If two points are at the same potential, does this mean that no worf4h0 3u*hjr blk is done in moving a test charge from one point to the other? Does this bhuj rh3*f 4l0imply that no force need be exerted? Explain.

If a negative charge is initially at rest in an elect* -o xt; 8txbg0rjhx3guq*40a 0ar vxdug9gu+ ric field, will it move toward a region of higher potential or lower potential? What about a positive charge? How does the potential energy of the charge change 8 h x r 0gub4qu-oxua0x0d g9 gat+r*;3gxvj*tin each instance?

State clearly the difference (a) between electric potential and electric 2he9wc uhi4(n field, (b) between electric potential and electric ph4iuhc(2w en9 otential energy.

An electron is accelerat:*d yvmq3;etr ed by 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 rmq; dev *t:y3voltage? Explain.

Is there a point along the line joining two equal positive charges where t jl5i zzeod7(/he electric field is zero? Where the electric potential isjli5 d /o(ez7z zero? Explain.

Can a particle ever move from a region of low elect;z0znpn .i zo9ric potential to one of high potential and yet have its electric potential energy de;.zoipn 0 zn9zcrease? Explain.

Compare the kinetic energy gain*dx gx*0w:zi,ze5 umpyc bziz0;st;. 7ql ev ,ed 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 crr5 e-erd-g0 xxoss? Explain.

Draw in a few equipotential ln) mmd,sr m5e 46rrcb:ines in Fig. 16 – 31b.

What can you say about thel n,gz52b(l(y )knv-/fphzod electric field in a region of space that has the same potenti lz5/yl2)bkz((gn,vfpd h-on al throughout?

A satellite orbits the Earth along a gravitational equipotential line. What y :6lz;cjinkxm mrn su:a++jb8 -wj+6shape muslyumj b6 jkw+m+jc;r8nz:sa-x 6ni:+t the orbit be?

When dealing with practical devices, we often take tzkp2 5v q6av+hhe ground (the Earth) to be 0 V. If, instead, we said the ground was how would this affect (a) the potential V, and (b) tvk26 qah +z5vphe electric field E, at other points?

When a battery is connected to a capacitor, why pf-ov1h b 0+l)u zpd0sdo the two plates acquire charges of the same magnitude? Will this be true if the two conductors are different sizes or sbh1zlf p u0)d- vo+p0shapes?

We have seen that the capacitance C depends on the size, shape, and posinr n07: tq -hfdxd1zeww2;3/hlihfv2tion of the two conductors, as well as on the dielectric consz/l hqi2;h3 vfd tf-dw0nn x1r:2we7h tant K. What then did we mean when we said that C is a constant in Eq. 17 – 7?

  How much work does the electric fixg*i0jsjn2 1by b)g f,eld 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 a4v6.una )e qcisk3xb b8aa .i, proton from a point with a potentia. xi8a64senvc u)kb,aa.bi3 ql 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 eea kd*3g(/o ehtie52t V) if it accelerates through a potential differenceg*5edo/eh ae3(t kt i2 of 23,000 V in a TV picture tube?
   $ \times10^{-15 }\,J$
   eV

  An electron acquires6vd .gplrr8s 4 $7.45 \times10^{ -16}\,J$ 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 paralff uk;eip wk4+63.kxdlel plates 5.8 mm apart if the potential difference between tkuwp3;fxkd6 ek i .4+fhem is 220 V?    $ \times10^{ 4}\,V/m$

  An electric field of 4gmkz/4c( e zw$640V/m$ is desired between two parallel plates 11.0 mm apart. How large a voltage should be applied?    V

  The electric field bet,w : uq.mwwd.a 0h t)uw;rs3-yctckpw6/ t;gcween 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 conneteabijm2+ d qi;de2szxvak30m 3- p*/cted to a 45-V battery is $1500V/m$ How far apart are the plates?    m

  What potential difference is needed to givepff 5atte0*8si x-1wj a helium nucleus $(Q=2e)$ 65.0 keV of kinetic energy?    $ \times10^{4 }\,V$

