If you charge a pocket comb by rubbing it with a silk scarf, how can you detwn :yg* lpr8g*ermine igyw gnlrp:8* *f the comb is positively or negatively charged?

Why does a shirt or blouse taken from a clothes dryer so+xxpxuq: cr9r2o1 c)imetimes cling to your boc+r2xu )qxo irx:19pcdy?

Explain why fog or rai dgaocse r; nex9):5q;n droplets tend to form around ions or electrons in the aie);a:;cn rosg 5e9dxq r.

A positively charged rod is brought close to a neutral piece omq;x8orq;; o of paper, which it attracts. Draw a diagram showing the separation of charge and ;8; mqoqr; ooxexplain why attraction occurs.

Why does a plastic ruler that has been rubbed with a cloth have the abixd q.hrh0um88 2n-.3zoh lgu xlity to pick up small piecesg3rhou-q xz dh 8mu8h.2x.ln0 of paper? Why is this difficult to do on a humid day?

Contrast the net charge on a conductor to the “free chargez,gu xzmi / iw8g7sr7ldn0f q3:q3js 7s” in the conductor.

Figures 16–7 and 16–8 show how a charged 13f4uib j;c()xxi h f/h3ptw wp2lh:v:3nnmmrod placed near an uncharged metal object can attract (or repel) electrons. There are a great many electrons in the metal, y(phl m2 /nh1j3)uitwfpm 33x4 ni wv:xbf c:;het only some of them move as shown. Why not all of them?

When an electroscope is charged, its two l86j. tdbgty ytb9.a1ceaves repel each other and remain at an angle. What balances the electric fb.tbga y86t 19cytdj .orce of repulsion so that the leaves don’t separate further?

The form of Coulomb’s law is very similar to that for Newto*el5 kqnd)w+ sn’s law of universal gravitation. What are the differences between these two laws? Compare also gravitational mass and electr5qs) kn*lw +edic charge.

We are not normally aware of the gravitlbompqlspn1 e73 x h+ ;6e:qu3ational or electric force between two ordinary objects. What is the e pu3 qel sn+ xo16m:q7;bp3lhreason in each case? Give an example where we are aware of each one and why.

Is the electric force a conservative force? Why or why not? (See Chapter 6.)0r(q w4 d,d*rj7dtfxf

When a charged ruler attracts small pi,a ji+g6 lk14sgj .cmoeces of paper, sometimes a piece jumps quickly away aftl ca,ojm6.1k+ g4 ijgser touching the ruler. Explain.

Explain why the test charges we use when measuring electrf 4yaz *:;3lbirgo7byehcoj s j*0 og( c,-j,vic fields must be smalli 7a3-*rc;o zjl j( :4b,b jfghv yoecg,*s0yo.

When determining an electric field, must we use a positive test cha5lt 28x. fbadcrge, or would a negative o8f.d 5 ax2cbltne do as well? Explain.

Draw the electric field lgr+bel6yw- 6zf;l;i fines surrounding two negative electric charges a distance l apart+f ;yglbrf6- el6iz;w.

Assume that the two opposite charges in Fig. 16–31a are 12.0 cm apa pp (tv,idu:b6rt. Consider the magnitude of the electric field 2.5 cm from the positive charge. On which side of this charge — top, bottom, left, or right — is the electric field t:tpd,pb 6u (ivhe strongest? The weakest? Explain.

Consider the electric field at points A, B, and C in Fig. 16–48. First draw an ny;z ;cm)4jpon 0ouc/wg *lo(qnqh40 armclogqn hw ;oq*)u n on4jcz(0/40p y;row at each point indicating the direction of the net force that a positive test charge would experience if placed at that point, then list the points in order of decreasing field strength (strongest first).

Why can electric field lines never croslpn8, 5hp3vj7rbf7 lts?

Show, using the three rules for field lines given wi:b0; rc *qj1x+2 b vzlg9ikqin Section 16–8, that the electric field lines starting or ending on a single point charge must be symmetricavk1 2i+w0:ijqbb9xz gq rl* c;lly spaced around the charge.

