If you charge a pocket comb by rubbing it with a silk-cwswz v/bo1xp 7fu6 a5 i7gz6 scarf, how can you determine if the comb iw b7/s5wpf voaz7cu 66iz1x- gs positively or negatively charged?

Why does a shirt or blouse taken from a clothes dryer sometimeuj*6 tg nsr+)ys cling to your bods*gjru6)nyt + y?

Explain why fog or rain droplets tend to wgv9ctpa1 rayo 4l:rd-;j25h form around ions or electrons in the air492j;o r d:h5gl1w- vparyact.

A positively charged rod is brought close to a. 7ioeaptt,dfyp7v;ue7 , 6pz neutral piece of paper, which it attracts. Draw a diagram showing the separation of charge and explain w6e ,ep7pt7u,d o taz;7ipy. vfhy attraction occurs.

Why does a plastic ruler that has been rubbed with a cloth have the abiliz59-lzd b.ub m;m3ft .2b1tzy ls-i yvty to pi. b-2y 3yttfszz-;lm9uz5l1. bb imv dck up small pieces of paper? Why is this difficult to do on a humid day?

Contrast the net charge on a conductor to the “free charges” ib)+o+7fdh b gen the conductor.

Figures 16–7 and 16–8 show how a charged rod placed near an uncharged metal obj6sv, m )6g61jn/u3exkhaqj snect can attract (or repel) electrons. There are a great many electrons in the metal, yet only some of them move as shown. Why not sx6qnv hg /jj6e,36as1)nkm uall of them?

When an electroscope is ctux0 36rft i9charged, its two leaves repel each other and remain at an angle. What balances the electric force of repulsion so that the leavf0 r6u 3ic9txtes don’t separate further?

The form of Coulomb’s law is ve lgchekrvu+q: 5g2heyf2b ; fvz0): 2nry similar to that for Newton’s law of universal gravitation. What are the differences between these two laws?cv5rvg22:fk uzhq 2e: 0)yf e; +gnbhl Compare also gravitational mass and electric charge.

We are not normally aware of the gravitational or *fy om30naa0kp+k- *x liu2qjelectric force between two ordinary objects. What is the reason in i*qouayl*0 fjka3x + kmnp2 0-each case? Give an example where we are aware of each one and why.

Is the electric force a conservative foiq.th58s d9mr dq 6-jajv 3/yfrce? Why or why not? (See Chapter 6.)

When a charged ruler attracts small pieces of paper, som fq2.0danvb73z);sy c bxa+k petimes a piece jumps quickly awafvp7b0y d k) +bxsa32z .q;cany after touching the ruler. Explain.

Explain why the test charges8z( p):foay ok we use when measuring electric fields must be smallzf:y 8(kpo) ao.

When determining an electric field, must we use a positive test char fxnfwtdxl:c9yi*h0d(zke2j 8v/ e 3 9ge, or would a negative one do as wellf0i ef nly/:w9 d32 vctjzhe9k8xx*d(? Explain.

Draw the electric field lines s-b7 jpf ,)k lh3.it g3xdk:lbbqhg0;h urrounding two negative electric charges a distance l apahk h3gki,7 ;g3d0. x bpj-fl btblq):hrt.

Assume that the two opposite charges in Fig. 16–31a are 12.0 cm apa,)rl9w ow, lz eadj34luo4b*nrt. Consider the magnitude of the electric field 2.5 cm from the positive charge. On which side of this charge — top, bbowu,j )4 9dzro*l43 ,neallw ottom, left, or right — is the electric field the strongest? The weakest? Explain.

Consider the electric field at points A, B, and C in Fig. 16–aph6l/swegc.v (ed. ;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 decreasinwvhgc .es;a6p.le( d/ g field strength (strongest first).

Why can electric field lines neveee a 1+e3qdk5vdnv x+2r cross?

Show, using the three rules for field lines given in Section 16–8, that thehcvul g5.jtmfjz 00(x2 lt2(e electric field lines starting or ending on a sin0 f5h(gv.u2t tmx0z ce(l2 jljgle point charge must be symmetrically spaced around the charge.

Given two point charges Q and 2Q, a distance l apart, is t/jfwqa4h -u p8jyz 5o8here a point along the straight line that passes through them where E=0 when /f a48j-y qujwo8p 5zhtheir signs are (a) opposite, (b) the same? If yes, state roughly where this point will be.

Consider a small positiveny7e4kf:,u(jjks5 cr test 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 chrucn, :fe kj4s75yk(jarge along this line? Discuss.

