If two points are at the same potential,* hho+iawn oh;qk,m40 does this mean that no work is done in moving a test charge from one point to the other? Does this imply that no force need b,w4+ om* n;k0hqh oahie exerted? Explain.

If a negative charge is initially at rest in an electric field, .;: jpo5vsl m7+v1 u qta1yeeewill 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 ieo1 1:+pa mvlt 7y .eesuvj;q5nstance?

State clearly the difference (a) between electric potential and hzib zv; :a0 li z2wy8+f8jggr1.wr,n electric field, (b) between electric potential and elez;v 0 .g:f1 rw2wazyzj gh +i,n8lir8bctric potential energy.

An electron is accelera2:aqj4 whk: e x( u*mixi.t0nxted by a potential difference of, say, 0.10 V. How much greater would its fx m2 e0qanw txi( *.j:ki4h:uxinal speed be if it is accelerated with four times as much voltage? Explain.

Is there a point along the line joining two equal positive chargebompnk,6+ l:id5 q)dbs where the elecd:qb p6bki+n mlo),d5tric field is zero? Where the electric potential is zero? Explain.

Can a particle ever move from a region of low electric potential ,f2s h5 yctr4 nf(myw7to one of high potential and yet ha s7ncftfw254ym,hry (ve its electric potential energy decrease? Explain.

Compare the kinetic energy gai5h7c fu*f253qa l*: l telmqcbned by a proton $(q=+e)$ to the energy gained by an alpha particle $(q=+2e)$ accelerated by the same voltage $V$.

If $V\,=\,0$ at a point in space, must $\vec{E}\,=0$ there? If $\vec{E}\,=0$ at some point, must $V\,=\,0$ at that point? Explain. Give examples for each.

Can two equipotential lineabc *b*t u6fxira( i2p*f *4wgb)4tods cross? Explain.

Draw in a few equipotential lines in Figo ,obk1:cmv7z. 16 – 31b.

What can you say about theupt;0omlv6 y:jx *i/f*hi8jk electric field in a region of space that has the same op6ku80*hmi*j/fyl jxv:;it potential throughout?

A satellite orbits the Earth along a gravitational equipotential line1jdk/ a +owqr.. What shape must+rjaq o. 1kwd/ the orbit be?

When dealing with practical devicei4tx60/l4vchwtu ct4h kf.k6)go7q t(xgor1s, we often take the ground (the Earth) to be 0 V. If, instead, we said the ground was how would this ok6/64f tx044t. ugxk) h(w o1vh r iglqtc7tcaffect (a) the potential V, and (b) the electric field E, at other points?

When a battery is connected v 4y7k)alej;b to a capacitor, why do the two plates acquire charges of t elyj)b a;47vkhe same magnitude? Will this be true if the two conductors are different sizes or shapes?

We have seen that the capacitance C depends on the size, shape, and py7q6i)/t9o xh ,q an/oe. gtfiosition of the two conductors, as well as on the dielectric constant K. What then did we mean when we said thatq,9a oqx6/i/ i ty7e .g)fohnt C is a constant in Eq. 17 – 7?

  How much work does the electric field do in movingaw5 i)c-u p)6sm dnap; a $-7.7\mu C$ charge from ground to a point whose potential is $+55V$ higher?    $ \times10^{-4 }\,J$

  How much work does the electric field do in moving a proton from a6xg * czx-9xlh point with a potexgl-x hz*c6x9 ntial of $+125V$ to a point where it is $-55V$ Express your answer both in joules and electron volts.
   $ \times10^{-17 }\,J$
   eV

  How much kinetic energy will an electron gain (in joules and ey*: lupx )hfsa; -8tohV) if it accelerates through a potential di8 *y fhsx-:p uloh)t;afference of 23,000 V in a TV picture tube?
   $ \times10^{-15 }\,J$
   eV

  An electron acquires + g(dw*fwg grui:l74e $7.45 \times10^{ -16}\,J$ 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 par*/x :j9nw(os1fvb enjiz3f,v allel plates 5.8 mm apart if the potential difference between them is 220 Vz,n9/oi1sf*fwne:v x jb vj(3 ?    $ \times10^{ 4}\,V/m$

