If two points are at the same potential, does this mean that no work is don-a* j cnz8syy/m8*gd le in moving a test charge from o8 gd-z*l8camjn/yy* sne point to the other? Does this imply that no force need be exerted? Explain.

If a negative charge is initially at rest in an electric field, will it moviy3z 8r;dop(mr+ g- cje toward a region of higher potential or lower potential? What aboumor - rdjpgi 8+y;3c(zt 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 field*6y9u)rwy6 +xrhs j mz, (b) between electric potential and +yzurxs69rhyw *)jm 6 electric potential energy.

An electron is acceleratedlb:jmpku /v *fa;2dr0x+b j6;a w ch8j by a potential difference of, say, 0.10 V. How much greater would its final spexblam62*+0fba ud vjch8/; kw j: ;rjped be if it is accelerated with four times as much voltage? Explain.

Is there a point along the line joining two equal positive char5p*yug(v4zlmpnc4 )nk ds 7*rges where the electric field is zero? Where the electric pon 7ypz)*5npuvmc44 l(gr *dks tential is zero? Explain.

Can a particle ever move from a region of low electric potential .iwf-6 xhb7 ;d3 sabri o89jxgto one of high potential and yet have its electric potential ene8bgw 9i-6rb . idx xfja;3s7ohrgy decrease? Explain.

Compare the kinetic energy gained by f(g8zy0-r1c zetwj1 v 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? Explain. ms90pr3 tkt9g6 fgbcm(20mns -fp5eu

Draw in a few equipotential lines in w+.uopl9i q,9 m6(oian7aqdnf3w(ihFig. 16 – 31b.

What can you say about the electric field in a region of spacccfp -.pb+n r;oo3mh9e that has the same potential thro 39c.p-; ncfprbho m+oughout?

A satellite orbits the,ojqenl ) /y144ox4xp gko k7oyw0h-l Earth along a gravitational equipotential line. What shape must th)xok4jy7gykwoql 1o04n4,xo p e /hl -e orbit be?

When dealing with practica( z/ty0 9 -kazgb/owfax bj-a:l devices, we 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 fxw -fjzabt a //k(9-a :bygzo0ield E, at other points?

When a battery is connectedh :/l, op ht6xcs5(mq o+8wh ;ib4smee to a capacitor, why do the two plates acquire charges of the same magnitudh/sc 4x ,t8lwms;omho56+ehb e:qi (pe? Will this be true if the two conductors are different sizes or shapes?

We have seen that the capacitance C depends on th ..xgpa +fazp8irn50 we size, shape, and position of the two conductors, as well as on the dielec zaxp5r.nw8f+a .igp0 tric constant K. What then did we mean when we said that C is a constant in Eq. 17 – 7?

  How much work does the elec7rk 69 1f)3zathkw peqtric field do in moving a $-7.7\mu C$ charge from ground to a point whose potential is $+55V$ higher?    $ \times10^{-4 }\,J$

  How much work does the electric field do in qa w:ys af(-.lmoving a proton from a point with a potent la-q.w(sfay :ial 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() j tw lh1awh5r3k-nu) if it accelerates through a potential difference of l 3t-1)un hkr (whw5ja23,000 V in a TV picture tube?
   $ \times10^{-15 }\,J$
   eV

  An electron acquires my;5wpws cdw20* uadz ;k-) te$7.45 \times10^{ -16}\,J$ 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 apart 4t7l w2q 3o/qidwejc3 if the potential differenc e/wqi3d3c 7 o4t2jlwqe between them is 220 V?    $ \times10^{ 4}\,V/m$

  An electric field ofemfac1wdn1sn ) r *x7ylq868e $640V/m$ 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 4yh/7nbzoyffm2 u0+ jto a 45-V battery is $1500V/m$ How far apart are the plates?    m

  The electric field between two parallel plates connected to a 45-V battery idl2yh8uf8 v3 ds $1500V/m$ How far apart are the plates?    m

  What potential difference is needed bvhy0o9a398 n1lghb hto give a helium nucleus $(Q=2e)$ 65.0 keV of kinetic energy?    $ \times10^{4 }\,V$

  Two parallel plates, connected to a 200-V usr/z(54f gis jen 2p3power supply, are separated by an air gap. How small can the gap be if the air is not to become conducting by exceeding its breakdown valur(s4/gp32fzen i5uj se of $E\,=3 \times10^{ 6}\,V/m$?   $ \times10^{-5 }\,m$

