If two points are at tvx ajq4pt: 2hbw05*9 zxrwee8he same potential, does this mean that no work is done in moving a test charge from one point to the other? Does this imply t r8xqtz:0wx 4ebv5 2e aj*w9phhat no force need be exerted? Explain.

If a negative charge is initially at rest in an electric field, will 4m e u3o, ciau+ln7be1it move toward a region of higher a ue1obi mc3e ,47nl+upotential or lower potential? What about a positive charge? How does the potential energy of the charge change in each instance?

State clearly the differdbpu) hm1+;c qence (a) between electric potential and electric field, (bc;quhb d+mp1) ) between electric potential and electric potential energy.

An electron is accelerated by a potential difference 5rs1i lmins:1ydu6a v3 gqc5:of, say, 0.10 V. How much greater would its final speed be if it is accelerated with four times as much voltage? Ex 1uq5:ai vcisls:d3 1n mgr56yplain.

Is there a point along the line joining two equal positive charges where th (wfyvz/x:i: 2 bqei1hc)pf*be electric field is zero? Where theqbcy: z* :xivf(2 fb)1ei/hp w electric potential is zero? Explain.

Can a particle ever move from a region of low electric potent dgx.0dvum6n; /aa h4yial to one of high pot0 4/adg 6h;xvya.dnmuential and yet have its electric potential energy decrease? Explain.

Compare the kinetic energy gained by a th* 1gl8 .bqlx.kqv 2oproton $(q=+e)$ 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 nt zgjts u27 /x/e4jv(cross? Explain.

Draw in a few equipotential lines in Fig. 16 – 3n46gff + enr+4 kylak.zy89b,xm oj9g1b.

What can you say about the electric field in a region of space that has the same neab,2na.jt q;vqc;* potentiaenaba;2q ,tjqn*v c. ;l throughout?

A satellite orbits the Earth along a gravitational equipotentialg 8 0q *izf vvz os,4kv//9pt86kffwmx line. What shape must the orbsmz6x*/8oqk4 8vfgtf,vkp 0vz i9fw / it be?

When dealing with prac k/1n4ukd/+rl iqlhn 1tical devices, we often take the ground (the Earth) to be 0 V. If, instead, we said the ground was how would this affect (a) the potential V, and (b) the electric field E, n/1 lku1/ih+lkqrd4n at other points?

When a battery is connected to vac m3y)hfl+sk0mx53a capacitor, why do the two plates acquire charges of the same magnitude? Will this be true if the two conductors are different sizes or shapesh xly53 3am v0km)cf+s?

We have seen that thqg 2oiesq dn20 nk*(e7e capacitance C depends on the size, shape, and position of the two conductors, as well as dko 7(q*neni2sg02 qe on the dielectric constant K. What then did we mean when we said that C is a constant in Eq. 17 – 7?

  How much work does the electric field d) y) gr30vhcfso 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 w)60t3vf p l8len2v ccxith a v06lc)c3 nx2lt8vp fe potential 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) +o fb 41e96tsf2bkyo k; pau.bif it accelerates through a po+b tk 6b2fpbkoa;uey41 sf.9 otential difference of 23,000 V in a TV picture tube?
   $ \times10^{-15 }\,J$
   eV

  An electron acquireskzd8 )3lt quag12swg y)3mv .f $7.45 \times10^{ -16}\,J$ 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 field3bt g19r xty05w qxfp. between two parallel plates 5.8 mm apart if the pote3r9bqx.g 1wt fy0pt x5ntial difference between them is 220 V?    $ \times10^{ 4}\,V/m$

  An electric field of opy)z:2x a,4nat.rwo $640V/m$ is desired between two parallel plates 11.0 mm apart. How large a voltage should be applied?    V

  The electric field between two parallel plates connected to a 45-V battery 5 cr1kc *q)l sdicx83eksds77is $1500V/m$ How far apart are the plates?    m

  The electric field betweendj/j( w4r7gwq *npr+6ol vh-z two parallel plates connected to a 45-V battery is $1500V/m$ How far apart are the plates?    m

  What potential difference is needed to give a helium nucle6/c q.+irxzu0p(vhe w us $(Q=2e)$ 65.0 keV of kinetic energy?    $ \times10^{4 }\,V$

  Two parallel plates, connected to a 200-V power supply, are separated bty xinbic 0t1uc- ),9qy an air gap. How small can the gap be if the air is not to become conducting by exceeding i, u-y90tccit1q bx)i nts breakdown value of $E\,=3 \times10^{ 6}\,V/m$?   $ \times10^{-5 }\,m$

  The work done by an external force to+dv p; hbfd18k5fvvj7 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,m:llvqj 0xbbe00vlplq *g; ) kinetic energy
(a) 750-eV,    $ \times10^{7 }\;m/s$
(b) 3.2-keV?    $ \times10^{7 }\;m/s$

  What is the speed of a proton whose kinetic enerhw. 7v 23iinxeicry,u1- -qu1kwy5j a gy is 3.2 keV?    $ \times10^{5}\,m/s$

