If two points are at the same potential, does this mean that no work is done inu-cgx-id21-onmn g 4q:. dgvo v 0gr9w moving a test charge from one point to the other? Does rvx mg.4d1 oin-cg-0w-:guv 9 do2q ngthis imply that no force need be exerted? Explain.

If a negative charge is initially at3wj1px2ia t7j rest in an electric field, will it move toward a region of higher potential or lower potential? What about a positive charge? How does the potentx1apjiw372t jial energy of the charge change in each instance?

State clearly the difference (a) between electric pa mmhxsvi-f5a,-3z 59tpjfvyxe(. e+ otential and electric field, (b) between electric potential ape5jasxv-.mhmyf x(t za ,95+ e-iv f3nd electric potential energy.

An electron is accelerated by a potential difference of, say, 0.10 Vqypal535 s k .;msa+jl. How much greater would its sm5;plak +ly53.aqsj final speed be if it is accelerated with four times as much voltage? Explain.

Is there a point along the line joining two equal positive charges where the el9 +d q;j8ck yx9 jafi8r8aec*lectr ;jk9d fyx ecj9ca8r 8ilqa+*8ic field is zero? Where the electric potential is zero? Explain.

Can a particle ever move from a region o 2mt+szvg 7)fp,sfbp (f low electric potential to one of high potential and yet have its electric potential energy decrease?m2pv(+)bfpz,f 7st sg Explain.

Compare the kinetic ene(* 8 kc,zjkjvo46nohw-i8b bz rgy 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 $\overrightarrow{E}=0$ there? If $\overrightarrow{E}=0$ at some point, must $V=0$ at that point? Explain. Give examples for each.

Can two equipotential lines cross? Exfo ki*gbk ed04g;j gj*9ht/5eplain.

Draw in a few equipotey;j 9- l(nvt4tpxl4c l/wvs)k ntial lines in Fig. 16 – 31b.

What can you say about the electric field in a region of space that h:ezt8fxe(l ;. zsad 5sas the same potential throughazlx8s5:(;dt. fezs eout?

A satellite orbits the Earz3r5xh( .3, 08esyubvg phqeik 9e)v rth along a gravitational equipotential line. What shapgy,qk zrpv8x uh)9 3h(.eer e 5iv3b0se must the orbit be?

When dealing with practical devices, we often take the ground (the Earth) 9a6zcvq3oj0 yizmh 8 )to be 0 V. If, instead, we said the ground was how would this affect (8o3mv6cz0a hj i9 qyz)a) the potential V, and (b) the electric field E, at other points?

When a battery is conn 44ef:c))o2 q dfkyzolected to a capacitor, why do the two plates acquire charges of the same magnitude? Will this be true if t4 yk)f:zdfo4cq )lo2e he two conductors are different sizes or shapes?

We have seen that the capacitance C de1x pz 3ghj8jq7pends on the size, shape, and position of thjqj3g1 7h8pzxe two conductors, as well as 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 thefamz 8 zq4*qn8 electric field do in moving a $-7.7\mu C$ charge from ground to a point whose potential is $+55V$ higher?    $\times {10}^{-4}J$

  How much work does the electric field do in moving a proton from a pogbi+ dcx m*bm8 8 1(mzxgs9(mcj;l 6hmint with a potentzxc;(+msg8 c8lm(im b ghbj 1d6 x9mm*ial of $+125V$ to a point where it is $-55V$ Express your answer both in joules and electron volts.
   $\times {10}^{-17}J$
   eV

  How much kinetic energy will an electron gain (in joules 01o c 1dvsyn hj/5t ze;8ejhg2and eV) if it accelerates through a potential eo2h; 1/dzs1gvty 0ec h8jjn 5difference of 23,000 V in a TV picture tube?
   $\times {10}^{-15}J$
   eV

  An electron acquires y+ nwwm.*oad s)2 nv/z$7.45\times {10}^{-16}J$ 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 para 6o woapj+q.vx3;ae7d llel plates 5.8 mm apart if the potential difference vd xe;p 6wjq 7o+ao3a.between them is 220 V?    $\times {10}^{4}V/m$

  An electric field of ce1d2sk 5) hnz$640V/m$ is desired between two parallel plates 11.0 mm apart. How large a voltage should be applied?    V

  The electric field between two paralleqdpzgms/ xp w/i)o3*9xnrp1 9l plates connected to a 45-V battery is $1500V/m$ How far apart are the plates?    m