Given two point charges Q and 2Q, a distance l apart, is t8o4 mw5 x5yjyfc 6 t6bd1rxyy3here a point along the straight line that passes through them where E=0 when their signs are (a) opposite, (b) the same? If yes, state roughly where txt3yyxfw854yrcd66 5bmo1 jy his point will be.

Consider a small positive t :g 6c(ithp)nrlczk7*utg pieo4m-( ,est charge located on an electric field line at some point, such as point P in Fig. 16–31a. Is the direction of the velocity and/or acceleration of the test charge along this li (kce-i * t p,or g4nighl(zt6mc:p)u7ne? Discuss.

Sketch the electric field lines for a uniform line of charge which z5fr b(*nv wu;is infinitely long. (Hint: Use symmetry.) Is the electric field unib w5u *(nv;zfrform in strength?

If the electric flux through a closed surface is zero, is the electric fisat,(c1i ;7vlk +k sopeld necessarily zero at all points on the1sclik k+vto,pa7s; ( surface? Explain. What about the converse: If $\vec{E}\,=\,0$ at all points on the surface is the flux through the surface zero?

A point charge is surrounded by a spherical gaussian surface of radius r. I)9z2 b oju, num:/wpgyf the bzpyn ou2u, jmw/9g ):sphere is replaced by a cube of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a chdr 3scmqrm,7,zn m n;,arge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attractieizc8bsii;, +w-pmbh k1+ j 4xon between an iron nucleus ic,j e4+;i1 k+xw m8-iz sbpbh$(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive pv/9y9j6e g*,i0b1 gq9vybibbb8rueelectrical force between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of the ubqzg0ypl*oq-: : oc6 force a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exert a force ,wp2fg+h f *2(elgibs of $ 3.2\times10^{ -2}\,N$ on each other. What will be the force if they are moved so they are only one-eighth as far apart?    N

  Two charged spheres ar*zfr,l( 3dh 6: y(aemu hcxv)me 8.45 cm apart. They are moved, and the force on each of them is found to have been tripled. How far apart ac, 3z am(lh*:vd6xf huy(m)er re they now?    cm

  A person scuffing her feet on a wool rug on a9t(1 +afk qhkg dry day accumulates a net charge oh+aktkf1(q9 gf $-42\,\mu C\,.$ How many excess electrons does she get,    $ \times10^{14 }\,electrons$
by how much does her mass increase?    $ \times10^{-16 }kg$

  What is the total charge of al5zhod-w v::u5cd/ imv:gb tl.l the electrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric forcv)m7r hb5.+vxw5s 8g-1eitxzriu fb 6e holding the electron in orbit $(r\,=\,0.53 \times10^{-10 }\,m)$ around the proton nucleus of the hydrogen atom, with the gravitational force between the same electron and proton. What is the ratio of these two forces?    $ \times10^{39 }\,C$

Two positive point charges are a fixed distance apart. Thewf s 5r3lnro49 sum of their charges is What charge must each have inn59l3rwsfo r4 order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge fz o7/ 5:drujz$+75$,$+48$ and $-85\,\mu C\,$ are placed in a line (Fig. 16–49). The center one is 0.35 m from each of the others. Calculate the net force on each charge due to the other two.

$F_{+75}$=   $NN$
$F_{+48}$=   $NN$
$F_{-85}$=   $NN$

  Three positive particles of bef)ge+ t**slsq;/ed equal charge, $+11.0\,\mu C\,$ are located at the corners of an equilateral triangle of side 15.0 cm (Fig. 16–50). Calculate the magnitude and direction of the net force on each particle.


the force on the lower left charge is of magnitude    N, and
will point    $^{\circ}$below the-x axis. The force on the lower right charge is of magnitude    N, and will point    $^{\circ}$below the +x axis.

