If two points are at the same potential, does this mean that n-xna7 lx kjgs, ;pmftxot:c),u dc2;9 o work is done in moving a test charge from one point to the other? Does this i o xgp 7-;2js)xcdtnac 9fu ,mx:l,tk;mply that no force need be exerted? Explain.

If a negative charge is initially at rest in an electric field, will it move tow ;( vfajurx2 dcnj6n/(ard a region of higher potential or lower potential? What about a positive charge? How does the potential energy of the charge cha(j/ c;fdvn 2(ajrnux6nge in each instance?

State clearly the difference (a) between electric potential and elecbgm88ljc 5s0 mn2 k5fttric field, (b) between ele5k0 m gc5jsnf8tlm28bctric potential and electric potential energy.

An electron is accelerated by a potential difference of, say, 0.10 V. How much ge zx7m;ja )3c/e(szh)qm 6 dtureater would its fj mz(q )suac3;tm6)exe /7zhdinal speed be if it is accelerated with four times as much voltage? Explain.

Is there a point alonw*vpz:6wz -wqn*e; vo g the line joining two equal positive charges where the electric field is zero?e*zv zqp;ow-:w *6w nv Where the electric potential is zero? Explain.

Can a particle ever move from sk d1mkh79ve .a region of low electric potential to one of high potent1kd svhk7me 9.ial and yet have its electric potential energy decrease? Explain.

Compare the kinetic thuxdh*8n9.l .ktz1w energy 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 $\vec{E}\,=0$ there? If $\vec{E}\,=0$ at some point, must $V\,=\,0$ at that point? Explain. Give examples for each.

Can two equipotential lines cross? Explain.7gk( +i xtix3pyjf)8 a

Draw in a few equipotential lines in Fig. 16 – - t3u w;i 0 v,j.q6ly5ogcmikl31b.

What can you say about the electric fie2ns ) 2auy6acyld in a region of space that has the same potential throug2)u 2c ans6yyahout?

A satellite orbits the Earth along a gravitational equipotentam/h 1ko* esl2ial line. What shapea2e lh*o/1ks m must the orbit be?

When dealing with practical devices, we often take the ground (the Eart/4 +e dag+kfkth) to be 0 V. If, instead, we said the ground was how wo afd+kgk4+e /tuld this affect (a) the potential V, and (b) the electric field E, at other points?

When a battery is connected to a capacitor, why do the two plates acquire charge342 bmpxd;0ei 5 a*fg1fbfokss of the same magnitude? Will this be true if the two conductors are diffk2*ba 03 s5bgp1 iodxmf;e4ff erent sizes or shapes?

We have seen that the capacitance fsfy zp 8csq yaor9tq-5p2*2)C depends on the size, shape, and position of the two conductors, as well as on the dielectric constant K. What ths8tqq)p z fs5c yo22*-ypa9fr en did we mean when we said that C is a constant in Eq. 17 – 7?

  How much work does the electrci9hq qd 9xhwu5u7l o:27(fszic 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 t0zyeu cp1y -nw3i;1l jznns26 he electric field do in moving a proton from a point with a 1n0wysz- ;zj3 6ynl21ie uc nppotential 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 3;h ,4w-tzr bqsl0snrand eV) if it accelerates through a potential dirtl-4 qh 3z;n,r0ssw bfference of 23,000 V in a TV picture tube?
   $ \times10^{-15 }\,J$
   eV

  An electron acquires 7bk7kar), n+ jmeky+e$7.45 \times10^{ -16}\,J$ 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 plates 5.8 mm a(onp mkll:78 ww* g(+db srs2wpart if the potential dkg2wdlm :*b 7+ l(prw(sw n8osifference between them is 220 V?    $ \times10^{ 4}\,V/m$

  An electric field of soyj klwg6:9u,u5e 6t$640V/m$ 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 connect txia az:/l85kq-k.nted 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 batty- v/ ((-nydf3 ruzadnery is $1500V/m$ How far apart are the plates?    m

  What potential difference is needed to give a helium nucleus nwpe+7640)5 udjh lc uy4grwwx 4wb1l $(Q=2e)$ 65.0 keV of kinetic energy?    $ \times10^{4 }\,V$

  Two parallel plates, connected to a 200-V power2i 7xxwd,/9apuk+.t2ka ksbr+ yp ii3 9uxqy / supply, are separated by an air gap. How small can the gap be if the air is not to become conducting by ep/2su.q ,92rukxita3+i b7x dp9 yakxw k+i/yxceeding its breakdown value of $E\,=3 \times10^{ 6}\,V/m$?   $ \times10^{-5 }\,m$

  The work done by an external force to move afk 3c1h)yhtj*odo6sy8f a3:c $-8.50\mu C$ 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 kineti1 3htuaptd9 /bc 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 kihrqoy0zug0 9 )nm k ;vwld974,w 8qyheV?    $ \times10^{5}\,m/s$

  An alpha particle (which is a helium nucleus, ;n.h9m7t pb bd$Q=+2e$, $m\,=\,6.64\times10^{-27 }\,kg$) 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 cj;*9-ff lc m- 6etyxb0n+lfgfrom a $4.00\mu C$ point charge?    $ \times10^{ 5}\,V$

  A point charge Q creates an electric potential om +)fo6 agd*x;astg ,*qbtbh 3f $+125V$ 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 carries aw-)7r0 uzb ptb net negative chaz)wt rbp-b0u 7rge, $-Q$. Draw in a dozen electric field lines and two equipotential lines.

