If two points are at the same potential1 m9a4cpn5dsv3ps+:dbm8e w h, does this mean that no work is done in moving a test charge from one point to the other? m9p dans+cw 45m:sepv8d1hb3 Does this imply that no force need be exerted? Explain.

If a negative charge is initially at rest in an electric field, will it monotu3z3q v23s 52h epmve toward a regem3uvth2qsz 3o2p3n5 ion of higher potential or lower potential? What about a positive charge? How does the potential energy of the charge change in each instance?

State clearly the difference (a) between electric potential and electric6zxn --zj)y5 vcz y kw*qbt)5f field, (b) between electric potential anz-n*5yc65wqx)zjf) t zby -vkd electric potential energy.

An electron is accelerated by a aq+46xl9psf (l*mr( nstt e f6potential difference of, say, 0.10 V. How much greater would its final speed be if it is accelerated withm6(fr9 tasxeq s6lpln+ *f4(t four times as much voltage? Explain.

Is there a point along the line joining two equal positive charges wheres3en1f0 ygpp)f 1ilxm n8l.mevp0 1v7 the electric field is zero? Where the electric potential is zero? Exfes 8y.x fp 0n mmvpgv)1l i3071pl1neplain.

Can a particle ever move from a region of low electrle6 p9 q8i7cgric potential to one of high potential and yet have its electric popl79i 8 grq6cetential energy decrease? Explain.

Compare the kinetic energy gained b7 n3e6u(ldmzk vne/m0 -exp g5y 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 lin vlu+nf t:u6lb3es; ,les cross? Explain.

Draw in a few equipotential lines i*0 v 4tsx5ppo;ygot6rn Fig. 16 – 31b.

What can you say about the electric field in a region of spaced7 6zq oul4x(wnyiv/ 0 that has the same/0zyn7w uxdv li6q o4( potential throughout?

A satellite orbits the Earth along a gravitational equipotentiahf 3.kdaqt *.qkq8 o ynrm/;;xddw66al line. What shape must theaqdn*odyt.8xmq/wr3;.dh 6a k k f6q; orbit be?

When dealing with practical devices, we often take the ground (thy6v5cte/,i r se Earth) to be 0 V. If, instead, we said the ground was how would this affect (a) the potential V, and (b) ther ey6i c,/v5ts electric field E, at other points?

When a battery is connected to a capacitor, why do the two plates acquire cif2 rgbb5av(/ harges of the same magnitude? Will this be true if the two conductors are different sib/5a2 g b(ifvrzes or shapes?

We have seen that the capacitance C depends on the size, shape, uzyr7w o :**pk+ctt.n and position of the two conductors, as well as on the dielectric constant K. What then did we m:oc r tyt*k p.uwnz+7*ean when we said that C is a constant in Eq. 17 – 7?

  How much work does the electric field do inh). ,mv7gyvlt 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 dow)sf/ qo;z02t vqok,h in moving a proton from a point with a potential f;wt2hvqq so o/k, 0)zof $+125V$ 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) if it ac.t)pq0l4 / rfwtn0 wlycelerates through a potential difference of 23,000 V in a TV picture tube? /04ntt wplq )rywfl0.
   $ \times10^{-15 }\,J$
   eV

  An electron acquires u01lu hv5jqs/ $7.45 \times10^{ -16}\,J$ 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 parag ee0c: +p;fjkllel plates 5.8 mm apart if the potential difference between themkcf:e g+0 j;ep is 220 V?    $ \times10^{ 4}\,V/m$

  An electric field of(rmgpn 2im 28h $640V/m$ is desired between two parallel plates 11.0 mm apart. How large a voltage should be applied?    V

  The electric field beuzq q;t9 nb,.n4vq0mgn an,:etween two parallel plates connected to a 45-V battery is $1500V/m$ How far apart are the plates?    m

  The electric field between two parallel plates connected to a 45-V batte(koc o-9 f2fpzq3( vijry is $1500V/m$ How far apart are the plates?    m

  What potential difference is needed 68jkk k254emfkbd mi:to give a helium nucleus $(Q=2e)$ 65.0 keV of kinetic energy?    $ \times10^{4 }\,V$

