If two points are at the same potential, does this mean that no worhe698q)wit 7o r vb9xlk is done in moving a test charge from one point to x68v9theq7wb ri 9o)l the other? Does this imply that no force need be exerted? Explain.

If a negative charge is initially at rest in an uf z)v3 ,vm hxuj0(o,xelectric field, will it move toward a region of higher potential or lower potential? What abu, fou)j0m3 vhx,v(xzout a positive charge? How does the potential energy of the charge change in each instance?

State clearly the difference (a) between eleckwc p,y (-ssc(tric potential and electric field, (b) between electric potential and els(c ,wsp(ck -yectric potential energy.

An electron is acceler 3r*pyy-j8n9 ch*n 1erq.ufw2j /osffated by a potential difference of, say, 0.10 V. How much greater would its final speed*nw-j/fphr y.9q 8 uj2 nfocsyf*e3 r1 be if it is accelerated with four times as much voltage? Explain.

Is there a point along the line joining two equal positive charges where the z7(+ yqz5; apl9a(vk)5/e eknds bine electric field is zero? Where the electric potential is zeroenp zka )5denl+bv ;s z/ieayq75k(9(? Explain.

Can a particle ever move from a region of low elect3 oj2e6q0*9ssijc sn2jru) gbric potential to one of high pot3rio06 2)cgeb*sqj j2 j9 nsusential and yet have its electric potential energy decrease? Explain.

Compare the kinetic energy /dmsvx,:*qhwprk)rv(g8a1 z apk5;s r6fqf1gained 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? Ej 1tc0 x;le2jsxplain.

Draw in a few equipotentialpcz qx:.m;1s a lines in Fig. 16 – 31b.

What can you say about the electric field in a region of spa+3srxvqx uv,*js. l j+ce that has the same potentialv j.*3x u+v+ xlqrss,j throughout?

A satellite orbits the Earth3xg*g.vb3x dt along a gravitational equipotential line. What shapexv x.33 tbgd*g must the orbit be?

When dealing with practicz,0.z1y6 ex mu,hzbp,r hwk0hal devices, we often take the ground (the Earth) to be 0 V. If, instead, we zhe 0.hkw r6p ,0myb,zz1, huxsaid the ground was how would this affect (a) the potential V, and (b) the electric field E, at other points?

When a battery is connected to a capaci7jp; +iao r2twtor, why do the two plates acquire charges of the same magnit+7;ar2w po tjiude? Will this be true if the two conductors are different sizes or shapes?

We have seen that the capacitance C depends on the size, shape, and positg f1h5g) sun;cion of the two conductors, as well as on the dielectricf g5)nhgs1 ;uc 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 fil2/ ah ilgkxb61q r.s;zswz;0 eld 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 the electric field do in moving a proton from a poi1lm084s pwx(v x dn,kint with a potential omn p8(x 0xldkwi1 ,vs4f $+125V$ 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 elec3)ut +9q 5nprufk*odjtron gain (in joules and eV) if it accelerates through a potential difference of jqup5 r+9 dtf)3un ok*23,000 V in a TV picture tube?
   $ \times10^{-15 }\,J$
   eV

  An electron acquires jkq w/no6np:- $7.45 \times10^{ -16}\,J$ 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 eled76a )37mnwpik+blyq ctric field between two parallel plates 5.8 mm apart if the potential difference between them is 220 V? wbn)pm+la7dqk yi 637   $ \times10^{ 4}\,V/m$

  An electric field of ys.zm3 zor06 sp/25fve ;odcu$640V/m$ 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 connected to xh8kv 61*hu4p6idtbs 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 balnhiug5ruq q, 9d 63vs4pm u8(ttery is $1500V/m$ How far apart are the plates?    m

  What potential difference is needed to gi;o*zbi.7kfn5oq zl.k u3 s1xkve a helium nucleus $(Q=2e)$ 65.0 keV of kinetic energy?    $ \times10^{4 }\,V$

  Two parallel plates, connected to a 200-V power supply, are separated by an air nfj5hdtq+ 7*psw zclh ;ul:t (6 vv88t5b6tihgap. How small can the gap be if the air is not to become conducting by exceedingtc76 t:hup wl jqdsvzf5l*i8+8 nvb(ht56th ; its breakdown value of $E\,=3 \times10^{ 6}\,V/m$?   $ \times10^{-5 }\,m$

  The work done by an external force to (n9j lxckw3 d8 9sj;vhmove 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 ws ogz2 f(j u1c1*2bdehith 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 ki3b;o5ulrhf7dp5 xq 4fjdz*+p netic energy is 3.2 keV?    $ \times10^{5}\,m/s$

  An alpha particle (wl2:-0d fkjjp 4csd/mr hich is a helium nucleus, $Q=+2e$, $m\,=\,6.64\times10^{-27 }\,kg$) is emitted in a radioactive decay with $_{KE}$ = $5.53MeV$ What is its speed?    $ \times10^{7}\,m/s$

  What is the electric potential 15.0 cm3 hui5fsk aspex; (2z6z-yji 6 from a $4.00\mu C$ point charge?    $ \times10^{ 5}\,V$

  A point charge Q creates a z angy67s*4t/xn+sxnn 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 shape of a football. This conductor carrigq)7vlaswgw4; joe x xb)33 6ies a net negative c6jsq 4wb io l7gax)e3vx)3 ;wgharge, $-Q$. Draw in a dozen electric field lines and two equipotential lines.

