If two points are at 8;/a e ptbxzq2the same potential, does this mean that no work is done in moving a t 2ea; pxzqt/b8est 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 in an electric field, will iwvgb vlk9/af c. k71)xt move toward a region of higher potential or lower potential? What about k wf xagvckvb.)7l9/1 a positive charge? How does the potential energy of the charge change in each instance?

State clearly the difference (a) between electric potential and electric field,r b*s/s7mnof jsz 2o(2+3duwb (b) between electric potent+/sbb32n*2zm 7w dsrs( ofujoial and electric potential energy.

An electron is accelerated by a potential difference of, sa40 uzkrx 3x6o*p gnpj2y, 0.10 V. How much greater would its final speed be if it is accele6x2j0krgxp *up zo3n4 rated with four times as much voltage? Explain.

Is there a point along the line joinirw.u e:4a i(),h qoo baa(+iwbxbf5 /n9ugi (ing two equal positive charges where the electric field is zero? Where the electric potential is zero? Exp bguih:. aioxbaawui/(5(rnib(4wef 9 ,)+ qolain.

Can a particle ever -zjh.hq5.ajk.w; hjc move from a region of low electric potential to one of high potential and yetkcj j.zjhhhw. a5q-.; have its electric potential energy decrease? Explain.

Compare the kinetic energqp9w3o (ikl6hy 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.xvo .,v8+99brvheiby 3k*l zl

Draw in a few equipotential lines in Fig. 16 – 31jn73k q+uqf*rk(wy bgevl-+9tt 9 qp)b.

What can you say about the hr/pt 5hix 3a:3rb7ca f0z/t zelectric field in a region of space that has the same potential through ba pzr3hif7 thcr053 z//x:taout?

A satellite orbits the Earth along a gravitational e9q/lw2/ viv)8si api,zcbg .: yyq:l+h:xjbi quipotential line. What shape must the+::xi ,yvvzi jq9h c g )q8.ylib/iw/ap b:2ls orbit be?

When dealing with practical devices, we often tn77 ftir.zf7;n v mha8e, :iwyake the ground (the Earth) to be 0 V. If, instead, we said the ground was ,yaer7ntv wifm;7f7h. :i 8nzhow would this affect (a) the potential V, and (b) the electric field E, at other points?

When a battery is connected to a capacitor, whyx rlks;,g34w:tg+ zxu do the two plates acquire charges of th;xu +:,gk4swx3r tlzge same magnitude? Will this be true if the two conductors are different sizes or shapes?

We have seen that the capacitance C depends on the(pwhunhelq(e*25/ f u size, shape, and position of the two conductors, as well as on the dielectric constant K. What then did we mean luuehpn/( w2f*e 5 hq(when we said that C is a constant in Eq. 17 – 7?

  How much work does the eu,24 q+u+udy2fetal g lectric 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 poi rgjx2*k 65pum*q.s7g x*kr z6vvm:nvnt with a 5u*jvxng6gk :vz72*v r *sx r.mmq6k ppotential 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) maz,7 7r wz-i:lq6wxfif it accelerates through a potential difference of 23,000 V in a TV picture tzfw:w rx77qmai, 6lz-ube?
   $ \times10^{-15 }\,J$
   eV

  An electron acquires bn0 ,xog5g, tzz59ofx h /q/a:tkuhq1$7.45 \times10^{ -16}\,J$ 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 parakx/kcgpf-qzl ,-*(a w llel plates 5.8 mm apart if the potential difference be/ w-qplxazf ,*g(k-cktween them is 220 V?    $ \times10^{ 4}\,V/m$

  An electric field of 05d)x ajknrg kb5f uae7/s 83 (o.tfuh$640V/m$ 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 con08euaxz d.5 uvlbc71fnected to a 45-V battery is $1500V/m$ How far apart are the plates?    m

  The electric field between two parallel plates d4hoo8*np eiav8+j 3i5ukit,connected to a 45-V battery is $1500V/m$ How far apart are the plates?    m

  What potential difference 2l2i wah pg:9sis needed to give a helium nucleus $(Q=2e)$ 65.0 keV of kinetic energy?    $ \times10^{4 }\,V$

  Two parallel plates, connected to a 200-V xfw0w7o.) y*hv.iarupower supply, are separated by an air gap. How small can the gap be if the air is not to become condu*xfu0w. .a yhwri7o)vcting by exceeding its breakdown value of $E\,=3 \times10^{ 6}\,V/m$?   $ \times10^{-5 }\,m$

  The work done by an external force to mmp q5xz 6h*;sjd.u, nrup:r: aove 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 gm pd8w :,5oxxelectron with 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 energy pa 5z g3,f3uwouq/(vdis 3.2 keV?    $ \times10^{5}\,m/s$

  An alpha particle (which is r0:x.map;mfzt 9 z:mwh* he g;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 p,2-1c cwvdnw gotential 15.0 cm from a $4.00\mu C$ point charge?    $ \times10^{ 5}\,V$

  A point charge Q creates an electric potential of 5n 3sddppy fd,-up+f;y* orcc (39 ioi$+125V$ 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 footjxv+v.a8099ltn g t jpball. This conductor carries a net negative c9jvx.+t0 9j8ntlvgp aharge, $-Q$. Draw in a dozen electric field lines and two equipotential lines.

