If two points are at the same potential, does thi7t69sbdw8i rbl1y;a* xg*s xds mean that no work is done in moving a ted6xgixw;db tr ysbl 19 8*as7*st charge from one point to the other? Does this imply that no force need be exerted? Explain.

If a negative charge is initially at rest inw*8wy7gsu mf m/qh )7y an electric field, will it move toward a region of higher potentia u7h)78wg y */qfwymmsl 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 electrid quaq)h2j.4m,3j vrrc potential and electric field, (b) between electric potentd .)jq 4uvhq,ra3 rm2jial and electric potential energy.

An electron is accelerated by a potential difference of4aaymmt;6vl o;r eeb; 9z)c v0, say, 0.10 V. How much greater would its final spetae ;0;z o9rm a )elvvc;4m6byed be if it is accelerated with four times as much voltage? Explain.

Is there a point along the line joining two equal positiv 5g eh+yb+s1i63 , xmlablv2rr xi3d-ke charges where the electric field is zero? Where the electric potential is zero? E-k+ 2gm s,d31i6 yh3lirx5v ebx lrb+axplain.

Can a particle ever move from a region of low electricmf 1wrxwnh/r3 2, in-u potential to one of high potential and yeu n-3m/in12wfhrr,xwt have its electric potential energy decrease? Explain.

Compare the kinetic energyz (d tdq 6v v*09cr3jo4p*nfketliu+ , gained by a proton $(q=+e)$ to the energy gained by an alpha particle $(q=+2e)$ accelerated by the same voltage $V$.

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

Can two equipotential lines cross? Explain)khc-*9yo ai x4j ojn-.

Draw in a few equipotential lines inzz* f odx6vj;e1q qz,p:(i;jr Fig. 16 – 31b.

What can you say about the electric field in.dd,-m;sq zut kfm+n 5uq+iua q5z2)e a region of space that has the same potential throughout? qez,z u2d nmd)i+u5;qs mu.+ta -k5qf

A satellite orbits the Earth aid8jggx8 e2 -along a gravitational equipotential line. What shape must 2xd-ge8 j ia8gthe orbit be?

When dealing with practical devices, we often take the ground (then:+p7+acxc jfy qem, 6bt2l :o Earth) to be 0 V. If, instead, we said the ground wap em72:yfq+cj+abctxl6 no,:s 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 the5hi i+93(qk 5 gr e(eenswwpzvj1a4 4z two plates acquire charges of the same magnitude? Will this be true if the tw4(eei+ sv w nk(ezpa5i49jw5r 13qgzho conductors are different sizes or shapes?

We have seen that the caph 9k ngywlw hk n2f6/40pyza62acitance 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 a constant in Eqh692a6 /phlg0wywn4f nzkk2y . 17 – 7?

  How much work does the electric field do in moving avkc*p hbmy :.0 $-7.7\mu C$ charge from ground to a point whose potential is $+55V$ higher?    $ \times10^{-4 }\,J$

  How much work does the electric field do inpxct j4h )cph.5db8g*mn*g)x moving a proton from a point with a potentmx h jcb pg4c8.hp)xgt )nd**5ial 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 g5wi*v: 0mmy8 4dlqos z-ltq6 it accelerates through a potential differencdl6qgi4zq*ws ml y-ot 0:v85me of 23,000 V in a TV picture tube?
   $ \times10^{-15 }\,J$
   eV

  An electron acquires;poko;lm 5 /+f/rd7f(poujo e $7.45 \times10^{ -16}\,J$ 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 ix14qt07 6s eu7i1 xdnx:irfj cf the potential difference between them is 220 Vdiu:nxq0srxf6t177 c 41 jex i?    $ \times10^{ 4}\,V/m$

  An electric field of-vluv2i ec- n)u:( eri6ivpxm4 bu13l $640V/m$ is desired between two parallel plates 11.0 mm apart. How large a voltage should be applied?    V

  The electric field between twog/ j lr/zslndzv /2n(yk7; a te/r0m0f parallel plates connected to a 45-V battery is $1500V/m$ How far apart are the plates?    m

  The electric field between two parallel plates contv-hy /ce(s 84 -btiwanected to a 45-V battery is $1500V/m$ How far apart are the plates?    m

  What potential difference is needed to give a hems6vewfc 1i-cvl8*,t lium nucleus $(Q=2e)$ 65.0 keV of kinetic energy?    $ \times10^{4 }\,V$

  Two parallel plates, connected to a 200-V power supp fpq-o c9h*tuw0a4 2jvly, are separated by an air gap. How small can the gah*- 40q9fwcojtp u2v ap be 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 external forao h) e0crc 5-nap5ln.ce 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 kiq2y0wa uz8tp, netic energy
(a) 750-eV,    $ \times10^{7 }\;m/s$
(b) 3.2-keV?    $ \times10^{7 }\;m/s$

  What is the speed of a proton whosa5f6os.8;fzsruy 2u xe kinetic energy is 3.2 keV?    $ \times10^{5}\,m/s$

  An alpha particle (which ij pzpel -80xh+s 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 pog9,s*3b ty 30uuuc6 c;apncnytential 15.0 cm from a $4.00\mu C$ point charge?    $ \times10^{ 5}\,V$

  A point charge Q creates an electric poten7 zothnovh15)tial 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 v0qd*-;en8jou p kjy.6/pjsca football. This conductor carries a net negatic-pj /eqsjp 6un 8 dkjo;y.0*vve charge, $-Q$. Draw in a dozen electric field lines and two equipotential lines.