Sketch the electric field lines for a uniform line of charge which is infinitel l.n*o xn,g6ssy long. (Hint: Use symnsn6, osxg.l* metry.) Is the electric field uniform in strength?

If the electric flux through a closed surface is zero, is the elec6n/q/ilhwqn5 xdgw c9gt(v9 g3eh00 itric field necessarily zero at all points on the surface? Expla00 5iqgqwxd6 hng/vg (wn 9i/3tce9 lhin. 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. 6uq6-jzwpyc ,+3d o94 znhxg dIf the sphere is replaced b,+y jqpg4c 6xz -z36n9ow uhddy a cube of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a char rm,v:(0qh cn 8cys0ewge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the eleky ejk*f wq(zyo;)2,w ctric force of attraction between an iron nucleuwj w,q )kk*;fe2oyy(zs $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical fd-z76fosuk 5*;i csplorce between two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of thepmx8k :6zptv/ force a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exert a f )ihpixb9l/br4ile nj 282tk9orce 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 8.4 q8+*:.8tuhu ocx ebws5 cm apart. They are moved, and the force on each of them is fhtcu .q+se*ox:bw8 u8ound to have been tripled. How far apart are they now?    cm

  A person scuffing her feet on z18t bdamt01qu 51k5 3xp dyhja wool rug on a dry day accumulates a net charge ofupx81h1d zt 5d qybja31 5ktm0 $-42\,\mu C\,.$ 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 t1 yjdbo8le8v)oyj5xh j )y22q he electrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding th9dcv9 k(g i0zze 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 d 7b.3rkpwysn6 istance apart. The sum of their charges is What charge must each hawspyrb k67n 3.ve in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge 4/n73)s g*k ,ozew+lyg hdjpq$+75$,$+48$ 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 equaljyli5. p6uz/n 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 sidp en12 qq/p.dz+tz na1e. Determine the magnitude and direction of the force on eqzqzen+t.ad/n2 1 p1pach charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the casee:c9 mlo ebj+12fpow, when two of the positive charges, on opposite corners, are replaced by negative charges l9coe,m: wjpeb2 f+1oof 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 chargmyl yu6s kt(x5yu/ 7q(es of magnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Dmy(y7(skq6l5xt yuu/ etermine the force on (a) the charge 2Q, and (b) the charge 3Q, 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 codv0 w m-usj/mt290wuq rners of an equilateral triangle of side 1.20 m (Fig. 16–53). Tqv 0j0 t/9uum2 mwdsw-he charges 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 charge of .7 mwc jrqcd*7n5b(v v$560\,\mu C\,.$ 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 have3eymj(e g +mi4 a total 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 uncharged plastic ball to an identict xgbq /l;1f(l3n;p ylal ball 12 cm away. The force of attraction is then 17 mN. How many electry1g blfx 3ln/( qt;pl;ons were transferred from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and direcphz2hzd77 q c7tion of the electric force on an electron in a uniform eh7 27dqp hcz7zlectric 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 electriuvf*(i-of9h*h:+ e1:yj2y w ztcwpgmc force of ovj*wh2 f(* iugywec-1 9zp h fm:+:ty$ 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 ec -/dqs53w,yoznhf ) axerted 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 of8cp m4vmbx 3-q the electric field 20.0 cm directly above an isolate-qcmvpx 3m 84bd $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experienced by an electron in an elec l(xk.pgz: zb b64mr8x.ppu y7tric field ozp:7p 8k bxuzgb.mrpy(x6l4 .f $750\,N/C\,?$ 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 figq fc8t6)llsq5x9)gf4 oyi1 reld at a point midway betwee6 oy9 8t) r4l1)qsig qlfcf5gxn a $-8.0\,\mu C\,$ 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 abow p mnr o5)-d.7ogcs;9c4t/.gau msrlut two point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength a i ta wr3:,mel*a1r5cgt 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 release a9uy(ld; vk8n60hmm ;q ae+etd from rest in a uniform electric field and accelerates to the north at a raymamk+ ed le u6t;v;q(0 9a8hnte 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 k1vw+ t2)gnejsq. +ydtwo 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 o0c 1kgl2i*c6nb: yzd t7mjb* vf a square 52.5 cm on a side if one corner is occupie 0 k:tcc*mg v6l*njb7yzd21bi d 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 of a square 1.00 m on azdly b9 ,wu,5jcau4mh 1o;f/e side if the other three corners are occupcf 5 uha;9z/1 ,myouwjbled,4ied by $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and magnitude o;sic(torg+4i 63ashx/i :btof the electric field at the point P in Fig. 16–54. The charges ti iosxb3s4 (rg6;+ tch:o/ aiare 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 el5v qe-xf a6/vcectric 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 direction of the el2i+: oa6x hpcfectric field ach6x:+ o2pa ift points A and B in Fig. 16–57 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 point charg)ycf 8x aw16jkul* f,ges, $Q_1$ 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 magnitude of the electric field at the point P s0g:nw ib7fub 7hown 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 i:7 fnu7wgb 0bcharges, 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 0kiuuwzvoycp) 5 316aof light enters a uniform electric field parallel to its direction of i1ky )wu vp0z6acuo35motion. If the electron is to be brought to rest 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 cm on a sijkawz*o+(t b7/q 3at(fp- oez de 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 uuo5tqexftr 2. z58x7bniform electric field of magnitude qx u2z7.x55tb8 rfeo t$ 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 objects, e xuz8rmv+mvr 1/xkwo 99:pn6 $O_1$ 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 fx/ (wnbm* 55brs ny-i5vpk(zzield $ 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 plates aygzc+*0zrwvbveh+7 g k 5 z++are 1.0 m on a side and are separagb+z zw5*+a7z0e +rhv vc kgy+ted 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 3.9 )oz-wcqai 2z50-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 peq vd2 u)(:k8qy,dss.00 m carries 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 vm )tndi. p5u7f bck15an uncharged thin spherical conducting shell. (See Fig. 16–33.) What is the electric fietfpdm5bc5u)i v nk7.1 ld 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 affect the shell?