  Two parallel plates, connected *ahud2 mli-uuu4z :5:fzjmzt6 1*c es to a 200-V power supply, are separated by an air gap. How small can th-uuuadl6h :i*c*m1 5zu:ts m jze2f4ze gap be if the air is not to become conducting by exceeding its breakdown value of $E\,=3 \times10^{ 6}\,V/m$?   $ \times10^{-5 }\,m$

  The work done by an external force to move aeos;njv,ors84 re, z 0 $-8.50\mu C$ charge from point a to point b is $15.0 \times10^{ -4}\;J$. If the charge was started from rest and had $ 4.82\times10^{ -4}\;J$ of kinetic energy when it reached point b, what must be the potential difference between a and b?    V

  What is the speed of an electron wit g/reb3vegv)w 7e97ieh kinetic energy
(a) 750-eV,    $ \times10^{7 }\;m/s$
(b) 3.2-keV?    $ \times10^{7 }\;m/s$

  What is the speed of a protix b94ot(lk oihyeob:6s h(1+ k(mm u(on whose kinetic energy is 3.2 keV?    $ \times10^{5}\,m/s$

  An alpha particle (whiu5)xjy*()c+laq:pw m8tjds ich is 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 potentialn mx+e+nlekbc+(x7d . 15.0 cm from a $4.00\mu C$ point charge?    $ \times10^{ 5}\,V$

  A point charge Q creates an electremwb -1kgbpo : cf:e0w2ajj+,ic potential of $+125V$ at a distance of 15 cm. What is Q?    $ \times10^{-9 }\,C$

  A $+35\mu C$ point charge is placed 32 cm from an identical $+35\mu C$ charge. How much work would be required to move a $+0.50\mu C$ test charge from a point midway between them to a point 12 cm closer to either of the charges?    J

Draw a conductor in the shape of a football. This conductor cazb (*- ;lnv/ jwctuezhylh88)rries a net negative 8)uhlcjbz; *-(wh /vnylz8te charge, $-Q$. Draw in a dozen electric field lines and two equipotential lines.

  (a) What is the electric potential a dist/)ggp-zh3pc cance 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 arrang.3b*ryh3k uo osb;mwul2.xtp*v p 9) zed at the corners of a square of side L as shown in Fig. 17–25. What is the potential at .;.9ro2ubp*m u wzvpsyo )t* 3lhb3xkthe fourth corner (point A), taking $V\,=\,0$ at a great distance?

  An electron starts from rest 32.5 cm from a fixed pointr7/z2f*npgz bss , apf 5q)mn: 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 electrons from 5 jpgmt6n .8uezt8kt dpo84n :a great distance apart o :p8gzpk u 8ndtj.e6ntt8m45to $1.0 \times10^{-10 }\,m$ from one another (at the corners of an equilateral triangle)?    $ \times10^{-18 }\,J$

  Consider point a which is 72 cm:x8eih3r9 b;3hdvr mm 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 pra.ac4j:83*c4xn / ahyexm dlg oton (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 charbn ;dwgv)jo(,/ :t+t by: zgy i9uez3bges are separated by a distance d, as shown in Fig. 17–27. Determine a form:gw9y+ be(t, 3i/n d j )vuty;:bzogbzula 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 electron orbits a proton (the nug,aq zlm -ifvzwg t/ w+99uz*5cleus) in a cir/wgzz,9+ v-a gwi5*ztlq m9fucular 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 proti u5kza(i6 +bub 2sgu2 ab/hc;on 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 v4/fglo- jx 6ua 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, co*k6ybvc1rf z (a*iga no/ag(0nsidered as a vector, points from the negative to the positive charge. The water molecule, vai*rag 0yb1(z6f( /nkg aco*Fig. 17–28, has a dipole moment which can be considered as the vector sum of the two dipole moments, $\vec{P}_1$ and $\vec{P}_2$as shown. The distance between each H and the O is about $ 0.96\times10^{ -10}\,m$. The lines joining the center of the O atom with each H atom make an angle of $104^{\circ}\,$, as shown, and the net dipole moment has been measured to be $p\,=\,6.1 \times10^{-30 }\,C\cdot m$ Determine the charge q on each H atom.    $ \times10^{ -20}\,C$