  Two parallel plates, connected to a 200-V power suppw3z uu(r /;jljly, are separated by an air gap. How small can the gap be if the air is not to become (r3jw;/u j lzuconducting by exceeding its breakdown value of $E\,=3 \times10^{ 6}\,V/m$?   $ \times10^{-5 }\,m$

  The work done by an external force to mqbv bjw 6fp/g0 fjj .1nj,j,7tove 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 kinetic izgb25)1-iuzv l cjp;4(rny f 0xv/pm energy
(a) 750-eV,    $ \times10^{7 }\;m/s$
(b) 3.2-keV?    $ \times10^{7 }\;m/s$

  What is the speed of a proton whos(*40mv 2qqjvpfvl: pme v9td3e kinetic energy is 3.2 keV?    $ \times10^{5}\,m/s$

  An alpha particle (which is a helium nucleus,vwt6 p3ve9cus d-s94r $Q=+2e$, $m\,=\,6.64\times10^{-27 }\,kg$) is emitted in a radioactive decay with $_{KE}$ = $5.53MeV$ What is its speed?    $ \times10^{7}\,m/s$

  What is the electric potential 15.0 cm from a us koq kk/whc1 w81fnh3bnc 8o4hvn6b -q.7 o7$4.00\mu C$ point charge?    $ \times10^{ 5}\,V$

  A point charge Q creates an ez(pt wh90qh(f gsb 72e kzy/2alectric 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 conductor carries a g 4 6,gx;1vxnuezo2uhw0:vbinet negativ16 i: gw;0ghevu4b xx,2uznove charge, $-Q$. Draw in a dozen electric field lines and two equipotential lines.

  (a) What is the electric potential a distance o zekn:by. b/n5o6 q6aof $ 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 side L as shown8adg x0t-8n*kvj 5 p54blmn sd in Fig. 17–25. What is tkgd88 m5t4nls*b vj a0-x5 npdhe potential at the fourth corner (point A), taking $V\,=\,0$ at a great distance?

  An electron starts f( tf ( a:vebhke:9o*lcrom rest 32.5 cm from 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 thzh6 c fx/6tmd+j:i u4cree electrons from a great distance apart 66d+ fz4c:t/i hmu cjxto $1.0 \times10^{-10 }\,m$ from one another (at the corners of an equilateral triangle)?    $ \times10^{-18 }\,J$

  Consider point a which is 72 cm norosur,u11w.w 9y k4agv th 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 r(uy- ru, x-u7ju l6 8:susxmaused to 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 are separated by a distance d, as shown ot+p)mx4jq2 0mrxu3c7z.kq f in Fig. 17–27. Determine a formula for mfzqctxxq+ j4.muo3pr2 07)k$V_{BA}\,=\,V_B-V_A$ for points B and A on the line between the charges.

  In the Bohr model of the hydroge ldg1,*j m4waf2jq)3k1tqh eln atom, an electron orbits a proton (the nucleus) in a cielfh q4,3)*21j1 tlqaw mkdjgrcular 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 af8hv w ;p(i)jtre $ 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 m28py/tv g; liwoment 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, consi:8odcazb9i tb 7l; *e(a1c6ix g/yvobdered as a vector, points from the negative to the positi9;ce1xt / b(6a8yog*z:l advboc7 ibive 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 capacit;:.+8zu 7glyw1qibtvuc i:g yor hold $+2500\mu C$ and $-2500\mu C$ of charge, respectively, when the potential difference is 850 V. What is the capacitance?    $ \times10^{-6 }\,F$

  The two plates of a capacitor he1dow gc0 ;b0re2pi2p old $+2500\mu C$ 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 0t3gm sc /vcxu1je:t 0rv/zl; holds plus and minus charges of $ 16.5\times10^{-8 }\,C$. What is the voltage across the capacitor?    V

  The potential difference between3n1gr h02p5rgg+he hm. nv wx: two short sections of parallel wire in air is 120 V. They carry equal and opposite charge of magnitudeg.r ve32 +g:h0nhnx 1prm5gwh 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(0oago9p) ocmahfm .+ connected to a o9a 0mc o.hgof+p)(ma$7.00-\mu F$ capacitor?    $ \times10^{-5 }\,C$

