If two points are at the same potentoy76 xvvv)8 0q;ttvh kial, does this mean that no work is done in moving a test charge from one point to the other? Does this imply that no force needv kv)y 6tt0oxvh8 ;v7q be exerted? Explain.

If a negative charge is initially atpq5f(ca ct 1p-1w vvzyz aeuk;42r: n6 rest in an electric field, will it move toward a region of higher potential or lower potential? What about a positive charge? How does the potential energy of the charge -vrv1ana5p:( 6 k pty ccq1uzz 4ewf;2change in each instance?

State clearly the difference (a) between electric potential and electrc 8 m2jtw+9waric field, (b) between electric powra t9jm8c2w+tential and electric potential energy.

An electron is accelerated by a potential difference of, say, 0.10 V. How muchn4n14u wvqg7yv4 b3 mq greater would its final speed be if it is accelerated w ugq4vvqn3mb7yn14 w4ith four times as much voltage? Explain.

Is there a point along the line joining two equal posit(lpbjh:uz i0l 9kwe j.7:0nyyive charges where the electric field is zero? Where the electric potentialj9wk: 0jph( zy :y7line u.0bl is zero? Explain.

Can a particle ever move from a region of low electric poten/c*gt0wss hq*tvj pr5ez f--8tial to one of high potential and yet have its electric potential energy decrease? Explait*zrth- wsq gcfje*s 8p /-50vn.

Compare the kinetic energy gained byttyqxb-w3 -d gqzu00vm 6l13d 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 cr7+z ckpevsl9jo..35g;wml p ioss? Explain.

Draw in a few equipotential lines in Fig. 16 – 31 uz,, vh.8kaxm fi2g8bb.

What can you say about the electric fieldp -w2ol.pg)ll.0gipg t8 kx e- in a region of space that has the same potential thrpept-g2)gw0l k8-l oxlgi. .p oughout?

A satellite orbits the 3jt 3 qw,k.pfo+s) 5y oby2wehg yh62cEarth along a gravitational equipotential line. What shape mu3 6e5ybg)ooyh2qc ww,h pky.fj3t2s +st the orbit be?

When dealing with practical devices, we 6t 6nup vd 1,3*-entpbe syly8often 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 fieldy e3p -nd*p,vbs6e6yl t1tun8 E, at other points?

When a battery is connected to a ah0i ;m0g+jtb capacitor, why do the two plates acquire charges of the same magnitude? Will thismbht; jaig+00 be true if the two conductors are different sizes or shapes?

We have seen that the capacitance C depends on the size2gmfw :czfljw /t(x :yeumycs3, /e- /, shape, and position of the two conductors, as well as on the dielectric constant K. What then tj/2emm/(/ s-eyu g3 xff y:z wl:,cwcdid we mean when we said that C is a constant in Eq. 17 – 7?

  How much work does the elect,gnv5 77mi y3jun *p; ifoo*qwric field 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 poif 99bfbmqpv(eq6n- 3 tnt with a potenqv9bbf9efp n t(6 -3mqtial of $+125V$ to a point where it is $-55V$ Express your answer both in joules and electron volts.
   $ \times10^{-17 }\,J$
   eV

  How much kinetic energy will an electron gain (in joules and wpg*:b5id 0r veV) if it accelerates through a potebd5* rgi:vw p0ntial difference of 23,000 V in a TV picture tube?
   $ \times10^{-15 }\,J$
   eV

  An electron acquires w mhoqy-/y06a $7.45 \times10^{ -16}\,J$ 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 electribigf3* hnd-r8*4a;qq 9k6 qkzls +f thc field between two parallel plates 5.8 mm apart if the potential differench 9n al6 rhbqqt; 4ifk*sgq*-+fz3dk8e between them is 220 V?    $ \times10^{ 4}\,V/m$

  An electric field of nf-mydq 4s;si lujserkm5)6l l3 v10wx40sb: $640V/m$ is desired between two parallel plates 11.0 mm apart. How large a voltage should be applied?    V

  The electric field between two fi d(yd 1vvx)0parallel plates connected to a 45-V battery is $1500V/m$ How far apart are the plates?    m

  The electric field between two43xgo6; 4khpj d5 cnssve;b 2m parallel plates connected to a 45-V battery is $1500V/m$ How far apart are the plates?    m

  What potential differenclz 7*w.qsi+ cze 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 power supya0g-:.k b7xog /qiq)erea2 yply, are separated by an air gap. How small can the gap be if the air is not to become conducting by exceeding its-aykga:b .qe7exgoyi2)r0 q/ breakdown value of $E\,=3 \times10^{ 6}\,V/m$?   $ \times10^{-5 }\,m$

  The work done by an externaow hm7:yag 5)+mcvdw-mvbmkzs *;)u 01tf9 nyl 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 kinetic energ1lmay ;okmzv1r(g u0 ,y
(a) 750-eV,    $ \times10^{7 }\;m/s$
(b) 3.2-keV?    $ \times10^{7 }\;m/s$

  What is the speed of a proton wht9zc-ip br/9i)tc (j nose kinetic energy is 3.2 keV?    $ \times10^{5}\,m/s$

  An alpha particle (which is a helium rbjjqebiq2.5)p (: pn 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 g*i/b2e52ia7n 3 6l ziz zte)vcf)eqhpotential 15.0 cm from a $4.00\mu C$ point charge?    $ \times10^{ 5}\,V$

  A point charge Q creates a7ry578a c6x 65)sqdehbeyjbwlfl 0,jn 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. Thi/njxlq ) f.ra9z(4ag ff 27rtas conductor carries a net negative charge, (l 2 9z.tja 4arfrfa)f/nqx7g$-Q$. Draw in a dozen electric field lines and two equipotential lines.

