If two points are at the same potential, d*3 w8iglrnxnj e/+ux (oes this mean that no work is done in moving a test charge from one point to the other? 3xnu ( r/gj+*le8n xwiDoes this imply that no force need be exerted? Explain.

If a negative charge is initially at rest in an electric field, will it move tr8*/jcq4 dwto oward a region of higher potential or lower potential? What about a positive charge? tw8/rc 4qjd*o How does the potential energy of the charge change in each instance?

State clearly the difference (a) between elk+ w)fgnw0 /du+vxu2bectric potential and electric field, (b) between electric potential and electric pofunwx+/)uv 02 gbd+k wtential energy.

An electron is accelerated p2fjr wvkpq4 9 f:c nm3,z(c.oby a potential difference of, say, 0.10 V. How much greater would its final speed be if it is accelera. wnpf(pf:4ojc, 3c9zq 2mk rvted with four times as much voltage? Explain.

Is there a point along the lv 9 )-9idtow3g5sgn vpine joining two equal positive charges where the electric field is zero? Where the electric potential5o3 sd vw)vg tp9-9ngi is zero? Explain.

Can a particle ever move from a region of low electric potential to one / bl8*zatoui9 .7 obghl- cwm:of high potential and yet have its electric potential eawcl 7t/ 8ouzg li*.b bh9:mo-nergy decrease? Explain.

Compare the kinetic energy gained by a p nd/nshl1z 6pc+i(e*g roton $(q=+e)$ 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 hdu6z( (pql+lnz -g4 tcross? Explain.

Draw in a few equipotential lines in Fig. 16 –bi alt ujy. *ttd 2o3v:v/58qg 31b.

What can you say about the elen d1sv/.ep heyr) t2-octric field in a region of space that has the same potd tyr1 epv esh2-.)/noential throughout?

A satellite orbits the Earth along a gravitational equipotential line. What shaaqs :opiug;, mm,g 3k8pe must the ok,g sgima :qp8 ,oum3;rbit be?

When dealing with practical devices, we oftfn/o:odelh+m) rt6 -bc2i p /f j2hp(zen take the ground (the Earth) to be 0 V. If, instead, we said the ground was how wo e:)p2 zjfcroh/i2n6( f-bt pdm/loh+uld 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 acqtbfl)lnf r3p:t-7 b*f ,ysr2ouire charges of the same magnitude? Will this be true if the two conductors are different siz7: *bl- fflf 3,btstprynr o)2es or shapes?

We have seen that the capacitance C depends on the si6x,j4a)/ t 9 pmgs v7mcb.jrwdze, shape, and position of the two conductors, as well as on the dielectric constant K. What then did we meanmmj4) c, sapg7x6bwt /rj. dv9 when we said that C is a constant in Eq. 17 – 7?

  How much work does the electric field do in z 7tmgabos 6;8moving 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 3 nb) *0fo dp5kgupy pq;znc1voi8: ;ya point with a potent;qp3p cnobvz):0yu o18i *g5dyf npk;ial 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 o8vu;b1f6ggp and eV) if it accelerates through a potential d8 ;p o6bgugf1vifference of 23,000 V in a TV picture tube?
   $ \times10^{-15 }\,J$
   eV

  An electron acquireskfx0oej i1)mv1s nn; : $7.45 \times10^{ -16}\,J$ 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 plal6q)(4r howd8x3 iieh jfn s2(tes 5.8 mm apart if the po4(w rhln2 hfej3o6ix)8i (qs dtential difference between them is 220 V?    $ \times10^{ 4}\,V/m$

  An electric field of q+tm7 9v9xsszkeezva 3izet*39 df71$640V/m$ is desired between two parallel plates 11.0 mm apart. How large a voltage should be applied?    V

  The electric field between two parallel pe y. +g* xkgol(lzc5 zl)po11tmv/t,plates connected to a 45-V battery is $1500V/m$ How far apart are the plates?    m

  The electric field between two parallel plates conne-i1s(h.jdpqcm jnt10 cted to a 45-V battery is $1500V/m$ How far apart are the plates?    m

  What potential difference is needed to give 3rnla n.t-)lta helium nucleus $(Q=2e)$ 65.0 keV of kinetic energy?    $ \times10^{4 }\,V$

  Two parallel plates, connected to a 200-V power supplfl7 js xcry*/4y, are separated by an air gap. How small can the gap be if the afry 4 7csx/jl*ir 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/ bjzatft9q 9x1kb9w(vp7v 9v 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 with k7ekxwst8 .f0 d37emc iinetic 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 energys-p 1w:-kigk z is 3.2 keV?    $ \times10^{5}\,m/s$

  An alpha particle (which is a helium nuclg)o :fn vmn2*wrf3o7peus, $Q=+2e$, $m\,=\,6.64\times10^{-27 }\,kg$) 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 fro qydb fb1na567m a $4.00\mu C$ point charge?    $ \times10^{ 5}\,V$

  A point charge Q creates an electric poth2vr.j+.aj7u4xt 57z heyq iw ential 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 th5n mmtha zif81ah( 5o;e shape of a football. This conductor carries a net negative charge ah1iz5mn(5h 8;mf tao, $-Q$. Draw in a dozen electric field lines and two equipotential lines.

