If two points are at the same potexi:m (p,o;)k: gd g cyubwsg;4og5 g:cntial, does this mean that no work is done in moving a test charge from one point to (; sb4pogy5 c;g cgm:ud)w ikg,xgo::the other? Does this imply that no force need be exerted? Explain.

If a negative chargeu 6f6.mxdc)/ wgfdl p8 is initially at rest in an electric field, will it move towap.ufx f/6gw)lc 86dd mrd 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 aqxbx*kzi3l/(xfb(y8f o )8 0lhwl) kznd electric field, (b) betw hf3l xz/88wxb(f k )lyl(*ikqzxob)0een electric potential and electric potential energy.

An electron is accelerated by a potential difference of, say, 0.10 lapqi3m+5ol9vqwq:l+ ) jh:j V. How much greater would its fin+qiqm:qvpwl:59 llj3 +a ojh) al speed be if it is accelerated with four times as much voltage? Explain.

Is there a point along the line j6r 1t3uuvxz qjmyj5g: p, .yh4oining two equal positive charges where the electri, vtx6jpm.u5yj4rqu :ygz3h1c field is zero? Where the electric potential is zero? Explain.

Can a particle ever move from a region ovt dc 9pz4oj 4nwp340pzu(2hgf low electric potential to one of high znhzpjugp34 0(c 4vot4w 9p2 dpotential and yet have its electric potential energy decrease? Explain.

Compare the kinetic enekdg-lj7+l0n gf k7ej4rgy gained by a proton $(q=+e)$ to the energy gained by an alpha particle $(q=+2e)$ accelerated by the same voltage $V$.

If $V\,=\,0$ at a point in space, must $\vec{E}\,=0$ there? If $\vec{E}\,=0$ at some point, must $V\,=\,0$ at that point? Explain. Give examples for each.

Can two equipotential lines cross? Ei2jut ie-s)nv * 7c9zi j.rx+dxplain.

Draw in a few equipotential lines in Fig. 16 – 31b.nnt;k 4zgg6z0t5d (k7x bs7qe

What can you say aboutd5h t1u6b.bk 4 m)fgnc the electric field in a region of space that has the same po 5g nmfkbht.b)ucd 641tential throughout?

A satellite orbits the Earth along a gravitational equipotentifi0u 5mii2jk-p9d v5xal line. What shape must thi p5f9ikxi -50vjudm2e orbit be?

When dealing with practi jnezi p(7*bv2 u,bp.94k2jr kail)nrcal devices, we often take the ground (the Earth) to be 0 V. If, instead, we said trb b 7pjn.i2zl, j2iar)k4npu (*9 kvehe ground 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 capacitor, why do the two plates acquiquxhz w 5; hsuui(v-*c(52earre charges of the same magnitude? Will this be true if t*uuqae2cx -5(wz;i u hvh5(rshe two conductors are different sizes or shapes?

We have seen that the capacitance C depends on thgb0+y uubji4g3 :qw *xe size, shape, and position of the two conductors, as well as on the dielectric constant Kg b0 w4qjgu*xiu b3y:+. What then did we mean when we said that C is a constant in Eq. 17 – 7?

  How much work does the electric field dyj z16uycm pjm/tw5+e 6e 8 *nl3karf2o 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 p0ict. hlb8hc -:7f 0jbewfgc2roton from a point with a cb 70jt0-. wb fhg:cei h8c2lfpotential 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) if it ad 1h-qii:l1ehqz 5 ph3ccelerates through a potential difference of 23,000 V in a TV picture tube? zeqh 11-hqd5 lp3:ihi
   $ \times10^{-15 }\,J$
   eV

  An electron acquires .m m shy7drsqz3y /z.4$7.45 \times10^{ -16}\,J$ 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 pargas:7ztxhvy7vr )f+ nx2gx9n96 /u poallel plates 5.8 mm apart if the potential difference between them is 220 V? pxrznf)yvvo/t 9ghx:2u 9s+ ng 7a6x7   $ \times10^{ 4}\,V/m$

