If two points are at the same potential, does this mean that no woq lm-,8sm1uvt6y dyg:3tp 4x jrk is done in moving a test charge from one point to the othqu8t-p1 4yvtx ,dg j ml6m3ys:er? Does this imply that no force need be exerted? Explain.

If a negative charge is initially at rest in an electric field, wisirrcruoe.) .245h hqw .(aaall it move toward a region of .sheaiu rr h.a2(4rq) a.cow5 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 poten,lqvm 27xoqsvd .bb8x g(:k( r1c x.xntial and electric field, (b) betweebbxk(2cx1. mdgnlv8rx:7.q(q , xso vn electric potential and electric potential energy.

An electron is accelerated by a potential di2-2 jix))-h suf1ekfhbrh y w2fference of, say, 0.10 V. How much greater would its final speed be if it is h21x2-hs u)2whfrfi-ej) by kaccelerated with four times as much voltage? Explain.

Is there a point along the line joining two equal positive kg3*vf9e0ul :+kenkmsvo /9qcff): tcharges where the electric field is zero? Where the electric potential i e q9 flt:k*c+kf0kum9 vog)evnfs 3/:s zero? Explain.

Can a particle ever move from a region of low ele.mgt9 5m6wx1 rj,iwep ctric potential to one of high potential an6wgmi9re. 1 wtxp,5 jmd yet have its electric potential energy decrease? Explain.

Compare the kinetic energy 9 zd+ewgwx 3p+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 c4a0mbfs)nce,4zb k/y6oh4 kcross? Explain.

Draw in a few equipotent8gpm 6wrdpm1+ial lines in Fig. 16 – 31b.

What can you say about the electric field in a region of sp*i//z 4pdzehu 8lifm1 ace that has the same potential throzd/ flp 8/h e41i*imzuughout?

A satellite orbits the Ear91u puw8gtvh*xzxf8.v jxcb+7 z w; )xth along a gravitational equipotential line. What shape must the orbit 8bx1vw;c9f*xhxjwtu7zzv+x ) p gu 8 .be?

When dealing with practical devices, we often take the ground (the Earth) t h9fgipu; bs6(h*mf. no 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 other phf;*up9 b h mgisnf6.(oints?

When a battery is connected td2,irxr7sh 1l:h h7fqo a capacitor, why do the two plates acquire charges of tilhs:f h1 ,72rxd q7rhhe same magnitude? Will this be true if the two conductors are different sizes or shapes?

We have seen that the capacitance C depends on the size, shape, ffy1)3kleao mdbg(2*m ch (s3t,j63qnp gpj/and position of the two conductors, as well as on the dielectric constant K. What then did we mean when we said that C is a constant in Eq. 17 – 7c3spopm,(3j2) /byenq( am k3 h flt6 *gd1fjg?

  How much work does the electric field 1us 5+m tp;xi w6bzzx0do 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 proton f ik,j1vj;tzwrmm ,b7* rom a point with a p1t,i;jrv mb,jwm7k*z otential 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 accepfvrfip 2hk)jcj x-3n; -q5 y7lerates2ch;kj yvr-)jfn i5x f-qpp73 through a potential difference of 23,000 V in a TV picture tube?
   $ \times10^{-15 }\,J$
   eV

  An electron acquires yu 6m5cw/ilz8 $7.45 \times10^{ -16}\,J$ 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 aparjkk.9ic7ovrtip0 7-c h+3lk tt if the potential difference 77jhktp-ic+r0kv 9 i3 l.tokcbetween them is 220 V?    $ \times10^{ 4}\,V/m$

  An electric field of: *auvu wtx+a7 $640V/m$ 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 87yfct5 fq8k ybattery is $1500V/m$ How far apart are the plates?    m

  The electric field between two parallel plates connected p mr6,lu,-qs 1dw2 hmcto a 45-V battery is $1500V/m$ How far apart are the plates?    m

  What potential difference is needed to give a helium nuclef0mc0 uym7w 2tus $(Q=2e)$ 65.0 keV of kinetic energy?    $ \times10^{4 }\,V$

  Two parallel plates, connected to a 200-V power supply, are separ lvn e)8r8rml j)x08dqated by an air gap. How small can the gap mvnrlxqldj8r0 )88)ebe 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 ex3g+i e aenf50wternal 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 offxp ,2 n4ba-lx an electron 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 ss dvwlx+4c7a2 r)m v lst/nvt5xf an*c(20k0energy is 3.2 keV?    $ \times10^{5}\,m/s$

  An alpha particle (which is a heli(dgfs.j xoc ;ow((lv+0 yurd: um 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 cm from a +7kyr3/rl w juj b)m,p$4.00\mu C$ point charge?    $ \times10^{ 5}\,V$

  A point charge Q creates an ele f/rla1c y4x9hctric 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 net neg0ope mple,*b-7p9 /lmhgjd ,zsfm5 (g ativeds bfe( hl 5-o07,lpzmg9emp, g/*pj m charge, $-Q$. Draw in a dozen electric field lines and two equipotential lines.