  The work done by an external force to move ( xhssykx8-a2 j(h0tikvfzn z 1+f7z9a $-8.50\mu C$ 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 electrt rxvrzq 0ru 376c3:xyon 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 eneocf:yj+r.z5 0f lyr -xrgy is 3.2 keV?    $ \times10^{5}\,m/s$

  An alpha particle (which is a helium nucleusp89xgnjrjp 4 (, $Q=+2e$, $m\,=\,6.64\times10^{-27 }\,kg$) is emitted in a radioactive decay with $_{KE}$ = $5.53MeV$ What is its speed?    $ \times10^{7}\,m/s$

  What is the electric potentuzg1*q8j s ce) splk1 j:/9ievial 15.0 cm from a $4.00\mu C$ point charge?    $ \times10^{ 5}\,V$

  A point charge Q creates an electric potential o y/fv ei i;of kb+r:;obwy9b/5f $+125V$ 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 carrv+f l/dyh, fv2 )2yh(ipi 2okkies a net negative charge/ hi2kp ff2io(klh) yyd,v v+2, $-Q$. Draw in a dozen electric field lines and two equipotential lines.

  (a) What is the electric potential a distao:-,z3 ubw m1tr,ik fpv-if/ qnce 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 5saw .vge .8v edfn2cstf41 l(the corners of a square of side L as shown in Fig. 17nlwfds4eva( .g v2tfc.s e518–25. What is the potential at the fourth corner (point A), taking $V\,=\,0$ at a great distance?

  An electron starts from rest 32.5 cm from a fixed point ch+n/53z-w qpg k4scgaq arge 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 electrons from e(j./i y 0wobo 7/awxa3cfn :na great distance apart toanc ae wf07io (y3/x:j/wb.on $1.0 \times10^{-10 }\,m$ from one another (at the corners of an equilateral triangle)?    $ \times10^{-18 }\,J$

  Consider point a which is 72 cm north g-j a gxo6xb.l q*c . eua3hb)r)8odzz dk-r.-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 tkpgq3;-xulcsq(*+g 2t ic +)l(skt mwo 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 .liq4,h 5ja sn,,oqul distance d, as shown in Fig. 17–27.usl qq4j,i,l,o5a .hn 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 eleccoab g 7e1k4hg4-de.u tron orbits a proton (the nucleus) in a circulaag4kud be 7-oc4g1he.r orbit of radius $ 0.53\times10^{-10 }\,m$.
(a) What is the electric potential at the electron’s orbit due to the proton?    V(Round to the nearest integer)
(b) What is the kinetic energy of the electron?
   $ \times10^{ -18}\,J$
   eV
(c) What is the total energy of the electron in its orbit?    $ \times10^{-18 }\,J$ $\approx$    eV(Round to the nearest integer)
(d) What is the ionization energy — that is, the energy required to remove the electron from the atom and take it to $r\,=\,\propto$, at rest? Express the results of parts b, c and d in joules and eV.   $ \times10^{-18 }\,J$    eV(Round to the nearest integer)

  An electron and a proton /34m9xysus phare $ 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 dipov27x+ 8md kwk: izgz/gle 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 vector, pointx;7k 5 h gy spev*nn/hz*/k4pes from the negative to the positivp pn4ke*s* hzy7/xg5 v/;en hke charge. The water molecule, Fig. 17–28, has a dipole moment which can be considered as the vector sum of the two dipole moments, $\vec{P}_1$ and $\vec{P}_2$as shown. The distance between each H and the O is about $ 0.96\times10^{ -10}\,m$. The lines joining the center of the O atom with each H atom make an angle of $104^{\circ}\,$, as shown, and the net dipole moment has been measured to be $p\,=\,6.1 \times10^{-30 }\,C\cdot m$ Determine the charge q on each H atom.    $ \times10^{ -20}\,C$

  The two plates of a capacitor hold )i9y q*pq)mtip m(b3d $+2500\mu C$ 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 capajbo(- b-g);/hoc t xumcitor 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 a9 yzxw f4kfe0o/)8rhznd minus charges of $ 16.5\times10^{-8 }\,C$. What is the voltage across the capacitor?    V

