If you charge a pocket comb by rubbingvj a)vg(-ydk0 it with a silk scarf, how can you determine if the comb is positively or negatively chargedkj(v-gdvy a )0?

Why does a shirt or blouse taken from a clothes dryer sometimes cling topy(vr( gp- jv.bep. 7n your boprpvg..b( -v ynje(p7dy?

Explain why fog or rain droplets tend to form aroun8kfu thqc;c* 8xwd*k0 d ions or electrons in the aih df;k*t0q8c8c x* uwkr.

A positively charged rod is brought close to a neutral piece of paput2e *)gxr ii70 x0ta *2bscijer, which it attracts. Draw a diagramx* *xia)srjt22g ie0i0 u 7tcb showing the separation of charge and explain why attraction occurs.

Why does a plastic ruru tau 1ry p*n.n63m77.iboevler that has been rubbed with a cloth have the ability to pick up a e.i.ut 6prvo7*m37nnr u y1bsmall pieces of paper? Why is this difficult to do on a humid day?

Contrast the net charge on a conductor to the “free charges” in thtum:y6b /3ls/flw:pce conductor.

Figures 16–7 and 16–8 show how a charged rod placed near an uncharg/fhfesc-j.0z ed metal object can attract (or repel) electrons. There are a great many electrons in the metal, yeff- c/se jz0h.t only some of them move as shown. Why not all of them?

When an electroscope is charged, its two leaves rep yu o o;buc1,p-sw *6qn0uc). vs7vykpel each other and remain at an angle. What balances the electric force ofy6 u*s)p.-ov s0yok b ccu7vq;,n u1pw repulsion so that the leaves don’t separate further?

The form of Coulomb’s law is4.ux zc.x9a/9+nmv2 utpbmkq very similar to that for Newton’s law of universal gravitation. What are the differences between these two laws? Comp q9p9+ .4a2xz/k x. uvmubcmtnare also gravitational mass and electric charge.

We are not normally aware of t(kno2n- inx 8qhe gravitational or electric force between two ordinary objects. What is the reason in each case? Ginn -(kx qnio82ve an example where we are aware of each one and why.

Is the electric force a conservative fjum)x. h9 p; zr8mp; mz;xv.z erd6y,rorce? Why or why not? (See Chapter 6.)

When a charged ruler attracts small pieces of paper, sometimes a5u93xyno ie m 1z v:w+x9calt zc7f2rhjx1 1e4 piece jumps quickly away after touchinew ft3zv 7:e ccx+zr541yh 2l x1ouim9 j1axn9g the ruler. Explain.

Explain why the test charges we use when measuring electrlc5r 7h 1zy ,ffkhhk0/ic fields must be small hczrhhfy,k/ 57l1 0kf.

When determining an electric field, zdbxl:(wnab; o w.h:0 must we use a positive test charge, or would a negative one do as well? Explain0z :hdxwbb;oan w(.l:.

Draw the electric field linesmgl7 ,ugtr- 9 sxanp 7g5.9bvbs0(lek surrounding two negative electric charges a distance l apartsbsr-v(l.n9xp, l0 egk7amgu 9 7g 5bt.

Assume that the two opposite charges in Fig.s k-1fbi5mn1)jft a p1hg1lb( 16–31a are 12.0 cm apart. Consider the magnitude of the electric field 2.5 cm from the positive charge. On which side of this chi (1ajmlgt)-1fsf p1nb1k 5bharge — top, bottom, left, or right — is the electric field the strongest? The weakest? Explain.

Consider the electric field at points A, B, and C in Fig.z/.henlswn:k 6:q w6g 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 /6 nknhe ls6z w:gw:q.at that point, then list the points in order of decreasing field strength (strongest first).

Why can electric field lines kt1av dn/0e. qnever cross?

Show, using the three rules z8qm1; . x xfp:(feqggfor field lines given in Section 16–8, that the electric field lif x(q.;fx1m pq:8z eggnes starting or ending on a single point charge must be symmetrically spaced around the charge.

Given two point charges Q and 2Q, a distance l apart, is there a po awfd:(fsy+dk mf 7i05int along the straight line that passes thr(:mi fd0+syfda kfw57 ough them where E=0 when their signs are (a) opposite, (b) the same? If yes, state roughly where this point will be.

Consider a small positive test charge located on an electric fieldr:3/,dazw p dz line at some point, such as point P in Fig. 16–31a. Is the direction of the veloci zdz/ :3adr,pwty and/or acceleration of the test charge along this line? Discuss.

Sketch the electric field lines for a uniform line of cp46cwfca( s+piwi 0 o)harge which is infinitely long. (Hint: Use symmetry.) Is the electric field uniform ip0 w4si icfcp+o6 )w(an strength?