  (a) What is the electw:wyx -7 o.q1wuuj0ay ric potential a distance of $ 2.5\times10^{-15 }\,m$ away from a proton?    $ \times10^{ 5}\,V$
(b) What is the electric potential energy of a system that consists of two protons $2.5 \times10^{-15 }\,m$ apart — as might occur inside a typical nucleus?    $ \times10^{ -14}\,J$

Three point charges are arranged at the corners of a square of side L as shownx 2p/,i89sldcnb qp*k in Fig. 17–25. What is the potential at the fourth corne/c8sn* i l2 ,xbpp9dqkr (point A), taking $V\,=\,0$ at a great distance?

  An electron starts from rest 32.5 cm from ) oy)d5lxz9xuo+whn..w o,x)elpi -xa 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 electronedeo6 70aio af2atn.9 s from a great distance apart tn 02o6if9aetd ae.oa 7o $1.0 \times10^{-10 }\,m$ from one another (at the corners of an equilateral triangle)?    $ \times10^{-18 }\,J$

  Consider point a which is 72 cm north of ahdsc, o9z6 1wlco1m 6c $-3.8\mu C$ 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 musrtj4w+/f)y o)9wrvb qt be used to 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 a dista:ofc3v)arzhkm )l r (f05y4vvnce d, as shown in Fig. 17–27. Determine a formulaf r kvz (hl4fc5oa3)m0vy r:v) for $V_{BA}\,=\,V_B-V_A$ for points B and A on the line between the charges.

  In the Bohr model of the hydroga/ndm 9fbl a,-en atom, an electron orbits a proton (the nucleus) in a circular orbit of radam- ,f/nd al9bius $ 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 aruj,cfgo 5aj(39r 3ku te $ 0.53\times10^{ -10}\,m$. apart. What is their dipole moment if they are at rest?    $ \times10^{-30 }\,C\cdot\,m$

  Calculate the electr,i,o )yazan-zic 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 vector, points from the negative to the posiq+85mdqv vn yyanr-1 w-k/5e rf-(qbk i:9bsitive charge. The water molecule, Fig. 17–28, has ae-iq+ rky- /bkf v5m5abnqnwq( i -v8d:s1y r9 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 hold jo1 .t9 myte2f bnp,9g$+2500\mu C$ 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 capa1vbftgx ;8 n4xo*dj5 gcitor 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 min(+) ja unnb ;oczs;u *wy7pn:b)p dn/vus charges of $ 16.5\times10^{-8 }\,C$. What is the voltage across the capacitor?    V

  The potential difference between two short sections oyrxj(9d4 ro :wf parallel wire in air is 120 V. They carry equal and opposite charge of magnitude 95 pC. What is the capacitance of the j(xr9:4doryw two wires?    $ \times10^{13 }\,F$

  How much charge flows from each terminal of a 12.0-V bat g(j z- d+c*jch (n vyv.wzi9+lb/4ryvtery when it is connected vczz d9rjwyyjn vb.(+h-(vi/+4*l gcto a $7.00-\mu F$ capacitor?    $ \times10^{-5 }\,C$

  A 0.20-F capacitor is desired. What area must the plates ha*q;bd5.njq ndcbns50 e9i5f7dmk u 6i ve if they are to be separated by a95nq c k*b05b;6.7dd 5jiduefsim nqn 2.2-mm air gap?    $ \times10^{ 7}\,m^2$

  The charge on a capacitor i nq(ujvf24s7kncreases 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 33 ftyuf:ov/,d z:hdtpc+co -$8.5 \times10^{ 5}\,V/m$ 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 oppo.lp;v -ohq(w) 0 b; yj/xphcwzsite $5.2\mu C$ 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 field betwevzwx5 3 +h;zi db7+iqhen 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 125e j9bq84czp upi;q- eyrp33 +f-V battery (Fig. 17–29a) and then is disconnected +e q8e9cjqr3-3 ppb ip4z;ufyfrom the 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 two square paralld+1xxq1 u )givel plates 5.5 cm on a side that are separated by 1.8 mm of paraffid)ig 1uvxqx+ 1n?    $ \times10^{-11 }\,F$

  What is the capacitance of a pair of circular nhm76 l/ufd8oz0uc a/plates with a radius of 5.0 cm sepa0z8h6nudof/ /m7aucl rated by 3.2 mm of mica?    $ \times10^{-10 }\,F$

