If you charge a pocket comb by rubbing it with a silk scarf, how can you de(uc2ig.s t /uq:gd-upc bks;d(:+tqytermine if the comb is posity/ssc;qddcpg+(:tk q.: tuu -ugb i 2(ively or negatively charged?

Why does a shirt or blouse taken 1mqctm uexmlu57).3o(qbmj:ao : t 4f from a clothes dryer sometimes cling to your bodybe( mt x7m:)q4q3o:.t1fuc m mjl5ao u?

Explain why fog or rain dr +owf;gu cx5d:oplets tend to form around ions or electrons in the air.;w xgfo +:udc5

A positively charged rod is brought close to a neutral piece k4mklplvmo/j.k .,)en)qu ps q 3hm1/of paper, which it attracts. Draw a d3.opmq)kkv4smqeu kj/pl)l hm/n. 1,iagram showing the separation of charge and explain why attraction occurs.

Why does a plastic ruler that has been rubbed with a cloth have the abf /: ddxthsb)4ility to pthx:4d )s df/bick up small pieces of paper? Why is this difficult to do on a humid day?

Contrast the net charge on a conductor to the wjab a6u2t r-z9bhbe63ao - )a“free charges” in the conductor.

Figures 16–7 and 16–8 show how a charw ,n 8n yu ev/za**owrjpst5:*ged rod placed near an uncharged metal object can attract (or repel) electrons. There are a great many electrons in the metal, yet only some of them move as shown. Why not alyv * a5u:/*ste8,wonz* nwj prl of them?

When an electroscope is charged, its two leaves repel each oot 9;zd w z.q84/keftd:.nwjfther and remain at an angle. What balances the electric force of repulsion so that the leaves don’t .:zd9zdq 4f.wwfe jt nt k/;o8separate further?

The form of Coulomb’s law is very similarpb +z b5l,b-ew to that for Newton’s law of universal gravitation. What are the differences between these two5, zbe-blp +wb laws? Compare also gravitational mass and electric charge.

We are not normally aware of the gravitational or electric upyiofmq4 r6 bp+j ( 6myruj, tswy)8v78o+/ nforce between two ordinary objects. What v u+i(7b6pj/ys4f ,rnmt pq 8)y8yoo6ujwrm+ is the reason in each case? Give an example where we are aware of each one and why.

Is the electric force a conservative force? Why orsgbntbb/p5 d p y )p/43umk+r ;d.a3bd why not? (See Chapter 6.)

When a charged ruler attracts small pieoc0qi1h9 unmg37tk o u 0*8hkhces of paper, sometimes a piece jumps quickly awa 980 cg1un30kmthuohqio* hk 7y after touching the ruler. Explain.

Explain why the test charges we use when measurin45 o5ve/elgtl0vg6gpm d,vx5g electric fields must be smalld4 gv,5v0g56e/g5 lte lxpmov.

When determining an electric field, must we use aclre) gx1 cn gg:083uf positive test charge, or would a negative o:lncgr g)ge80fu3 xc1ne do as well? Explain.

Draw the electric fi+ z6rvcmm)h yh-8x4 6xnb8h:dlo1 iwxu es3s1eld lines surrounding two negative electric charges a distanw 636vhyxio8 4 -8 s m1uhxrcbhmxnsl:e1)z+dce l apart.

Assume that the two opposite charges in Fig. 16–31a are 12.0 cm apart. e6pbqhq 2 wgz7:;y) vpConsider the magnitude of the electric field 2.5 cm from the positive charw gq:z7behy qpv);2p6ge. On which side of this charge — top, bottom, left, or right — is the electric field the strongest? The weakest? Explain.

Consider the electric field a )4giiq 58j7ni*grni(dy+g2 k:b,nzeq yucv4t points A, B, and 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 e(yuri,kn2v:cdi8i*z yjgbg in e5 47q)g+ 4nqxperience if placed at that point, then list the points in order of decreasing field strength (strongest first).

Why can electric field linmh1)yv )goo m0;uv+e des never cross?

Show, using the three rules for field lines given in Section 16–8,q4 ja0cjb/onfw)6w 1 w that the electric field lines starting or ending on a single point charge must be symmetrically spaced)q46 o0njjwcab w fw/1 around the charge.

Given two point charges Q and 2Q, a distance l apart, is there a point along buzw2:d (/kl;(berc pthe straight line that passes through them where E=0 when their signs are (a) opp d(u:bkbl e2/crw p(z;osite, (b) the same? If yes, state roughly where this point will be.

Consider a small positive test charge locat. /8s9r owkgape+ -siwed 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 8ps 9g.+wok i-a wr/esthis line? Discuss.