  A charge of 6.00 mC is placed at each corner of a square 0.100 m on a side. vc1twfoy(2:+n +y e hrDetermine the magnitude and direction of the force on each nyy +htverc(: 1f2w+ocharge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when twn5lr 8gx pj 2z;gt3yn,o of the positive charges, on opposite corners, are replaced by negatl n2y8r p3xtngz,g5j;ive charges of the same magnitude (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l there are point cp (+ az0pbprm)harges of magnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determine the force on (a) the charge 2Q, and (b) the charge 3Q,pz)am + (ppr0b due to the other three charges.
$F_{2Q}$ =    $\frac{kQ^2}{l^2}$
$\theta_{2Q}$ =    $^{\circ}$
$F_{3Q}$ =    $\frac{kQ^2}{l^2}$
$\theta_{3Q}$ =    $^{\circ}$

  Three charged particles are placed at the cornev mp3;jo7np5o* lqs ,xrs of an equilateral triangle of side 1.20 m (Fig. 16–53). The chargesp,s;oq5v nm*3jol px 7 are $+4.0\,\mu C\,,$$-8.0\,\mu C\,,$ and $-6.0\,\mu C\,.$ Calculate the magnitude and direction of the net force on each due to the other two.
$F_1$ =    N
$\theta_1$ =    $^{\circ}$
$F_2$ =    N
$\theta_2$ =    $^{\circ}$
$F_3$ =    N
$\theta_3$ =    $^{\circ}$

  Two point charges have a total ch4 58fj1x pkyp hh,hok:q.gu 5sarge of $560\,\mu C\,.$ When placed 1.10 m apart, the force each exerts on the other is 22.8 N and is repulsive. What is the charge on each?
q = $ 5.54\times10^{a }\,C$ a =  ,
$ 5.54\times10^{b }\,C $ b =   
Q-q = $ 5.54\times10^{a }\,C$ a =  ,
$ 5.54\times10^{b }\,C$ b =   

Two charges, $-Q_0$ and $-3Q_0$ are a distance l apart. These two charges are free to move but do not because there is a third charge nearby. What must be the charge and placement of the third charge for the first two to be in equilibrium?

  A $+4.75\,\mu C\,$ and a $-3.55\,\mu C\,$ charge are placed 18.5 cm apart. Where can a third charge be placed so that it experiences no net force?    cm

  Two small nonconducting spheres have a totalux tz+)m43e8 tntr 2zp charge of $90.0\,\mu C\,.$
(a) When placed 1.06 m apart, the force each exerts on the other is 12.0 N and is repulsive. What is the charge on each?    $ \times10^{ -6}\,C$$\;\;\;\;$    $ \times10^{ -6}\,C$
(b) What if the force were attractive?    $ \times10^{ -6}\,C$$\;\;\;\;$    $ \times10^{ -6}\,C$

  A charge Q is transferred from an initially uncharged8xzjoc1ih gbf(2 x 4w :ack(b2 plastic ball to an identical bahx482i fac:(1oc2j w b gxzkb(ll 12 cm away. The force of attraction is then 17 mN. How many electrons were transferred from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and directi 8;b+n5ihk - npfapkf3on of the electric force on an electron in a unifor 8pnk bn- 5;ap+3ffkhim electric field of strength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a uniform electric field, and it experiences an electra rl/(pt0h((h:h o *ryhkj8yric forc0o(rr*8h yy/ar t:(pjhk lh( he of $ 3.75\times10^{ -14}\,N$ toward the south. What are the magnitude and direction of the electric field?
   $ \times10^{5 }\,N/C$
 ----待选择----southnorth 

  A downward force of 8.4 N is exert6h b:c;,q snqsed on a $-8.8\,\mu C\,$ charge. What are the magnitude and direction of the electric field at this point?    $ \times10^{5 }\,N/C$ ----待选择----updown 

  What are the magnitude and direction of the apy.0nte,kob d: s79telectric field 20.0 cm directly above an iso p97:a0.te ytsn ,obdklated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of kg o1u(kd98zl h3bvw, the acceleration experienced by an electron in an electric field o9(1dk,ow8 v 3lkz hbguf $750\,N/C\,?$ How does the direction of the acceleration depend on the direction of the field at that point?    $ \times10^{ 14}\,m/s^2$  ----待选择----opposite to the field in line with the direction of the field 

  What are the magnitude and direction of the electric field at a pointxl7*i 3sqghl9 midway between aqxl7slh*3i 9 g $-8.0\,\mu C\,$ and a $+7.0\,\mu C\,$ charge 8.0 cm apart? Assume no other charges are nearby.    $ \times10^{7 }\,N/C$ ----待选择---- towards the negative charde opposite to the negative charge 