  The two strands of the helix-shaped DNA molecule are held togethe8ydn6/alcb.pi 7 m*is r by electrostaiayd/ c86 msb.7 *lnpitic forces as shown in Fig. 16–44. 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 tg1-irj;ucn*r he electric force between them is equal to the weight of either agrj-1nc;u r i*t the Earth’s surface?    m

  A 3.0-g copper penny has a positive ch o6x*tl0((qjqi wbl*9jq 0zjharge 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 electric field surrounding the Eag0dz-i/+*j-og9u o ca1xvh *:z yi jzbrth. Its magnitude is about hgvzg*xo-izi/ 1y o0*zcj-9b: j +uad$150\,N/C$ 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 acceleration e;8 ykud:n xqq4u blu03c2*vdexperienced by an electr4 ue yd28ck3udxq;0*:lbv n quon near 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 0.05c( ,f -l7 ,kl ntbqonuvycmdo/): ch818 mm remains stationary in the air. If the downward-directed electric field of thm/)f u8:v5o cd nhctol,(7-qkcyln,be 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 5i . 7p;u; k*wvvmxtsoHN group shown in Fig. 16–62*7vm5oi ; puxstkw .v;. The 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,wk:wxvxe;p) k z4kbvlyh3)x0: xx/ y / the electron revolves in a circular orbit wexw0k / );:)zy/kyx lx 4vp3bkhxv :xaround the proton with a 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, wer3(b q s0t;kpmoe responsible 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 thes t30b(m qp;kose 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 spesmv30 g:bwr: m.n.dys ed $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 char,f40wsh sus t3ge $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 insul8 ez76nqii3 5vst2 vxbating plastic and suspended vertically from an b3 in76s5qte2z8vvxi 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 “lcbfn u knkdjv +a 0 zp4s7-q)0ht,d3 t(-oxd0beaves” that are 78-cm-long wires with tiny 24-g spheres at the ends3z4sjqv+dt u knf 0d,07b -h p0abkdo)(x-tnc . When charged, nearly all the charge resides on the spheres. If the wires each make a $30^{\circ}$ 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 field exceedskrw x t,h4ge3m)/w jm( about t 3rmmx,4(/e)whg wkj $ 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 ne +0zjlnvoe.(x t 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 of all the electrons in a 15-kg bar of alub)a yc l)qud/eji+yjlt4 ; mm, w803o,zb2bhj minum?    $ \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 andce 3mrncwyllt-p1 ,;u y xs,17 B are a 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 sputpcy ,n1e;clr3- m 7lxwys1,here 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 is the force on sphere A in this third case?

Given the two charges shown in Fig. kkl.3hn g7 fagtgn)cpigm z y0 4)9(t.16–68, at what position(s) x is the electric field zero? Is the field zeromk 9ac0z)ygtt4n.(7n g l pgk. 3hig)f at any other 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, 9vifis9c0 *co each 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?