If two points are at the same potential, does this mean that )5g d.b oqkq3lno work is done in movi.k qld 5)oq3bgng a test 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 +9 q96v/ehh (u5yisekzoum/ i electric 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 in each in6/eqiih/+uosk9vmheu59z ( y stance?

State clearly the difference (a) between electric pote(aea 4qu htc;1ntial and electric field, (b) betwe4e q;ha au1c(ten electric potential and electric potential energy.

An electron is accelerated by a potential diffr-in8x *bvxfrtb; 97jerence of, say, 0.10 V. How much greater would its final speed be if it is accelerated with four times as much vo -9jbnifr8xvt; 7 rx*bltage? Explain.

Is there a point along the line joining two equal positive charges where thv l w4 ip+19/rkks;pzke electric field is zero? Where the electric potential is zero? Explai;+9l kspzkk / i14rwpvn.

Can a particle ever move from a region of low elect(m ;r kuf5c +pxfdy*x g0j7ip+ric potential to one of high potential and yet have its elect+ f*+g7kpym 0rd5 jfx(puic;xric potential energy decrease? Explain.

Compare the kinetic energy gained by a pr d 2 wj*0 ek;n/x/jt 0qbn3va8dtj,baxoton $(q=+e)$ 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 line-+1yvjy80yw uiqam / d 2d5vydn/3fgfl0q f j3s cross? Explain.

Draw in a few equipotential lines in Fig. 16 – 35p3 f/ dpt-:y;eirc tu1b.

What can you say about qc)1 qxyhky-7 the electric field in a region of space that has the same potential throughou)qq7 kyx-y1hc t?

A satellite orbits the lm 5y /.slw) )sbehtw(m1yl1eEarth along a gravitational equipotential line. What shape must the orbit sy)1ml eyb5w /etl w)l(hs 1m.be?

When dealing with practical devices, we oftenq9x .skdo,kp. take the ground (the Earth) to be 0 V. If, instead, we said the ground was how would s q k,p.9okd.xthis 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 plates acquire o,em o2 +tfbh+charges of the same magnitude? Will this be true if the two cond +e,f2htmbo o+uctors are different sizes or shapes?

We have seen that the capacitance C depends +o(rhtw;(pw4twgs8 fc43 m nbon the size, shape, and position of the two conductors, as well+(wbt; 4 c wow3gmst n84fpr(h 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 the ncegg(/ 4r/tvcix r( wv822vselectric 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 prodm,z t*liru5l3) ywlr,4gzx/ton from a point with a potential of3t*lz, , z4dl/)rxugylriw m 5 $+125V$ 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) i1f,/3-c cp6 y-q ouajvujf(gw f it accelerates through a potential difference of 23,000 V in a TV pictujjc,3o(g-qa-y puw v /c61fufre tube?
   $ \times10^{-15 }\,J$
   eV

  An electron acquires cd - oqwq,wx:x;b5*zo$7.45 \times10^{ -16}\,J$ 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 parallel plat948rl 4; weha gwe (aj8pai:woes 5.8 mm apart if the potential differo:h e;84wa8(grpwiw a9l jea 4ence between them is 220 V?    $ \times10^{ 4}\,V/m$

  An electric field ofj xy 7jybz jz:ons9a2p0.48rk $640V/m$ 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 4 djuosju4+)f 29d(av h5-V battery is $1500V/m$ How far apart are the plates?    m

  The electric field between two parallel plates connecteda) gv87yfjkv, to a 45-V battery is $1500V/m$ How far apart are the plates?    m

  What potential difference is needed to give a helium nuc)h bbhpa u7n,:leus $(Q=2e)$ 65.0 keV of kinetic energy?    $ \times10^{4 }\,V$

  Two parallel plates, connected to a 200hf /p;tzqvh0q6e 4a/y -V power supply, are separated by an air gap. How small can the gap be if the air is not to become conducting by exceed4hah 6e; vyzq0q /ft/ping its breakdown value of $E\,=3 \times10^{ 6}\,V/m$?   $ \times10^{-5 }\,m$

  The work done by an ext8nh7uw.,c2gnd yd 9 t+mwsn3b ernal 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 elexx32mg 7b6 m.z.o slkpctron 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 is 3.2 k 6i5a 0uz7tqwfgoc99qph j w6*eV?    $ \times10^{5}\,m/s$

