If two points are at the s 9k;ude fk:o+game potential, does this mean that no work is done in moving a test charge from one point to the other? Dgoukd;k 9e +f:oes this imply that no force need be exerted? Explain.

If a negative charge is initially at rest in/s3 9k. )r denaqr:za;)dtjsn an electric field, will it move toward a region of highen 3e;a9 k.:tzsrj/n)ddsar)q r potential or lower 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 kmvuqm +02g1 8pw7ykepotential and electric field, (b) betwke m2v 7umgwk8q01 yp+een electric potential and electric potential energy.

An electron is accelerated by a potential difference of, say, 0.1 s xf/dbs 4a;4cpw7p:s* kwfq)0 V. How much greater would its final speed be if it is accelb:s*ppx) fc w sq;w4s7kf4/a derated with four times as much voltage? Explain.

Is there a point along the line joini-ip9m vn;wu;o ng two equal positive charges where the electric field is zero? Where the e-o9;mu; vw ipnlectric potential is zero? Explain.

Can a particle ever move from a regionln7o m7w44rk q of low electric potential to one of high potential and yet have its ew kq744r7mln olectric potential energy decrease? Explain.

Compare the kinetic energ fu(p sr9tq2e w+k//yg3; vbqhy gained by a proton $(q=+e)$ to the energy gained by an alpha particle $(q=+2e)$ accelerated by the same voltage $V$.

If $V\,=\,0$ at a point in space, must $\vec{E}\,=0$ there? If $\vec{E}\,=0$ at some point, must $V\,=\,0$ at that point? Explain. Give examples for each.

Can two equipotential lines cross? Ex7cq3ex. ,lmuq (wwud 1plain.

Draw in a few equipotential lines in Fig. ltewi io) q(z;b+ /l/qtwy 42x16 – 31b.

What can you say about the electric field in a region (7 b4rrma4lhw5t pqq8of space that has the same potential thrmlqwh 48( 5atrqb4p 7roughout?

A satellite orbits the Earth along a gravitational equipotential line. Wha/lcogt6/ a,l2xfs :1 ptt0y htt shape must the orbit l0p61 xa2st /gy/co:f,tth lt be?

When dealing with practical devices, we often take the ground (the Earo -n d+z:u168z7dk ,xcp +sspzlr2ldgth) to be 0 V. If, instead, we said the ground was how would this affec+k782+ssdr pg-6 uzlx,n p1zldz:doct (a) the potential V, and (b) the electric field E, at other points?

When a battery is connected to a capacitor, why tesesx fnrq /8e;7a;mw n /c6:do the two plates acquire charges of the same magnitude? Will this be true if the two conductors are differe 6s8x:mef/a/;ws c7e ;teq nrnnt sizes or shapes?

We have seen that the capacitance C depends on the si41+ wbz+ddg c 0fz nzvbvk37-xze, shape, and position of the two conductors, as well as on the 3dngz z04v1 wvbcf+bk-zx+d7 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 in moving6b:td bwy k1(.0hybis 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 wiz 10i fh*ypfufeg 9z-3th a potgufez9ipf y-z*31 fh 0ential 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 i6*njm2 o2p1jj2opf nelectron gain (in joules and eV) if it accelerates through a potential diffep16ofjj2 pn* 22 jominrence of 23,000 V in a TV picture tube?
   $ \times10^{-15 }\,J$
   eV

  An electron acquires o m;+s 4ozg9hs;rjnpf: x,c7z $7.45 \times10^{ -16}\,J$ 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 apr// e( sq8osjm sr;5hjart if the potential difference between them is 220 V? jhsr8ej/;mss o 5q(r/   $ \times10^{ 4}\,V/m$

  An electric field of a3 k :c8br/kfqjl+vd7 $640V/m$ 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 a 45-V batterc44 eblww1ta3 y is $1500V/m$ How far apart are the plates?    m