  An alpha particle (which is a helium nuclrs*-: yry p; zf p:58oecxsaa1eus, $Q=+2e$, $m\,=\,6.64\times10^{-27 }\,kg$) is emitted in a radioactive decay with $_{KE}$ = $5.53MeV$ What is its speed?    $ \times10^{7}\,m/s$

  What is the electric potential 1t e huirqn+5 s,itwoc(g6/myb:q*13 kb;h. lz 5.0 cm from a $4.00\mu C$ point charge?    $ \times10^{ 5}\,V$

  A point charge Q creates an elec. -nqhez *p1iatwlq,)tric 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 aq gc:4) anfeqf+ug.+qd:l,xg-jz tv ; football. This conductor carries a net negative ch t ggq,j4:dex+):cnq- vu+gafz;.qfl arge, $-Q$. Draw in a dozen electric field lines and two equipotential lines.

  (a) What is the electric potentiqvo)kq wv8 tiepka4.*y va+ (8al 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 tjzt. bx9cr1+z/gly,g n -gcjb+1vt k:he corners of a square of side L as shown in Fig.j bg +9knt-.lxgcz:t+vg ,c 1zrjby/1 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 frohfuu;f m6:) rdm 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 from j (b9qak2wu4 aa great distance apart to 2 b9uqjaw(ak4$1.0 \times10^{-10 }\,m$ from one another (at the corners of an equilateral triangle)?    $ \times10^{-18 }\,J$

  Consider point a which is 2a 11clbdp(q o,in0 7wzv ky)s72 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 (radpw gf -,a/a:7mnn k0 pok44hllius $1.2 \times10^{-15 }\,m$) 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 d, as sh do8kijatn 5pio)o;qz73 l/+rown in Fig. 17–27. Determine akt il3nr5 jq/o)oi8z ao7d ;p+ 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,l mz j4/.p/qtq.s/a.+r* l rbxmlu db a proton (the nucleus) in a pammb/ .ld.ql/ /xtz,b+ *r s4.u qjlrcircular 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 qbh1 5a)+) iaoc+is mm+epup8are $ 0.53\times10^{ -10}\,m$. apart. What is their dipole moment if they are at rest?    $ \times10^{-30 }\,C\cdot\,m$

  Calculate the electric potential due to a dipole whose dipole mome1 g8spqi49n imnt 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 vectkuf7wq 1h89jq0wxy7c /m +lfu ade d:*or, points from the negative to the positive charge. The water molecule, Fig. 17–28, has a dipole moment which lkfd9u :7 mx 1hwedycuqwa/80 qf+*7jcan 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 capht3red2) e ci:jqt9r3a t1m+j 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 capacim7zs (3csbik ql-.jr4 tor 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 minus chargeyb5kizcs 1g4 4s of $ 16.5\times10^{-8 }\,C$. What is the voltage across the capacitor?    V

  The potential difference between two short secuhy7i1 )fc6 mztions of parallel wire in air is 120 V. They carry equal and opposite charge y6z7mfi)cu1 h of magnitude 95 pC. What is the capacitance of the two wires?    $ \times10^{13 }\,F$

  How much charge flows from each terminal of a 12.0-V battery when it is connectehvcy1sw +r:+ gd to a wyv gc+r1h:+s $7.00-\mu F$ capacitor?    $ \times10^{-5 }\,C$

  A 0.20-F capacitor is desired. What area must the plates have if they are tok5 +j4 p2hxnmm be separated by a 2.2-mm air gap? hmn kpj 5m+4x2   $ \times10^{ 7}\,m^2$

  The charge on a capacitor increases bf)zk 4***oq h ruu gj/5l+uczly $18\mu C$ 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 ;vi* 0jpnk pc:$8.5 \times10^{ 5}\,V/m$ 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 ,vc/lmatq+ xu w0 ;-u dtnk2x1$5.2\mu C$ 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 plates of zl vgo:km..k2 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 disconnk)vz ;53lbd a*lhsbkg*/c ;w jfq.5eq ected from the battery. When t/fd);z geab h qc kq3.l*l5v*;s j5bkwhis capacitor $(C_1)$ is then connected (Fig. 17–29b) to a second (initially uncharged) capacitor, $C_2$, the final voltage on each capacitor is 15 V. What is the value of $C_2$? [Hint: charge is conserved.]    $ \times10^{ -5}\,F$

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

  What is the capacitance of two square parallel plates 5.5 cm on a side that are irjt6/)ejkd /w d; 2st9rmvw)separateietk9/vm t2jw 6/))w dr;ds jrd by 1.8 mm of paraffin?    $ \times10^{-11 }\,F$

  What is the capacitance of a pair of circulaj4za.tf5s- :vm k ax0jr plates with a radius of 5.0 cm separated by 3.2 m4xjfvatma0 z. :sj k-5m of mica?    $ \times10^{-10 }\,F$