  An electric field ofol:wx t.7yfp 3 $640V/m$ is desired between two parallel plates 11.0 mm apart. How large a voltage should be applied?    V

  The electric field between two paralj6e )02alyqcflel plates connected to a 45-V battery is $1500V/m$ How far apart are the plates?    m

  The electric field between two parallel plates coy)2g1 e*u/zc*zcpmh f nnected to a 45-V battery is $1500V/m$ How far apart are the plates?    m

  What potential difference is 7rory4fbr:i+s2dxq) needed to give a helium nucleus $(Q=2e)$ 65.0 keV of kinetic energy?    $ \times10^{4 }\,V$

  Two parallel plates, connected to fur0nwqj*8uo9j26 t5 3prolk *t u4rna 200-V power supply, are separated by an air gap. How small can the gap be if the o9utuj5op 30*6tn*fw4 rln2 j rqu8krair 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 an xnga253, cde $-8.50\mu C$ 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 with kineticlq.5i,fbpxw. energy
(a) 750-eV,    $ \times10^{7 }\;m/s$
(b) 3.2-keV?    $ \times10^{7 }\;m/s$

  What is the speed of a proton whose kineticu9sobey1(k , b energy is 3.2 keV?    $ \times10^{5}\,m/s$

  An alpha particle (whi9mx2k0gap7jb+c lz /nt l-s -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 potential 15.0 cm fr us -hn*c.4 cf j6kttd70iga(zom a $4.00\mu C$ point charge?    $ \times10^{ 5}\,V$

  A point charge Q creates an electric potential of tm;xb,; r mzm 48-5hgerh1rb*u bi(6a1fqq wd$+125V$ 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 uw7gjuio9 pu w3ht 2)1the shape of a football. This conductor carries a net negative charge,79 hwo2wjpu)tu3gu1i $-Q$. Draw in a dozen electric field lines and two equipotential lines.

  (a) What is the electra p jg*2qum.kz8u :2byic potential a distance 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 arrf*tq 1 3nn 4ue+ifwdc2anged at the corners of a square of side L as shown in Fig. 17–25. What is the pof4qidf +n*t32 nwc1uetential at the fourth corner (point A), taking $V\,=\,0$ at a great distance?

  An electron starts fhje,p9/+ b(cmds m9t vrom rest 32.5 cm from a fixed point charge with $Q\,=\,-0.125\mu C$. How fast will the electron be moving when it is very far away?    $ \times10^{7 }\,m/s$

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

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

  How much work must be done to bring three electrons py ::-kx9mj4gp,ujyh from a great distance apart ty,jmh -4k:u j:9pxp gyo $1.0 \times10^{-10 }\,m$ from one another (at the corners of an equilateral triangle)?    $ \times10^{-18 }\,J$

  Consider point a which is 7az0tamm: 2 (yw2 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 prot;x7enb6h:2y5f i/j h erlxvm7on (radius $1.2 \times10^{-15 }\,m$) so that it has sufficient energy to just penetrate a silicon nucleus? A silicon nucleus has a charge of $+14e$, and its radius is about $ 3.6\times10^{-15 }\,m$. Assume the potential is that for point charges.    $ \times10^{6 }\,V$

Two equal but opposite charges are separated by a distancekxt kg, j 9;few/8stn1 d, as shown in Fig. 17–27. Determine a formula foren/tx; ,s wf1gtk8k9j $V_{BA}\,=\,V_B-V_A$ for points B and A on the line between the charges.

  In the Bohr model of the hydrogen atom, an electron orbits a proton (th 1mf1q- kv.1;w;it qew,apzvre nucleus) in a circular orbaqwefz 11pr ,;v;kq m- it1w.vit 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 are wfes7ok50841 af0o zf 7kgkge $ 0.53\times10^{ -10}\,m$. apart. What is their dipole moment if they are at rest?    $ \times10^{-30 }\,C\cdot\,m$

  Calculate the electri .z+*ewpak yx(0lb c)tc potential due 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, considered az5ydu +x3m8 jiqtc 5w 9 yoy(ugq86up4s a vector, points from the negative to the positive charge. The water molecule, Fig. 17–28, has a dipole moment which can be considered as the vector sum of the two85q5 + 89zpd6 qmcty ug4uwxouji y(y3 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 caiki:n,c 6jc a6pacitor 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 hopu)x 78 a7vawmld $+2500\mu C$ 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 holdseuw8w1 jj h00)u-qp)c5aw w cs plus and minus charges of $ 16.5\times10^{-8 }\,C$. What is the voltage across the capacitor?    V