  The electric field between two parallel plates connected to a 45-w t6ges h6z 5oon+3c6qV battery is $1500V/m$ How far apart are the plates?    m

  What potential difference is n:egdd*m u9 pd4eeded to give a helium nucleus $(Q=2e)$ 65.0 keV of kinetic energy?    $ \times10^{4 }\,V$

  Two parallel plates, connected to a 200-V pow8+cr3 f (jvxcfer supply, are separated by an air gap. How small can the gap be if the air is not to become conducting by exceeding its brjfv f 8c(cr3+xeakdown value of $E\,=3 \times10^{ 6}\,V/m$?   $ \times10^{-5 }\,m$

  The work done by an external foal,,a w gex(z6rce 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 kinetic eneduf*,cxzr:/ r1yb gn- )0kyil rgy
(a) 750-eV,    $ \times10^{7 }\;m/s$
(b) 3.2-keV?    $ \times10^{7 }\;m/s$

  What is the speed of a protoig cs2 (3-z; bgzm0fugn whose kinetic energy is 3.2 keV?    $ \times10^{5}\,m/s$

  An alpha particle (wh gmf,pdq:1u7jich 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 cm from a mbm 8v6owbnt:a(q 93b$4.00\mu C$ point charge?    $ \times10^{ 5}\,V$

  A point charge Q creates an electric poteox:ngj3d(v /x4wm+ nx4r(zq 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 the shape 0j0mzszcs d,) of a football. This conductor carries a net negative ch0,sdzc0 j)mzs arge, $-Q$. Draw in a dozen electric field lines and two equipotential lines.

  (a) What is the elect+n:te c1ydcd 7ric 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 +3w)tkw 88;l z 7sg5nwlkw6q xbid7eqas shown in Fig. 17–wg8k deskw lxq6w ;z3b7+i)t8wnq 7 5l25. What is the potential at the fourth corner (point A), taking $V\,=\,0$ at a great distance?

  An electron starts from rest 32.5 cm froi r/cgm8o1vnc q x3/o)m 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 dimd6q;beb3j3y5y:c0y a2dsvb stance apart to 5y y; 6b2v bb:qdce yad3m3js0$1.0 \times10^{-10 }\,m$ from one another (at the corners of an equilateral triangle)?    $ \times10^{-18 }\,J$

  Consider point a whichv17:*,1u jfw ;n7vfuagbzlsv iz0 w9n 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 acceleratof,*lta 1bc0n e 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 esj9r z rv(fys(ogq/4h5i ;-va distance d, as shown in Fig. 17–27. Determine a foyrg4-;qs/(hzsvr ji 9evf (5ormula 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 7 v3vgrg9xwz,dni;z ql5 ig73proton (the nucleus) in a circu;wz,i rvgd9n7 zx3i 73lgqg 5vlar 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 protzhxv rv 2-c5yzhsq25 1qw9a7/pfkw0mon 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 potentiaos3j7 kl4dtu; aq r4s6l 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 + wsrr54v tjv8positive charge. The water molecule, Fig. 17–28, has a dipole moment which can s 48jwvrv 5+trbe 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 ql7 zy is+t/wp;imd;9-ud ca,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$

  The two plates of a caqpmhb 8.9l2 a/ tbdrm11et (2un,krrgpacitor 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 mjyf136dg 9g xvinus charges of $ 16.5\times10^{-8 }\,C$. What is the voltage across the capacitor?    V

  The potential difference m3nu4e llij4a75)c kibetween two short sections of parallel wire in air is 120 V. They carry equalujn75ilie ml k43a) 4c and opposite charge of magnitude 95 pC. What is the capacitance of the two wires?    $ \times10^{13 }\,F$

  How much charge flows from each terminal of a 12.0-Vpk:6 m)( ede ob1l*k(s alzi2i battery when it is connectedek1 bk (ls6z:eplimai d*o() 2 to a $7.00-\mu F$ capacitor?    $ \times10^{-5 }\,C$

