If two points are at the same potential, does this mean that no work ajnz //8p0nc u og4nn/is done in moving a test charge from one point to the other? Does this imply thatzn nn4c/ nj 0//a8ogup no force need be exerted? Explain.

If a negative charge is initially at re s+:gcd 8)s32wbaybhlcrc (i, st in an 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 the charge changs8 (+,3 cgsydc wba2clb ri)h:e in each instance?

State clearly the difference (a) ko vohkt(0md4 85q f lenz3.1bbetween electric potential and electric field, (b) between electric potential and electric potential ene.35t8e bokmdnqfohl0 4 k v(z1rgy.

An electron is accelerated by a p1w y7v6k(*g qa lbd48ve kahxn9)pnq8otential difference of, say, 0.10 V. How much grenq*ak8 1dh kvwbl6a7nx(vq)89py4 g e ater would its final speed be if it is accelerated with four times as much voltage? Explain.

Is there a point along the liv(gz n,9vfy6jmcca ni7 0f**zt k 2:vine joining two equal positive charges where the electric field is zero? Where the electric potential is zero? tf,z c0v zk 72yga 9mn**6vciv :fjni(Explain.

Can a particle ever move from a region of low el2)bjs2 3l:f;vfqd.1j iul fyf si-t tc) j)wi+ectric potential to one of high potential and yet have its electric potential energy decrefd )li2;c 1jsif vyu3 w2-sf:fb) ilt .jqjt+)ase? Explain.

Compare the kinetic energy gvnc82kmef quw7:hc.1 v)y b-m ained 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 equipotentialwy)hno7nra+-kue )gm. 8s. pl lines cross? Explain.

Draw in a few equipotential lines (4 x(bc ika*n+kina:q in Fig. 16 – 31b.

What can you say about the electric field in a region of space that hrl0h*q44/ek (,s,rypuido z was the same potential thse,( rlz/ r0piqy4 o*4u w,dhkroughout?

A satellite orbits the Earth along a graq5 / e1;ia ljl 5avpp*pxdne5,vitational equipotential line. What shape must the orbit b,x* 5/ neiqvl5e15pdl;appja e?

When dealing with practical devices, we often take the ground (the Earth) to bea4tal .nwi70nql ejozn*x0+ x qe d6f(6q*km( 0 V. If, instead, we said the ground was how would this affect (a) the potential V, and (b) the electric field E, at 0+n6 ea0aqjw.nxnze *f q(x md tl *o7(l64qkiother points?

When a battery is connected to a capacitor, why do the two08,kt p/ unig 4wyln1u plates acquire charges of the same magnitude? Will this be true if the two c4g0puln8 ,1t/n yuiwkonductors are different sizes or shapes?

We have seen that the capacitan/ih-m3v wq,2k,gf 3hkd zyk; pce C depends on the size, shape, 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 g k ,kmphkiwd;33qv2fyz, h -/a constant in Eq. 17 – 7?

  How much work does the electk g:tql,ic,vhv;d (g1ric 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 fielqf4dh*cc.nrx w16vl e 2p1 /mte/dv 5gd do in moving a proton from a point with a potential*ctm 1g 1/e ddpwlf2v/ r6qnxv5 hc.4e 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 a )zktw v;vfa73 exb0n)k.w8i and eV) if it accelerates thbe;7 vwik)taw. )f z8va 3nk0xrough a potential difference of 23,000 V in a TV picture tube?
   $ \times10^{-15 }\,J$
   eV

  An electron acquiresm4 txxkj;w6 6eh8 ./ykwuyt9.ck1 jvz $7.45 \times10^{ -16}\,J$ 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 p)ze4nl,v( ) hhyqj9itlates 5.8 mm apart if the potential difference betw9)e( tnjlyqvih4 ,h)zeen them is 220 V?    $ \times10^{ 4}\,V/m$