Sketch the electric field lines for a unifo)lgi,gn1-k vprm line of charge which is infinitely long. (Hint: Use sym,glknv g) pi-1metry.) Is the electric field uniform in strength?

If the electric flux through a closed surface is zero, is the el3zri0c:i 4gcel4 e(krle(7h wectric field necessarily zero at all points on the su:r(l3weh i ere4cc0 kzg 47li(rface? 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 surbi/. poy;hf9je0d83yc6a p wdface of radius r. If the sphere is replaced by a cube of si / fp6 3dboc0;ey9hja .wiyp8dde r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up e80nq/xd qxul 3 95t9vkunr2ra charge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of atty /v/k5v;m9lr *ui cwlraction between an iron nucleus mi; kl9u /wlvv/ 5*yrc$(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical force betwcnk 2c 2v j y/w1r2ys+4mhnd x3x/n-seeen two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitud7 pra;q,y0r/l qh h8yre of the force a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particleh0ed4i+ e+ulq ,46h t gjp)rwes exert a 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 8.45 cm ap-6rtoz knm/lzzq- .1oart. They are moved, and the force on each of them is found to have been tripled. How far apart ar 1mr/ . -zoqzotln-k6ze they now?    cm

  A person scuffing her feet on a wool rug on a dry day ac/a,)k oouc 63g dch2qbcumulates a net charge oobo q)h3gd,6c /uk2ca f $-42\,\mu C\,.$ 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 ep34d ,da(gmr+ rrwhm,lectrons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric fh smci* e0tanw623dp) orce 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 di4 mg:,,vj fbeglp6e 0hstance apart. The sum of their charges is What cm:,j4,gbgevhp6 fe0l harge must each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge 6tcm 6emtdxz k,x+h, 7$+75$,$+48$ 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/i6nb bkx 7u7qi(k x7c of 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 squareie x ska p)b7/+nl6p7q 0.100 m on a side. Deteq7+s7pxkaie6lp n)/ b rmine the magnitude and direction of the force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case m2yl,cwtm42n si(rpgqxy 3md37..ng when two of the positive charges, on opposite corners, are replaced by negative charges of the same i mtx 2ysnc3.,dml2gwrp.7 4qmg3ny (magnitude (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l there are point charges of m bou(96; qix00foktxr l8*tsoagnitude Q, 2Q, 3Q, and 4Q (Fig. 16–52). Determine the force on (a) the charge 2Q, and (b) the charge 3Q, dueku l;toi8xs9 o or 0tfxb0(q*6 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 placak.ho) ) q5yrqpr+s7 red at the corners of an equilateral triangle of side 1.20 ms5 ))aroqhqp7 +ryr .k (Fig. 16–53). The 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 of7vmdk :nbm(3,ozgn 9 b0zx 0nk $560\,\mu C\,.$ 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 total char8) h.dtstxtsa 3m 2rs+ge 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 transferredh4y+( b kj9aky from 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 ona yh(+4y9kjbk e ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and direction of the electric force onqxk.,lu/v 4pw5.1glopw 4wz wsbo l(5 an electron in a uniform electric field of s.pozs4kw,54l(5 /q.ubwlo1pwlw gv xtrength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a uniform electric field, and it experiences; (ga kfa5m6k7lyw a(g an electric force ofgw6l ( k7aaam; k(yf5g $ 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 ishjyto b0r8 9f. exerted 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 electric fiel0 yov4 zhr5 mw,d,ng oqk5a 3qbf9 )q2g0q.ntxd 20.0 cm directly above an isolated3 0krqo nh).5ngf b,m9 t4 qy0xoqzawdg5v,q2 $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experienced by an electron in an e fw6/ 15ud0 ph/rcdgwzlectw51 0c/r pf6dd/wz hguric field 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 dil0cxpi3 fz :a8rection of the electric field at a point midway between 0p8l :i f3zxaca $-8.0\,\mu C\,$ 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 lin9bbi-wl pjrrshit7rl/w97 (dw13 p.jes about two point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at a point in space where ) 4sse33rt kcoa 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 fiedl;en. + f(slzld and accelerates to the nf.s+nlze;dl( orth 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 twrj9m i/c i 7,epcvr).ho 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 atc c:(b e:ffye1u 8y:qg the center of a square 52.5 cm on a side if one corneru: qf: 18fece :(cbyyg is occupied 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 1.00nai xh4*. t3vdiy *0tv m on a side if the other three corners are occupieav v0n.* tyt*d 3xihi4d by $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and magnitu9s a1c9;ktz vkde of the electric field at the point P in Fig. 16– sa;k19vkz ct954. The charges 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 tz rrnwi(-d-3 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 dlln: wes4on*2 etermine the magnitude and direction of the electric field at points A and B in Fig. 16–57 due ens2w4l*n: o lto 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 poz ,3xyf0c qsx9xag8*i int 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 magniq,w;+ ,*pysbxo-.v uaoxm yl /tude of the electric field at the point P shown in Fig. 16–59. The two charges are/wubxyo,*sxp;m.aq+ - v,ly o 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, 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 lo*wv5vlrz -cszl . 16xight enters a uniform electric field parallel to its 6*crwxzo v5-sl.lv1z direction of motion. 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 28.0a1kn5ab p6rd;8 lax 4h cm 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 182h sb.f fhz 1ac/m-9vt cm is placed in a uniform electric field of magnitude f1tc /9m2ab -fv .shhz$ 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 obje*a vra.)ku oqgru.ry+ gr05)vcts, $O_1$ 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 j 7xz1ck,1xjybyg.(v placed 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 ddlv qym (om:307l,cf The plates are 1.0 m on a side and are separated by 3.0 cm. 7 vldlmoy: (,3cmqd0f 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 b.v4+j0um. q fctu.cbb:nqk k 8 8usef2all 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 lw/ r+d:3je lc3.00 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 an unchare(e k q/el:h v//os n(k9lhht;ged thin spherical conducting shell. (See Fig. 16–33.) What is the electric field E as a function of r (a) for r leseo/e( ks(h/l;eq l ht h9vnk:/s 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 together by electrosta, s/:c9fb mgkhtic forces as shown in Fig. 16–kb/m,hgs:c 9f 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 the electrii5ze5 9vy obyqr0 72yir au3j7c force between them is equal to the weight 7q y 5 9ueyirbj237oavryz05iof either at the Earth’s surface?    m