  The potential difference between two short sections of parallel +x jhgdf(drxy oyxd07-)at-2wire in air is 120 V. They carry equal and opposite charge of magnitude 9+-jto xdya7(20h)-gx xd ryfd5 pC. What is the capacitance of the two wires?    $ \times10^{13 }\,F$

  How much charge flows from each termina:6d0hq4*g7gbq+ m;dlil byecio wt ;0l of a 12.0-V battery when it is connected to a;lo4mwyg*hic0+i0 bq7: ld tq6e;bgd $7.00-\mu F$ capacitor?    $ \times10^{-5 }\,C$

  A 0.20-F capacitor is desired. What aro;zf1bc.m3 r e fx:lw.lkyy27ea must the plates have if they are to be separated by a y frfl:y.k.z7;23l mwbc x eo12.2-mm air gap?    $ \times10^{ 7}\,m^2$

  The charge on a capacu:jj4cz+5q 8nmmdb8f-yjzj* itor 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 ofjx;(u 76 frsrd $8.5 \times10^{ 5}\,V/m$ 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 op 6vjg9j q7n26d;jenhdposite $5.2\mu C$ 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 fi 9w n:v3i sbekij/h-2aeld 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–xl9kkg- s 4v;z29a) and then is disconnected from the battery. When this capacisk-lvkg94;x ztor $(C_1)$ 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 5.5 cm on a side that are 6gtpx y+e fshycg)3 :0separatex6 s+f3 g:tpg0y )hcyed by 1.8 mm of paraffin?    $ \times10^{-11 }\,F$

  What is the capacitance of a pair of circular plates with a radius uw;12f +nnovmttpcx+ -t, e4j of 5.0 cm separated by 3.;c 1n++,vputj2xen tftwm-o 4 2 mm of mica?    $ \times10^{-10 }\,F$

  A 3500-pF air-gap capacit -oil,3mcv mb2 ng yr5a4:twj)or is connected to a 22-V battery. If a piece of mica is placed between the plates, how much chargewiv-bnj ,omr)3 a ly2g5:4mtc will flow from the battery?    $ \times10^{ -7}\,C$

  The electric field between the plates of a pape.udqc-d5+ qq1gn/t ykr-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 2200jrr )99mrh5nv-pF capacitor. How much energy is stored?    $ \times10^{-4 }\,J$

  A cardiac defibrillator is used to shock a heart 9*a 5brpl k) hjdnd:7fthat is beating erratically. A capacito)r:dp jk7nbdl9 af5* hr in 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 by the electricx6yuz61ca .ha field between two square plates, 8.0 cm on a side, separated by a 1.5-mm air gap? The charges on the plates axcu6a a1y.hz6re equal and opposite and of magnitude $420\mu C$.    J

  A homemade capacitor is assembled by placing two 9-in. pie pans 5 cm apartx*0q h gwms-(y ka;if6 and connecting them to the opposite terminals o-0a*wgyfxh6m;( q s kif 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 charges ;d5wjh1bj;gv r -jl kj2r9s5q $+Q$ 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 potentiad,,+:cg u:gtr.ouei ( a o/uhal difference is doubh,g ue:,a/o+. c:touaidug(rled, 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,    $ \times10^{-4 }\,J$
(b) after they are connected.    $ \times10^{-5 }\,J$
(c) What is the change in energy?    $ \times10^{-4 }\,J$

  In a given CRT, electrons are accelerated horizontally by 7.0 x6h2ffd5 s)b ua9bsrov.pg- ox8,ho 9kV. They then pass through a uniform electric field E for a distanceo ghdb ohfs 28.xr)vx9 fbs9o5up,6a- 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 acceleraef esv 9 w7.p5tghmvs5xir(19ted by 6.0 kV in a CRT. The screen is 30 cm wide and is 34 cm from the 2.6-cm-long deflection plates. Over what range must the horizontally deflecting elsm ip5rse75vg 99vt.hewx 1f(ectric field vary to sweep the beam fully across the screen?    $ \times10^{5 }\,V/m$ to    $ \times10^{5 }\,V/m$