  The potential difference between two short sections o 8zi6yfyswruy3-b 6 n0f parallel wire in air is 120 V. They carry equal and opposite charge of magnitude 95 pC. What is the capacitance of the two wires08zw iy6bysn6- ryf 3u?    $ \times10^{13 }\,F$

  How much charge flows from each terminal of a 12.0-V (*d9povkq 1ucn;5hq f battery when it is connected to ah kv95qcn (1o;qdp*fu $7.00-\mu F$ capacitor?    $ \times10^{-5 }\,C$

  A 0.20-F capacitor is desired. What area must the plates have if they are to kf;z *8sg8),sgmrri n6; zzeybe separated b6 g eym8r szrk)sgf z;;*niz8,y a 2.2-mm air gap?    $ \times10^{ 7}\,m^2$

  The charge on a capacitor incre.w+, hv tpc8hlases 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 owbfg 5-jsg **$8.5 \times10^{ 5}\,V/m$ 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 opposites2tc94nm , qff $5.2\mu C$ 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 platii9.i uw8 k mc)xbx 24edvpq78es 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 (Fig. 17–29a) and then is dtrd,+h z bpoz)s4f;cx v)2)idisconnected fhtz,z v;4)2pd x)dfbr) i sco+rom the battery. When this capacitor $(C_1)$ is then connected (Fig. 17–29b) to a second (initially uncharged) capacitor, $C_2$, the final voltage on each capacitor is 15 V. What is the value of $C_2$? [Hint: charge is conserved.]    $ \times10^{ -5}\,F$

  A $2.50-\mu F$ capacitor is charged to 857 V and a $6.8-\mu F$ capacitor is charged to 652 V. These capacitors are then disconnected from their batteries. Next the positive plates are connected to each other and the negative plates are connected to each other. What will be the potential difference across each and the charge on each? [Hint: charge is conserved.]
$V_{final}$ $\approx$   V(Round to the nearest integer)
$\begin{array}{l}
Q_{1}\\
\text { initial }
\end{array}$   $ \times10^{-3 }\,C$
$\begin{array}{l}
Q_{2}\\
\text { initial }
\end{array}$   $ \times10^{-3 }\,C$

  What is the capacitance of two square parallel plates 5.5 cm on a side 3vtj-xjn*h/ pzvz* 2nthat are separated by 1.8 mm of parafftz-jnhzp /*v3*2j vxn in?    $ \times10^{-11 }\,F$

  What is the capacitance of a pair of circular plates :;3ecnllol))gvjt2hr . ,j lgwith a radius of 5.0 cm separated by c: eo2n)jj3th,v rlll;. glg)3.2 mm of mica?    $ \times10^{-10 }\,F$

  A 3500-pF air-gap capacitor is conne t6zmycmdr.um*g/ s iu36 uy19cted to a 22-V battery. If a piece of mica is placed between t6zg ucs/t mm3 69*ur iumy.d1yhe plates, how much charge will flow from the battery?    $ \times10^{ -7}\,C$

  The electric field between ths dmpz57ar5 fr2*xmnu;i/tp u ux+1/ge 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. How much energy is sku.. b9vp)1vjupfu7 gtored?    $ \times10^{-4 }\,J$

  A cardiac defibrillator is used to shock a heart that is bf834xk,hthgis9x8 sn c0 al7aeating erratically. A capacitor in thih x clk79h4s8a xigf 3,s8na0ts 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 fielcd:70xsk; rgp7*q z0 zn8tbtv d between two square plates, 8.0 cm on a side, separated by a 1.5-mm air gsxdr g*0t7ktnvp:cq 0 zb8z;7ap? 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 8 m1tf9vp0u7 s/hcm vpw9kh3l 5kd0tsu8 f1wr apart and connecting them to the opposite terminals of a 9-V battery. Es3ps9vfrkd7/1smcf lpt 1wutwhv9h k 8580 0 umtimate
(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 cha8oi o4ql57+lsja+krjeuc (/ u rges $+Q$ 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 ifxbtfdjm,*.vn( sk*/ i u0+b5lbg3six ty0vm7 (a) the potential difference is doubled, and (b) the charge on each plate is doubled, as the capacitor remains vfv30xid7s*5(tm y+igsb/0b j,u .tkx bl m*nconnected 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 horizontalbr3lne27 7f7m8uie/,wco (j j ,vwtualy by 7.0 kV. They then pass through a uniform electric field E for a distance of 2.8 cm, which deflects rj7b uo/3lf,(u e,a7jvww7e2m n8 citthem 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 bf 3elb;bkp)63o5y cpiy 6.0 kV in a CRT. The screen is 30 cm wide and is 34 cm from the 2.6-cm-long deflection plates. Over what range must the b i56lcf );ppoek3b3yhorizontally deflecting electric field vary to sweep the beam fully across the screen?    $ \times10^{5 }\,V/m$ to    $ \times10^{5 }\,V/m$