  (a) What is the electric potential a dis0u)gov)zwr7cz:f s q1tance 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 t1-cx m5g5olz side L as shown inm-clt og55 1xz Fig. 17–25. 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 ch7xxi. wv;1az1ulg :edqqd; a9arge 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 a great distanceo yy/ ry:nm-ckd a;g/j+6*pdb apart t6y +d/jmyr b:;a -/oycn* gdpko $1.0 \times10^{-10 }\,m$ from one another (at the corners of an equilateral triangle)?    $ \times10^{-18 }\,J$

  Consider point a which 2):p jjw/olht is 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 proton (l8gmvwc, . 2g6-fvrjxx gfgh( .u(l0d 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 sepa3fm q j+tvk0x*7y 0owwrated by a distance d, as shown in Fig. 17–27. Detmwt+wyv0qko*73x 0 f jermine 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 thewvl8kxs2yc++d;y1* ykf d*i8 lm hh+o hydrogen atom, an electron orbits a proton (the nucleus) in a cirf8m;2 + 1+h*d kwvll+ syckyho*y ixd8cular 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 arem(w, zo bbcoo c- w7 th6iri,.h5y4pv8 $ 0.53\times10^{ -10}\,m$. apart. What is their dipole moment if they are at rest?    $ \times10^{-30 }\,C\cdot\,m$

  Calculate the electri a ;x(by3fw qjc:bw6s3c potential 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 fxsx;jn1y2aj .g4d ( ajl-czb0s n7rl7 my7e(mrom the negative to the positive charge. The water molecule, Fig. 17–28, has a dipole moment which can be considered as the vector sum of t2jz-db( j;1 snjlm7yrlsy04 ae a c. nx(7gmx7he 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 capacitort/zm1rx( 7uf fv7v( y htvg acl01k9g. 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 capacitor7z3qa*jb0w),k3 i qwra c7tt q 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 andi7y0c0 mxv jrlkuj( 3a: r*jy) minus charges of $ 16.5\times10^{-8 }\,C$. What is the voltage across the capacitor?    V

  The potential difference between two short sections of parall/424u;f ysumxss; kmpel wire in air is 120 V. They carry equal and opposite charge of ; 42/xy4sm;su mpfuskmagnitude 95 pC. What is the capacitance of the two wires?    $ \times10^{13 }\,F$

  How much charge flows from each terminal of a 12.0-;f0zbfrv i49vV battery when it is connected t0f vfz;ivr4b9 o a $7.00-\mu F$ capacitor?    $ \times10^{-5 }\,C$

  A 0.20-F capacitor is desired. What area must the plates htzbm ab 6;hobfg- 2ri(9zh 2a2ave if they are to be separated by abbf-m;r b(ha 2iz 62t agzho29 2.2-mm air gap?    $ \times10^{ 7}\,m^2$

  The charge on a capacitor increasesda2cb6(r,vmysqf1c - 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 o c(obiksuuc .. 7we:q:.vxm3$8.5 \times10^{ 5}\,V/m$ 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 ok/lp p (m0mb bha4hl88pposite $5.2\mu C$ 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 j5a/ h vmtozd. 0d:l9othe 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 be57djk 2 6wvzv.tw7ryattery (Fig. 17–29a) and then is disconnected from the battery. Whek5 277vdvwtey wj.r z6n 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 (xn fka,)qlt8side that are separated by kq8) ft nl(,xa1.8 mm of paraffin?    $ \times10^{-11 }\,F$

  What is the capacitance of a pair of circular plates 3a 2fueh*ws ki( yfpyu(8 z)zx*u-2un with a radius of 5.0 cm separated by 3.2 mm ofuuhyyu ef*38zai*(zpx-2u 2sn k( wf) mica?    $ \times10^{-10 }\,F$

  A 3500-pF air-gap capacitor is m m2n+ pw3d+ q1v/jq tf*hg *hq;bqfx;connected to a 22-V battery. If a piece of mica is placed between thq* +f +3m pq;m nbx;fqj/gdvht2q*1w he plates, how much charge will flow from the battery?    $ \times10^{ -7}\,C$

  The electric field between the plates of a paper-separ0 kps7;p6; . swxol u-hnd.3 opixtdu2ated $(K=3.75)$ 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 capacitmtl+f nd5r3d 1t 2au,dor. How much energy is stored?    $ \times10^{-4 }\,J$

