If two points are at the sag3v23by e b ykn1,slfw:pug 8r5fhe34me potential, does 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 be exerted? Explain.5efupvybe2w8g433sh : r,nfkl3 gyb1

If a negative charge is initially at rest in a*x.wtn;rj0xa rrl1r22xd t 9m n electric field, will it move toward a region of higher potential or lower potential? What about a positive charge? How does the potential energy of a9;2lxr1r jrw*ttnr. 2dx0xmthe charge change in each instance?

State clearly the difference (a) between electrimi1d. ,xu;qd7m(* h z 6lhjqznc potential and electric field, (b) between electric potential and enm (,q.h ju6i1m7*d d;qzhzlxlectric potential energy.

An electron is accelerated by a potential difference of, say, 0.10;md-dqo- afvdi d*t+. V. How much greater would its final speed be if it is accelerated with four timeav --. id*ddd qfmot;+s as much voltage? Explain.

Is there a point along the line joining two equal positive charges where the elex1, kf2yperu2) k34l8j ffsdqctrs8d k2k 2fleqf3ry,1u 4xfp) jic field is zero? Where the electric potential is zero? Explain.

Can a particle ever move from a region of low elecdmcd,h* ctd75tric potential to one of high potential and yet have its electric potential energy decrease? Explainc*h 7mtc,ddd 5.

Compare the kinetic energy g 9:fqf0 l.zd 7oie,po/wuay5fained 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 : -yhydw.rplp 0wkep/1.h;jc ngol( ,k0m:it cross? Explain.

Draw in a few equipotential lines in Fig. 16 tnmm5nsfg *69 – 31b.

What can you say about the electric fa8 *hr+zpw+6yke 1 j33 7ylqmwto0oiz 8b6uvjield in a region of space that has the same potential throrwk+qy+j3wj8 b017 uemzt6 zolv *oih3a y8p6ughout?

A satellite orbits the Earth along a g 5 +vdfe54ai-wlc zoa(wm:1hcravitational equipotential line. What shape must the orbizham: d+lww5ef1i5 4(o ca-vc t be?

When dealing with practical devices, we often take the ground (the Ear:/o1guae h2p ksz26 anth) to be 0 V. If, instead, we said the ground was how would this affect (a) the potential V, and (b) the ele: 6 2op1h/au2n zgasekctric field E, at other points?

When a battery is connected to a capacitor, why do the two z- /ndzjr2(v 6xi3k ;m ;aubmwplates acquire charges of the sa/uman; wzxj2(vd; mkrb 6i z3-me magnitude? Will this be true if the two conductors are different sizes or shapes?

We have seen that the capa-ivxa6 8uxz4w1j qye;ph* nkpcf- 4-lcitance C depends on the size, shape, and position of the two conductors, as welllw-4i v1;f 46az jcqn-x*k y-8pp uxhe as on 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 du p5w(3ddlvt 9o 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 pr,w;hf:aq+48z srxa ci srhj:-1jhsy2oton from a point with a potentia:s2+ 8czrhfh q1 yiaxr:j;a s-jh4,wsl 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 joules and eV) s i/o .lnwk.w(if it accelerates through a potential differencel/..iow ks(w n of 23,000 V in a TV picture tube?
   $ \times10^{-15 }\,J$
   eV

  An electron acquires rcz;4 saw ay57jd*a;yq av l(30r.rrc$7.45 \times10^{ -16}\,J$ of kinetic energy when it is accelerated by an electric field from plate A to plate B. What is the potential difference between the plates, and which plate is at the higher potential?
   V
plate ----待选择----AB 

  How strong is the electric field between two parallel plates 5.8 mm aj/3b8+ji g jpypart if the potential difference betwg+yj pb8 i3/jjeen them is 220 V?    $ \times10^{ 4}\,V/m$

  An electric field ofpkkjiet 94:o: r. e*my $640V/m$ 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 tov o7h:r co .r*sgjg9-r a 45-V battery is $1500V/m$ How far apart are the plates?    m

  The electric field between two parallel plates,pv 5czgt,dx( m c +n6hj;ht0i connected to a 45-V battery is $1500V/m$ How far apart are the plates?    m

  What potential difference is needed to giv0cdawwj9 we *1dv wbu7bv*0)qe a helium nucleus $(Q=2e)$ 65.0 keV of kinetic energy?    $ \times10^{4 }\,V$

  Two parallel plates, c,(juid-(s;di jg 6 flkukws(; onnected to a 200-V power supply, are separated by an air gap. How small can the gap be if the air is not to become condd(fk; ui(disjslw uj(- g;k ,6ucting by exceeding its breakdown value of $E\,=3 \times10^{ 6}\,V/m$?   $ \times10^{-5 }\,m$

  The work done by an external+m+x6/cf y:gkhb+kbf 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 of an elecrb6+ baxh m0+f g2nb8rtron 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 energy is *gxqd:d1-y tc 3.2 keV?    $ \times10^{5}\,m/s$

  An alpha particle (which iqn7yx67 l -yp84 b1awtaa7kh ns 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 pote7r bg+sy2e p (iqq4eu6ntial 15.0 cm from a $4.00\mu C$ point charge?    $ \times10^{ 5}\,V$

  A point charge Q creates an electri bg3leu 4z :unpe ;0rvik07/dvc 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 ccr r qbw/-1 ef4+rmfk-arries a net negatimb14f-rew - /qkcr r+fve charge, $-Q$. Draw in a dozen electric field lines and two equipotential lines.