  An electric field of -cbqg;e a)q56vi c)t t$640V/m$ 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 mbnmd647)hsi j g-3rfto a 45-V battery is $1500V/m$ How far apart are the plates?    m

  The electric field between two para aiy), +akogf:llel plates connected to a 45-V battery is $1500V/m$ How far apart are the plates?    m

  What potential difference is i: .2vnqmwpq+u(*ns m needed to give a helium nucleus $(Q=2e)$ 65.0 keV of kinetic energy?    $ \times10^{4 }\,V$

  Two parallel plates, connected to a 200-V power supply, are separated bo x +*w4txf g4of(3xbyeh*-hwy an air gap. How small can the gap be if the air is not to become conducting by exceeding its breakdowh+ fy4xb4wo-*thf xw*eg 3ox(n value of $E\,=3 \times10^{ 6}\,V/m$?   $ \times10^{-5 }\,m$

  The work done by an external force to mo:u+4g.ghkr nso6 .t o uk,h2ybve 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 electron5l)f g1ob 0*q6gfyjhh 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 dsd 9o*g/g jwps)qs pq02jd03energy is 3.2 keV?    $ \times10^{5}\,m/s$

  An alpha particle (which is a helium nucl (9/lf3bnqou(j q/ xz ;bxrec;eus, $Q=+2e$, $m\,=\,6.64\times10^{-27 }\,kg$) 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 -fowu l,zr c* oi4v.c-cm from a $4.00\mu C$ point charge?    $ \times10^{ 5}\,V$

  A point charge Q creates an electric potential okz(ow(kh +/ 6r. j urufxi8ed4f $+125V$ 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.3 6 gngr*0ypnm This conductor carries a net negati0m r3g y*nnpg6ve charge, $-Q$. Draw in a dozen electric field lines and two equipotential lines.

  (a) What is the electric potential a dist,(k-ziq fszbkq* oh 22ance 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 arranginvx24/ rxyic(w.p8 ncqhtg7 9-wm6 xed at the corners of a square of side L as shown in Fig. 17–25. What is thnq9v.m/ic nxp2yg7w6 8cx-4wxr h (ite potential at the fourth corner (point A), taking $V\,=\,0$ at a great distance?

  An electron starts from rest 32.5 cm from a fixr8zvn4z+6wwq c:c 26ohw.g mked 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 bel*nw, )uh tsl2 done to bring three electrons from a great distance apart to *l 2hl,su) tnw$1.0 \times10^{-10 }\,m$ from one another (at the corners of an equilateral triangle)?    $ \times10^{-18 }\,J$

  Consider point a which is 72 cm nn4xn 0: m6tm1(wz sblwcz3:jjorth 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 to8+gmrg bv7:ep c:sf 5o 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 by a distance srd g/f7v2ek4 d, as shown in Fig. 17–27. Determine a fo d274grv se/fkrmula 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 p9+m 01ie,sski abe :rcroton (the nucleus) in a circular orbit of radius a:,0im seekb1i+rcs 9 $ 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 proton1z9xn,a2 orc y are $ 0.53\times10^{ -10}\,m$. apart. What is their dipole moment if they are at rest?    $ \times10^{-30 }\,C\cdot\,m$

  Calculate the electric potenti0qbe/ ob8c0 ug.0tv cial 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 vectorm t,d6j k( oeyzbp1t9w2,m4hh, points from the negative to the positive charge. The water w9dy 4tz2m, eb 1k6oph,jth(m 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 capc551w4b b 5cgk zcg.cqd5s:xmacitor hold $+2500\mu C$ and $-2500\mu C$ of charge, respectively, when the potential difference is 850 V. What is the capacitance?    $ \times10^{-6 }\,F$

