If two points are at the same potential, does this mean that no work is dd- ip 1ee5 /wg:cjh)jg29a pfjone in moving a test charge from one point to the other? Does this imply that no i adjc)5e g f1hp-2gj/j9ewp: force need be exerted? Explain.

If a negative charge is initiallyalr e+q/d-8 ghgwr a+3 at rest in an electric field, will it move toward a region of higher potential or lower potential? What aboutr - e+w/aq8l hag+3rgd 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,6ra2jd)n 1nig (b) between electric poteinr2dnja1 6)gntial and electric potential energy.

An electron is accelerated by a potential difference of, say, 0.10 7 aww ho5.tohdl ,lute6 .3)8v(+hm4nkdi msnV. How much greater would its final speed be if it is accelerated with four times as much voltage? Explain.dwi)4. k ,.(nt+m5 h h8nslvu3lw7at6domoeh

Is there a point along the line joining two equal positive charges where ts;ev hnd xa9 (0n;bl5phe electric field is zero? Where the electrlhp 9exba;d v0ns5(;nic potential is zero? Explain.

Can a particle ever move from a region of low electr f,3 a:t,cabzgic potential to one of high potential and yet have its electric potential energy decreaseagcb ,a:, tfz3? Explain.

Compare the kinetic energy gained by a protoirlty r)yerr x-r ./4:n $(q=+e)$ 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 crd.9oyx8 0nt;kv s3g, prq(gvsoss? Explain.

Draw in a few equipotentw/cia) 9so;xq ial lines in Fig. 16 – 31b.

What can you say about the electric fd 0 j, bh81zqbxjwv3)v, :h dp.b.ujhzield in a region of space that has the same potential through81bzbxv .)dujzdbj j0,:hhwvh.q ,p 3out?

A satellite orbits the Earth along a gravitational equipotential lin; bvb( jk:pk2zxhhk )5pxi8 -te. What shape musti:h-bvxzjx5k )pph;b 2(8ktk the orbit be?

When dealing with practical devices, we often take the ground (the Earth) to 9u8pfj l1oad9be 0 V. If, inste99 u8pdfja1 olad, we said the ground was how would this affect (a) the potential V, and (b) the electric field E, at other points?

When a battery is connected to a capacitor, why do the two plate/)c w,kqam 3l/9m0d y;h dyxqns acquire charges of the same magnitude? Will this be true if, dq/ykn qm) xlc 3/whym90d;a the two conductors are different sizes or shapes?

We have seen that the capacitance C depends on the size, shape, and positioacs4h) : ux+y0sbit0v n of the two conductors, as well as on the dielectric constant K. What th0c:)0avsh 4sx +tibyuen did we mean when we said that C is a constant in Eq. 17 – 7?

  How much work does the electric fielt 8fm 8f4 ,zxi*lyule3d 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 v f8;wfk6qn i.d4;dk tvf/.w qa proton from a point with a potent8kwqf 4 ;tk vd6 w/q.df.i;fvnial 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 joulerb7 k13h3wptm 3d7myk q1a7 mcb0xe.es and eV) if it accelerates through a potentiyqc0. kbr317dmb 7xwhea31m mp e3kt7al difference of 23,000 V in a TV picture tube?
   $ \times10^{-15 }\,J$
   eV

  An electron acquires a,emy;myc 6t4$7.45 \times10^{ -16}\,J$ 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 paral-b*aw2;q2tl7 v* mga-u dktvi 9*ivd2w6 jm emlel plates 5.8 mm apart if the potential div -v*kai; dwm 6et m2-2jlgmv *b *wqua97t2difference between them is 220 V?    $ \times10^{ 4}\,V/m$

  An electric field of .f9pfkgl :r,nya,atb8ew4 p.x8d6z i$640V/m$ 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 53xkfpm0 ) .y)qksx fkis $1500V/m$ How far apart are the plates?    m

  The electric field between two parallel plates connected to a 45-V batterko b.-fz1eng0 y is $1500V/m$ How far apart are the plates?    m

  What potential difference is needed l3fsqks2 v52qtr (.dkto give a helium nucleus $(Q=2e)$ 65.0 keV of kinetic energy?    $ \times10^{4 }\,V$

  Two parallel plates, connected to a 200-V power supply, are separated by ankt o;-sdkjd) n )z0u/v air gap. How small can the gap be if the air is nt dk uzno-0jd);/)kvsot to become conducting by exceeding its breakdown value of $E\,=3 \times10^{ 6}\,V/m$?   $ \times10^{-5 }\,m$

  The work done by an externa,ez dg.no7e q1)n8nl jaei .+kl force to move a $-8.50\mu C$ charge from point a to point b is $15.0 \times10^{ -4}\;J$. If the charge was started from rest and had $ 4.82\times10^{ -4}\;J$ of kinetic energy when it reached point b, what must be the potential difference between a and b?    V

  What is the speed of an elrp +mi0.lvo2qx 04betectron 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 whn bp*gl297vj 5jdeuj 6ose kinetic energy is 3.2 keV?    $ \times10^{5}\,m/s$

  An alpha particle (which is a hec isk9puz 4wj )duisbt 111,1glium 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 potential 15. doozl jo71.k30 cm from a $4.00\mu C$ point charge?    $ \times10^{ 5}\,V$

  A point charge Q crec4ik;dxf mx/9zciyc.1 .r yl1ates 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 2ilr8qb(:/zykjp ku7sm:k n( of a football. This conductor carries a net negative ch(nsrlu q 8:/k7 kjmikzp(y2 :barge, $-Q$. Draw in a dozen electric field lines and two equipotential lines.

