If two points are at the same potential, does this m5;yih z-bcwf.:muw 8qean that no work is done in moving a test charge from one point to the other? Does this imply that no force need be exerted? Explai zy.;mq w hwc85ib:-ufn.

If a negative charge is initially at rest ieb6fw dal 9e 0)xtw7ge2 lk4l8n an electric field, will it move toward a region of higher potential or lower potential? What about a positive 094 8led2g)tx wkel6f ble wa7charge? How does the potential energy of the charge change in each instance?

State clearly the difference (a) between electric potential and electrc+rh hby4o)( vic field, (b) between electric potenh(v+ b)ycroh4tial and electric potential energy.

An electron is accelerated by a potential difference of, say, 0.10 o.q0* zy jd v39mbe+bhV. How much greater would its final speed be if it is0*9ezm dq ybb3j+ .ohv accelerated with four times as much voltage? Explain.

Is there a point along the line joining tw;nh 1hzlq7 nl/)b-hpho equal positive charges where the electric field is zero? Where the electric-n l1hhzhql;n/7b)ph potential is zero? Explain.

Can a particle ever move fwrs0j v3it 7p1rom a region of low electric potential to one of high potential and yet have its electric potej0 ip rv7s1wt3ntial energy decrease? Explain.

Compare the kinetic energy 41,fzrzy-sir8a5expn8 2s 1jj dh ko: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 p lwguyb6;6lf5k 0)3dassu8c cross? Explain.

Draw in a few equipotential lines in Fig. 16 – 31b. hpq6b8 6b gl(;2es aig

What can you say about the electric field in a reg 9xnd:5xb0 7diwhx w/eion of space that has the samed0/79d w 5:xeibw nhxx potential throughout?

A satellite orbits the Earth along a gravitational equipotgs3(.01fojawax v ef5ential line. What shap 3f51a(0xfawo e gs.vje must the orbit be?

When dealing with practical devices, we often take the ground (the Eartb+rkn b0hfk1 8+b-l geh) to be 0 V. If, instead, we said the ground was how would this affect (a) the potential V, and (b) the electric field kh bb +r1-g80b+nelfkE, at other points?

When a battery is connecteda llk5j b4-1tv*zs( ogqwh+(l to a capacitor, why do the two plates acquire charges of the same magnitude? Will this be true if the two conductors are different sizes or shapeg*laj-v h1((qslo+b t4 l5kzw s?

We have seen that the capacitance C depends on the size, shape, y. ekk:1nj v)zo+f.y 6jp v2k:htw4uy and position of the two conductors, njk2zvuk6o: .4y.jk p )vhy1:wtyef +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 7y:9vqomx6hh 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 point with a hlet7cdh2u; f8f/x6y potential oc7ly2tx/6dh ;fu hf 8ef $+125V$ 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 (iny)f2 ijas7otfot:+/d joules and eV) if it accelerates through a potential difference of 23oa/ij t2ff7t)d :o+s y,000 V in a TV picture tube?
   $ \times10^{-15 }\,J$
   eV

  An electron acquirespowagy7z7 h 34 oa*0xsw+e7be $7.45 \times10^{ -16}\,J$ 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 apart if 7ymz84ze mhi;the potential difference between them is 2204zh my ez8i7;m V?    $ \times10^{ 4}\,V/m$

  An electric field ofi1 agd)/lvs,l6gujrq1 x1;s-/r k rwh $640V/m$ 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 h6lh pj:;q)bqnowjpzez d//0kq9d3 z/ p98gm45-V battery is $1500V/m$ How far apart are the plates?    m

  The electric field between two parallel onm 0qotciy100f3:ow plates connected to a 45-V battery is $1500V/m$ How far apart are the plates?    m

  What potential difference is needed to give a helium n(x/4 bk5g 0mka1;1qidesvx eeucleus $(Q=2e)$ 65.0 keV of kinetic energy?    $ \times10^{4 }\,V$

  Two parallel plates, connected to a 200-V power supply, are separaxq)s;0e, sq ef*/ol5; vfjkolfr-oe s8*(bj hted by an air gap. How small can the gap be if the air is not to be8jsfkfx;j/* b,f5 sqq;(0e*o )hos-reole lv come conducting by exceeding its breakdown value of $E\,=3 \times10^{ 6}\,V/m$?   $ \times10^{-5 }\,m$

  The work done by an ex 17+xev. ik27zj,n ux tpvn4jfternal force to move a $-8.50\mu C$ charge from point a to point b is $15.0 \times10^{ -4}\;J$. If the charge was started from rest and had $ 4.82\times10^{ -4}\;J$ of kinetic energy when it reached point b, what must be the potential difference between a and b?    V

