 7, 2ktial 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 showi mg8im(ram ;5o34-er t .saawn ia o5(m- eimg.wa4 amrtsi8;3r n Fig. 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 cti, oz*4,znapm from a fixed point charge with $Q\,=\,-0.125\mu C$. How fast will the electron be moving when it is very far away?    $ \times10^{7 }\,m/s$

  Two identical $+9.5\mu C$ point charges are initially 3.5 cm from each other. If they are released at the same instant from rest, how fast will each be moving when they are very far away from each other? Assume they have identical masses of 1.0 mg.    m/s

  Two point charges, $3.0\mu C$ and $-2.0\mu C$ are placed 5.0 cm apart on the x axis. At what points along the x axis is
(a) the electric field zero    cm leftof $q_2$
(b) the potential zero? Let $V\,=\,0$ at $r\,=\,\propto$.

  How much work must be done to bring three electr m hq;.fx5v/gqons from a great distance apart to h x5q;fvq/g 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 cm north of 0bry0e (t/jdf 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 ac vgxgwm,*2/ 3rx4ss skcelerate a proton (radius $1.2 \times10^{-15 }\,m$) so that it has sufficient energy to just penetrate a silicon nucleus? A silicon nucleus has a charge of $+14e$, and its radius is about $ 3.6\times10^{-15 }\,m$. Assume the potential is that for point charges.    $ \times10^{6 }\,V$

Two equal but opposite charges are separated by a distn7khd f5zfq 2/rt .bp;i7zga;ance d, as shown in Fig. 17–27.7 ginq5hbd r2zkp /ftaz7;f.; Determine 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 4y3g4m l x4rfc)sfsv o )4bzw(nucleus) in a circular orb )fz 4yr4m4o f)g3w x(lcv4ssbit 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 a20 qcz0djm)( otg:+6 c io ;t/kixeixfre $ 0.53\times10^{ -10}\,m$. apart. What is their dipole moment if they are at rest?    $ \times10^{-30 }\,C\cdot\,m$

  Calculate the electric potential due to a dipole whose- (z0 mdxhps1w 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 from thgayp qc4fzm :oa /.9q+ef1u9re negative to the positive charge. The water molecule, Fig. 17–28, has a dipole moment which can be consiao 9./u1m9a4e cqfg+ q:py zrfdered 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/: hfowxt(+-p3 7qty nhihiz0pacitor 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 capacom80 l2 hjt0raitor 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 chargta-aim4:c7vt f*flr 0 es 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 1cydp w)mt;w e 209*ulz2090wwe y* dt;clm)2 puz V. They carry equal and opposite charge of magnitude 95 pC. What is the capacitance of the two wires?    $ \times10^{13 }\,F$

  How much charge flows from each ter; eo :u8inr.vcminal of a 12.0-V battery when it is connected to a r. o ve;:unic8$7.00-\mu F$ capacitor?    $ \times10^{-5 }\,C$

  A 0.20-F capacitor is desnrr9nkgdi8 zb 19 q1,k:i(u2o3 v;d6hfgypmoired. What area must the plates have if they are to be separated by a 2.2-mm air gap?9f 1pu8n;rqv y o(ggd3zin1r:d, h9k6 mkb2io    $ \times10^{ 7}\,m^2$

  The charge on a capacitor increagzwdhnlc:o uy r/w re 366h9,:ses 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 ofjzz bcxksno2/1 cz 4//v5lv7n $8.5 \times10^{ 5}\,V/m$ 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 opp(w:5l9mmjxxi6 bm7zzosite $5.2\mu C$ 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 plates3qsk q(-r* jch 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 12(nt8 a//uyc3 l;f2sxz:t2cr zg iyyo*5-V battery (Fig. 17–29a) and then is disconnected frifyloy snz /ttyu:2zg83cr(2;x /* caom 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 t5z j d2 i8ip)c.tggay1wo square parallel plates 5.5 cm on a side that are sydgc8 zt.2p)iij1g5a eparated by 1.8 mm of paraffin?    $ \times10^{-11 }\,F$

  What is the capacitance of a pair of circular plates with a radius of 5d,1xwsl,n74bwb h ;mr.0 cm sepabb41d7lhrxm ; ,ws,w nrated by 3.2 mm of mica?    $ \times10^{-10 }\,F$

  A 3500-pF air-gap capacitor is connecte x:o k r6oy4-as(vken(d to a 22-V battery. If a piece of mica is placed between the plates, howvsk6rk: yo o4(na(e-x much charge will flow from the battery?    $ \times10^{ -7}\,C$