  (a) What is the electric potential a distance of l yf myr j9lh)vn1)*g0*l/ioj$ 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 ar dzk/k5yxea2;4fmtq - e arranged at the corners of a square of side L as shown in Fig. 17–25. What is the potential at; ae5-m 42zdy/f kqxkt the fourth corner (point A), taking $V\,=\,0$ at a great distance?

  An electron starts from rest 32.5 cm from a fixed lza55a 95s*fx+ dw3 h lynffp5point 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 bringlkp 15thgf -b,uvj9t * three electrons from a great distance apart to j9l tg,t 5 -fkp1hubv*$1.0 \times10^{-10 }\,m$ from one another (at the corners of an equilateral triangle)?    $ \times10^{-18 }\,J$

  Consider point a which is 777gqxb;x5fy(zn)7,2f rkb sf 9smo hj 2 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 (rneyd42)glw.d )h h1rz8 bbum/)me b8wadius $1.2 \times10^{-15 }\,m$) 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 sh2p( xpk((cl2iqdamas j: 0. inown in Fig. 17–27. Determine a formula p(xjks.iq:2 d0i(( l2cpa anm 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 electrfd/i xe :5fy;x/qv3l aon orbits a proton (the nucleus) in a :5i fveyfx/;3d/ alxq circular 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 x )j1cle/n9eie1/nrh vw.)(i6x a a byare $ 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.bz 5 :dxwaf49o1:pj ejlh-sco 9ii:u 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, consi 9 hd*deu+vr mocn.zp6 15fl3gu2g x:qdered as a vector, points from the negative to the positive charge. The water molecule, Fig. 17–28, has a dipol*u. d1 u29eon 6gdfgzmrhp 35lx:+cvqe 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 cai) p; aot a1ch/z8h77/ bpk.r lu8smnkpacitor 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 capacitorpd( *xdscb2 m3ytsdz5 zci2, 6 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 charges of /x5(mr*oe+2mkj 6wg-q imrhj $ 16.5\times10^{-8 }\,C$. What is the voltage across the capacitor?    V

  The potential difference between two short sections of pa3 um4ar (k:+qrjmanla ,.5kop rallel wire in air is 120 V. They carry equal and opposite charge of magnitude 95 pC. What is the capacitlk 4km ra,.auq5jrm3 (:oap+n ance of the two wires?    $ \times10^{13 }\,F$

  How much charge flows from each terminal of a 12.0-V battery when it is co 9j,by(xoh(e2v-;ik /y bio +r4wmrgopr n-;mnnected t n( ioi y9rpwrk(;-xh e-rb4obvy+j2; ,mmog/o a $7.00-\mu F$ capacitor?    $ \times10^{-5 }\,C$

  A 0.20-F capacitor is desired. What area must the plates have if they arec-4o w4av +tsld1x0rt to be separated by a 2.2-mm axtac10 wtvr4 ls-d4o +ir gap?    $ \times10^{ 7}\,m^2$

  The charge on a capacitor inc hcs-g4yw;hs 9reases 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 ofy o2y-tf7em e+ $8.5 \times10^{ 5}\,V/m$ 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- b zmp4ba;le-e $5.2\mu C$ 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 elect7mclx+hr 33 /q;d hojtric 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 byf 5 r,ug11onj 8nt*)8xsj 3 6pkppcqxu a 125-V battery (Fig. 17–29a) and then is disconnected from the battery. When thio836p sjx5) *ufgn1 8x1kcprnt,qu jps 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 prmpcl01f v(f/arallel plates 5.5 cm on a side that are separated by 1.8 p(v0f/f 1cmlrmm of paraffin?    $ \times10^{-11 }\,F$

  What is the capacitance of a pair of circular plates with a radigtw/i2r .g57ox 5lhi) cnn cm,us of 5.0 cm separated bc,.i c75l )/rthx5ngoi2w gnmy 3.2 mm of mica?    $ \times10^{-10 }\,F$

  A 3500-pF air-gap capacitor isslf-zue w.b+ , connected to a 22-V battery. If a piece of mica is +lsu wfbe,z .-placed between the plates, how much charge will flow from the battery?    $ \times10^{ -7}\,C$

  The electric field between t1f d.g i /dnwl 5*df22+q agmup.g8hcdhe 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. Howrwk0*w 5i km1s much energy is stored?    $ \times10^{-4 }\,J$

