If you charge a pocket comb by rubbing it with v(mqm48a eepisv y mfs 2:-a1vu1k4hl 2wtm +:a silk scarf, how can you determine if the comb is posa1::2vve mumkmimvh4y4qf+(1p -82e stswl aitively or negatively charged?

Why does a shirt or blouse taken fd(79bd kk3uav rom a clothes dryer sometimes cling to your bodd 3a(v7k9kd uby?

Explain why fog or rain droplets tend to folc /g +ahvz.k*rm around ions or electrons in the air.z h/c*k+ vgal.

A positively charged rod is brought closef58lpz2r i4 hmu7y;3qdcmh . y to a neutral piece of paper, which it attracts. Draw a diagram showing the slpcr d2 mi4;3qzy7ufy 8.5mhh eparation of charge and explain why attraction occurs.

Why does a plastic ruler that hasbx b2;dh0ll522 nvfsw been rubbed with a cloth have the ability to pick up sm2l wvbsxfnh2l52db;0 all pieces of paper? Why is this difficult to do on a humid day?

Contrast the net charge on a conductor to the “free ch l(ep+xymhpx7j *v/8iarges” in the conductor.

Figures 16–7 and 16–8 show how a charged rod placed near an uad6c)rm r7xw9pr4y 1 qncharged metal object can attract (or repel) electrons. There are a great many electrons in the metal, yet 7a9p yrw1mcdr4)rxq6only some of them move as shown. Why not all of them?

When an electroscope is charged, its two leaves repel each other and remain at ax tlniej7w-b,m s2r;9n angle. What balances the electric force of repulsion so that the leaves don’t separate further?r9txm-wij,nle2s7 ;b

The form of Coulomb’s law is very similar to that for Newton’s +irg lt8xctvht qizq+)2+ 0k *law of universal gravitation. What are the differences between these two laws? Compare also gr80l)qtg2cqztrhik* x vt++i+ avitational mass and electric charge.

We are not normally aware of the gravitational o03z1y f bf6agnr electric force between two ordinary objects. What is the reason in each case? Give an example where we are aware of eaa3ffg10z 6bny ch one and why.

Is the electric force a conservative force? Why or why not? (*j; ykp/-f 7ajileji+See Chapter 6.)

When a charged ruler attracts small pieces ofmk8kquy cvkoe,h2 s2wj1.. c0 paper, sometimes a piece jumps quickly away after touch08s uyc21.k.w ocek qvm2j, khing the ruler. Explain.

Explain why the test charges we use when measuring electric fields must be smallc 9)oqh 1u6kna;j8n ln:(zqll):z qnl1c ln(8 u 69;konqjhla.

When determining an electric field, must we use a positiv;7h fl p.;096w bqvip-iscmelas6+vl e test charge, or would a negative one do aisl0;+q6b -s67;c iwpp l9ah.vfeml vs well? Explain.

Draw the electric field lines surrounding two negative electric charges a u1 tjcz:+1c9e zlaa+kd )ws3kdistance: za 1k3a lw)c1e dkjs+9zc+ut l apart.

Assume that the two ox)6k*qyyh8bh ; ohu;vpposite charges in Fig. 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 charge —bh6xouh ; )hy* kv;y8q top, bottom, left, or right — is the electric field the strongest? The weakest? Explain.

Consider the electric field at points A, B, and4kio7 xpets (yi6:v+j C in Fig. 16–48. First draw an arrow avp4(i tkes6yx 7: ioj+t each point indicating the direction of the net force that a positive test charge would experience if placed at that point, then list the points in order of decreasing field strength (strongest first).

Why can electric field louzb .y6 lbi5:ines never cross?

Show, using the three rules forin;:xy( d wtlcmx 7u0v .1g1tti kx*(p field lines given in Section 16–8, that the electric field lines starting or ending on a single point charge must be symmetrically spac idk c ntmv(t:7it1u1 x*0plx.(ygw;xed around the charge.