  An electron starting fre 4t:cb,qq )1 zmpco5xom rest acquires 6.3 keV of KE in moving from point A to point c,oq)q1e:b mtpzxc4 5 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 si f0zu, -di:1yyw:rv 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 Ea(wtkr mka xe t+.6)l+brth’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, eleh5rl ;)tig .s c c(a;i2;madoictrons are accelerated by thousands of volts through a vacuum. If a television set were laid on its back, would electrons be able to move upwa ;5dgr;ii2.hac l (maitsc) ;ord against the force of gravity? What potential difference, acting over a distance of 3.0 cm, would be needed to balance the downward force of gravity so that an electron would remain stationary? Assume that the electric field is uniform.    $ \times10^{ -12}\,V$

  A huge 4.0-F capacitor has enough sv34xex fms 3e*tored 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 2hs88 pobabs h)e-8bm(4.0-V battery until it is fully charged, after which it is disconnectedh)(-bm a8s h8beo bs8p from the 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 e5;xf1 6 a ni:+cyhstjeik 3x4zxceeds $3.0 \times10^{6 }\,V/m$. 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 (sidenn4 0ab4eoby+ L) as shown in Fig. 17–30. Determine the potential at the mid n404 yeba+obnpoint 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 connecc6.agxx ,yorj- 4u mqlzl,;,5p;lolj ted to a 9.0-V battery. If a piece of Pyrex glass is placed between the plates, how mucg5,,;lx.r6myllz qj-op a, ;4lxjou ch charge will then flow from the battery?    $ \times10^{-8 }\,C$

  An electron is accelerated horizonta-u x6-xq5kheqlly from rest in a television picture tube by a potential difference of 5500 V. It then passes between two horizohqqku-x5 e- 6xntal 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 xd-k s5h0o3 6ou(tauk fds29z$C_1$ 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 want to make a 1-F air-filled pa)g tcyb4uen5l hi7n q.jj*93srallel-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 have to be between the plates? Is this pra9n.ihj 5qt4ybc 3s 7eln)j*g uctically achievable?    $ \times10^{-16 }\,m$  ----待选择----YesNo 

  Near the surface of the Eazrwyj/*m /8vyg/7wscyf-p(7 oj s*mjrth there is an electric field of about $150\,V/m$ which points downward. Two identical balls with mass $m\,=\,0.540kg$ are dropped from a height of 2.00 m, but one of the balls is positively charged with $q_1$ = $650\mu C$ ,and the second is negatively charged with $q_2$ = $-650\mu C$. Use conservation of energy to determine the difference in the speed of the two balls when they hit the ground. (Neglect air resistance.)    m/s

  The power supply for a pulsed nitrogem8pynvyc 7v1c0s 4ry; n 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 aw 7nt(o6kin; jnd the bottom of the thunderclouds w6kinjt o7n(;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) light provides enough energy to si5db,5o;onl8r tc rd8rl u(i.ome electrons in barium metal to eject them from a surface at high speed. See Fig. 17–33. To measure the maximum energy of t b o(n 8;5. ri5iuotr8drl,lcdhe 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 pxq untf)aq 1u.z-+ 3pzlaced 36 cm from an identical $+33\mu C$ charge. A $-1.5\mu C$ charge is moved from point a to point b in Fig. 17–34. What is the change in potential energy? $\approx$    J (round to one decimal place)

  A capacitor is made from two 1.1-cm-diamete9ashc6 (atxt;x4 8rk wr coins separated by a 0.15-mm-thick piece of paxs ttxakw8 r;(c94a 6hper $(K=3.7)$ 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 are;fmk g q6/eoe2a $2.0cm^2$ 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 apad;)2m vabsh8 nvw /yv8w7qq2o rt 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 Fe1j:7m) n3bsuuw+hvy ig. 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$