  (a) What is the electric potential a distacyssct6slj+2,nc / -ance 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 squamg s(8l(9 eet9yz c,k.ckmnd 2re of side L as shown in Fig. 17–25. What is the s2me8gz .ke9cln (,(tcy9kmdpotential at the fourth corner (point A), taking $V\,=\,0$ at a great distance?

  An electron starts from rest 32.5 cm from a fixed poibr klib)*2;drc,zl6 bd2 xs /znt 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 a great distance a)f61n*nhwt ts3qct(k+wx r4g0j2 yrepart 41)r3(gw*t 0 htq+nwjyftck26 s xrento $1.0 \times10^{-10 }\,m$ from one another (at the corners of an equilateral triangle)?    $ \times10^{-18 }\,J$

  Consider point a which is 72 cm north , rprsc8i2:6vez+ jr xof 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 (radius tk)nj0 li :8vz$1.2 \times10^{-15 }\,m$) 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 dgg yg;k /l xj.ve9h90v2*v9 dzrivt3w, as shown in Fig. 17–2dxvwg vz;2g r0/v*y h3.i 99jglt9kve7. 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 hydrogct+ tbg qekma4:xnq5fn 64t 4/en atom, an electron orbits a proton (the nucleus) in a c +5k q6tmbf44/ant4t enxg: cqircular orbit of radius $ 0.53\times10^{-10 }\,m$.
(a) What is the electric potential at the electron’s orbit due to the proton?    V(Round to the nearest integer)
(b) What is the kinetic energy of the electron?
   $ \times10^{ -18}\,J$
   eV
(c) What is the total energy of the electron in its orbit?    $ \times10^{-18 }\,J$ $\approx$    eV(Round to the nearest integer)
(d) What is the ionization energy — that is, the energy required to remove the electron from the atom and take it to $r\,=\,\propto$, at rest? Express the results of parts b, c and d in joules and eV.   $ \times10^{-18 }\,J$    eV(Round to the nearest integer)

  An electron and a proton/ c9bl d2kxc5iq*5b yo 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 -h xn5 su24sridipole 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 as a vector, points from the +- anl8 ld xiyp;*on8:fhdw k-ucph6/negative to the positive charge. The water molecule, Fig. 17–28, has a dipole moment which can b d:fud/*hyx w+ckah n--8;o lpipn6l8e 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 capacitor hozd o/o 7y:z 7wh;fmb;p+;/snzvvg 5mmld $+2500\mu C$ 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 holbi7epxq yz8e:;fs.lw ;s:ux8d $+2500\mu C$ and $-2500\mu C$ of charge, respectively, when the potential difference is 850 V. What is the capacitance?    $ \times10^{-6 }\,F$

  A 9500-pF capacitor holds plus and minus chargesak8 dlba3 :do: of $ 16.5\times10^{-8 }\,C$. What is the voltage across the capacitor?    V

  The potential difference between two short sections of parallel wire in air in;hbidt:xr+ 5s 120 V. They carry equal and opposite charge of magnitude 95 pC. What i5hdr;+ xtn :bis the capacitance of the two wires?    $ \times10^{13 }\,F$

  How much charge flows from each terminal of a 12.0-V bqg 5 76 37akdbgowhnl .fr(s)aattery when it is connected to a .rfs5o7k6 g dw)gq3aha l(n7b $7.00-\mu F$ capacitor?    $ \times10^{-5 }\,C$

  A 0.20-F capacitor is desired. Whai;; gtw3o sn+kt area must the plates have if they are to be separated by a 2.2-mm 3;+owngk its; air gap?    $ \times10^{ 7}\,m^2$

  The charge on a capacitor increases bk(h0 o t2eg ;kn(:xe4kwh8et vy $18\mu C$ 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 .dbencrbtz2 vgq y,*w.)/ ,jt$8.5 \times10^{ 5}\,V/m$ 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 opposite1izwky aa9qyc1j 1c:wi, 2.u-uvx g.u $5.2\mu C$ 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 fie bj/*kbf gmwh :+-mm v8s9mvg:ld 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. 17–29a) and then is disco jh5kpn63de u6nnected from the battery.j5 hu6n3ke6dp 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 of two square ppbt;u bm-x* w*arallel plates 5.5 cm on a side that are b*xt ;bp*mw-useparated by 1.8 mm of paraffin?    $ \times10^{-11 }\,F$

  What is the capacitance of a pair of circular plates with a radius of 5.0 cm sep6gwo. kg s5lgnr, 5c7harated6wgk 7lhn.5grscg5 o , by 3.2 mm of mica?    $ \times10^{-10 }\,F$