  The electric field between two para ) tf7p2forvi9llel plates connected to a 45-V battery is $1500V/m$ How far apart are the plates?    m

  What potential difference is needed to givo(v ,v wm7wt y+gx1n;qe a helium nucleus $(Q=2e)$ 65.0 keV of kinetic energy?    $\times {10}^{4}V$

  Two parallel plates, connected to a 200-V power supply, are separauuwukq p71*v 1ted by an air gap. How small can the gap be if the air is not to become conducuk1u7u q1v pw*ting by exceeding its breakdown value of $E=3\times {10}^{6}V/m$?   $\times {10}^{-5}m$

  The work done by an external force to move a yms a yp.t+f yhwy7ah 8g. ,.knj97)wg$-8.50\mu C$ charge from point a to point b is $15.0\times {10}^{-4}J$. If the charge was started from rest and had $4.82\times {10}^{-4}J$ 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 i )0 *kjsfnse 4 fqonzw8s2w2)kinetic energy
(a) 750-eV,    $\times {10}^{7}m/s$
(b) 3.2-keV?    $\times {10}^{7}m/s$

  What is the speed of a proton whose kinetic e4fb qu/w:orjsd g;k --0 7hp w3j9diclnergy is 3.2 keV?    $\times {10}^{5}m/s$

  An alpha particle (which is a hh0:x-rs9 v6 mg r1u(hjeyhls, elium nucleus, $Q=+2e$, $m=6.64\times {10}^{-27}kg$) is emitted in a radioactive decay with ${}_{KE}$ = $5.53MeV$ What is its speed?    $\times {10}^{7}m/s$

  What is the electric potentisf i q+ ipkqx14-7yj8h ja;rb-al 15.0 cm from a $4.00\mu C$ point charge?    $\times {10}^{5}V$

  A point charge Q creates an ;u qi ,4k07fqcw7qtqrelectric potential of $+125V$ at a distance of 15 cm. What is Q?    $\times {10}^{-9}C$

  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 cajm;l(shkmj+f kj .7s(rries a net negative chargm s+ (f7slmjhj(. ;kkje, $-Q$. Draw in a dozen electric field lines and two equipotential lines.

  (a) What is the electric potentialn1)xjzdb 4 pjg 97wp(f a distance of $2.5\times {10}^{-15}m$ away from a proton?    $\times {10}^{5}V$
(b) What is the electric potential energy of a system that consists of two protons $2.5\times {10}^{-15}m$ apart — as might occur inside a typical nucleus?    $\times {10}^{-14}J$

Three point charges are arranged at the corners of a square :sgkfvn*92 gq of side L as shown in Fig. 17–25. What is the potential at the fourth corner (point A), taking sk 2 g9f*qgnv:$V=0$ at a great distance?

  An electron starts from rest 32.5 cm from a qgk+jf/zy ;uj35ba *a n**cjf,ua uj;fixed point charge with $Q=-0.125\mu C$. How fast will the electron be moving when it is very far away?    $\times {10}^{7}m/s$

  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 electrozyz90qzzs ahja:(x 3,u24qs bns from a great distance apart zq(hazy9, b034 uaq zxs:s2jzto $1.0\times {10}^{-10}m$ from one another (at the corners of an equilateral triangle)?    $\times {10}^{-18}J$

  Consider point a which im(5,+b0ib ru9gvs 3g(3 l yavyodv -pts 72 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) ${\overrightarrow{E}}_b-{\overrightarrow{E}}_a$ (magnitude and direction).
   V/m
   ${}^{\circ }$

  How much voltage must be used to acce wo/jn04j kph4lerate a proton (radius $1.2\times {10}^{-15}m$) 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 $3.6\times {10}^{-15}m$. Assume the potential is that for point charges.    $\times {10}^{6}V$

Two equal but opposite charges ho:pff)p 4 ia,are separated by a distance d, as shown in Fig. 17–27. Determine a ffpo p),hia: 4formula for $V_{BA}=V_B-V_A$ for points B and A on the line between the charges.

