If you charge a pocket comb by rubbing it with a silk scarf, how can ysp a gg7pk6omcb-1k8 (k)+nrp)e: rgd ou determine if the r7r18ks+)gb- n6kmgpp c ga:e(pdo ) kcomb is positively or negatively charged?

Why does a shirt or blouse taken from a clothes dryer sometimes cling to your b,js :kp )wiq6na s1*cmod,1s*6pkja )iw ms:q cny?

Explain why fog or rain droplets tend to form around ioneo f, :ou4wzm2s or electrons in the aiw4:ofz 2oeum ,r.

A positively charged rod is brought close to a neutral piece of paper, whi l(h a2jl:rsz;ch it attracts. Draw a diagram showin :ls;2hzrjal( g the separation of charge and explain why attraction occurs.

Why does a plastic ruler that has been rubbed with a ckokm.:e l, pk:loth have the ability to pick up small pieces of paper? Why.olkek: m,:kp is this difficult to do on a humid day?

Contrast the net charge on a conductor to the “free co *q33q k+ g5pc;kszdx a4-vw8y+ygwcharges” in the conductor.

Figures 16–7 and 16–8 show how a charged ci (vx(lha*hfuz p3*;rod placed near an uncharged metal object c z(chh3lfxvi*(; * puaan attract (or repel) electrons. There are a great many electrons in the metal, yet only some of them move as shown. Why not all of them?

When an electroscope is charged, its two leaves repel each other and rema or4f3g. hi7e hmx;lx*in at an angle. What balances the electric force of repulsion so that the lea.egm* xxio f3hhrl;74 ves don’t separate further?

The form of Coulomb’s lawj9, z n8l lqx+1yv(jps bp *kmz06-x+qlm.rek is very similar to that for Newton’s law of universal (sqlpzjr*zpj.8-0 lqv knmb96xel1 + ymx +,kgravitation. What are the differences between these two laws? Compare also gravitational mass and electric charge.

We are not normally aware of the gravitational or emn q1fn:8+03 -xlwy kfuk 12k,esfi sylectric force between two ordinary objects. What is the reason in each case? Give an example where we are aware of each one a10 8n2, kmy1kefx3l s+q:f-funy w siknd why.

Is the electric force a conservative force? Why or why not? (See Chapter f3m wlkg 916mi6.)

When a charged ruler attracts small pieces of paper, sometimeg2uxcmi 5-k; xfh)biau2a e;5s a piece jumps quickly 5 cexa iumgh 2 xk-ufa;5;)2ibaway after touching the ruler. Explain.

Explain why the test charges we use when measuring electricnf+p9s *zwb108/sbula0 b a js fields must be small.81w9z/jsasb0ps0 f*a bb nlu+

When determining an electric field, must we usepfqs ;zqw0 e+4 a positive test charge, or would a negative one do as well? E4w+0qspe z ;fqxplain.

Draw the electric field lines surrounding two negative electric vqja i ( 3*k:pznoi98bcharges a distance l (vbj: qa o*pkii9zn 38apart.

Assume that the two opposite charges in Fig. 16–31a are 12.0 cm abka ea e7udwna*-*7b 8part. 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 the strongest? The weaknw7 abuk*e b-8aa7* edest? Explain.

Consider the electric field at points A, B, an15 kuu;wq h d.-h5.jasd( k h;no/ghmud C in Fig. 16–48. First draw an arrow 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 decreaah. .1h;kn;do5/-w dh jqm(uh uu ksg5sing field strength (strongest first).

Why can electric field36de;pp z5g i(6rxuk3 wyeqo/ lines never cross?

Show, using the three rules foredqc6 i dh-b tt24b3cvztfz1-9a 3dc) field lines given in Section 16–8, that the electric field lines starting or ending on a single point charge must be symmet att c- tecb4dz-zid63v9)d2cf3 1bqhrically spaced around the charge.

Given two point charges Q and 2Q, a distance-hl +vsckn))9 kyegv9 l apart, is there a point along the straight line that passes through them where E=0 when their signs are (a) opposite, (b) the+klcsn)9vv )yk heg-9 same? If yes, state roughly where this point will be.

Consider a small positive test charge located on an electric field line at l66qie4z1fkg*k:bww some point, such as point P in Fig. 16–31a. Is th ezwq6k 6wl1b*: i4fkge direction of the velocity and/or acceleration of the test charge along this line? Discuss.

Sketch the electric field lines for a uniform line of charbd: 9*sv 3wtwa2ajecjik)42wge which is infinitely long. (Hint: Use symmetry.) Is the electric :dwj j4sb9wvat3ca iw22 *e)kfield uniform in strength?