Given two point charges Q and 2Q, a distance l apart, is tpwllg(9+ti6mpq q 84bhere a point along the straight line that passes through them where E=0 when their signs are (a) opposite, (b) the same? If yeqlplq6+ t i(48bgw mp9s, state roughly where this point will be.

Consider a small positive test cha 5usyp,fiz/. cs4eau 6rge located on an electric field line at some point, sucic, a.4 zuu/esf sy56ph as point P in Fig. 16–31a. Is the direction of the velocity and/or acceleration of the test charge along this line? Discuss.

Sketch the electric field lines for a uniform line o ,ext cwrv6is8 -:yp1wf charge which is infinitely l6wisr ,:x1pwt -y8cevong. (Hint: Use symmetry.) Is the electric field uniform in strength?

If the electric flux through aklegwrxkj,q d920 b0u5u /yd9 closed surface is zero, is the electric field necessarily zero at all points on the surface? Explain. What 5jkd0 0lwq2u9,9eky/burdgx about the converse: If $\vec{E}\,=\,0$ at all points on the surface is the flux through the surface zero?

A point charge is surroun ezw u.w/5,td:ry*fe3s ,zaxeded by a spherical gaussian surface of radius r. If the sphere is replacea/. zuf s*tzexew ye5:d,3wr,d by a cube of side r, will $\Phi_E$ be larger, smaller, or the same? Explain.

  

  How many electrons make up a charg .k4lvs)+al kie of $-30.0\mu C\,?$   $ \times10^{ 14}\, electrons $

  What is the magnitude of the electric force of attraction between an iron n c,r :invne w08co,yewl *cmz(j i+nuu2b 7:9xucleuz(mc*cb2 j8 iev ,:7+x:9ouy,uncnlr n wewi0s $(q\,=\,+26e)$ and its innermost electron if the distance between them is $ 1.5\times10^{-12 }\,m\,?$    $ \times10^{-3 }N$

  What is the repulsive electrical force between two protr1h , 7/b2yvusetj9pbons $ 5.0 \times10^{ -15}\,m$ apart from each other in an atomic nucleus?    N

  What is the magnitude qo5ek6ar2 qylk;a 5e9 of the force a $+25\,\mu C\,C$ charge exerts on a $+\,3.0\,mC$ charge 35 cm away?    N

  Two charged dust particles exert a force of(hrf ff9 8+azn $ 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 are moved, and the force on eac7 85nwj vam)qy) lzj+vh of them is found to have been triz5) lvynjw)+v a 8q7mjpled. How far apart are they now?    cm

  A person scuffing her feet on a wool rug on a dw lz9dfyf* +-p5w( jk;jbybn,ry day accumulates a net charge o9kjw fd ;5y (lb-wyz*+jnfb,p 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 electrons in 1.0 um gg c.o4al 1/z6yd3dkg of $H_2O\,?$    $ \times10^{ 7}\,C$

  Compare the electric )lagkl2jwx t7b) r 4j+force 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 cha0cj6 ta8k3vtq rges are a fixed distance apart. The sum of their charges is 8ct3vak t06jqWhat charge must each have in order to
(a) maximize the electric force between them,
(b) minimize it?

  Particles of charge a x u:n *wk4;tm72nhwr$+75$,$+48$ 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 particle-2sf(ri *ba3kbh/b n os 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 ofr3j.*vr w3kr+wau+m l1;a s rb a square 0.100 m on a side. Determine the magnitude and dir;wbuvr r1.a+ralrjw s3m+*k3 ection of the force on each charge.
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  Repeat Problem 14 for the case when two of 1vyvcu p1qtva:z 89y/ the positive charges, on opposite corners, are replaced by negative charges of the same magny pvac / 8z1y:1qt9vuvitude (Fig. 16–51).
$F_4$ =   $ \times10^{ 7}\,N$
$\theta$ =    $^{\circ}$

