If two points are at the same potential, does this me/xvkmu*2 9 lus m;e,u6bgwj0r an that no work is done in moving a test charge from one point to the other? Does this imply that no force need be exerted? Exsr ukvb6/j;u ge*lm u2,m0w9 xplain.

If a negative charge is initially at rest in an electric fxws 0w-(.ch dgm0g .zyield, will it move towayw 0h-zsdgw(x0.mc g .rd 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 differv.v) lqzah*9svb uanj wm)2)5 ence (a) between electric potential and electric field, (b) between electric potential and elech 95bu.svm z v)q)lva*aw)2jntric potential energy.

An electron is accelerated (r a80 p0sdnwwby a potential difference of, say, 0.10 V. How much greater would its final speed be if it is accelerated with four times as much vola00sndr(wpw8 tage? Explain.

Is there a point along the line joining twr7;ifo nf 94i0kb 7rayo equal positive charges where the electric field is7r7i4 afr 9k of0y;ibn zero? Where the electric potential is zero? Explain.

Can a particle ever move from a region of low electric potential to one of hnhz5o,ucdko5ry*ge g +9 m(ik* xac+,igh potential and yet have its electric potentialg(exc+r+kdokym9ngoi, h zca55 ,** u energy decrease? Explain.

Compare the kinetic energy gained by a ik clsh2b.8s **sah5 yproton $(q=+e)$ 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 cro+zmj5vnoxb 5ut+kg0,.a/ tl -l ppiy. ss? Explain.

Draw in a few equipo 18ev )zx nzc9imncui x ycx3:yi7u07;tential lines in Fig. 16 – 31b.

What can you say about the ev b y fc3v ga9x5/k8x4metq1,mlectric field in a region of space that has the same potente8q b xyg/1v4 ,mxtck93v5af mial throughout?

A satellite orbits the Earjhr7cae9)6g cv-h -hith along a gravitational equipotential line. What shape must the ovi9 e-ar hhj)g7-cch6rbit be?

When dealing with practical demc oi77h( 2c+t,ic2v qdv*s ykvices, we often take the ground (the Earth) to be 0 V. If, instead, we said the groundid72cm2 * ht+s7y vcqkvio,c( 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 plat41wu1my 7zy6 snrpya4es acquire charges of the same ma1myaurp yynz1w464 7 sgnitude? 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, and posit9yrl4s q ib.0mion 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 i4im9sl. 0ryqb n Eq. 17 – 7?

  How much work does the electric field do in mov i4fagjo3ac1nz0+9 qg v t(u.ting 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 from a poi(*n- qw,h stmba(f 8bknt with a potential f, *m-ns thbk(8q( bawof $+125V$ 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 joulesux6jb/dbgdu 2.,. lus and eV) if it accelerates through agd /.d lbuu2s,.6xbuj potential difference of 23,000 V in a TV picture tube?
   $ \times10^{-15 }\,J$
   eV

  An electron acquiresgb n54iiy(y 8v $7.45 \times10^{ -16}\,J$ 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 elec.f7smshh*up) tric field between two parallel plates 5.8 mm apart if the potential difference between them is mp .h)7s*suhf 220 V?    $ \times10^{ 4}\,V/m$

  An electric field of- fzma/xvt sd3u+ 7*iuc,w;p i $640V/m$ is desired between two parallel plates 11.0 mm apart. How large a voltage should be applied?    V

  The electric field between two ppms wpocp-)ac0st*+ c ll66x0arallel plates connected to a 45-V battery is $1500V/m$ How far apart are the plates?    m

  The electric field between two parallel plat rp4ys1qe3e)7cjmley 6r*1ox ,nzh 3tes connected to a 45-V battery is $1500V/m$ How far apart are the plates?    m

  What potential difference is needed to give a helq pmr1iz) x6*pium nucleus $(Q=2e)$ 65.0 keV of kinetic energy?    $ \times10^{4 }\,V$

  Two parallel plates, connected to a 200-V powehm ,s pt9pc0of7 yxd5k)kzuje-,m r01r supply, are separated by an air gap. How small can the gap be if the air is not to become conducting by exceeding its breakdom0 j5 0uzx1 yhec 7 -km)f9rdks,ot,ppwn value of $E\,=3 \times10^{ 6}\,V/m$?   $ \times10^{-5 }\,m$

  The work done by an external force to move a-+xmxnis;h,p83yljtb ef9:vel; o5b $-8.50\mu C$ 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 kinetu0 en 0:hyu)glic 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 ener evf0yzui9.a/ gy is 3.2 keV?    $ \times10^{5}\,m/s$

  An alpha particle (which lkg9,n3rk 4 qga( l-l/qa b8ylis 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 potent;j (3 pibejh ,0aaqkp1qna+v. ial 15.0 cm from a $4.00\mu C$ point charge?    $ \times10^{ 5}\,V$

  A point charge Q creates an electric poteng sren(ijomfq 9aoqrdfw 0(;oi r+l90(ye -*5tial 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. T9 q0nyj3ncs7dh7:xjb his conductor carries a net negative charyj9cqb:dnn0 7 sj3xh7ge, $-Q$. Draw in a dozen electric field lines and two equipotential lines.