Draw, approximately,zv;,*iv2er 4div3 wfj the electric field lines about two point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric 5wp()fo b/3b3lmr ;8f yjpkgjfield strength at a point in space where a proton $(m= 1.67\times10^{ -27}\,kg) $experiences an acceleration of 1 million “g’s”? $\approx$    N/C（Round it to one decimal place.）

  An electron is released from n q,2 0dkute 2dmhda) kq(qa23rest in a uniform electric field and accelerates to the north at 2)ehaq2dd tdqk n0 q,mu3(2ak a rate of $115\,m/s^2\,.$ What are the magnitude and direction of the electric field?    $ \times10^{-10 }\,N/C$ ----待选择----northsouth 

  The electric field midway between tu/ 3fbssp0zq 7f 5 9seel/uno7wo equal but opposite point charges is $745\,N/C\,,$ and the distance between the charges is 16.0 cm. What is the magnitude of the charge on each?    $ \times10^{-10 }\,C$

  Calculate the electric field at the center of a square 52.5 cm on a side if onwcty:; *l rsfb9z9)s we corner is oss bwlc9fr; y:tw*z)9ccupied by a $+45.0\,\mu C\,$ charge and the other three are occupied by $-27\,\mu C\,$ charges.    $ \times10^{6 }\,N/C$ at    $^{\circ}\,$

  Calculate the electric field at one corner ofe-ja50ddce p68q,ef t a square 1.00 m on a side if the other three corners are occupje0tac8 p-ed6 5 de,qfied by $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and magnitude of thdvf tfx5p) w2jo)+n ret //f-ee electric field at the point P in Fig. 16–54. The charges are separated by a didfrt/wjvf)e+- )5 2fpoxet /n stance 2a, and point P is a distance x from the midpoint between the two charges. Express your answer in terms of Q, x, a, and k.

  Two point charges, $Q_1\,\equiv\,25\,\mu C\,$ and $Q_2\,=\,+50\mu C\,,$ are separated by a distance of 12 cm. The electric field at the point P (see Fig. 16–55) is zero. How far from $Q_1$ is P?    cm

(a) Determine the ell) e;rr0z)klzfjo 89 dectric field $\vec{E}$ at the origin 0 in Fig. 16–56 due to the two charges at A and B. (b) Repeat, but let the charge at B be reversed in sign.

  Use Coulomb’s law to determine the magnitude and diz u2/; dyoljz5rection of the electric field at points A and B in Fig. 5jloz/udz;2 y16–57 due to the two positive charges $(Q\,=\,7.0\mu C\,)$ shown. Are your results consistent with Fig. 16–31b?
$E_A$ =    $ \times10^{6 }\,N/C$
$\theta_A$ =    $^{\circ}\,$
$E_B$ =    $ \times10^{7 }\,N/C$
$\theta_B$ =    $^{\circ}\,$
(16-51)
(16-31b)

  You are given two unknown :,vi:ia tvca(point charges, $Q_1$ and $Q_2$ At a point on the line joining them, one-third of the way from $Q_1$ to $Q_2$, the electric field is zero (Fig. 16–58). What is the ratio $Q_1/Q_2\,?$   

Determine the direction and oc+ n7c s;zn r00xzj,mmagnitude of the electric field at the point P shown in Fig. 16–59. The two charges are separated by a distance of 2a. Point P is on the perpendicular bisector of the line joining the charges, a distance x from the midpoint between them. Express your answers in terms of Q, x, a, axszzn 0rn0c;+oj, mc7nd k.

  An electron (mass $m\,=\,9.11 \times10^{ -31}\,kg$) is accelerated in the uniform field $\overrightarrow{\mathbf{E}}\left(E=1.45 \times 10^{4} \mathrm{~N} / \mathrm{C}\right)$ between two parallel charged plates. The separation of the plates is 1.10 cm. The electron is accelerated from rest near the negative plate and passes through a tiny hole in the positive plate, Fig. 16–60.
(a) With what speed does it leave the hole?    $ \times10^{ 6}\,m/s$
(b) Show that the gravitational force can be ignored.