  An electric field of feuk ip b).m)5m0f2un $640V/m$ 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 cuhd7,s+mwv t e mq0*3qonnected to a 45-V battery is $1500V/m$ How far apart are the plates?    m

  The electric field between two parallel plates connec 1/iegncc,4 kpg*7m)o mt ozk-ted to a 45-V battery is $1500V/m$ How far apart are the plates?    m

  What potential difference is needed to give a helium wqwc79g)j 9 eunucleus $(Q=2e)$ 65.0 keV of kinetic energy?    $ \times10^{4 }\,V$

  Two parallel plates, conneze j1v pgmlabn*kisg;j + w -g8yk7k+9w1c9r+cted to a 200-V power supply, are separated by an air gap. How small can the gap be if the air is not to bk1 jelj8igc pk+w99;+ma y b gg+s7rn-v* w1kzecome conducting by exceeding its breakdown value of $E\,=3 \times10^{ 6}\,V/m$?   $ \times10^{-5 }\,m$

  The work done by an ,u( am2y4w : nnnte,icexternal 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 electron with kinebf-a h1uk- bl)l.4ogs60qbe ntic energy
(a) 750-eV,    $ \times10^{7 }\;m/s$
(b) 3.2-keV?    $ \times10^{7 }\;m/s$

  What is the speed of a proton whose kinetic energy is 3.2 keVrp(oiy9e(chyd m+qd4i2/. 0 azm)ewg?    $ \times10^{5}\,m/s$

  An alpha particle (which f5-w+ la4hqux s8 mf)bx9q-bnis 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 potentiaooaul1: (c. yyl 15.0 cm from a $4.00\mu C$ point charge?    $ \times10^{ 5}\,V$

  A point charge Q creates an e cak38my6z*us lectric potential of $+125V$ at a distance of 15 cm. What is Q?    $ \times10^{-9 }\,C$

  A $+35\mu C$ point charge is placed 32 cm from an identical $+35\mu C$ charge. How much work would be required to move a $+0.50\mu C$ test charge from a point midway between them to a point 12 cm closer to either of the charges?    J

Draw a conductor in the shap)3nwa9ll c+tx e of a football. This conductor carries a net negativ+c3 axlw 9lnt)e charge, $-Q$. Draw in a dozen electric field lines and two equipotential lines.

  (a) What is the electric potential p: e rqqgr 3b/);y1 frcy+7vsag2j/hy 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 sideuzmv jz9hbl 3- e ns85k.gg.1jrmj2,u L as shown in Fig. 17–25..lg .sz-z m hrkgu 5,unj me283jb1jv9 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 charzws3;vdv yr tbg )mb7zchzjo;jz o+5 )5;*o*kge 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 tx ox3f3yxc 4u:hree electrons from a great distance apart too 3:xx4fyxcu 3 $1.0 \times10^{-10 }\,m$ from one another (at the corners of an equilateral triangle)?    $ \times10^{-18 }\,J$

  Consider point a which is wh t0,jlo+r9- qk 7gyb72 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 proton (rabi 5t97rb1)0ytnevdd pgp 3 +rdius $1.2 \times10^{-15 }\,m$) 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 g..bxk71pwe x d, as shown in Fig. 17–2w eb7k1xp x.g.7. Determine a formula for $V_{BA}\,=\,V_B-V_A$ for points B and A on the line between the charges.

  In the Bohr model of the hydrogen atom, an electron orbits a proton (the+y8ag8hq a+q e nucleus) in a circular hae+8qygq 8 a+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 are9au7qzjzmg r()wt7pp6kqi-rz qt5- 5 $ 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 t n;rc swmj8iu-a f0sxx9y8 8;jo 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 vector, points from the ne.cg+2 fsir8(rx9mf lr gative to the positive charge. The water molecule, Fig. 17–28, has a dipole moment which c 8 i.2 crrm(l9frxfs+gan 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 capo4kzhalc d zns-8khoy +d72..acitor 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 h qtu*v68/yay1 x (v mmqo9v:cmold $+2500\mu C$ and $-2500\mu C$ of charge, respectively, when the potential difference is 850 V. What is the capacitance?    $ \times10^{-6 }\,F$