  (a) What is the electric poti x+2mvqnln+/ ential 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 arranged at the corners of a square of side L as 0 5ukrdq+g9bf shown in0qr +9u f5gbkd Fig. 17–25. What is the potential at the fourth corner (point A), taking $V\,=\,0$ at a great distance?

  An electron starts from vny d1vayp cr 1f) ,mdi:7mrao3mz31de2 ml/-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 diswz 6skiox +2o5tance apart t xsoi56 w+ko2zo $1.0 \times10^{-10 }\,m$ from one another (at the corners of an equilateral triangle)?    $ \times10^{-18 }\,J$

  Consider point a which is 72 cm nortad9zm:hzv 4pc29x n* ih 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 v:7+ pr4g5ptt z mc+wmaccelerate a proton (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, as shown in Fig. ymnd66 f- vw-m17–27. Dnmm6 fv-wd-6y etermine 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, a *7zkhdy8 fd 6fiiciv,;l4mmm17k yiw9i4 o r2n electron orbits a proton (the nucleus) in a circulay4i8;64m1 yizd,w7 2 9ikmif*lc7h rmkiodvf r 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 areqy*x rrks(c9z-4e q8r $ 0.53\times10^{ -10}\,m$. apart. What is their dipole moment if they are at rest?    $ \times10^{-30 }\,C\cdot\,m$

  Calculate the electr3ul 4emymer,i dyv0+8ch5e d:ic 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 as a vectorf 10nes4 yf/;lmq2ofn /reo6 u, points from the negative to the positive charge. The water molecule, fenu/qsf lmon1o;f2r6/ e4y0 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 capacitor i+,7,a ,va ke:dsketbhold $+2500\mu C$ 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 d:38k+2jy r/uarf 4ff ;mc irocapacitor hold $+2500\mu C$ and $-2500\mu C$ of charge, respectively, when the potential difference is 850 V. What is the capacitance?    $ \times10^{-6 }\,F$

  A 9500-pF capacitor holdsz j* jyqo4 ;sq4cyx+6e plus and minus charges of $ 16.5\times10^{-8 }\,C$. What is the voltage across the capacitor?    V

  The potential difference betwe.gb 99;qxs:ag-nicwa ..jt u aen two short sections of parallel wire in air is 120 .uj-q ;xnt bi.9g.w ca:s 9agaV. They carry equal and opposite charge of magnitude 95 pC. What is the capacitance of the two wires?    $ \times10^{13 }\,F$

  How much charge flows from gb /o z7(b8omgeach terminal of a 12.0-V battery when it is connected to a gb obgozm/78($7.00-\mu F$ capacitor?    $ \times10^{-5 }\,C$

  A 0.20-F capacitor is desired. What area must the plates hsk2 h6u h3jw1mave if they are to be separ61msjku3hw h2 ated by a 2.2-mm air gap?    $ \times10^{ 7}\,m^2$

  The charge on a capacitor increase2 pc+f, vc0o* ba(xitks 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 ofn1 5 i1qocghb k.s**dulo r5-i $8.5 \times10^{ 5}\,V/m$ 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 oppositp+pata4jw biy /, 2vp/e $5.2\mu C$ 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 electriev;yv /mk 8xe8c 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. 17–29a) and the)u)v sxzt1 y)-9b1sh xf*cv avn is disconnected from the battery. Wsx1z )f)ax utv9cbhv v1*)-syhen this capacitor $(C_1)$ is then connected (Fig. 17–29b) to a second (initially uncharged) capacitor, $C_2$, the final voltage on each capacitor is 15 V. What is the value of $C_2$? [Hint: charge is conserved.]    $ \times10^{ -5}\,F$

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

  What is the capacitance of two square parallel d06(vbn3q bjh, can+ rplates 5.5 cm on a side that are separated by 1.8 mm n3h,6cj qrbvb+dn 0a(of paraffin?    $ \times10^{-11 }\,F$

  What is the capacitance of a pair pq-x.5:ptcobof circular plates with a radius of 5.0 cm separated byx.cp: o- p5tbq 3.2 mm of mica?    $ \times10^{-10 }\,F$

  A 3500-pF air-gap capaci)8iry1xa6w q qao 7-lptor is connected to a 22-V battery. If a piece of mica is placeo)rq1 lyx6ai 7-qapw8 d between the plates, how much charge will flow from the battery?    $ \times10^{ -7}\,C$

  The electric field be re ggn20g6f7m9x y;uytween 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 2200-pF capo r-pqa+dyl;l ,x3p5hacitor. How much energy is stored?    $ \times10^{-4 }\,J$

  A cardiac defibrillator is used to shock a heart that is 86 cfkwb, dgot9qp0)dbeating erratically. A capacitor in this device is charged to 5.0 kV and stores 1200 J of energy. W )f, od9qk0w 8cpdbt6ghat is its capacitance?    $ \times10^{-5 }\,F$

