If two points are at the same potential,cxh5xe.mz9*qz0 t r3a does this mean that no work is done in moving a test charge from one point to tr* zt9qm h53acz. e0xxhe other? Does this imply that no force need be exerted? Explain.

If a negative charge is initially at rest in an electric field,m*pd .xfta0.:; rgdgzq0y s1/c:j vs c will it move toward a region of higher potential or lower poten vdgz g xpsqj.01/r*sdc m: :cf0.y;attial? What about a positive charge? How does the potential energy of the charge change in each instance?

State clearly the difference (a) between electric potential and electric:t9 e u4pul)cxe db*/v field, (b) bet*etlxp9e )cdv u/b4u:ween electric potential and electric potential energy.

An electron is accelerated by a potential di7u:nfy+jebg2 fference of, say, 0.10 V. How much greater would its final speed be if it is accelerated with four tng+f2uey :j7 bimes as much voltage? Explain.

Is there a point along the line joining two equal positive charges where the el n 8v/1c5+8skt.gl742 rqksn ygfy cjeectric field is zero? Where the electric potential is zeroqgl8ce14rn 7sn gy+ f2c kt/j5sy8vk.? Explain.

Can a particle ever move from a region of low electric potential to one -s :2igas4 o73adfa4m2anq/ p ebp4ngof high potential and yet have its e4-d n4/bae7 psnf 4oq asp23amg2ia :glectric potential energy decrease? Explain.

Compare the kinetic energy gained by a proton vz4+)(*wonxj ga +sxoe *q2cs $(q=+e)$ 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? E; od nc(-app(sxplain.

Draw in a few equipotepy2lgm ;d,ix5 ntial lines in Fig. 16 – 31b.

What can you say about the electric field in a region of space that has the aob2c z3z2x311 ofdrasame pobzr3x1 ad13faz2o2o ctential throughout?

A satellite orbits the Earth along a gravitational equipotential line. What shldn p:)w08xgu ape must the orbit ):xnwdl8 0pug be?

When dealing with practical devib36e )f/kkgoe ces, we often take the ground (the Earth) to be 0 V. If, instead, we said the ground was how would this affect (a) the potential V, and (b) the electric field E, at other point/efkg e36) okbs?

When a battery is connected to a capacitor,w6igc9g6 53yi2vij nq why do the two plates acquire charges of the same magnitude? Will this be true if the two conductors are different sizes or s6 q69cvy5niig g2ji3whapes?

We have seen that the capacitance C depe0 xltj(,3p;oc3uj n,5h1ylxxnw 3rmmnds on the size, shape, and position of thlx0cj;3 jxnhmlor t,1,mxw3( 5p y3nue two conductors, 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 fieveaiiuu 4+.dr vzd0(+ld 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 movin)9oyspmbfb :m-i38x0 sp g /ya sok82mg a proton from a point with a potensis 8p 02yab8x/o:o)k-9m3 bgys fmmp tial 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 2 0fftafs,mt* and eV) if it accelerates through a potential difference of 23,000 V in a TV picture a*m0 ,2t sfftftube?
   $ \times10^{-15 }\,J$
   eV

  An electron acquires 2n8 t86k lhb0xwhkoy8lt.z)b $7.45 \times10^{ -16}\,J$ 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 parallkym6vl jzl -v/7st--qw:wj2qel plates 5.8 mm apart if the potential difference between them is 220 V?vy:6l /sqvwtw -klq-7 j j2m-z    $ \times10^{ 4}\,V/m$

  An electric field of irk7q/ten g yn*4y b/5$640V/m$ 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 r ypns*ek/f e3:vs5 k)q6m, mgk( alp:45-V battery is $1500V/m$ How far apart are the plates?    m

  The electric field be qtklnoxc *1m /r;5x5m+by8fk tween two parallel plates connected to a 45-V battery is $1500V/m$ How far apart are the plates?    m

  What potential differen 10wc8pmo j/+8xltvab1a . vigce is needed to give a helium nucleus $(Q=2e)$ 65.0 keV of kinetic energy?    $ \times10^{4 }\,V$