  (a) What is the electric dh(ck) 4hx9yg potential a distance of $ 2.5\times10^{-15 }\,m$ away from a proton?    $ \times10^{ 5}\,V$
(b) What is the electric potential energy of a system that consists of two protons $2.5 \times10^{-15 }\,m$ apart — as might occur inside a typical nucleus?    $ \times10^{ -14}\,J$

Three point charges are a 94z0e/lpg) kan ct4azc 3id3hrranged at the corners of a square of side L as shown in Fig. 17–25. What is the potential at thetapd3h03/k a 4cen9 4lzizg)c fourth corner (point A), taking $V\,=\,0$ at a great distance?

  An electron starts fromcw8c9iviv7n v th) o rw492b1b rest 32.5 cm 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 b2eb hwm1h4vscb6h.1.. +bag our yv)oe done to bring three electrons from a great distance apart to +4).b hyu vh1ema6svg2 h.r1oc.bbwo$1.0 \times10^{-10 }\,m$ from one another (at the corners of an equilateral triangle)?    $ \times10^{-18 }\,J$

  Consider point a which hgq cm *-r,:izis 72 cm north of a $-3.8\mu C$ point charge, and point b which is 88 cm west of the charge (Fig. 17–26). Determine
(a) $V_{ba}=V_b-V_a$    V
(b) $\vec{E}_b-\vec{E}_a$ (magnitude and direction).
   V/m
   $^{\circ}\,$

  How much voltage must be used to accelerate a p+9n 6mhczk73trfvw s:roton (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 d, as shown 7we4*nxrf29pi q8ak0 b1jjc/ ojpp.g in Fig. 17–27. Determine a formulaq b8frn*/o. ajj7p pjp0ei2cw94g1kx 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 prxes j9b -:m5 rhnac77; ke w2puwu3-mjoton (the nucleus) in a circular orbijsh7mmcp3-e- wbe29 w5u7j xrn:u ak;t 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*th(rem;.)qf wg lll0 $ 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 qc/f ,60ozhb yis $ 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 the negative to the po ec zs 89t63ar6gidfr0sitive charge. The water molecule, Fig. 17–28, has a dipole moment which can be considered as the vector sum of th8 s9rer 0gfa6ditz6c3 e 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 capacjn/-wec gx cjcabm 1a;ym3509itor 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 ho n:dw:el 2b-rwld $+2500\mu C$ 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 a.y. su3jrzj)d nd minus charges of $ 16.5\times10^{-8 }\,C$. What is the voltage across the capacitor?    V

  The potential difference between two short seu.n qmddya9*k 0ve k+vv6y5q+ ctions of parallel wire in air is 120 V. They carry e+ed vkvqyu06a+5kymndv*9 q.qual and opposite charge of magnitude 95 pC. What is the capacitance of the two wires?    $ \times10^{13 }\,F$

  How much charge flows from each termin/ka*hc9dlo3y al of a 12.0-V battery when it is connected to lyo *d9c 3ha/ka $7.00-\mu F$ capacitor?    $ \times10^{-5 }\,C$

  A 0.20-F capacitor is desired. What area must the plates hi/o4de(w hpafl 03m)n -8 stxvave if they are to be separated by a 2.2-mm air gap0e3ml 4ifo-dp8 /(ns hwva)tx ?    $ \times10^{ 7}\,m^2$

  The charge on a capacitopgdc: 22c j qhmgdn9p-imy/ kb*ai-4 5r increases 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 kgilx 5 98ucy/7zphc; $8.5 \times10^{ 5}\,V/m$ 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 oppositfs p tw)xnj8,)e $5.2\mu C$ 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 betw/ez cjr +tip1o0 /h*p.uog br2een 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 j o-ip2 ayk5e c,8zkr-by a 125-V battery (Fig. 17–29a) and then is disconnected from the batty zj r-5-okka8ipce ,2ery. 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 pa;q5 )d6 eueermrallel plates 5.5 cm on a side that are separated by 1.qe m ;erd5ue6)8 mm of paraffin?    $ \times10^{-11 }\,F$

  What is the capacitance of a pair of circular plates with a radius of 5.0 cm sep9ecoz d)9smo rw4r( (tarated by 3.2 mm of(et(wzor4s) rdc 9o9 m mica?    $ \times10^{-10 }\,F$

  A 3500-pF air-gap capacitor is connected to a 22-V battery. If a piece of micn4dt3 k,(mcjv0 *.c.qmfqam fa is placed between the plates, how muc.ff v( ,jct4c0mmdqqamn3.*kh charge will flow from the battery?    $ \times10^{ -7}\,C$

  The electric field between th emy,crk 5ba.h+ *drel( vvoj9(.vtm;e plates of a paper-separated $(K=3.75)$ capacitor is $ 8.24\times10^{4 }\,V/m$. The plates are 1.95 mm apart, and the charge on each plate is $0.775\mu C$. Determine the capacitance of this capacitor and the area of each plate.
   $ \times10^{--9 }\,F$
   $m^2$