  An alpha particle (which is a helium nue( g dda1f zrh):zzq53i .qm+xcleus, $Q=+2e$, $m\,=\,6.64\times10^{-27 }\,kg$) 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 frp9* eg+5*ilhw dp emz*om a $4.00\mu C$ point charge?    $ \times10^{ 5}\,V$

  A point charge Q cre.x.wxe1kpvin77b;r6ikvg j4) xu vkxm/f, y0ates 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 of a football. This conduva xz x d8s7i+p* cj(cr5 q j-a:,p0/buizkv1bctor carries a net negativ,vjqpr*+ x(acx1-iv/u:zzab75ijcb 8k0dspe charge, $-Q$. Draw in a dozen electric field lines and two equipotential lines.

  (a) What is the electric potential a dial:wj,t; x z8 :f 0y8f2ikvmyxstance of $ 2.5\times10^{-15 }\,m$ away from a proton?    $ \times10^{ 5}\,V$
(b) What is the electric potential energy of a system that consists of two protons $2.5 \times10^{-15 }\,m$ apart — as might occur inside a typical nucleus?    $ \times10^{ -14}\,J$

Three point charges are arranged at the corners of a square7kxjvu lcwi4 (at3 ca -h,58rfe8 o(me of side L as shown in Fig. 17–25. What a3ceexi8cj-o( htwvru4k8a m f57(,l is the potential at the fourth corner (point A), taking $V\,=\,0$ at a great distance?

  An electron starts from rest 32.5 cm from a fixed point c;bi h x/1f:wf jg6qj( pp 7hjj/6nzrl0y-t1afharge with $Q\,=\,-0.125\mu C$. How fast will the electron be moving when it is very far away?    $ \times10^{7 }\,m/s$

  Two identical $+9.5\mu C$ point charges are initially 3.5 cm from each other. If they are released at the same instant from rest, how fast will each be moving when they are very far away from each other? Assume they have identical masses of 1.0 mg.    m/s

  Two point charges, $3.0\mu C$ and $-2.0\mu C$ are placed 5.0 cm apart on the x axis. At what points along the x axis is
(a) the electric field zero    cm leftof $q_2$
(b) the potential zero? Let $V\,=\,0$ at $r\,=\,\propto$.

  How much work must be done to bring three electrons from mm 1i+dk:iyr7(9aag ya great distance apart t1r(gkya dmyam9ii7+: o $1.0 \times10^{-10 }\,m$ from one another (at the corners of an equilateral triangle)?    $ \times10^{-18 }\,J$

  Consider point a which is 72 cm 1u ua5)k( c vti**):4sncc.zzbq) 7 xjwaiarenorth 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 (rado 2*bufl4yi k+ +wj)iym0cq:m ius $1.2 \times10^{-15 }\,m$) 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 .w,kmvn5 - 2w /lekxvud, as shown in Fig. 17–mkkl,vww /2- 5evxu.n27. Determine a formula for $V_{BA}\,=\,V_B-V_A$ for points B and A on the line between the charges.

  In the Bohr model of the hydrogen ato5er8nmqj72d1 dzxp;ck xm xvh3e0k55m, an electron orbits a proton (the nucleus) in a circun xz 27xq5;15x j3v0pkermddc 5m 8hkelar 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 protony,k 4e9jr6qnz rz: szu;iw4r, are $ 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 momu7cjr ktcq;7/y5ov-b0f* kb sent 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 negatii /t (ni/;(l ip6krybtve to the positive charge. The water molecule, Fig. 17–28, has a dipole moment which can be coni6 kr /y(itbl ;/pt(insidered 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 c;/g rr: 7l5wo 61ayqm gfxv3:-jrdtf fapacitor 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 capacivd*k( pst)a xq)o7u4b3- hd qdm,h z0nkcm()rtor 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)h-x v1fu cshigb+c )o8 -nis) minus charges of $ 16.5\times10^{-8 }\,C$. What is the voltage across the capacitor?    V

