If two points are at the same potential, does this mean tha g(ix *,s,l8+umfky w ru/v,fbt no work is done in moving a test charge from one point to the other? Does this imply that no force need be exertedy+/*lk,fvmsiub , 8xgrw f,(u ? Explain.

If a negative charge is initially j -vhb ryf+++jat rest in an electric field, will it move toward a region of higher potential or l+b-+vfy+hj jr ower potential? What about a positive charge? How does the potential energy of the charge change in each instance?

State clearly the difference (a) between electric potentzt,m )v:roc2 cial and electric field, (b)tc): rc2mz,ov between electric potential and electric potential energy.

An electron is accelerated by a potential difference offo.i3pvrsqe2d8d 1x )1vc *lt , say, 0.10 V. How much greater would it fsp e)8lv23xvoc. idd t1rq*1s final speed be if it is accelerated with four times as much voltage? Explain.

Is there a point along the line joining two equalmwe p*ub*v 7/cxw j;l+.m6qh h positive charges where the electric field is zero? Where the electric potential vwue**h7mqx m l+w j;b6p/c.his zero? Explain.

Can a particle ever move from a region of low electric potential to oj:bki55k 8 ukup0r njl u(0t.xne of high potential and yet have its el . xrk(:t5kpjj0nk5uiu 0u8b lectric potential energy decrease? Explain.

Compare the kinetic enerron tl358t99txayhi (hp l+q;gy 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 lined8x/d8a kdl/mu m cboc6o (rov+,zi2*s cross? Explain.

Draw in a few equipotential diunwvsr / c;;6/c6 fllines in Fig. 16 – 31b.

What can you say about tmrf3qkd wz39*he electric field in a region of space that has the same potenti9*dr mf zqk3w3al throughout?

A satellite orbits the Earth along a gravitational equipotential libvupxw;e* 25ine. What shape must the orbit iuwxev2; *5bpbe?

When dealing with pract1zcip n(c m q r.)4gyh,zq8tus4d(2lx ical devices, we often take the ground (the Earth) to be 0 V. If, instead, we said the ground was how would this affect (a) pdzqtq8lc1 nu(2z,h44s.)x(g cm riythe potential V, and (b) the electric field E, at other points?

When a battery is connected krebw6,9y uovo mv1aqa .nzbj49+2z0 to a capacitor, why do the two plates acquire charges of the same magnitude? Will this be true if the two conductors are differenova+nj 6qu z v91rk y.e40 92awmb,ozbt sizes or shapes?

We have seen that the capacimm 7-kv9txd;f; w,r irtance C depends on the size, shape, and position of the two cifk,;r dr;wm m9 x7t-vonductors, as well as on the dielectric constant 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 in2: scm w0j0 ;i(o:kpnls sdxi* moving a $-7.7\mu C$ charge from ground to a point whose potential is $+55V$ higher?    $ \times10^{-4 }\,J$

  How much work does the electric field do in moving a proton from a point with a 81imgl bnrb)0 potb)1r8gbmn0 i lential 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 eV) if it;c p*ewn7e(i ;hg :ifq accelerates throughe;7e:pgc(iq wfih* n; a potential difference of 23,000 V in a TV picture tube?
   $ \times10^{-15 }\,J$
   eV

  An electron acquires wp0 n56 pdhi)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 :kx5-ns eqdw 8mm apart if the potential difference betwee8 kdn q:5-wesxn them is 220 V?    $ \times10^{ 4}\,V/m$

  An electric field of o,s/ (d-qpkfg $640V/m$ is desired between two parallel plates 11.0 mm apart. How large a voltage should be applied?    V

  The electric field between two paraj5:e b7s9j xlsllel plates connected to a 45-V battery is $1500V/m$ How far apart are the plates?    m

  The electric field between two parallel platess.4ogc yf3 s*zk :q*nnz2tcc2 connected to a 45-V battery is $1500V/m$ How far apart are the plates?    m

  What potential difference is nee vbgr4x4jwk5n )yaq-tl+j i /7c- i/heded to give a helium nucleus $(Q=2e)$ 65.0 keV of kinetic energy?    $ \times10^{4 }\,V$

  Two parallel plates, connected to a 200-V power supplpq, s4pv rlq,4x a8ls7y, are separated by an air gap. How small can the gap be if the air is not to become cond4spl,pqxa4, 8ql vrs7ucting by exceeding its breakdown value of $E\,=3 \times10^{ 6}\,V/m$?   $ \times10^{-5 }\,m$

  The work done by an external f:q xvrp( vn*et/9q j0;njdi/d j+mm3horce 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 with kinetm :s.:qc3) bk,j8f vkppau1q yic energy
(a) 750-eV,    $ \times10^{7 }\;m/s$
(b) 3.2-keV?    $ \times10^{7 }\;m/s$

  What is the speed ofux cb,p39q,k c a proton whose kinetic energy is 3.2 keV?    $ \times10^{5}\,m/s$

  An alpha particle (which is a helium nucleus,iw. lromsz52 - nyfj-9 $Q=+2e$, $m\,=\,6.64\times10^{-27 }\,kg$) is emitted in a radioactive decay with $_{KE}$ = $5.53MeV$ What is its speed?    $ \times10^{7}\,m/s$

  What is the electric 9(: hmijbo/ktpotential 15.0 cm from a $4.00\mu C$ point charge?    $ \times10^{ 5}\,V$

  A point charge Q creates a0d /ecj))rqmvn electric potential of $+125V$ at a distance of 15 cm. What is Q?    $ \times10^{-9 }\,C$

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

Draw a conductor in the shwzl2d7krxgz 4*gw(l 1ape of a football. This conductor carries a net negative ch rgl*wzxw4( g21dzlk7arge, $-Q$. Draw in a dozen electric field lines and two equipotential lines.