  A 0.20-F capacitor is desired. What ask smjz flw e08/6 ur)9f:nrz*rea must the plates have if they are to be separated by a 2.2-mm air gas8u) znme 6wf*rjlfszr/:9k0p?    $ \times10^{ 7}\,m^2$

  The charge on a capacitor increase d w fjew x)+- zv)u4,8p,wb8ahmy:shqs 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 ofr)93g n dbr3p+edq;1ie(v npdpaki4 ; $8.5 \times10^{ 5}\,V/m$ 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 opposit ev/hif*j6q *le $5.2\mu C$ 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 betwekm yap38* fmin6w4mh( en 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) andl+cl9(h p, lwl then is disconnected from the battery. When this callhw pl+c(,l 9pacitor $(C_1)$ 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 plates 5.5 *i1vg ,+wbxakcm on a side that are separated by vk,a+1iw *xgb1.8 mm of paraffin?    $ \times10^{-11 }\,F$

  What is the capacitance ol;higo8yu-l t mi5*4 tg6ek 2pf a pair of circular plates with a radius of 5.0 cm separated by gl5lt*tk g-i;6i4y up82eom h3.2 mm of mica?    $ \times10^{-10 }\,F$

  A 3500-pF air-gap capacitor is connected to a 22-V battery.bca4wv197ux d)0 ltkk If a piece of mica is placed between the plates, how mucxkbvwk0)9td7l 4u a1ch charge will flow from the battery?    $ \times10^{ -7}\,C$

  The electric field between the plates of a paper-sepjthq8mwv +c4 rz 541xxv- ,vqkarated $(K=3.75)$ 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-pzvxtjs* :h1b15 q1fctF capacitor. How much energy is stored?    $ \times10^{-4 }\,J$

  A cardiac defibrillator is used 0 kn9n allabs 1ppf):c jh860kto shock a heart that is beating erratically. A capacitor in this device is charged to 5.0 kV and stores 1200 J of energy. What is lc0 j90an f pb6kl:h1s8n)ap kits capacitance?    $ \times10^{-5 }\,F$

  How much energy is stored by the electric field between two squardwc zq4ns(g:lk+,) f p,m4e kte plates, 8.0 cm )qgw4,st : n d4ce,fkpm(k+zlon a side, separated 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 by placing two 9-in. pie pans 5 cm apac spx r,z-dwtbo:79m /rt and connecting them to the opposite terminals of a 9-V battery.r9ocpb xzwst7d:-,/ m 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 h 3;dy /a nq nmhsq;aed yiaa-rk+(-(lvqv .(,las 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 change if (a) the potential differencc-x50 ihw/q/q u dv d;q*xuxi4e is doubled, and (b)ui;0xx cqqqwi/4du- *hvd 5/x the charge on each 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 ku0m6mq3es gz+V. They then pass through a uniform electric field E for a distance of 2.8 cm, which deflects them upward so they reach the screm0uzs qme36+ gen 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 me f+c:m g+v4w3f wh3bu(/f uva CRT. The screen is 30 cm wide and is 34 cm from the 2.6-cm-fe:+w/hfg (3mu4vmw vfcb u3 +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 33rb:n-ng/kky fpu d 9jgnh6/rest acquires 6.3 keV of KE in moving from point A to point B. yg bn ndfn9p3jkk3g-//6r h: 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 o1dk1j9a5j ovqf 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 needw4wk t0: ,kz5c h22u1e hebzar 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 acce3- (x5fncz yxslerated by thousands of volts through a vacuum. If a television set were laid on its back, would electrons be able to move 3x yfcn(x5-zs 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 st x:n,,nma1n, oio vs6dored 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 isd7al4wy2;0klqwb8js connected to a 24.0-V battery until it is fully charged, after which it is dyq4lj;02bl k awdw 8s7isconnected 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 dow1uvzfe.k9,rly2xt1, ydg,g cn if the electric 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 an equilater,2l:5+ notb fa;f d8kuseq gd,al triangle (side L) as shown in Fig. 17–30. Determine the psa;8f+l,:e5df bok,d tq2u ng otential 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 ish-m9caxz gj c8klf*(; connected to a 9.0-V battery. If a piece of Pyrex glass is placed between the plates, how muchaxc9j c ;gz-lkmh(f8 * charge will then flow from the battery?    $ \times10^{-8 }\,C$