  (a) What is the electric potential a distance of r6pw zh.c+b-wpt;+ ii$ 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 arrange;nb lb0cgt/v 5pvp)v ;d at the corners of a square of side L as shown in Fig. 17–25. What is the pot v c5)bb0ltvg;p;v/pn ential at the fourth corner (point A), taking $V\,=\,0$ at a great distance?

  An electron starts from rest 32.5 cm from km x2lk (mla (,5:khmqa 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 electror yabs6+msty 6*(pw b5ns from a great distance apart tbyar m+ sb6( y6p*s5wto $1.0 \times10^{-10 }\,m$ from one another (at the corners of an equilateral triangle)?    $ \times10^{-18 }\,J$

  Consider point a which is 72 cm n2 wy5)xn u4xbr-u; uw,v 6fapxorth 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 p/lc(qio .tnz: hn*dby c-8h0mroton (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 in F0t9dcvl gb4 ji,3 s4jf/73,dpb wfsv mig. 17–27. Determine a formula f f 94lvd,, mwj /pfsbs 3vgidtjb30c47or $V_{BA}\,=\,V_B-V_A$ 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 nucl /zbx9sg;pz;(dt6 mv lr9uee;eus) in a circular orbit of radb r;zzxg uve tp9;ld;(6m/e9 sius $ 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 ar3u.6/p 1yvh z;yw guvte $ 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 e .;04c1hfl0cqnhhyz2 x(x rnto a dipole whose dipole moment is $ 4.8\times10^{-30 }\,C\cdot m$ at a point $1.1 \times10^{ -9}\,m$ away if this point is
(a) along the axis of the dipole nearer the positive charge;    V
(b) 45° above the axis but nearer the positive charge;    V
(c) $45^{\circ}\,$ above the axis but nearer the negative charge.    V

  The dipole moment, considered as a vector, points from the negatx9z5 r4g77zuqobnst up(nzt c6rya5*m8sr6 +ive to the positive charge. The water molecule, Fig. 17–28, has a x5z86b 7tgnnas z4 zr6ormup t5+*sc(y79uqr 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 capacit7rl ewx qmg/5y(-gs:a or 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 hold t)9akjtae g0f.t1m b6$+2500\mu C$ 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 hold.j,nwxn;az :, aojh6ms plus and minus charges of $ 16.5\times10^{-8 }\,C$. What is the voltage across the capacitor?    V

  The potential difference between two short sections of parallel wire iyv srox2t50*p6j4x r *hm wqxgay6(8zxxy(d 8n air is 120 V. They carry equal and opposite charge of magnitude 95 py4xoad x g 2h(qxrpwm xv0j8yt56 (6*xrys8*zC. What is the capacitance of the two wires?    $ \times10^{13 }\,F$

  How much charge flows from each terminal of a 12.0-V batterqsv/jw yn / 87r85caffy when it is connected to a n7r5cy js88w / avqf/f$7.00-\mu F$ capacitor?    $ \times10^{-5 }\,C$

  A 0.20-F capacitor is desired. What area mus :pn m4oa/nr26j g7ulkt the plates have if they are to be separated by a 2.264ln/ j:r72po ukag mn-mm air gap?    $ \times10^{ 7}\,m^2$

  The charge on a capacitor incwg-hei,/ fs;t reases 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 7 ./u 1a8 hufphnfwj:w$8.5 \times10^{ 5}\,V/m$ 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 oppoh j.5 34)ee (w) o/kqaufgq aw95anumosite $5.2\mu C$ 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 electrick, fkd idzpt*,efy+ 92 field between the plates of a $0.80-\mu F$ air-gap capacitor if they are 2.0 mm apart and each has a charge of $72\mu C$ ?    $ \times10^{4 }\,V/m$

  A capacitor is charged by a 125-V battery (Fig. 17–29a) and d3pgn o5d l8ufvxg(:7then is disconnected from the(vg53d:nf o8ug 7 xdlp 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 /yq8d5sm pkbntrgw; 0hh 91m:two square parallel plates 5.5 cm on a side that are separated m:yqt51 ghrhb mp s80/kdw;9nby 1.8 mm of paraffin?    $ \times10^{-11 }\,F$

  What is the capacitance of a pair of circular plate+ 4y rmz3whv*zs with a radius of 5.0 cm sepay43wv+mr zz* hrated by 3.2 mm of mica?    $ \times10^{-10 }\,F$

  A 3500-pF air-gap capacit;fcpa+,hj5k .a sbb,i or is connected to a 22-V battery. If a piece of mica is placed beta5ksf,j.ca,; p h+ibb ween the plates, how much charge will flow from the battery?    $ \times10^{ -7}\,C$

