If two points are at the same poten + nrr94bfr(p;xebkk2tnjv 40 cw+vr-tial, does this mean that no work is done in moving a test charge from one povt;rn+ 4ck0w9rx fbp 4+nb 2ej(kvr-rint to the other? Does this imply that no force need be exerted? Explain.

If a negative charge is initially at rest in an electric field, wiztaq8ep fix1b b41v(.ll it move toward a region of higher potential or lower potenti 4 f.bbxapz 1v81ie(tqal? 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 electric fjib-0mt zv-s 7ield, (b) between electric potential jt--z0mib7vs and electric potential energy.

An electron is accelerated by a potentialp6b9kh* 8 rghg difference of, say, 0.10 V. How much greater would its final speed be if it is acceler*hh p kggbr698ated with four times as much voltage? Explain.

Is there a point along the line joining two equal positive charges where the el4: ( v1pwaeorqectric fi(rp :e1oaw4vqeld is zero? Where the electric potential is zero? Explain.

Can a particle ever move from a region of low electric pot-a( pa9larza)ential to one of high potential and yet have its electric potential energy decrease? Exzaa(9a)lp r -aplain.

Compare the kinetic energy gained yvhqeazbe16 )xg y; 8auj9/nua/h/b(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 b/o ws.k6s/3svi8l rb? Explain.

Draw in a few equipotential lines in Fig. 16 – 310w2 f jg t 8mq2u.;gsdwkz(or4b.

What can you say about the electric field b;on4w x8*mfuin a region of space that has the same potential throughoubnw4fo8;m *xut?

A satellite orbits the Earth along a gravitational equhkmq; -aetxi n ns*/6 dx267toipotential line. What shape mu7atm;/d6e n x to-xhnsqk i*26st the orbit be?

When dealing with practical devices, we often take the ground (tj8t-eum/p7zxu yv /e 0he Earth) to be 0 V. If, instead, we said the ground was how would this affect (a) the pou0-m/et p8ju v /ey7zxtential V, and (b) the electric field E, at other points?

When a battery is connectey+q1l:9zoat a6b ,bl1 i k/3bxee c6uxd to a capacitor, why do the two plates acquire charges of the same magnitude,6kc lt9/b3 a:6ieo zylqxb1 ba+uxe1? Will this be true if the two conductors are different sizes or shapes?

We have seen that the capaci99x.()ha9dbb f i2w6tifyv ratance C depends on the size, shape, and position of the two conductors, as well as on the dielectric c rb wbv9(iiff2t9had xa9y) 6.onstant K. What then did we mean when we said that C is a constant in Eq. 17 – 7?

  How much work does the electric field do in movgu px 3/ey f;.k 99qnc+wr-riring 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 a point with ar-l9t uldb lc-z-/o/ a ta1s4y,* oeyy potene-ztt-ycr/ llso*a, b u 9l1/ yd-oa4ytial 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.ewv:g-e r0ye.bixj* an electron gain (in joules and eV) if it accelerates through a po0w.xr e e.yb-ij: *vegtential difference of 23,000 V in a TV picture tube?
   $ \times10^{-15 }\,J$
   eV

  An electron acquires /,s jcrflqfin+c6d0.*h + 4hxvqg3 md$7.45 \times10^{ -16}\,J$ 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 aparyas0p d l;*ogkmhe *:q k.1dp6t if the pot1d6 pp*ys :m; edoa .khqk*gl0ential difference between them is 220 V?    $ \times10^{ 4}\,V/m$

  An electric field of dhj / nzfmz, +dj)k0,p$640V/m$ is desired between two parallel plates 11.0 mm apart. How large a voltage should be applied?    V

  The electric field betwydr9n019vw, mh 7cie jeen 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 r4 ;;tngkj ,0/9(af- ti+wajwdtxlhf45-V battery is $1500V/m$ How far apart are the plates?    m

  What potential difference is needed to g8il w-b ;) vbo2.ut u5-huhkpmive a helium nucleus $(Q=2e)$ 65.0 keV of kinetic energy?    $ \times10^{4 }\,V$

  Two parallel plates, co 1iaajqw;5cc 6nnected to a 200-V power supply, are separated by an air gap. How small can the gap be if the air is not to become conducting by exceeding its break1 cq ;cwjaa56idown value of $E\,=3 \times10^{ 6}\,V/m$?   $ \times10^{-5 }\,m$

  The work done by an extjh4su,v5 4 slo,zw n0kernal 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 electron bv5xl.cq *) js efr8-we nye)4with 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 ui1kt;ntr 9dr.b/h d*c fo yx6lzr;39.2 keV?    $ \times10^{5}\,m/s$

  An alpha particle (which is a heliu9bnb,cr jlshx)p.) p (m 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 ;u5*tn.+ yr n60wd0j:p tw wq dl;rchlpotential 15.0 cm from a $4.00\mu C$ point charge?    $ \times10^{ 5}\,V$

  A point charge Q creates an electric sjk4h rq1 qt2w,g3pc 51wmo*apotential 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 conduckuqvz )j-mf-7tor carries a net negative charjvu zm -f-q)7kge, $-Q$. Draw in a dozen electric field lines and two equipotential lines.