  The two plates of a capac.j)b qeoo 3 3;9+zqeipgnqciig99o f/itor 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 h .nl8. *szuraga 4yz+cold $+2500\mu C$ 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 plu7fj7qj/ w 0p :fx-njkxpkr1(c s and minus charges of $ 16.5\times10^{-8 }\,C$. What is the voltage across the capacitor?    V

  The potential difference between two shor5rqev yneso3 *w1h xp-y 8ic,2t sections of parallel wire in air is 120 V. They carry equal and opposite charge of magnitude 95 pC. Whq3ey 2yips o 1hr ex*,n5c8v-wat 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.cf8wt5 z;b qh connected .zwbf8h;q ct5to a $7.00-\mu F$ capacitor?    $ \times10^{-5 }\,C$

  A 0.20-F capacitor is desired. What :tgly:gwd 2/j 7lrtj/ area must the plates have if they are to be separated by a 2.2-mmtj7wg 2ry/g:tj ll:/d air gap?    $ \times10^{ 7}\,m^2$

  The charge on a capacitor increaseqz9q 3+0 ; dsd )hoipynxl38cfs 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 of0g, p8( tpcdi9 m20con w(-(mtxdporr $8.5 \times10^{ 5}\,V/m$ 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 opplzv sno9l; py d*/vbvk82) i:tflwh y0u-rl9; osite $5.2\mu C$ 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 elec(j 5qipr::v l+n8gjl8 us/fz ftric 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. 17–2gsa-7fn 7fbm r50c/mw9a) and then is disconnected from a/5mgw n770srffc bm-the battery. When this capacitor $(C_1)$ is then connected (Fig. 17–29b) to a second (initially uncharged) capacitor, $C_2$, the final voltage on each capacitor is 15 V. What is the value of $C_2$? [Hint: charge is conserved.]    $ \times10^{ -5}\,F$

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

  What is the capacitance o2 87eps;owxsmh8r:bsv,as u9 f two square parallel plates 5.5 cm on a side that are separated by sp woxbv2a:es8,7us hr s89;m1.8 mm of paraffin?    $ \times10^{-11 }\,F$

  What is the capacitance of a pair of circular plates with a radius of 53n)nkg tw(s d/.0 cm separated by 3.2 mm of mic)3g snnt/(wdka?    $ \times10^{-10 }\,F$

  A 3500-pF air-gap capacitor is connected to a 22tex(5- fx kn/q-V battery. If a piece of mica is placedn( x f-5tkxeq/ between the plates, how much charge will flow from the battery?    $ \times10^{ -7}\,C$

  The electric field between the plates of a paper-separapz24g n dl+u7bted $(K=3.75)$ 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. Howcjgui(: 22g f/; w rtvne t:g1pp*lfn9 much energy is stored?    $ \times10^{-4 }\,J$

  A cardiac defibrillator is used to shock a heart that is beating erratically. ju:qx(g.o i p 9i5qy/mpim0:yA capacitor i i5(. qi::xugymj i/ppym9 q0on this device is charged to 5.0 kV and stores 1200 J of energy. What is its capacitance?    $ \times10^{-5 }\,F$

  How much energy is stored bi6 rqs s o39:rlchd*exv:1o7 gy 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 iv39r rl7g6o ocd:1 :e*h xsqsand of magnitude $420\mu C$.    J

  A homemade capacitor is assembled by placing two 9-in. pie pans 5 cm pr7pgx3w t);l-n75h m nlh/pbapart and connecting them to the oppositg/7hp 73 ln-ppm)h;wl5 bx rnte 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 fixro1:b, zqcew4lm:qj9 84er teed 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 msy3pn7 ;4 lu:)5iglx nyl k7jif (a) the potential difference is doubled, and (bu:;ymiln37x snkgl7) 5yj p4l ) 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,    $ \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 accelerav8q,* gsg 1cwq5k p;ytted horizontally by 7.0 kV. They 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 cen,kqtv5p; 81qgw* cgsyter. Estimate the value of E.    $ \times10^{5 }\,V/m$

  Electrons are accelerated by 6.0 kV ii78p0-/oy co.+fvz; j euvhuvn a CRT. The screen is 30 cm wide and is 34jv;uvf. u0+h io/-z py ev8oc7 cm from 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 hm8t9jjkqr (5uss ;. kin moving from point A to sr(mj5 kus9ht.j kq8 ;point B.
(a) How much KE would a proton acquire, starting from rest at B and moving to point A?    keV
(b) Determine the ratio of their speeds at the end of their respective trajectories.   