If the electric flux through a closed surfact;u ;0y xdhqh,1ph6uce is zero, is the electric field necessarily zero at ahd 1uty up6;c 0,hqx;hll points on the 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 sugo) zuj60-) xghg mlo/rrounded by a spherical gaussian surface of radius r. If the sphere is replaced by a cube of sidm)og-j /h)g uzl6xgo0e r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a charge ofw*gfgv fy j9)n0mnuc (fd9tp*3 n,5kf $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the e 8lyr0nfq7( wylectric force of attraction between an iron nucleus07rlnyqw 8y(f $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical force bi1gic+)+g y1q : kjtqcetween two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude k ctk.;tx:( +w:ok6n;yebtuiof the force a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exert a47 0h3,mf+rfvp;usi iqf; i0iyr6hm5t vky6 c force 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 are 8. vv 8*xf4 jv3)nyasu5m45 cm apart. They are moved, and the force on each of them is found to have been tripled. How far apart are they n 48)j5xmvvya3* fsnu vow?    cm

  A person scuffing her feet on a wool ruvr9 6 c5iv 1meua1.brnpz 0hdu.xv.i4g on a dry day accumulates a net charge of vvru.c hb1.6 drz40v9p1x.mia5unei $-42\,\mu C\,.$ 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 all the electrons ig7pohjje0zo.mka7u 2 ck3 9(vn 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force ig; ehim68d4k g2,ywpholding 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. The sum of the2fafyuy fti 2+8:f e5hir charges is What charge must each have u yyf252f +h ietaff:8in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge 4 zyctd gsmn9h9hi88+$+75$,$+48$ 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 equal ; tju)(mm: dsvkjyk m43:ems 0charge, $+11.0\,\mu C\,$ 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 nt; lk-l4dd-*;*c+vljv lofqa square 0.100 m on a side. Determine the magnitude and direction of the force on each charg- vclq*lv+ ok-d fl*ltd4;;jne.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when twohkt 63zp n5.ps of the positive charges, on opposite corners, are repla z5.tp6kn h3psced by negative charges of the same magnitude (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of sidci5ewlfif5 fult )50s1 :9w /rwc,vjh e l there are point charges of magnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determine the force on (a) the charge 2Q, and (b) the charge 3Q, r: lf50twh e9 v /)filwwu5c,j1fci5 sdue 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 corners of vxo:.*oz8q lm an equilateral triangle of side 1.20 m (Fig. 16–53). The charlm.8*xqvz :o oges 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*8kw-mal kp ,uyo f5/y total charge 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 n7 t yh- peq+s8q8kuv8total 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 frotqt vb/,qc3t/ m an initially uncharged plastic ball to an identical ball 12 cm away. The force of attraction is then 17 mN. How many electrons were transferred from one ballq/v3b q,ct tt/ to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and direvxiq / zzr4,ku )3ea,b*jyx8tction of the electric force on an electron in a uniform electriq3z,4 ab*j/,eurkvx) iy 8zxtc field of strength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a uu,u 2rnof ic 3l3),s)b7emlbmniform electric field, and it experiences an electric force ofc,ebi3lmus)u )fbm2 l ,nro37 $ 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 e4uevd48 + h5r,wqazufxerted 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 directio;ujx 9/ dnp+wom* s:zq e1.smjn of the electric field 20.0 cm directly above :uo 1j/9j z;ws.m+edqmns * xpan isolated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experiencev:vqg j 3(i )9(iwshoud by an electron in an electric field whjv:q3 )iovgs9i( u(of $750\,N/C\,?$ 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 ;mh4 t9t dcrsu(2 ljgq+1 ,pttat a point midway between am 4td rgc p2(9; th1ulsjqt+,t $-8.0\,\mu C\,$ 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, the electric field lines about two pojf ntr7l kb- p:xaw390int charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at ve*jt l2:k8;em2uvno 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 rest in a uniform electric fva4vfwn;y fv/12kt+m pbf*4 jield and accelerates to the nojwv21a;k yb4f fv+4ptv f* nm/rth at 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 two equal but opposite point charges zczs.4-wuzf. 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+c:ufga0 4gre 1wwk)sp+cw8 j cm on a side if one corner is occupied bp+kw8 j a04wesrc1:)g+gucwfy 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 of a square 1.00 m on a side if v(-ewdgvq qa2 b/l: 7w7 rl/jrthe other three corners are occupied 7r/7a2gljw d- (wqvq :be/vrlby $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and magnitude of thxxc2o9 ,eh-d:h nq ,oae electric field at the point P in Fig. 16–54. The chargeso9 e2d:,aqcx hxo ,hn- are separated by a distance 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 electric field cyl*p r9p y*bwn76:ba $\vec{E}$ 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 dir;pzx rilf8t;6(i(c g)h ih8zmection of the electric field at points A and B in Fig. 16–57 due to the two8r (;)p6h;hlzm8xzc( ii g ift 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 point charges, .hlt bpt lb;9;$Q_1$ 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 magninc j 38x td hfw oip:n4p,-/47qh6aprjtude 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 chargep64c :7,hn4fa -r/qjw3ppx injh to8ds, a distance x from the midpoint between them. Express your answers in terms of Q, x, a, and 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 speed of lighai m+iody4 84ij2axp;4. 9 pmmgsul-d t enters a uniform electric field parallel to its direction of motion. If the electron is to be brought to resm-od;miy.dspx4im+894g2a il u4 ajp t 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 cxn p,)pi2qi m(m 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 placed in a uniform)7npa4 *da.7oso1w4qa vx:5al cyhi z ot o;)y electric field of magnitude1w7n)txcaqoyai.dh 4o;:zyo5*o7a v) 4 lspa $ 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 ovk.tc 6vr.2iebjects, $O_1$ 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 placed in a uniform fin9 c6yc(7;wlxpxz9mk71szy geld $ 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:i:alwepioj-5(u e v; metal plates is The plates are 1.0 m on a s:o5il jpu;:iwvae e-( ide and are separated by 3.0 cm. What is the charge on each plate (assume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-cm-radius metal byf0 epc tmxny(t j1 l/48td4y2iz8u0hall 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 carre).eh0k1j2qe yl8t qties a total charge of $-3.5\mu C$ 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 thin spherical conducting4f e6rzfxhqde46) yiqh5x ++7zd,def 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 the field due to Q alone? Does the charge Q aff) xfz564e d++,drzhhq eei4q7fx6fy dect the shell?