  In the Bohr model of the hydroo:br- .lfi;x(phc gk9gen atom, an electron orbits a proton (the nucleus) in a circular orbi9cblho-r;x (k p.:gfit of radius $0.53\times {10}^{-10}m$.
(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?
   $\times {10}^{-18}J$
   eV
(c) What is the total energy of the electron in its orbit?    $\times {10}^{-18}J$ $\approx$    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.   $\times {10}^{-18}J$    eV(Round to the nearest integer)

  An electron and a protonad+ , ks9y3.ohdqv7qc are $0.53\times {10}^{-10}m$. apart. What is their dipole moment if they are at rest?    $\times {10}^{-30}C\cdot m$

  Calculate the electric potential duah16xix m 2e z032tjl5ub:sdh e to a dipole whose dipole moment is $4.8\times {10}^{-30}C\cdot m$ at a point $1.1\times {10}^{-9}m$ 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 negative to c y -d buj3,p(ow0rup8the positive charge. The water molecule, Fig. 17–28, has a dipole moment which can be considered as the vector sum of th pdjp b3yc-wruu0 o8(,e two dipole moments, ${\overrightarrow{P}}_1$ and ${\overrightarrow{P}}_2$as shown. The distance between each H and the O is about $0.96\times {10}^{-10}m$. 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 $p=6.1\times {10}^{-30}C\cdot m$ Determine the charge q on each H atom.    $\times {10}^{-20}C$

  The two plates of a capacit5u0hx 9-mi*iccp8u5j8+bjz hz,nk njor hold $+2500\mu C$ and $-2500\mu C$ of charge, respectively, when the potential difference is 850 V. What is the capacitance?    $\times {10}^{-6}F$

  The two plates of a capacitor hol0y q q,f/p3d;hjovvq5d $+2500\mu C$ and $-2500\mu C$ of charge, respectively, when the potential difference is 850 V. What is the capacitance?    $\times {10}^{-6}F$

  A 9500-pF capacitor holds plu9rlr9dapfe) 2s and minus charges of $16.5\times {10}^{-8}C$. What is the voltage across the capacitor?    V

  The potential difference between two sho( z/rw1tjtx0vqrr0.wk d +er 5rt sections of parallel wire in air is 120 V. They carry equal and opposite charge of magnitud.d1+/vt t w x5z0kqw0(jrrrere 95 pC. What is the capacitance of the two wires?    $\times {10}^{13}F$

  How much charge flows from each terminal of a 12.0-V batteryq 29c;e w9fbo//dqze97p2hi dt /p qqa when it is connected to a 92zpb7w /e/29 hcqo/ itp;q qfdqde9a$7.00-\mu F$ capacitor?    $\times {10}^{-5}C$

  A 0.20-F capacitor is vl u3w ly2jor)jx regd382( t6desired. What area must the plates have if they are to be separa3j 3uw 2oydr x6gj(2)8 rtvlleted by a 2.2-mm air gap?    $\times {10}^7{m}^2$

  The charge on a capacitor ia5c 8 d7tkmjm(pcx1 x.ncreases by $18\mu C$ when the voltage across it increases from 97 V to 121 V. What is the capacitance of the capacitor?    $\times {10}^{-7}F$

  An electric field of ; b9kyjx-8d w5mll xo)$8.5\times {10}^{5}V/m$ is desired between two parallel plates, each of area $35c{m}^2$ and separated by 2.45 mm of air. What charge must be on each plate?    $\times {10}^{-8}C$

  If a capacitor has oppou)x* i-lec.g8rjvxa 7f7n**; dhlwnj site $5.2\mu C$ charges on the plates, and an electric field of 2.0 $2.0kV/mm$ is desired between the plates, what must each plate’s area be?   $m^2$

  How strong is the electric field between 0x r4kl, s80dbh hdb0qthe plates of a $0.80-\mu F$ air-gap capacitor if they are 2.0 mm apart and each has a charge of $72\mu C$ ?    $\times {10}^{4}V/m$

  A capacitor is charged by a 125-V battery (Fig. 17–29a) and then is disconnch3jn2 v08j)92hp + kb7 rsvhiqek8c wected from the battery. When 0+pjcbih2k r8 e )chv2nwk7v sqj8h39 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.]    $\times {10}^{-5}F$

  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)
$\begin{array}{l}{Q}_1\\ \text{ initial }\end{array}$   $\times {10}^{-3}C$
$\begin{array}{l}{Q}_2\\ \text{ initial }\end{array}$   $\times {10}^{-3}C$

  What is the capacitance of two square parallel plates2u g0dev1( zeo 5.5 cm on a side that are separatedeg(o v u21ed0z by 1.8 mm of paraffin?    $\times {10}^{-11}F$