  A cardiac defibrillator is used to shock a heart that i5by -.j s:n) pgbg)vzsxj;if:s beating erratically. A capacitor in this device is chargedfg:b)vn) ijx by:z; ss-j pg.5 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 s z 4sl7trzy.:eb1z:jxquare plates, 8.0 cm on a side, separated by a 1.5-mm air gap? The charges ozjz71r:y:l t4es x.zb n the plates are equal and opposite and of magnitude $420\mu C$.    J

  A homemade capacitor is assembled by placing two 9-in. pitvgyg* 5;3hzu e pans 5 cm apart and connecting them to the opposite terminals of a 9-V gtyu5v3;* hz gbattery. 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 cap el*c pdw bzgl psvr *z(us2;79v(zr4/acitor 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 capacitc wfbrn*bj- cy 56)1.on*kvj por change if (a) the potential difference is doubled, and (b) the charge on each plate isrbfb*5y16j cvpnc.- kjo )w n* doubled, as the capacitor 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 horizontakibnq; 3 9lmpx d;qhd gy7,7jp a(x6x6lly by 7.0 kV. They then pass through a uniform electric field E for a distance of 2.8 cm, which deflects them;a7kipynd 6xx 76dh3,xqb l( mj;p9gq 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 sc zoc6w+.i mpim6k7.l775ed ufy+ phjereen is 30 cm wide and is 34 cm frop cw6+dl7z6mio m .hepu7 7y5+fjk.i em the 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 from rest acquires 6.3 keV of KE in movin+n(ld h +i6;mopk ce(rkc+;mgg from point A to point B. k;kng r(i c(hlmo++;c+dmpe6
(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 annor6 s+xw *o,xd 4.2 MJ of energy to the Earth.
(a) Across what potential difference did it travel?    $ \times10^{ 6}\,V$
(b) How much water could this boil and vaporize, starting from room temperature?    kg

  There is an electric field near the Earth’s surface whose magnitude is aboute17:/kw xb 0g zr0vout $150\,V/m$ How much energy is stored per cubic meter in this field?    $ \times10^{-7 }\,J/m^3$

  In a television picture tube, electrons are accelb 6yd, 8qqjk*berated 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 bald6kj8byb*,q qance 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 from 2t1c8(l0 w vwof1$^{\circ}\,C$ to 95$^{\circ}\,C$. What is the potential difference across the plates?    V

  An uncharged capacitor is connected to a 24.0-V battery unti)qlh0xq i+hn/tah5 q d-8c,vbl 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 vol q)c8ha x tlhhd 0vq,bqi-+5n/tage between the plates?    V

  Dry air will break down if the elecauj2wav7sy,21bwibp3m .z*x tric 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 t- ml. ;: p4nitqp3 )ukijqmzton/k:r+he corners of an equilateral triangle (side L) as shown in Fig. 17–30. Determine the potential at the midpoint i:u ij43qtrkp.p/ t:+; knq)-mzmlo n 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 P+fn4;r 8wj iqwyrex glass is placed between the plates, how much charge willw8i f+w rqjn4; then flow from the battery?    $ \times10^{-8 }\,C$

  An electron is accelerated horizontally from rest inbb9ntrk 07iy j-; :wcv 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 y-tk b 7n9c0j:;wib rvV (Fig. 17–31). At what angle $\theta$ will the electron be traveling after it passes between the plates?    $^{\circ}\,$

A capacitor of capacita. f:dc1j:yo nknce $C_1$ 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 tb/fj/7 nxdfm50 0 lucio make a 1-F air-filled parallel-plate capacitor for a dfji0lcbn0fmx/ u/57circuit 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 t)rj 3:ydnd w+phe Earth there is an electric field of about $150\,V/m$ which points downward. Two identical balls with mass $m\,=\,0.540kg$ are dropped from a height of 2.00 m, but one of the balls is positively charged with $q_1$ = $650\mu C$ ,and the second is negatively charged with $q_2$ = $-650\mu C$. Use conservation of energy to determine the difference in the speed of the two balls when they hit the ground. (Neglect air resistance.)    m/s

  The power supply for a pulsaa 5 jt(bqc7g tsmd 6dxyqxp+3ed: /*9ed 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, theprg232kc +lroeb0zt b94oz6 k potential difference between the Earth and the bottom of the thunderclouds can be askb z+2zorcpkgor0 b4t3 2e 6l9 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 enoul mc o;ptjgj. ;2y*u7rgh energy to some electrons in barium metal to eject them from a surface ol;. jp7 *muryctgj ;2at 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 36 cm from an iden991ih iync8 kwns o7:gtical $+33\mu C$ 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 fdfltpy.--uvq yy -79 from two 1.1-cm-diameter coins separated by a 0.15-mm-thick pq fd-9tu -l7y-fyy .vpiece 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 with plate area i3j / lmwu:qpdz //gmagt ,7,ey6g3 wd kao64e$2.0cm^2$ 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 arepux2yjg0 1)wq6/e hnf fixed 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 aj: uh4p/n -wp3;kwfx6q z ihvcn2 tx33s shown 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$