  The two plates of a capacitor kg0e mnmfvte)r:opr+**pn7+ mepk1: 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 l pl .vmi)ze1o2*:alnholds plus and minus charges of $ 16.5\times10^{-8 }\,C$. What is the voltage across the capacitor?    V

  The potential difference between two sh2)m uql6du4so ort sections of parallel wire in air is 120 V. They carry equal and opposite charge of magnitude 95 pC. What is the capacitanceo)muqd l 2u46s of the two wires?    $ \times10^{13 }\,F$

  How much charge flows from each terminal of a ;zub yonb ,7vzta ;+99nth7j a9 i0aoz12.0-V battery when it is connected 9anhzv9,y0t inaz+ bo;j9b77u;ota z to a $7.00-\mu F$ capacitor?    $ \times10^{-5 }\,C$

  A 0.20-F capacitor is desired. What area must the plates have ifr c( fti4uzwa g6iy1-; they are to be separated by a 2.2-mm a 1rca ui6t(4wg zfi-;yir gap?    $ \times10^{ 7}\,m^2$

  The charge on a capacitor increases bt, 1qpsnr2y/a/lxe q2 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 of9dj;oynmsmya2,, lv 7p:1c kt $8.5 \times10^{ 5}\,V/m$ 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 oppos) 9-bmvm ij2h 1me/pawite $5.2\mu C$ 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 ke- kl8euqq0. 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 byx*4niu yk).w yhe(v;k-:pu ld a 125-V battery (Fig. 17–29a) and then is disconnected from the batteyl.(uk np yhw d;v*: kxeui)-4ry. 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 paralle il ;yos;c--anl plates 5.5 cm on a side that are separated by 1.8 mm of paraffia syl;;o-nci- n?    $ \times10^{-11 }\,F$

  What is the capacitance of a pair of circular plates with a kox h*m)9/g 8 fcnlb pz+my4a+t,1wguradius of 5.0 cm separated by 3.2 mm of mica?yt8ga+ k+,c z)o1np 9wfx u*b/mg4 mhl    $ \times10^{-10 }\,F$

  A 3500-pF air-gap capacitor is connected to a 22-V battery. If a piece o2px6f 4nij0r0 gki* pwf mica is placed between the plates, how much chaxw 0r4kgjfp ii06 p*2nrge will flow from the battery?    $ \times10^{ -7}\,C$

  The electric field between the plat u wo3j1l*-ywq jq:o5xes 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 capaktgi/h7 n(bcpf 8,d8kcitor. How much energy is stored?    $ \times10^{-4 }\,J$

  A cardiac defibrillator is useq0i a:dts,5wx (y f8xld 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 c:x58ti dl0qswxf( ,ayapacitance?    $ \times10^{-5 }\,F$

  How much energy is stored by the electric field ks*z4rf +mjrl9dkz -;between two square plates, 8.0 cm on a side, separated by a;9-jmzks kzl+ 4rd*f r 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 placing two 9-in. pie pans 5 cm apart and myl, qo.ivgi9+s/8w+t. lrri7ws i5p connecting them tso,iwyv .il8 .qtr7lriw9g m5+ p/si+o 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 capacitor has fixe 8apm7p7 arn xo2te-zs4y44 ifd 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) t4,fvb/zz b/ivk( pa 5xqm( 4wow)a h4)bjhj8lhe potential difference is doubled, and (b) thzmw4j,w a voil5bv8z)p jh ) 4bfqk/a/h xb((4e 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 horizfw vh7:qmy.m u2 ec:3iontally by 7.0 kV. They then pass through a uniform electric field E for a dihmm yuei.wq:27 3f:cv stance 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 CRTd k04 6mwa dixhp7bd;.. The screen is 30 cm wide and is 34 cm from the 2.6-cm-long deflection plates. Over what range must the horizontally deflecting electric field vary to sweep t0 b6.4mi h dawkxd7d;phe 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 ixs+7;1vhz v hmoving from point A to point Bz vh+ sx7hv1;i.
(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 nc6ah6vq4xl*hn )1m 8z q7 gdfand 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 electrichj9za ) ia8p(h field near the Earth’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 ;geemk*szl2:tube, electrons are accelerated by thousands of volts through a vacuum. If a television set were laid on its back, would electrons be able to move upward against the force of gravity? What potential difference, ask e2;ge*:l zmcting over a distance of 3.0 cm, would be needed to balance the downward force of gravity so that an electron would remain stationary? Assume that the electric field is uniform.    $ \times10^{ -12}\,V$