  (a) What is the electric potential a*iztu10iz3 gn1 flz2z 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 ar+u pozqzmmbf4ky-/1jn p 9)njp5h5b-ranged at the corners of a square of side L as shown in Fi b z5p)m5+j1 yh f/pj9n-mqk4bo-puzng. 17–25. What is the potential at the fourth corner (point A), taking $V\,=\,0$ at a great distance?

  An electron starts fatkbwja5z v-, -i4lxk(um2p 5rom 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 from a great distanclhn)xcusa7g : b7 (8uoe apart tobus8c a7 olxuh(:n7g ) $1.0 \times10^{-10 }\,m$ from one another (at the corners of an equilateral triangle)?    $ \times10^{-18 }\,J$

  Consider point a which cgjyl2 40ptir4 jm s3*is 72 cm north of a $-3.8\mu C$ point charge, and point b which is 88 cm west of the charge (Fig. 17–26). Determine
(a) $V_{ba}=V_b-V_a$    V
(b) $\vec{E}_b-\vec{E}_a$ (magnitude and direction).
   V/m
   $^{\circ}\,$

  How much voltage must be used to accelerate a prqu9s1+r7 d llaoton (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 distance d, n8 qo/e( 3grvhas shown in Fig. 17–2e3h n/o8(rvqg 7. 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 atom, an electron orbits a , *n0ffibd3 uvl0-hak sh:ti6proton (the nucleus) in a circular o*a 0h st3b06 dfi-fhulk,ni :vrbit 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 amxu7sp pr4 u, g :-kf2z5byzw9x1+wk $ 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 momentby ;e*, ;v(f bshqr9sy 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 z /dcgx7-wq2p- ;p xidrt4e4knegative to the positive charge. The water molecule, Fig. 17–28, has a dipole moment which4e/d xq-ki prtp-dw7 2xz4cg; 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 capacitor hud6zwy*4 cy0k9r(t3fbv v b7z b.4dbiold $+2500\mu C$ 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 hold + nwjeu.5 4g(3shvsqy$+2500\mu C$ 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 chargesp6uj uozuf-(,f7ym6d gxtm 59 of $ 16.5\times10^{-8 }\,C$. What is the voltage across the capacitor?    V

  The potential difference between two short sections of parallel ;w6 ey(4 7 mwukjje-zmwire in air is 120 V. They carry equal and opposite charge of magnitude 95(;mym6 e-4wzju7ke wj pC. What is the capacitance of the two wires?    $ \times10^{13 }\,F$

  How much charge flows from each terminal of a 12.0-V batte; )mfwoz:d.is ry when it is connected omds.f)z wi;:to a $7.00-\mu F$ capacitor?    $ \times10^{-5 }\,C$

  A 0.20-F capacitor is desired. What area must the plates have if w;o(r- *nj:b(dj ta f uoa4p:ethey are to be separated by a 2.2-mm air *w pjr - (fe(o:a;ou: tda4bjngap?    $ \times10^{ 7}\,m^2$

  The charge on a capac66m+ 79 x* pdyavax8 aacemn9bitor 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 ofghyx bqgrw1-05qy6wp(tq5u)y*y d t7 $8.5 \times10^{ 5}\,V/m$ 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 ove+i,pf 2zt*fpposite $5.2\mu C$ 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 fizpaax n847ro7 gwr8p( *rhdr*eld 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 (cr; j s3hq9i b8k*bu:cFig. 17–29a) and then is disconnected from the;b8 ij :3*qcrcs hb9ku 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 of tv7ro 3wtl 7c vk.czm)9wo square parallel plates 5.5 cm on a side that are separatevvw 97lozm7 c)c3r. ktd by 1.8 mm of paraffin?    $ \times10^{-11 }\,F$

  What is the capacitance of a pair of circular plates with a ,i1/hlq 9wwwy radius of 5.0 cm separ1whiqww / y,l9ated by 3.2 mm of mica?    $ \times10^{-10 }\,F$

  A 3500-pF air-gap capacitor is akfd8;dzg6r;c; v )o tb ix52uconnected to a 22-V battery. If a piece of mica is placed between the plates, how much charge will flow from the battery?f;vaug 8o ti5r6 2)ddzxb;c;k    $ \times10^{ -7}\,C$