  A 3500-pF air-gap capacitor is connected to a 22-V battery. b a p89kydpj+d-+lv2eIf a piece of mica is placed between the plates, how much charge wila vl8+j ekydb2pp+ 9d-l flow from the battery?    $ \times10^{ -7}\,C$

  The electric field bm )s2- n;hw0w9lgwj0sk okm6jetween 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 u y3bm0 -bxr6enz1-qw7bc60e +zy1lah1x vwv a 2200-pF capacitor. How much energy is stored?    $ \times10^{-4 }\,J$

  A cardiac defibrillator is used to shock a heart that is beating erra3h ;d75 hdlgiatically. A capacitog5lh h7da i;3dr in this device is charged to 5.0 kV and stores 1200 J of energy. What is its capacitance?    $ \times10^{-5 }\,F$

  How much energy is stored by the electric field between two square plates, 8.0 c ux/ja v0-en/vm on a side, separated by a 1.5-mm air gap? The charges on the plates are equal and opposite and 0njauvv xe//-of magnitude $420\mu C$.    J

  A homemade capacitor is assembled by placing two 9-in. pie pans 5,x ) 9bq/yogiumb4xfm ,l9/rs cm apart and connecting them to the opposite terminals of a 9-V/ ri f ),lo ,suxqy9m/b94mgxb 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 b +akp6/lc4btharges $+Q$ 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 in7g 8 w+ou+ wdkj9g-dla a capacitor change if (a) the potential difference is doubled, and (b) the charge on each plate is doubled, as the capacitor remains connectedd g7w8guj+9alw o+kd - 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 horizy2x (yd (dpc8lontally by 7.0 kV. They then pass through a uniform electric field E for a distance of 2.8 cm, which deflects them upward sodx2yl8((cydp 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 b8 m/-syl.kuxby 6.0 kV in a CRT. The screen is 30 cm wide and is 34 cm from the 2.6-cm-long deflection plates. Over what range must the horizontally deflecting electric field vary8-. ux/ybmskl 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 movifla -.s/-uza7rwq 8 ulng from point A to point B..-z8 wl qrsaful7 a/-u
(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 .,me rhv15nca5 )eayt2h+/ jaetp9fje 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 magnitude is ab /5;efywow4d nk5 g 4bevi7*(a6uz jvlout $150\,V/m$ 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 thousands0 y 635/pf+cccasydum of volts through a vacuum. If a television set were laid on its back, would electrons be able to move pc3/cycsm ayf05d6 +uupward 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 gbsdrcsi6t 34 )t t0v5has 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 battery until it tfk(c9 d7rh ucs0l02pqu z.,l is fully charged, after which it is disconnected from the bt.z2kcf0 0uq ( ,cdsh l9lu7rpattery. 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). zpubn iso+. field exceeds $3.0 \times10^{6 }\,V/m$. What amount of charge can be placed on a parallel-plate capacitor if the area of each plate is $56cm^2$?    $ \times10^{-7 }\,C$

Three charges are at the corners of aat +8gp.(f rzge98)d9fmp o tet-svs6n equilateral triangle (side L) as shown in Fig. 17–30. Determine tp)6 dtzp9s(mtr s.gta8 +fe9 ovf8ge-he 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+) 8e f 7qsgh6w uia0yn-s8ncr a 9.0-V battery. If a piece of Pyrex glass is placed between the plates, how much charge will then flow from the battnc i8sgf6y8w q0n+ah7-use r)ery?    $ \times10^{-8 }\,C$

  An electron is accelerated horizontally fraqov,u3; z b3ys(x0bu om 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 apart that have a potential d0y qa3 vu;xsbb zo,3(uifference 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 capacitoz+g-du oe h3.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 ar9q9pa hc xcz1ym5+ .kir-filled parallel-plate capacitor for a circuit you are building. To make it a reasonabm9 . q5 +1hkcrxzcy9aple 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 the Earthymo*a bx)poo p(8s+(kg(( m zy 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 f7gp)y2c2x gevvvw96 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 difference between ff / js1ry6lx8the Earth and the bottom of the thunderclouds can be as high as 35,j6f r1l/sy8x f000,000 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) la m5))e-b r 3swjay2m*fb b5mnight 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 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 vom*a e 5m-sr5)w)b3jman2byfb ltage 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 phe.qv3k7 * jnrlaced 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-diameter coins separated by a 0.150qk q0u4ulgl r(r9zac1 r8cm6 -mm-thick piece of pau( 0r9l0uqcaz 1m4r k6 qg8rclper $(K=3.7)$ 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 area3is6dxy))foe)hxwc )gn. v. xfc 3e :u $2.0cm^2$ 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. Thei83sin**lg 3ojf 3 taoh9a npi;r 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 placeus4.vb.0bj3 ,:q e7u gdisxie d 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$