If the electric flux through a closed surface is zero, is the electriw; pnwcgy;9 +etrfl( .c field necessarily zero at all points on thnw9(. ;; efgtr wplyc+e 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 o baw/c gd2/q8ps7 d 18jefpnk0f radius r. If the sphere ikw d2b agsc0dq7/jppn/818efs replaced by a cube of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make ups6eq.bf;s. 5,zhj da,li 5,w3 mdnxrv a charge of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude je ;+hj- 82m8rvto+r. r0f zu+evw3. lcgzpfoof the electric force of attraction between an iron nucleus o-j0.m zu;f+er83 ovfp jz+8 . ewrclgv2+rh t$(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical force begmhwnzts3fgc. w ,9 (jdd4qf5 pf0m/ 3tween two protons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude of the forceon*1nl2sr 9 zo a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exert a for1;:iok j,8bulkz2nbx -zmp t5ce 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 apart. They areajmk) 9l0w, xp moved, and the force on each of them is found to have been tripled.)p lj,mkx 9wa0 How far apart are they now?    cm

  A person scuffing her feet on a wool rug on a dry in3v7bi3f5 j rday accumulates a net charge off35i riv7 3nbj $-42\,\mu C\,.$ 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 elect9ulyu*b j .h+prons in 1.0 kg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric force holding the electron in orbit rk,3 lzjxw1(r6n+hfdrp11 yx8 /p swi$(r\,=\,0.53 \times10^{-10 }\,m)$ 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. Thj-eo0l ip57f ze sum of their charges is What charge must each have in-poil05ej 7zf order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge td.xq )a ot35zr yq7x)$+75$,$+48$ 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 c--cnhixgo 3;xi1,m uvharge, $+11.0\,\mu C\,$ 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;t(c sr3ykz0ku*t e4h square 0.100 m on a side. Determine the magnitude and direction of the force ;3 kset40(kry zc tuh*on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when two of the positive charges, on opposit*6r((y/ot*fwn qg euae corners, are replaced by negative charges of theu/a(*otqwy* nrg 6e( f same magnitude (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a s: trp.ez0rxeclslf7( . 0oz5a quare of side 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, due to the othezs0e orz (5fpxrle:7.l ac 0.tr 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 pla 3ts1 47:ohokvk5vyp3n v*sh jced at the corners of an equilateral triangle of side 1.20 m (Fig.h7*t s4jy3ovkvkn1 ph3 5vs o: 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 of0x)gy z e0f;z,mplt3 w $560\,\mu C\,.$ 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 charwi io40-sdju nfvp*ms+272pxlb v4 :ege 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 transferr sc.s ctuh-f)- m8zcq3ed from an initially uncharged plastic ball to an identical ball 12 cm away. The force of attractiu.c-8sczf s- q)m hct3on is then 17 mN. How many electrons were transferred from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitude and direction o92n,kq (u5hnp k- gc yn2:ofwcf the electric force on an electron in a uniform electric field gc 9nknqu,kop( hy2cn-5w:f2 of strength $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a uniform electric fj, s7vfq oj-gpip4kqz/ 0uxcq bhm4;w(7p33xield, and it experiences an electric force of7jp, x7bv3 pqux/mwpj0 qh4f- sk3ogi;4(zcq $ 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 .)x zr7053syn1oizb;4em oyob4y;wei f o rw) is 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 -p r u.0hpe v+eakq xid4777jxdirection of the electric field 20.0 cm directly above an isolat p qu-x+hk77xae7d jriv4e0 .ped $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acceleration experience,ie9 1ni4 eb 41uvbqkfd by an electron in an electric e44 bnqi, ivuke b91f1field 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 fieoz+68jw ukg*9+r npjrld at a point midway between+* p+ ugzro rnj6w9kj8 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 electrihti)z0knz )zbt 05 :zvc field lines about two point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength at*5s0abanua 0zr3u d x9mr. rl6 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 field and accelerat8i; knmtkyekl+ mr7wyo ,9/c-es to the north arc-/ iekkynm w+ ;yt,79o8kmlt 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 midwaynx ivsn86zq.bs -)qy / between two 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 fiel cz+v kvj1u4a(d at the center of a square 52.5 cm on a side if one corner isj v14vz+c(auk 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 1.00 m on a si5racaoo 71qyn7a / q* .rwem3a(lo7gnde if the other three corners qoeno 7qw aala1mn 3o *a77ryr(c.5g/are occupied by $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and magnitude of the electric field at themmt6 :o9pkxh4+a 0e ux point P in Fig. 16–54. The charges are separated by a distance 2a, and point P is a distance x from the midpoint 0k mt+e o46xa9p :mhuxbetween 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 ele/z0yp kqh11y h9rhn-ectric 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 tu-nedh sf21 klh)x9:vhe electric field at points A and B in Fig. 16–57 due to the two positive char uhh 2n dekl9)s-xv1f:ges $(Q\,=\,7.0\mu C\,)$ 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 ch6cfd+mu vu( xqk73j4 narges, $Q_1$ 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 o9vnid l* .vbvbl+r3i2 f 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 nb dl29vi.v l*vb+3r ijoining 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 t :w81b ucpx 9ilf4m4czo the right at 1.0% the speed of light enters a uniform electric field parallel to its d w:pcbz4l9fc84mui1 x irection 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 cubicad,1l1w o,e,eq y(xw ppq u;qx(l box 28.0 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 18 cm is placed in a gqj*: m7ltdb la1bt7; uniform electric field of magnitude7l:t 7at1mjlbg ;d*bq $ 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 os v( djkm5fv;.bjects, $O_1$ 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 u img )xap98qfxt )52nsniform 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 f,+n64lejrpg+ v,ov n; z f1dm The plates are 1.0 m on a side and are separated by 3.0 cm. What is the charge 1ljr g+fvmo,;f,en+ zpd46nv on each plate (assume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3.50-cm-radius metal ball efxlq np/.8 7eis $ 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 radiu3ul8l5w/co f7o k6ch ls 3.00 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 uncharged tjtvrx1 znr:qdw4 +u r.:oy7 c4en p.-nhin spherical conducting shell. (See Fig. 16–33.) What is the electric field E as a function of r (a) for r less th:7 :znwx ypte4c-4 +vn1drrr..quoj nan 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 elet98-+ qr*yvmvuigiv+r ln4i:ctrostatic 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 rur9v v4qnvltm:+8y*- giii +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 electpy69) b qhtz.nrons be if the electric force between them is equal to the weigh) znbp6h.q ty9t of either at the Earth’s surface?    m