  A 9500-pF capacitor holds plus and minus charges ofk-ut ,4zd1vtk61gq vk $ 16.5\times10^{-8 }\,C$. What is the voltage across the capacitor?    V

  The potential difference between two short sectid j0s b 6t nyya8x.3/rkb27uoeons of parallel wire in air is 120 V. They carry equal and opposite charge of magnitude 95 pC. Whtybb6 8r e7.0k3sd2nyu o/x jaat is the capacitance of the two wires?    $ \times10^{13 }\,F$

  How much charge flows from each ter4ek jyr;:i qv*minal of a 12.0-V battery when it is connected to a rq:ve ky j*;i4$7.00-\mu F$ capacitor?    $ \times10^{-5 }\,C$

  A 0.20-F capacitor is desired. What area musb8 frs hy2z(f4dfj5z(4pf tw9 t the plates have if they are to be separated by a 2.2-trpfz42yf(sjbhd 5 z8f9(fw 4mm air gap?    $ \times10^{ 7}\,m^2$

  The charge on a capacitor increa3lgc+suc vf,i* l8(-ub ynky(ses by $18\mu C$ when the voltage across it increases from 97 V to 121 V. What is the capacitance of the capacitor?    $ \times10^{ -7}\,F$

  An electric field of gl49k+wo: z,-jhxm*lbjyzz- epq 9b4 $8.5 \times10^{ 5}\,V/m$ 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 opposite ou/y(le8j *hd7 xf7ws $5.2\mu C$ 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 pmo0v s7-npj.ns- yk g7lates 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 bapgx7s,:el8:xq *ppn attery (Fig. 17–29a) and then is disconnected from the battery.qp x* e7,pxn::gs lpa8 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 0yt r,c5,c sgsside that are separated by 1.8 mm of paracs,s50 t y,rgcffin?    $ \times10^{-11 }\,F$

  What is the capacitanu6:bl(xf o) vkce of a pair of circular plates with a radius of 5.0 cm separated by 3.2 mm )lf b:6v(okxuof mica?    $ \times10^{-10 }\,F$

  A 3500-pF air-gap capacitor is connected to 6*g +bta :x -w:fo5vdx:ea qbga 22-V battery. If a piece of mica is placed between the plates, hfbg -+exv: w x5a :abq:t6*dogow much charge will flow from the battery?    $ \times10^{ -7}\,C$

  The electric field between the plates of a pap9s:;bjb +bvq zer-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 e.f*+(2lwxgh q8bnrn / hats-dnergy is stored?    $ \times10^{-4 }\,J$

  A cardiac defibrillator is used to shock a heart that is beae+yn ppf27 q(eting erratically. A capacitor in this device is charged to 5.0 kV and sto pe7+e2pf qny(res 1200 J of energy. What is its capacitance?    $ \times10^{-5 }\,F$

  How much energy is stored by the electric fiel x g+sq0wbw78p 4fzyd.d between two square plates, 8.0 cm on a side, separated by a 1.5-mm air gap? The charges ox48wb py.7 gfzs0qd +wn 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 andxu7 q+)pn6et/ml a3zd connecting them to the opposite terminals of a 9-V battery. Estimate )a7p t6n demu3lqzx+/
(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 fi t, xfs.1ym01xztpbfp3pkb, ,xed 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 capaci,/1zs-0 pe 7d i)pnajpdyor 5wtor change if (a) the potential difference is doubled, and /oj,yi75 n1 -p )zperpwd0ads (b) the 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 hor-5 frmei3, rka d-(fuyizontally by 7.0 kV. They then pass through a uniform 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 abovm3ea, u(fi- frdk5r -ye the center. Estimate the value of E.    $ \times10^{5 }\,V/m$