  The electric field betflh:-x 3 ;at ygxt5rgitfw5* *p ep**xween the plates of a paper-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 pro 5f7ir p(6/ /:4b- pln5w/fpkx8z ixqt qgy2200-pF capacitor. How much energy is stored?    $ \times10^{-4 }\,J$

  A cardiac defibrilla1gic seu y)ha4:u)l:jtor is used to shock a heart that is beating erratically. A capacitor in this device is charged to 5.0 kV and ue)c:i 4 jlua1)sy:gh stores 1200 J of energy. What is its capacitance?    $ \times10^{-5 }\,F$

  How much energy is stored by the electric field between two square pl2ulqzfgr t; - :4zto5 pmcos:-ates, 8.0 cm on a side, sepatg otflz; cm- up:r:oz24 s5q-rated by a 1.5-mm air gap? The charges on the plates are equal and opposite and of magnitude $420\mu C$.    J

  A homemade capacitor is assembled bsq:49 or-egox y placing two 9-in. pie pans 5 cm apart and connecting them to the opposite terminals of a 9-V battery. Esx o:4egq9r -sotimate
(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 52q 1v5 brpyhb$+Q$ and $-Q$ The separation of the plates is then doubled.
(a) By what factor does the energy stored in the electric field change?
(b) How much work must be done in doubling the plate separation from d to 2d? The area of each plate is A.

How does the energy stored in a capacitor change if (a) the potential differen n/r(zgvq(,wq ce is doubled, and (b) the charge on each plaw(nvr ,q(z/qg te 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 kV. Theaxb xze0fs335rzdbipv (72t:1s; g ksy then pass through a uniform electric field E for a distance of 2.8 cm, which deflects them upward so they reach the 3:(53zbd b2 0sf giaxks 7e st1zvx;prscreen 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 inz1j 6)aoe- fcb a CRT. The screen is 30 cm wide and is 34 cm from the 2.6-cm-long deflection plates. Over what6 co f)1azeb-j 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 in movs6t k 0yo1l+vfing from point A to 6t0lv+k1ys fopoint 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 th n; vd -2tiba9b)mllx7e 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 fiel:yyisrb4 y)jn/sd2 3fd near 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 tv+stt fwxv4dvh ,4*6 ohousands 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+, wt vx*s46ofd4h vtv 3.0 cm, 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 capacitg7jj+hi1l /d v1( lv( rn8zuvior has enough stored energy to heat 2.5 kg of water from 21$^{\circ}\,C$ to 95$^{\circ}\,C$. What is the potential difference across the plates?    V

  An uncharged capacitor is connected to a 24.0-V b3)r n ogwfj i5zf u;*,cph3w5rattery until it is fully charged, after which it is discowchf* 3g3 z5w,5)friojup; nr nnected from the 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 the electric fie8im. rgqx-ezgv/:x4s kvs,x)ld 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)iuh5n k.diii* 6h2u8-ye;p z y as shown in Fig. 17–30. Determine the potential at the midpoint of each of the sid8upzeyu h56 2-ikd.; iyn*h iies.

  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 ba* uuyro5 ::jkzttery. If a piece of Pyrex glass is placed between the z:*r u5o:y kujplates, how much charge will then flow from the battery?    $ \times10^{-8 }\,C$

  An electron is accelerated horizontally from rest in a television i3fm4u itf rpa r*03jkrh3 8:opicture tube by a potential difference of 5500 V. It then passes betwejh034 rtf mpu:afk *ro38iir 3en 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 capacitance 2hggxg)f7b q0wv,h ,u+ dbo assa55l5$C_1$ 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-frk./r(sx+ +,fx2xmpkczw-zg illed parallel-plate capacitor for a circuit you are building. To make it a reasonable size, suppose you limit the plamxk/-w zr,x.zsg+2( k +pcrfxte 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 tf imko+xwv6y8w9j m,*ai9y 0xm :1y gat:ao /phere 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 j8kanr,m;3 d5zghp *f nitrogen 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 and the bow r tdk+j)5z;ottom of the thunderclouds can be as high as 35,000,000 V. The bottoms of the thunderclouds are typically 1500 m above tr jd w5+)oktz;he 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 providesnih,q,)w tyfm4 3y,1srwnlt , 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 ene i1nqw f l4myhrsw,t)3 ,,tyn,rgy 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 placg54g +cyaqnj1ed 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-cw7; xvi7b 0drti2/* / jirha+n8mwvp im-diameter coins separated by a 0.15-mm-thick piece oi hwjt+p7/*x8id2; v/imwvr b7 nra0 if 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 with plate area xu3ea:e+qet4 f7f :ta-2m ws h$2.0cm^2$ 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 fro:xqb5i1 u f+s r*v(ghsm 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 place * mfn;m.jx2amd as shown 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$