  The potential difference between two short sections of parallelcjerlp/i/h 7wx r yv)vn8b5/)-,y aim wire in air is 120 V. They carry equal and opposite charge of magnitude 95 pC. Whaa5er8vj/rn )/xmyb7ic, )-wv/i yph lt 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 k;to y:g bqzzut/4krw4q::k 5connected to/:kkw : yt4ozqzu5bqk; :rt4g a $7.00-\mu F$ capacitor?    $ \times10^{-5 }\,C$

  A 0.20-F capacitor is desired. What area must the plates have if c ;segqb zm //30nvzb1xw/)fyt q ;2hqthey are to be separated by a 2.2-mm ai;qbzm);gqsc0 b//f3v nqxezy1/wth2 r gap?    $ \times10^{ 7}\,m^2$

  The charge on a capacitor8cpcr8i( k 2ptj7vk) la uk**h increases 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 ),ydt e;m mdre:n 1zz;$8.5 \times10^{ 5}\,V/m$ is desired between two parallel plates, each of area $35\,cm^2$ and separated by 2.45 mm of air. What charge must be on each plate?    $ \times10^{ -8}\,C$

  If a capacitor has opposite 9e4+pz)keo m 1 zr+eph$5.2\mu C$ 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 pm16bio we0co.bu+u 0c3/zq wvlates 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 bat0zh* f ofhd/:;3blvcdtery (Fig. 17–29a) and then is disconnected from the battery. Whl f hdd:;0bcz f3*ov/hen 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 5n2(fif fz k8b5.5 cm on a side that are separated by 1.8 mm of paraffi8kf ff5z (b2nin?    $ \times10^{-11 }\,F$

  What is the capacitance of a pair of circular plates with a radius of 5.0 cmkw 7vkm5.zl8 4 (kinw)hr vsc3 separated bkw7swl. rh k583i)vmnc 4 kzv(y 3.2 mm of mica?    $ \times10^{-10 }\,F$

  A 3500-pF air-gap ca-6cz klg,l5dcpacitor is connected to a 22-V battery. If a piece of mica is placed between the plates, how much g,c6l dkl-zc5 charge will flow from the battery?    $ \times10^{ -7}\,C$

  The electric field between the plates of a paper-s6 2wp 9gyegypb9 +)vgleparated $(K=3.75)$ 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. How much energy is storli(g:* mdn/sl ed?    $ \times10^{-4 }\,J$

  A cardiac defibrillator is used to shock a heart that is beating erraticallnxvx g)jgj4 m ;f4t 5(8vufnip6(9dfj y. A capacitor in this device is charged to 5.0 kV and stores 12004d9gxfp6 v ( )5;4unjxmvt(jfgj if8n J of energy. What is its capacitance?    $ \times10^{-5 }\,F$

  How much energy is stored dx (( ;gzekmn1by the electric field 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 opposite andn(mz1xg (;kd e of magnitude $420\mu C$.    J

  A homemade capacitor is assembled by f:cbx*hw af+.x no54v placing two 9-in. pie pans 5 cm apart and cobn c:x+ahfowv54f* x. nnecting them to the opposite terminals of a 9-V battery. Estimate
(a) the capacitance,    $ \times10^{-12 }\,F$
(b) the charge on each plate,    $ \times10^{-11 }\,C$
(c) the electric field halfway between the plates,    V/m
(d) the work done by the battery to charge the plates.    $ \times10^{ -10}\,J$
(e) Which of the above values change if a dielectric is inserted?

A parallel-plate capacitor has fixed chargd;,ieqpdzcz +,, 1yajes $+Q$ 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) hbm1f 4odjdn d 6g80s4the potential difference is doubled, and (b) the charge on each plate is doubled, as the capacitor remsddgfn8j4hb m04o1 d6 ains 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 horizonta -3jhkj;x,hmbq8k4a 6trf1ch :ks cd4lly by 7.0 kV. They then pass through a uniform electrqd 1f44tmhshjkkc;k3 c 6h , -jrbx:a8ic field E for a distance of 2.8 cm, which deflects them upward so they reach the screen top 22 cm away, 11 cm above the center. Estimate the value of E.    $ \times10^{5 }\,V/m$