  A 3.0-g copper penny has a positive charge of y)s p; jul:wvtva9n4+$38\mu C$. 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 ther)qx1txj7 zbtd*0kybo 0p /v8q e is an electric field surrounding the Earth. Its magnitudejqy)/xz0vd1q b*x7k 0p t8tob is 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 fieln0mjnpp +m,3* x(yoq hd of what is the acceleration experienced by an elecoyn,0p+ x(qp *mn mjh3tron 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 0.018 mm r;fx1f os5t 7fur-bat4 2i.oq qemains stationary in the air. If the downward-directed electric fielbot fq 7ffa u-ir 25ts4;x.q1od of the Earth is $150\,N/C$ how many excess electron charges must the water droplet have?    $ \times10^{ 6}$ electrons

  Estimate the net force between vp dzp hy48x qat0 y.2g)b3ki/the CO group and the HN group shown in Fig. 16–62. The C and O have charga)/3hq d i4tp2vpykx byz8.0ges $\pm0.40e$, 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 ehl3 aqsdvb:v32 q40tklectron revolves in a circular orbit around tklb423q a h30dvv s:tqhe 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, asxz7 r* 6h1tg c43xntwere responsible for holding the Moon in orbit around the Earth. If equal and opposite charges Q were placed onrzgxts1 a736tc xhn* 4 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 spe3jjt) d9 pw0g0nzdeo +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 chau;if l2x75 v zb :6mr:cabjc2urge $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 enca gua dco x55g5ml g2o..(w*ttrsed in insulating plastic and suspended vertically from an ideal spt*ogw cl5g g .x( 5oumd.t52arring $(k\,=\,126N/m)$ 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 wires with +:3 v mgi)m5zdwmus zkbzp+w q712e(ttiny 24-g spheres at the ends. When charged, nearly all the charge resides on the spheres. If the wires each make a ++3ds: u2z(wzv 1mm)ewgbmi7 z ptqk5$30^{\circ}$ 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 electr(rovo /angl)(ifgk8 :ic field exceeds aboutv(o(:g)kni8f rlgo /a $ 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, an7g/ hxhe. i np+it 47hs(+xwfjd 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 of all the electrons in a 15-kg bar of alu- b+hsozzil., i4e8pe 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 conducti+e c8qn y.;hq qia kpql08 (qbn)(6ftkng spheres A and 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 sphere B and is then moved very far away. What is the net force now acting on spca;8 qqi608)n nkfq( qtby.hl +eq(kphere 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. 16–68, at what position(s) x is the eleo-)rls equblo6 wd1o; )45x dfctric field zero? Is the field zero at aru14e)dlwo6 ) lf x;-oo5dqbsny 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, each of c(ao7u r x5xn8oharge $8.0\,\mu C$ 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?