  A 3.0-g copper penny has a positive chabuli )x bzjgga8 ,-50yrge 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 th86q trgkb g5m72(u- ca4pgi1byik i4ze Earth. Its magnitude is about i4 gc 2mybqi5-6b 78k4p iazgrk1g ut($150\,N/C$ 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 accelerati s klq5b; r/f:gqsj6ft3ig3i,on experienced by an e lr:gbi3 sj36if/g ; q,qf5stklectron 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 remains stationary in the air. If the downwarpe zncdo://e3xk.t m0d-directed electric //dpzcm.3 nktx0 e:eofield 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 the CO group and the HN gro -gg*-m kb,f i2dsmin/up shown in Fig. 16–62. The C and O have chfsd2g b-,*k mmgi/ ni-arges $\pm0.40e$, 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 electron revolves(fb 98-b mntlr 4:yusd in a circular orbit around the proton with(umslb-:b9 y ntf8 rd4 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, were re- 5whov4-rk+bq.0f w 3fct wujsponsible for holding the Mo4-qcu. 3k5whfr t-ww b+0fvj oon 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 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 speedjjd41*im pz vuz n ,bcw/:e*4c $v_0\,=\, 21.5\times10^{6}\,m/s$ 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 chargemw98f *vpnz+s)tq0z x-uj* mc $Q_1\,=\, 2.5\times10^{-5}\,C$. 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 e1r kpvfc4zis l.l:s: pfpu . :,,s+bjjncased in insulating plastic and suspended vertically frc:krl.,:,pj:p1ls. uzs4 fip+bsv fjom 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 ep6awov1j6g.pey4 )u wires with tiny 24-g spheres at the ends. When charged, nearly all the charge resides on the spheres. If the wires each mae1jpg6)av eu 6w4. poyke 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 generaojm1; m5kyxh b51 l-cote a spark if the electric field exceeds about obm lo5ycjmk1;h5x- 1 $ 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 ser2t0 0. ybjl0.210 kg, and 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 electr ybx fi/8+gywgl -,*wqons 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 distance w1.itf2 9b5zg(rtg oj1sa7p k R apart; each carries thb1ktot 9wj z5.ggrf(1 s2p7 aie 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 is the force on sphere A in this third case?

Given the two charges shown ji (s: ep1nta,37sfcrin Fig. 16–68, at what position(s) x is the electric field zero? Is the field zero at any other points, not on the x axi pa7:e3c,ij stn(s1rfs?

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 charge y9r e-f9xr oe2$8.0\,\mu C$ 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?