  A cardiac defibrillator is used to shock a heart that is beating erratis,dxz ,et )5nxh zsj*r;vlw2 5cally. A capacitor in this device is charged to 5.0 kV and stores 1200 J of energy. Whath,el)d5rsvzt xn2 z; s, *jwx5 is its capacitance?    $ \times10^{-5 }\,F$

  How much energy is stored by the electrk33qqyle-4)dukhom , 2yfcx + ic field between two square plates, 8.0 cm on a side, separated by a 1.5-mm air gap? The ch -k2oduhyy m )k43qxcf+qe3l,arges on the plates are equal and opposite and of magnitude $420\mu C$.    J

  A homemade capacitor is assembled by placing two 9hyob2* j8 bz2ngn 6f1r-in. pie pans 5 cm apart and connecting them to the opposi y *boj2hzfn2b 8ng1r6te 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 yn(t , jh(n8gshas 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 capacitoecs7wx ngw-7 -r change if (a) the potential difference is doubled, and (b) the charge on each plate is doubled, as the capacitor rexseg c-- 77wwnmains 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 accelera9 0.s-jaoee rrted horizontally 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 0 rs9oj rae.-e22 cm away, 11 cm above the center. Estimate the value of E.    $ \times10^{5 }\,V/m$

  Electrons are accelerated by 6.0 kV inpe0qrce mq1+2v5q g1 y1uz/rh 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 horizontally deflecting electric field vary to sweep the bze p+h2q 1/qgv5qcy 1e1m0rru eam fully across the screen?    $ \times10^{5 }\,V/m$ to    $ \times10^{5 }\,V/m$

  An electron starting from rest acquires 6.3 keV of zv:dwob9b -pd zz8 (f+(e qor1KE in moving from point A to point B.eoz1+vq (f8d:o p-bwdb9 (zrz
(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 transfer5yve,jl4/ (jjr: fj dzs 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+2lpcwc6k /7hwc/m fh 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 tub;+df(( aotsh ze, electrons are accelerated by thousands of volts through a vacuum. If a television set were laid on its back, would electrons be able to move upward against the foz(;f+s (o dtahrce 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 capacitokrf( z2y,o/df5jf f4k )m 7fwhz1fu4ir has enough 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 24.0-V battery 6 t wu,r*0a6qgzmv -6vipy2ophz4+bs until it is fully charged, after which it is disconnected from the battery. A slab of paraffin is+26-0b uyh6t4zor,g6sza pv m *wvp qi then inserted between the plates. What will now be the voltage between the plates?    V

  Dry air will break down if the elz bw ms78dbi68ectric 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 caiix )t r*kttw(3qfw )q;g.4d(4 ubkforners of an equilateral triangle (side L) as shown in Fi)f((q*i ig .awtb4dtq rktux;f 3w)k4g. 17–30. Determine the potential at the midpoint of each of the sides.

  A $3.4\mu C$ and a $-2.6\mu C$ charge are placed 1.6 cm apart. At what points along the line joining them is
(a) the electric field zero,    cm left of $q_2$
(b) the electric potential zero?

  A 2600-pF air-gap capacitor is connected to a 9.0-V battery. If +wy)riy42h kca5aby( a piece of Pyrex glass is pla +h4w 2rykcb)aiy(ay5ced between the plates, how much charge will then flow from the battery?    $ \times10^{-8 }\,C$

  An electron is accelerated horizontally from rest in aaah /4q0dk6p m 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 wha /a40p6hmq kdat angle $\theta$ will the electron be traveling after it passes between the plates?    $^{\circ}\,$

A capacitor of capacitancbd8u(- eq( oxhe $C_1$ 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 a; n(bh88:aginfa8 ng qir-filled parallel-plat g(n8qn88ghafa: n ;ibe 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 theylq/fdcky cp*-t i cwl)1tpdkj2 g,i.f3055 o 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 a pulsed na5)aulk)f +bek) 7t9jos 1hq kitrogen 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 potentia1h bg aa3lkp4:l difference between the Earth and the bottom of the thunderclouds can be as high as 35,000,000 V. The bottoms of the thunderclouds are typically 15ak :gapb 314lh00 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 provideesd8 g .fx1.gus enough energy 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, anu. .gde g1fx8sother 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 identi ih37bc6bu c5zjfs4c j3l/g/ ucal $+33\mu C$ 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 separated by a 0.15-mm-/cety0tw -mk- r;z0p rthick piece oc; t0--pzyr/rm k0t wef 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 wvqxdx 7n t(i1r.pp1t 4l6yg8plate 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 are0e ;ij8idkgq2a7fat nvp)/.o $Q_1$=$Q_2$=$5.0\mu C$, 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 2 l2d7 uc5 d)zsltm;nffda6 5uwith $q_1$=$1.5\mu C$ and $q_2$=$-3.3\mu C$ Find the potential difference between points A and B.    $ \times10^{ 5}\,V$