  A 3500-pF air-gap capacitor ebm 9 axm;gfp) u8h(*qq))evv is connected to a 22-V battery. If a piece of mica is placed between the pq(9pux*fevvb ; ))ghqme8m )alates, how much charge will flow from the battery?    $ \times10^{ -7}\,C$

  The electric field between the plates of a paper-separat raps;7su. i d9zn3t)med $(K=3.75)$ 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 ener4ommx b)f4.ved(zp kp: ia z8:gy is stored?    $ \times10^{-4 }\,J$

  A cardiac defibrillator is used to shock ah.79 -x1/gn2c ohcscq;x eu ip heart that is beating erratically. A capacitor in this device is charged to cx sp 9;7.- q/hun1ciehx2ogc 5.0 kV and stores 1200 J of energy. What is its capacitance?    $ \times10^{-5 }\,F$

  How much energy is stored b+oin ut t5baj:3di0r9y the electric field between two square plates, 8.0 cm on a side, separated by a 1.5-mm air g9:td0i 5+ain3 jo rutbap? The charges on the plates are equal and opposite and of magnitude $420\mu C$.    J

  A homemade capacitor is assembled by placing two 4vqv+ ayhlb: rq/jb*r2f2rs .. set)e9-in. pie pans 5 cm apart and connecting them to the opposite terminals of a 9-V battery. Estimatee qr.qh2sfy.) +avvbe jst 2l/* :br4r
(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 chargy22r m1 -9mj fglyovs-es $+Q$ 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 potentga 755ytaur9rial difference is doubled, and (b) the charge on each plate is doubled, as the capacitor57atrr gy59 au 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 kVb)jmcew 1ywfv:,uvqbs 7 ,r+,. They then pass through a uniform electric field E for a distance of 2.8 cm, which dee,vw c: w,ry ujbv1sb7mf,+)qflects 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 an7 wnr,m5m omzox62y- CRT. The screen is 30 cm wide and is 34 cm frxm6 zom7m,ny5w -2ron om 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:ms;y689ogq o4z pxof KE in moving from point A to poio f98ypoxsqg6;:4 zmont 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 energ3wy - h99gcyi7 6a;uk/mgllyry 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 netkzm3 l:lfj o+p70 ludke,/o3ar 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 accelerated by thousand b nzhx 1h*hk5dzo+).es 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 c)zx5 *.+nozedh1 bhkhm, would be needed 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 q13 g* iqx/btxps0c k+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 fhe nn -l2.m;nzully charged, after which it is disconnected from the battery. A slab of paraffin is then inserted bmnhe .z-n2n;l etween the plates. What will now be the voltage between the plates?    V

  Dry air will break down if the ebl6(b2+ wpatilectric 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 corndq b vw.wh /5qvm:5q lzr9;t9rers of an equilateral triangle (side L) as shown in Fig. 17–30. Determine the potential at the mq.dtl/9wr 5 59w h ;m:vqbqrzvidpoint 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.cqn)3 sp5xv+s If a piece of Pyrex glass is placed between the plates, how much charge will theq3v psxn+5)cs n flow from the battery?    $ \times10^{-8 }\,C$

  An electron is accelerated horizontally from restrv.jq6eo4c l c/b 74ga in a television picture tube by a potential difference of 5500 V. It then passes between two horizontal plates 6.5 cm long and 1.3 cm apart that have a potential differenrcq/7cj.e4og l6bav 4ce 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 capac9 tw wyl3c(bi0itance $C_1$ 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+ xt6lc1 k4ioa to make a 1-F air-filled parok 16xl4i t+caallel-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 practically achievable?    $ \times10^{-16 }\,m$  ----待选择----YesNo 

  Near the surface of th-qqt0v fy+* wce Earth there is an electric field of about $150\,V/m$ which points downward. Two identical balls with mass $m\,=\,0.540kg$ are dropped from a height of 2.00 m, but one of the balls is positively charged with $q_1$ = $650\mu C$ ,and the second is negatively charged with $q_2$ = $-650\mu C$. Use conservation of energy to determine the difference in the speed of the two balls when they hit the ground. (Neglect air resistance.)    m/s

  The power supply for a pulsed nitrogen las a bq,z/hv(.oher 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 bot nnp- e9wx2j)etom of the thunderclouds can be annp)j e2w9-xe s 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, ultravioletwg 7ae++zm5y s (UV) light provides enough 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, another plate above the barium 7+yw ezgs+5m asurface 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 plap f9ykv;a()hkced 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-diam4fih yfsq9*vy0t54qg eter coins separated by a 0.15-mm-thick piecefq 95yvy0* q4g4 ihsft 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 capacitordzmc efw.7 0c /y5yq-x 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 cmi plr(:7xa-u z apart from each other. Their charges are $Q_1$=$Q_2$=$5.0\mu C$, and their masses are $m_1=1.5mg$ and $m_2=2.5mg$
(a) If $Q_1$ is released from rest, what will be its speed after a very long time?    m/s
(b) If both charges are released from rest at the same time, what will be the speed of $Q_1$ after a very long time?    m/s

  Two charges are placed as shown in 0bodwc1n+sfy,5 hot6 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$