  At each corner of a square of side l there are point charges of magnxm ym r321j;p.syq/ kpitude Q, 2Q, 3Q, and 4Q (Fig. 16–ykys3 m2pm;.xj / 1rpq52). Determine 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 placezw 0njk4o; ;lrd at the corners of an equilateral triangle of side 1.20 m (Fig. 1;z0rjkl n4;ow 6–53). 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 en;u1 poz2cw5total 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 total8d+fo* fix - (4b z8)qqqujwdr 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 u)6rta0tmvn * wncharged plastic ball to an identical ball 12 cm away. The force of attraction is then 17 mN. How many electrons were transferred)mr* ta6w vt0n from one ball to the other?    $ \times10^{ 12}$ electrons

  What are the magnitud(l-xzcs8i ,mxe and direction of the electric force on an electron in a uniform electric field of strengtxisc , (x8lzm-h $2360\,N/C$ that points due east?
   $ \times10^{ -16}\,N$
 ----待选择----westeast 

  A proton is released in a uni9* jj;qr;kh: pcwxoqa; j3lq 9form electric field, and it experiences an electric pxr wq ;lq ca:hjo;jq3;9j k*9force of $ 3.75\times10^{ -14}\,N$ toward the south. What are the magnitude and direction of the electric field?
   $ \times10^{5 }\,N/C$
 ----待选择----southnorth 

  A downward force of 8.4 N is exerted 3c m/96x6tbl g9vag sjon 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 fiel 7gyt y(/(ipdowj,fx,d 20.0 cm directly above an7,dy (g jftoyi, xp/(w isolated $33.0 \times10^{ -6}\,C$ charge?    $ \times10^{6 }\,N/C$ ----待选择----updown 

  What is the magnitude of the acc s 4 ufhooa-z5n56f.*dis r-mwo6 i/fleleration experienced by an electron in an electric asir4 /swfui6d*flo -5on f 5h6-o. mzfield 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 e/cnwea46 9.xvy xdb(v yzpj9+ lectric field at a point midway bety w4d bj (zxep6v+yv.an/xc 99ween 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 abou3ffm 8 n5l(gh/dzeb;-vq6geh t two point charges, $+Q$ and $-3Q$ which are a distance l apart.

  What is the electric field strength aagzm;p 8n,f xv06oufb ;;)ikqt 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 fyum2 -:tv2bxlt ug m10rom rest in a uniform electric field and accelerates to the north at 21uttb02mml x-uy v:g 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 /23./v2c fdyc nqjvjatwo equal but opposite point charges is $745\,N/C\,,$ and the distance between the charges is 16.0 cm. What is the magnitude of the charge on each?    $ \times10^{-10 }\,C$

  Calculate the electric field at the center of a square 52.5 cm vjeh2 o;+two( on a side if one corner(tvw2 + ohjeo; 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 s(9omrer+y(kd c ,obq ah:s 1l2quare 1.00 m on a side if the other three corners are occupied m + by9r (sc(o:oq,alerh1k2dby $ 2.25\times10^{-6 }\,C$ charges.    $ \times10^{4 }\,N/C$   $^{\circ}\,$ from the x-direction.

Determine the direction and q2po 46mievgb h7cf+vrg0a 4:magnitude of the electric field at the point P in Fig. 16–54. The charges are separated 64h:cbv7rp 0fvomi2 q+eg ga4by 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 l eeth 42nk72lfield $\vec{E}$ 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 electric qt 9su my9l41ij.z-dq field at points A and B in Fig. 16–57 due to the two poslqt .jsmz-914 dqyiu9itive 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 chay, /authcu.g, rges, $Q_1$ 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 firp+.0 z)ztbjs rgi+xawn3*y- eld at the point P shown in Fig. 16–59. The two charges are separated by a distance of 2a. Point P is on thia z jy-*+prwtzb)+.0r x3ns ge 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% thh0ktj:s)jc /za g kqd + j(h;aj,rj5.le speed of light enters a uniform electric field parallel to its direction of motion. If the electron is to be brought(rj;0. +/)j ha:l s,qkzgjj djthck5a 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 cubic 004-k j2bfs.mynmbp jal 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 placew388t+s pw: dhda qpt-d in a uniform electric field of magnitude-dp ta8 +dq:wst8h wp3 $ 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 objec/*caiq eup9ez( o*)twlp.w :nts, $O_1$ 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 uyviy6- z3ba3kniform 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 0+t qoh4qlritge) + tt8t.lq3o;:d qp The plates are 1.0 m on a side and are separated by 3.0 cm. What is the charge on each plate (aqtt8t h l;tpg0r:e+ doqo 3q4q )lt+.issume equal and opposite)? Neglect edge effects.    $ \times10^{-9 }\,C$