  What is the speed of an electron with kinerbyvgqh 9;y+5k 8(uzahf ex8 2hhh-,r tic energy
(a) 750-eV,    $ \times10^{7 }\;m/s$
(b) 3.2-keV?    $ \times10^{7 }\;m/s$

  What is the speed of a proton whose ki7c;i 25jhcw2w a .bxxmnetic energy is 3.2 keV?    $ \times10^{5}\,m/s$

  An alpha particle (which is a heligtb *:pzad0/*p5m ulovx+y5oh8 ke7fum 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 gz0 j0 3st)ql2t,(bls2y fht k15.0 cm from a $4.00\mu C$ point charge?    $ \times10^{ 5}\,V$

  A point charge Q creates an electref-eqb qxp:qq )0.kf+ic 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 c m1+4hsio47hebtp bjbv )( r-r3/n4ihzocmj.arries a net negativ j3mr +7moh/ -bh (vbc4hntse1jprb ).4i4zi oe charge, $-Q$. Draw in a dozen electric field lines and two equipotential lines.

  (a) What is the electric poteni1(w h:r v)lzt* exm7ntial 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 sqbtg)+jk l nm:c 0.z/htuare of side L as shown in Fig. 17–25. What is the potential at the fourth corner (point .k0zcgjmthb) lnt/ :+ A), taking $V\,=\,0$ at a great distance?

  An electron starts frol;icr 8qp5 ezrfh t483m 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 2wqjm y/3y.w.h 6)btkdqckg + great distance apart kh .+q)qkb/ c wjtw. d63ymy2gto $1.0 \times10^{-10 }\,m$ from one another (at the corners of an equilateral triangle)?    $ \times10^{-18 }\,J$

  Consider point a which iej*lv/v; mian ax ,5he9ndb9w4f +e o,s 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 musgp- 1 t:p*jh;tpr 88uha nag4zt 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 arere ea00otb,p (j2, r x5jw,tzs separated by a distance d, as shown in Fig. 17–27. Determine a foo r a5etb2rsp0w j,,, z(etxj0rmula 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 ele:y:wwt9oz3 z ;0pjdxbctron orbits a proton (the nucleus) in a circular o wpowz 9;:bt30 :xzjydrbit 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 prot//-.xzh uiuf 9;zovr,y9 vfrc on 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 mgr -n;*zg7vn 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, considlk0b2xs8l,rd ered as a vector, points from the negative to the positklsr 2, 8bdl0xive charge. 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 cajqly4- n66q+yhs b x4fpacitor 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 capacito)d /sk:dsk-b6ec llu/r 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 plmr7ghxz) ij 8xf6;,me us and minus charges of $ 16.5\times10^{-8 }\,C$. What is the voltage across the capacitor?    V

  The potential difference betwee0i) f /kvw fcf+b8avs-,n4 pbnn two short sections of parallel wire in air is 120 V. They carry equal and opposite charge of magnitude 95 pC. What is8 isv)vpnafw,-0nkcbb /ff4+ the capacitance of the two wires?    $ \times10^{13 }\,F$

  How much charge flows fromy;jc/cva*i4t 8x.qz.zqva-y6 bw3fv each terminal of a 12.0-V battery when it is connected to a 8zqfy6 azj q/3vayc ivv.-*.4cx tw ;b$7.00-\mu F$ capacitor?    $ \times10^{-5 }\,C$

  A 0.20-F capacitor is desired. What area must cc cm;ctqb)k1g1s5 9qthe plates have if they are to be separated by a 2.2-mm air gap?g1sq mtc1)bc 5c;c9kq    $ \times10^{ 7}\,m^2$

  The charge on a capacitor incr-b j)utyy: c3veases 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 qael mtjm -oaw ,xvj * (xh78z5927lmw$8.5 \times10^{ 5}\,V/m$ 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 oppositeaew/vcs::1q7 u 5ft 9 v ,yiqog2wq3is $5.2\mu C$ 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 between th,5f5 r.q//+ im pq4avocrf utxe 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 125-0f2zd,bdcz9p y ): akxV battery (Fig. 17–29a) and then is disconnecte d yzz2)x9 afc0bk:,pdd from 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 parallel plates 5.5 cm o1gv76wa )rasyn a side that are separated byr)g6 sy1vw7 aa 1.8 mm of paraffin?    $ \times10^{-11 }\,F$

  What is the capacitance of a pair of circular plates with : 8wr bvl-eotah6+x 2ta radius of 5.0 cm separated by t82br+ hae6 vtw:-xl o3.2 mm of mica?    $ \times10^{-10 }\,F$