  (a) What is the electric potential a distance of-fd9 ljjnzw/ sto be 231phu43 $ 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 shonega:-s o )m 2jb*dl2d3yto 2vwn in Fig. 17–25. What is the potential at the fourth corner (point A):g32-moo2 n eyb d)tlvd2ja*s, taking $V\,=\,0$ at a great distance?

  An electron starts from rest 32.5 cm from a fixed point charge with wa+pu4 os6nq c9)mx-h $Q\,=\,-0.125\mu C$. 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 thr4ktbg+lh t,r1z7 zrh9npk+s ct b )0w5ee electrons from a great distance apart 9t4 bkt +rl, rb1znhw c+t0)pg s5z7hkto $1.0 \times10^{-10 }\,m$ from one another (at the corners of an equilateral triangle)?    $ \times10^{-18 }\,J$

  Consider point a which is oyouugs +* 2znqn*6a;y;n0my 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 acceq7 l3x9i p vjs.8olgt5lerate 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 distance d, as show(-q8xe3 ppwn vni9ck5 n in Fig. 17–27. Determini8(q-ck pvn wxen p935e a formula 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 prstye f z/i9lym vf39za-60*izoton (the nucleus) zy9e- y lv/mz zi9 t*saffi036in a circular 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 proton s2wq 6d:xcce3 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 momeda ;w mge6qg ( 4..s vhm9zdyj/r*p8vpnt 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 negativ 67h4hdvu rd.ke to the positiv7d 6 khv.udhr4e 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 erc3 aj/xa5j u820ju6 5 vhhfuf ,f4jncapacitor 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 capacitor holdoyd-6s9(baf sqrxc:jn *3m 4kt k qf/. $+2500\mu C$ 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 minusor2t x iht9.2t charges of $ 16.5\times10^{-8 }\,C$. What is the voltage across the capacitor?    V

  The potential difference betweh bf4afd*j:: yc+ej6b o,2i iren two short sections of parallel wire in air is 120 V. They carry equal and opposite charge of magnitude 95 pC. What is the capacitance of the two wires? i f ,:2fieybaor bjc*6j 4+d:h   $ \times10^{13 }\,F$

  How much charge flows from each terminal of a 12.0-V battery when it ed6-,vg8 )/mo 9)2xcchzpjzsz dvd-i is connected to om8v2dc-,9 /)d)g zzijpes6czdv-h x a $7.00-\mu F$ capacitor?    $ \times10^{-5 }\,C$

  A 0.20-F capacitor is desired. What area must the plates have if they arez60es :/37xfh vl,jo0rsntnq to be sx0, zlssnt 6/eorhf:n v73q0jeparated by a 2.2-mm air gap?    $ \times10^{ 7}\,m^2$

  The charge on a capacitor increases und acr 6(*lyjw4,d8m 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 u.sygj5t/3k(,rhqf ayza 1+t$8.5 \times10^{ 5}\,V/m$ 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 oppositpk(hm 7)d nz(pt. aoe7e $5.2\mu C$ 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 do1ma+t 3xibztj 8 6k*between the plates of a $0.80-\mu F$ air-gap capacitor if they are 2.0 mm apart and each has a charge of $72\mu C$ ?    $ \times10^{4 }\,V/m$

  A capacitor is charged by a 125-V battery (vxklegomgw, eio35l:/qg2k0t3h88 wFig. 17–29a) and then is disconnected from the battery. Wh2ow i3wh3m,v88o ketel x0lg5: /ggqken 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 on a si2n;5r mjb7sb* ,tr1z pz yhfz6de that are separatedb5 myzfp1 tz;jb*r ns6,z 27hr by 1.8 mm of paraffin?    $ \times10^{-11 }\,F$

  What is the capacitance of a pair of cjsz loc 9fvkxh7 *)ev/ahx(-9j .zsm 3ircular plates with a radius of 5.0 cm separated by 3.2 )ao cf7h9k *lj.smzh9 v3/v ej-z(sxxmm of mica?    $ \times10^{-10 }\,F$

  A 3500-pF air-gap cap4wji j 7)2m/;kkx wc5 ja acq.gro3 q*xu:*pbjacitor is connected to a 22-V battery. If a piece of mica is placed r aqxj w25 gp /ac)wkjk*4o7u *jm:b;cjxqi. 3between the plates, how much charge will flow from the battery?    $ \times10^{ -7}\,C$