  (a) What is the electric potential/w yx z(z+i aku4bh;71 alil7 3ahbfk: 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 shownl1mg 4fy3in jzi3, pw8 in Fig.w ipiz j1lgn3348 ,fym 17–25. What is the potential at the fourth corner (point A), taking $V\,=\,0$ at a great distance?

  An electron starts from rest 32.5 cmlmhj*0) 8 0w3utbez7lk)u ttw 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 distance ap0y,+7fiw4a u,0+w sfuadh byqart to,f 0bd0 ,wu ifasyy++7hwqa4u $1.0 \times10^{-10 }\,m$ from one another (at the corners of an equilateral triangle)?    $ \times10^{-18 }\,J$

  Consider point a which is 72 cm n,+slp, f0a8kvx 58 fmrg dgsv)orth 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 ,-xdjfm(tk( ah ,w s(tto accelerate 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 a3 xt(2+weiro s:9u dcl 6wet,n distance d, as shown in Fig. 17–27. Determine a formula foe6eu sln3,2wwr c+9x i(:otdtr $V_{BA}\,=\,V_B-V_A$ for points B and A on the line between the charges.

  In the Bohr model of the b8dj+iqv6: b/w;z,w gla3njk hydrogen atom, an electron orbits a proton (the nucleus) in a circular orbit of rw8ngz3i:; qkvl +bdj/6jaw,badius $ 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 proton5k1b*mg v /k61r9bti8x oh zrb13el pp 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 dipole whose dipole moment is vos vl4px;x4xst9t.(0rf u l4$ 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, considermv ubowe0leq( 3(hsq+;-yfa4hrb g8 (ed as a vector, points from the negative to the positive charge+0ly3o(bvh(;e gar wu4s8f(m-h q ebq. The water molecule, 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 ho-/plwcd0s/qztn .gcmw mk(64 5 hruwum(g 6s.ld $+2500\mu C$ 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 capac43tix j;kk 8l-d5bfvfvtf i5oa1:. kkitor 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 holds plus and minus chargej:6v73 h: zh1dba3(6m: aczgkmpaqins of $ 16.5\times10^{-8 }\,C$. What is the voltage across the capacitor?    V

  The potential difference between two short section.m)y9 :j op86tylrcrc s of parallel wire in air is 120 V. They carry equal and opposite charge of magnitude 95 p9tro6 )j c.yyrc8lpm:C. What is the capacitance of the two wires?    $ \times10^{13 }\,F$

  How much charge flows from each terminal of a 12.0-V batteo0mf yt8y) g9rry when it is connected torgo)y9 80fy tm a $7.00-\mu F$ capacitor?    $ \times10^{-5 }\,C$

  A 0.20-F capacitor is desired. What area must the plates have if z+7v ytsbyh0sa7 0bm2they are to be sehstsyb+70myva b 70 z2parated by a 2.2-mm air gap?    $ \times10^{ 7}\,m^2$

  The charge on a capacito3s,ey+m- huxx r 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 of (d1zzd m/cs.6y(r6n u7/yuu. mmuohh$8.5 \times10^{ 5}\,V/m$ 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 o,v 5*j1p s*lb k.g;7uex-jhjvut4gku pposite $5.2\mu C$ 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 electri eyz oxmbf r:,h2a)ql -s(t3,sc 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 batteryu 12nk8 gku)9x.znmbyp:6zcf (Fig. 17–29a) and then is disconnected from the battery. When this cakzz pxn61 8u:yf u)g9k .2cnbmpacitor $(C_1)$ 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 *ad( 8zr0 1h- tlhjovf)izk k,parallel plates 5.5 cm on a side that are ad,z1hif( k -0 tvo*h)zkrlj8 separated by 1.8 mm of paraffin?    $ \times10^{-11 }\,F$

  What is the capacitance of a pair of circular plates wit;r;y qljbx9)p j-nej ,h a radius of 5.0 cm separated by 3.2 mm of mejpj-q) ;yrl n,;x 9jbica?    $ \times10^{-10 }\,F$

  A 3500-pF air-gap capacitor is connected to a 22-V battery. wy2mxi+9a wl; c e-3hzIf a piece of mica is placed between the plates, how hxle2w3a-iwc+ z9 ;m ymuch charge will flow from the battery?    $ \times10^{ -7}\,C$