  (a) What is the electric potential 5 v.-cg ,2;,uwysqed4 n;k.x pifdbhb 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 Lk :e8vh5w;ut ;)mx3jz6sm8 ,crscqqo as shown in Fc t:rh6 ;z8cm,vqmj8se qwk5ou;x 3s)ig. 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 frvznsk f ) 4h7qh7nb,i)om 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 d 7t4wr j(gifv;1gf6q;.ilnrbone to bring three electrons from a great distance apart to bv(f;f7g;14gq r. itirj nw6l$1.0 \times10^{-10 }\,m$ from one another (at the corners of an equilateral triangle)?    $ \times10^{-18 }\,J$

  Consider point a which is 72 cm north of a 3c,d:su/vy vfdb .. h;il7ddo$-3.8\mu C$ 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 bejoif6ca 0+om 6z9+xqp 2pgf (u used 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 separated bnz-7e7p qjs,lxzy 50ay a distance d, as shown in Fig. 17–27. Determine a formusnjlx7 zqzy-0a5e, p 7la 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 vq:wi;z la66wi td*d: (the nucleus) in a circular : v*itl6w: ;z qw6dadiorbit 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 a tfxc- ovk14 s(:p7ourre $ 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 dipole moment iseqtudyg;:rn9 7wtb0 - g-sp( w $ 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 ve aadwm6o-/ vre.o6, xkctor, points from the negative to the positive charge. The water molecule, Figmao v.a,/eok6rwx -d6. 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 cb2kr xjnx4p z*9)sn m.apacitor 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 capac cx8t6c7cyqa e2 ev4 s)4rp-kcitor 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 pl(nuh 4g:s.d htus and minus charges of $ 16.5\times10^{-8 }\,C$. What is the voltage across the capacitor?    V

  The potential difference between two short sections of parallel wire pwr .7 hp6/gxo0rsbq7(/mifc in air is 120 V. They carry equal and opposite charge of magnitude 95 pC. pr/ixsm7bf wg( .6/q0 r chp7oWhat is the capacitance of the two wires?    $ \times10^{13 }\,F$

  How much charge flows f hhw)a2gxuat-9o4fz8 rom each terminal of a 12.0-V battery when it is connected to aw8ta z 2-f)gx4o9ha uh $7.00-\mu F$ capacitor?    $ \times10^{-5 }\,C$

  A 0.20-F capacitor is desired. What area must the plates have if they are to ge)hwf cp:s0 /be swchg)fpse:0 /eparated by a 2.2-mm air gap?    $ \times10^{ 7}\,m^2$

  The charge on a capacitor increases brha (5qg8q 1ney $18\mu C$ 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 of1-lq d) wfc1 st jk6mia(5o;*f eom:xi $8.5 \times10^{ 5}\,V/m$ 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 opposa 2y:o,k59 aj6/vjug*c wsq hrite $5.2\mu C$ 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 elec,;agx 5k wu4ib0 bhb h6,khj5uh4lr,rtric 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 (Fils1)52 gjcj edg. 17–29a) and then is disconnected from the battery. When this capacitor )jl2 g51scedj$(C_1)$ 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 that aremi/0x n -d6h1yyos(cu/xj--gelk p1 p separated by 1.8 mm 6y1p/ljxi0o-y/e h1gkcmp un --(dsx of paraffin?    $ \times10^{-11 }\,F$

  What is the capacitance of a paimg3 csr5 xnu 3eo1-o/tr of circular plates with a radius of 5.0 cm sepacgm n3 1 xoesru/35-torated by 3.2 mm of mica?    $ \times10^{-10 }\,F$

  A 3500-pF air-gap capacitor is connected to a 22-g50+lbeq g;8ew rxxw;V battery. If a piece of mica is placed between the plates, how much charge will flow from the battwrqbg;+w ;5x 8x0 legeery?    $ \times10^{ -7}\,C$

  The electric field between the plates of a paper-sep9kri71ln*d v karated $(K=3.75)$ 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 q9 *y-bkt6/ e0le ads oaw4j7ga 2200-pF capacitor. How much energy is stored?    $ \times10^{-4 }\,J$

  A cardiac defibrillator is used to shock a heart that is beating errazbcmbk3404d ee:2 bnj tically. A capacitor in this device is charged to 42emec 0z 4nbjb:3 kbd5.0 kV and stores 1200 J of energy. What is its capacitance?    $ \times10^{-5 }\,F$