  The electric field between the plates of a paper-separai.ue: t69jv:x+mktw w ted $(K=3.75)$ 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 capx rf-ojd-i :( fvpy8q*acitor. How much energy is stored?    $ \times10^{-4 }\,J$

  A cardiac defibrillator is used to shock a heart t 2cw cxa:ne3c/o7 tnm6hat is beating erratically. A capacitortncc7x m3 2e:oa 6wn/c 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 platesga p2 ke: fo()u7i4lrdh-c e*m, 8.0 cm on a side, separated e a- ) fhil4ru*emocdg2(k:p7by 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. pi/w 1gab2 ud1s*nf d*kae pans 5 cm apart and connecting them to the opposite terminals of a 9-V batte12*fb/* kd1n gsuwadary. 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 c7whc mc*r h o;d9r )rt0,)fm+ext-gzjharges $+Q$ 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 potentia5 n1ctyr).kkj l difference is doubled, and (b) the charge on each ).5ck1y jr kntplate 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 kV. They then paz - 9.lj3pe)y 99;d olntquol2mbp)abss through a uniform electric field E for a distance of 2.8 cm, whichd9lqla .t)y 9j) o3lo9b-p2zbnup ; em 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-m w,;1yo-- ye bmttxa 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 musea-yt1mob w;,- txy m-t 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 6.3 keV of KE in moving from poojom+ovp-htz8y *xnq4641x uint A to point1phnq*t-yoo xj6v m4 84u+zxo 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 transfers 4.0 C of charge and 4.2 Me. nt6o08kyuhpq ,x0v J 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 th( do8jlfeo1hf;bb c3 0e 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 accelerated by thousanxd4 ,c 2abm+wld* qyg4x-z3,bt.sr ytds of volts through a vacuum. If a television set were laid on its back, would electrons be able to move upward against the force of gravity? What potential difference, acting over a distance of 3.0 cm, would be needed to balance the downward force of gravity sotlc 4 ,4dawb3 gdx2+xt,zqyry -mb*.s that an electron would remain stationary? Assume that the electric field is uniform.    $ \times10^{ -12}\,V$

  A huge 4.0-F capacitor has enough sec:amn1vdx7m)o 82j utored 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 bat.7ync 8xqkv i;egmy0 )tery until it is fully charged, after which it is disconnected from the battery. A slab of paraffin is then inn)7qi y;cgkxey80mv .serted between the plates. What will now be the voltage between the plates?    V

  Dry air will break down if the electric fie g)gaseskxuk /.n-n:/s 5d q0(br4zva (uzs2pld 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 (si3j4t6dja g7gx b66djyde L) as shown in Fig. 17–30. Determine the pxgb6gyj6t3j 76j4d daotential at the midpoint of each of the sides.

  A $3.4\mu C$ and a $-2.6\mu C$ charge are placed 1.6 cm apart. At what points along the line joining them is
(a) the electric field zero,    cm left of $q_2$
(b) the electric potential zero?

  A 2600-pF air-gap capacitor is connected to a 9.0-V bav(e 0x8oqlk/qux- iw*ttery. If a piece of Pyrex glass is placed between thexe l qwoi*xk/q0(u8 -v plates, how much charge will then flow from the battery?    $ \times10^{-8 }\,C$

  An electron is accelerated horizontally from rest in a television picture 6 s1 +usty0w/ yvv)xentube by a potential difference of 5500 V. It then passes/xs u )nes01wt6vy+vy 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 capacit*mi ba+do zyshu), ev3x9:ll*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 wantrekwq2 w/ x().svf1 ql to make a 1-F air-filled parallel-plate capacitor for a circuit you are building. To make it a reasonable size, suppoxqw2 klw rsf vq(1)e./se 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 bxb w(hpm/y /*the 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 pib 4tq4k j,fqol */q1culsed 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 the Earth 7ws 7i:wprs1 wand the bottom of the thunderclouds can be as high as 35,000,000 V. The bottoms of the thunderclouds are typicapi:1w 7rsww7slly 1500 m above the Earth, and can have an area of $110km^2$ Modeling the Earth–cloud system as a huge capacitor, calculate
(a) the capacitance of the Earth–cloud system,    $ \times10^{-7 }\,F$
(b) the charge stored in the “capacitor,”    C(Round to the nearest integer)
(c) the energy stored in the “capacitor.”    $ \times10^{8 }\,J$

  In a photocell, ultraviolet (UV) light provides enough energy t; zyjo4 nolank/;f1 bs2)6-ndq vwf,ko some electrons in barium metal to eject them from a surface6zj;y)k,s14qawlvf nof ;/odnnb -k 2 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 cm fr8003 nh pgaski 98w,pf;bloh 4y :wrwbom 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 from0d -rsm-p)o .wup7tol3gn)ee two 1.1-cm-diameter coins separated by a 0.15-mm-thick piece of paper .s dnwp0ot3g- )r7mpeeuo)l - $(K=3.7)$ 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 capar3j pl,w yz q p:8mjq((gy:jv5citor with 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 are fixed 4.0 cm apart from ey:w l+o(x1,1xaay n)4sxpk.ex izs+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– m).0b-1r f-iii qrdce35 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$