  (a) What is the electric potential a distl2.ht dgf00c yance 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 arrangedbz f cby)xc:)uq6s 62d at the corners of a square of side L as shown in Fig. 17–25. What is the potential at the fourth corner (point A), taking6cdqc)fbsu6 2:y) b zx $V\,=\,0$ at a great distance?

  An electron starts from rest 32.5 cm from2wx0ru qdf, ag5a jeb1 *vxb(:,kyz06x;ivja a fixed point charge with $Q\,=\,-0.125\mu C$. How fast will the electron be moving when it is very far away?    $ \times10^{7 }\,m/s$

  Two identical $+9.5\mu C$ point charges are initially 3.5 cm from each other. If they are released at the same instant from rest, how fast will each be moving when they are very far away from each other? Assume they have identical masses of 1.0 mg.    m/s

  Two point charges, $3.0\mu C$ and $-2.0\mu C$ are placed 5.0 cm apart on the x axis. At what points along the x axis is
(a) the electric field zero    cm leftof $q_2$
(b) the potential zero? Let $V\,=\,0$ at $r\,=\,\propto$.

  How much work must be done to bring three electrons 7epnr5sq x l8t tp::ws0qsm90from a great distance apart tsttqq wn8pmpl0: 5ex: s 79sr0o $1.0 \times10^{-10 }\,m$ from one another (at the corners of an equilateral triangle)?    $ \times10^{-18 }\,J$

  Consider point a which is6q b4mtgqp * x:zkp;-v 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 t: t5 2 tfzg9smb/aff+s j;bo-oo 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 ac7* q qzstp y4vg*c8o.re separated by a distance d, as shown in Fig. 17–27. Determine a4g7y*qqzso.* c8 ctpv 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 hydrdti1q hvka7+ndv78 (nogen atom, an electron orbits a proton (the nucleus) in a circular orbit o q1a8nhk vt7d7(vn di+f 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 protoni l- k43jzpye)i)ff/56q* jmyxw n iq- 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 potentis2cir4m3h+ug:h/xje j:fb 7oda;y : iu1:jdial 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 vector, points from the negatip5 ro3y5 4its7mci -etve to the positive charge. The water molecule, Fig. 17–28, has a dipole moment which can be considered as the vector sum of the two s5i5 7r3tepcyo-tm4i 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 capb741lf q a-v9e6lyaew*-cxk +;eu ixpacitor 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 caja6l)bt3y(p s pacitor 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 and mii+r8kx ca /rr+ +a7jzbnus charges of $ 16.5\times10^{-8 }\,C$. What is the voltage across the capacitor?    V

  The potential difference between c1 (sg6behn l )*xw;ontwo short sections of parallel wire in air is 120 V. They carry equal and opposite charge of magnitude 95 pC. What is the capacitance (wbo*;nsh 16g) lcxneof the two wires?    $ \times10^{13 }\,F$

  How much charge flows from each terminal of a 12.0-V battery when :fl ylx fo(9z8it is connecte of8l9 zylf:x(d to a $7.00-\mu F$ capacitor?    $ \times10^{-5 }\,C$

  A 0.20-F capacitor is desired. What area must the plates have if they are to dvdgb- i24bw* be separate d2 biv4w-dg*bd by a 2.2-mm air gap?    $ \times10^{ 7}\,m^2$

  The charge on a capaci git* z t 11ilbr))r)a/pq7oautor 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, txqs/4rur ;u :nkgq+ $8.5 \times10^{ 5}\,V/m$ 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 opposm 2hsoxtv-kp-6c-3vzf5sy o )ite $5.2\mu C$ 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 fieldz+ ).q v)cxpfci5 ylkms5:w n9 between the plates of a $0.80-\mu F$ air-gap capacitor if they are 2.0 mm apart and each has a charge of $72\mu C$ ?    $ \times10^{4 }\,V/m$

  A capacitor is charged by a 125-V battery (Fig. 17–29a) andj 80 ki5ig2lw8s.*e nb )wgzyv then is disconnected from the battery. When 5*g8jizviw.kg )y 8 nels0b2wthis 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 cmin wy*dphq05w j83;e l on a side that are separated by 1.8 mm of paraffin?whwj83 qyip;dn*l e 05    $ \times10^{-11 }\,F$

  What is the capacitance of a pair n8w09 x.zrq *7w xbxwtof circular plates with a radius of 5.0 cm separated by 3.2 mm ofx*wzn 89t7b 0x.wxrw q mica?    $ \times10^{-10 }\,F$

  A 3500-pF air-gap capacitor is connected to a 22-V battery. If a pn v -v7 v3whipke-o pclb*r1/nb9oq1 6iece of mica iq lbw 3pknv6c1heorp9 /b-n7-i1v*vo s placed between the plates, how much charge will flow from the battery?    $ \times10^{ -7}\,C$