  The two strands of the helix-shaped DNA molecule are held together bygn0i b84hxja26qiq7j -)fd f x electrostatic forces as shown in Fig. 16–44qj4gnf f-02 djba8hqx i6i)x7. Assume that the net average charge (due to electron sharing) indicated on H and N atoms 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 force between therc 0d z(8bd/sal1 i25 ifbeyy)m is equal to the weight of either at the Eaziyyd 2f1d0/ bbal5(cse) ir8 rth’s surface?    m

  A 3.0-g copper penny has a positive cp+bs; v1+ s-zwyef*c dharge 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 indicatepu(0 lf 0fkj8q that there is an electric field surrounding the Earth. Its magnitude iuq0l 8k( pjf0fs about $150\,N/C$ 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 o/ur7lwrem6 7mngr)9az 8o4 m of what is the acceleration experienced by an electron near the surface of )u/rareg7wo7z8 4nmm om9r6 lthe 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 remains sdy6w5i8nr od.,3,9kb f hleyntationary in the air. If the downward-directed electric field o fnnke dwry l6 3,.9dbh58,oiyf 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 Hmjz9ov7bt6wfpd:+ j+ zk(;6kb0pujeN group shown in Fig. 16–62. Thepk fbjjpb0ou96 6k7+;vdj:tmw+z z(e 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 electn)pdu-enk x(r4p1,h q9br s t3ron revolves in a circular orbit around the proton with a speed( 1qrk) xppd93snn -b4rt uhe, 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 respobdkv 9yx+c 2k)nsible for holding the Moon in orbit around 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 thesx9bd )kcv yk+2e 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 spe) ynn(per; )s;s:qkmxed $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 charg;w7i9bc:fm9ry3 i svye $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 in5i1x2/tr cq ux -,icotly y /d1cz,8b5(tb rml insulating plastic and suspended vertically from15bx tc8io r 5 lt-bqxrcl,i,d u/c(zy1ymt/2 an ideal spring $(k\,=\,126N/m)$ 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 wk ,ktmj 1l,rb*t5eu(vires with tiny 24-g spheres at the ends. When charged, nearly all the charge resides on the spheres. If the wires each make arlu5emj, (*tv,b t kk1 $30^{\circ}$ 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 down and generate a spark if the electric ft2uhhe0x4g: d,nv;le ield exceeds about ,:xdh un2 gveet 0lh;4$ 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 +7alwbl x1g(c net charge $+0.340\,\mu C$, 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 charge d18;j7xoogwd9/kox u 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 a dis+3iknne 6 gc*vnre/y3tance 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 sphere A and is then moved far away. What i 3 n*nvk 3rcye+g6e/nis the force on sphere A in this third case?

Given the two charges shown in F9clpx*b d85 e mz3/kziq*bnt*ig. 16–68, at what position(s) x is the electric field zero? Is the field zero at any x5izml e*q 9dpnc*b*83k/t bzother points, not 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, each of c/aj*n *d luszn5q9g-tharge $8.0\,\mu C$ 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?