  An electron starting from restyf2zqh6f 1z yft1f.x) acquires 6.3 keV of KE in moving from point A to poinz qfzf1f).y1fy2 xht6 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 to the* rc)4rvmha5 j 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 nearp +2xbax;hb/v the Earth’s surface whose magnitude is about $150\,V/m$ How much energy is stored per cubic meter in this field?    $ \times10^{-7 }\,J/m^3$

  In a television picture tube, electrons are accele k6s8gr f7q7oxrated 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 balance the downward gxor q778skf 6force 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 eno( lx9y /dbe-b+9a oc.+rbj+hp(jtgmz ugh 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 24.0s4 (10ryk*vsfkhrci,0.t5 efnj y( ur-V battery until it is fully charged, after which it is disconnected from the10nh r.*r v5 (0syjue i ,r4ytkcsf(kf battery. A slab of paraffin is then inserted between the plates. What will now be the voltage between the plates?    V

  Dry air will break down if ,7z+luig82n(chf3vxqj o ps-the electric 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 equilateral triangle (side L) as x- +xti 8:t)xe)nrqgcshown in Fig. 17–30. Determine the8inctrxxg)tex)+ - q: 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 9.0-V battery. If a piec 8+)4vwqs 92dvs w ,sirxkg9oce of Pyrex glass is plvd98,qsv2ocs+ r9 g )wx kiws4aced between the plates, how much charge will then flow from the battery?    $ \times10^{-8 }\,C$

  An electron is accelera-w 0qig4 kdv6tted horizontally from rest in a television picture tube by a potential difference of gq0 iv6k 4twd-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 capacita5iyz224 7v ;5 vvmno pq),jkwmv*fv 2wc-kfbmnce $C_1$ 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 wantlpzuo1)le k 11 8aqj6nnnu/y(, lr 7hg 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 between the plates? Is this practicallynjl1)n /,h1uko 1la g6ru8nzp( 7q ely achievable?    $ \times10^{-16 }\,m$  ----待选择----YesNo 

  Near the surface of the Earth there is an elect oel+*pxo+n/ iric 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 ni25y4xo+fb) h9vfp mbm trogen 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 Earth an ;ihs:9(,u-4g a* o sdczfjjwbd the bottom of the thunderclouds can be as high as 35,000,000 V. The bottoms of the thunderclouds are typically g*duwz, 9a4i:c(o hsjfbj -;s 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 pro23 fce :oz*o 7mik,pazz 2qukgu6y2r 6vides enough energy to some electrons in barium metal to eject them from a surface at high speed. See Fig. 17– f2i*o,672z:u3 zyzuoek2c akgmp6qr 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 identicpg7 k v0qpc* 1+w8g3j-xq qcplm ihl(/al $+33\mu C$ 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.vdng c3g * ()g3; hqjcv.erm4o.y7g/u2ormqw15-mm-thick piece of paper o*uqg7ve /(r)c w3rvygh.qg odgc342;.mjn m $(K=3.7)$ 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 capacis7o ednz3)6eator with plate area $2.0cm^2$ and air-gap separation 0.50 mm is connected to a 12-V battery, and fully charged. The battery is then disconnected.
(a) What is the charge on the capacitor?    $ \times10^{ -11}\,C$
(b) The plates are now pulled to a separation of 0.75 mm. What is the charge on the capacitor now?    $ \times10^{ -11}\,C$
(c) What is the potential difference across the plates now?    V
(d) How much work was required to pull the plates to their new separation?    $ \times10^{-10 }\,J$

  A $2.5-\mu F$ capacitor is fully charged by a 6.0-V battery. The battery is then disconnected. The capacitor is not ideal and the charge slowly leaks out from the plates. The next day, the capacitor has lost half its stored energy. Calculate the amount of charge lost.    $ \times10^{-6 }\,C$

  Two point charges are fixed 4.0 cm apart from each other. Thel0kd( ,fk dr:yir 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 7 wb ehlu.*0y9djo au5f5hen1n,b i6r. 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$