  Two parallel plates, connected to a 200-V 3x+zeb *8oej3pv v3gfo +cf7rpower supply, are separated by an air gap. How small can the gap be if the air is not to become conducting by exceeding it3ez vpf*+e xjgbo 3fr83v+7ocs breakdown value of $E\,=3 \times10^{ 6}\,V/m$?   $ \times10^{-5 }\,m$

  The work done by an exth.m q;z x1nzz-ernal 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 avlyt-3igod( ie p 3r/)n electron with 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 kinetic energy is 3.o7u 2d x rih6r 4z26a*dmxq0+omqkui,* r7 wnz2 keV?    $ \times10^{5}\,m/s$

  An alpha particle (which is a helium nucleu* (tlhs8cr5klya7e 2g s, $Q=+2e$, $m\,=\,6.64\times10^{-27 }\,kg$) is emitted in a radioactive decay with $_{KE}$ = $5.53MeV$ What is its speed?    $ \times10^{7}\,m/s$

  What is the electric potential kg e0;q5nt np (8g.xyp15.0 cm from a $4.00\mu C$ point charge?    $ \times10^{ 5}\,V$

  A point charge Q creates an electric pot8x ct3/i ,i0xktf9,c5jhb p n/yvlr/nential 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 6 sgt8ea9rw qdt;9z k1yo vob-+x1ks2the shape of a football. This conductor carries a net negative cha vo+1srb sqy2dt e-ag;z98oxt k6k91wrge, $-Q$. Draw in a dozen electric field lines and two equipotential lines.

  (a) What is the electric potential a distansuqjs,oeqogd0 k2(zpt*c6 x6df+i14ce 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 9qogd *l4 xz,lk8*m clas shown in Fig. 17–25. What is the potential at the fourth corner (point A)*omkl*8dqzc 9x 4l,l g, taking $V\,=\,0$ at a great distance?

  An electron starts from rest 32.5 cm from a fixed point charge w8d-t*+ oj iaddt)/x sgith $Q\,=\,-0.125\mu C$. 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 7e/.va r+c uaedistance apart to+cvu e/eraa. 7 $1.0 \times10^{-10 }\,m$ from one another (at the corners of an equilateral triangle)?    $ \times10^{-18 }\,J$

  Consider point a which is 72 cm north 4y)i:*zmg8uz s/ e bxaof 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 accelerate a pr pgvxy3/gw- 1yoton (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 sepa )rvdp8c fd.*q0o5auzrated by a distance d, as shown in Fig. 17–27. Determine a 0ucqo8 zvr 5d d.a)p*fformula for $V_{BA}\,=\,V_B-V_A$ for points B and A on the line between the charges.

  In the Bohr model of the hydrogeuoz8f+; if ;djn atom, an electron orbits a proton (the nucleus) in a circular orbit of rjiof; 8z;ud+f adius $ 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 arerpwkpl-s 15d a r4bza*p:4q;k $ 0.53\times10^{ -10}\,m$. apart. What is their dipole moment if they are at rest?    $ \times10^{-30 }\,C\cdot\,m$

  Calculate the electricyvz wn4 rn*2(-jwa9wb:t h*vs8: ufe q 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, conlv yoxgqzg vd .v:481-pt/bl( sidered as a vector, points from the negative to the positive charge. The water molecule, Fig. 17–28, has a dipole moment which can be-t o (v.g/l8q4:b1gd xvyzv lp 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 hw97:mw7q m:eianp a1otq 9z8hold $+2500\mu C$ 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 capacitor holf.zzs m05 ;shed $+2500\mu C$ 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 charges 8 66bryde.w5bivy,xka8boku v5, w4pbeqq, 8of $ 16.5\times10^{-8 }\,C$. What is the voltage across the capacitor?    V

  The potential difference between two sbcw3 2,l,i(ot arq8rbhort sections of parallel wire in air is 120 V. They carry equal and opposite charge of magnitude 95 pC. 2w(3bc qrb8,,ortlai What is the capacitance of the two wires?    $ \times10^{13 }\,F$

