If two points are at the same potentiaw1 okyecf c,0)qdw1/ul, does this mean that no work is done in move0 wo/cfuyq,11 )wdkcing a test 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 i4 bt 7addqt6j z /0mb0e c4;*gme;leafn an electric field, will it move toward a region of higher potb;mdt;l70e tc04*a/ b 6fjg4 zdmeaqeential or lower potential? What about a positive charge? How does the potential energy of the charge change in each instance?

State clearly the difference (a) between electric potential and electrisv/a.5a1d*o;xz +9z ne,obw.gs n cwic field, (o n9vb+degs;,w.xz.osacw ni az/51*b) between electric potential and electric potential energy.

An electron is accelera v+uujbvabar: m,++4 cted by a potential difference of, say, 0.10 V. How much greater woul b+ muv:b+ua,jac v+4rd its final speed be if it is accelerated with four times as much voltage? Explain.

Is there a point along the line joining two equal positi.bc 9t 1rs8 e7qga7 jqk2a9kw.dwhn+ vve charges where the electric field is zero? Where the electric potentaak v8qr2gbw9+ 7.edct n17k9jqhw.sial is zero? Explain.

Can a particle ever move from a region ofn w1r) ,yb3gxo low electric potential to one of high potential and yet have its r), 3nybo wg1xelectric potential energy decrease? Explain.

Compare the kinetic energy gained by a protonc ax1tcxjo2 p)o 2a:m 08;mfat6y wwi9 $(q=+e)$ 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 crorwzvcbbk kl rp60,pj: 60l55 vss? Explain.

Draw in a few equipotential lb xl 3bsv(v2z7e 6 wy70xbijm.ines in Fig. 16 – 31b.

What can you say about the electric fiem 9*lwsfl:a*1ioa 7vu ld in a region of space that has the same potential t:moa9ui7v1 **lla fw shroughout?

A satellite orbits the Earth along a gravitatibu4d kn,c 5nq)onal equipotential line. What shape must tn5kdun q4,)cbhe orbit be?

When dealing with practical devices, we often take the ground (the Exkbszs6hlwq 7/;o -v-rfoe,/ arth) to be 0 V. If, instead, we said the ground was how would this affect (a) the potential V, and (b) the e s, x o7-6whvbeo/ f-qr/kzs;llectric field E, at other points?

When a battery is connected0lbiokbmbj 8n:(-hs6 to a capacitor, why do the two plates acquire charges of the same magnitude? Will this be true if the two conductors are -bi:n8s6bjbomlh0 k( different sizes or shapes?

We have seen that the capacitance C depends on the size, shapea(m p yi nn8fd;b1;m0lnhj3 3j/2dypm , and position of the two conductors, as well as on the dielectric constant K. What then dindi hy ppbf;8( 0na23jlmj nm3/d;1ymd we mean when we said that C is a constant in Eq. 17 – 7?

  How much work does the elec 29k erm;df,dej9s,lctric 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 moving a proton from a point z9r-;1f+orw/w3 gzx ns0c m fmwith a potential o3x w sg9rfcn-z/f;+0mwz 1rmof $+125V$ 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. +qyr;v(cmuz*fd+ sa joules and eV) if it accelerates through a potential difference of dqs;zm *vu(+yc +ar.f 23,000 V in a TV picture tube?
   $ \times10^{-15 }\,J$
   eV

  An electron acquiresc)dxqy8:) xm ona-v*m $7.45 \times10^{ -16}\,J$ 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 a7i+vrgy-1n g 2qs 1l8 5hxeeampart if the pot1 +8ml 172ixh ayqnese vrg-g5ential difference between them is 220 V?    $ \times10^{ 4}\,V/m$

  An electric field of gqzjhk9v 6yq5 wey5w+ 8h9 plld3-r3x $640V/m$ is desired between two parallel plates 11.0 mm apart. How large a voltage should be applied?    V

  The electric field betweeupms0gp c2* b5zrzn 3 ij x.7xzoe*52wn two 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 cbjdzrhh.ykd)wcn ba 74 l6(z-f7cs6 ). w x2pvonnected to a 45-V battery is $1500V/m$ How far apart are the plates?    m

  What potential difference is needed to give a helium ( (s5vd:dst ulnucleus $(Q=2e)$ 65.0 keV of kinetic energy?    $ \times10^{4 }\,V$

  Two parallel plates, connected to a 200-V power supply, 8qmh ,ed,e 9 jj*l9ocxare separated by an air gap. How small can the gap be if the air is not to become conducting bycm jhqe,dxj 8el*9o,9 exceeding its breakdown value of $E\,=3 \times10^{ 6}\,V/m$?   $ \times10^{-5 }\,m$

  The work done by an external force to move a n.cs )/,5 bjvhoo m;4mk4usc n$-8.50\mu C$ 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 kine.a ,zj56 pceostic energy
(a) 750-eV,    $ \times10^{7 }\;m/s$
(b) 3.2-keV?    $ \times10^{7 }\;m/s$