  The electric field betwause,mtzy)os/b 56s 1 5hy ps8een 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 ca9kod3og l6 y5gd )gum3pacitor. How much energy is stored?    $ \times10^{-4 }\,J$

  A cardiac defibrillator is used to shock a heart that is beatin9e+za7uy f j 0.nkex;u;hg*b kg erratically. A capacitor in this device is charged to 5.0 kV and stores 120jekb+0yu k*. ex;g9zf;hau7n 0 J of energy. What is its capacitance?    $ \times10^{-5 }\,F$

  How much energy is stored by the electric field between two squvz 7y1 ztn:- fa,qx8akare plates, 8.0 cm on a side, separated by a 1.5-mm air gap? The charges on the plates are equal and o- nza:q, k8f17 xzvaytpposite and of magnitude $420\mu C$.    J

  A homemade capacitor is assembled by placi:ys 4eqkd,f5 ing two 9-in. pie pans 5 cm apart and connect 4ds5f:ye,k qiing them to the opposite terminals of a 9-V battery. Estimate
(a) the capacitance,    $ \times10^{-12 }\,F$
(b) the charge on each plate,    $ \times10^{-11 }\,C$
(c) the electric field halfway between the plates,    V/m
(d) the work done by the battery to charge the plates.    $ \times10^{ -10}\,J$
(e) Which of the above values change if a dielectric is inserted?

A parallel-plate capacitor has fixed c(- vdo ;ph-iya7m+-js/v g zvpharges $+Q$ 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 iflwvbm,ud;f *, (a) the potential difference is doubled, and (b) the charge on each plate is doubled, as the capacitor remains connected to a battw,d,;*m ufvl bery?

  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 horizonta/gu ogsc-c6n7 lly by 7.0 kV. They then pass through a uniform electric field E for a distance of 2.8 cm, which deflects them upward so they reach the screen occs/6nug- 7 gtop 22 cm away, 11 cm above the center. Estimate the value of E.    $ \times10^{5 }\,V/m$

  Electrons are accelerated by 6w uj w:0pbu .cu./hz)f 5)sgce.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 electric field vary to sweep the beam fully across the screeup5 jsc0/.w:e.wguu )) czbhfn?    $ \times10^{5 }\,V/m$ to    $ \times10^{5 }\,V/m$

  An electron starting from rest acquires 6.3 keV of KE in moving fro 3aj;z*ov1d,cos2)d w 0o oalqm point A to point ;coz 013w2sv ao)d *jad q,looB.
(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 Earth. f v +m.t 3/ww-n pv3nf4wjflw.
(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 su7kgslye,jj :9iwh no8+e *wk :rface 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 bwuw 1ihhb yu1+r q7f/3y 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 force of gravity so that an electron would remain stationai+3wuh 1rub1hfw 7qy/ry? Assume that the electric field is uniform.    $ \times10^{ -12}\,V$

  A huge 4.0-F capacitor has enough stpnys,inr0.c35 9au guo w4zq8 ored 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 capacit rltf(0ys m)/wor 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 between the plates? ws/m)tr 0(ylf   V

  Dry air will break down if the electric field exc(qiz ti hc53a*eeds $3.0 \times10^{6 }\,V/m$. 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 v5)xyjm eo md cu0g7o+*w*0vxoa9fa:triangle (side L) as shown in Fig. 17–30. Determine the potentic7d9w+v*:v5)oyja xmmog x afo00 e* ual 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. 0y me1bt du8-dIf a piece of Pyrex glass is placed between the plates, how much charge will then flow from the batt u 80yt1bdemd-ery?    $ \times10^{-8 }\,C$

  An electron is accelerated mmn6z t,0sm l03-f vw2lckb2p horizontally from rest 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 av6 t2ml ,z0fc2-w sm30pkb mlnpart 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 capacitanho2d+ m3ge)ance $C_1$ 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 mvu5o-fd f9w4parallel-plate capacitor for a circuit you are building. To make it a reasonable size, suppose you do4v mu9w5f-flimit 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 the Earth there i+d5p /z, rv7 5fyoxqbks 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 for6 eh;zlwqdyq,4zv(ybe6;x j /qi0r4j a pulsed 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 differp 6ro xwmvn;f7/ bhrx1n5zl7;ence between the Earth and the bottom of th;7whr6n;z xpbfm7 ro 15nvx/le thunderclouds can be as 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, ultraviolet (UV) light provides enough en) +fvw ss5msh(d e(pv7ergy to some electrons in barium metal to eject them from a surface at high speeds h(+p efs)(v5wmv7d s. 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 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 fr:v0kw8z: s(nu u)jb( q2gw; t,dljv ftom 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-diameter coins separatej9acp vkf(lfwx 8u4,n5) 8as bhv:ck (d by a 0.15-mm-thick fk9w(j,bv)a pcn xkh a4lc:5u8sfv( 8piece 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 capacitor with plate ag4iw q2pmpd 03rea $2.0cm^2$ 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.:u;wbi -thukg(+l w p(b.w h;qd;oo- q 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 9 i)jkzo1; sbdin 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$