  How much charge flows from each terminal of a 12.0-V battery when it is co6 fve:i9ez4qcmr hb9up,4h d9nnected to b9fvi6h9 r dqe 4 ce:,49muphza $7.00-\mu F$ capacitor?    $ \times10^{-5 }\,C$

  A 0.20-F capacitor i.ccy )rwr:-tw s desired. What area must the plates have if they are to be separ.w trc-wr:cy) ated by a 2.2-mm air gap?    $ \times10^{ 7}\,m^2$

  The charge on a capaca 9ou+wq ;4 b6ev0pmqwitor 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 dmggz,:sn.3 ;g3f qjr $8.5 \times10^{ 5}\,V/m$ 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 opposi8 2x9so* xo*njm ;bgfxte $5.2\mu C$ 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 ttqzyp4..) 8sw rs hf+whe 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 12n a,1n3pq*y md5-V battery (Fig. 17–29a) and then is disconnected from the battery. When *yadq p,nn31 mthis 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 paralle6a, kqpvmc9l4u t e+zsj07 sg8l plates 5.5 cm on a side that are separated zt ksjc8a, 7 msqvg lu04+e9p6by 1.8 mm of paraffin?    $ \times10^{-11 }\,F$

  What is the capacitance of a pair of circ b13i1xbr0zbc ular plates with a radius of 5.0 cm separated by 3.2 mm 1 zcx0ib13bbrof mica?    $ \times10^{-10 }\,F$

  A 3500-pF air-gap capacitor is connected to a 22-V battery. If aaola +* dv dz(tb8+ktk0c*9ir piece of mica is placed between the plates, how much charge will flow from the battery? ibk9t dvr 8+ak dzc0(lta** o+   $ \times10^{ -7}\,C$

  The electric field between the plates of a paper-separat,m-knovm7: ocg z (xi6ed $(K=3.75)$ 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 capn8 z2num8o*kb acitor. How much energy is stored?    $ \times10^{-4 }\,J$

  A cardiac defibrillator is used to shock a heart th tffakcgcyn;k7,9o ) (at is beating erratically. A capacitor in this gcytok 9nkfa;(,f )c7 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, 8.0v4oc*xe x-)(t: 8zs,oaqwumy cm on a side, separated by a 1.5-mm air gap? The charges on the plates are equal and opposite and of magnitud4 *v sy(8ceaxxt:m-owu) ,z qoe $420\mu C$.    J

  A homemade capacitor is assembled by placing two 9-in. pie pans 5 cm apart ah,o *0skryax)9ss8pg nd connecting them to the opx0pogssh k9, 8a)r*y sposite 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 0r- qjqph(oy3fixed 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 xuk yp92xh:jao, cx9+ change if (a) the potential difference is doubled, and (b) the charge on each plate is92 : x,a9ok+xcjyxuhp 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, elec / ;td;egap5m( x0fcimk p0mhdx6u9r8 trons are accelerated horizontally by 7.0 kV. They then pass throudf (pxi gp9k80cue;hrtma0m6m5;/ dxgh a uniform electric field E for a distance of 2.8 cm, which deflects them upward so they reach the screen top 22 cm away, 11 cm above the center. Estimate the value of E.    $ \times10^{5 }\,V/m$

  Electrons are accelerated by 6.qkb colf39 udw7km77*0 kV in a CRT. The screen is 30 cm wide and is 34 cm from the 2.6-cm-long deflecmuko7 qcb*fw7l 7dk 93tion plates. Over what range must the horizontally deflecting electric field vary to sweep the beam fully across the screen?    $ \times10^{5 }\,V/m$ to    $ \times10^{5 }\,V/m$

  An electron starting from rest acquires 10pldi (k( chai(pz4 4id;fueh3 a dz;6.3 keV of KE in moving from point A to pointldhi3i 4ia ;z;e (h(u(14cdpakd0 fpz B.
(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 tra4obgc2a 1ez0i nsfers 4.0 C of charge and 4.2 MJ of energy to the Earth.
(a) Across what potential difference did it travel?    $ \times10^{ 6}\,V$
(b) How much water could this boil and vaporize, starting from room temperature?    kg