  What is the capacitance of a pair of circular plates with a rjpnmxv6yi3sg qoo7kl 8 99029+ qoc swadius of 5.0 cm separated by oj3xsq 69ns80 7qm +2 v9o pwlocky9gi3.2 mm of mica?    $\times {10}^{-10}F$

  A 3500-pF air-gap capacitor is connected to a 22-V battery. If a piece of mica iyxu.b7dn0v)h* d:h 6hxy h lmjkv44k0s placed between the plates, how much charge will flow from the batteryx*y404vlu x .6y :kd7j 0hbdvh)nhmhk?    $\times {10}^{-7}C$

  The electric field between the plates of a paperi*/c,r/ q chpdgg nka-eh;/7j-separated $(K=3.75)$ capacitor is $8.24\times {10}^{4}V/m$. 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.
   $\times {10}^{--9}F$
   $m^2$

  650 V is applied to a 2200-pF capacitor. Hoj(k isod udh6:-s. 8mxw much energy is stored?    $\times {10}^{-4}J$

  A cardiac defibrillator is usey* 6bg6tw ;rfe80mgxq)1 gbpsd to shock a heart that is beating erratically. A capacitor in this device is charged to0 gegwq*;bm6 ys) fxrt6bg1p 8 5.0 kV and stores 1200 J of energy. What is its capacitance?    $\times {10}^{-5}F$

  How much energy is stored by the electrilc*6okign-h ;c field between two square plates, 8.0 cm on a side, separated by a 1.5-mm air gap? The charges on the plates n-6 ;c oih*glkare equal and opposite and of magnitude $420\mu C$.    J

  A homemade capacitor is asse /zjn 3/li48gy.0, hfksru hklmbled by placing two 9-in. pie pans 5 cm apart and connecting them to the opposite terminals of a 9-V s3f kl ygnhk/rjih./u0z48l,battery. Estimate
(a) the capacitance,    $\times {10}^{-12}F$
(b) the charge on each plate,    $\times {10}^{-11}C$
(c) the electric field halfway between the plates,    V/m
(d) the work done by the battery to charge the plates.    $\times {10}^{-10}J$
(e) Which of the above values change if a dielectric is inserted?

A parallel-plate capaci3x 4 wh-ddk-ve rw*iwp0 ea7,ytor 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 (a) the potential n:) .f)clobiluwo5:jdifferencei)lo.:wjbnf c5)l: uo is doubled, and (b) the charge on each plate is 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,    $\times {10}^{-4}J$
(b) after they are connected.    $\times {10}^{-5}J$
(c) What is the change in energy?    $\times {10}^{-4}J$

  In a given CRT, electrons are accelerated horizontally by 7.0 kV. Thtt ff0.pt0o.s o0 vksw+ d0.jtey then pass through a uniform electric field E for a distance of 2.8 cm, which deflects them upward so they reach the screen top 22 cm away, 11 cm above the center. Estimate the value of E. 00.toft.w0sv t . psf0odk+tj   $\times {10}^{5}V/m$

  Electrons are accelerated by 6.0 kV in a CRT. The screen is 30 cm wide z(7z(wdnc m 3p2f 1xeuand is 34 cm from the 2.6-cm-long deflection plates. Over what rangz m(xew(p7c 12dn3zfue must the horizontally deflecting electric field vary to sweep the beam fully across the screen?    $\times {10}^{5}V/m$ to    $\times {10}^{5}V/m$

  An electron starting from rest acquires 6.3 keV of KEem, p8;duo7tv1e ff3y5j (wh81dcik v in moving from point A to poinmy38(td7wji5 1,v v hep8 focedu f1k;t 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 to1yb;-vb;ux rsnwg0 -c the Earth.
(a) Across what potential difference did it travel?    $\times {10}^{6}V$
(b) How much water could this boil and vaporize, starting from room temperature?    kg

  There is an electric field near the Earthwfm2r11s9lljl )f7 9* ggsn7dp xyk9 l+p bc-f’s surface whose magnitude is about $150V/m$ How much energy is stored per cubic meter in this field?    $\times {10}^{-7}J/m^3$

  In a television picture tube, electrons are acc8z( tr+fz+:ab 1cy()nw x f-cpn8ydkgelerated 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 czc-fcwxbny:z+8 n+(8 (kyg atfrp 1d )m, would be needed to balance the downward force of gravity so that an electron would remain stationary? Assume that the electric field is uniform.    $\times {10}^{-12}V$