  The electric field between the plat.2cdo 0pll-mg3er . dres 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 mucdt43ve/i5ct3fia9szp j8s /hh energy is stored?    $ \times10^{-4 }\,J$

  A cardiac defibrillator is used to shock a heart that is beating erratica :u4fu(; qpkjllly. A capacitor;:ulp (fj4 kqu in this 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 bcxs unr-vo8w84pj4 (ketween two square plates, 8.0 cm on a side, separated by a 1.5-mm air gap? The charges on the plates are equal and opposite and w44 u8-sr x8c(kvn pjoof magnitude $420\mu C$.    J

  A homemade capacitor is ajhh1r u-o9c5ap0- lev m2cq4;r/mtfossembled by placing two 9-in. pie pans 5 cm apart and connecting them to the opposite term m- ;qholjatm14/ucr cf 2e 5oh09r-vpinals 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 capacipsw9k9, c ;6ond2(e 5ebltxkmtor has fixed charges $+Q$ and $-Q$ The separation of the plates is then doubled.
(a) By what factor does the energy stored in the electric field change?
(b) How much work must be done in doubling the plate separation from d to 2d? The area of each plate is A.

How does the energy stored in a capacitor change if (a) the potentiaem (-(xgvt+hdnov0p/ xp k7q+ l difference is doubled, and (b) the charge on each plate is doubled, as the capacitor rema x+0edogpk+/nm(h (v-tvx 7pq ins 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 horizontally by ixgo c5-.wy5 *1ogahx 7.0 kV. They then pass through a uniform electric field E for a distance of 2.8 o.1gw5 o*5 gxcah- xiycm, 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 )) v7rwly pic4CRT. 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 the beam w)i7r y)pv lc4fully across the screen?    $ \times10^{5 }\,V/m$ to    $ \times10^{5 }\,V/m$

  An electron starting from rest acquires 6.3 keV of KE in mov h1 bxg5yg3f+xing from point A to point 1y5 bx g+gf3xhB.
(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 charg ox4rk:;: lofqe 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 i+ o r3,a8ld fiz 13ev-lhtto 9zit*q6ms 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 accelerated by thousasvv..ga z+ rid; -qg5ends 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? Whae5v g.digrav -+ ;sq.zt 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 storep n4i f;ujn2wjmw4:o fk0h-v(d 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 24.0-V battery until it in1s,iw2u745sjtjcl -mkk ;kr0q u, f es fully charged, after which it is disconnected from the battery. A slab of paraffin is then inserted between the plates. What wi 2qwc4s 7s,;njj ,k01ltk kmeru5ui-fll now be the voltage between the plates?    V

  Dry air will break dor8/qdws i; 5cbdgd1me:62bq hwn 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) as sho-r7 +y rn 0,;ifonr2qramlyug*0 6bw,zvzx9 cwn in Fig. 17–30. Determine the potential at the midp6 0xu;obrl+0 rq7rn zc,w-9m2rgy*f a iz,yvnoint 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 is1byl8+ +cr s,.vndjtg connected to a 9.0-V battery. If a piece of Pyrex glass is placed between the plates, how much charge will then flow from the battery?rjg1ytc,+lbsnd + .8 v    $ \times10^{-8 }\,C$

  An electron is accelerated ho j -3xnfbrnsta28r 8:wc,; q1rl6hig trizontally 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 difference of 250 V (Fig. 17–31). At s :t l,r8x6 a- r8trcj3 qinnwhb2g1f;what angle $\theta$ will the electron be traveling after it passes between the plates?    $^{\circ}\,$

A capacitor of capaciv.b8.tr yue8hmywmq4vou2fk3 0 cp: 6tance $C_1$ 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 krda 1cd84er/ qscia6(d 9( bq1-F air-filled parallel-plate capacitor for a circuit you are building. To make it a reasonable size, supposer(d/6 akiq 4 d9ceda1cs(q8rb 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 Earthesgfbu9 c/ tq91.r.p exo :gm0 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 nitrogen ;evcn sa,7,ox 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 the)h) 8frt/p g5us3 l pz/pq/ifa bottom of the thunderclouds can be as high as 35,000,000 V. The bottom3 5phz /p8) a )/g/rsqtlffupis 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 some electgnpy7f*r7you, q3 y2 ,2endturons in barium metal to eject them from a surface at high speed. See Fig. 17–33. To measure the maximum energy of the elect2*yut gn, dey,qu r7o p2y73nfrons, 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 pl5a1s dy ;qp(vuu5b2*l wn13hlnx4 ux waced 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 1.1twfhp + jq6; kmwh l81sy80ds)z5j2hp-cm-diameter coins separated by a 0.15-mm-thick jpsq)th80hwy1 z58flksd w+mpj2;6hpiece 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 capacitor x ast zn:,6dm7with 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 charges a;(5puqlj 2confz;)vfbd/ fqkyz ;4+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 wit +lw glar0sjk+ 9vmeyh ar1*/: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$