  There is an electric field near the Earth’s surface whose magni6lxpxxn*d .*si 2ivw 9 6/nhfkyv7s4mtude is about $150\,V/m$ How much energy is stored per cubic meter in this field?    $ \times10^{-7 }\,J/m^3$

  In a television picture tube, electrons are accelerated by thousanq .h e qnhwp7twr +sgi.*t.s5ix /oc0(ds of volts through a va.wg e (. qht+ /.ts0pqoni w7xrh*5csicuum. If a television set were laid on its back, would electrons be able to move upward against the force of gravity? What potential difference, acting over a distance of 3.0 cm, would be needed to balance the downward force of gravity so that an electron would remain stationary? Assume that the electric field is uniform.    $ \times10^{ -12}\,V$

  A huge 4.0-F capacitor has enough stored energy to heat 2.5 kg of water from 21zwfkj10, vrp5q g7tw6$^{\circ}\,C$ to 95$^{\circ}\,C$. What is the potential difference across the plates?    V

  An uncharged capacitog-g )oibrmj3u2x )uvko 82t .v9ht i;er is connected to a 24.0-V battery until it is fully charged, after which it is disconnecteutr;)j)m vig92io t xv-2ekghbo83 .u d 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 down if the electriowez/3 z51gah ( jb8u5sq,ls a+wsem6 c 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 (side L) as xroc5pc zq*9 vf )3,dbshown in Fig. 17–30. Determine the potential at the midpoint ofq9,f*or3 5v )cc pdxzb 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 connxzfj:kzs*w ;q 0,w1ey ected to a 9.0-V battery. If a piece of Pyrex glakyx :f; qe1j*,zw0 szwss is placed between the plates, how much charge will then flow from the battery?    $ \times10^{-8 }\,C$

  An electron is accelerated horizontally from rest in a 3+ qa7hixmo28m8,ftnh)yj lf: q,dvttelevision picture tube by a potential difference of 5500 V. It then passes between two horizontal plate)a7:, mnlhd2 t8yqm o8q hf ,jt+fv3xis 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 capacitanceuvhn)xn)2g+ 1d xof5*x( tsqd $C_1$ 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 aifzv-n32 jh8+smeqc 1rr-filled parallel-plate capacitor for a circuit you are building. To make it a reasonable size, suppose you limit the plate area tqh r3+jzf2 ecm-s 8v1no 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 is an ele994w/qkuq9e h)lg+ l lnm v lz:5,n2s:d ciqlectric 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 nitrogen laser has a eoxy62m w0hv ru 73,ih$0.050\mu F$ capacitor with a maximum voltage rating of 30 kV.
(a) Estimate how much energy could be stored in this capacitor.    J
(b) If 12% of this stored electrical energy is converted to light energy in a pulse that is 8.0 microseconds long, what is the power of the laser pulse?    $ \times10^{5 }\,W$

  In lightning storms, the potential difference between the Earth and the botto3ke6cx u(/4al u b1,b)8aou thvwrk 6ccu0c,v m of the thunderclouds can be as high as 35,000,000 V. The bottoms of the thunderclouds are typically 1500 m above the Earth, and can have6c( uarub16 kb43, u,xe)ucca8hc vvlo0kw/ t 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 provid(/ spxvjl:fm 4 l1oh*pes enough energy to some electrons in barium metal to eject them from a surface at high speed. See Fig. 17–33. To(jh m14v:*lpl xsp/fo 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 36125wn0mv v;kt svlhr9 jjquh,x 7d6h4 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 se5en/qfk;0 gys2 od xfsnj3ck(xz*p2 5parated by a 0.15-mm-thick piece of03fxp(q2ckon/;s5ndjefzy2s *k5g x 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 area 5k.po+v hm4 vu$2.0cm^2$ 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 fromt8r:iif y4/y5e qd.i e 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 showxa3nbc 9it4(ri -h7mhiz1qf g0ye : ohj1.*uyn 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$