  A 3500-pF air-gap capacitor is connected to a 22-V battery. If a pphp,., ; qmgakw7rhcs urk9 72iece of mica is placed between the plates, how muc7ks, wh kp.2rap mugcqh;7r 9,h charge will flow from the battery?    $ \times10^{ -7}\,C$

  The electric field between the plates of akaci;p: yiii4 9jx,pyo x s7p:9 c;nd7 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-pF3xsu adw 8--o9i0smjt capacitor. How much energy is stored?    $ \times10^{-4 }\,J$

  A cardiac defibrillator is used to shock a heart that is beating ed f;7prx( aenky1 m:s7rratically. A capacitor in this device is charged to 5.0 kV and stores 1200 J of energd ;p(r y7nkxm s17f:aey. What is its capacitance?    $ \times10^{-5 }\,F$

  How much energy is stored by the electrifmwh9 8thy4xa 0o,uo. phid (3c field between two square plates, 8.0 cm on a side wmohth4u,p.a8 x(39hoy 0df i, 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 placq4i6z+ d4(r9-dtwgod jhxs n 4ing two 9-in. pie pans 5 cm apart and connecting them to the opposite termigr64 q-dwj+ds4nz9di 4h otx(nals 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 chaih58uu e: +rthrges $+Q$ 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 mnm(q y;g. iq9 7n(9ddx mqels0v8qn; (a) the potential difference is doubled, and (b) the charge on each plate is doubled, as the capacitor remains connected to a bagnmndm .7l;n 9mq((0x8qs d yviqeq9;ttery?

  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 ac) .cjx;y qdraw* 6+qymcelerated horizontally by 7.0 kV. They then pass through a uniform electric field E for a disrm;)+d xqj ywac* .6qytance 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 accelerate 6l,epi9f7s mc*ikmy 8d by 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 tp67s,m ify98lem*ki che 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 poixs3a95j/nufrppu:l e m :03cn (urts4nt A to point B.9u0: a5 3npnu4l:scxtp(jr/ ues frm3
(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 e6u,pjwcy cr )e72nv( bnergy 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 0ilwacb) uc03the 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.i:df1n5j)k mf uh. xn accelerated by thousands of volts through a vacuum. If a television set were laid on its back, would electrons be able to move upwfn m5 :1uj) .hdiknxf.ard 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 en+a(q :1rfrdk:g45x . dvr igx ajx2yif4bi*i3 ough 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 connected6wlokyym cv ;+g2s3 (ehk r7;e 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. ;ye3 glw e76o(hcvr2km ks+y;What will now be the voltage between the plates?    V

  Dry air will break down if the elecej:+suh3u0mx a3t jb.(qylo 7-g6gs bu0lo 8 ctric 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 equilateral triangle (xprvnms/f 2x 9o 8s-: 23rgiiw8 d .md;ci5vryside L) as shown in Fig. x-2 p5; yfwsdcri2 :38vd i8nvo9.mr/mxs igr 17–30. 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. i/:yxl fu*oe(0-V battery. If a piece of Pyrex glass is placed between the plates, how much charge wiu x:yl/*(feoi ll then flow from the battery?    $ \times10^{-8 }\,C$

  An electron is accelerated horizontally from rest in a television pi/q5 riv0 ykm0ncture tube by a pkr0/y qmn0 vi5otential 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. 17–31). At what angle $\theta$ will the electron be traveling after it passes between the plates?    $^{\circ}\,$

A capacitor of capacitance j: .eq;m4p 1nk8okjdo ;na u-x$C_1$ 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 youza41 hn4- p5ccm8m pya want to make a 1-F air-filled parallel-plate capacitor for a circ am5pph 4c-z41cnm8 yauit 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 plates? Is this practically achievable?    $ \times10^{-16 }\,m$  ----待选择----YesNo 

  Near the surface of the275zl r;qzlez 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 nitrog od q rgf,bx(0s,wp2o8en 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 pote )pd1+k+g,kloopw9 a lntial difference between the Earth and the bottom of the thunderclouds can be as high as 35,000,kol+ a po 9+g,)klpwd1000 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) lik:n; ,popw ckakcet4)je3 q;/ ght provides enough energy to some electrons in barium metal to eject them fropt;j /eckwnpo,ec kqk34 a;):m 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 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 cmskvi v-*hk8 oxkvje ,t2uka:7fw5.i0 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 twmfd7jfs)*k *k o 1.1-cm-diameter coins separated by a 0.15-mm-thick piece of papej)k*mfsd kf 7*r $(K=3.7)$ 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 plateo;ad)5kf, qu s 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 areov7va4(jch)z 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 shozq(9nmys awo4 15i8u ewn 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$