  650 V is applied to a 2200-pF capacitor.3qww yb/.-/6avd bes v How much energy is stored?    $ \times10^{-4 }\,J$

  A cardiac defibrillator is used to shock a heart that is beating erratically. w( x qvf::m4vyA capacitor in thisq4v:v f (mywx: device is charged 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 sqb 6b*5j e64ju kubvu7tuare plates, 8.0 cm on a side, separated by6j5 7b v *uu6bj4bktue a 1.5-mm air gap? The charges on the plates are equal and opposite and of magnitude $420\mu C$.    J

  A homemade capacitor is assembled by placing thbx ,/kbq/4 kj*mlc7xwo 9-in. pie pans 5 cm apart and connectibl 74ckjx k,//mxh*bqng them to 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 fixed chargx 76 xcfyy 0zs1tg/bt0bke;5 des $+Q$ 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) tl+)4ykt19 u ajl k:njthe potential difference is doubled, and (b) the c+:ayjk)kn ll9ut1 j 4tharge 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, electronp z( 8/o-oh*0sqglmwfs are accelerated horizontally by 7.0 kV. They then pass through a unso- h*lpof z(/wqm0g 8iform 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. Estimate the value of E.    $ \times10^{5 }\,V/m$

  Electrons are accelerated by 6.0 kV in a CRTe(r;c/2wtne h 7hf2x03 lgc wy. The screen is 30 cm wide and is 34 cm from the 2.6-cm-long deflection plates. Over what range must the horizontally de70w whgrc3n/xy(l22 fe te;c hflecting 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 acquireso4lcc 1q 9 sfesqm4obw,* 6fs5 6.3 keV of KE in moving from point A to poin41 cqmq4lf ,e56f*wco9s bs ost 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 ikkme )9*3 ;cxo,k5dt/lisuxand 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 surfaceq c5n0(z6fh9; bhj;lukf8dftk3an-oj 5s h z4 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 acceleratek06y nz)x z tzuhrcm7l 1xpt7t6:6w 1ld 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 downx6z ktztrhy:w)1cl u06 zl7761xt pnmward 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 enoug rb1l v;.meaq4m2w,m3 ,splj hh 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 24vlrpdt5w bed;h9*t ma 98-7m b.0-V battery until it is fully charged, after which it is disconnected from the battery. A slab of paraffin is then inserted between the plates. What wilt5*89 b-vr lmhpat7we;md db9 l now be the voltage between the plates?    V

  Dry air will break down if the electriw0 a y,etju-wzl)oz+ 3c 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 trn zh(cn7uaddxc *.i)qsa0 qt9p /41tmiangle (side L) as shown in Fig. 17–30. Determine the potential at the midpoint of eact0ux)sp1dnq q m nt*ha.ca/9z d c7i(4h 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 ry0n) 5tdx r:n0a zu1htow.) d5vh4mbbattery. If a piece of Pyrex gla wbddhmtnzav1 5.r)u0to0hxn4ry :)5ss is placed between the plates, how much charge will then flow from the battery?    $ \times10^{-8 }\,C$

  An electron is accelera,sxi0b e(t-(jbw0fhoted horizontally from 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 diff0sexb 0- ,hb ftjoiw((erence 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 capacitancecp(7wjg,vv7wy e i)2amdgm5umn9/ (f $C_1$ 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, suppose you ug9k fpyt,xual3 bi ;-l07z*vwant to make a 1-F air-filled parallel-pla;3 auxklf7-t,0p9yl *v zb uigte capacitor for a circuit you are building. To make it a reasonable 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 of abogcfl::bh ny9 a;uh o9t.o;*za ut $150\,V/m$ 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 has (o6akv )p ev(*d.ap yma $0.050\mu F$ 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 betweenyd*h1v:0 (qxcok e*og the Earth and the bottom of the thunderclouds can be as high as 35,000,000 V. The botto cy*g dxkh(qov1* 0o:ems 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) lighpt+( +frk7(k yz7cyr(6yu cqct provides enough energy to some electrons in barium metal to eject them from a surface at high speed. See Fig. 17–33.7(yyt y (6+cu+crkk pcrqz 7(f 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 placed 36 cm from an ide or5 /.ssm7xj znzdn-(ntical $+33\mu C$ 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 sepa dshb5z7 +j)r7wbaj l5rated by a 0.15-mm-thick piece l wsz) a 7j5d7+rh5jbbof paper $(K=3.7)$ A 12-V battery is connected to the capacitor. How much charge is on each coin?    $ \times10^{-10 }\,C$

  A $+4.5\mu C$ charge is 23 cm to the right of a $-8.2\mu C$ charge. At the midpoint between the two charges,
(a) what are the potential    $ \times10^{ 5}\,V$
(b) the electric field?    $ \times10^{6 }\,V/m$  ----待选择----leftright 

  A parallel-plate capacitor with plate areaxxyl6h6 kshs7ok+jx) n s80k+ $2.0cm^2$ 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 otht:nzsi8ks7/ b er. 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 a*xfya9 1tcvb: -d 5;w3nur*lriu6mwjs shown in 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$