  A 0.20-F capacitor is dzx5u :e3iat6z0rd 5meesired. What area must the plates have if they are to be separated by a 2.2-mm ait0:i6ze z3u 55er adxmr gap?    $ \times10^{ 7}\,m^2$

  The charge on a capacitor increc eaksd-dgirx05,;*dw, g4 ixases 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.y/jc, h)lscnnf6o )huq86 xz $8.5 \times10^{ 5}\,V/m$ 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 opposi cf.dz qaqx2akok ;y8+un+ c84te $5.2\mu C$ 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 o ht77-t*r9g9l mi6it skv2z a8tc hua*f 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 disconnemwxehy3o5 8i u3x5*h tcted f5* t y833mhx5i xwehourom the battery. When this capacitor $(C_1)$ is then connected (Fig. 17–29b) to a second (initially uncharged) capacitor, $C_2$, the final voltage on each capacitor is 15 V. What is the value of $C_2$? [Hint: charge is conserved.]    $ \times10^{ -5}\,F$

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

  What is the capacitance of two square parallel plates 5.5 cm on a side thatczg5txd) +/ 6acczyq( are separated by 1.8 mm of paraffin? gy(5/cq)zx+ztcac d6    $ \times10^{-11 }\,F$

  What is the capacitance of a pair of circular plates with7q hid 7b b9k:)l4owhm a radius of 5.0 cm separateqb 7 wbm9h7olhi:4dk)d by 3.2 mm of mica?    $ \times10^{-10 }\,F$

  A 3500-pF air-gap capacitor is connected to a 22-V battery. Ifp -fndrmpbajmk25-n;yw (ula 4 w-(a/ a piece of mica is placed b 5 2m-a/4l-wnwbaampfn(u(kyp;jr d-etween the plates, how much charge will flow from the battery?    $ \times10^{ -7}\,C$

  The electric field between the plates of a mh2c* gy; d1xx ds;5*zqz:t5yvgi g5qpaper-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.myx+yd:i9c zh*flum qh7j 1r.7e6e/y How much energy is stored?    $ \times10^{-4 }\,J$

  A cardiac defibrillator is usgp*xq n1jl*a 1bo5r+,+l1.fxa9i ebr ci4se v ed to shock a heart that is beating erratically. A capacitor in this device is charged b* af+srr4e9aqcivp*xe jl1l1 1g .+o,xbin5to 5.0 kV and stores 1200 J of energy. What is its capacitance?    $ \times10^{-5 }\,F$

  How much energy is stor 1klr32m7zt+ 8jbkxdf ed by the electric field between two square plates, 8.0 cm8+ 7t23jb xzm1krk dlf on a side, separated by a 1.5-mm air gap? The charges on the plates are equal and opposite and of magnitude $420\mu C$.    J

  A homemade capacitor is assembled by pxq5ya2 bn3 f k3k 9.tik.hbwpspf 54-hlacing two 9-in. pie pans 5 cm apart and connecting them to the opposite terminalb.ha s 9itk3fp-3k5fhx4py b qn2k. 5ws 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 has fixed crhstd7a8 awj5p)x 7um6) i ytnn2)ur 2harges $+Q$ 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 capaci0r:g)c7ihhlh d1c+yvkr 0 zl )tor change if (a) the potential difference is doubled, and (b) the charge on each plate is doubled, as the capacitor rec izr d+0gv:l)h01kr h)hlyc7mains 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 7.0 kV. They then p3,24 zb kd wzpg9fo:weass through a uniform electric field E for a distance of 2.8 coz 2,weg3wf:4zk b 9pdm, 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. The screen is 30 cm y b7r+z5hwpi7* ozbj3wide and is 34 cm from the 2.6-cm-long deflection plates. Over what range must the horizontally deflecting electric field vary to swo yr zb3j7p5zhiw+b7 *eep the beam fully across the screen?    $ \times10^{5 }\,V/m$ to    $ \times10^{5 }\,V/m$