  A lightning flash transfers 4.0 C of charge and 4.2 MJ of energy to zuk-)tdl0 o6e 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 magnitudemw9meuslaq5z;s(b ,y;.s2b kb4g r-v 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 ,)al ),-pf bn70r+qvqvkjbbsare 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 need)aqfn b k7r-, svb ,+vbqp)0ljed 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 oqrhw;hvrlx2a9;y4 0e f 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 itn52 q+9psbxp8v 4t xvh is fully charged, after which it is disconnected from the battery. A slab of paraffin is then inserten+htx2b5v48x 9psq vpd between the plates. What will now be the voltage between the plates?    V

  Dry air will break down if the elecwilad.zj -4g6g nma h(:d 3 i,mcb.se: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 the corners of an f d)zt v3q 5j6(vn9xvbequilateral triangle (side L) as shown int 5dvjqfb v63vz()9 nx Fig. 17–30. Determine 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 e4( 4ivdc )06ey ehfr wkf jvv1*3xfvzj/6 4etis connected to a 9.0-V battery. If a piece of Pyrex glass is placed between the plates, how much charge will then flow from ) 6e06yf/j*jex dtv ffzvr3 (v44iek c1ehv4wthe battery?    $ \times10^{-8 }\,C$

  An electron is accelerated horizontally from rdv;.kqu)zpv0:mx:iz a23c w1e(y6 i -pjworlest in a television picture tube by a potential difference of 5500 V. It then passesvq)w3i.z2mo rcw :j 61:zpyxdle vk; u(-0ap i 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 capacitaa4dykv 6j *)ab6z (bx:p*cppx6fr;efnce $C_1$ 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 1-F air-fi7k7zvt64hbvbn up2shk u xnj4b)8.ihn + p0*ylled parallel-plate capacitor for a circuit you are building. To make it a reasonable size, suppose you limit the +syhbku78h72 vu )b ji6z*vnx0 p4bt4pkh.nn plate area to What would the gap have to be between the plates? Is this practically achievable?    $ \times10^{-16 }\,m$  ----待选择----YesNo 

  Near the surface of the Earth there is an ))u5y3 h g 0mu8mmxjp .qa6oznbp7lk,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 nitrogen ll67lb3in 5n mvaser 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 Earth and the bottom by/x+mxuwa ;a 8u/gx+of the thunderclouds can be as high as 35,000,000 V. The bottoms of the thunderclouds aremu;x/axb 8ux++ y a/wg typically 1500 m above the Earth, and can have an area of $110km^2$ Modeling the Earth–cloud system as a huge capacitor, calculate
(a) the capacitance of the Earth–cloud system,    $ \times10^{-7 }\,F$
(b) the charge stored in the “capacitor,”    C(Round to the nearest integer)
(c) the energy stored in the “capacitor.”    $ \times10^{8 }\,J$

  In a photocell, ultraviolet (UV) light provides enough energy to some electrons nlfa y2ki.viosm- w9a)3w 2v :in barium metal to eject them from a surface at high speed. See Fig. 17–33. To measure the maximum energy of the electron9ska3f)n y m2 :vvow-i2wia.l s, 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 identicac1nu nrsr e.d;y8uwuuh0gi9ju n+1:.l $+33\mu C$ 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.ver) 3bft */kr15-mm-thick piece of paper 3 kv/ftrb*er) $(K=3.7)$ 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 a(xj5 79 nenyxlrea $2.0cm^2$ 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 :ge ;ssgxxv/; 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 showni2n 2j db1;kjkqhqf5: 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$