  Electrons are accelerated by 6.0 kV in a CRT. The screen is 30 cm wide and is 348 s1) eeijtz:ztigx 45 cm )z1:tetsze8gj54 ixifrom the 2.6-cm-long deflection plates. Over what range must the horizontally deflecting electric field vary to sweep the beam fully across the screen?    $ \times10^{5 }\,V/m$ to    $ \times10^{5 }\,V/m$

  An electron starting from rest acquires 6.3 k2, i yte26ex6us:ef9x3fb -e nhh hpu3eV of KE in moving from point A to point B. xnup3s9tf u6e6e-3fb: e ixeh2 ,2yhh
(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 transferv6d1u/7 sd inas 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 about q,l2lxcfk*cf y**p :w$150\,V/m$ How much energy is stored per cubic meter in this field?    $ \times10^{-7 }\,J/m^3$

  In a television picture tube, electrons are accelerated by thousands orabm( a+zj(5b. *g+f xf3x0h ou;a9yrslnzo4 f volts through a vacuum. If a televisix um0yo rg.b4+ 5bz9ra lff oz(;s*(nja3+a xhon 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.    $ \times10^{ -12}\,V$

  A huge 4.0-F capacitor has enough stored energy to heat 2.5 kg of water from k+uyspu.:,wy 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 it .mitdgqib0jis / v 3,9is fully charged, after which it is disconnected from the battery. A slab of paraffin is then inserted between the plates. What will now be the volts qijbiid t,3vm/.0g 9age between the plates?    V

  Dry air will break down if the electric field exceedsdq)fl; jaslo3 u3 *uebf7g v4) $3.0 \times10^{6 }\,V/m$. 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 qy:h67t/upyu the corners of an equilateral triangle (side L) as shown in Fig. 17–30. Determine the potential at the midpoint of each/puy uhqy7 t6: 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 battery. If a piece of za puf3.93p)fpk2 tft7hnh2kPyrex glass is pla9 nkuf)23h z2 ph t.f7tkpfp3aced between the plates, how much charge will then flow from the battery?    $ \times10^{-8 }\,C$

  An electron is accelerated horizontally from rest in a teuc.-zz *a,nm*.c - pcyisxk8 ;)qzudglevision 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 uzc ;dn*8.-- ,g ka yximzczs*puqc.)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 seuu0mwy6+ ju+,3het $C_1$ 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 yz/+38c0iucnjc kjfvwo( c) 8xou 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 p(ick0ocjc/ 8cj)fvwzx+ n3 8ulate 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 qpyk.4f83i g zthe Earth 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 aei,sw,b ct b;pgea304 pulsed nitrogen 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,h;gj 10 qanm7va /n0f(kb g;ew the potential difference between the Earth and the bottom of the thunderclouds can beavqg 0gak ehf1 (;/nm0b j7nw; 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 8 gc0(ahinxa8leodo 6n. 2sh5v f8lz( jf .jt0energy to some electrons in barium metal to eject them from a surface at high speed. See Fig. 17–33. To measure the maximum energy of the electrons, another plate above the barium 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 voltagn olg(s0. 2xz5 tdvh6e(.0ha njij l888facofe 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 identica oz si4c95)jbmwy,z.4plwk l4l $+33\mu C$ 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 coinsqbn*8gu)8+ uz *db-j swghp v,hy5l )x separated by a 0.15-mm-thick piece of pap )u5by,wdh)8vgsj pgh-* x*nz u+bl8qer $(K=3.7)$ 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 w5xczw se xjgwiy9*0dxk;rsrtaz7hb.9 ;+ 1/a $2.0cm^2$ 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 apahbhg fz6dd 7+xu h-+q5rt 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 Fig. 17–35 witfje4b/ us:ot0 h $q_1$=$1.5\mu C$ and $q_2$=$-3.3\mu C$ Find the potential difference between points A and B.    $ \times10^{ 5}\,V$