  An electron is accelerated horizontally from mq-. + a8 kqgvtoe8lik;xn+2frest in a television picture tube by a potential diffeva geolq i.f8 +2+ m;tkx-qkn8rence 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. 17–31). At what angle $\theta$ will the electron be traveling after it passes between the plates?    $^{\circ}\,$

A capacitor of capacpdi5xx,8i8 84wbzd l y,lu3nb e7 (xyiitance $C_1$ 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 mozeur +ixz15)4u4cezl1 mm5- y jl k6jake a 1-F air-filled parallel-plate capacitor for a circuit you arezexmleky 5 z)rj1-c+u zj5m14li64uo building. To make it a reasonable size, suppose you limit the plate area to What would the gap have to be between the plates? Is this practically achievable?    $ \times10^{-16 }\,m$  ----待选择----YesNo 

  Near the surface of z mxb*jm6x.-vthe Earth there is an electric field of about $150\,V/m$ which points downward. Two identical balls with mass $m\,=\,0.540kg$ are dropped from a height of 2.00 m, but one of the balls is positively charged with $q_1$ = $650\mu C$ ,and the second is negatively charged with $q_2$ = $-650\mu C$. Use conservation of energy to determine the difference in the speed of the two balls when they hit the ground. (Neglect air resistance.)    m/s

  The power supply for a pulsed n.1k dx)ybn/i bitrogen 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 differenceyof mn1 ,u(5(bdr t- u/wzxxq6 between the Earth and the bottom of the thunderclouds can be as high as 35,000,000 V. The bottoms of the 5u ,r( -6xtuwnxdo y1m( z/fqbthunderclouds 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 proviong ye- g ,0w;1wqwqz/des 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 tw-nw ,o;e q0/zqw1g yghe 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 from an identy5z/,sb7 kg/byy rnk7q(-rif ical $+33\mu C$ 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 0.15-mm-thu+fq6 qg4:yi14txzom ick piece ofymgt fqz1o 46iqu:x 4+ 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 )t0wdr(3bkuawith plate area $2.0cm^2$ and air-gap separation 0.50 mm is connected to a 12-V battery, and fully charged. The battery is then disconnected.
(a) What is the charge on the capacitor?    $ \times10^{ -11}\,C$
(b) The plates are now pulled to a separation of 0.75 mm. What is the charge on the capacitor now?    $ \times10^{ -11}\,C$
(c) What is the potential difference across the plates now?    V
(d) How much work was required to pull the plates to their new separation?    $ \times10^{-10 }\,J$

  A $2.5-\mu F$ capacitor is fully charged by a 6.0-V battery. The battery is then disconnected. The capacitor is not ideal and the charge slowly leaks out from the plates. The next day, the capacitor has lost half its stored energy. Calculate the amount of charge lost.    $ \times10^{-6 }\,C$

  Two point charges arad/:g 2llr0 pme fixed 4.0 cm apart from each other. Their charges are $Q_1$=$Q_2$=$5.0\mu C$, and their masses are $m_1=1.5mg$ and $m_2=2.5mg$
(a) If $Q_1$ is released from rest, what will be its speed after a very long time?    m/s
(b) If both charges are released from rest at the same time, what will be the speed of $Q_1$ after a very long time?    m/s

  Two charges are placed as shown in Fig. 17–35 witekx*v1-lwl4 wh $q_1$=$1.5\mu C$ and $q_2$=$-3.3\mu C$ Find the potential difference between points A and B.    $ \times10^{ 5}\,V$