  An electron moving to the right at 1.0% the+qoomxi8+h+s. xag r7 speed of light enters a uniform electric field parallel to its direction of motion. If the electron is to be brought to rq+7m o.gh+axr s o+i8xest in the space of 4.0 cm,
(a) what direction is required for the electric field,  ----待选择----rightleft 
(b) what is the strength of the field?    N/C

  The total electric flux from a cubical box 28.0 c) g2r 6yqmd twr5ruam-/-o 5kpm on a side is $1.45 \times10^{3 }\,N\cdot m^2/C$. What charge is enclosed by the box?    $ \times10^{ -8}\,C$

  A flat circle of radius 18 cm is placelrtio1 9kd8am(+0fp ev t ;k6ed in a uniform electric field of magnitude +elr16 oimtk(e; 8fdkapv9t 0 $ 5.8\times10^{2 }\,N/C$ What is the electric flux through the circle when its face is
(a) perpendicular to the field lines,    $N\cdot m^2/C$
(b) at 45° to the field lines,    $N\cdot m^2/C$
(c) parallel to the field lines?   

  In Fig. 16–61, two objectsvzn35 /ibsovk8* 7fti, $O_1$ and $O_2$ have charges $+1.0\mu C$ and $-2.0\mu C$ respectively, and a third object, $O_3$ is electrically neutral.
(a) What is the electric flux through the surface $A_1$ that encloses all three objects?    $ \times10^{5}\,$$N\cdot m^2/C$
(b) What is the electric flux through the surface $A_2$ that encloses the third object only?   

A cube of side l is placwcj0o,7;c:39bhmsk)pppdq )g gwub5ed in a uniform field $ E\,=\,6.50\times10^{3 }\,N/C$ with edges parallel to the field lines.
(a) What is the net flux through the cube?
(b) What is the flux through each of its six faces?

  The electric field between two square metal plates is The pwt *53dt;dpxi6 suf xce4c3s 0lates are 1.0 m on a side and are separated by 3.0 cm. What is the;txed53p4c6c *wxs dtus 03fi charge on each plate (assume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outsid9yvpr -;z 6*g5hl icmfe a 3.50-cm-radius metal ball is $ 2.75\times10^{2}\,N/C$ and points toward the ball. What charge resides on the ball?    $ \times10^{-11 }\,C$

  A solid metal sphere of radius 3.00 m carries a total charge of5vq:nytp+ im:w a8qy 2 $-3.5\mu C$ What is the magnitude of the electric field at a distance from the sphere’s center of
(a) 0.15 m,   
(b) 2.90 m,   
(c) 3.10 m,    N/C
(d) 6.00 m?    N/C
(e) How would the answers differ if the sphere were a thin shell?

A point charge Q rests at the center of an uncharged th up;4 2jh8cnp egb9x*j .rf pt2ytr(:sin spherical conducting shell. (See Fig. 16–33.) What is the electric field E as a function of r (a) for r less than the inner radius of the shell, (b) inside the shell, and (c) beyond the shell? (d) Does the shell affect theh(jts xft;p gbu 92ny2perp.cjr:84* field due to Q alone? Does the charge Q affect the shell?

  The two strands of the helix-shaped DNA molecule are held togetds: jfl+q5li+ her by electrostatic forces as shown in Fig. 16–44. Assume that the net average charge (due to electron sharing) indicated on H and N atom:dl +i+ljsq f5s is 0.2e and on the indicated C and O atoms is 0.4e. Assume also that atoms on each molecule are separated by $ 1.0\times10^{ -10}\,m$. Estimate the net force between
(a) a thymine and an adenine;    $ \times10^{-10 }\,N$
(b) a cytosine and a guanine. For each bond (red dots) consider only the three atoms in a line (two atoms on one molecule, one atom on the other).    $ \times10^{-10 }\,N$
(c) Estimate the total force for a DNA molecule containing $10^5$ pairs of such molecules.    $ \times10^{-5 }\,N$

  How close must two electrons be if the electric forcej dl,kt,(v 9nq between them is equal to the weight of either at the Earth’s surface? t, ,jvd n(lkq9   m

  A 3.0-g copper penny has a positive cu6kx mex1oy 0g(s o3pgkhn0:7harge of $38\mu C$. What fraction of its electrons has it lost?    $ \times10^{-10 }\,$