  A huge 4.0-F capacitor has enbd zbiwn 7g6.v x0hqhb6a 0+7rjqc)7qough stored energy to heat 2.5 kg of water from 21${}^{\circ }C$ to 95${}^{\circ }C$. What is the potential difference across the plates?    V

  An uncharged capacitor is connected to a 24.0-V battery until it is fully charge,.q kbd6cnp 1 w;tps(id, after which it is disconnected from the battery. A slab of paraffin is then insert( pn,w.;cptbiq 6 1skded between the plates. What will now be the voltage between the plates?    V

  Dry air will break down if the eujuy9dufh)pdh7 4 5 :tlectric field exceeds $3.0\times {10}^{6}V/m$. What amount of charge can be placed on a parallel-plate capacitor if the area of each plate is $56c{m}^2$?    $\times {10}^{-7}C$

Three charges are at the corners of an equilateral trianglmc1wh7cog lyd6c 3z1;/ uadbk e9u-d1e (side L) as shown in Fig. 17–30. Determine the poy b1dldko1-c m6;ugwu 1zhe7 a9/ cd3ctential 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 capacfi rh+5j s +y qz0 zlnr82wwb0gm7c83 ,rfdhs2itor is connected to a 9.0-V battery. If a piece of Pyrex glass is place8hy5+zh,s0q gb2r fir7jw2 c3dn l08w rszf+m d between the plates, how much charge will then flow from the battery?    $\times {10}^{-8}C$

  An electron is accelerated horizontally fro:e ixj sttg 6x o08.8(h5orwqjm rest in a television picture tube by a potent5 to68 si:qj gwx.oe t8r0x(jhial 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 capacitanc aphv8lqq0oeg .bgg;*rna 5: *e $C_1$ carries a charge $Q_0$. It is then connected directly to a second, uncharged, capacitor of capacitance $C_2$, as shown in Fig. 17–32. What charge will each carry now? What will be the potential difference across each?

  To get an idea how big a farad is, suppose you want to make a kn9 wj.m yu;r 9iol.:rej5+yb1-F air-filled parallel-plate capacitor for a circuit you are building. To make i.mk r r+ b.n9lyw5 ;9uiejyj:ot a reasonable size, suppose you limit the plate area to What would the gap have to be between the plates? Is this practically achievable?    $\times {10}^{-16}m$  ----待选择----YesNo 

  Near the surface of the Earth there is an electric field of agx2 v 3 sz*6a8+n0u1 nwrqs8/ukk +kajvwt5hbbout $150V/m$ 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 nitroubkbq + x2a3.tej:zd0dnvx4i d8sh7 +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?    $\times {10}^{5}W$

  In lightning storms, the potential diffez hv1nvjbg :- 26cghi*rence between the Earth and the bottom of the thunderclouds can be as high as 35,000,000 V. The bottoms of the thunderclouds are typically 1500 m above the Earth, ag b26 :-vich1hzgj *vnnd can have an area of $110k{m}^2$ Modeling the Earth–cloud system as a huge capacitor, calculate
(a) the capacitance of the Earth–cloud system,    $\times {10}^{-7}F$
(b) the charge stored in the “capacitor,”    C(Round to the nearest integer)
(c) the energy stored in the “capacitor.”    $\times {10}^{8}J$

  In a photocell, ultraviolet (UV) light provides enough energy .y0ysuf)gwof6 *p y+i to some electrons in barium metal to eject them from a surface at highyfiwpg 0 f.)+uyy*6os 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?    $\times {10}^{6}m/s$

  A point charge is placed 36 cm from an *d 0gsv,+ypycidentical $+33\mu C$ 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.g+z tr2-cjz -2egdve h 8*h*bi15-mm-thick picebget-+hhdzg *vj*2 r8z2-iece of paper $(K=3.7)$ A 12-V battery is connected to the capacitor. How much charge is on each coin?    $\times {10}^{-10}C$

  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    $\times {10}^{5}V$
(b) the electric field?    $\times {10}^{6}V/m$  ----待选择----leftright 

  A parallel-plate capacitor with plate aream r53x 3irc el g2o.6n9b3gbca $2.0c{m}^2$ 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?    $\times {10}^{-11}C$
(b) The plates are now pulled to a separation of 0.75 mm. What is the charge on the capacitor now?    $\times {10}^{-11}C$
(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?    $\times {10}^{-10}J$

  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.    $\times {10}^{-6}C$

  Two point charges are fixed 4.0 cm apart from each a.dboz-e vg* c;n2t8jg4dh9q 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