  What is the speed of a proton whose kinetichtfzth* z* +uf, 43whdlhlw96 energy is 3.2 keV?    $ \times10^{5}\,m/s$

  An alpha particle (which h mz gvyl)+bj:lrmrt*i9)e93is 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 potenti ml18noo 1v qqqbs9g94al 15.0 cm from a $4.00\mu C$ point charge?    $ \times10^{ 5}\,V$

  A point charge Q createa (cyx 0m(zyw7vl(v8k s an electric potential of $+125V$ at a distance of 15 cm. What is Q?    $ \times10^{-9 }\,C$

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

Draw a conductor in the shape of a football. This conoj h1)xpj+:mmsm *t 6mductor carries a net negative charg 1mtj)os :m+ jx6phm*me, $-Q$. Draw in a dozen electric field lines and two equipotential lines.

  (a) What is the electric potential a distan8xz :mb54vk ejce 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 sidee)g esx1z rl8( L as shown in Fig. 17–25. What is the potential at the fourth corner (point A), takinge zs1e rxg8)(l $V\,=\,0$ at a great distance?

  An electron starts from rest 32.5 cm from a fixed por k6cmy ,mu9yhf938- jv.s vdcint 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 from a great distancx-nd0 *y cj+urub ghrk0ry1, *e apart to d*1*0 br cunuyh,gyxj-rk+0r$1.0 \times10^{-10 }\,m$ from one another (at the corners of an equilateral triangle)?    $ \times10^{-18 }\,J$

  Consider point a which is 72 cm ne* jpp3ao) xyfbt3*4 b4 u.75jgxwkgforth 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 ,ws rm ,;ylaw6(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 klz/ eek,e2;x charges are separated by a distance d, as shown in Fig. 17–27 klz/2xk, ee;e. 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 nucowd * i js03o8rx1mlfffh2 /:xleus) in a circular orbit w j2d08: 1h msl3orf/oxix*ffof 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 pr3(wxil g4:fgfk-ofd9( y jr6: zu xtj(frb3i; oton 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 potential duo.00cd m zfa*ie 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 aew2w7w 1v w3:g6ga-jqn9b9 weghw a0ls a vector, points from the negative to the positiv ee-wh gawwlww1 nv0qgj92a3gw:6b 7 9e 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 ca bif z1q1fd85pn5rz :jmkx *a++i rao1pacitor 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 capacito7p o*yxf:c1t r 0v8vywr 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 a ,70azb2.ee czw s(esep2yuu*q.y jg5nd minus charges of $ 16.5\times10^{-8 }\,C$. What is the voltage across the capacitor?    V

  The potential difference between two short sections of pafv r4zk8qj-g x(1d) mjrallel wire in air is 120 V. They carry equal and opposite charge of magnitude 95 pC. What is thdqx) r f(vg 81m-jk4jze capacitance of the two wires?    $ \times10^{13 }\,F$

  How much charge flows from each terminal of a 12.0-V battery when it is connect;7 1kf:hvcfevjch 1 v2e b)m/ped to /1fchv7k jvvp)2be:c; 1h fema $7.00-\mu F$ capacitor?    $ \times10^{-5 }\,C$

  A 0.20-F capacitor is desired. What area must the plates have if they are to be xuc)b* z/ hs;ed/u )vyseparated by a 2.2-dsuce/)) z; vyu hx*b/mm air gap?    $ \times10^{ 7}\,m^2$

  The charge on a capacitor increasx3 p(wl8 k,p yeuap*k3es 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 zbfzqeg9;,cnu:n -9x8jbi9p $8.5 \times10^{ 5}\,V/m$ 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 opposit 3.o kno:7o ejhdjn*q q/.5jyxe $5.2\mu C$ 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. gz)k( apm;tm 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) and then is disco:fm+irf. mvy2 nnected from the battery. When f vfr:mym i2.+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 twoex:k--;.(qdnyp- vs 6criwz o square parallel plates 5.5 cm on a side that are separated by 1.nespk 6(z-: qxo;- cdyv-wi.r8 mm of paraffin?    $ \times10^{-11 }\,F$

  What is the capacitance of a pair of circular plates with a radius of 5.0 cm sep qxraw /-c:n8parated by 3.2 mmpc-x :n /qawr8 of mica?    $ \times10^{-10 }\,F$

  A 3500-pF air-gap capacit3yf8xq y xg cm.(s.u5eor is connected to a 22-V battery. If a piece of mica is pla3yg8y uscex. fxq.m (5ced between the plates, how much charge will flow from the battery?    $ \times10^{ -7}\,C$

  The electric field bo ;z 3eaew0bo+etween the 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. Hoislt*ndf 1:l; w much energy is stored?    $ \times10^{-4 }\,J$