  A proton $(m\,=\,1.67 \times10^{-27}\,kg)$ is suspended at rest in a uniform electric field $\vec{E}$. Take into account gravity at the Earth’s surface, and determine $\vec{E}$.    $ \times10^{-7 }\,N/C$  ----待选择----updown 

  Measurements indicate that there is an el ;n+c7x ueqbd2ectric field surrounding the Earth. Its magnitude is about nq x;72 cb+due$150\,N/C$ at the Earth’s surface and points inward toward the Earth’s center. What is the magnitude of the electric charge on the Earth? Is it positive or negative? [Hint: the electric field outside a uniformly charged sphere is the same as if all the charge were concentrated at its center.]    $ \times10^{5 }\,C$  ----待选择----positivenegative 

  (a) Given the local electric field of what is the accelerath wj4awp0z e/.*qlk0n z xt1 md/)ou6qion experienced by an electron neu jnma6zho40xp/w/.q*dw)kl q 0ze1 tar the surface of the Earth?    $ \times10^{13 }\,m/s^2$, ----待选择----updown 
(b) What about a proton?    $ \times10^{10 }\,m/s^2$, ----待选择----updown 
(c) Calculate the ratio of each acceleration to $g\,=\,9.8\,m/s^2$ For the electron: $\approx$    $ \times10^{12 }$ For the proton: $\approx$    $ \times10^{9 }$

  A water droplet of radius 0.018 mm cu7+t+e0rhx 1yguxui z)t v12 remains stationary in the air. If the downward-directed electric field o1g+yxzu+ct uv0 2ehr 1) tuix7f the Earth is $150\,N/C$ how many excess electron charges must the water droplet have?    $ \times10^{ 6}$ electrons

  Estimate the net force between the CO group and the H 5+zhh aws5q+mN group shown in Fig. 16–62. s+zhhaqm5 +5 wThe C and O have charges $\pm0.40e$, and the H and N have charges $\pm0.20e$, where $e\,=\, 1.6\times10^{-19}\,C$. [Hint: Do not include the “internal” forces between C and O, or between H and N.]    $ \times10^{ -10}\,NN$

  In a simple model of the hydrogen atom, the electro,ff6 5ea: -+vs gwgxdtn revolves in a circular orbit around the proton with -dagfs:e5v , x6tf+gwa speed of $ 1.1\times10^{6 }\，m/s,$. Determine the radius of the electron’s orbit. [Hint: See Chapter 5 on circular motion.]    $ \times10^{-10 }\, m$

  Suppose that electrical attraction, rather than gravity, were responsiv -q xrsphixhw88/-+ dble for holding the Moon in orbit ar-pw/8xsihv8q r- xd+ hound the Earth. If equal and opposite charges Q were placed on the Earth and the Moon, what should be the value of Q to maintain the present orbit? Use these data: mass of $Earth\,=\, 5.98\times10^{24}\,kg$, mass of $Moon\,=\, 7.35\times10^{22}\,kg$, radius of $orbit\,=\, 3.84\times10^{8}\,m$. Treat the Earth and Moon as point particles.    $ \times10^{13 }\,C$

  An electron with speedir8vm6) kdc8l $v_0\,=\, 21.5\times10^{6}\,m/s$ is traveling parallel to an electric field of magnitude $E\,=\, 11.4\times10^{3}\,N/C$.
(a) How far will the electron travel before it stops?    m
(b) How much time will elapse before it returns to its starting point?    $ \times10^{-8 }\,s$

  A positive point chargel: xm;o0ftc )l $Q_1\,=\, 2.5\times10^{-5}\,C$. is fixed at the origin of coordinates, and a negative charge $Q_2\,=\, -5.0\times10^{-6}\,C$. is fixed to the x axis at $x\,=\,+2.0m$ Find the location of the place(s) along the x axis where the electric field due to these two charges is zero.    m from $Q_1$,   m from $Q_2$

A small lead sphere is encased in insula(y ifwz1,6lay dfp*c+*5 wmf z lwex+6ting plastic and suspended vertically from an ideal spwyiemw6z +( ld*+fa 6,y 1zc lp5ff*wxring $(k\,=\,126N/m)$ above a lab table, Fig. 16–63. The total mass of the coated sphere is 0.800 kg, and its center lies 15.0 cm above the tabletop when in equilibrium. The sphere is pulled down 5.00 cm below equilibrium, an electric charge $Q\,=\, -3.00\times10^{-6}\,C$ is deposited on it and then it is released. Using what you know about harmonic oscillation, write an expression for the electric field strength as a function of time that would be measured at the point on the tabletop (P) directly below the sphere.