  The electric field between the pl fjprrf:*7-p if;;v8sb. m jwfates 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 227 v5i z75lqemm00-pF capacitor. How much energy is stored?    $ \times10^{-4 }\,J$

  A cardiac defibrillator is used to shock a heart that is beating erratically3t *v*,fgu o 0+rf1wfrchgj6z. A capacitor in this device is charged to 5.0 kV and stor+tf63*wz1 ogjf ufh0r*g,v cres 1200 J of energy. What is its capacitance?    $ \times10^{-5 }\,F$

  How much energy is stored by the electric field between two sq dy 4vqu 1258nh2fvgupuare plates, 8.0 cm on a side, separated by a 1.5-mm air gap? The charges on the plates are equal and oppositeu 2qypfv18 2v4dhun5g and of magnitude $420\mu C$.    J

  A homemade capacitor is assembled by placing two 9-in. pie pans 5 cm apart ij9 6;p*qwdy vand connecting them to the opv9;6q*iwy dj pposite 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 ha5d* ydx:o5pefatg0vk 8 -:*ufr*txo ws 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 differencua; cx7 )5o.uhygs7ji e is doubled, and (b) the charge on each plate is doubled, as the capacitor remains connectsgc.i 7;ouxjah75y u)ed 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. They then passp)sbn 3 yc3;rf,9 :uaqwzwf n6 through a uniform electric field E for a distance of 2.8 cm, which deflects them upward so ther)sf yuz 3 ;36n pw9nawcf:,bqy 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 wb,a +/z(uxyfu ide and is 34 cm from the 2.6-cm-long def (x/abz+fuy u,lection 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 K -8dpf0(njw lhe(u1pa E in moving from point A to poin(al- e p0h(1wf8duj pnt 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 trans io,4og(fdmax - 15 fn6nyqkj1fers 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’9wmzzir2wesg8 fxv0 u. , rh)+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 tube, electrons are accelerated by thousands of voltspvbf9rmo /l-0 :nfigu9qe8.f i 0h)nb through a vacuum. If a television set were laid on its back, would electrons be able to move upward againonnmbfq )eh bg8ui0/f f-rv9. 9p: il0st 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 capacitor4c q02s.b x6+smax kdj 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 is connected to a 24.0-Vd*,olzu90 iv,kazk5 kh e(hg4 battery until it is fully charged, after which it is disconnected from the battery4ieh,zvok(5, 9kkzag dh *0ul . A slab of paraffin is then inserted between the plates. What will now be the voltage between the plates?    V

  Dry air will break down if the electric field9 kgtz;zz 2xd; 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 triange 0ue 0n9/ dn*u,aq1hsu(ar egle (side L) as shown in Fig. 17–30. Determine the p1*0d0sar9q geuu(nau e/ h,e notential 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-Vyqu nz(p5 ej-q(hri 4jmg-4wcxc h0:2 battery. If a piece of Pyrex glass is placed between the plates, how 0xizc-:w((ej yhcm -2ngqp u4q r 54jhmuch charge will then flow from the battery?    $ \times10^{-8 }\,C$

  An electron is accelerated horizontally from rest;,c.a ; zyxrt4/b woev7cx c,t in a television 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 ;wtvzcy.,xc4ta7r, c ; /xoe b(Fig. 17–31). At what angle $\theta$ will the electron be traveling after it passes between the plates?    $^{\circ}\,$

A capacitor of capacitak; x(w*b)-dzwrrt x y:nce $C_1$ 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 c 8sh(x; tm15x du kkuk:g0-5 vtgiaq6farad is, suppose you want to make a 1-F air-filled parallel-plate capacitor for a circuit you are building. To make it a reasonabl;v-8c1a skxkx0m56gqgh iku5 d:t(tue 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 there is an electric fice a r3: liw+f0l(p8cneld 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 lasp) ,n b2kix;0qg,mp jkv1 ru.xer 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 and the v6 s, (pdw3n34oniv azbottom of the thunderclouds can be as high as 35,000,0pionz n6v43 vawd3(s,00 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 en( l qt8;0i+ olbmdni0xough 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 barium su+xo0m tlqin 8;ild 0b(rface 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 identical / o5tmehw:jk* i9v;mg$+33\mu C$ 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 hw z9hjbxr(9pl7xj200.15-mm-thick piece of paj wh 9rxp20b79x(ljzhper $(K=3.7)$ 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 platf.a-zr:-jt o 1m8qabte 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 41j b7ig,d4(l j .rok*j h(zwzc.0 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 Figger+8 xrsqef,ec 4j(i27 ,uqc . 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$