  A huge 4.0-F capacitor has enough stored energy to heat 2.5 kg of water frx+f* v m4i1nm3 fs.o3mz/uh 9pgtey(nom 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 vsig 82yj9bhb zpk/ 8)it is fully charged, after which it is disconnected from the battery. Ab28k p 8)yibg/z9vhjs slab of paraffin is then inserted between the plates. What will now be the voltage between the plates?    V

  Dry air will break di(t * 0z+w,twdxzk 3s3 h;x8ke ftsn2jown if the electric 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 (side L) vif aio2qotb(2s/3m* ()g mmnas shown in Fig.v3(ti( g)mmo 2sio abnq*f2 m/ 17–30. Determine 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 capacitor is cop qx-rz5 v dx*n0smng35s )3mlnnected to a 9.0-V battery. If a piece of Pyrex glass is placed between the plates, how muchl5m 0qvs5npn) xds3-*3 g zxrm charge will then flow from the battery?    $ \times10^{-8 }\,C$

  An electron is accelerated horizontally fr/gz. 0vqqyng ./x0 t-vlpt dh.om rest 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 25x q htqvz/v0 0/gnpy. t-gd.l.0 V (Fig. 17–31). At what angle $\theta$ will the electron be traveling after it passes between the plates?    $^{\circ}\,$

A capacitor of capacitj oy r97 adk5mgb:pv 8l+u1j0aance $C_1$ 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 aps3( zrjc,as 5e ghv,mf o78,g farad is, suppose you want to make a 1-F air-filled parallel-plate capacitor for a circuit you are building. To make it a ramz g7s( vh,5r,p8,sgj3 oefceasonable 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 field oe/pxb n k;cf44f 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 qc/ e;nq;o7 p)t3vq canitrogen laser has a $0.050\mu F$ capacitor with a maximum voltage rating of 30 kV.
(a) Estimate how much energy could be stored in this capacitor.    J
(b) If 12% of this stored electrical energy is converted to light energy in a pulse that is 8.0 microseconds long, what is the power of the laser pulse?    $ \times10^{5 }\,W$

  In lightning storms, the potential difference between the Earth and zr,gv4h2z*bu the bottom of the thunderclouds can be as high as 35,bz zhr*,2uv4g 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) light provides enough energy mlpq9gd*yw:m-9j;p 6t w.1mu bs+fez to some electrons in barium metal to eject them from a surface at high speed. See Fig. 17–33. To measure the maximum j +ledp*sw6 -mm. 9g1;9uwy:tzm fbpq energy of the electrons, another plate above the barium surface is kept at a negative enough potential that the emitted electrons are slowed down and stopped, and return to the barium surface. If the plate voltage is $-3.02V$ (compared to the barium) when the fastest electrons are stopped, what was the speed of these electrons when they were emitted?    $ \times10^{6 }\,m/s$

  A point charge is placed 36 cm from an identical::j+o)g - 3an2lyuhqk nkcl) f $+33\mu C$ 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 fromzt1 kb7xu 3*gvn7mfj: two 1.1-cm-diameter coins separated by a 0.15-mm-thick pf7kgjb v*17u3t z: nmxiece 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 capk3xvn+p0q.xkoku - r)qqvj( ox*0hmjr 8 id5(acitor with 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 chargig)dn*o p cd4p(a0sd6es 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 in9i+tboxvpo84 h8n/kpkqbt :, 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$