  A large electroscope is made with “leaves” that are 78-cm-long wireb-2zo0 0kj 3ygrz/a i,esfpv;s with tiny 24-g spheres at the ends. When charged, nearly all the charge resides on the spheres. If the wires each make a r0oz ;gs0-/i2bpy 3 k,vjfae z$30^{\circ}$ angle with the vertical (Fig. 16–64), what total charge Q must have been applied to the electroscope? Ignore the mass of the wires.    $ \times10^{-6 }\,CC$

  Dry air will break dowe4.wcs,hmn uo)p6f k )d gk*y(n and generate a spark if the electric field exceeds about kpmgo4 6))u(s yfch.,ed wnk*$ 3\times10^{6 }\,N/C$. How much charge could be packed onto a green pea (diameter 0.75 cm) before the pea spontaneously discharges? [Hint: Eqs. 16–4 work outside a sphere if r is measured from its center.]    $ \times10^{-9 }\,C$

  Two point charges, $Q_1\,=\,-6.7\mu C$ and $Q_2\,=\,1.8\mu C$ are located between two oppositely charged parallel plates, as shown in Fig. 16–65. The two charges are separated by a distance of $x\,=\,0.34\,m$ Assume that the electric field produced by the charged plates is uniform and equal to $E\,=\,73,000\,N/C$ Calculate the net electrostatic force on $Q_1$ and give its direction.    N  ----待选择----right left 

  A point charge $(m\,=\,1.0\,g)$ at the end of an insulating string of length 55 cm is observed to be in equilibrium in a uniform horizontal electric field of $12,000\,N/C$ when the pendulum’s position is as shown in Fig. 16–66, with the charge 12 cm above the lowest (vertical) position. If the field points to the right in Fig. 16–66, determine the magnitude and sign of the point charge.
   $ \times10^{-7 }\,C$
 ----待选择----positivenegative 

  A point charge of mass 0.210 kg, and net +b)m eex;jd5k2eyk9 mzd b3,mcharge $+0.340\,\mu C$, hangs at rest at the end of an insulating string above a large sheet of charge. The horizontal sheet of uniform charge creates a uniform vertical electric field in the vicinity of the point charge. The tension in the string is measured to be 5.67 N. Calculate the magnitude and direction of the electric field due to the sheet of charge (Fig. 16–67).    $ \times10^{7 }\,N/C$  ----待选择----updown 

  What is the total chahg rto1 toa-hwl))(trmymv7l 3x7x:)rge of all the electrons in a 15-kg bar of aluminum?    $ \times10^{8 }\,C$What is the net charge of the bar?    C (Aluminum has 13 electrons per atom and an atomic mass of 27 u.)

Two small, identical conducting spheres A and B are aotbe cuq+*)w+ distance R apart; each carries the same charge Q. (a) What is the force sphere B exerts on sphere A? (b) An identical sphere with zero charge, sphere C, makes contact with sphere B and is then moved very far away. What is the net force now acting on sphere A? (c) Sphere C next makes contact with sphereb q)te c*o+uw+ A and is then moved far away. What is the force on sphere A in this third case?

Given the two charges shown in Fig. 16–68, at what position(s) x is the electrien4vzay e k, 31,6gn l-hslt3gc field zero? Is the field zero at any other points, notl 4v1 nt3-g3gnk6,e ysz, lahe on the x axis?

Two point charges, $+Q$ and $-Q$ of mass m, are placed on the ends of a massless rod of length L, which is fixed to a table by a pin through its center. If the apparatus is then subjected to a uniform electric field E parallel to the table and perpendicular to the rod, find the net torque on the system of rod plus charges.

Four equal positive point charges, eacj*ls u.own y0o//;y cbh of charge $8.0\,\mu C$ are at the corners of a square of side 9.2 cm. What charge should be placed at the center of the square so that all charges are at equilibrium? Is this a stable or unstable equilibrium (Section 9–4) in the plane?