  A cardiac defibrillator is used tom ..zcxju kd4m/7q .o,(adybd shock a heart that is beating erratically. A capacitor in this device is charged to 5.0 kV and stores 1200 J of energy. What is its ( x/ud mkqmc .4o abzdd.7.,yjcapacitance?    $ \times10^{-5 }\,F$

  How much energy is stored by the elecbqxwqlf7(tfep;8 ) 9dtric field between 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 opposif89f qe;7x(pqwdtb l )te and of magnitude $420\mu C$.    J

  A homemade capacitor is assembled by placing two 9-in. pie pans 5 cm apru :37 vdmsgo1art and connecting them to the opposite terminals of a 9-V battery. Es1os7v :3rdgmu timate
(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 w*x9d,6 ,;bowhd7m fa-pc5pvtik;iyhas 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 potential dii;t aiyz9o*sg0e 77kw- sebr 46mjv*u fference is doubled, and (b) the charge on each plate is doubled, as the capacii*segb67*47 ysrz ot- ;kaw9ujiev0 mtor 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 horizoncx2 4qu 80hyp eg)ln(ytally 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 above the center. Estimate glyx8uh np0()c2e yq4the value of E.    $ \times10^{5 }\,V/m$

  Electrons are accelerated by 6.0 kV in a CRT. The screeniy9ome( jrjy4 8d3oq. d1 o,lxfm:/zv is 30 cm wide and is 34 cm from the 2.6-cm-long deflection pm q8:e9/ 1ojl4zv ddi(yx jy.r,o3fom lates. 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 fr 6jfw-2m- wamlom rest acquires 6.3 keV of KE in moving from point A to point B. w2-m m-wf6a jl
(a) How much KE would a proton acquire, starting from rest at B and moving to point A?    keV
(b) Determine the ratio of their speeds at the end of their respective trajectories.   

  A lightning flash transfers 4.0 C of charge and 4.2 MJ of energy to th., dh *zzx0b;fo5w ml,ko 0ifhe 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 about3h1d 8tjzxxj.63 woo r $150\,V/m$ How much energy is stored per cubic meter in this field?    $ \times10^{-7 }\,J/m^3$

  In a television pict :aqx:gd;pr,pnp(ha 1ure tube, 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 force of gravity? What potential difference, acting over a distance of 3.0 cm, would be needed to balaa:,r;ppad g: n qp(h1xnce 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 enou;+xl- yedr57pxt ,qqjbf 2.n fgh 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 until it is fully char,ez)xfarjsr7vr3; bel4 )/fw ged, after which it is disconnected from the battery. A slab of paraffin is then inserted between the plates. What will now xfz34sj)rlr wb)eve,f7/r a ;be the voltage between the plates?    V

  Dry air will break down if 9ti7vvs sx7;+cjmq8f 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 cornp3 ) -kree3nznl 0u3maers of an equilateral triangle (side L) as shown in Fig. 17–30. Determine the potential at the midpa3pu 3em)z-0nkln3er oint 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 a piece of Pyreye01kqn/9ucu. iam- sx c 0qeku9.-/ua1 y snmiglass is placed between the plates, how much charge will then flow from the battery?    $ \times10^{-8 }\,C$

  An electron is accelerated horizontally from rest in a televisionv. 33gx;uv1tz-mw eg rgpca6h8q ;k ;z picture tube by a potential difference of 5500 V. It then passes between two horizontal plates 6.5 cm long and 13q31agzp-zktr ;;8;ugv ghmvw e6xc. .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 ) me7; ,dvjvej$C_1$ 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 v+kd2y c.raqr7(xp i tm7g 4zyl9y6-fair-filled parallel-plate capacitor for a circuit you are building. To make it a reasonable size, suppose you limit the plate area to What would the gr r4ma7fyc-p76di2k9xzlvtq+ gy .y(ap have to be between the plates? Is this practically achievable?    $ \times10^{-16 }\,m$  ----待选择----YesNo 

  Near the surface of the Earth y,xq 4q3 qqedf c2+,ccthere 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 pulsedj fo+jy0kx94 h;s9qvc 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, the potential difference between the Earth and the bottom opu60m u24uorm bimcy/(1kft t+)5r w kf the thunderclouds can be as high as 35,000,000 V. The bottoms of the thunderclou(pkc5+byrmm0iumu kttouf1264 r /w )ds 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 enou*kvhqmjm uf ;.zs h84.gh energy to some electrons in barium metal to eject th*m ;h mjhfus4v. q.zk8em 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 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 lhr5t2b y ,(pb36 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-diameter coins separatcti1 t0nb272h4., ah cg3 donw :najzced by a 0.15-mm-thick pnwih.gd7a b4o03 nj2 hca t2,cc1z t:niece 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 capacitoax -3.zz,t a aa2od fsike/x9;r with 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 fix9 efe3b k /-ehfhit1k46dgw1ned 4.0 cm apart 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.1jv7o 7y gbz :zp,qsfqew4// 6;xkadu 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$