  The field just outside a 3. i 7j,j/f;*t zphj:dog50-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 3.0i l(l 56w i9gb1u8qyuj0 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 cente0sl:r )zegk4 zon h(z5r of an uncharged thin spherical conducting shell. (See Fig.4z kenrzg zls5 )(h:o0 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 affect the shell?

  The two strands of the hg mi0x6hdc;cof ;w 5h7elix-shaped DNA molecule are held together by electrostatic;om7fg5i w 0ccd;hhx 6 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 the electric force between ttjr0co . ir5s2dnh3z: hem is equal to the weight of either at thj c53ntoh:s.r d2ir0 ze Earth’s surface?    m

  A 3.0-g copper penny has a positive charge /fw(,c6bv *uq iwz3xvrt9sn, 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 surroundin81b ckhe. ;-njm+l mmjg the Earth. Its magnitude is about ; kjl h1m8b.c n-memj+$150\,N/C$ 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 al)cf2p b.fayj h5j :0occeleration experienced by an electron near the surface of .0 hfap yj o52l)jfc:bthe 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. dna.zsf8wplp b1m 2bpa*-617iol;p hIf the downward-directed electric field of the Earth11zd nb 2p;*la obap .ps6pw-lhfi7m8 is $150\,N/C$ how many excess electron charges must the water droplet have?    $ \times10^{ 6}$ electrons

  Estimate the net force between thj wbcw89zbh,; e2 0dbwe CO group and the HN group shown in Fig. 16–62. The C and O hwjh 0wd8 ec; b29bb,zwave 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 electron revo752iqko9xfelb,9 nk m lves in a circular orbit around the proton with a speedl qk ie995mbxk2o ,nf7 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 responsibleebjo fm-u :eot*u9, /j for holding the Moon in orbit around the Earth. If equal and opposite charges Q were placed on the Earth and the Moon, w umfube e:jjt ,/-*o9ohat 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 speed zqbjqb j w7;z1 p2-k ,rboqka3(0ip:k$v_0\,=\, 21.5\times10^{6}\,m/s$ 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 charge 97so dzmx: x5m$Q_1\,=\, 2.5\times10^{-5}\,C$. 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 insulatiba6oet- s,rb4/ n lo 3wz:)cvgng plastic and suspended vertically from anlng -43o),as6:cwvzber /b ot 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-chyc8 3dht(obw5lr * b+m-long wires with tiny 24-g spheres at the ends. When charged, n 8lb53o+yc* h(hwrdtb early 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 anz(pm*aje s(c8 d generate a spark if the electric field exceeds about c( eamjzsp(*8 $ 3\times10^{6 }\,N/C$. How much charge could be packed onto a green pea (diameter 0.75 cm) before the pea spontaneously discharges? [Hint: Eqs. 16–4 work outside a sphere if r is measured from its center.]    $ \times10^{-9 }\,C$

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

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

  A point charge of mass 0.210 kg, and net chkpsbsays)3 86 vzd1 ,rarge $+0.340\,\mu C$, 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 o6+j8 8fv txnijf 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 dv jdioq :m k/7r1a5q c,4q4bqnyx:x2conducting 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. Wdqxcd2q,o4mrb7 5: k4v 1nj q: q/xaiyhat 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. 16–68, at what position(s) luj.x8yo aa;6 x is the electric field zero? Is the fiely 6;xuloaaj 8.d zero 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 poinf8-fh 8 r;ymeut charges, 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?