  How much energy is stored by the electric field between tw 4u( /7ppbg6uq6p 8hy)zk ugcdo 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 and ofpupyk(udcb6qgg p7)/86 z4uh magnitude $420\mu C$.    J

  A homemade capacitor is assemb xad 1cfsl 41v8)b*erwled by placing two 9-in. pie pans 5 cm apart and connecting them to the opposite terminals of *lxd 4r e8sv 11fc)abwa 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 dvg,aglmtox2yd ,7pz53 r4 o8 has fixed 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 bzjlo. n-ojy(f 2,5+ x7ghgs/e vyym:change if (a) the potential difference is doubled, and (b) the charge on eayon yv/,l - hjg.5m7eyfxs:jg(2 ob z+ch 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 kV. They then pasa z323:mul eqsu1fh:h s through a uniform electrq:3h1zm32s lfuau:e hic field E for a distance of 2.8 cm, which deflects them upward so they reach the screen top 22 cm away, 11 cm above the center. Estimate the value of E.    $ \times10^{5 }\,V/m$

  Electrons are accelerated by 6.0 kV in a CRT. The sc::dd- .s3kgm :pz okn 8wn3amareen is 30 cm wide and is 34 cm from thed3: . 3nw -an8d kk::mzgpmosa 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 in moving from point zk vuy17l :2ll:hsbd) A to point B.z1v hy):2bdu :ls lk7l
(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 transfe rg)mba+k5ci t,**c3zwu*aqo rs 4.0 C of charge and 4.2 MJ of energy to the Earth.
(a) Across what potential difference did it travel?    $ \times10^{ 6}\,V$
(b) How much water could this boil and vaporize, starting from room temperature?    kg

  There is an electric field near the Earth’s surface whose magnitudeyafwx ra5kk1p005 ngq12ukf6 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 thousanv0 tt oxa1,j*cds of volts through a a1xtocj0 vt*,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 force of gravity so that an electron would remain stationary? Assume that the electric field is uniform.    $ \times10^{ -12}\,V$

  A huge 4.0-F capacitor has enough stored energy to heat 2.5 kg of w.iv -2+lap)t 6tu jgjyater from 21$^{\circ}\,C$ to 95$^{\circ}\,C$. What is the potential difference across the plates?    V

  An uncharged capacitua6ty e* 0x8cqor is connected to a 24.0-V battery until it is fully charged, after which it is disconnected from the battery. A slab of paraffin is then inserted between the plates. What will now be the voltage ba*t8ey6c0x uqetween the plates?    V

  Dry air will break down if the electric field exceeds y0q 9 ..nu nui (kc9qrvbj(oz)$3.0 \times10^{6 }\,V/m$. 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) u ;fyvds:1fp.0 )a;oly6nrkras shown in Fig. 17–30o1k;rr6a:ufln0f. ; pvy)sdy . 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 is connected to a 9.0-V battery. If a piece ofsusv qwem.+lk :4gk6**: e(nkpot e 5y Pyrex glass is placed between the plates, how much charge will then flow from the battery?k(q5ee:y+gs*m l4*:e.6 k swnuvtk op    $ \times10^{-8 }\,C$

  An electron is accelerated horizontally from rest in a television pictures: cgjur1rpqxiqn2/ w067k+v 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 difference of 250 V (Fig. 17–31i6 upr gk/vnwc:7+ jxqsqr02 1). At what angle $\theta$ will the electron be traveling after it passes between the plates?    $^{\circ}\,$

A capacitor of capacitanr0vtcf- l)tt ;o*+o frce $C_1$ 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-filled thgr 7ki+*rzj7cbr1rjw/ 9 7fparallel-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 platt79/cbjr+frjwhzg i7rr 71k*es? Is this practically achievable?    $ \times10^{-16 }\,m$  ----待选择----YesNo 

  Near the surface of the Earth there is an e8 hfmq+7y jcrd;i: 8vflectric 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 nitre tinco m53e4:nnly1 1 8xvz0jogen 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 ap;e 2.:2q a kd9npugudnd the bottom of the thunderclouds can be as high as 35,000,000 V. The bottoms of the thunderclouds are typically 1500 m above the Earth, a;ueag2. p2k :pun9q ddnd 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 enoughbp mun8kg rr3yce:./3 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 surface is kept at a negative enough potential that the emitted electrons are slowed down and stopped, and return to the bariu3:/ke8.mbgr np3uc yrm 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 placedsx7r- b +uou-c 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,xba3/ fu ii;0d8iugq two 1.1-cm-diameter coins separated by a 0.15-mm-thick piece of paperqd /,;u38ia uf0x igib $(K=3.7)$ 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 w 1io1 zkzt8k5 9mkx7 :y1tqibplate 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 ) ycdz;my8dm9i)9bh gfrom 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 Fi221o v9q7xy*j6m7kq t n hzavvg. 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$