  Electrons are accelerated by 6.0 kV in a CRT. The screen is5nxb y2kg7 p(s 30 cm wide and is 34 cm from the 2.6-cm-long deflection plates. Over what range must the horizontally deflecting electric field vary 2ksxg( p5by7n 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 kel wmo6 6/tf*dq8v,tnq9 u*yq7 2wm mvjV of KE in moving from point A to pq6l*vmqm f2o/yuq*9nw86j7 tmtvdw , oint 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 chazh b 9iw9)hrj)c:wj *brge and 4.2 MJ of energy to the Earth.
(a) Across what potential difference did it travel?    $ \times10^{ 6}\,V$
(b) How much water could this boil and vaporize, starting from room temperature?    kg

  There is an electric field near the Earth’s surface whose magnitude is aboua*l9v8gcixd o nw+4 c1t $150\,V/m$ How much energy is stored per cubic meter in this field?    $ \times10^{-7 }\,J/m^3$

  In a television picture tube, ets/ eh7umjh* (lectrons are accelerated 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 te u/(7 sh*mjhto 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 watdrss8,s c121 f*ownnyofzs7 5 er from 21$^{\circ}\,C$ to 95$^{\circ}\,C$. What is the potential difference across the plates?    V

  An uncharged capacitor is connectedn fgxj0/9p v16lq )dym to a 24.0-V battery 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 lyxp f j0dgv9n/1m q)6the plates?    V

  Dry air will break down if the electric5s : *ayim*cdn ;oc9ed 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 equiwi-i gd*b,w/p8 l)c -sdp+k ihlateral triangle (side L) as shown in Fig. 17–30. Determine sdbwi -c 8lkw)p ih+ip*gd-/,the potential 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.t+vmtc3np- p +x0ff6t0-V battery. If a piece of Pyrex glassp+mc f03f t+ nvxtp-6t is placed between the plates, how much charge will then flow from the battery?    $ \times10^{-8 }\,C$

  An electron is accelerated horizontally from rest in a televi7b wjcpq lbbjbon48ur ,0(igo-/km. / sion picture tube by a potential 84/b j,jk/ow 7ibu(lbom 0rcnb . q-gpdifference 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 capacitance3zef, /,mmflg- .qp7bz g5yo o $C_1$ 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*b tbg3q k4cv:, 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, suppose you limit the plate area to What would the gap have to be*btb: ckv g4q3 between the plates? Is this practically achievable?    $ \times10^{-16 }\,m$  ----待选择----YesNo 

  Near the surface of the Earth the w2;umrnmklz35 0hq fxc) 1iay1;m8o lre 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 pulsed nitroge4 +dvgey- r.tjn laser has a $0.050\mu F$ capacitor with a maximum voltage rating of 30 kV.
(a) Estimate how much energy could be stored in this capacitor.    J
(b) If 12% of this stored electrical energy is converted to light energy in a pulse that is 8.0 microseconds long, what is the power of the laser pulse?    $ \times10^{5 }\,W$

  In lightning storms, the potential difference between the ige-g38a *dnaEarth and the bottom of the thunderc i*8an-aegd g3louds 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 enoughyb ,zh g6kcd z; hi031v:ajomvu84u9k energy to some 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, another8z9zhk:gam64 u1cbo ,;y0 khuvj v3d i 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 *22b vopc6miv v*,hodplaced 36 cm from an identical $+33\mu C$ charge. A $-1.5\mu C$ charge is moved from point a to point b in Fig. 17–34. What is the change in potential energy? $\approx$    J (round to one decimal place)

  A capacitor is made from two 1.1-cm-diameter coins separated byfec qn07xvy i*:s-m-m xeu87g7e/x fa a 0.15-mm-thick pie0xfu7 eyf*-x cmeve7m7ni:qs ax g8-/ ce 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 d ja(kw6 do6iumm e9)0with 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 fromq,j 9 hf,hhy9aseuah+dpb+s d83p +3 g each other. Their charges are $Q_1$=$Q_2$=$5.0\mu C$, and their masses are $m_1=1.5mg$ and $m_2=2.5mg$
(a) If $Q_1$ is released from rest, what will be its speed after a very long time?    m/s
(b) If both charges are released from rest at the same time, what will be the speed of $Q_1$ after a very long time?    m/s

  Two charges are placed as shown in Fig. 7kddj 6r vd16:t3gign 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$