  An electron starting from rest acquires 6.3 keV of KE inkhgztb) tgm+q6 gv;1/ moving from point A to qb/k hzt1v ;tg+g )mg6point 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 4.0 C of charge and 4.2 MJ of energy to the Earth. ffc wf(y9 8o5 l g6d39jduq sm8:gbg9dsjd5q-
(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 who4 lxgy.kjak4xc7l ;/:;7szv /xwp hc hse 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 accegwuxq/w cg7x0l dy( 75lerated 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 u0y(dgwc57q wx7x/ glof 3.0 cm, would be needed to balance the downward force of gravity so that an electron would remain stationary? Assume that the electric field is uniform.    $ \times10^{ -12}\,V$

  A huge 4.0-F capacitor has enough stored energy to heat 2.5 kg of water f2z ht9l 4um+chrom 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 battery8*qiy on jiw-2 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 voltage between tqy *nw 28ioji-he plates?    V

  Dry air will break down if the elect61n (z0bx:powdsd* d nric 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 tgbah7 u u 7xm6 ,)p52gbksrr2nriangle (side L) as shown in Fig. 17–30. Determine the grxkpghm r,u 72 bn2)b75a6uspotential 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 batz 2 /*5cfqxkfutery. If a piece of Pyrex glass is placed between the plates, how much charge will then flow from5/ kfcu zf2q*x the battery?    $ \times10^{-8 }\,C$

  An electron is accelerated horizontally from rest i(ahwjeauy+dkq 5wu31l :x*w 0n 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). A:31dyw5 (uaqx0k uw je a*lwh+t what angle $\theta$ will the electron be traveling after it passes between the plates?    $^{\circ}\,$

A capacitor of capacitang( 8 ex73qgxqjce $C_1$ 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 bigi .u6gkflv5 +x a farad is, suppose you want to make a 1-F air-filled parallel-plate capacitor for a circuit you are building. To make it a reasonable size, fig vxu6k+5.l 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 elm c2u ewh7uh io2n4,5 2hr/hucectric 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 56i f)kjo3nqs,2zlttnitrogen 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, nwr9yhkv ct7-w:yo+oweqnr58 q )0i /the potential difference between the Earth and the bottom of the thu -7twy wi/r+krho:c nqvq50 n)weoy98nderclouds can be as high as 35,000,000 V. The bottoms of the thunderclouds are typically 1500 m above the Earth, and can have an area of $110km^2$ Modeling the Earth–cloud system as a huge capacitor, calculate
(a) the capacitance of the Earth–cloud system,    $ \times10^{-7 }\,F$
(b) the charge stored in the “capacitor,”    C(Round to the nearest integer)
(c) the energy stored in the “capacitor.”    $ \times10^{8 }\,J$

  In a photocell, ultraviolet (UV) light provides enough energy to some electronsp4oh *65wfz7mb s2fxe in barium metal to eject them from a surface at high speed. See Fig. 17–33. To measure the maximum energy of the electrons, another plate above the barium surface is kept at a negative enough potential that the emitted electrons are slowed down and stopped, and return to the barium surface. If the plate voltage 5f hxfobzp2wm *s47e6 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 identical 7f8bapk/ vop 12*scon $+33\mu C$ 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-thick 2op,r7s.cr wppiece ofp2cwp,.r ro7 s 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 capacitj:1j8 k5:c g7tmab5byj ubwe-or 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 fixed 4.0 cm apart from eaolaczc q3)(* m0ln,dk: :ulg t pa3uc5nr:s)jch other. Their charges are $Q_1$=$Q_2$=$5.0\mu C$, and their masses are $m_1=1.5mg$ and $m_2=2.5mg$
(a) If $Q_1$ is released from rest, what will be its speed after a very long time?    m/s
(b) If both charges are released from rest at the same time, what will be the speed of $Q_1$ after a very long time?    m/s

  Two charges are placed as shown in Fig. 17–35 wp)fd*c9bkyao6 rz f 0s+vt6 5sith $q_1$=$1.5\mu C$ and $q_2$=$-3.3\mu C$ Find the potential difference between points A and B.    $ \times10^{ 5}\,V$