  The electric field between t xh jv. ,4ib.cvealt8e/ ps7vf*z5ig7he 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 capacitorwg4 q 7 c8uxwx3( nn+*c7shtyv. How much energy is stored?    $ \times10^{-4 }\,J$

  A cardiac defibrillator is used to shock a heart that is beat0nx p zsmneles-8l1edcy2d;(): kt, jing erratically. A capacitor in this device is charged to 5.0 kV and stores 1200 J of energy) ez e(pj0 cxd-k,2medsltn: ;ysl8n1. What is its capacitance?    $ \times10^{-5 }\,F$

  How much energy is stored by the electric fi (eb b*78*nkhcnfd-omeld 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 o7m dcnk*bbhen8- *(f opposite and of magnitude $420\mu C$.    J

  A homemade capacitor is assembled by placing two 9ym4 n hc013ley lf(p,h-in. pie pans 5 cm apart and connecting them to the opposite tpn ll,hcmfye y3h10( 4erminals 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 capaciaj p,a.r1 kobfk5x5p0tor 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 nh +yl.;i z*mfstored in a capacitor change if (a) the potential difference is doubled, and (b) the charge on each plate is doubled, as the capacitor remains connected i*lm fyn; z.+hto 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 7l * ,af2on/5n4wir bom;;* hu7wzj/qpd9 ezl q.0 kV. They then pass through a u5nj l,h9/qm4elw;;f uozd*2* i zw /rpao qb7nniform 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 accelerf)x4 jjs(o08b nm w7juated by 6.0 kV in 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 varwnm jjbjs8uf7()x04o y to sweep the beam fully across the screen?    $ \times10^{5 }\,V/m$ to    $ \times10^{5 }\,V/m$

  An electron starting from (zs sh . ox0mw)x02nheue/z*i rest acquires 6.3 keV of KE in moving from point A to poinoxuems(hi)0 zz* xshew0. 2/nt 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 o0c, 1/g5hbiqvs p8kvdf 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 swov 2q prga6r4 j ;f,b9hd69saeybf/k8 j q6q)urface 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 acc uw.vfebix,dzgp3 9(( g4up.h.m xu )pelerated by thousands of volts through a vacuum. If a television set were laid on its ba4xe ug.ufu((hg.vp )w.p3p , i9mbdxzck, 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 capacitor has enough stored energy to heat 2.5 kg of wao7l 1iy3*k lc0)f very mnz7y-ter from 21$^{\circ}\,C$ to 95$^{\circ}\,C$. What is the potential difference across the plates?    V

  An uncharged capacitor is cocfac1g/to9e 3 nnected to a 24.0-V battery until it is fully charged, after which it is disconnected ot9 e13cfcag/ from the battery. A slab of paraffin is then inserted between the plates. What will now be the voltage between the plates?    V

  Dry air will break down if the electric field e4l: , p,d-lqis zq9fhxxceeds $3.0 \times10^{6 }\,V/m$. What amount of charge can be placed on a parallel-plate capacitor if the area of each plate is $56cm^2$?    $ \times10^{-7 }\,C$

Three charges are at the corners of an equilateral triangle (side L) as shown i,*dar9xqurs b/cmc4i1 n/mr 2n Fig. 17–30. Determine the potential at the midpoint of each of the sidrr/ *d,nmsbcq a9ri 2/cxum14es.

  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 is5somr0- 4m,ghg /lqkp connected to a 9.0-V battery. If a piece of Pyrex gk/504 gpgso, lrhm qm-lass is placed between the plates, how much charge will then flow from the battery?    $ \times10^{-8 }\,C$

  An electron is accelerated horizontally from rest ul*f5i tl:jr4in a television picture tube by a potll:f4jri 5 *tuential 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 what angle $\theta$ will the electron be traveling after it passes between the plates?    $^{\circ}\,$

A capacitor of capacisvzh b(p8xlh.x,;(ic tance $C_1$ 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*l 58zn,n hp6ya5 epei make a 1-F air-filled parallel-plate capacitor for a circuit you are building. To make it a reasonable size, suppose you limit the plate area to What p5 a *6ynz eh8e5li,npwould 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 electricx ou)qa l:rbh63(yp7a 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 nitronf e/ fc-4bx;)wjc 4bbgen 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,;rga aqz +z3t9cz0bgt9 (k9o:w az ;mg the potential difference between the Earth and the bottom of the thunderclouds can b qambz+ggtt9o z; ( aa09 wk;:r3zzc9ge 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 sow:/w ;kugig u wxkf/-3me 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, another plate above the bariuug/-3k fkxi:w g/; wwum 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 c qkns*q;js1i 4m 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 separated by a + xfimp/7d/eb0.15-mm-thick piece p/7dmex i/+ bfof 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 capacime :pvv7hi -i*tor 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 each other. Their charges 9x-rqub pplb:iili 6gq *1trj;* *z5zare $Q_1$=$Q_2$=$5.0\mu C$, 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 w/0ijt kbd o62qur 761f;zso fvith $q_1$=$1.5\mu C$ and $q_2$=$-3.3\mu C$ Find the potential difference between points A and B.    $ \times10^{ 5}\,V$