  How much energy is stored by thehgmll2-9e s;okj ui /u,6o;ov electric field between two square plates, 8.0 cm on a side, separated by a 1.5-mm air gap9o l2osluk u;o;eg-,6i / mhvj? The charges on the plates are equal and opposite and of magnitude $420\mu C$.    J

  A homemade capacitor x0kb6f+qtdj; is assembled by placing two 9-in. pie pans 5 cm apart and connecting them txjd q;t60 +bkfo 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 capac b5g-rc5e 5gduitor 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 potentia2j7zw29n )j.tac7 tpz7yfhr kfn/h s:l difference is doubled, and (b) the charge on e2a7fj: tf )hnrc/ k. j7y9zt ph72zsnwach 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, electron5tipi*p7 yq9rs are accelerated horizontally by 7.0 kV. They then pass through a uniform electric field E for a distancei 5pp9 iyt*7rq of 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.4b6(huv4h:wj o,a psx The screen is 30 cm wide and is 34 cm from the 2.6-cm-long deflection plates. Over haxb6,:phuov(wj4 s4 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 ofhhr 1l 8fz9w9m KE in moving from point A to poi8hlr9m9hz f w1nt 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 ,yu 7) gvv/ov5a+h hmlhp3t5bfers 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 surface whose magnitude is abb/5z pt9 ysr r168rq;hw a1yhpout $150\,V/m$ How much energy is stored per cubic meter in this field?    $ \times10^{-7 }\,J/m^3$

  In a television picture tube, electrons2gwthll+k1c ms /a+z za1di. 0 are accelerated by thousands of volts through a vacuum. If a television set were laid on its back, would electrons be able to move upward against the force of gravity? What potential difference, acting over a distance of 3.0 cm, would be needed to balance the downward force of gravity so that an electron would remain stationary? Assume that the electric field is uniform. ag.1+1z/azdl2 scktmih+ wl0   $ \times10^{ -12}\,V$

  A huge 4.0-F capacitor has enough stored e- bo,v-fbzf, q0z jsr iwq1r(v(n t6v4nergy 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 connecty g6n: xdkc (i4il3du8ed to a 24.0-V battery until it is fully charged, after which it is disconnected from t6uc:n(y dilig3 x d84khe battery. 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 field f 5*+oq9x qmhiexceeds $3.0 \times10^{6 }\,V/m$. 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 trx:ft+ z1-vrq *gcnjp uz(8dj ,dk+isd / 30mnfiangle (side L) as shown in Fig. 17–30. Dets8-r*+1uizc 0m fn(:gkvd fz 3 n,dtqjx p/dj+ermine the potential 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 capatc(dvpr+6 tp8ru+y933 idhg ecitor is connected to a 9.0-V battery. If a piece of Pyrex glass is placed betwepu y vd g3t3pi98hrc(e dtr++6en the plates, how much charge will then flow from the battery?    $ \times10^{-8 }\,C$

  An electron is accelerated horizontally fr+j,aqo* ki8. eyj ,wryom rest in a television picture tube by a potential difference of 5500 V. It then passes between twy,q , ewri. *jjyaok+8o horizontal plates 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 capacitance ug-4 2u *oeyntlfu3j sswy:/ )$C_1$ 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, suppos2vj g ds-hy(i(2lg3tdvjz3/ s e 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 limit the plate area to What would the gap has 22 zvsvh3dd3 -tg(j/yl i(jgve 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 field oropp.cu4t) +;oasizw o 2 q8.uf 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 avk01yb (7ir sx*:vsahas 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 bot yw4w.(lfg7 kutom of the thundercloudu. yf4lwg(k7ws can be as high as 35,000,000 V. The bottoms of the thunderclouds are typically 1500 m above the Earth, and can have an area of $110km^2$ Modeling the Earth–cloud system as a huge capacitor, calculate
(a) the capacitance of the Earth–cloud system,    $ \times10^{-7 }\,F$
(b) the charge stored in the “capacitor,”    C(Round to the nearest integer)
(c) the energy stored in the “capacitor.”    $ \times10^{8 }\,J$

  In a photocell, ultraviolet (UV) mhme.1z() -ejx.2mhi c f)cotlight 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, ano)hm e..hfx-1jcemotz c(2m ) ither 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 36 cm from an identical 93 uw,ahbo +fh 1l6mjjdpkh26$+33\mu C$ 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-c, y-zc *kr) imqgv2mi(m-diameter coins separated by a 0.15-mm-thick piece of pcq ymiv)gi,z- r2( mk*aper $(K=3.7)$ 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 wityhc( *c-i k*nrh 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 dov*mci 7ui, 2other. 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. 17–35 with 3.o e()w 2pjhs7ik; q iipksu8$q_1$=$1.5\mu C$ and $q_2$=$-3.3\mu C$ Find the potential difference between points A and B.    $ \times10^{ 5}\,V$