  A 3500-pF air-gap capacitor is connectu*)aq h g39lq,kqx +ered to a 22-V battery. If a piece of mica is placed between the plates, how much charge will flow 3a,ru+q gkqe h*q )x9lfrom the battery?    $ \times10^{ -7}\,C$

  The electric field between the plates of a papl 518kw/rnapcnr rs0xg * (oz4-t:ack er-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 capacito d0yug-nrbm 3nf/qb 2+i)dr4i r. How much energy is stored?    $ \times10^{-4 }\,J$

  A cardiac defibrillator is used to shock a heart that is beating erratically. g;s+7(xe2gnig0)zeo hd3c lkA capacitor in this device is cg;23 ceiod nhgz( 7l0)gxe+skharged 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 between two k7sx dp h1:bz)xs84u.z4qcj9k ni8eo square plates, 8.0 cm on a side, separated by a 1.5-m kz7osn8ip9.84c1: bsdx jk)zqeuh4xm air gap? The charges on the plates are equal and opposite and of magnitude $420\mu C$.    J

  A homemade capacitor is assembled by placing two 9-in. pie pans 5 cm apart and bqp ue:7orx52j. x,c gconnecting them to thx:2gxjbuq r5co7,pe. e opposite 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 capacitf0n;kuq.p )4 yy oiga/or 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 ( ridsb4; f8ewuf1gw7e* cug 6(a) the potential difference is doubled, and (b) the charge on each plate is doubled, as the capacitor remains conng(7 b d6f1wf;wu4*8cugeeir s ected 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 7.0 *y+4n; fyae xyhqhn/; kV. They then pass tn;/ h4yx n;fyq *yah+ehrough 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 the value of E.    $ \times10^{5 }\,V/m$

  Electrons are accelerated by 6.0 kV in a CRT. T8kbar5f 42*w3jdiv ml sg.e m)he screen is 30 cm wide and is 34 cm from rg)k.d lmv2a5 8 *3f4ej ismwbthe 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 fro w4u/bqg 9n)zjm rest acquires 6.3 keV of KE in moving from point A to pwnu9b z)4jg/ qoint B.
(a) How much KE would a proton acquire, starting from rest at B and moving to point A?    keV
(b) Determine the ratio of their speeds at the end of their respective trajectories.   

  A lightning flash transfers 4r9(2(lv) te+asgz r*oft :bkoz;wx(h.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 surfl :x6iyg8 qri3ace whose magnitude is about $150\,V/m$ How much energy is stored per cubic meter in this field?    $ \times10^{-7 }\,J/m^3$

  In a television picture tube, electrons are accelerated by thousands of vof-5itbk x0lif4r x7; .ybzf 1)bvfo /tlts throtbbl75/ fbyi f 1kv i4 fxz-;.)rfox0tugh 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 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 capacitm. mt0lj/h +b08zpj lr4wru2v or 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 bat)ararw g z*amcq. d8-q;lgx11tery until it is 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 voltaa qqrdm wlr)za - c1g1a8;*g.xge between the plates?    V

  Dry air will break down if the electric field emlj2bkb, 9xlf87ucv1 / yqt 7oxceeds $3.0 \times10^{6 }\,V/m$. 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 llf ;,. (duhd , 4 5j,szemexouzslr./corners of an equilateral triangle (side L) as shown in Fig. 17–30. Determine the potential at the midpoint of each of the sideur5.,o;zl.,(llxe,f ms / sd e 4jdhzus.

  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 lfpo-x5-m co6peea69battery. If a piece of Pyrex glass is placed between the plates, how much charge will then flow fm-oe 5ao9pf6e- xlc6p rom the battery?    $ \times10^{-8 }\,C$

  An electron is accelerated horizontally from rest in a television picture tube 7 m vwc0-/ktnsby 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. 17–31ntsvm - w0k7/c). At what angle $\theta$ will the electron be traveling after it passes between the plates?    $^{\circ}\,$

A capacitor of capaclt0m ;*q qmg,t7kan h.itance $C_1$ 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, suppos/g7z2of(d g use you want to make a 1-F air-filled parallel-plate capacizg (2sdgo/f u7tor 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 the Earth there is an electric field c62qmdm 2 lv p056gh;zwyq1 t+jbth 1uof 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 nitro ja qv*uj7w5/2j4heko gen 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 uu fr)8 rd1(ebgnvi,4potential difference between the Earth and the bottom of the thunderclouds can be as high as 3erb,dg41v8irn(u f u)5,000,000 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 eclh*(/xfbk) d nergy to some electrons in barium metal to eject them from a surface at high speed. See Fig. 17–33. Tk*)c b/h(xlfdo 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 **p)mygilexcj 6*mkqt - k20j36 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 coins0zexf ,upl,2 p separated by a 0.15-mm-thick pi2lfu,0e zxp ,pece 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 ,v esbsya+ o6i; 3h9d kwilx0/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 fixe2 0pwd z)n6v mu+iqd;hd 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 shoo 608isq,a;*l g89pcjy ewefuwn in Fig. 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$